| Author |
Year |
Title |
Source |
Sort |
Language |
Abstract |
Descriptors |
Remarks |
Alla, N.;
Bérest, P. et al. |
1993 |
In situ tests in brine-filled caverns |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.445-454 |
Paper |
|
Mechanical properties of the rock mass surrounding
an underground salt cavern can be measured through different
tests performed in brine filled caverns. Dynamic and static
tests are discussed and a nine years long static test is fully
described. |
In-situ
tests |
- |
Allemandou, X.;
Dusseault, M. B. |
1993 |
Procedures for cyclic creep testing of salt
rock, results and discussions |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.193-204 |
Paper |
|
In the experimental research we present here,
we demonstrate that sampling damage causes opening of grain
boundaries and generation of sufficient microfractures as
to significantly affect mechanical properties. We show through
CAT-scan experiments that sampling damage can be healed and
annealed under a hydrostatic stresses. We demonstrate that
unconfined and confined compressive strength of salt rock
are strongly influenced by this healing process. Finally,
we validate a test procedure, and we prove that transient
creep of salt rock can be evaluated using a series of compressional
and extensional cycles. Experiments were conducted under various
stress deviator and mean stress levels from one cycle to another;
the results obtained are consistent with our interpretation
of annealing, and have led to the development of a phenomenological
model for salt rock. |
Creep behavior |
- |
Allison, H. G.;
Ford, E. C. |
1988 |
The first plug is the key to a good plug and
abandonment or liner job |
SMRI Spring Meeting, Mobile, 25.04.88 |
Paper |
|
The plugging and abandonment of caverns and
the cementing of a liner into a leaking wellbore have the
same critical first step: how to establish the first plug
to work against. This paper will discuss five methods that
are being used, these are:
1) Inflatable Packer
2) Umbrellas or oversized cement baskets
3) Section Milling and inflatable packers
4) Lightweight Cement using perlite additives
5) Foamed Lightweight Cements
The success and the cost effectiveness of each method is dependent
upon the borehole geometry, and these considerations will
also be discussed. |
Borehole
seal |
- |
Anthony, T. R.;
Cline, H. E. |
1974 |
Thermomigration of liquid droplets in salt |
Proc. 4th. Symp. on Salt, Vol. 1, pp.313-320 |
Paper |
|
The salt mine burial of fission waste products
resulting from the reprocessing of spent fuel elements is
now planned as a permanent means of disposal of these highly
radioactive wastes. Although salt mine burial is apparently
the best method of disposal the vigorous self-heating of these
waste products leads to some potential problems. Natural salt
formations regularly contain small brine inclusions which
will migrate up the thermal gradients generated by the self-heating
of the waste products. The resulting inflow of water into
the nuclear waste crypts is undesirable because water vapor
may accelerate waste container corrosion and/or lead to fission
product contamination of currently unused sections of the
salt mine. In addition, contaminated vapor-liquid biphase
droplets generated on the walls of the nuclear waste crypt
are capable of dispersing fission products throughout the
salt formation since these unusual inclusions migrate down
thermal gradients, in contrast to the normal thermomigration
of simple gas or liquid droplets up thermal gradients in salt.
By considering viscous gas flow, vapor diffusion, liquid diffusion,
evaporation and condensation, and liquid currents driven by
surface tension gradients, the odd thermomigration behavior
of the vapor-liquid droplets observed in the present investigation
is explained. It is concluded that a modest dispersal of radioactive
wastes may occur in the salt formation. However, because of
droplet trapping by the grain boundaries in the salt, the
escape of radioactivity to the outside environment is unlikely
even on a geological time scale. |
Permeability of rock salt |
- |
| Arnold, W.; Förster, S. et al. |
1974 |
In situ investigations of fracturing in salt
cavities for determining stress components |
9th World Oil Congress, Tokyo, 1974, PD21 (3),
pp.89-96 |
Paper |
|
Knowledge of the state of stress in salt rocks
plays an important role in dimensioning the size of cavities
and the pressure load in underground storage. By laboratory
tests the questions and problems occurring in them cannot
be solved clearly. Therefore, in situ tests are necessary
in different depths. Field tests are reported. wherein salt
rock boreholes gas pressure was produced up to fracturing
of the originally impermeable rocks. Connections appear in
outline between the mechanical strength of the salt rocks,
the presence of so-called etching pits, the strain behavior
and the pressures necessary for the formation of fracturing
in salt rocks in situ. |
Hydrofracturing |
- |
Aubertin, M.;
Gill, D. E. et al. |
1991 |
An internal variable model for the creep of
rock salt |
Rock Mech. Rock Eng. 24 (1991), pp. 81-97 |
Journal Article |
|
The creep strain rate e of rock salt, like
that of other ductile crystalline materials, can be described
by a power law equation of the type ea(oa)n where the active
stress oa is the difference between the total deviatoric applied
stress o and an internal stress oi. In this paper, the origin
and the nature of this internal stress, which develops during
inelastic deformation of the material, are discussed. It is
shown that this internal stress can serve as an internal (or
state) variable in the constitutive model of rock salt, which
reflects the microstructure evolution of the material under
the competitive action of hardening and recovery mechanisms.
An analysis of experimental data, both our own and those taken
from the literature, demonstrates that such a law is able
to correctly reproduce rock salt creep test results in the
steady-state domain. The proposed model is in accordance with
the macroscopic and microscopic behavior of salt, and with
direct measurements of the internal stresses made by others
on this material. |
Creep behavior |
- |
Aufricht, W. R.;
Howard, K. C. |
1961 |
Salt characteristics as they affect storage
of hydrocarbons |
J. Petrol. Technol. (1961) 8,. pp.733-738 |
Journal Article |
|
Results of laboratory tests, field tests and
field observation of salt characteristics pertinent to either
the storage of hydrocarbons or the disposal of industrial
wastes are given. Of particular significance is the indication
that under many conditions dry salt may be sufficiently permeable
to allow appreciable flow of non-aqueous fluids. This flow
appears to occur along crystal boundaries and cleavage planes
and through bands of impurities, including dehydrated shales
or mudstones. Present data indicate that water, even in very
small quantities, materially affects these characteristics.
The variation and the presence or absence of permeability
appear to be a function of (1) the type and amount of impurities
(including shale), (2) the crystalline structure and cleavage
planes, (c) the confining or overburden pressure and (4) water
content. Additional study of these properties will be required
before an accurate evaluation of the feasibility of storage
or disposal under various conditions can be made. The amount
and effect of moisture content are particularly important,
and additional study of both the amount and effect of in situ
moisture is needed. |
Permeability of rock salt |
- |
Baes, C. F.;
Gilpatrick, L. O. et al. |
1983 |
The effect of water in salt repositories, final
report |
Oak Ridge : Oak Ridge National Laboratory,
ORNL-5950 |
Report |
|
Additional results confirm that during most
of the consolidation of polycrystalline salt in brine, the
previously proposed rate expression applies. The final consolidation,
however, proceeds at a lower rate than predicted. The presence
of clay hastens the consolidation process but does not greatly
affect the previously observed relationship between permeability
and void fraction. Studies of the migration of brine within
polycrystalline salt specimens under stress indicate that
the principal effect is the exclusion of brine as a result
of consolidation, a process that evidently can proceed to
completion. No clear effect of a temperature gradient could
be identified. A previously reported linear increase with
time of the reciprocal permeability of salt-crystal interfaces
to brine was confirmed, though the rate of increase appears
more nearly proportional to the product of dDP rather than
dDP² (d is the uniaxial stress normal to the interface
and DP is the hydraulic pressure drop). The new results suggest
that a limiting permeability may be reached. A model for the
permeability of salt-crystal interfaces to brine is developed
that is reasonably consistent with the present results and
may be used to predict the permeability of bedded salt. More
measurements are needed, however, to choose between two limiting
forms of the model. |
Inter-
dependence
rock stresses – permeability |
- |
| Battelle Ingenieurtechnik GmbH et al. |
1995 |
Bestimmung des Diffusions- und Permeabilitätsverhaltens
von Wasserstoff in Steinsalz und kompaktiertem Salzgrus
[Determining diffusion and permeability behavior of hydrogen
in rock salt and compacted salt fines] |
Battelle Ingenieurtechn. GmbH, BMBF-Förderkennzeichen
02 E 8492/3 u. 02 E 8462/9 |
Report (Abstract) |
|
It must be expected that repositories for radioactive
wastes situated in salt rock formations will, in certain zones,
generate and release hydrogen. It must therefore be guaranteed
to ensure long term integrity of the repository that this
does not represent a hazard. In order to be in the position
to make reliable statements concerning the location or transport
of the hydrogen, it is necessary to acquire data on the permeation
and diffusion behavior of salt rock. To achieve this, a number
of model salt cores were prepared using salt fines during
which the following parameters were varied: compaction density
(porosity), compaction time, compaction pressure, mineralogical/chemical
composition, grain size, moisture and temperature. These cores
were then tested for hydrogen permeability and diffusion.
In order to allow comparisons with natural salt rock, a number
of salt cores were also investigated.
In order to prepare the test cores and to perform the comprehensive
permeability and diffusion measurements under various parameters,
a number of suitable test apparatus were constructed.
The tests were carried out using salt fines from the former
Asse salt mine taken at various depths (Staßfurt and
Leine series) and from the Bernburg pit (Leine salt rock).
The cores tested were for the most part recovered from the
Asse salt mine (Staßfurt series).
In order to quantify the various influential parameters, the
salt specimens were analyzed for chemical and mineralogical
composition, grain distribution and their water content and
absorption isotherms were determined.
In preparatory tests a number of different techniques were
reviewed in connection with achieving diffusion-tight clamping
of the salt specimens and the influence of the specimen diameter
and the salt aggregate size on the permeability behavior.
The results were used to perform the main tests using both
original cuttings (recovered from a partial road header) as
well as strained original material (< 10 mm) with in-part
modification of anhydrite content.
The permeability tests on the salt fines samples were performed
while varying type of salt, porosity (compaction density),
mineralogical composition and time. Insodoing the permeability
was found to be in a range of 10-12 m² and 10-23 m².
It was found that the salt dampness, the anhydrite and polyhalite
contents, and the size of the grains had the most influence
on reducing permeability over time (with appropriate overburden
pressure) as well as with falling porosity.
Similarly the temperature of the compaction had a greater
than negligible influence on the permeability behavior of
the specimens over time. In particular, the specimens compacted
hot had a major difference in their pore structure (smaller
pore radii, larger access porosity) than did those compacted
cold. Also the diffusion behavior of the hot compacted specimens
was considerably different to the cold compacted, even with
the same permeability.
The experimentally proven connection between porosity and
permeability allows two ranges to be identified. In the total
porosity range between 7% and 1.5% the permeability drops
exponentially from approx. 1·10 to the power of 13
m² to approx. 5·10 to the power of 17 m².
The influence of the type of salt as well as salt dampness
and mode of preparation (cold or hot compacted) has a virtually
negligible effect in this range. Only those samples prepared
with hygroscopic salt drawn from 490 m and 700 m depths were
found to have a temporal permeability drop of up to four powers
of ten down to the lower permeability detection level within
only a few days in the porosity range between 1.5% and 5%.
The specimen porosity after the measurement was found to be
still in the order of 2%.
In the case of all salt types in the porosity range of <
1.5% the influence of all the above named parameters was found
to be greater than negligible. Below this porosity the permeability
of the salts with low anhydrite content fell dramatically
down to the lower detection limit of k = 8·10-23 m2.
The decisive factor determining the permeability of the porous
material is the accessible porosity of the flow medium. In
order to determine the accessible porosity a number of methods
were investigated. Determining the accessible porosity and
comparing this with the overall porosity shows that the period
of compaction and the pressure of compaction have a decisive
influence on the ratio on these two pore factors in compacted
salt fines. In the case of samples prepared with low compaction
pressure and long compaction time the difference between total
and accessible porosity is a great deal lower than those specimens
compacted at high pressure.
Long term tests and an overburden pressure of 200 bar (creep
compaction) allows a differentiation between samples with
larger k <10-15 m2) and lower initial permeability. In
the case of higher initial permeability (e.g. low compaction
density, large porosity) the influence on the overburden pressure
on the temporal permeability reduction is low - depending
upon type of salt. However, the lower the initial permeability
the larger the temporal permeability falls whereby this also
depends on type of salt and salt moisture. In the case of
intensively dried salt cores the influence on the overburden
pressure on the temporal permeability drop is minor even for
lower values of initial permeability.
Within the permeability measurements the influences resulting
from the method of evaluation (Darcy equation) such as slip
flow, turbulent effects and pore structure, were investigated
as was their influence on the accuracy of the permeability
measurement. The deviations resulting from the evaluation
method between the measured "apparent" and the "true" permeability
are identifiable by suitable tests yet play only a subordinate
role compared with the influential factors referred to above.
During the overall project over 400 salt core samples were
subjected to permeability testing.
The testing of diffusion was undertaken on an apparatus with
open, semi-open and closed systems using nitrogen and hydrogen
as measurement gases. The system differences refer to the
degree of freedom of the gas located on both sides of the
salt specimen core in the hydrogen and nitrogen circuits.
The test conditions were adapted to the conditions found in
the salt mine.
The objectives of the diffusion tests were to arrive at statements
concerning the value of hydrogen diffusion currents and to
quantify the dependence of diffusion on permeability.
The transport of material as a result of a concentration gradient
is predominantly by Fick's diffusion. The influence of molecular
motion after Knudsen is negligible. This is apparent if one
considers the differences between the effective binary diffusion
coefficient D12 and the Knudsen coefficient Dkn,1. At a gas
pressure of only 1 bar the binary diffusion coefficient is
already smaller than the Knudsen coefficient by a factor of
10. As gas pressure rises the effective binary diffusion coefficient
falls hyperbolically. Diffusion is always dependent upon the
larger resistance (lower coefficient of transport).
The results of the diffusion test show that the diffusion
behavior of the salt samples can vary greatly despite having
the same permeability. In the case of samples with a large
Klinkenberg factor (small pore diameters), a larger effective
binary diffusion coefficient was measured than on samples
with a smaller Klingenberg factor but with the same permeability.
Furthermore, tests were made to determine which transport
mechanism was dominant and from which pressure gradients upwards
the material transport by permeation dominated material transport
by diffusion. In practice it can be assumed that from a pressure
gradient pe - pa > 1 bar onwards for permeabilities of > 10-18
m2 the diffusive fraction on the overall transportation of
material is negligible.
The diffusion current and the product of the diffusion coefficient
and gas pressure De·p is only slightly dependent upon
the gas pressure in a pressure range of 1.2 to 10 bar in the
case of the salt specimens tested. In the case of the salt
samples with the same permeability the different diffusion
coefficients result from the different pore structure.
Effective binary diffusion coefficient of between 1·10-7
and 6·10-12 m²·s-1 (at a pressure level
of 1.2 bar) were determined for the measured permeability
of 1.7·10-17 m² to 7·10-21 m².
The results of the diffusion measurements are based on the
testing of approx. 150 salt specimens. |
Permeability of rock salt;
Reservoir |
only abstract; German original at KBB |
Bazargan, W.;
Telandro, S. et al. |
1994 |
In situ gas and brine permeability test in
salt: design and deployment of experimental device |
Proc. 4th Progress Meeting PEGASUS, Exeter,
26.-27.06.94, EUR 16001, pp.171-183 |
Paper |
|
The in situ test conducted in the Potash Mines
of Alsace is designed to measure the permeability of a salt
formation to gas and brine for purposes of long-term safety
assessment of a radioactive waste repository. This paper describes
work relating to the design and deployment of the experimental
device, which is comprised of seals, a resin sealant, a fluid
injection system, data acquisition systems for temperature
and pressure and a heat regulating device for the test. |
Permeability of rock salt |
- |
Beauheim, R. L.;
Saulnier, G. J. et al. |
1991 |
Interpretation of brine-permeability tests
of the Salado formation at the Waste Isolation Pilot Plant
site: First interim report |
Albuquerque : Sandia Nat. Lab., SAND90-0083 |
Report |
|
Pressure-pulse tests have been performed in
bedded evaporites of the Salado Formation at the Waste Isolation
Pilot Plant (WIPP) site to evaluate the hydraulic properties
controlling brine flow through the Salado. Hydraulic conductivities
ranging from about 10-14 to 10-11 m/s (permeabilities of about
10-21 to 10-18 m²) have been interpreted from nine tests
conducted on five stratigraphic intervals within eleven meters
of the WIPP underground excavations. Tests of a pure halite
layer showed no measurable permeability. Pore pressures in
the stratigraphic intervals range from about 0.5 to 9.3 MPa.
An anhydrite interbed (Marker Bed 139) appears to be one or
more orders of magnitude more permeable than the surrounding
halite. Hydraulic conductivities appear to increase, and pore
pressures decrease, with increasing proximity to the excavations.
These effects are particularly evident within two to three
meters of the excavations. Two tests indicated the presence
of apparent zero-flow boundaries about two to three meters
from the boreholes. The other tests revealed no apparent boundaries
within the radii of influence of the tests, which were calculated
to range from about four to thirty-five meters from the test
holes. The data are insufficient to determine 9 brine flow
through evaporites results from Darcy-like flow driven by
pressure gradients within naturally interconnected porosity
or from shear deformation around excavations connecting previously
isolated pores, thereby providing pathways for fluids at or
near lithostatic pressure to be driven towards the low-pressure
excavations. Future testing will be performed at greater distances
from the excavations to evaluate hydraulic properties and
processes-beyond the range of excavation effects. |
Pore pressure
in permeable
salt / high deviatoric
stress;
Reservoir Mechanics |
- |
Bérest, P.;
Bergues, J. et al. |
1996 |
A tentative evaluation of the MIT |
SMRI Spring Meeting, Houston, 14.-17.04.96 |
Paper |
|
In order to check the validity of the nitrogen-leak
MIT, a gas-brine interface was lowered to half-height of a
cavern well in order to minimize the risk of (real) gas leak.
The cavern, which had been leached out 14 years ago, has stabilized;
creep, percolation or thermal effects can be considered negligible.
Mock leaks were then provoked by injecting or withdrawing
known quantities of nitrogen or brine through the well-head.
The test gives clear evidence of the so-called barometric
effect; measured and calculated values of the gas-brine interface
displacement and leaks were found to be in good agreement. |
In-situ tests |
- |
Bérest, P.;
Blum, P. A. |
1993 |
In situ tests in salt caverns |
Proc. 7th. Symp. on Salt, Kyoto, 1993, Vol.
1, pp. 353-362 |
Paper |
|
Three original in situ tests performed on salt
caverns are described and discussed. The first is the measurement
of the natural vibrations of the brine mass contained in the
cavern and tubing. It is proved that their period is of the
order of one minute and is related only to the cavern volume,
therefore the estimation of cavern volume is a very simple
procedure. The second test consists of measuring the dips
induced at ground level by a sudden pressure variation in
a deep salt cavern. The average elastic properties of the
ground at a very large scale can be deduced from these measurements,
which are recorded by a high resolution tiltmeter.
The last test is the measurement of the volume rate of brine
naturally expelled from a salt cavern. The interpretation
is difficult, for many phenomena play a role in the expulsion
of brine. Slowly-varying phenomena are brine heating, cavern
creep and brine percolation. These three phenomena can be
quantified; their relative importance is variable during the
whole test, which lasted nine years. Atmospheric pressure
and temperature at ground level vary widely even during one
day. When these phenomena are taken into account, the effects
of the daily earth tides, in spite of being extremely small,
can easily be observed. |
In-situ tests;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. |
1996 |
Behavior of sealed solution-mined caverns |
Proc. ISRM Int. Symp., Eurock '96, pp.1127-1131 |
Paper |
|
When solution-mined caverns are sealed, rock-salt
creep and brine heating generate a brine pressure build-up
which in many cases leads to fracture. Brine seepage through
the rock-mass mitigates pressure build-up and can prevent
fracturing. |
Cavern abandonment;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. et al. |
1995 |
Behavior of sealed solution-mined caverns |
SMRI Spring Meeting, New Orleans, 1995 |
Paper |
|
Solution-mined caverns will be one day sealed
and abandoned. Due to an increasing concern in environmental
and safety issues, the long term behavior of brine bubble
initially enclosed in the cavern has been analyzed by several
authors, who lay emphasis on the fracturation risk due to
the progressive pressure build up in the cavern caused by
brine heating and cavern creep. In this paper we suggest to
take into account the rock salt permeability : even if small,
it allows some pressure release and leads to a final equilibrium
pressure which is substantially lower, in many cases, than
the lithostatic pressure. |
Cavern abandonment;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. et al. |
1995 |
Some comments on the MIT test |
SMRI Fall Meeting, San Antonio, 22.-25.10.95 |
Paper |
|
We discuss several aspects of the so-called
MIT test which is performed by lowering a nitrogen/brine interface
in the annular space of a salt cavern hole.
1. In case of a gas leak, the leak rate is underestimated
by a factor comprised between 1 and 2 when multiplying the
annular cross section by the interface rise rate.
2. The interface level, as measured by a logging equipment,
can be checked by:
i. Comparing the brine and gas pressures as measured at the
well head.
ii. Measuring the cavern compressibility and brine pre-pressure.
iii. Measuring the nitrogen injected mass.
3. Several factors, like thermal expansion, steady state and
transient creep, brine percolation can modify the interface
rate even in the case of absence of leak. The effect of some
of those factors can be precisely estimated.
4. A thorough examination of brine and gas pressure at ground
level allow for estimating the gas leak. |
In-situ tests; Thermo-dynamics; Rock Mechanics |
- |
Biggers, J. V.;
Dayton, G. O. |
1982 |
Brine migration in hot-pressed polycrystalline
sodium chloride |
ONWI-415 |
Report |
|
This report describes experiments designed
to provide data on brine migration in polycrystalline salt.
Polycrystalline samples of various grain sizes, density, and
purity were prepared from several commercial grade salts by
hotpressing. Three distinct experimental set-ups were used
to place salt billets in an induced thermal gradient in contact
with a brine source. The test designs varied primarily in
the way in the thermal gradient was applied and monitored
and the way in which brine migration was determined. All migration
was in enclosed vessels which precluded visual observation
of brine movement through the microstructure.
Migration velocities were estimated either by the timed appearance
of brine at the hot face of the sample, or by determination
of the penetration distance of migration artifacts in the
microstructure after tests of fixed duration. For various
reasons both of these methods were subject to a large degree
of error. Our results suggest, however, that the migration
velocity in dense polycrystalline salt may be at least an
order of magnitude greater than that suggested by single crystal
experiments.
Microstructural analysis shows that brine prefers to migrate
along paths of high crystalline activity such as grain and
subgrain boundaries and is dispersed rather quickly in the
microstructure. A series of tests were performed using various
types of tracers in brine in order to flag migration paths
and locate brine in the microstructure more decisively. These
attempts failed and it appears that only the aqueous portion
of the brine moves through the microstructure with the dissolved
ions being lost and replaced rather quickly. This suggests
the use of deuterium as a tracer in future work. |
Permeability of rock salt |
- |
| Borgmeier, M. |
1992 |
Untersuchungen zum belastungsabhängigen
Durchlässigkeitsverhalten von Salzgestein unter besonderer
Berücksichtigung der Porenraumbeladung
[Investigations on the load-dependent permeability behavior
of saliferous rock focusing on pore space loading] |
Clausthal-Zellerfeld : Techn. Univ., Fak. f.
Bergbau, Hüttenwesen u. Maschinenwesen |
Thesis (Abstract) |
German |
The shallow north German salt domes appear
to be ideal locations for natural gas storage caverns or as
repositories for nuclear and hazardous waste. One of the most
important conditions to be met for the safe operation of cavern
storages is the impermeability of the enclosing salt layers.
The stress field around cavities created by mining is considerably
disturbed for long periods of time as a result of this activity.
This can lead to changes in the permeability and porosity
in the area proximal to the emplacement chambers.
This work was carried out with the objective of investigating
the effect of various factors on permeability, and primarily
the influence of external loading and the internal pore pressure,
as well as fluid loading and temperature. The investigations
were carried out in a triaxial permeameter on natural salt
cores from cavern wells, as well as on model salt cores made
out of salt granulate.
The following parameters were varied systematically as part
of the test programme: the isostatic and anisotropic external
loads were varied between 5 - 60 MPa, and the gas injection
pressures were varied from 1 to 20 MPa. The tests revealed
that permeability decreases exponentially with increasing
isostatic and radial loading. No significant change occurs
by increasing axial load.
A considerable increase in permeability was determined for
each different load with a gas injection pressure/relocation
pressure ratio of 0.9 - 0.95 under isostatic stress conditions.
This increase can be attributed to the formation of microfractures
as well as a reduction in capillary saturation where a capillary
bound water is present in the pore space. The humidity level
of the fluid is a significant influencing factor on the permeability
behavior. Even minute levels of humidity in pore spaces at
an isostatic load of 20 MPa lead to a strong decrease in permeability
over time. In contrast, no change in permeability over time
can be measured if the humidity is removed from the core by
drying. A continuous temperature increase from 25°C to
80°C led to a linear decrease in permeability. Irreversible
permeability changes were determined during the investigations
looking at the influence of the relocation pressure as well
as temperature. Analogous trends were revealed between natural
salt cores and model salt cores with respect to most of the
factors influencing permeability. |
Interdependence rock stresses - permeability;
High deviatoric stress;
Pore pressure in permeable salt |
only abstract; German original at KBB |
Borgmeier, M.;
Weber, J. R. |
1992 |
Gaspermeabilitätsmessungen an homogenen
Modellsalzkernen
[Permeability investigations of homogenous model salt cores] |
Erdöl Erdgas Kohle 108 (1992) 10, pp.
412-414 |
Journal Article |
German |
In this paper permeability investigations of
homogeneous model salt cores using a triaxialpermeameter are
introduced and discussed. Of major interest was the influence
of stress on the gas flow through the core under different
water saturation conditions. In experiments outer stress was
varied between 5 MPa and 100 MPa while pressure at the entrance
of the pores was differed between 0.5 MPa and 15 MPa. The
results showed a clear dependence of gas permeability on the
inner and outer stress. Furthermore it could be proved that
the permeability behavior. is to a great extent subject to
loads on the pore space. |
Interdependence rock stresses - permeability;
High deviatoric stress |
- |
| Borns, D. J. |
1983 |
Petrographic study of evaporite deformation
near the Waste Isolation Pilot Plant (WIPP) |
Albuquerque : Sandia Nat. Lab., SAND83-0166 |
Report |
|
The Delaware Basin of southeastern New Mexico
contains ~ 1000 m of layered evaporates. Areas in the northern
Delaware Basin, bordering the Capitan reef, have anomalous
seismic reflection characteristics, such as loss in reflector
continuity. Core from holes within this zone exhibits complex
mesoscopic folds and extension structures. On a larger scale,
anticlines and synclines are indicated by structure contours
based on boreholes. The deformation is probably gravity-driven.
Such a process is initiated by basin tilting during either
a Mesozoic or Cenozoic period of uplift. The age of deformation
is equivocal, ranging from Permian to Recent small-scale structures
suggest that deformation was episodic with an early, syndepositional
stage of isoclinal folding. Later, open-to-tight asymmetric
folding is more penetrative and exhibits a sense of asymmetry
opposite to that of the earlier isoclinal folding. The younger
folds are associated with development of zonal crenulation
cleavage and microboudinage of more competent carbonate layers.
At the same time, halite beds developed dimensional fabrics
and convolute folds in anhydrite stringers. Late-stage, near-vertical
fractures formed in competent anhydrite layers. Microscopic
textures exhibit rotated anhydrite porphyroblasts, stress
shadow growth, and microboudinage. Except during late-stage
deformation, anhydrite and halite recrystallized synkinematically.
Drastic strength reduction in anhydrites through dynamic recrystallization
occurs experimentally near 200°C. However, evaporates
of the WIPP site never experienced temperatures >40°C.
Microscopic fabrics and P, T history of the evaporates suggest
that pressure solution was the active mechanism during deformation
of evaporates at the WIPP site. This conclusion stresses the
importance of fluid in facilitating deformation in low-temperature
evaporate sequences. The formation of pressurized brine pockets
is empirically associated with deformation. The development
of high-angle fractures in the uppermost anhydrite unit of
the Castile in response to folding provides the reservoir
for the brines. Brine fluids may have emanated from deforming
halite and anhydrite units through pressure-solution-induced
reduction of porosity. |
Creep behavior - phenomenological approach |
- |
| Borns, D. J. |
1987 |
Rates of evaporite deformation: The role of
pressure solution |
Albuquerque : Sandia Nat. Lab., SAND85-1599 |
Report |
|
Evaporite sequences have been intensely studied
for hazardous waste disposal and hydrocarbon development:
and storage. Rates of deformation are important in evaluating
the long-term performance of different evaporites. Reported
naturally occurring strain rates (x) are: 5 x 10-11 s-1 for
a salt glacier; 10-11 for mine closure; 3 x 10-14, 10-15,
and 10-16 for salt domes; 3 x 10-16 for bedded salt. Rates
are controlled by temperature, differential stress, and active
mechanism of deformation for each specific type of evaporate
and setting.
Strain rates are estimated through in-situ measurements and
the integration of geometric strain analysis and stratlgraphic
arguments for the time required for the observed deformation
to occur. An inherent problem in such calculations is the
large extrapolation of rates through time. Another approach
for rate estimation is to calculate x directly, using the
constitutive models for different deformation mechanisms that
may be dominant. Specific mechanisms can be determined from
petrofabric study, as at the WIPP site, SE New Mexico, where
textures indicating that pressure solution was active are
observed. Calculations based on experimental data are limited
by the relatively poor data on diffusion in intergranular
fluids. A variety of grain boundary diffusion models have
been used. Some models (e.g., cubic approximation of the grain
shape) leave gradients undefined at the grain edge.
For gravity-driven deformation near the WIPP site, geometric-stratigraphic
integration predicts a x of 10-14 s-1 to 10-16 s-l. Strain
rates of 10-15 to 10-16 s-1 are predicted using models for
dislocation creep and pressure solution. The rates using two
approaches, geometric-stratigraphic and constitutive, are
basically in agreement. These rates for the gravitydriven
flow structures near WIPP reflect lower temperatures and stresses
than salt domes. At the temperatures and stresses estimated
for the WIPP flow structures, pressure solution is probably
the dominant mechanism, rather than dislocation creep. It
remains to be determined where in the transition from transient
to steady-state response to an underground excavation in rock-salt
pressure solution becomes a major mechanism. |
Creep behavior - phenomenological approach |
- |
Borns, D. J.;
Stormont, J. C. |
1989 |
The delineation of the disturbed rock zone
surrounding excavations in salt |
Proc. 30th. U.S. Symp. Rock Mechanics, Morgantown,
19.-22.06.89, pp. 353-360 |
Paper |
|
At the Waste Isolation Pilot Plant (WIPP) in
southeastern New Mexico, the Disturbed Rock Zone (DRZ, the
zone of rock in which the -mechanical and hydrologic properties
have changed in response to excavation) has been characterized
with visual observations, geophysical methods, and gas-flow
measurements. The visual observations, geophysics, and gas-flow
tests have defined a DRZ at the WIPP mending laterally throughout
the excavation and varying in depth from 1 to 5 m. Desaturation
and microfracturing has occurred to some degree within the
zone. The dilation that results from the microfracturing in
the DRZ provides a component of the observed closure. |
Permeability of rock salt |
- |
| Bosworth, W. |
1981 |
Strain-induced preferential dissolution of
halite |
Tectonophys. 78 (1981), pp. 509-525 |
Journal Article |
|
Previous experiments on the effect of a fluid
phase in deforming rock and rock analogue systems have failed
to differentiate between the relative roles of stress and
permanent strain in controlling preferential dissolution at
fluid-grain boundary interfaces. Experiments are described
here in which halite single crystals were loaded under dry
conditions, followed by removal of load and immersion of the
crystals in brine. A correlation between net dissolution rate
and plastic strain of the adjacent crystalline material was
then observed at free crystal surfaces. Calculation of the
increase in free energy of the solid phase due to deformation
indicates that plastic strain should play a greater part in
controlling dissolution than elastic strain in the experimental
design reported here.
Although pressure gradients or differences in normal stress
may dominate over strain energy terms in producing solution
transfer or diffusion through disordered phases in natural
rock systems, these halite-water experiments demonstrate that
caution must be used in interpreting mechanisms from petrographic
and other observations of the phenomena now commonly referred
to as "pressure solution". |
Interdependence rock stress - permeability |
- |
Boulanger, A.;
Rousseau, A. J. |
1991 |
Method of rapidly abandoning large cavities
washed-out in rock salt |
US 5 004 298 |
Patent |
|
After they have been washed out, cavities (4)
in rock salt contain a large quantity of brine (8) at a temperature
which is lower than the temperature of the surrounding formation
(2). This means that the cavity cannot be sealed quickly because
the brine will expand progressively as it heats up. The method
of the invention serves to shorten the time period between
the end of working the cavity for salt and being able to abandon
the cavity finally from about 30 years to about 2 years. The
method consists in injecting quantities of a mixture (12)
into the cavity (4), the mixture being of greater density
than brine (8) and being capable of setting, with equivalent
quantities of brine (8) being returned to the surface, and
then in keeping the cavity (4) open after it has been completely
filled with mixture (12) for as long as it takes the rock
salt (2) to creep and fill up the shrinkage voids which appear
during setting of the mixture (12), after which the cavity
(4) can be sealed. To do this, it is advantageous to make
use of waste material for constituting the mixture (12). |
Cavern abandonment |
- |
| Bredehoeft, J. D. |
1988 |
Will salt repositories be dry ? |
EOS Transact., Am. Geophys. Union 69 (1988)
9, pp.121 + 131 |
Journal Article |
|
Data from the Waste Isolation Pilot Plant (WIPP)
site in southeastern New Mexico suggest an alternative hypothesis
to the widely held view that salt in a geologic environment
below the water table is "dry" and impermeable. The alternative
is that the salt section, which for the most part is of low
permeability and low porosity, is saturated with brine. The
implication of this hypothesis is that a repository in salt
will fill with brine once the ventilation of the facility
ceases to remove moisture. The rate of inflow to the facility
will depend on the permeability of the salt. Data from the
WIPP facility suggest an undisturbed salt permeability of
»10 nanodarcies (10-12 cm/s). Given such a low permeability,
the rate of brine inflow to an underground facility will be
quite low, of the order 0.01 L/day/m of tunnel. |
Permeability of rock salt |
- |
Bredehoeft, J. D.;
Papadopulos, S. S. |
1980 |
A method for determining the hydraulic properties
of tight formations |
Water Res. Res. 16 (1980) 1, pp. 233-238 |
Journal Article |
|
A method for testing formations of very low
permeability is presented. The method is based on an analytical
solution that describes the decay of a head change caused
by pressurizing the volume of water stored in a shut-in well.
Type curves prepared from this solution are matched with observed
data to determine the hydraulic properties of the formation
tested. The test is similar to the conventional slug test;
however, its much shorter duration makes the testing of extremely
tight formations feasible. |
Permeability of rock salt |
- |
Bush, D. D.;
Barton, N. |
1989 |
Application of small scale hydraulic fracturing
for stress measurements in bedded salt |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 26 (1989) 6, pp.629-635 |
Journal Article |
|
In situ rock stress measurements by small-scale
hydraulic fracturing were performed in two salt beds in the
Texas Panhandle, approximately 60km (36 miles) south of Amarillo,
Texas. Data analysis indicates that small-scale hydraulic
fracturing is applicable for determining the magnitude of
the minimum principal stress and the direction of the maximum
stress in salt. However, when hydraulic fracturing equations
based on elasticity are applied to salt (a non-elastic medium),
anomalously high in situ maximum stress and tensile strength
values are calculated. Due to the non-elastic properties of
salt and it's solubility, neither the derived maximum stress
nor the tensile strength values are considered valid using
the elastic hydraulic fracturing stress equations. |
Hydrofracturing |
- |
Cauberg, J.;
Walters, J. V. et al. |
1986 |
Rock mechanical behavior. and sealing aspects
of a closed-in salt cavity filled with brine (SMRI) |
SMRI Fall Meeting, Amsterdam, 21.-24.09.86 |
Paper |
|
Magnesium and potassium salts are being solution-mined
from carnallite/bischofite layers in the north-east of The
Netherlands, near Veendam. It is planned that, at the end
of the mining process, the brine-filled cavities will be abandoned.
The paper presents some rock mechanical considerations with
respect to cavity behavior. after abandonment, assuming perfect
cavity sealing. A finite element analysis of the cavity response
after shut-in, and the design requirements for a suitable
sealing plug for the borehole, are discussed.
The finite element calculations indicate a rise in brine pressure
after shut-in, followed by a gradual pressure increase towards
an asymptotic value. This change in pressure is accompanied
by adjustments in the cavity roof, wall and floor stresses.
Different sealing principles and plug designs are considered.
Cavity response after abandonment, long-term reliability,
and general compatibility with in-situ conditions are the
major criteria in the selection of a suitable sealing plug
material. |
Cavern abandonment;
Borehole seal;
Rock mechanics |
- |
Chan, K. S.;
DeVries, K. L. et al. |
1995 |
A damage mechanics approach to life prediction
for a salt structure |
Computational Mechanics '95, Proc. Int. Conf.
Comp. Eng. Sci., Hawaii, 30.07.-03.08.95, Vol.1, pp.1140-1145 |
Paper |
|
Excavated rooms in natural bedded salt formations
are being considered for use as repositories for nuclear waste.
It is presumed that deformation of the rooms by creep will
lead to loss of structural integrity and affect room life
history and seal efficiency. At projected repository temperatures,
two possible fracture mechanisms in salt are creep-induced
microcracking in triaxial compression and cleavage in tension.
Thus, an accurate prediction of the time of room life and
seal degradation requires a reliable description of the creep
and damage processes.
While several constitutive models that treat either creep
or fracture in salt are available in the literature [1-4],
very few models have considered creep and damage in a coupled
manner. Previously, Munson and Dawson [1] formulated a set
of creep equations for salt based on the consideration of
dislocation mechanisms in the creep process. This set of creep
equations has been generalized to include continuum, isotropic
damage [5] as a fully coupled variable in the response equation
[6]. The extended model has been referred to as the Multimechanism
Deformation Coupled Fracture (MDCF) model. A set of material
constants for the creep and damage terms was deduced based
on test data for both clean and argillaceous salt [7-9].
In this paper, the use of the MDCF model for establishing
the failure criteria and for analysing the creep response
of a salt structure is demonstrated. The paper is divided
into three parts. A summary of the MDCF model is presented
first, which is followed by an evaluation of the MDCF model
against laboratory data. Finally, finite-element calculations
of the creep and damage response of a salt structure are presented
and compared against in-situ field measurements. |
Creep behavior |
- |
Chester, F. M.;
Logan, J. M. |
1990 |
Frictional faulting in polycrystalline halite:
correlation of microstructure, mechanisms of slip, and constitutive
behavior |
American Geophysical Union: Geophysical Monograph
56, pp. 49-65 |
Paper |
|
The relation between friction constitutive
behavior and the mechanisms of shearing in a monomineralic,
polycrystalline material that deforms by combined cataclasis
and crystal-plasticity has been investigated by shearing thin
layers of halite between blocks of quartz sandstone at room
temperature (22°C), constant normal stresses between 20
and 70 MPa, and shear-displacement rates between 300 and 0.030
mm s-1 in a triaxial rock deformation apparatus. Constant
and stepping displacement rate modes of testing were utilized,
and some tests were preceded by a confining pressure (Pc)
reduction load path involving the reduction of Pc after establishing
a differential axial load. Pc-reduction causes the shear stress
to increase as the normal stress approaches zero, and , promotes
compaction and the formation of a slip surface in the halite
at small shear displacements relative to that for constant
normal stress and constant Pc load paths. Discrete changes
in the steady state microstructure and constitutive behavior
of halite with normal stress and displacement rate define
distinct mechanism fields of frictional faulting. Cataclastic
mechanisms dominate at normal stresses less than 40 MPa and
at all displacement rates tested, and the coefficient of friction
varies from 0.6 to 1.0 as a function of displacement rate.
Relatively large magnitude rate-weakening is observed at high
displacement rates and is associated with stick slip sliding
on a discrete surface. Because steady state shear involves
localized slip at these conditions,.the use of Pc-reduction
prior to shearing reduces the magnitude of displacement necessary
to achieve steady state. Small magnitude rate-dependence at
low displacement rates is associated with distributed cataclastic
flow and stable shearing behavior. Both the comminution rates
and stability transition at low normal stresses suggest that
the microstructural state is similarly affected by an increase
in normal stress and a decrease in displacement rate. At normal
stresses greater than 40 MPa and at all displacement rates
tested, halite undergoes nearly homogeneous simple shear by
dislocation mechanisms. However, the frictional behavior displayed
at these conditions implies that stable microfracturing or
some other pressure-sensitive process is operative, and that
flow is semi-brittle. |
Creep behavior |
- |
Clark, J. E.;
Papadeas, P. W. et al. |
1991 |
Gulf Coast borehole closure test well Orangefield,
Texas |
SMRI Fall Meeting, Las Vegas, 27.-19.10.91 |
Paper |
|
A borehole closure protocol for a Gulf Coast
site near Orangefield, Texas was developed by Du Pont. These
procedures were based largely upon recommendations provided
by EPA Region 6 and created a borehole closure test to demonstrate
that, under a worst case scenario, any artificial penetration
will seal naturally. The borehole closure test successfully
demonstrated natural sealing. Within one week of setting the
screen, tubing and pressure transducers in the borehole, testing
confirmed the absence of upward movement of fluid from the
test sand. The documentation for the absence of upward movement
included: 1) Schlumberger Water Flow Log* and 2) the absence
of pressure response on the upper transducer located outside
the tubing and inside the casing. Testing was conducted in
accordance using specified procedures, with pressure testing
conducted at even higher pressures to allow an added margin
of confidence. The borehole closure test provides a significant
additional margin of confidence that there will be no migration
of hazardous constituents from the injection zone for as long
as the waste remains hazardous. |
In-situ tests |
- |
| Cosenza, P. |
1996 |
Sur les couplages entre comportement mécanique
et processus de transfert de masse dans le sel gemme
[Coupled effects between mechanical behavior and mass transfer
phenomena in rock salt] |
Paris : Univ. |
Thesis |
french |
The results of a field experiment carried out
in the Mines de Potasse d'Alsace (MDPA, France) show that
rock salt is permeable to gas and to brine, at least around
underground facilities (four radii far from the gallery wall).
In contrast to gas flow rate, brine flow rate is interpreted
in a satisfactory way using a model based on Darcy's. law.
On the other hand, after brine percolation into the rockmass,
capillarity has a significant effect on the gas injection
flow rate.
During laboratory compressive triaxial tests, under high confining
pressure (up to sixty Mpa) unjacketed samples of MDPA.salt
show a lower damage initiation and a lower compressive strength
than jacketed samples. These effects induced by salt permeability
become more marked when brine is used as confining fluid.
In the theoretical part, a framework is proposed and used
to discuss dissolution/crystallisation phenomenon leading
to a change of transport properties. The "healing process",
associated with viscoplastic strains of grains can explain
the extremely low permeability of rock salt at a geological
time scale.
Results of the calculations on underground structures show
that a very low permeability which may not be measurable using
existing techniques, modifies in a significant way the long
term evolution of an underground storage. |
Rock mechanics;
Permeability - High deviatoric stress;
Interdependence rock stress - permeability;
Reservoir |
French thesis separately;
(1 copy for SMRI) |
Cosenza, P.;
Ghoreychi, M. |
1993 |
Coupling between mechanical behavior and transfer
phenomena in salt |
Proc. 3rd Conf. Mech. Behavior of Salt, Palaiseau,
14.-16.09.93, pp. 271-293 |
Paper |
|
After a review of the basic coupling phenomena
for salt subject to gas and /or brine migration, Thermodynamics
of Open Porous Media is used to set up a model taking into
account Thermal, Hydraulic, Chemical and Mechanical couplings.
The model is simplified and applied to a spherical structure
in salt. The results show that the structure response is very
sensitive to hydro-chemical effects which change the thermo-mechanical
behavior of salt. |
Interdependence rock stress - permeability |
- |
Cosenza, P.;
Ghoreychi, M. |
1997 |
Évolution de la perméabilité
du sel gemme sous sollicitations mécano-chimiques
[Permeability evolution of rock salt under mechano-chemical
stresses] |
Bull. Soc. Géol. France; in Press |
Journal Art.(Abstr.) |
|
The results given in this paper deal with experimental
and theoretical studies performed on rock salt permeability,
in the framework of hydrocarbon or radioactive waste storage.
The results of a field experiment carried out in a salt layer
in the Mines de Potasse d'Alsace is in agreement with those
of the experiments performed in other salt formations : rock
salt is permeable to gas and to brine, at least around underground
facilities. Its permeability is about 10-21 m². This
permeation is due to damage resulting from excavation or tectonics.
Considering rock salt as a porous, permeable and reactive
medium, a theoretical framework is used to discuss two phenomena
playing a role on permeability: (a) dissolution/crystallisation
in microcracks due to brine solubility changes (b) healing
process due to hydrostatic loading. The results of calculations
are in agreement with those of laboratory tests, and show
that a mechano-chemical coupled effect associated with viscoplastic
deformation of grains can explain the extremely low permeability
of rock salt at a geological time scale. |
Rock mechanics;
Permeability - High devitoric stress;
Interdependence rock stress - permeability |
only abstract, in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1997 |
Mesure de la perméabilité in
situ du sel
[In situ permeability measurement in salt] |
Rev. Franc. Géotechn.; in Press |
Journal Art.(Abstr.) |
|
In order to measure rock salt intrinsic permeability
located far from underground facilities, an in situ experiment
was performed in the Amélie mine belonging to the Mines
de Potasse d'Alsace (MDPA, Mulhouse, France). A vertical borehole
was drilled from a niche excavated to access to the S1 bed,
very pure in halite. The selected salt bed is approximately
one meter thick and is located 16 meters away from the gallery
floor. Test fluids were nitrogen and saturated brine. In order
to minimize and to control disturbing phenomena (thermal effects,
solution/crystallization and creep), constant temperature
and constant pressure tests were recommended. As a matter
of fact and because of the geological conditions (low thickness
of the tested halite bed), a special device had to be designed
and its principal components (packers and fluid injection
systens) needed to be tested in the laboratory and in the
field.
The results of the field experiment show that rock salt is
permeable to gas and to brine, even far enough from underground
openings.
The results of the tests with brine are interpreted in a satisfactory
way using a model based on the Darcy's law and characterized
by a permeability value of 2 x 10-21 m2 and an initial pore
pressure value of 1 MPa. Analysis of measured gas flow rate
shows that:
- after a brine percolation, capillary pressure effect
is significant
- fluid migration in salt is not controlled by Darcy diffusion,
Knudsen effect and partial saturation
may play an important role. |
Pore pressure;
Permeability of rock salt;
Reservoir Mechanics |
only abstract, in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1996 |
In situ gas and brine permeability measurements
in salt |
Proc. 4th Conf. Mechanical Behavior of Salt,
Montreal, 1996; in Press |
Paper |
|
The results of a field experiment carried out
in a salt layer in the Mines de Potasse d'Alsace (France)
confirm that rock salt is permeable to gas and to brine, at
least around underground facilities.
A simple analysis of measured gas flow rate shows that (a)
capillary pressure effect is significant (b) fluid migration
in salt is not controlled by Darcy diffusion.
The results of the tests with brine are interpreted in a satisfactory
way using a model based on Darcy's law characterized by a
permeability value of 2 x 10-21 m² and an initial pore
pressure value of 1 MPa. The following non linear effects
are considered : (1) salt damage created by borehole drilling
(2) effective stress changes (3) change in salt concentration
of brine saturation state resulting from pressure changes. |
Pore pressure;
Permeability of rock salt;
Reservoir Mechanics;
Interdependence rock stress - permeability |
in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1995 |
First results and interpretation of in situ
permeability measurement in salt to gas and to brine |
Proc. 5th Progress Meeting PEGASUS, EUR 16746,
pp.167-175 |
Paper |
|
An in situ experiment is being performed in
the Mines de Potasse d'Alsace (M.D.P.A., Mulhouse, France)
in the framework of a C.E.C. contract (coordinator: ANDRA,
contractor: G.3S, technical assistance : COSEREP). The objective
of this test is to measure the permeability of salt to brine
and to gas.
This paper deals with the experimental procedure, the measurements,
and the first interpretation of the results.
Two tests with nitrogen under the pressure levels of 4 and
6 MPa, and three tests with brine under 2, 4 and 6 MPa of
pressure have been performed. The experiments are completed
with three more tests, again with gas under 2,4 and 6 MPa.
These last tests allow to check that a salt formation previously
subjected to brine is not permeable to gas regarding capillary
effects.
The experimental set up is capable to measure very low values
of permeability about 10-21 m². The basic flow mechanism
involved in gas flow is possibly a multiphase flow for which
capillary pressure may play an important role. On going and
further studies will allow the final interpretation of the
experimental results. |
Interdependence rock stress - permeability;
Permeability of rock salt;
Reservoir Mechanics |
- |
Doe, T. W. ;
Boyce, G. |
1989 |
Orientation of hydraulic fractures in salt
under hydrostratic and non hydrostratic stresses |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 26 (1989) 6, pp. 605-611 |
Journal Article |
|
Laboratory experiments of hydraulic fracturing
in salt have shown that the breakdown pressure does not vary
significantly with the differences between the maximum and
minimum stresses normal to the borehole axis. The presence
of a non-hydrostatic stress in salt may be determinable from
the form of the hydraulic fracture alone. A series of laboratory
experiments were performed to determine the influence of deviatoric
in situ stress on the form and orientation of hydraulic fractures
in salt.
The hydraulic-fracturing tests were run on prismatic blocks
in a polyaxial loading frame over a range of stress ratios
from 1 (hydrostatic) to 1.5. The fracturing oil contained
a fluorescent dye that marked the fracture traces for mapping
after the samples were split.
The results indicate that the form of the hydraulic fracture
reflects whether or not the stresses are nearly hydrostatic.
For large stress ratios (> 1.5), the fractures are straight
and strongly oriented. For stress ratios near one, the fractures
are poorly oriented and exhibit significant branching. Thus,
proximity to hydrostatic conditions can be determined from
the form of the hydraulic fracture alone, regardless of ambiguities
in the interpretation of pressure-time records from the fracturing
experiment. |
Hydrofracturing |
- |
| Durup, J. G. |
1994 |
Long-term tests for tightness evaluations with
brine and gas in salt (Field test n° 2 with gas) |
SMRI Fall Meeting, Hannover, 1994 / SMRI Res.
Proj. Rep. No. 94-0002-S |
Paper + SMRI-Report |
|
Hydraulic fracturing tests were performed at
about 900 meters (2950ft) deep in a bedded salt formation
at ETREZ, eastern France. These tests comprised a "Field Test
N°2 with gas" that followed an initial field test, using
brine as the test fluid, which was performed in the same Well
EZ58.
The principal objectives were to determine hydrofrac gradients
at different pressurization rates, to compare hydrofrac gradients
values obtained with liquid and gas, and to study in such
in-field conditions, self-healing effects and percolation
of fluids in the salt massif. These are believed to be relevant
data for defining maximum operating pressures in salt formations.
With nitrogen as the test fluid, the hydrofrac gradient with
slow pressurization (long-term test over a one-year period)
was 0.237 bar/m (1.05 psi/ft). A value of 0.236 bar/m (1.04
psi/ft) was obtained with relatively, fast pressurization
(short-term test over a one-day period). With brine as test
fluid the values were 0.240 bar/m (1.06 psi/ft) and 0.256
bar/m (1.13 psi/ft) for the long and short-term tests respectively.
The salt massif seems more resistant to hydrofracture (higher
frac gradient) when only one phase (brine) is present in the
crystal interstices.
Testing in Well EZ58 began in 1989 and ended in 1994. For
each test fluid, the short-term test was performed some time
after the end of the long-term test. It was concluded that
under field conditions, recrystalization processes can heal
fractured salt rapidly, in about one month. These tests demonstrate
clearly, that this self-healing process entirely, restores
the mechanical strength of the salt massif.
The test results establish that the test fluids percolated
in the salt massif around the tested openhole before hydrofrac
at all the pressure levels tested. With equivalent conditions,
higher percolation rates were observed for gas than for brine.
With brine, interpretation as Darcy flow gave satisfactory
fitting of calculated and measured flow rates. The estimated
permeability was 6 x 10-20 m² assuming 1 % porosity.
With gas, interpretation was more problematic because of two-phase
flow and pronounced capillary effects. However, the extent
of gas infiltration into the salt massif at close to lithostatic
pressures was estimated as being limited to about one meter
over the one-year testing period. |
In-situ tests;
Permeability - liquid pressure above confining pressure;
Reservoir Mechanics |
- |
| Durup, J. G. |
1994 |
Essais de perméabilité dans un
massif salifère
[Permeability tests in a salt mass] |
Ann. Ass. Franc. Techn. Petrol. Conf. / Pétrol.
Tech. 387, pp.17-20 |
Journal Article |
french |
In this tightness/fracturing test at brine,
the pressure in the free space was gradually raised in steps
of 0.1 MPa. The pressure reached was held constant for a period
of 1 month by precisely controlled injection of fluid. The
results presented here were obtained by applying Darcy's Law
to interpret the development of the fluid injections |
Permeability of rock salt;
Hydrofracturing;
Reservoir Mechanics |
- |
| Dusseault, M. B. |
1989 |
Saltrock behavior as an analogue to the behavior
of rock at great depth |
Maury; Fourmaintraux (Eds.): Rock at great
depth, 1989, pp.11-17 |
Paper |
|
The elastoviscoplastic behavior of saltrocks
may be interpreted in terms of a number of different fundamental
deformation mechanism that act at different rates at different
shear and normal stress levels. The paper presents a new approach
to a constitutive law for these materials, recognising the
complex behavior, and making distinctions between different
types of yield criteria and viscous flow laws. An attempt
is made to develop this behavior as an analogue to the behavior
of rock at high temperatures and stresses, where viscous mechanisms
become possible. It is emphasized that an appreciation of
the dominant deformation mechanisms acting at particular conditions
will guide the form of macroscopic constitutive laws for non-saltrocks. |
Creep behavior |
- |
Ehgartner, B.;
Linn, J. K. |
1994 |
Mechanical behavior of sealed SPR caverns |
SMRI Spring Meeting, Houston, 25.-27.04.94 |
Paper |
|
It is inevitable that sealing and abandonment
will someday occur in a U.S. Strategic Petroleum Reserve (SPR)
cavern or caverns. To gain insight into the long-term behavior
of a typical SPR cavern following sealing and abandonment,
a suite of finite element analyses were performed. The analyses
predict how quickly and to what extent a cavern pressurizes
after it is plugged. The analyses examine the stability of
the cavern as it changes shape due to the increased pressures
generated after plugging. Internal fluid pressures in a brine
filled cavern eventually exceed lithostatic pressure in the
upper portion of the cavern resulting in enlargement and stress
reduction. The buildup of fluid pressure after plugging is
largely determined by salt creep, salt dissolution, and geothermal
heating of brine. Volumetric closure due to creep increases
brine pressure. Salt dissolution and geothermal heating occur
when the brine is unsaturated and cooler than the surrounding
salt at the time of plugging. The individual and coupled effects
of creep, dissolution, and geothermal heating are modeled.
The analyses suggest that the predicted rate and magnitude
of fluid pressurization in SPR caverns is not high enough
to result in fracturing of the salt. However, cavern pressure
can be substantially mitigated by delaying plugging until
the brine has come closer to thermal equilibrium. |
Cavern abandonment;
Thermodynamics;
Creep behavior |
- |
Faske, B.;
Stein-Lausnitz, E.-G.v. et al. |
1987 |
Vorrichtung zum Einbringen eines Dichtmittels
in ein Bohrloch
[Apparatus to inject a sealant into a well] |
DD 262 887 A1 |
Patent |
German |
The apparatus is used for the preservation
and maintenance of wells filled with liquid media, in particular
caverns in evaporites, following termination of usage. Below
the well seal a container is positioned containing the sealant/protective
medium, the walls of which vessel are made either totally
or in part of a single material which is heavily corroded
by the content of the well and which decomposes as a result.
If as a result of geomechanical processes the gas cap is displaced
and the level of the liquid rises up to that of the container
then the corroded metal is perforated and the sealant can
escape from the containers and spread across the surface of
the liquid. |
Borehole seal |
- |
Finley, R. E.;
Zeuch, D. H. et al. |
1994 |
Sealing of boreholes using natural, compatible
materials: granular salt |
Eurock '94, Delft, 29.-31-08.94, pp. 753-760 |
Paper |
|
Granular salt can be used to construct high
performance permanent in boreholes which penetrate rock salt
formations. These seals are described as seal components of
the host rock, the seal material, and the seal rock interface.
The performance of these seal systems is defined by the complex
interactions between these seal system components through
time. The interactions are largely driven by the creep of
the host formation applying boundary stress on the seal forcing
consolidation of the granular salt. The permeability of well
constructed granular salt seal systems is expected to approach
the host rock permeability (<10-21 m² (10-9 Darcy))
with time. The immediate permeability of these seals is dependent
on the emplaced density. Laboratory test results suggest that
careful emplacement techniques could result in immediate seal
system permeability on the order of 10-16 m² to 10-18
m² (10-4 darcy to 10-6 darcy). The visco-plastic behavior
of the host rock coupled with the granular salts ability to
'heal' or consolidate make granular salt an ideal sealing
material for boreholes whose permanent scaling is required. |
Borehole seal |
- |
Fischle, W. R.;
Stöver, W. H. |
1986 |
Construction of a bulkhead and measurement
under brine pressure |
SMRI Fall Meeting, Amsterdam, 21.-24.09.86 |
Paper |
|
The intrusion of water or brine into a final
repository for radioactive waste in salt rock is regarded
as the greatest hypothetical accident scenario.
The intrusion of water or brine into a final repository for
radioactive waste in salt rock is regarded as the greatest
hypothetical accident scenario. The most crucial aspect is
the prevention of dispersal of the dissolved radionuclides
into the biosphere. Special plugs or seals in addition to
the natural barriers of the host rock and caprock play a significant
role in preventing the escape of nuclides through cavities.
The decision to flood the abandoned potash mine at Hope, north
of Hannover, was made in 1982. In addition to geochemical,
geophysical and aeomechanical investigations this provided
the first opportunity for testing the tightness of a bulkhead
in situ at a pressure of 6 MPa at the real scale of 1:1. |
Borehole seal;
In-situ tests |
- |
| Fokker, P. A. |
1995 |
The behavior. of salt and salt caverns |
Delft : Techn. Univ. |
Thesis |
|
Salts are mined for both storage and extraction
purposes, either via dry or solution mining techniques. For
operational, environmental and geological purposes, it is
important to understand and predict the in situ behavior.
of salt, in particular the creep and strength characteristics.
A micro-mechanically based explanation and quantification
of primary (strainhardening) creep in rock salt have not yet
been reported. Creep models for primary creep are still mainly
based on curve fitting. At relatively low temperatures (0-200
C°), as encountered near all excavations, the primary
creep phase is very important, certainly at laboratory time
scales.
Since understanding of the mechanism may be important in extrapolating
relatively short term laboratory tests to long term creep
in situ, an attempt is made in this thesis to explain (and
simulate) both primary and secondary (steady state) creep
via a micro-mechanical approach. Deformation in this model
is governed by dislocation motion, which becomes increasingly
hindered with strain by crystal lattice defects, resulting
in strain hardening. The defects in turn are assumed to be
dislocation dipoles (two mutually trapped dislocations of
opposite sign). Recovery in this model is related to the thermally
activated generation of vacancies and interstitials by the
disintegration of dipoles consisting of very near dislocations.
These vacancies and interstitials in turn precipitate on other
(more rigid) dipoles, allowing them to annihilate by climb.
This model describes the observed measurements very well,
especially in describing transition zones after changing a
strain rate. Unfortunately this model does not result in a
simple constitutive equation, although possible in theory.
Simpler, but for general practice usually sufficiently accurate,
curve-fitting laws have been implemented in the DIANA Finite
Element Code, now capable of simulating salt creep behavior.
Rock salt at greater depth is usually impermeable, thus forming
a good seal against fluid penetration. A combination of high
deviatoric and low confining stresses leads to dilation and
even failure during deformation. Tensile stresses can result
in micro- or macro-fracturing of the salt. These mechanisms
affect the sealing capacity of salt. Contrary to common opinion
so far, it is shown here that fluid pressures (as present
in, for instance, caverns or aquifers) do not increase the
sal'ts bearing capacity. Hence, salt needs to be treated like
a Terzaghi material, subtracting fluid pressures from the
stress field when determining dilation or fracture criteria.
The risk of fracturing or failure implies that care should
be taken with cavern operations. In fluid storage caverns,
fracturing can occur after a period of low cavern pressures
and subsequent filling and pressurizing. The stress field
around the cavern may be relaxed, whereby the salt stress
no longer coincides with the initial stress situation. Fractures
become possible, particularly if the cavern is not embedded
in a large salt mass but is close to a non-creeping overburden,
taking stresses from the salt by arching eventually. Similarly,
such a stress relaxation can lead to a fracture connecting
an aquifer to a cavern or mine, flooding being the result.
Another consequence of the relatively easy fracturing of salts
is that large fluid volumes cannot be sealed permanently by
plugging the cavern entrance (casing). Density differences
between fluid and rock salt will finally lead to an excess
fluid pressure near the top (roof) of the cavern, resulting
in permeation and fracturation of the cavern roof, resulting
in cavern fluid leakage. Although occurring very slowly, the
caverns will vanish in time, resulting in surface subsidence.
Special attention has been paid to the Veendam solution
mines, which have been mined in multicomponent salts (sodium,
magnesium, potassium salts). These offer unique opportunities
to observe creep and fracture related features over a short
period of time (compared to caverns constructed in rock
salt only). |
Creep behavior;
Interdependence rock stress - permeability;
Permeability - liquid pressure above confining p;
Reservoir Mechanics |
- |
Fokker, P. A.;
Kenter, C. J. et al. |
1993 |
The effect of fluid pressures on the mechanical
stability of (rock) salt |
Proc. 7th. Symp. on Salt, Vol. 1, pp.75-82 |
Paper |
|
The effect of fluid pressures on the behavior.
of salt has not been investigated thoroughly until now, since
salt rocks at great depths have been considered impermeable
and non-porous. Recent investigations have shown, however,
that permeability of salts may be significantly increased
both at sub and above lithostatic pressures, which may have
a large influence on the strength. This permeability increase
is believed to be caused by the viscous micro fracturing at
above lithostatic fluid pressures, or by shear dilatancy at
sublithostatic fluid pressures and sufficiently large deviatoric
stresses. The implication of this permeability increase is
that pressure communication between pore fluid and cavern
fluid needs to be taken in account and salt needs to be treated
as a Terzaghi material, splitting total stresses in effective
stresses and pore pressures. Hence conventional cavern analysis
with cavern pressures treated as boundary loads rather than
boundary pore-pressures may not be right for caverns with
sublithostatic pressures at greater depths and for caverns
with above lithostatic pressures in general. Also standard
salt strength determination on jacketed triaxial samples may
not be directly applicable, as for those cavern conditions
fluids will penetrate into salts. The above theory is supported
by laboratory tests and field evidence; for example, unjacketed
triaxial tests have been conducted on halite, which showed
that the strength measured this way does not exceed the UCS
value of approximately 300 bar, regardless of the lateral
pressure applied. From fracture tests on halite it was found
that fracturing occurs at fluid pressures of about 20 bar
in excess of the lowest ambient salt pressure, whilst earlier
tests showed that permeability was significantly increased
at lower excess pressures. Results were further found to be
in agreement with the EZ58 field test of Gaz de France and
lab tests reported in literature. |
Interdependence rock stress - permeability;
Permeability - High deviatoric stress;
Perm. - Liquid pressure above confining pressure |
- |
Fokker, P. A.;
Kenter, C. J.. |
1994 |
The micro mechanical description of rock salt
plasticity |
Proc. Eurock '94, Delft, 29.-31.08.94, pp.705-713 |
Paper |
|
The constitutive behavior. of rock salt is
explained from micro mechanical concepts. Rock salt plasticity
(or primary creep) can be well explained by a dislocation
glide mechanism, where gliding becomes increasingly hindered
by dislocations (in fact dislocation pairs or dipoles), disturbing
the glide paths. Such dipoles are both the main source for
hardening, as well as the main source for time dependent behavior.
From such a description a deformation model can be derived
that relates strain rates to stresses, strains and the temperature.
The resulting creep curve bears great similarity with the
Lemaitre and the Menzel-Schreiner deformation law. However,
different from these curve fitting laws, primary creep here
is based on proper micro-mechanical considerations and moreover
can cope with the transient effects as occurring when load
or strain rate increments are suddenly changed. |
Creep behavior |
- |
| Förster, S. |
1974 |
Durchlässigkeits-und Rißbildungsuntersuchungen
zum Nachweis der Dichtheit von Salzkavernen
[Permeability and fracturing investigations to verify the
tightness of salt caverns] |
Neue Bergbautechn. 4 (1974) 4, pp. 278-283 |
Journal Article |
German |
The main criteria for the construction of storages
or for the use of existing underground cavities for storage
is the tightness of the rock surrounding the cavity. The maximum
working pressures for the cavity must therefore be selected
to ensure that the host rock will not fracture, thereby excluding
possible leakage. The investigations described here focus
on the rock surrounding the salt cavity. |
Permeability of rock salt;
Interdependence rock stress - permeability;
Hydrofracturing |
- |
| Förster, S. |
1985 |
Gasdruckbelastbarkeit und Rißbildung
der für die unterirdische Gasspeicherung in Kavernen
bedeutsamen Salinargesteine des Zechsteins
[Stressability by gas pressure and fracturing of evaporites
of Zechstein-formation relevant to gas cavern storage] |
Freiberger Forsch.-H. A 724 |
Report (Abstract) |
German |
Proceeding from both the theoretical relations
between initial fracturing and fracture propagation in tight
saline rock and the prevailing stress state numerous results
of in-situ investigations gained in several salt deposit areas
are interpreted in a uniform mode. Data are estimated serving
as a basis for the calculation of maximum working pressure
in cavern storage. The results obtained are also important
in designing sealing measures in potash and rock salt mining. |
Hydrofracturing |
only abstract; German original at KBB |
Fuenkajorn, K.;
Daemen, J. J. K. |
1996 |
Sealing of boreholes in rock: an overview |
in: Aubertin et.al.: Rock Mechanics, 1996,
pp.1447-1454 |
Paper |
|
This paper describes the process, criteria,
and considerations for design of borehole seals in rock, with
a main emphasis on the hydraulic and mechanical performance
of the cementitious and bentonitic seals. It is recommended
that design and material selection for borehole seals be site-specific.
Evaluation of sealing effectiveness should be made on the
entire seal system, i.e. seal, seal-rock interface, and the
surrounding rock. |
Borehole seal |
- |
Fuenkajorn, K.;
Serata, S. |
1994 |
Dilation-induced permeability increase around
caverns in salt |
Proc. 1st. North American Rock Mechanics Symp.,
Austin, 01.-03.06.94, pp.649-656 |
Paper |
|
A permeability model is developed from triaxial
flow test data to predict the permeability increase of rock
salt around storage caverns, as affected by excavation, confining
and internal pressures, age and shape. The confining and internal
pressures may increase the surrounding salt permeability from
its in-situ value of 10-22 m² to as high as 10-16 m².
The permeabilities increase with time and reach their ultimate
value at within one year after excavation. Salt permeabilities
around elliptical caverns are several orders of magnitude
higher than those around the spherical cavern. |
Permeability - High deviatoric stress |
- |
Garg, S. K.;
Nur, A. |
1973 |
Effective stress law for fluid-saturated porous
rocks |
J. Geophys. Res. 78 (1973) 26, pp. 5911-5921 |
Journal Article |
|
The functional relationship between various
definitions of effective stress, i.e., conventional, Biot-Willis-Nur-Byerlee,
and theory of interacting continua (Tinc), is explored both
theoretically and experimentally. Stress-strain data on dry
and saturated Weber sandstone demonstrate that the conventional
effective stress law grossly overestimates the pore pressure
effect, whereas Biot-Willis-Nur-Byerlee and Tinc laws somewhat
underestimate this effect. Failure is examined from a microscopic
point of view. It is shown that Tinc-type effective stress
laws cannot account for the effect of pore pressure on failure
in a simple manner. Failure is one aspect of material response
in which the conventional effective stress law is useful.
In summary, it appears necessary to have two effective stress
laws, i.e., one to describe the stress-strain response and
a second to delineate the failure surface. |
Pore pressure in permeable salt;
Reservoir Mechanics |
- |
| Gaz de France |
1990 |
Field tests in well EZ 58 |
SMRI Res. Proj. Rep. No. 90-0002-S |
SMRI Research Report |
|
The matching curves are presented on figures
20 and 21.
It was made clear during the simulation progress that it was
not possible to correctly match the injected volumes over
the whole test, taking into account the assumptions about
pressures initialization and salt petrophysical characteristics
invariance in the vicinity of the well during pressure gradient
increase.
Indeed, if the permeability is chosen so as to adjust the
brine quantities on the first steps (1.6 to 2 gradient), the
volume required for the next steps will be much too high.
If, on the contrary, the matching is made on the last steps
the computed values will be too small for the first steps.
In the first case, we have to assume that the characteristics
of the open hole sail change during the test : the permeability
in the vicinity of the well or, at least the productivity
index would decrease with time.
In the second case, it is possible to think that the uncertainty
on the initial pressures condition prevents to correctly simulate
the flow rate at the beginning of the test, while its influence
becomes less important on the last steps.
This last assumption was eventually retained for the interpretation.
The matching was mainly performed on the permeability as it
is less sensitive to the porosity. It is possible, for instance,
to obtain similar computed flow rates with the following values
:
k = 6 x 10-5 mD = 1 % (mean value)
k = 5.5 x 10-5 mD = 2 % (mean value)
k = 6.5 x 10-5 mD = 0.5 % (mean value)
The influence of other parameters was also examined : if
rock or fluid compressibility is increased, the variation
of the injected volumes from one gradient to another one
stays similar, but it is again necessary to decrease the
permeability to find the same values.
Eventually, the simulations were performed with a permeability
of 6 x 10-5 mD and a porosity of 1 %. |
In-situ tests;
Permeability - liquid pressure above confining pressure;
Reservoir Mechanics |
- |
Gloyna, E. F.;
Reynolds, T. D. |
1961 |
Permeability measurements of rock salt |
J. Geophys. Res. 66 (1961) 11, pp. 3913-3921 |
Journal Article |
|
A method is described for measuring the permeability
of rock salt. Different specimens of salt were studied, and
the technique was checked by use of a solid crystal of sodium
chloride. Both reactive and nonreactive fluids were used in
collecting permeability data. Permeability tests were run
on rock salt from both dome and bedded formations. The dome
salt was found to have a very low permeability, and the bedded
salt was found in general to be impermeable. Where there was
some measurable permeability under the conditions of the test,
it was found that the permeating flow occurred through cracks
or fractures in the salt and not through the crystals themselves.
These fractures were apparently caused by the relaxation of
stress which occurs when underground samples are removed from
a compressed formation. The dome salt was found to have more
fractures than the bedded salt, owing probably to its lower
elastic strength. Such surface fractures, found in both types
of salt, will be localized in the vicinity of a mine and consequently
will not extend throughout a formation. |
Permeability of rock salt |
- |
Gniady, C. T.;
Ehgartner, B. L. |
1993 |
Fracture predictions for over-pressurization
of sealed wellbores |
SMRI Fall Meeting, Lafayette, 24.-28.10.93 |
Paper |
|
The finite element method is used to evaluate
the mechanical response of a wellbore that is internally pressurized
above lithostatic pressure. The uncased wellbore is emplaced
in salt, a rheologic media. Salt creep tends to relax the
stress state in the salt around the wellbore making it possible
to expand the size of the wellbore without fracturing the
surrounding salt. This is a very desirable sealing feature
as plugging and abandoning a cavern typically results in wellbore
pressures that exceed lithostatic pressure. The analyses show
that the rate of pressurization determines the hoop stress
in the salt surrounding the wellbore. Pressurizing the wellbore
above the surrounding lithostatic pressure reduces the hoop
stress and, for very quick pressurization rates, the hoop
stress can become tensile and fracture the salt. For most
cavern fields, the pressurization rates after sealing and
abandonment should be well below that required to mechanically
fracture the salt surrounding a plugged wellbore. In the long-term,
however, other mechanisms may contribute to fracture, or to
increase the permeability in the salt. |
Cavern abandonment;
Rock mechanics |
- |
Hambley, D. F.;
Dusseault, M. B. et al. |
1988 |
Characterization of saltrock creep behavior |
Key questions in rock mechanics: Proc. 29th
U.S. Symp., pp.179-189 |
Paper |
|
Improvement of saltrock creep laws requires
microscopic mechanisms incorporation, adequate tests, appropriate
equation forms, and better use of field data. A low-stress
pressure solution mechanism, affected by grain size, may he
important for field modeling, leading to a stress exponent
of 1.0 in situ for saltrocks with sufficient moisture content. |
Creep behavior |
- |
| Herrmann, A. G. |
1980 |
Geochemische Prozesse in marinen Salzablagerungen:
Bedeutung u. Konsequenzen f. d. Endlagerung..
[Geochemical processes in marine salt deposits: their significance
and their implications in connection with disposal of radioactive
waste within salt domes] |
Z. dt. geol. Ges. 131 (1980), pp.433-459 |
Journal Article |
German |
Attempts to effect permanent disposal of radioactive
wastes in marine evaporates should do nothing to disturb,
either in the short or the long term, the present relative
stability of such bodies of rock. It is necessary to take
account of all of the geochemical and physico-chemical reactions
known to have been involved in the processes which formed
the evaporates before proceeding to an acceptable strategy
for disposal of radionuclides.
These processes can be represented as three kinds of metamorphism:
1. solution metamorphism, 2. thermal metamorphism, 3. dynamic
metamorphism. In all of the evaporate occurrences in Germany
such processes have been influential in altering, on occasion
significantly, the primary mineralogical composition and have
also promoted a considerable degree of transposition of material.
Given similar geochemical and physico-chemical premises, these
metamorphic processes could become effective now or in the
future. It is therefore necessary to discuss the following
criteria when examining salt domes as permanent repositories
of highly radioactive substances:
(1) Temperatures 90° ± 10°C at the contact
between waste containers and rock salt;
(2) Temperatures 75°C within zones of carnallite rocks;
(3) Immobilisation of high-level waste in crystalline forms
whenever possible;
(4) Systems of additional safety barriers around the waste
containers or the unreprocessed spent fuel elements. The
geochemical and physical effectiveness of the barriers within
an evaporate environment must be guaranteed. For example:
Ni-Ti-alloys, corundum, ceramic, anhydrite. |
Permeability of rock salt |
- |
| Hofrichter, E. |
1976 |
Zur Frage der Porosität und Permeabilität
von Salzgesteinen
[Remarks on the porosity and permeability of salt rocks] |
Erdöl-Erdgas-Zs. 92 (1976) 3, pp.77-80 |
Journal Article |
German |
The velocities of elastic waves and the thermal
conductivity of rock salt -measured both in situ as well as
in the laboratory - were compared with the corresponding values
calculated theoretically. The basis of these theoretical values
are the elastic and thermal data of NaCl crystals.
The comparison shows that an undisturbed salt deposit has
the same properties as those of quasiisotropic crystalline
NaCl which is free from voids. Rock salt, in situ around cavities
in the mine and in the form of specimens, must have a looser
structure on account of different elastic and thermal properties.
Experiments with air under high pressure in salt mines have
proven the impermeability of the salt rocks. Bituminous material
in salt formations is usually of syngenetic origin. Its presence
does not indicate a migration into the salt. C02 gas under
high pressure occurs in the salt of the Werra Basin in Germany
as a consequence of Tertiary volcanism. This gas could not
escape since that time because of the impermeability of the
salt. |
Permeability of rock salt;
Pore pressure in permeable salt |
- |
| Horseman, S. T. |
1988 |
Moisture content - a major uncertainty in storage
cavity closure prediction |
Proc. 2nd. Conf. Mechanical Behavior of Salt,
Hannover, 24.-28.09.84, pp. 53-68 |
Paper |
|
This paper examines one of the major uncertainties
in the application of laboratory test results to the design
of solution-mined storage cavities in rock salt The properties
of salt are such that water will, when present, have significant
effects on mechanical behavior., including enhanced ductility,
strength variation, an increased capacity for creep deformation
and possible volume changes associated with the hydration
of secondary minerals. Although these effects are widely recognized,
surprisingly few observations have been recorded and the available
data, discussed here, can only be assessed in a qualitative
manner. The evidence is, however, sufficiently conclusive
to indicate that, unless special measures are taken to reproduce
the in situ condition of the salt in the laboratory, the experimental
results will be grossly incorrect. The uncertainty lies in
the selection of appropriate laboratory test conditions. An
argument is advanced here that, for cavity closure prediction,
salt specimens should be thoroughly dried and tested under
conditions devoid of moisture. |
Creep behavior |
- |
Horseman, S. T.;
Russell, J. E. et al. |
1993 |
Slow experimental deformation of Avery Island
salt |
Proc. 7th. Symp. on Salt, Kyoto, 1993, Vol.
1, pp. 67-74 |
Paper |
|
Two 100 mm diameter by 200 mm long cylinders
of Avery Island (A.I.) rock salt have been subjected to a
constant strain rate 10-9 s-1 at 15 MPa confining pressure
and 50 and 100°C. The experimental conditions have been
virtually constant over a period of about 3.5 years during
which the samples have shortened homogeneously by about 11%.
The specimen deformed at 100°C (Test 47) reached a steady-state
stress of 4.7 MPa at 2% strain whereas that at 50°C (Test
46), still slightly work-hardening, reached a quasi steady-state
stress level of 12.6 MPa. Microstructural analysis reveals
that dislocation glide and cross-slip dominated deformation
at 50°C whereas, at 100°C, subgrain development is
excellent indicating extensive dislocation climb.
These data points from Tests 46 and 47 were combined with
nine earlier constant strain rate steady-state test results
to provide, by nonlinear least squares, the relation
e8 = 6.5 x 10-5 exp (-69.7/RT 10-3)s5.9
When added to 27 A.I. constant stress test data points
of RE/SPEC Inc., ten of the low stress, low strain rate
tests at 100 and 200°C are very well fit by e a s3.4
whereas the remaining high strain rate, high stress quasi
steady-state data are well fit by e a s5.2. This change
in behavior, which must result from a change in dominant,
rate-limiting, mechanism bears importantly on inferences
concerning rates of natural salt deformation. At comparable
temperature and stress, the e a s3.4 relation predicts strain
rates two orders of magnitude higher than does the e a s5.2
equation; the latter is likely to be most pertinent to geotechnical
engineering applications. |
Creep behavior |
- |
Howarth, S. M.;
Peterson, E. W. et al. |
1991 |
Interpretation of in situ pressure and flow
measurements of the Salado formation at the Waste Isolation
Pilot Plant |
SPE Paper 21840 |
Paper |
|
This paper describes preliminary interpretation
of in-situ pressure and flow measurements of the Salado Formation
at the Waste Isolation Pilot Plant (WIPP). The WIPP facility
is located 660 m underground in the Salado, a bedded salt
deposit. Shut-in pressure tests were conducted prior to, and
subsequent to, the mining of a circular drift in order to
evaluate excavation effects on pore pressure, permeability,
and host rock heterogeneity. Borehole deformation was measured
during these tests and used to correct for changes in the
test region volume due to salt creep effects.
Preliminary pre-excavation results indicate that the flow
properties of this layered host rock are heterogeneous. Resulting
pore pressures range from 1 to 14 MPa and permeabilities range
from below measurable to about 1 nanodarcy. Normalized borehole
diameter change rates were between -4 and 63 microstrains/day.
Shut-in pressures and borehole diameters in all test boreholes
were affected by the excavation of Room Q coincident with
the advances of the boring machine. Preliminary results from
post-excavation test results show decreased pore pressures
compared to pre-excavation values. |
In-situ tests;
Permeability of rock salt;
Reservoir Mechanics;
Pore pressure |
- |
Hunsche, U.;
Schulze, O. |
1993 |
Effect of humidity and confining pressure on
creep of rock salt |
Proc. 3rd Conf. Mechan. Behavior of Salt, pp.
223-234 |
Paper |
|
Uniaxial tests with stepwise variation of the
relative humidity f of the surrounding air show that steady
state creep rates are increased by a factor of about 55 between
f = 0 and 75 %RH. Triaxial |
