Fact Sheet - Beneficial Reuse of Drilling Wastes
Recycling of Muds
Most water-based muds (WBMs) are disposed of when the drilling job is finished. In contrast, many oil-based muds (OBMs) and synthetic-based muds (SBMs) are recycled when possible. Sometimes the physical and chemical properties of the used muds have degraded somewhat, and the muds must be processed to rejuvenate the necessary properties. In other cases, the muds have been degraded sufficiently that they cannot economically be reused as new muds, and they must be put to a different type of reuse or final fate.
There are many relatively simple processes that can be used on drilling rigs to capture clean mud that would otherwise be discarded and return it to use. Examples include pipe wipers, mud buckets, and vacuuming of spills on the rig floor. Recovery of mud during tank cleaning may also allow the mud to be reused. Solids control equipment, like centrifuges, can be used to remove solids from the recirculating mud stream.
Some new drilling mud formulations are designed to aid vegetative growth so that the muds can be land-applied. These could have application in horticulture or in reclamation of damaged or low-quality soils.
Reuse of Cuttings
Drill cuttings are made up of ground rock coated with a layer of drilling fluid. Most drill cuttings are managed through disposal, although some are treated and beneficially reused. Before the cuttings can be reused, it is necessary to ensure that the hydrocarbon content, moisture content, salinity, and clay content of the cuttings are suitable for the intended use of the material. Some cuttings, particularly when a saltwater-type mud was used to drill the well, may need washing to remove dissolved salts prior to beneficial use. Water used for washing can be disposed of in an injection well.
Road Spreading: One use of cuttings is to stabilize surfaces that are subject to erosion, such as roads or drilling pads. Oily cuttings serve the same function as traditional tar-and-chip road surfacing. Not all regulatory agencies allow road spreading. Where it is permitted, operators must obtain permission from the regulatory agency and the landowner before spreading cuttings. Some jurisdictions limit road spreading to dirt roads on the lease, while others may allow cuttings to be spread on public dirt roads, too. Operators should make sure that cuttings are not spread close to stream crossings or on steep slopes. Application rates should be controlled so that no free oil appears on the road surface.
Reuse of Cuttings as Construction Material: After primary separation on shale shakers, cuttings are still coated with mud and are relatively hard to reuse for construction purposes. Various further treatment steps can be employed to render the cuttings more innocuous. Some cuttings are thermally treated to remove the hydrocarbon fractions, leaving behind a relatively clean solid material. Other cuttings are screened or filtered to remove most of the attached liquid mud. If cuttings contain too much liquid, they can be stabilized by adding fly ash, cement, or some other materials to improve their ease of handling.
Treated cuttings have been used in various ways:
- fill material,
- daily cover material at landfills,
- aggregate or filler in concrete, brick, or block manufacturing.
Other possible construction applications include use in road pavements, bitumen, and asphalt or use in cement manufacture. At least one state oil and gas agency reports that cuttings can be used for plugging and abandoning wells. The economics of this approach is rarely based on the value of the finished product, but rather on the alternative cost for the other disposal options. Properly done, drilling waste can be used as a filler or base material to make other products; however, the legal liability will always stay with the company who produced the waste initially.
Restoration of Wetlands Using Cuttings: Another new application for drilling wastes involves using them as a substrate for restoring coastal wetlands. The DOE funded several projects to test the feasibility of treating cuttings and using them to help restore damaged wetlands in Louisiana. The first phase of work involved greenhouse mesocosm experiments, in which several species of wetlands plants were grown in treated cuttings, topsoil, and dredged sediments (the typical substrate used in wetlands restoration operations). The results indicated that properly treated cuttings grew wetlands vegetation as well as the dredged material. However, neither the U.S. Army Corps of Engineers nor the EPA would issue a permit to conduct a field demonstration of the approach. To date, no field demonstrations of this promising waste management approach have been tried in the United States or elsewhere, but it is likely that over the next decade the approach will be tested somewhere.
Use of Cuttings for Fuel: Several trials have been conducted in the United Kingdom using oily cuttings as a fuel at a power plant. Cuttings were blended in at a low rate with coal, the primary fuel source. The resulting ash was much the same as the ash from burning just the coal. Generating stations should be located near the point where cuttings originate or are landed onshore from offshore operations, to minimize the need to transport cuttings.
Additional Thoughts on Recycling
In most situations, reusing or recycling wastes or byproducts is a desirable practice. The Drilling Waste Management Information System supports and encourages legitimate recycling and reuse, where it is practical and cost-effective. However, there are some cases in which individuals or companies may attempt to circumvent legitimate waste management regulations or laws by "sham recycling" in order to avoid costly waste management requirements (e.g., some wastes are recycled for end uses with little value solely to avoid complex and expensive hazardous waste management rules). Readers are advised to consult the regulatory agency with authority in the area where the drilling or waste management occurs to ensure that recycling is allowable under the relevant regulatory requirements.
Cordah, 2001, "Research on the Re-use of Drill Cuttings Onshore," prepared by Cordah Limited, Aberdeen, Scotland, for Talisman Energy (UK) Limited, September 11
Page, P.W., C. Greaves, R. Lawson, S. Hayes, and F. Boyle, 2003, "Options for the Recycling of Drill Cuttings," SPE 80583, SPE/EPA/DOE Exploration and Production Environmental Conference, San Antonio, TX, March 10-12.
Veil, J.A., 2002, "Drilling Waste Management: Past, Present, and Future," SPE 77388, SPE Annual Technical Conference and Exhibition, San Antonio, TX, September 29-October 2.