Drilling Waste Management is process which use solids control equipment and chemical material to deal with drilling waste. Solids control equipment removes drilling cuttings are often reported as drilling waste.
Some quantitiy of drill solids will accumulate in the drilling fluid and must be removed by the solids control equipment or reduced in concentration by dilution.
Drilling Waste Type
The well-drilling process generates two types of wastes — used drilling fluids and drill cuttings.
Drilling fluids (or muds) are used to aid the drilling process. Muds are circulated through the drill bit to lubricate the bit and to aid in carrying the ground-up rock particles (drill cuttings) to the surface, where the muds and cuttings are separated by mechanical means. Most onshore wells are drilled with waterbased or oil-based muds, while offshore wells may also use synthetic-based muds.
Waste Management Hierarchy
Historically, oil field wastes were managed in ways that were found to be most convenient or least expensive.
Over the past decade, oil and gas operators have looked to waste management approaches that minimize the generation of wastes and to disposal techniques that offer greater environmental protection and public safety.
A three-tiered waste management hierarchy is followed, in which the operator attempts to manage wastes in the most environmentally friendly tier first, then progresses to the second and third tiers as necessary. In the first tier (waste minimization), processes are modified, technologies are adapted, or products are substituted so that less waste is generated. When feasible, waste minimization can often save money for operators and can result in greater protection of the environment.
For those wastes that remain following waste minimization, operators next move to the second tier, in which
wastes are reused or recycled. Some wastes cannot be recycled or reused and must be managed through the third tier (disposal). For some of the disposal options, wastes are treated before disposal.
The History Of Drilling Waste Management
In the early years of the oil and gas industry, drilling wastes were looked upon as undesirable commodities that needed to be disposed of in the easiest or quickest way possible. Waste management practices were nearly all in the third waste management tier – disposal. The oil and gas industry was not unique is this approach; 50 to 100 years ago, nearly all of the nation’s major industries were growing and the economy was expanding.
Given the prevailing philosophy of those earlier times, few coordinated or environmentally beneficial waste management approaches were employed. Onshore drilling wastes were generally discarded on lease sites or on nearby roads or properties, and offshore drilling wastes were typically discharged to the ocean.
Some practices are carried over to the present, but now are controlled by suitable restrictions and requirements.
Examples of these are landspreading, road spreading, and ocean discharge.
In the early days, landspreading was used solely to get rid of drilling waste with little concern about the biological degradation of organic constituents of the waste. In more current times, regulatory agencies have established more formal guidelines on landspreading practices. Restrictions are now placed on:
- The chemical constituents of wastes to be landfilled (e.g, chlorides, total petroleum hydrocarbons [TPH]).
- The application rates.
- The distance from property boundaries and the water table, and slope of the land.
- The need to add fertilizer and till the waste mixture into the soil.
It was recognized early on that oily cuttings and spent muds could be used to apply a more weatherresistant
surface to dirt roads on leases or surrounding lands. Presumably, little concern was given to runoff or groundwater
contamination. In contrast, current standards for roadspreading often include similar restrictions to those listed above for landspreading.
In early offshore oil and gas development, drilling wastes were generally discharged from the platforms directly to the ocean. Until several decades ago, the oceans were perceived to be limitless dumping grounds. During the 1970s and 1980s, however, evidence mounted that drilling waste discharges could have undesirable effects on local ecology, particularly in shallow water.
When waterbased fluids were used, only limited environmental harm was likely to occur, but when operators employed oil-based fluids (usually for deeper sections of wells), the resulting cuttings piles created impaired zones beneath and adjacent to the platforms. Some early U.S. Environmental Protection Agency (EPA) regional permits in the 1980s began placing restrictions on ocean discharges.
In 1993, the EPA adopted national discharge standards for the offshore oil and gas industry. These standards are known as effluent limitations guidelines or ELGs. These established:
- Restrictions on oily sheens (precluded discharges of oil-based muds and cuttings).
- Aquatic toxicity testing using the mysid shrimp for drilling waste discharges.
- Limits on the amount of mercury and cadmium in the raw barite used as part of the drilling fluids.
Current Situation Of Drilling Mud Treatment And Disposal
As shown in the previous section, the current suite of drilling waste management practices contains options, but all
options are subject to restrictions.
The country’s environmental awareness grew during the 1970s as the U.S. Congress passed laws to protect water (Clean Water Act, Safe Drinking Water Act) and air (Clean Air Act) and to control new and past wastes (Resource Conservation and Recovery Act, Comprehensive Environmental Response, Compensation, and Liability Act).
Faced with this national direction, states began developing oil field waste management practices that
met the needs of both the environment and the business community in their states.
In 1988, the EPA determined that all oil and gas exploration and production wastes (including drilling wastes) were exempt from the hazardous waste requirements of the Resource Conservation and Recovery Act (RCRA) [July 6, 1988; 53 FR 25477].
In 1993, EPA concluded that associated wastes would also have the same exemption [March 22, 1993; 58 FR 15284]. The federal government determined that state agencies were adequately managing the wastes and did not impose its own regulatory requirements. Therefore, regulation of oil field wastes continues to be managed at the state level.
To aid the states, the Interstate Oil and Gas Compact Commission (IOGCC) published environmental guidelines for state oil and gas programs. These guidelines are not mandatory standards but are intended to give states useful information about the range of options and the sorts of controls that are appropriate.
Most onshore drilling wastes are disposed of at the site of the well from which they were generated. At offshore
platforms, most water-based muds and cuttings and syntheticbased cuttings are discharged to the ocean. However, some onshore drilling wastes are sent to offsite commercial disposal facilities and any oil-based and cuttings from offshore must be brought onshore for disposal or be injected underground at the well site.
Note that most oil-based and synthetic-based muds are recycled. The various methods used to dispose of oil field
wastes at such facilities are described in several references. Reference also includes information on disposal costs.
Different wastes are managed with different approaches. Some of the methods used for managing drilling wastes
- Land spreading.
- Road spreading.
- Burial in pits or landfills.
- Salt caverns.
- Thermal treatment.
- Reuse following treatment.
Each of these methods is discussed below in relation to the waste management hierarchy.
The oil and gas industry has worked diligently to develop new drilling products and technologies that help minimize the volume and environmental impact of drilling wastes.
In the 1990s, drilling fluid companies devised new types of fluids that used nonaqueous fluids (but
that were not oils) as their base. Examples of these base fluids included internal olefins, esters, linear alpha-olefins, poly alpha-olefins, and linear paraffins.
Synthetic-based fluids have revolutionized offshore drilling by creating syntheticbased muds (SBMs) that share the desirable drilling properties of oil-based muds but that are free of polynuclear aromatic hydrocarbons, have lower toxicity, faster biodegradability, and lower bioaccumulation potential. For these reasons, SBM cuttings are less likely than oil-based cuttings to cause adverse sea floor impacts.
The EPA has identified this product substitution approach as an excellent example of pollution prevention that can be accomplished by the oil and gas industry. Synthetic-based muds drill a cleaner hole than water-based muds, with less sloughing, and generate a lower volume of drill cuttings. Synthetic-based muds are recycled to the extent possible, while water-based muds are discharged to the sea.
Because SBMs were not considered by EPA in its 1993 offshore oil and gas ELGs, there was considerable uncertainty
about whether offshore operators could use the SBMs and discharge the resulting cuttings.
The EPA, DOE, the Minerals Management Service, and numerous companies and industry associations worked together following an innovative expedited rulemaking process to finalize new ELGs for SBMs in 2001 [January 22, 2001; 66 FR 6850].
It is also worth noting that much useful information came out of the intensive cooperative efforts of industry and government during the rulemaking process. The EPA’s official public record (the Docket) contains volumes of useful data on various aspects of SBMs, environmental effects, and treatment technologies.
The DOE funded several studies that looked at the actual disposal practices that were being used by U.S. offshore
operators in the late 1990s and a framework for a comparative environmental assessment of different types of
drilling fluids used offshore.
The advent of coiled tubing drilling equipment allows wells to be drilled with much smaller cross-sectional areas,
thereby reducing the volume of cuttings leaving the well and the volume of mud used for the drilling process. While coiled tubing may not be suitable in all applications, where it is employed it will directly help to reduce and minimize waste generation.
Directional (or slant or horizontal) drilling has opened many new opportunities for waste minimization. The most
obvious example is that fewer central drilling facilities, such as offshore platforms, need to be established if this type of drilling is employed. Some wells have been drilled to end targets up to tens of thousand of feet of horizontal separation away from the wellhead. Avoidance of multiple drilling facilities is a wonderful environmental benefit, albeit not one directly related to drilling waste.
The ability to drill multilateral wells from the same starting wellhead does reduce the volume of drilling waste, however. The upper portion of each well is larger in diameter than the lower portion of the same well, and drilling the upper section generates more waste per foot drilled than does the lower section. Thus if multiple sidetracks can be drilled at lower depths from the same main well bore, production can be increased without the need to drill several sets of large-diameter upper well bores.
Used oil-based and synthetic-based drilling fluids are typically recycled to the extent possible. Recycling
avoids the potential release of large quantities of waste to the environment.
Most drill cuttings are managed through disposal, although some are treated and beneficially reused. Some
drilling wastes are thermally treated to remove the hydrocarbon fractions, many of which can be recovered for
reuse, leaving behind a relatively clean solid material that can be used for landfill cover.
In other cases where a market exists for concrete aggregate or construction fill, cuttings that have been screened or filtered to remove most of the attached liquid mud fraction can be beneficially reused for such purposes. The chemical characteristics of the cuttings and any remaining fluids must be carefully controlled to avoid any conflicts or problems with the reuse.
Drilling Fluid Disposal
A wide range of onsite and offsite disposal options are available to operators.
The most common onsite practices are drainage of liquids from the drilling pit and burial of the remaining solids in place or land spreading of drilling wastes on the lease sites. Neither burial nor land spreading is appropriate at some geographic locations, such as areas with high water tables or those that experience periodic flooding.
Some states may allow road spreading under carefully controlled situations, as noted above. Another onsite option that has been used in some cases, particularly in offshore settings, is reinjection of ground and slurried drill cuttings into underground formations. Wastes can be injected through the annulus of a well being drilled or sent into a dedicated injection well at the same location.
Offsite disposal facilities are generally more costly than onsite disposal, but in some situations, operators are not able to dispose of drilling wastes onsite. In other circumstances, operators elect to send their drilling wastes to an offsite commercial disposal company rather than manage it within their own company.
Many offsite disposal options are available in the United States, but they are not always available in other oil producing countries that do not have well-developed waste management infrastructures. Several years ago, the author was directed by DOE to work with a consultant team that was developing a new framework for management of drilling wastes in Mexico. At that time, Mexico had only limited disposal options available for drilling waste, primarily thermal desorption. The team developed a list of both onsite and offsite waste management practices that could be approved, on the basis of chlorides and total petroleum hydrocarbon concentrations of the waste. The team’s recommendations were not formally published, but the framework was presented at a conference.17 The framework was favorably received by the Mexican government.
Some of the methods used for offsite drilling waste management are described below.
Burial in Landfill
Some landfills dedicated to oil and gas waste are located in areas of high oil and gas production such
as West Texas. In other areas where insufficient oil and gas production exists to support a network of commercial oil field waste disposal facilities, operators may take drilling wastes to municipal or industrial landfills, as long as the wastes can meet the acceptance requirements for the landfills.
The concept of injecting drilling waste to an underground formation was discussed previously as an onsite option, although perhaps its greatest utility may be as an offsite disposal method for large volumes of drilling wastes
and other oil field wastes.
There are several approaches to injecting wastes underground, including injection of slurries above fracture pressure to cracks and fractures in formations, injection of slurries below fracture pressure to naturally cracked formations, and disposal to salt caverns.
Injection above fracture pressure can be used to dispose of large volumes of solid wastes. For example, an injection
well was drilled in southern Louisiana to dispose of more than 1 million barrels of old drilling pit solids mixed into 3 million barrels of slurry. Solids were screened, ground to small and relatively uniform particle size, blended with water, and injected.
Even larger volumes of offshore wastes have been disposed of at a series of injection sites in East Texas, where
the geologic formations are naturally cracked so that only low pressure is required to inject the slurry. As of 2001, more than 22 million barrels of slurried waste has been injected using this mechanism.
In the early 1990s, several Texas brine companies obtained permits to receive oil field waste, much of which was drilling waste, for disposal into caverns they had previously developed as part of their brine production operations.
Uncertainty about this process led the DOE to fund several baseline studies of the technical feasibility, legality, cost, and risk of cavern disposal.22-25 These studies found that cavern disposal was feasible, cost-effective, lowrisk, and legal where states had enacted the appropriate rules.
As of spring 2002, only Texas has adopted disposal cavern regulations, although Louisiana is expected to adopt
regulations in the near future. Several disposal caverns are also operated in Alberta and Saskatchewan, Canada.
In the past few years, a new cavern disposal operation has opened along the eastern Gulf coast of Texas to compete
directly with the facilities using slurry injection below fracture pressure. Those facilities had previously disposed of more than 80% of offshore wastes brought back to shore.
Overlook Drilling Waste Management
The direction that drilling waste disposal takes in the future will be determined by several factors. The first key
factor is regulatory changes. In developed regions, like the United States and the North Sea, requirements for managing offshore drilling waste are becoming stricter over time and are likely to continue on that course.
In regions with developing oil and gas production, regulatory programs are likely to become more mature and better thought out. In onshore U.S. areas, there will likely be a movement away from disposal options that place wastes at or near the surface and a greater emphasis on methods that either beneficially reuse the waste or dispose of it deep underground. These changes will be primarily attributable to regulatory shifts.
A second key factor is waste management cost. If an operator or a service company can develop a method for drilling waste disposal that offers significantly lower cost and equivalent or better environmental protection, operators are likely to shift their waste management patterns to the new options. There will most likely be a delay in wide acceptance of the new approach as both operators and regulators gain familiarity and comfort with the new option.
The third key factor is liability to the operator. The total cost of waste management to an operator includes more than just the immediate cost of managing the waste. Under the U.S. Superfund law, a company could dispose of its waste in an approved fashion today yet face remediation liability in the future if the disposal operation later results in environmental contamination or harm.
Therefore, operators must make an educated guess about the long-term suitability of their chosen waste management approach. New management options that are believed to reduce long-term liability may be given higher priority.
The next few sections offer some thoughts on the directions that drilling waste management may take in the
future, categorized according to the three tiers of the waste management hierarchy.
Drilling Waste Minimization
Drilling fluid companies are developing new fluid systems that are much more amenable to different types of land application of the subsequent drilling wastes. It is likely that companies will develop fluids with suitable drilling properties yet that contain fewer components or additives that would inhibit vegetative growth.
Other developments in drilling fluids could lead to entirely different formulations. Several examples were
discussed at a March 2002 conference by persons advocating new formulations. Drilling fluids based on formate brines were reported to be more environmentally friendly than traditional fluids.
Wider use of such drilling fluids may or may not reduce waste volumes, but according to that author,
could reduce the mass of undesirable chemical constituents that are released into ocean waters.
In a similar vein, substitution of some of the key components of drilling fluids with new, more environmentally
friendly products could reduce mass loadings to the environment. A proposed example of this practice is the use
of ilmenite (FeTiO3) instead of barite (BaSO4) as a weighting agent in drilling fluids.
The improved drilling technologies identified above in The Present section will be further developed, and new tools
and methods will continue to reduce the volume of drilling waste generated.
Drilling waste Recycle/Reuse
Thermal treatment was discussed as a present option. The technology, while certainly in use today, tends to
be expensive and not suitable for use onsite at offshore platforms. Improvements will likely be made to thermal
treatment technology that result in lower treatment cost, good recovery of organic base fluids, and new models that improve safety sufficiently so that they can be used on platforms.
Although no written paper was made available, a presentation at a March 2002 conference described a new thermal treatment system that can be deployed on platforms and that would convert oil-based cuttings into recycled oil, water, and rock powder.
Another new application for drilling wastes is to use 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 laboratory 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.
New beneficial reuses for drill cuttings as additives to products will probably be developed. As waste management costs increase over time, companies are likely to become more creative in developing new reuse strategies.
Drilling Waste Disposal
Some of the most basic waste management approaches, such as burial of drilling pit contents, may become used less frequently. A strong motivating factor for this trend to occur would be regulatory pressure against pit burial. The approaches involving underground injection are likely to receive more interest and attention.
The author is currently working on a feasibility evaluation of slurry injection technology that will pull together extensive technical and regulatory information on that technology. When published in late 2002 or 2003, that evaluation will provide a centralized source of information on how slurry injection has been used in the past and the important aspects of siting and using the technology.
One of the companies currently operating a salt cavern for waste disposal in Texas has applied to the U.S. Minerals
Management Service (MMS) for permission to operate an existing brine-filled cavern located offshore as a disposal
cavern. As of May 2002, the MMS is deliberating this request.
Conclusion Of Drilling Waste Management
The oil and gas industry has made great strides in environmental protection from its early years. A choice of several suitable drilling waste management practices currently exists. Operators select the most appropriate waste
management option on the basis of regulatory requirements, cost, and the concerns of future environmental liability.
Although the current suite of management options offers alternatives, research efforts are underway to develop
improved waste management strategies. Of particular interest are those approaches based on waste minimization and beneficial reuse. Several projects funded by the DOE should lead to more publicly available information on drilling waste management.