Drilling fluid environmental considerations
A prime objective in all drilling operations is to minimize safety and environmental risks, while maintaining drilling performance. Operators and service companies alike take a proactive stance to reduce the potential for hazardous incidents, and to minimize the impact of any single incident.
Health, safety and environment policies
The health, safety, and environmental (HSE) policies of many companies are more stringent than those required by national governments and the various agencies charged with overseeing drilling operations. All personnel who take part in the well-construction process must comply with these standards to ensure their own safety and that of others. On most locations, a “zero-tolerance” policy is in effect concerning behaviors that might endanger workers, the environment, or the safe progress of the operation. Additionally, all personnel are encouraged to report potentially hazardous activities or circumstances through a variety of observational safety programs.
The packaging, transport, and storage of drilling-fluid additives and/or premixed fluid systems are closely scrutinized regarding HSE issues. Personnel who handle drilling fluid and its components are required to wear personal protective equipment (PPE) to prevent inhalation or other direct contact with potentially hazardous materials. Risk-assessed ergonomic programs have been established to reduce the potential for injuries related to lifting sacks and other materials, and operating mud-mixing equipment.
Transportation and management
When possible, drilling-fluid additives, base fluids, and whole mud are transported in bulk-tote tanks or are containerized. These transport methods help reduce packaging-related waste, and minimize the risk of harming personnel, polluting the environment, and impairing operations. High-volume materials such as barite, bentonite, salt, and base fluids almost always are provided in bulk to offshore installations. Onshore locations might use both bulk and packaged-unit materials, depending on the well depth and complexity.
The drilling-fluids specialist and operator representative at each location are responsible for ensuring that the available volume and properties of the drilling fluid will meet the immediate demands of a well-control situation, for example:
- A loss of circulation
- A tripping of a wet string
- A material-delivery delay caused by adverse transport conditions
- The need to mix additional volumes of drilling fluid with the appropriate properties at the rigsite
- The need to obtain additional volumes of drilling fluid with the appropriate properties in a timely manner
Published well-control guidelines recommend storing a riser volume plus 200 bbl (for pumping and line losses) in water depths ≥ 1,000 ft. Many deepwater-drilling operations take place in water depths exceeding this and approaching 10,000 ft. Nonsettling, ballast-storable drilling fluids have been used offshore to eliminate the risk of disruptions to supply created by inclement weather, and to prepare for drilling through SWFzones.
Protecting the environment
Keeping drilling-related accidents to “few and far between” not only provides the obvious benefit of minimizing, if not eliminating, sources of pollution and related threats to the ecosystem, but also enables the oil and gas industry more easily to obtain governmental permission to acquire and develop commercial reserves worldwide.
The drilling activities of countries that are emerging as energy producers should reflect the successful practices established by operators in well-regulated areas, as outlined in Table 1, which is modified from the CAPP Technical Report 2001-0007. The associated technologies, procedures, financial arrangements, and records serve as project blueprints for newcomers to the industry. Developing nations can better protect their natural environments and resources by implementing proven standards. Environmental-protection agencies and industry associations worldwide continue to study the effects on air and water quality had by drilling-fluid- and cuttings-related discharges specifically and by drilling operations generally.
Table 1-Examples Of Worldwide Requirements For Drilling-Fluid And Cutting Dischange
Attention to international environmental issues often is channeled through the Intl. Assn. of Oil and Gas Producers (OGP), the membership of which consists of 45 oil companies, 10 industry associations, and 2 service companies operating in more than 80 countries. The OGP Environmental Quality Committee addresses environmental issues such as:
- Drilling fluids and cuttings
- Environmental-performance indicators
- Related regulatory issues
The United Kingdom Offshore Operators Assn. (UKOOA) and the Oljeindustriens Landsforening /Norwegian Oil Industry Association (OLF), a corresponding Norwegian organization, have been formally examining the effects of drill-cuttings beds in the North Sea since June 1998. Nearly U.K. £5 million was budgeted to:
- Assess the environmental impact of existing cuttings beds
- Compare options for accelerating degradation
- Investigate the risks associated with removing the beds mechanically
In the United States, an API report on environmental protection indicates that, in 2000, the U.S. oil-and-gas industry spent $7.8 billion in this area, an amount that represents approximately 10%; of the net income of the top 200 oil and natural gas companies. Since such record keeping began in 1992, the oil-and-gas industry has spent an estimated $90 billion to protect that nation’s environment.
Drilling-fluid companies strive to maintain an “econo-ecological” balance when choosing drilling-fluid systems and additives. An ecologically friendly drilling-fluid system that performs poorly will be used seldom because its poor performance extends drilling time, and increases both the likelihood of hole problems and the cost of well construction. Conversely, using a properly managed high-performance synthetic-based fluid (SBF) can shorten the duration of the drilling operation and/or help maintain wellbore stability, thereby reducing opportunities for environmental damage. These and other factors must be weighed in the design of any drilling-fluid system.
Sources of contamination
Land and offshore drilling locations are regulated regarding:
- Disposal of whole mud
- Drilled cuttings and other solids
- Runoff generated by rainfall
- Wave action
- Water used at the rigsite
Industrywide efforts to eliminate environmental hazards resulting from accidents or the negligent handling of drilling fluids and/or drilled cuttings encompass several contamination issues related to drilling fluids:
- Formulation (chlorides, base oils, heavy metals, and corrosion inhibitors)
- Natural sources (crude oil, salt water, or salt formation)
- Rigsite materials (pipe dope, lubricants, and fuel)
In some cases, reformulating drilling-fluid systems makes them environmentally more benign. For example, chrome lignosulfonate water-based fluid (WBF) is available in a chrome-free formulation. The development of SBFs stemmed from the need to replace diesel- and mineral-oil-based fluids (OBFs) because of environmental restrictions.
The discharge of conventional OBFs and drilled cuttings effectively was prohibited in the North Sea in 2000. According to the Convention (OSPAR) Commission for the Protection of the Marine Environment of the North-East Atlantic, 98% of the total hydrocarbon discharge volume consists of produced water and drilled cuttings generated with SBFs.
Cuttings that are generated by drilling with certain compliant SBFs may be discharged overboard in the western Gulf of Mexico if they comply with the retention-on-cuttings (ROC) limits introduced in 2002 by the Environmental Protection Agency (EPA). Neither traditional OBFs nor the drilled cuttings produced while using them can be discharged in the Gulf of Mexico. The rare offshore operation that uses a diesel- or mineral-based fluid must include a closed-loop process for continuously capturing all drilled cuttings and returning them to shore for regulated disposal.
Gulf-of-Mexico compliance-testing profile
In deciding to permit the use of SBFs rather than restrict operators to WBFs, the EPA acknowledged the importance of the econo-ecological balance. The EPA felt that switching solely to WBF would cause more WBF development wells and more discharges to the ocean, because WBF operations produce more waste per well than do SBF wells. WBF and OBF operations also progress more slowly than do SBF operations, leading to increased air emissions and fuel usage. Furthermore, the technical demands of drilling in deepwater locations require the use of either an SBF or OBF, and the pollution risks from a riser disconnect where OBF is in use are far greater than with SBF. Therefore, SBFs became the generally approved fluids for the Gulf of Mexico.
The toxicity of a drilling fluid and/or of cuttings that are generated with the fluid is determined by the fluid composition and is measured using a variety of testing protocols. Table 2 lists tests that the 2002 modifications to the EPA General Permit require to be performed where SBF is used. Discharge of whole SBF is prohibited. Unblended linear paraffin and linear alphaolefins (LAO) base fluids are not expected to comply with the modified requirements because of biodegradation and/or toxicity issues.
Although technical advances in the design and formulation of SBFs have been spurred mainly by offshore drilling conditions, the biodegradability and relatively low toxicity of ester- and isomerized olefins (IO)-based fluids make them suitable for onshore operations as well. Experimentation with various soil types, plant germination, and earthworm survival rates indicates that these base oils respond well to bioremediation.
- Deepwater Well Control Guidelines IADC, 1–83. 1998. Houston.
- Whitfill, D.L., Heathman, J., Faul, R.R., and Vargo, R.F. Jr. 2000. Fluids for Drilling and Cementing Shallow Water Flows. Presented at the SPE Annual Technical Conference and Exhibition, Dallas, 1-4 October. SPE-62957-MS. http://dx.doi.org/10.2118/62957-MS.
- Country-Specific Requirements for Discharge of Drilling Muds and Cuttings. CAPP Technical Report 2001-0007, Canadian Assn. of Petroleum Producers, Calgary (February 2001) I-1–I-11.
- Drill Cuttings Initiative Has Begun Its Second Phase Drilling. 2001. Drilling Contractor 57 (3): 43.
- Arafa, H. 2003. U.S. Petroleum Industry’s Environmental Expenditures (1992–2001). Washington, DC: API (20 February 2003). http://api-ep.api.org/filelibrary/FinalEnvExpS01%20022003.pdf.
- Annual Report of the OSPAR Commission, 2000–2001, 30. 2001. London: OSPAR Commission.
- Final NPDES General Permit for New and Existing Sources and New Dischargers in the Offshore Subcategory of the Oil and Gas Extraction Category for the Western Portion of the Outer Continental Shelf of the Gulf of Mexico GMG290000, 37. US EPA, Washington, DC (December 2004).
- Lee, B. et al. 2002. Reducing Drilling Fluid Toxicity. Drilling 75 (6): 30.
Noteworthy papers in OnePetro
Roger Bleier, Arthur J.J. Leuterman, M-I Drilling Fluids Co.; Cheryl Stark, Millpark Drilling Fluids: Drilling Fluids: Making Peace With the Environment, 24553-PA, http://dx.doi.org/10.2118/24553-PA
R.K. Clark, SPE, Shell Development Co.: Impact of Environmental Regulations on Drilling-Fluid Technology, 27979-PA, http://dx.doi.org/10.2118/27979-PA
J.M. Getliff, A.J. Bradbury, C.A. Sawdon, J.E. Candler, M-I ; G. Loklingholm, STATOIL A/S: Can advances in drilling fluid design further reduce the environmental effects of water and organic-phase drilling fluids?, 61040-MS, http://dx.doi.org/10.2118/61040-MS