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Muddied Waters

A Survey of Offshore Oilfield Drilling Wastes and Disposal Techniques to Reduce the Ecological Impact of Sea Dumping

by Jonathan Wills, M.A., Ph.D., M.Inst.Pet., for Ekologicheskaya Vahkta Sakhalina (Sakhalin Environment Watch); 25th May 2000

Minimising Waste Discharges and Their Effects

There are several ways to reduce the volume of drilling waste produced and to minimise its effects on the sea:

Using less toxic alternatives is a favoured solution in both Europe (OSPAR. 2000. Draft Measures Proposed by the OSPAR Working Group on Sea-based Activities (SEBA), February 2000. Annex 7(6.5b): Draft OSPAR Decision 2000/? on a Harmonised Mandatory Control System for the Use and Reduction of the Discharge of Offshore Chemicals. OSPAR, Amsterdam. See also: CEFAS. 2000. Guidelines for the UK Revised Offshore Chemical Notification Scheme in Accordance with the OSPARCOM Harmonised Offshore Chemical Notification Format. London. ) and North America, where governments and industry are continually searching for improved and less harmful offshore drilling fluids. SBMs, most of which failed to satisfy European standards, were such an attempt to deal with the problem at source and the US may yet prove that some forms of SBMs really are an environmentally acceptable alternative to OBMs. For WBMs, improvements to the purity of stock chemicals, and measurement of their toxicity prior to mixing into the drilling fluid, are among the most promising prospects for environmental improvement in cases where waste discharge is unavoidable.

Cleaning onboard prior to discharge is also a rapidly-developing technology. The crude shale-shakers and sieves once employed to separate solids from drilling fluids after use have been superseded by much more efficient equipment that can greatly improve the separation of mud from cuttings and oil from produced water. Technology exists, but has not yet been widely adopted offshore, that can very largely remove the residual pollutants in cuttings and, particularly, in produced water. The obstacles are financial rather than technical. Whether such equipment is installed and used offshore is, of course, a matter for government enforcement.

Shipment of wastes ashore for recycling, landfill and/or incineration is one of the options being considered for dealing with the very large accumulations of contaminated drill cuttings in the North Sea. It is already used to dispose of some ongoing waste streams and thus prevent the build-up of new drill cuttings piles on the seabed. While making a contribution to both the environment and the local economies of North Sea coastal regions, (In the UK, for example, new equipment to process cuttings and other wastes shipped ashore from North Sea fields has recently been installed in Peterhead, Aberdeen and Shetland (where one firm has been handling contaminated cuttings waste for over 10 years). See, for example: Burgess & Garrick. 2000. Waste Management. Website: Lerwick) the air pollution, landfill space demands and energy costs associated with transporting, processing and disposing of the material seem likely to influence governments in favour onsite re-injection technology as a more practical and cost-effective method - wherever geological conditions are suitable.

Re-injection Offshore

Cuttings re-injection (CRI) is a waste disposal technique where drill cuttings and other oilfield wastes are mixed into a slurry with water and pumped at high pressure down an injection well. Sometimes it is necessary to grind up the particles in the slurry to make them finer. The hydraulic pressure can also be used to break open layers in the rock to make subsequent injection easier and to contain the wastes in a defined area - hence the term slurry fracture injection commonly used in the US and Canada, where the technique was pioneered. (For accounts of early work on re-injection, see: 1. Beak Consultants and Imperial Oil Limited 1974. Disposal of waste drilling fluids in the Canadian Arctic. APOA project no.73. APOA, Calgary. 2. Dome Petroleum Limited 1974. Interim guidelines for waste management in exploratory drilling in the Canadian north. Dome Petroleum Ltd., Calgary. 3. French, H. M. 1980. Terrain, Land Use and Waste Drilling Fluid Disposal Problems, Arctic Canada. Arctic 33:794-806. 4. Friesen, G. 1980. Drilling Fluids and Disposal Methods Employed by Esso Resources Canada Limited to Drill in the Canadian Arctic. Proceedings of a Symposium: Research on Environmental Fate and Effects of Drilling Fluids and Cuttings, Lake Buena Vista, Fla.: pp. 53-69. American Petroleum Institute. Washington, DC. 5. Lam, L. 1982. Report on Offshore Oil and Gas Drilling Fluid Disposal in the Canadian North Technical Report No. 3.6. A Survey of Methods of Waste Fluid Treatment and Disposal for Canadian Offshore Drilling. Canadian Superior Oil Ltd. 6. Canada Dept. of Indian Affairs and Northern Development, Environment Canada, Canada Dept. of Fisheries and Oceans, Industry/Government Working Group on Disposal of Waste Fluids from Petroleum Exploratory Drilling in the Canadian North, and Arctic Petroleum Operators Association. 1982. Report on offshore oil & gas drilling fluid disposal in the Canadian North. Yellowknife, N.W.T. 7. Hillman, S.O. 1983. Drilling Fluids: Disposal in the Alaskan Beaufort Sea. Issues of the 80's: Twelfth Annual Arctic Environmental Workshop held at Fairmont, British Columbia, May 8th-11th, 1983, p.162-166. )

One of the clearest explanations of CRI is by the British company Gidatec (See the Gidatec website at for more details), which describes it as "a cost effective means of complying with environmental legislation concerning discharges of oily wastes" and says it has "proven to be viable in many different areas and formations around the world, with the most activity in the North Sea, Alaska, Gulf of Mexico and Venezuela":

Re-injection of drill cuttings normally involves collection of the waste from solids control equipment on the rig, followed by transportation to a cuttings processing station. Cuttings are slurried in this unit by being milled and sheared in the presence of water, usually seawater. The resulting slurry is then disposed of by pumping it into a dedicated disposal well, or through the open annulus of a previous well into a fracture created at the casing shoe set in a suitable formation. Operations are usually batch by nature and carried out at low pump rates (2.0 - 8.0 bpm). These kinds of operations have been carried out all over the world, with disposal into many different types of strata.

On logistical and cost grounds the means of disposing of waste cuttings from [offshore] platform based operations can usually be narrowed down to one of two choices. These are either re-injection into a dedicated disposal well, which if newly drilled can be re-completed as a producer at a later date, or re-injection through the annulus of a well drilled prior to the current live well. Drilling and cuttings disposal into the same well is possible but to date, because of well control concerns, it is not a preferred option with operators.

Sequential annulus injection is invariably the preferred means of disposing of cuttings, particularly in offshore locations. This is because of its flexibility and that it avoids the cost of drilling a dedicated disposal well. For cost reasons, dedicated re-injection wells are usually only practical on land or in shallow water. They do have advantages, however, including ease of cleaning out with coiled tubing in the event of plugging, can be designed to accommodate high volumes of waste, the ability to inject larger sized solids and a reduced risk of tubing plugging. Even so, unless annular cuttings re-injection is not viable, for example because of lack of annular access to a suitable deposition horizon, drilling a dedicated disposal well is usually ruled out on cost grounds. Thus, annular re-injection of waste cuttings is invariably the method of choice. Typically the 13 3/8" by 9 5/8" annulus is selected as the disposal location.

One of the first oil companies to make extensive use of cuttings re-injection was BP. The company had opened up its Alaska North Slope oilfields by using "reserve pits" - a euphemism for holes in the ground where drillers dumped almost anything. Within a few years BP had a serious environmental problem on its hands, as poisonous wastes began to leach out of the pits and spread across the tundra on top of the permafrost. (United States Department of the Interior (DOI), Fish and Wildlife Service (FWS). 1987. Effects of Prudhoe Bay Reserve Pit Fluids on Water Quality and Macroinvertebrates of Arctic Tundra Ponds in Alaska. US DOI Biological Report 87(7). Washington D.C.) Although it was out of sight from most people, the pollution in the Arctic wilderness north of the Brooks Range was not out of mind. As controversy grew about the oil industry's plans to drill in the Arctic National Wildlife Refuge (ANWR) critics pointed to the mess at the reserve pits as evidence that BP's environmental credentials were suspect. This caused serious public relations problems for BP and its compradors in the Alaska State Legislature and business community. During the late 1980s and early 1990s the company cleaned up the pits, volunteered its services to deal with other organisations' waste dumps (some dating from World War II and earlier) and, to some extent, salvaged its reputation among American environmentalists. The results certainly looked impressive and showed what an organisation like BP could achieve when management and workers were given the resources to do a thorough job. (1. Taylor, S. 1998. Status of North Slope Environmental Protection (video presentation), BP Exploration, Anchorage. 2. Minton, R. C. and Secoy, B. 1992. Annular Re-injection of Drilling Wastes. IADC/SPE Paper 25042. Society of Petroleum Engineers, Richardson, Texas. 3. Brasier, F. 1992. Injection Control Regulations - Federal Framework and Alaska Regulations. Proceedings of a Seminar on Subterranean Disposal of Drill Cuttings and Produced Water. Stavanger). By 1993 the E&P Forum could boast: "In Alaska the injection of cuttings and waste fluids has led to much smaller drilling pads, and therefore less impact from the rig rites, and less heavy traffic transporting materials across the tundra. (E&P Forum. 1993. Guidelines for the Planning of Downhole Injection Programmes for Oil Based Mud Wastes and Associated Cuttings from Offshore Wells. Report No. 2.56/187. E&P Forum, London) There were also economic benefits because the reserve pits had been costing about $2,000,000 per well, whereas grinding and downhole injection cost about $500,000 per well thereby saving about $1,500,000 per well. (ADEC informant, pers. comm.. 2000.)

BP was also in the forefront with CRI offshore. In January 1991 BP engineers injected 5,700 barrels of drilling wastes 5,100 feet below the bottom of the Gulf of Mexico, in tests at the Ewings Bank platform. In the Norwegian sector of the North Sea, BP was involved in a case study on the Gyda oilfield from July 1991 (Molland, G. 1992. Re-injection of Cuttings on Gyda. Proceedings of a Seminar on Subterranean Disposal of Drill Cuttings and Produced Water. Stavanger). In September that year BP did a test injection of 1,500 barrels of waste from the Clyde platform in the UK sector. Other case studies on CRI were carried out in the early 1990s by Conoco in the southern North Sea (January - March 1992) and the Gulf of Mexico (Block EC56, December 1991 - January 1992), by Statoil on the Norwegian Gullfaks field (October 1991) and by Amoco, also in the Norwegian sector, on the Valhall oilfield (January 1992). (E&P Forum. 1993. op. cit. ) These, however, were all described as case studies, tests or experiments.

By 1993 CRI was such a well-established technique offshore that- the E&P Forum produced detailed guidelines (Ibid) for operators planning to use it for OBM wastes and oil-contaminated drill cuttings. The document gave examples of the kinds of problems staff might encounter and, in addition to practical advice, laid down recommended procedures for monitoring and reporting re-injection work. The working group that drew up the guidelines included two representative of Exxon, alongside experts from Agip, Amoco, BP, Chevron, Elf, Enterprise Oil, Statoil, Texaco and Total.

They agreed that re-injection had "a successful history to date, particularly in Alaska and the Gulf of Mexico" but in Europe it had "only recently been evaluated". They described a Drilling Engineering Association project, with 12 operator sponsors, that had "been involved in developing the concept" between 1990 and 1993 and added:

Injection has been adopted by operators in the Norwegian and UK sectors of the North Sea, and is seen as a viable route to oily waste disposal.

The adoption of this approach to the disposal of oilfield wastes is particularly attractive since it means that the overall environmental impact of operations is minimised. Injection offers a cost effective disposal option with minimal energy utilisation.

This view is confirmed by a review of the extensive literature on the subject in the public domain. (For example, see the following: 1. Lal, M. and Thurber, N. 1989. Drilling Wastes Management and Closed-Loop Systems. In Engelhardt, F. R. et al. (eds). 1989. Drilling Wastes. pp. 213-228. Elsevier Science Publishers Ltd, Barking, England. 2. Dusseault, M.B., Bilak, R.A., and Rodwell, G.L. 1997. Disposal of dirty liquids using Slurry Fracture Injection, SPE 37907, Proc. 1997 SPE/EPA Expl. and Prod. Env. Conf., Dallas, TX, March 3-5, 1997, pp. 193-202. 3. Dusseault, M.B., Bilak, R.A., Bruno, M.S. and Rothenburg, L., 1995. Disposal of granular solid wastes in the Western Canadian sedimentary basin by Slurry Fracture Injection, Paper presented at the International Symposium of Scientific and Engineering Aspects of Deep Injection Disposal of Hazardous and Industrial Wastes, Berkeley, CA, May 10-13, 1994. 4. Dusseault, M.B. and Bilak, R.A., 1993. Disposal of Produced Solids by Slurry Fracture Injection, Paper presented at the 4th Pet. Conf. of the S. Saskatch. Sec., Pet. Soc. of CIM,, Regina, Sask., Oct 18-20, 1993. 5. Sipple-Srinivasan, M.1998. U.S. Regulatory Considerations in the Application of Slurry Fracture Injection for Oil Field Waste Disposal. International Petroleum Environmental Conference (IPEC) '98 , Albuquerque, N.M. 6. Sipple-Srinivasan, M., Bruno, M., Bilak, R., and Danyluk, P. 1997. Website: Field experiences with oilfield waste disposal through Slurry Fracture Injection. SPE 38254, Society of Petroleum Engineers' 67th Annual Western Regional Meeting, Long Beach, CA. )

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"Muddied Waters":



List of Abbreviations

Summary of Conclusions

Drilling Waste Streams from Offshore Oil and Gas Installations

The Law on Offshore Wastes Discharges in Different Jurisdictions:

The OSPAR Convention

United Kingdom



United States

Inviting Regulation

Environmental Effects of Drilling Waste Discharges

The SBM Controversy

"Non-Water Quality Environmental Impacts"


Drill Cuttings

Produced Water

Minimising Waste Discharges and Their Effects

Reinjection Offshore

Cleaning Produced Waters

List of Main Sources

Selected References



Articles on Offshore
Oil&Gas and Environment

Impact of Offshore Oil&Gas Industry


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