Water Disposal Technology During Offshore Drilling

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Each year, the oil industry generates millions of barrels of wastes that need to be properly managed. For many years, most oil field wastes were disposed of at a significant cost. However, over the past decade, the industry has developed many processes and technologies to minimize the generation of wastes and to more safely and economically dispose of the waste that is generated. Many companies follow a three-tiered waste management approach. First, companies try to minimize waste generation when possible. Next, they try to find ways to reuse or recycle the wastes that are generated. Finally, the wastes that cannot be reused or recycled must be disposed of. Offshore oil and gas operations generate a variety of solid and liquid wastes. Some of these wastes are attributable to exploration and production (E&P) activities (drilling wastes, produced water, treatment and workover fluids), while others are due to either human presence (sanitary wastes, food wastes) or generic industrial operations (wastepaper, scrap metal, used paints and solvents). This paper focuses on the E&P wastes, nearly all of which are disposed of in one of three ways – by discharge to the ocean, by injection into a dedicated injection well or into the annulus of a well being drilled, or by transport to a disposal site onshore. Here we look at the various techniques of drilling waste disposal.

Oil field wastes are generated through well drilling, through the process of producing oil and ga.% and through associated activities. The drilling process generates two types of wastes – drilling fluids and &ii cuttings. Drilling fluids (or muds) are used to aid the drilling process. Muds are circulated through the drii bit to lubricate the bit and to aid in carrying the groundup rock particles (drill cuttings) to the surface, where the muds and cuttings are separated by mechanical means. Most onshore wells are drilled with water-based or oil-based muds, while offshore wells may also use synthetic-based muds. The American Petroleum Institute (API 2000) estimates that about 150 million barrels (bbl) of drilling waste was generated at U.S. onshore wells in 1995. When oil and gas are produced to the surface, they are accompanied by formation Water known as produced water. Produced water is generally salty and is the largest volume waste stream generated in the oil and gas industry. API (2000) estimates that aImost 18 billion bbl of produced water was generated at U.S. onshore wells in 1995. Various other wastes, known as associated wastes, are generated through the process of collecting, treating, and storing oil and gas. Examples of these wastes are tank bottoms, soil contaminated by spills of produced water or crude oil, spent chemicals used to complete and stimulate wells, and pipe scale and sludges. API (2000) estimates that about 20 million bbl of associated waste was generated at U.S. onshore wells in 1995.

How Are Wastes Managed?
In 1988, the U.S. Environmental Protection Agency (EPA) determined that oil and gas exploration and production wastes (including drilling wastes and produced water) were exempt from the hazardous waste requirements of the Resource Conservation and Recovery Act (RCRA) [53 FR 25477]. In 1993, EPA concluded that associated wastes would also have the same exemption [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 is done at the state level. Most onshore oil field wastes are disposed of at the site of the well from which they were generated. Common practices are pit disposal or land spreading of drilling wastes and injection of produced water. At offshore platforms, most produced water and some drilling wastes are discharged to the ocean. Some wastes are sent to offsite commercial disposal facilities. Veil (1997) describes the various methods used to...
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