Feasibility evaluation of downhole oil/water separator (DOWS) technology.

The largest volume waste stream associated with oil and gas production is produced water. A survey conducted by the American Petroleum Institute estimated that 20.9 billion barrels of produced water were disposed of in 1985 (Wakim 1987). Of this total, 91% was disposed of through disposal wells or was injected for enhanced oil recovery projects. Treatment and disposal of produced water represents a significant cost for operators. A relatively new technology, downhole oil/water separators (DOWS), has been developed to reduce the cost of handling produced water. DOWS separate oil and gas from produced water at the bottom of the well and reinject some of the produced water into another formation or another horizon within the same formation, while the oil and gas are pumped to the surface. Since much of the produced water is not pumped to the surface, treated, and pumped from the surface back into a deep formation, the cost of handling produced water is greatly reduced. When DOWS are used, additional oil may be recovered as well. In cases where surface processing or disposal capacity is a limiting factor for further production within a field, the use of DOWS to dispose of some of the produced water can allow additional production within that field. Simultaneous injection using DOWS minimizes the opportunity for contamination of underground sources of drinking water (USDWs) through leaks in tubing and casing during the injection process. This report uses the acronym 'DOWS'although the technology may also be referred to as DHOWS or as dual injection and lifting systems (DIALS). Simultaneous injection using DOWS has the potential to profoundly influence the domestic oil industry. The technology has been shown to work in limited oil field applications in the United States and Canada. Several technical papers describing DOWS have been presented at oil and gas industry conferences, but for the most part, the information on the DOWS technology has not been widely transferred to operators, particularly to small or medium-sized independent U.S. companies. One of the missions of the U.S. Department of Energy's (DOE's) National Petroleum Technology Office (NPTO) is to assess the feasibility of promising oil and gas technologies that offer improved operating performance, reduced operating costs, or greater environmental protection. To further this mission, the NPTO provided funding to a partnership of three organizations a DOE national laboratory (Argonne National Laboratory), a private-sector consulting firm (CH2M-Hill), and a state government agency (Nebraska Oil and Gas Conservation Commission) to assess the feasibility of DOWS. The purpose of this report is to provide general information to the industry on DOWS by describing the existing uses of simultaneous injection, summarizing the regulatory implications of simultaneous injection, and assessing the potential future uses of the technology. Chapter 2 provides a more detailed description of the two major types of DOWS. Chapter 3 summarizes the existing U.S. and Canadian installations of DOWS equipment, to the extent that operators have been willing to share their data. Data are provided on the location and geology of existing installations, production information before and after installation of the DOWS, and costs. Chapter 4 provides an overview of DOWS-specific regulatory requirements imposed by some state agencies and discusses the regulatory implications of handling produced water downhole, rather than pumping it to the surface and reinjecting it. Findings and conclusions are presented in Chapter 5 and a list of the references cited in the report is provided in Chapter 6. Appendix A presents detailed data on DOWS installations. This report presents the findings of Phase 1 of the simultaneous injection project, the feasibility assessment. Another activity of the Phase 1 investigation is to design a study plan for Phase 2 of the project, field pilot studies. The Phase 2 study plan is being developed separately and is not included in this report.

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