A Review of Downhole Separation Technology

Abstract

Abstract In recent years, a technique of separating water downhole to reduce the volume of produced water and decrease the chance of surface pollution has been developed. It is called downhole oil-water separation (DOWS) technology. This technique allows water to be separated in the wellbore and injected into a suitable injection zone downhole while oil with traces of water is produced to the surface. Subsequent to the introduction of the DOWS technology to the oil industry in the 1990's, several trial applications have been undertaken to test the technology. These trials allowed significant information to be collected on the feasibility of the DOWS technology. Through the joint efforts of Argonne National Laboratory, CH2M-Hill, and the Nebraska Oil and Gas Conservation Commission, a comprehensive technical report was issued in January 1999 discussing this technology. Additional reports on trial applications and feasibility studies have been presented by various study groups. This paper reviews the status of and issues surrounding the application of downhole separation technology. This review summarizes the various papers and reports dealing with DOWS technology and its application in the oil and gas industry. This technology has the potential to provide significant reductions in produced water as the technology is adopted by the industry. It can also reduce produced water handling costs and increase oil and gas production in the right application. The wide-spread adoption of DOWS technology is dependent on improving the understanding of the process and its applications throughout the oil and gas industry. Introduction One of the waste by-products of crude oil and natural gas production in the upstream industry is produced water. Produced water has been defined as the water produced to the surface from the hydrocarbon bearing formation during the extraction of oil and gas, and can include formation water, injection water and any waste chemicals added downhole or during the oil/water separation processes. Conventional production processes involve producing both oil and water to the surface and then separating them at the surface. This separation occurs through the use of separation and dehydration equipment including skimmer vessels, plate coalescence, hydrocyclones, and, in some cases, cross-flow membrane filters to reduce the oil content in the water phase and enhance the quality of the water prior to disposal. However, as a reservoir matures and oil and gas production peaks, there is often an associated increase in water cut and a corresponding increase in both lifting and water disposal costs. The increased water cut also necessitates additional maintenance for production equipment and downhole treatment for corrosion, bacteria, scale, and naturally occurring radioactive material (NORM). Although producers still have a variety of choices in either disposing the water or re-using it, there is a growing concern from the public related to the handling of this waste product. Public concern about the environmental impacts of produced water disposal has therefore become a major issue in the industry especially related to surface damage due to spillage or subsurface contamination of drinking water due to poor injection activities. Environmental regulations pertaining to produced water management are expected to become more stringent in the future necessitating new practices and techniques of managing produced water. Downhole oil-water separation (DOWS) technology was introduced to the industry in the 1990's and further work to assess its feasibility was sponsored by the US Department of Energy in 1999.[1,2] "DOWS, unlike the conventional separation process, separates oil and gas from produced water at the bottom of the well and injects the separated produced water into another formation usually deeper than the producing formation, while the oil and gas are pumped to the surface."[2]