Development of a Centrifugal Downhole Separator

Abstract
Oak Ridge National Laboratory (ORNL) is currently developing a Centrifugal Downhole Separator (CDHS) which will extend the application of remotely operated separations equipment developed for the nuclear industry to in-well recovery of oil with in-situ recycle of the produced water. These units have been successfully used for surface treatment of produced water and wastewater generated during environmental clean-up operations. Performance data have shown that centrifugal units are capable of separating stable emulsions into "single-phase" streams with generally less than 1% cross-phase contamination.
Initial testing will be conducted with a bench-scale separator to determine the separation efficiency of various crude oils and to provide information necessary to scale up the separator. Information from the bench-scale unit will be used in the design of a larger prototype, which will have a much larger height/diameter ratio and will incorporate some of the components necessary for downhole operations. The prototype separator will be operated in the lab to verify scale-up parameters and separation efficiencies, as well as to provide information necessary to design a full-scale system. The full-scale system will be fabricated, installed in the field, and operated to demonstrate the technology. This paper discusses the testing to date of the bench-scale separator with a crude oil having an API gravity of 34.06°.

INTRODUCTION
Produced water is the largest generated waste stream by volume in the Gulf Coast region and is typically a mixture of formation and injection process water that contains oil, salts, chemicals, solids, and trace metals. In 1991, Louisiana generated over 1 billion barrels and Texas generated 7.5 billion barrels of produced water as a result of oil and gas operations. More than 250 million barrels of produced water are discharged each year to surface waters in both Texas and Louisiana (1).
Because of the tremendous volume of water generated and the specific constituents typically present, discharge of produced water from oil and gas production operations has been increasingly scrutinized in recent years for potential impacts on sensitive habitats. The discharge of produced water to the environment is regulated by the Environmental Protection Agency (EPA) in the United States. The maximum concentration of contaminants in produced water that can be discharged will be limited by the latest EPA regulations under the Clean Water Act. These rules are expected to reduce current discharges of toxic pollutants (including arsenic, cadmium, and lead) by more than 200,000 lb/year, conventional pollutants (such as oil, grease, and solids) by 2,800,000 lb/year, and nonconventional pollutants (such as chlorides, ammonia, and aluminum) by about 1,500,000,000 lb/year. Future regulations are likely to be more restrictive and may include zero-discharge standards (2,3).
As a result of these regulations, the industry has limited options for disposal of produced water. Traditional treatment and disposal of produced water primarily have been direct discharge to surface waters or subsurface formations. Zero discharge will dramatically increase the operating costs for produced water disposal in the Gulf Coast region and significantly limit the economic life of producing wells and fields. The American Petroleum Institute (1) estimated in March 1995 that the initial cost for compliance with zero-discharge guidelines would be $0.3 billion for coastal areas and over $3.2 billion for offshore areas.