Investigation of a centrifugal separator for in-well oil water separation

A liquid-liquid centrifuge has been tested for possible application as a downhole method for separating crude oil from produced water. Centrifugal separators of various sizes (from 2- to 25-cm rotor diameter) have been built and operated over the past three decades at various US Department of Energy facilities. These units have several characteristics that make them attractive for downhole applications, including excellent phase separation, reliability in remote applications with >20,000 h of operation prior to maintenance, and the ability to handle high volumetric throughput with a very low residence time. In these studies, water-to-oil feed ratios of 10:1 to 1:19 were tested with a light Gulf of Mexico crude oil, and the separator operated efficiently for the full range of feed ratios. Air was added to the oil stream in one test to model the effect of gas in the oil. Air additions up to 20% of the feed flow rate (the maximum tested) did not have any impact on the performance of the separator. The separator also effectively processed a very viscous North Sea heavy crude oil. The heavy crude was used to determine the effect of higher temperatures on the performance of the separator. Increasing the temperature of the oil and water feed stream improved overall performance and decreased the concentration of oil in the water discharge stream.