Separation of Oil From a Brackish Water Stream

In the past 40 years, a variety of enhanced oil recovery (EOR) methods have been developed and applied to mature and mostly depleted oil reservoirs. Chemical and sonic stimulation are two enhanced oil recovery methods in which emulsions are created either as a primary or secondary effect. The resulting emulsion viscosity is considerably lower than that of dry crude thus increasing permeability of and recovery from pay zones. During Chemical enhanced oil recovery, caustic or preformed surfactants are injected into oil reservoirs, which results in flooding and periodic breakthrough of stable oil-water emulsions. The emulsions from chemical enhanced oil recovery floods can be very stable, and as such, traditional demulsifiers are often not effective on these emulsions.When considering alternatives for oil-in-water demulsification, there are various options that can be considered. The use of pH manipulation was investigated, however the addition of harsh chemicals is not ideal and only mildly effective. Multiple effect evaporation will produce potable water; however, the energy and capital costs are high. Another option is to use centrifugal separation, which is capable of achieving high degrees of separation but it is energy and capital intensive. Coalescence, which was investigated, is particularly attractive because of its simplicity and efficacy. Ultrafiltration, also investigated, is highly effective at producing oil free brackish water but cannot produce a pure oil stream. Due to the low concentration (~ 200 ppm) of oil in the feed, ultrafiltration was paired with coalescence to produce a brine free of dispersed phase oil and a marketable oil stream.The WERC task statement specifies a high degree of removal of oil from the brackish water stream. The full-scale process will be robust, remove all of the dispersed oil from a 100 gpm feed stream, and produce oil with low water content, preferably marketable.Laboratory work produced brackish water filtrate free of any dispersed oil and produced an oil phase substantially free of water, deemed marketable. Additionally sonication was used very successfully to produce an oil in water emulsion with an average droplet size < 6.0 microns. The full-scale UF/Coalescence process was designed to be highly mobile to satisfy the transient nature of the fraccing industry. The capital cost for this process to separate all the entrained oil from the oil in water dispersion is $250,000 and the operating costs are less than $20,000/year, excluding any additional operating labor. At 8,000 hrs/year of operation, 4 operators will be required, incurring an added annual operating cost of $200,000 to $250,000.