Downhole Emulsification: Viscosity Reduction Increases Production

Abstract

Abstract The purpose of this paper is to present a further update on the use of surfactants to assist in the pumping of viscous crude oils in Western Canada. Typically, crude oils present downhole pumping problems due to the high natural viscosity of the oil, such as Alberta's heavy oils, or in lighter oils which may have formed viscous oil exterior emulsions in situ, during combustion or by the agitation of the rod string and downhole pump during production. Viscosity reductions using DownHole Emulsification (DHE*) technology are possible, with oil viscosities from 10,000 to 500,000 centipoise capable of being reduced to less than 200 centipoise by the formation of water continuous emulsions. Wells which have high fluid levels, rod fall problems, high hydraulic pressures, poor pump efficiencies or excessive pressure losses in gathering systems are good candidates. Solving these viscosity concerns can cause production to be significantly enhanced, with costs being minimal: in general, less than 50 cents per incremental barrel. Reduced power consumption, decreased mechanical loads, reduced flowline pressures, more constant daily production and the reduction of flushbys or well loading are other potential benefits. Background Many techniques have been used to assist the producer in the production and handling of heavy oil. The use of heat by downhole combustion, steam drive or cyclic steam (Huff n' Puff) come readily to mind. One of the more easily understood techniques is the addition of condensate or light hydrocarbon diluent to cut viscosity in the tubing or flowlines. This is used primarily to mitigate rod fall problems and the sanding of pump checks, and allows rod speed to be increased. With rotary equipment, the addition of diluent causes pump efficiencies to be improved, torque to decrease and pump speed to increase. Another method of producing crudes that has the same effect as the use of diluent, is to make a water continuous emulsion of the oil in the wellbore by means of adding surfactants. It is likely that diluent will be required in the final processing of the oil, at the treaters and for gravity control in order to meet pipeline specifications. However, one has more economical control of the amount of diluent required at these sites, than by trying to alter the viscosity of the wet sandy crude in the wellbore. Figure 1 shows the viscosity of the crude oil and that of the emulsions formed (depending on the oil/water ratio) over a reasonable temperature range. This graph is for oil from the Clearwater formation, but other oils such as the Cummings exhibit similar responses. When emulsions are formed having water as the exterior phase, the viscosity of the final emulsion is almost independent of the original oil viscosity. Noticeably, the emulsion viscosity is only about 1% of the original oil viscosity at the bottomhole temperatures of these shallow wells (22 °C). It is evident that the use of surfactant and water can accomplish significant reductions in well bore viscosity. Nevertheless, as Figure 2 shows, not every heavy oil well is a good candidate.