Controlling Sand Production During Downhole Emulsification

Abstract

Abstract Experiments were carried out using a physical model to emulate the downhole-emulsification conditions in the presence of produced sand in a well containing a progressive cavity (Moyno) pump. Five commercially available emulsifiers were, tested for their ability to reduce pressure drop in the flowline by forming low-viscosity oil-in-water emulsions and at the same, time retain sand within the oil phase. The chemical concentrations were varied from 100 to 1,711 mg/L and sand and water cuts were maintained at 5% (v/v) and 30% (v/v), respectively. Laboratory experimental results showed that the Rexol 25/10 chemical had strong sand-retention and moderate pressure-reduction characteristics. Addition of polymer material, Flocon 4800C, to the Flothin F2 chemical also showed excellent sandretention and sufficient pressure-reduction capability. The tests indicated that to attain the optimum conditions of pressure reduction and sand retention, one should have an effective emulsion viscosity of about 800 to 900 rnPa.s (dead-oil viscosity is: 8.000 mFa.s) for an 11 ° API oil. Based on the laboratory results, the Rexol 25/10 chemical was field tested in a five-well downhole-emulsification project. The results of the field trial showed an increase in both productivity and surface sand cut. Introduction The high viscosity of heavy oils causes several operational problems, which include low pump volumetric efficiency, slow rod drop rare, rod parting and high flow-line pressure drop. Several methods including the application of bottomhole heaters and light oil diluents(1), water injection2 and downhole emulsification(3–6) (DHE) have been implemented to overcome these problems. Among these methods, DHE proves to be a relatively effective operational technique to produce heavy oil. The DHE process primarily involves injection of an aqueous surfactant solution either into the tubing-casing annulus or through the hollow rod system into rhe bottomhole area to convert high-viscosity oil or W/O emulsion into low-viscosity oil-in-water (o/w) emulsion. The olw emulsion is fanned by the mixing action that occurs as the surfactant solution falls through the oil and water. This mixing may be aided byturbulence caused by gas liberation, and/orthe intermingling of the fluids entering the pump This mixing action causes the continuous oil phase to break into small droplets, which disperse in the water phase. The presence of surfactant reduces the interfacial tension between water and oil and aids in the formation of oil dispersion with a minimum of mechanical energy input. Proper selection can also cause the surfactant to concentrate at the oil-water interface and aid in regarding the coalescence of the oil droplets. Both ionic and non-ionic types of surface-active chemicals form low-viscosity O/W emulsions under downhole conditions. Non-ionics are preferred because of the following Characteristic4their emulsifying action is nor adversely affected by the salinity of the produced water.the emulsions formed generally have a low viscosity,the produced emulsions are easier to separate in conventional oil-water separators, andnon-ionics do not introduce an inorganic residue that will affect the crude oil during refining. Both reciprocating and progressive cavity pumps can be used in the field for the downhole emulsification process.