Down-Hole Emulsification for Improving Viscous Crude Production

Abstract

Abstract The down-hole emulsification process has been developed to improve productivity and operating efficiency of oil wells that produce viscous crudes. The process involves using surface active chemicals in the wellbore to convert high viscosity oil or water-in-oil (W/O) emulsions to low viscosity oil-in-water (O/W) emulsions. Improved pump efficiency, faster rod drop rate, and lower flow-line pressure-drop result. pressure-drop result. Benefits obtainable from down-hole emulsification have been demonstrated in a series of field tests. The principal test, of 6 months duration, involved three wells, and showed that surfactant injection increased oil production 34 percent for a surfactant cost of $0.08/bbl of incremental oil produced. Introduction The economics of producing viscous crudes from pumped wells are affected by pumping unit limitations. pumped wells are affected by pumping unit limitations. The high viscosity of the crudes or the water-in-oil (W/O; water droplets surrounded by oil as the continuous phase) emulsions produced with the crudes causes low pump volumetric efficiency, slow rod drop rate, and high flowline pressure drop. Various methods, such as the use of bottom-hole heaters and light oil diluents, and water injection, have been used in the past to overcome these limitations. The purpose of this paper is to describe a new and improved method the down-hole emulsification processfor improving the economics of viscous crude production. Down-hole emulsification involves the use of surface active chemicals to convert high viscosity fluids in a wellbore into low viscosity oil-in-water (O/W; oil droplets surrounded by water as the continuous phase) emulsions. These emulsions result in improved pump performance and economical increases in productivity and operating efficiency. Process Description Process DescriptionThe down-hole emulsification process, illustrated in Fig. 1, consists of three primary steps: preparation, production and separation. Preparation of low viscosity O/W emulsions from viscous crude oils and the W/O emulsions produced with the oils is accomplished simply by mixing these fluids with the proper surfactants. The surfactants can be dissolved in water and injected, either continuously or in batches, into the tubing-casing annulus. The O/W emulsion is formed by the mixing action that occurs as the surfactant falls through the oil and water. This mixing may be aided by turbulence caused by gas liberation or the intermingling of the fluids entering the pump and flowing up the tubing. The oil is broken into droplets and the water forms a continuous phase surrounding the droplets. It is the continuous water phase that imparts low viscosity to the O/W emulsions. The surfactants concentrate at the oil-water interface, retarding oil droplet coalescence. At least 10 percent water cut is needed in the wellbore to make the surfactant effective. Details of emulsion preparation and viscosity data are in the Appendix. Production of the O/W emulsions formed in the wellbore is accomplished in the usual manner by pumping up the tubing and through the surface gathering lines. Because the emulsion has a lower viscosity than the crude oil, it is possible to obtain increased pump efficiency and rod drop possible to obtain increased pump efficiency and rod drop rate, and decreased rod loading and gathering-line pressure drop. pressure drop. Successful application of down-hole emulsification requires preparation of O/W emulsions that are stable when flowing; this avoids premature separation or inversion to a high viscosity W/O emulsion. (Conditions required to maintain stability are discussed in the Appendix.) Conversely, in surface equipment, O/W emulsions must separate readily into dry oil and disposable water. Emulsions prepared with nonionic surfactants meet these requirements prepared with nonionic surfactants meet these requirements more easily than those prepared with anionic surfactants. Separation of a variety of crude-oil-in-water emulsions has been accomplished by processing them in conventional horizontal separators (having hold-up times ranging from 1 to 4 hours) at elevated temperatures. Increasing temperature reduces solubility of nonionic surfactants in water, but increases their solubility in oil, thus reducing the coalescence barrier at the oil-water interface. pH control may be desirable in some applications. Data on O/W emulsion separation are in Fig. 6. Field Applications Down-hole emulsification has been successfully field tested in eight oil fields. The results of two tests are reported here. JPT P. 1349