Horizontal Separators Research Articles

Analysis off Gravity Separation in Freewater Knockouts

Summary The selection of a freewater knockout depends on the desired performance. The design criterion developed here is based on the perception that most FWKO's are installed to remove the bulk of the water from a high-water-cut flow stream so that the oil can be dehydrated economically to salable specifications and to discharge water requiring minimal treatment before disposal. Only the gravity separation process is considered; the contribution of coalescing devices is excluded. Vertical FWKO's are discussed briefly, but the bulk of this paper is devoted to horizontal FWKO's, which constitute a majority of vessels. Hydraulic similarity of horizontal FWKO's and API separators is demonstrated, and a design criterion for FWKO's is developed with the basis used in the design development for API separators. This analysis discloses that commonly used criteria overrate the ideal flow capacity of FWKO's by a factor of 4/π. It shows that maximum FWKO capacity occurs when the oil/water interface is maintained at a level of 0.769 diameters in the case of ideal vessels and somewhat higher for nonideal vessels, rather than 0.50 as commonly believed. Published FWKO residence-time distributions (RTD's) indicate nonideal flow. Consequently, a design allowance for short-circuiting and turbulence effects was incorporated into the FWKO design. The effect of vessel proportions on cost per unit capacity is analyzed and an equation is developed for determining optimum proportions.

Oil removal from water in parallel plate gravity-type separators

Aspects of oil removal by gravity separation in parallel plate separators have been investigated both theoretically and experimentally. Attention has been paid to the possible influence of retention time distribution, co- or countercurrent flow (in tilted plate separators) and to the effect of perforation of the plates. Perforation enables an easy removal of separated oil in horizontal plate separators. It appears that the overflow rate-related to the horizontal projection of the real plate area-determines the performance of a plate separator in all these cases. A residence time distribution will lower the separation efficiency only when it is caused by a velocity profile over the width of the tank or by an extremely unequal distribution of the influent over the plates. A tilted full plate separator and a horizontal perforated plate separator with the same overflow rate perform equally well as to separation efficiency; only secondary, practical reasons will determine the choice between either construction.

Down-Hole Emulsification for Improving Viscous Crude Production

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