Performance of Heavy Oil Dehydrators

Abstract

Results from field tests of heavy oil dehydrators verify a general dependence on the fluid physical properties, on the charge rate, and on the electric field intensity, but reveal no apparent dependence on the water content or particle size distribution of the feed. Introduction Accompanying the crude oil produced from underground formations are often varying amounts of connate brine. It is generally necessary to separate ("dehydrate") the bulk of this water from the crude before it leaves the oil field in order to have a marketable product. The dehydration of production fluids has historically been a problem in conventional petroleum production operations. Recent use of thermal recovery production operations. Recent use of thermal recovery techniques has resulted in increased interest, partly from the belief that thermally produced emulsions are more refractory (and hence more expensive to resolve) and partly from the fact that production costs often represent a greater fraction of the crude oil selling price for thermal projects than for conventional production. The generally higher temperatures, production. The generally higher temperatures, increased driving forces, higher production rates, and addition of fresh water are often given as reasons for expecting emulsions from thermal production projects to be more refractory. There are occasional suggestions in the literature that dehydration of such emulsions can increase expenses. Because the annual expenditure in the Western Hemisphere for crude oil dehydration equipment presently exceeds $10 million, and that for treating presently exceeds $10 million, and that for treating chemicals ("demulsifiers") may double this amount, a better understanding of the fundamental processes governing crude oil dehydration can lead to appreciable cost reductions. It is the purpose of this paper to compare equipment design and operating criteria found in the literature with the results of field tests in order to evaluate the applicability of these relations to general oilfield practices. Emulsion Characteristics and Their Reported Effects on Process Design Emulsions encountered in petroleum production generally consist of two immiscible liquids with differing densities, one of which (the discrete phase) is finely enough dispersed within the other so that the rate of separation due to the density difference is unacceptably low. Most oilfield problems involve an emulsion in which an aqueous phase, containing both connate brine and any fresher water associated with the production process, is dispersed within the hydrocarbon production process, is dispersed within the hydrocarbon phase. phase. Emulsion Characteristics From a physical point of view, a crude oil emulsion can be characterized in terms of the properties of the two liquid phases and the state of dispersion of the aqueous phase within the crude oil. Traditionally, the interfacial film (third phase) that surrounds the individual droplets and is supposed to hinder their coalescense has been included in the characteristic properties of an emulsion; however, reliable properties of an emulsion; however, reliable characterization of such films and, more particularly, of their relation to dehydration problems, has proven elusive. JPT P. 1285