Computer-Assisted Tomography: From Qualitative Visualization To Quantitative Core Analysis

Abstract

The effects of temperature and sand content on the flow resistance of high concentration heavy oil in water emulsions have been studied experimentally. The flows were laminar in a recirculating flow test loop with pipe diameter 53 mm. The effect of temperature could be explained through changes in the viscosity of the brine used to prepare the emulsions. Sand concentrations in the flow experiments were limited to 3% (mass) of the produced oil. Sand in the oil either increased or decreased the flow resistance depending upon the amount of water present initially in the oil. The sand flowed in a distinct layer at the bottom of the pipe and the velocity necessary to transport the sand was strongly dependent on emulsion effective viscosity. Velocity distribution measurements and a finite element simulation showed that a region of low viscosity forms at the pipe wall as a result of oil droplet migration into the flow. Introduction Crude petroleum is a multiphase mixture of oil, water sand and gas whose flow properties are known to be complex. For these mixtures, the resistance to flow depends strongly on the nature of the nature of the continuous phase. With no gas phase present the flow resistance can be minimized by using a surfactant to ensure that an oil in water emulsion forms. Heavy oil producers in the Lindbergh. A1betta, area have examined emulsion technology to improve the performance of oilfield pipeline gathering systems(1,2) Widespread use of flow lines would reduce truck traffic and minimize the proliferation of surface facilities. Emulsions for short distance flow lines must be easy to prepare using produced water, a minimal amount of chemical additive and simple mixing equipment. These emulsions need not be particularly durable but the oil and water must separate readily once the emulsion enters the treating facility. Unlike long distance emulsion pipelines, these short distance gathering systems may have to cope with substantial amounts of produced sand and highly variable flow rates. This investigation considered the effects of temperature and sand content on the flow resistance of high concentration heavy oil emulsions. The emulsions were prepared with moderate shear using fairly low surfactant concentrations in an attempt to simulate flow in gathering system pipelines. Sand transport by fluids in turbulent flow is comparatively well understood, but little is known about laminar flows. Because high concentration oil in water emulsions have high viscosities, laminar flow is likely to occur and the test program was restricted to this case. Emulsion Flows The resistance to flow of a single phase or multiphase mixture in a pipeline is expressed in terms of the frictional pressure gradient (ΔP/L) (kPa/m). For single phase fluids (ΔP/L) is a linear function of the viscosity µ as long as the flow is laminar. Equation 1 (available in full paper) where V is the bulk velocity and D is the pipe internal diameter. The viscosity can be measured conveniently in a variety of viscometers which do not involve pipe or tube flow.