Development of a method for the quantification of oil-water mixing in severe service control valves

Abstract

Control valves in the oil and gas industries frequently handle oil-water flow. Pressure drops and energy dissipation in the valve generate turbulence mixing in the flow which causes higher shear forces resulting in emulsification. This highly emulsified mixtures require a large size separator, extra time and chemical additives that increase the cost of the mixture flow and separation operations. Therefore, it is essential to quantify the extent of shear forces generated and degree of oil-water mixing resulting because of valves present in the oil transportation pipeline system and also to evaluate the performance of different valves. In this study, a novel quantification method is proposed to evaluate the extent local and global oil-water mixing within and because of valves. A widely used indicator; Mixing Coefficient (Mc) together with other novel proposed indicator Modified Mixing Coefficient (Mmc) and Velocityinvolved Modified Mixing Coefficient (Vmmc), are used as indicators to evaluate the local oil-water mixing degree at various cross-sectional planes of the valve. The variances of Mc, Mmc, and Vmmc are used to evaluate the global oil-water mixing performance of the valve. A well validated computational fluid dynamics model is used to evaluate the oil-water mixing degree globally and locally caused by two valves equipped with tangentially oriented and directly oriented orifices respectively. It has been concluded that at higher inlet velocities, the tangentially oriented orifices can reduce the oil-water mixing better than directly oriented orifices. At lower velocities, however, the directly oriented orifices are providing better separation properties. When considering the in-situ oil volume fraction, the tangentially oriented orifices can always produce a higher change in in-situ oil volume fraction compared with directly oriented orifices. The quantification method and the comparison of tangentially and directly oriented orifices can be used to inform the control valve design in oil and gas industries.