Experimental study of viscosity effects on heavy crude oil-water core annular flow pattern

It is well known that in multiphase flow, different flow patterns lead to different pressure gradients. One remarkable example is the oil-water core-annular flow with water in the annulus and viscous oil in the core. Researchers have thus studied this flow pattern as a possible artificial lift technique for the production and transport of crudes and/or petroleum mixtures of high viscosities, which application might imply in energy efficiency increase and costs reduction for the oil industry. Hence, in this work, a set of experiments with vertical-upward heavy crude oil water flows were carried out to study the influence of viscosity on the core annular flow parameters. The oil was diluted with diesel to present tests with oil viscosities of 557, 1112, 1561, and 1729 cP and tap water as working fluids in a vertical 59-mm-id. and 13-m-length test section. The slip ratio between phases and holdup were obtained by a slow-motion footage technique and compared with literature models. The measured core-annular flow frictional pressure gradient had the same magnitude of water single-phase flow at the mixture flow rate and total pressure gradient was smaller than for single-phase oil flow. Total reduction factors up to four times were observed. Minimum oil holdup for core-annular flow exists, having an oil viscosity influence and its effects on flow parameters were presented.