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-i.d. 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.