NUMERICAL STUDY ON THE INFLUENCE OF GAS VOLUME FRACTION ON THE TWO-PHASE FLOW OF HEAVY OIL AND NATURAL GAS MIXTURES IN AN OIL WELL

Abstract

Petroleum is an important fossil fuel that results from the decomposition of organic matter stored in sediments. Most petroleum reservoirs produce simultaneously oil and gas, which flow up to the surface through oil wells. Different amounts of gas are produced in different reservoirs depending on their characteristics. For some purposes, a single-phase model can describe the oil behavior quite well even in two-phase flow phenomena. In the present work, the influence of gas volume fraction on the flow patterns of biphasic mixtures comprising heavy oil and natural gas was investigated. The pressure drop and fully developed oil velocity profile were analyzed by numerical simulations, which were performed using the commercial software Ansys CFX 13.0. The governing equations were written in cylindrical coordinates and solved by the finite volume method. The numerical results for the oil velocity profile were compared with a single-phase model. The results show that the single-phase flow can be properly applied to describe the characteristics of oil velocity profiles in the presence of gas, in cases where the gas volume fraction is lower than 20 %. For 25 % of gas, a discrepant behavior could be noted . The pressure drop data were compared with theoretical results considering the mixture density. The maximum error in percentage between numerical and theoretical results for pressure drop was less than 2 %.