Review of Downhole Gas Liquid Separators In Unconventional Reservoirs

Abstract

Abstract The accumulation of liquid in deeper wells poses a critical problem as it significantly reduces the well's productivity index. One of the methods used to lift the accumulated liquid is the sucker rod pump system (SRP). However, lifting large volumes of liquid and associated gas to the surface artificially has been challenging, particularly with rod pump systems. To address this issue, a downhole gas separator can effectively be deployed below the pump intake to separate the free gas from the produced liquid. The gas separated downhole can then be extracted through the tubing-casing annulus while the liquid is artificially lifted through the tubing. The paper endeavors to provide a comprehensive review of recent advancements, technologies, and challenges related to downhole gas-liquid separators. The findings of this study can serve as a valuable guide for the development of downhole gas-liquid separation technologies in the industry, particularly for installation in unconventional wells. This review includes various laboratory evaluation tests and field examples that outline the efficiency and reliability of some downhole gas-liquid separators. There are two approaches implemented to design separators. The first approach is called static gas separation, based on the gravity principle. The second approach is dynamic gas separation, which is based on applying centrifugal forces through rotational speed. However, several downhole gas-liquid separators have low efficiency and lack an acceptable guideline for their optimum design. In some fields that suffer from liquid loading problems, it may be imperative to design and install an SRP and a downhole gas-liquid separator, to prevent gas lock problems. Based on the reviewed literatures, it was shown that centrifugal separators had better gas/liquid separation efficiency comparing to gravitational separators. Cyclone centrifugal separators consistently exhibit separation efficiencies ranging from 90% to 98%, whereas gravity-based separators typically achieve efficiency levels between 70% and 90%, depending on the design and operational variables. Centrifugal separators consistently deliver exceptional separation efficiencies, with effectiveness ranging from 90% to 99%. Moreover, the swirl tubes have showcased an approximate separation efficiency of 90% and effectively handle the fluctuating gas flow rates encountered in the well. This review comprehensively examines the advancements, limitations, and applications of downhole gas-liquid separators in oil and gas operations, specifically in conjunction with artificial lift systems. The paper aims to bridge the gap and differentiate between different types of downhole separators, offering researchers an extensive guide for their current and future investigations. Additionally, it proposes suitable technologies that can be deployed alongside the sucker rod pump (SRP) to enhance its efficiency in wells facing challenges related to liquid loading.