Abstract
Gas-wetting alteration is a versatile and effective approach for alleviating liquid-blockage that occurs when the wellbore pressure of a gas-condensate reservoir drops below the dew point. Fluorochemicals are of growing interest in gas-wetting alteration because of their high density of fluorine groups and thermal stability, which can change the reservoir wettability into more favorable conditions for liquids. This review aims to integrate the overlapping research between the current knowledge in organic chemistry and enhanced oil and gas recovery. The difference between wettability alteration and gas-wetting alteration is illustrated, and the methods used to evaluate gas-wetting are summarized. Recent advances in the applications of fluorochemicals for gas-wetting alteration are highlighted. The mechanisms of self-assembling adsorption layers formed by fluorochemicals with different surface morphologies are also reviewed. The factors that affect the gas-wetting performance of fluorochemicals are summarized. Meanwhile, the impacts of gas-wetting alteration on the migration of fluids in the pore throat are elaborated. Furthermore, the Wenzel and Cassie-Baxter theories are often used to describe the wettability model, but they are limited in reflecting the wetting regime of the gas-wetting surface; therefore, a wettability model for gas-wetting is discussed. Considering the promising prospects of gas-wetting alteration, this study is expected to provide insights into the relevance of gas-wetting, surface morphology and fluorochemicals, further exploring the mechanism of flow efficiency improvement of fluids in unconventional oil and gas reservoirs.
Highlights
Over 172,700 billion cubic m of proven natural gas reserves worldwide can be found in gas-condensate reservoirs [1,2,3]
The liquid bridge refers to the liquid trapped in a multiphase flow system where the neighboring pore throats can be connected by small volumes of encountered liquid, which can tremendously confine the gas flow in the wellbore region, leading to a sharp decline in gas production
The conclusions can be drawn as follows: (1) The liquid-blocking effect occurring during the development of the gas-condensate reservoir has
Summary
Over 172,700 billion cubic m of proven natural gas reserves worldwide can be found in gas-condensate reservoirs [1,2,3]. Gas in low-permeability condensate occupy important positions in by the the global energy supply [4]. Gas in rocks low-permeability condensate reservoirs is mainly recovered elastic energy accumulated and fluids. 2 in Figure 1), to aonce sharp in gas productivity, known as upper liquid-blocking effect.(point. The the migration and allocation imbibes of fluids in theretains pore throat arephase governed byliquid reservoir wettability; rock spontaneously and liquid due by to reservoir capillary wettability; the rockthe spontaneously imbibes anddecreasing retains liquid phase due to capillary force, increasing the force, increasing liquid saturation and gas permeability [10]. The effect gas-wetting on the flow behaviors of fluids in in porous media is summarized, better insight the behaviors of trapped liquids in media is summarized, providingproviding a better ainsight into theinto behaviors of trapped liquids in gasgas-condensate reservoirs.
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