Chemical water shutoff agents and their plugging mechanism for gas reservoirs: A review and prospects

Using a chemical water shutoff method is one of the most effective ways to control formation water and enhance gas recovery. Numerous water shutoff agents have been applied to successfully address water influx in gas fields. Basically, according to the differences in plugging mechanisms, the water shutoff agents can be divided into nine categories: inorganic salts, resins, particles, polymer bridge bond adsorption agents, polymer gels, foams, wetting alteration agents, micro-emulsions, and composite water plugging agents. The typical water shutoff agents and corresponding water plugging mechanisms, materials, properties, and adaptability analysis have been summarized to identify water shutoff agents suitable for gas reservoirs. A systematic performance evaluation of water shutoff agents has been conducted from the perspectives of plugging strength, temperature tolerance, salt tolerance, corrosion tolerance, long-term stability, selectivity of water plugging, migration capability, convenience of construction, and gas reservoir adaptability. We identified four types of water shutoff agents—polymer bridge adsorption agents, polymer gels, micro-emulsions, and composite water plugging agents—along with innovative construction techniques that satisfy the results for water shutoff in gas reservoirs. The concept of water shutoff for gas reservoirs is proposed, namely, optimizing water shutoff agents and construction techniques to establish a large-area barrier layer with a high compressive strength and good tolerance of temperature and salinity in gas-water interface to inhibit formation water flow around the barrier layer.