Development of Dilution-Resistant Gel for Deep-Source Water Control in Deep Fractured-Vuggy Reservoirs

Abstract Fractured-vuggy reservoirs have the characteristics of large reservoir space and extreme heterogeneity, which can easily cause water channeling. The commonly used water channeling regulator is gel. However, a large amount of formation water in the water channel will dilute the gelling fluid injected into it, thus losing its gelling ability and leading to the failure of water plugging operation. Therefore, a concept has been introduced that employs a dilution-resistant interfacial membrane to isolate formation water, thus preventing the dilution of the gelling solution and ensuring successful gelation. A novel, dilution-resistant gel for deep-source water control in deep fractured-vuggy oil reservoirs has been developed. The gelation effect under simulated reservoir conditions was systematically evaluated, and its dilution resistance and strengthening mechanism were clarified. In the formulation of this gel, the salt-sensitive and dilution-resistant additive sodium alginate is incorporated, which can interact with calcium ions in the formation water to form an impermeable interfacial membrane. Based on the stability of interfacial membrane, the optimal concentration of sodium alginate utilized is determined to be 0.4%-0.6%. The rheological characteristics showed that sodium alginate could enhance the elasticity and viscosity of the gel by 60.17% and 24.52%. At 10 times the volume of water, the dilution-resistant gel has a good gelation effect. A systematic study focusing on the reinforcement mechanism of sodium alginate in the gel was conducted from multiple angles including interfacial rheology, microstructural morphology, and thermal stability. The elastic and viscous modulus of the interfacial membrane are stable at 5.99 Pa and 3.52 Pa in the amplitude of 0-100%. Relative to conventional gels, the dilution-resistant gel possesses a more intricate three-dimensional network structure, which aids in improving its water retention capabilities. The thermal stability of dilution-resistant gel before and after aging at high temperature and high salt (130°C, 220,000mg/L) increased by 3.9°C and 9.3°C. As a result, this dilution-resistant gel presents itself as a potential option for deep-source water control in complex deep fractured-vuggy oil reservoirs, providing an effective strategy to manage water production and enhance hydrocarbon recovery.