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Acrylamide-based polymer gels have been applied to control the preferential flow in the subsurface for decades. However, some commonly used crosslinkers, such as Cr (III) and phenol–formaldehyde, are highly toxic and are being phased out because of stringent environmental regulations. This work uses l-lysine as the green crosslinker to produce acrylamide-based polymer gels. This article systematically studied the effect of lysine and polymer concentration, salinity, pH, and temperature on gelation behavior and thermal stability. Besides, the gelation mechanism and crosslinking density were elucidated in this work. A high-permeability sandstone core was used to test the plugging efficiency of this novel green gel system. This polyacrylamide/lysine system has a controllable gelation time. It can form gels at temperatures higher than 80 °C, with the gelation time from hours to days, and the elastic modulus of the gel can reach over 400 Pa. In addition, the crosslinked gels have been stable at 80 to 130 °C for over 200 days. This novel gel system could decrease rock permeability by over 1000 times. Besides, the F rrw is two times higher than the F rro, confirming that the current gel system can reduce the permeability to water more than that to oil. As a green gel system, this novel polymer gel system could replace the current toxic gel systems for the preferential fluid control for water management projects in oil and gas reservoirs, enhanced geothermal systems, and carbon capture and sequestration projects.

Summary Recrosslinkable preformed particle gel (RPPG), a preformed particle gel (PPG) of which particles can bond together to form a strong bulk gel system after being placed inside the target formation, has been successfully applied to control conformance problems for waterflooding projects. However, no research has been conducted about whether RPPG is feasible in improving gasflooding performance in mature reservoirs. The study presents a systematic evaluation of acrylamide (AM) and 2-acrylamide-2-methylpropane sulfonate acid (AMPS)-based RPPG including phase stability under different gel-gas kinetics and plugging performance to natural gas and water. Different experimental apparatuses were designed to quantify and visualize the RPPG phase stability under static and dynamic gel-gas interactions. The RPPG phase stability was evaluated under a different range of injection pressure, gas exposure time, and swelling ratio (SR). Also, the RPPG stability was compared to the in-situ gel system hydrolyzed polyacrylamide crosslinked with chromium acetate [HPAM/Cr(III)], which has been applied in oil fields to control gas injection conformance. The RPPG plugging efficiency was evaluated using open fractured cores with different apertures. The results showed that the RPPG was stable under both static and dynamic gel-natural gas interactions and was stable when being exposed to an acidic environment with an insignificant total percentage weight loss (<3%). Additionally, the strength of the RPPG was further improved with the longevity of the gas exposure. Furthermore, different from the in-situ gel system HPAM/Cr(III), which exhibited a high degree of dehydration under natural gas and exhibited substantial syneresis under acidic conditions, the microstructure of the RPPG remained stable after the dynamic gas exposure. The results of the coreflooding experiments demonstrated that the RPPG had excellent plugging efficiency, which was closely related to the SR and the fracture aperture. This is the first study where a polymer gel system has been systematically assessed through varied testing methodologies using natural gas as opposed to other studies where nitrogen (N2) was used to simulate natural gas behavior. The robustness of the RPPG system makes it a viable candidate for improving the gasflooding processes in mature reservoirs dominated by conformance problems such as void space conduits (VSCs), fractures, and high-permeability channels.

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