Lysine Crosslinked Polyacrylamide─A Novel Green Polymer Gel for Preferential Flow Control

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 Frrw is two times higher than the Frro, 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

Feasibility Study of Recrosslinkable Preformed Particle Gels for Natural Gas Injection Profile Control

Recrosslinkable Preformed Particle Gel (RPPG), a novel preformed particle gel 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 water flooding projects. However, no research has been conducted about whether RPPG is feasible in improving gas flooding 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. Also, the RPPG stability was compared to the in-situ gel system HPAM/Cr (III) which has been applied in oilfields 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 (\u3c 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 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 swelling ratio 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 was used to simulate natural gas behavior. The robustness of the RPPG system makes it a viable candidate for improving the gas flooding processes in mature reservoirs dominated by conformance problems such as void space conduits, fractures, and high permeability channels

Laboratory Evaluation of a Novel Self-Healable Polymer Gel for CO₂ Leakage Remediation during CO₂ Storage and CO₂ Flooding

For CO2 storage in subsurface reservoirs, one of the most crucial requirements is the ability to remediate the leakage caused by the natural fractures or newly generated fractures due to the increasing pore pressure associated with CO2 injection. For CO2 Enhanced Oil Recovery (EOR), high conductivity features such as fractures and void space conduits can severely restrict the CO2 sweep efficiency. Polymer gels have been developed to plug the leakage and improve the sweep efficiency. This work evaluated a CO2 resistant branched self-healable preformed particle gel (CO2-BRPPG) for CO2 plugging purpose. This novel CO2-BRPPG can reform a mechanical robust adhesive bulk gel after being placed in the reservoir and efficiently seal fractures. In this work, the swelling kinetics, self-healing behavior, thermal stability, CO2 stability, rheology, adhesion property and plugging performance of this novel CO2-BRPPG were studied in the laboratory. Results showed that this CO2-BRPPG has good self-healing abilities, and the self-healed bulk gel has excellent mechanical and adhesion strength. Gel with a swelling ratio of ten has an elastic modulus of over 2000 Pa, and the adhesion strength to sandstone is 1.16 psi. The CO2-BRPPG has good CO2 phase stability at 65 °C, and no dehydration was observed after 60 days of exposure to 2900 psi CO2 at 65 °C. Core flooding test proved that the swelled particles could reform a bulk gel after being placed in the fractures, and the reformed bulky gel has excellent CO2 plugging efficiency. The supercritical CO2 breakthrough pressure gradient was 265 psi/feet (5.48 MPa/m). This work could offer the experimental basis for the field application of this CO2-BRPPG in CO2 storage and CO2 enhanced oil recovery