Evaluation and Plugging Performance of Carbon Dioxide-Resistant Particle Gels for Conformance Control

Abstract

Summary Traditional polyacrylamide (PAM)-based superabsorbent polymer has been applied to control excess carbon dioxide (CO2) production in CO2-flooding fields. Nevertheless, the application results are mixed because the polyacrylamide-based superabsorbent polymer dehydrates significantly when exposed to supercritical CO2; therefore, we evaluated a novel CO2-resistant gel (CRG) with reliable stability and CO2-responsive properties. Particularly, the CRG swelling ratio (SR) and gel-volume increase after CO2 stimulation if additional water is available. Swollen CRG was placed in high-pressure vessels to examine the weight loss and the property changes before and after exposure to CO2. The breakthrough pressure and CRG-plugging efficiency to CO2 were measured using partially open fractured-sandstone cores. Two water/alternating/gas (WAG) cycles were conducted to test the CRG-plugging performance after CRG injection. The high-pressure vessel-test results show that the CRG is very stable under the supercritical-CO2 condition and no free water is released from the samples. The scanning-electron-microscope (SEM) images confirm that no structural damage was observed in CRG after exposure to CO2. The breakthrough pressure increases with the matrix permeability, which is mainly induced by the internal and external gel cake formed on the rock surface. CRG can reduce the water permeability more than CO2 permeability. CRG-plugging efficiency to CO2 decreases with the increase of WAG cycles. However, in the 0.5-mm fracture model and the 390-md model, CRG-plugging efficiency to water increases with WAG cycles. This phenomenon further indicates that CRG can be stimulated by CO2, which allows CRG to absorb additional water during post-waterflooding. In general, this study reports the concept of the novel CRG and a systematical evaluation of CRG stability under supercritical-CO2 conditions and CRG-plugging efficiency using a partially open fractured-sandstone model.