Reinforcement of polyacrylamide-co-tert-butyl acrylate base gel using nanosilica for conformance control at low and high reservoir temperatures

Abstract

Challenges of water shut-off, which is categorized under conformance control, are nowadays common in the oil and gas industry. The excessive water quantities produced from oil reservoirs can make the production process economically infeasible. The target of water shut-off process is plugging fractures or high permeability zones to decrease water cuts. Polyacrylamide tert-butyle Acrylate (PAtBA) is used for such applications. Silica (silicon dioxide) has been found to have a strengthening effect as well as it enhances the thermal and mechanical stability of the system. The objective of this study is to introduce nanosilica to reinforce PAtBA crosslinked by polyethyleneimine (PEI) and chromium Acetate (CrAc3) for low and high temperature conformance control applications. In this study, different ratios of polymer to crosslinker were investigated to choose the optimum combination. Then, nanosilica (NS) with different sizes (20, 50 and 85 nm) was added to the polymeric formulation with the inorganic crosslinker (CrAc3) to study the effect of silica content and size on gel strength. While, the reinforcement of the organically crosslinked gels with PEI was accomplished at 130 C. Evaluation of different systems was based on testing the rheological behavior of the mature gel based on the final storage modulus (G). Differential scanning calorimeter (DSC) technique was also employed to understand the nature of chemical interaction between the various chemicals. The investigation reveals that PatBA:CrAc3 of 9:0.5 is the optimum ratio producing the most strong gel. Silica with the size of 20 nm has produced the strongest gel by increasing the storage modulus by more than 150 %. At high temperature (130 C), 50 nm silica with PAtBA/PEI showed the highest storage modules compared to other sizes. DSC investigation discloses that silica is an inert and has no effect on the gelation reactions. Thus, silica has physical interactions with the polymer in the form of hydrogen bonding which enhances the strength of the gel in comparison with silica-free gels. Therefore, this study introduces a new polymeric formulation that serves as a water shut-off agent for reservoirs at low and high temperatures. The formulation that consists of PAtBA, CrAc3 and NS makes the system more stable and gives it more resistivity toward high shears. Whereas higher gel strength was achieved when PAtBA/PEI/NS was used at high temperatures.