Performance Evaluation on Profile Control and Flooding of QPD Thermosensitive Gel in High-Temperature and High-Salinity Reservoir of Block X

The reservoir of Block X is classified as a typical high-temperature and high-salinity formation, with a formation temperature of 83 °C and a total salinity of 16,000 mg/L. To further boost oil recovery, gel profile control and flooding was adopted to optimize the field development performance. Nevertheless, conventional phenolic gel systems suffer from poor gelling properties and insufficient stability under such harsh reservoir conditions, leading to unsatisfactory application outcomes. This creates an urgent demand for the development of an innovative gel system with superior adaptability. In this research, dimethyl carbonate, a green chemical reagent, was applied to partially quaternize poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) copolymers, replacing traditional halogenated alkanes. This approach yielded a novel copolymer with enhanced thermal resistance. By blending the modified copolymer with stabilizers and crosslinking agents, a temperature-responsive gel system named Q-PDMAEMA-DMC (abbreviated as QPD gel) was successfully formulated. Multiple characterization methods were adopted to clarify the structural features and comprehensive performance of the QPD gel, including nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, Zeta potential testing, SEM microtopography, gelling property evaluation, and rheological analysis. Core flooding tests were also conducted under laboratory conditions simulating the actual reservoir environment of Block X. The testing results reveal that the QPD gel maintains stable internal structure, reliable gelling performance and favorable rheological behavior across the temperature range of 50 °C to 100 °C. When deployed for profile control and flooding in Block X, the QPD gel delivered remarkable enhancement in oil recovery. Compared with conventional water flooding alone, the final recovery degree increased by 16.9 percentage points; meanwhile, it achieved an improvement of 6.2 percentage points relative to the original unmodified PDMAEMA gel system. These findings confirm that the QPD gel can effectively mobilize residual oil in high-temperature and high-salinity reservoirs. It therefore serves as a technically feasible and promising solution to further improve oil recovery efficiency in Block X.