Preparation and Experimental Study of a Low-Initial-Viscosity Gel Plugging Agent

The development of dominant seepage channels after polymer flooding makes it more difficult to effectively exploit reservoirs, and gel plugging technology is an effective method to solve this problem. However, conventional gels experience problems such as high initial viscosity and they easily contaminate the medium- and low-permeability layers. Therefore, a low-initial-viscosity gel plugging agent is proposed in this paper. By optimizing the concentration of polymer, cross-linking agent, and other functional auxiliaries, the best gel formulation was obtained. To test the plugging ability of the gel system on the core and its oil displacement effect, a plugging performance test experiment and three-tube core parallel oil displacement experiment were performed. The research results showed that the best formulation of gel plugging agent is as follows: 500-1000 mg/L polymer LH2500, 1000-2500 mg/L cross-linking agent CYJL, 200-500 mg/L citric acid, 100-150 mg/L sodium sulfite, and 100-200 mg/L sodium polyphosphate; its initial viscosity is less than 10 mPa·s, the gelation time is controllable within 10 to 40 days, and the gelation viscosity is above 2000 mPa·s. Core flooding experiments showed that the gel system has good core plugging performance, and the plugging rate of water from 0.48 to 3.9 μm² is more than 99%; for the secondary polymer flooding reservoir, the recovery factor can be increased by 13.6% after plugging with 0.1 PV gel. At present, the gel has been successfully used in field tests and provides good oil increase and water control effects.