Preparation and crosslinking mechanism of delayed swelling double-crosslinking nano polymer gel microsphere for anti-CO2 gas channeling

CO2 flooding is often used in low permeability reservoirs, but there is general fracture in the reservoir, resulting in the problem of gas channeling. To achieve anti-gas channeling in deep formation, acrylamide (AM), sodium p-styrenesulfonate (SSS) and dimethyl diallyl ammonium chloride (DMDAAC) were used as functional monomers, N′ N-methylene bisacrylamide (MBA) and polyethylene glycol 200 diacrylate (UCA) were used as crosslinking agents, a double-crosslinking nano polymer gel microsphere (DCNPM-A) was synthesized by inverse microemulsion polymerization. The synthetic process of gel microsphere was optimized by initial particle size and swell multiple (defined the ratio of gel microsphere volume after and before water absorption) as evaluation indexes. The gel microsphere was characterized by scanning electron microscopy (SEM) and elemental analysis (EDS). The anti-gas channeling ability was evaluated by one-dimensional fracture core. The structure of the copolymer without crosslinking agent was verified by 1H NMR. The results showed that the DCNPM-A gel microsphere was regular spherical shape under the optimal synthesis process, and EDS analysis showed that the microsphere contained all the characteristic elements of monomers. The initial particle size and swell multiple of DCNPM-A gel microsphere were 217.3 nm and 13.5 respectively. The gel microsphere possessed delayed swelling. The plugging rate of DCNPM-A gel microsphere was 95.48% in the anti-gas channeling experiment. The study in this paper can provide theoretical support for the anti-gas channeling in low-permeability fracture reservoirs.