Degradable preformed particle gel as temporary plugging agent for low-temperature unconventional petroleum reservoirs: Effect of molecular weight of the cross-linking agent

Abstract

The development of unconventional petroleum resources has gradually become an important succession for increasing oil production. However, the efficient development of this type of reservoir is paying more and more attention to the application of temporary plugging agents. The use of temporary plugging agents can further expand the stimulated reservoir volume (SRV) and facilitate the flow of oil and gas to the bottom of the well. Particle-gels used as temporary plugging agents have the characteristics of the simple injection process, good deformation, high plugging strength, and complete self-degradation performance, which has been widely applied in recent years. In this paper, five samples of DPPG polymerized by different molecular weights of cross-linking agents were prepared. In addition, infrared spectroscopy analysis, differential calorimetry scanning (DSC) analysis, static particle gel swelling and degradation performance evaluation experiments, and dynamic temporary plugging performance experiments in cores were used to study the influence mechanism of the cross-linking agent molecular weight ( M w ) of the DPPG molecule on its temporary plugging performance. Results show that as the molecular weight of the cross-linking agent (at 0.01 g) in the DPPG molecule decreases from 1000 to 200 Daltons, the fewer cross-linking sites of DPPG, the looser the microscopic three-dimensional mesh structure formed, and the swelling ratio is increased from seven to 33 times. However, the complete degradation time increases from 40 to 210 min. Moreover, the DSC scanning results confirmed that the larger the molecular weight of the cross-linking agent, the worse it is chemical stability and the more prone it to self-degradation. The DPPG particle samples have good temporary plugging performance in reservoir cores. The DPPG prepared by the cross-linking agent with smaller molecular weight has a smaller expansion ratio, higher gel strength, and greater plugging strength in the core. Moreover, the degraded DPPG is less damaging to the cores. However, its slower degradation rate takes a slightly longer time to reach complete degradation. The results of this paper can provide new ideas and a theoretical basis for the development of particle gel-based temporary plugging agents (TPA) with controllable degradation time in low-temperature reservoirs. It can help to expand further the application range of existing DPPG reservoir conditions.