Targeted delayed viscosity-thickening polymer solution for enhancing oil recovery in mature reservoirs

In oilfield applications, it has been found that the shell-broken and unbroken targeted viscosity-thickening polymers (TVTPS) were distributed at different locations in the formation during injection and migration. This differential distribution created distinct zones of compositional heterogeneity and viscosity gradients throughout the reservoir, so that the utilization degrees of remaining oil in different locations was different. To evaluate the displacement efficiency of TVTP and analyze the utilization degree of remaining oil in distinct reservoir zones, we conducted laboratory simulation experiments. The fundamental properties of TVTP were systematically investigated, and parallel sand-pack models and large-scale plate sand-pack models were utilized to analyze their oil displacement efficiency and the utilization degree of remaining oil at different locations. The experimental results indicate that TVTP can achieve shell-breaking and viscosity-thickening in the reservoir. In the parallel sand-pack test, the oil displacement efficiency of unbroken and shell-broken TVTPS were compared. It was found that shell-broken TVTP, due to their better viscosity-thickening effect and strong plugging capability, can more effectively increase the recovery, recovery increment can reach 42.4%. In the large-scale plate sand-pack test, the advantages of shell-broken TVTP in enhancing the sweep efficiency and recovery of high and low permeability layers were further verified, recovery increment can reach 37.1%. In summary, TVTP as an effective chemical oil displacement agent, can significantly increase the recovery of crude, especially after shell-breaking, where the effect is more pronounced.