New insights into the DPR mechanism of elastic energy released by polymer gel for enhanced oil recovery

Abstract

Polymer gel was widely used as water shutoff agent in mature oil fields. And the results of single-phase plugging experiments show that the plugging rate of the polymer gel to the oil phase is lower than that of the water phase. However, the disproportionate permeability reduction (DPR) mechanism of polymer gels still remains controversial. In this paper, we used four gel formulations including Polyethyleneimine (PEI) and Phenol-formaldehyde crosslinked gel with and without adding laponite to investigate the effect of gel elastic property on the water shutoff mechanism. The result of sand pack flooding experiments shown that the gel with higher elastic modulus has better effects on decreasing water cut and increasing oil recovery. After adding laponite, the elastic modulus of Phenol-formaldehyde crosslinked gel increased from 64.2 Pa to 192 Pa, and the elastic modulus of PEI crosslinked gel increased from 27.4 Pa to 36.5 Pa. Compared to the Phenol-formaldehyde-HAPM gel, the oil recovery of Laponite-Phenol-formaldehyde-HPAM gel increased by 5.2% and the maximum water cut decreased by 8.3%. Besides, comparing with PEI-HPAM gel, the oil recovery of Laponite-PEI-HPAM gel increased by 2.7% and the water cut dropped by 27.8%. In the meanwhile, the Laponite-Phenol-formaldehyde-HPAM gel with higher elastic modulus obviously swells in the formation water but almost remains constant in oil at 105 °C. The mass of gel soaked in the formation water increased from 42 g to 96 g and the gel volume increased by 300% within 48 h. This study improves the understanding of the DPR mechanism of polymer gel for water shutoff. • The elastic properties of conventional gel can be significantly improved by adding laponite. • The plugging rate of gel to the oil phase is less than that of the water phase at the same permeability. • The gel with higher elasticity has better effects on reducing water cut and increasing oil recovery.