An Experimental Evaluation of a Hybrid EOR Method Combining Low-Tension-Gas and Polymer-Gel

Abstract

Heterogeneous sandstone reservoirs pose many challenges to oil recovery, one of them being recovering oil from the low permeability zones. Low-tension-gas (LTG) flooding has been proven to be effective in mobilizing oil trapped in low permeability reservoirs. Meanwhile, polymeric gel systems have been used successfully for conformance control in heterogeneous reservoirs. The objective of this study is to maximize oil recovery in a high-temperature, high salinity, and heterogeneous sandstone reservoir by LTG flooding with the assistance of a polymeric gel for conformance control. In this study, a dual parallel core flood was designed by setting up a high permeability core and a low permeability core in parallel and conducting simultaneous injections. The LTG flood and polymer gel placement were investigated separately first to confirm the efficacy. All experiments were conducted at 92°C. Bulk foam tests were performed to evaluate the stability and injectivity of ultralow-IFT foam and foam drive. The LTG core floods were completed in outcrop sandstone cores and composite reservoir cores to test the designed injection scheme. The plugging efficiency of formulated polymer gel was studied by a core flood in an outcrop sandstone core. It decreased the permeability from 1.4 Darcy to 0.4 mD after 1 week of incubation period. In the dual core flood test, we carried out waterflood and LTG flood before and after the gel application. The recovery analysis showed that before introducing the gel system LTG itself could provide a certain degree of profile control. The formulated polymer gel could provide stronger profile control and the following waterflood and LTG greatly improved oil recovery from the low permeability region by 41% and 37% respectively. The result of dual core flood demonstrates the effectiveness of a novel hybrid EOR process in the high temperature-high salinity heterogeneous reservoirs.