Gas and foam injection with CO2 and enriched NGL's for enhanced oil recovery in unconventional liquid reservoirs

Abstract

In order to extend the economic life of existing horizontal wells and improve oil production for newly drilled wells in unconventional liquid reservoirs (ULR), testing of enhanced oil recovery (EOR) techniques is essential. The interaction of the fluids in the fractures system with the oil stored in the matrix is the key to understanding and implementing all EOR techniques in ULR. This study focuses on investigating the performance of different EOR agents (CO2, rich gas, and foam) through laboratory tests.A correlated set of Huff-n-Puff experiments were performed at reservoir temperature using different gases and foam on side-wall core samples from the Wolfcamp formation. The experimental setup was mounted into a Computed Tomography Unit (CTU) to capture time-lapse CT images which were used to monitor the fluid movement inside the core plugs, track the foam quality in glass beads pack around the cores.Various gases (CH4, a mixture of 85% CH4 - 15% C2H6, enriched gas (50% CH4 - 50% C2H6), and CO2) were used for Huff-n-Puff experiments at reservoir conditions to explore the effects of gas composition on the recovery factor in ULR. Enriched gas (50% CH4 - 50% C2H6) showed the most promising potential of improving oil recovery in the Wolfcamp formation. An increase in pressure does not always correspond to higher oil recovery in gas Huff-n-Puff experiment. During the CO2 injection experiment conducted at 5000 psi, we recovered a smaller amount of oil than previous experiments performed at lower pressure. The primary mechanism of gas injection is multi-contact miscibility, and diffusion has a minor effect on enhancing oil recovery in ULR. Surfactants enhance oil recovery by wettability alteration and interfacial tension (IFT) reduction. Implementing surfactants into completion fluids or re-frac fluids results in additional oil recovered from ULR. From the results obtained, a combination of EOR techniques (foam or sequencing surfactant and gas injection) opens the possibility to achieve optimum oil recovery in ULR.