Improved efficiency of miscible CO(sub 2) floods and enhanced prospects for CO(sub 2) flooding heterogeneous reservoirs. Annual report, June 1, 1997--May 31, 1998

摘要

The goal of this project is to improve the efficiency of miscible CO(sub 2) floods and enhance the prospects for flooding heterogeneous reservoirs. This report provides results of the first year of the three-year project that will be exploring three principle areas: (1) Fluid and matrix interactions (understanding the problems): interfacial tension (IFT), phase behavior, miscibility, capillary number, injectivity, wettability, and gravity drainage; (2) Conformance control/sweep efficiency (solving the problems): reduction of mobility using foam, diversion by selective mobility reduction (SMR) using foam, improved injectivity, alternating water and gas injection, and using horizontal wells; and (3) Reservoir simulation for improved oil recovery (predicting results): gravity drainage, SMR, CO(sub 2)-foam flooding, interfacial tension, injectivity profile, horizontal wells, and naturally fractured reservoirs. Studies of surfactant foam quality were performed during this first year. Simulation studies on a foam pilot area resulted in an acceptable history match model. The results confirm that the communication path between the foam injection well and a production well had a strong impact on the production performance. A laboratory study to aid in the development of a gravity drainage reservoir was undertaken on the Wellman Unit. Experiments were begun meant to duplicate situations of injectivity loss in WAG flooding and identify factors affecting the injectivity loss. The preliminary results indicate that for a given rock the injectivity loss depends on oil saturation in the core during WAG flooding. The injectivity loss is higher in cores with high in-situ oil saturations during WAG flooding. This effect is being verified by more experimental data.