Development of Gas Assisted Gravity Drainage (GAGD) Process for Improved Light Oil Recovery

Abstract

Abstract Attempting to overcome natural gravity segregation by alternating gas injection with water has yielded better EOR performance in WAG floods than continuous gas injection (CGI) field projects. However, WAG is still a method to ‘combat’ the natural phenomenon of gravity segregation. In attempting to resolve one problem of adverse mobility, the WAG process gives rise to other problems associated with increased water saturation in the reservoir including diminished gas injectivity and increased competition to the flow of oil. The disappointing field performance of WAG floods with oil recoveries in the range of 5–10% is a clear indication of these limitations. In order to find an effective alternative to WAG, we have initiated the development of the Gas-Assisted Gravity Drainage (GAGD) process. Unlike WAG, the GAGD process takes advantage of the natural segregation of injected gas from crude oil in the reservoir. Although gravity-stable gas floods have long been practiced in selected dipping reservoirs and pinnacle reefs, this project is aimed at a systematic development of a recovery process that would be widely applicable to different reservoir types in both secondary and tertiary modes. The GAGD process consists of placing a horizontal producer near the bottom of the payzone and injecting gas through existing vertical wells used in prior waterfloods. As the injected gas rises to the top to form a gas zone, oil and water drain down to the horizontal producer. The new GAGD process is being developed using a three-pronged approach: (1) Design and construction of a scaled physical model to demonstrate process feasibility and to investigate and understand the interplay of capillary, gravitational and viscous forces. (2) Process optimization by determining miscibility pressures and compositions through the use of the Vanishing Interfacial Tension (VIT) technique. (3) The process demonstration at reservoir conditions by conducting horizontal WAG floods and vertical GAGD floods in 2-meter long cores. This paper will present the GAGD concept and its advantages over WAG and a summary of the experimental evidence collected so far.