Demonstration of the Gas Assisted Gravity Drainage (GAGD) Process in Carbonate Rocks.

The Gas Assisted Gravity Drainage (GAGD) process was developed and patented by Dr. Rao at LSU in the early 2000s. The process involves the use of several existing or new vertical injection wells to inject gas and use the natural segregation of reservoir fluids from the density difference and the gravitational forces to displace the trapped oil and mobilize the oil downwards to be produced by a horizontal producing well. The GAGD process can be implemented as a secondary or tertiary oil recovery method. Several physical model experiments have been conducted to demonstrate the effectiveness of the GAGD process for improving oil recovery. This research study is to expand the existing knowledge of the GAGD process and to apply it for carbonate rocks as more than 60% of world’s oil is held in carbonate reservoirs. In particular, this study focuses on the impact of type of gas injected, injection rate of gas, and the grain size of the porous media. A glass model similar to a Hele-Shaw type model was used for performing the experiments using carbonate rocks as the porous media, water and n-decane for oil. The results from this study show that using nitrogen gas provides slightly higher recovery for the GAGD process in carbonate rocks compared to carbon dioxide. Further, the optimal injection rate is at an intermediate injection rate that doesn’t disturb the stable front which can create an earlier breakthrough at higher injection rates. Finally, the larger grain size shows a significant improvement in overall oil recovery since increasing grain size diameter increases permeability and thus better overall oil recovery is obtained. The oil recovery from this study ranges from 70.9% to 87.7% of OOIP