| Summary: | The Gas Assisted Gravity Drainage (GAGD) process, currently being developed at LSU, is designed to take advantage of gravity to allow vertical segregation between the injected gas and reservoir crud oil due to their density differences. GAGD is recommended for use with CO2 gas. CO2 dissolves in oil and causes both swelling and viscosity reduction of oil. The GAGD process uses the existing vertical wells for CO2 gas injection, and a horizontal well near the bottom of the payzone for oil production. GAGD, as an EOR process, is not restricted to tertiary oil recovery only.
In this research study, a visual glass model has been used to visually discern the mechanisms operative in the GAGD process. The model was also designed to fit different vertical well configurations. The model experiments have proven that GAGD is a viable process for secondary and tertiary oil recovery. Oil recovery in the immiscible secondary mode was as high as 83% IOIP and the oil recovery in the immiscible tertiary mode was 54% ROIP. The model has also shown that the gas injection depth may not have an influence on oil recovery as long as there is vertical communication between reservoir layers. Four different injection depths resulted in oil recovery values between 71% IOIP and 76% IOIP. The visual model experiments have also demonstrated that GAGD is applicable to naturally fractured reservoirs. The oil recovery in the fractured porous media was as high as 76% IOIP, which was higher than the average in homogenous porous media (73% IOIP). Additionally, the GAGD process was found to be viable for higher viscosity oils as well, where secondary immiscible oil recovery was 64% IOIP.
Miscible secondary injection was performed by using naphtha as the oil phase and decane as the miscible gas phase to simulate the miscible GAGD process. The visual model has resulted in a microscopic sweep efficiency close to 100% in the miscible GAGD process. The visual model experiments have demonstrated three possible mechanisms responsible for high oil recoveries: Darcy-type displacement until gas breakthrough, gravity drainage after breakthrough, and film drainage in the gas invaded regions.
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