Alternating N₂ and CO₂ Injection as Prospective Technique for Delaying CO₂ Breakthrough During During Enhanced Gas Recovery in Consolidated Rocks.

The use of carbon dioxide (CO₂) for simultaneous methane recovery and CO₂ storage is gaining recognition globally within the oil and gas industries. On the other hand, most of the residual natural gas recovered during the EGR process is highly contaminated with the injected CO₂ due to their nascent miscibility nature, resulting in premature breakthrough. In this study, N₂ gas was used as a buster to mitigate such early mixing between the CH₄ and CO₂. The experiment was administered at reservoir conditions of 40oC temperature, 1500 psig of pressure, the optimum injection rate of 0.4ml/min, and at varying N₂ cushion volumes (8-36 cm³) using Bandera gray as the porous medium. Further experimental tests were administered to study the effect of this technique on connate water salinity with 5-20% water salinity been considered. The increase in buster gas volume was in direct proportion to delayed CO₂ breakthrough, with the maximum at 36cm³ buster volume. This breakthrough occurred at 177 minutes which is 110min additional delayed than the conventional CO₂ flooding with a breakthrough time of 67 minutes. This was due to the high shielding barrier inhibited by nitrogen, making it difficult for the CO₂ to dispersed itself and mixed with the nascent natural gas resulting in delayed breakthrough as it plumes transverses into the CH₄ during the displacement process. Furthermore, a poor performance was observed with the inclusion of the connate water salinity, especially at 20% wt. This was because the free pore spaces were already occupied by connate water molecules prior to the cushion gas injection which hinders its economic potential application.