Optimization of huff-n-puff gas injection in shale oil reservoirs

Earlier studies show that huff-n-puff injection is preferred to continuous gas flooding to improve liquid oil production in shale oil reservoirs. Compared to gas flooding, huff-n-puff has more operational parameters to optimize so that liquid oil production can be maximized. This paper is to discuss the optimum huff-n-puff times, number of cycles and soaking time under practical operational and reservoir conditions. The operational and reservoir conditions dictate the maximum injection and production rates, and the maximum injection pressure and minimum production pressure. The numerical simulation results and discussions show that the optimum huff time is so long that the pressure near the wellbore reaches the set maximum injection pressure during the huff period; and the optimum puff time is the time required for the pressure near the wellbore to reach the set minimum production pressure during the puff period. The benefits of soaking may not compensate the loss in injection and production due to the time lost in the soaking period. Therefore, soaking may not be necessary during the huff-n-puff gas injection in shale oil reservoirs. The number of huff-n-puff cycles is determined when an economic rate cut-off is reached.