Optimization of huff-n-puff gas injection in a shale gas condensate reservoir

Condensate blockage is a serious problem in shale gas condensate reservoirs. As the pressure decreases lower than dew point pressure, condensate forms. This condensate reduces the relative permeability of gas and the productivity of shale gas condensate reservoirs.

Huff-n-puff gas injection is an EOR method in which a well alternates between injection, soaking, and production. Based on the laboratory study conducted by Meng et al. (2015), huff-n-puff gas injection was proven as an effective method to enhance condensate recovery for Eagle Ford shale cores. In this paper, a numerical reservoir simulation study is conducted to optimize the application of huff-n-puff gas injection in an Eagle Ford shale gas condensate reservoir. During the injection and soaking process, the pressure of the reservoirs built up, the condensate was revaporized to gas, and then was produced during the production process. Different parameters were investigated including injection time, soaking time, production time, and cycle numbers.

The results show that huff-n-puff gas injection is an effective method to enhance condensate recovery in the Eagle Ford shale gas condensate reservoir. It was found that the optimum injection time is the time during which the pressure of the main condensate region can be increased higher than dew point pressure. Also, shorter or even no soaking is more effective. The production time depends on the production decline rate. It is more profitable to start another cycle of huff-n-puff gas injection when the production rate is decreased to a low value.