The objective of this paper is to compare oil recoveries by huff ‘n’ puff gas injection using methane (CH4), carbon dioxide (CO2), hydrogen (H2) and rich gas (70% CH4, 20% C3H8, plus 10% C6H14), and to advance some ideas regarding carbon capture, utilization and storage (CCUS) of CO2, and storage of hydrogen when these gases are used in huff ‘n’ puff operations.
The procedure considers a real huff ‘n’ puff pilot well in the Eagle Ford shale of Texas with methane injection. Following history match of the pilot well, the injected gas is switched in the reservoir simulator to CO2, H2 and rich gas. Key to success in this process, is geologic containment, which occurs when large volumes of hydrocarbons remain over geologic time in the windows where they were generated. This is the case of the Eagle Ford shale, where hydrocarbons display an upside-down distribution, with oil on the top, condensate in the middle and dry gas at the bottom. Geologic containment permits the implementation of simultaneous huff ‘n’ puff, utilization and storage of CO2 with nil probabilities of leakage.
Results show that huff ‘n’ puff gas injection can significantly increase oil recoveries to be 25-35% of the OOIP (depending on the specific injected gas), compared to about 10% by primary means during the simulation time. The benefits of huff ‘n’ puff gas injection are also applicable in other shale reservoirs where oil, condensate and dry gas present an upside down distribution. One example in Canada is the Duvernay shale. Geologic containment allows adequate and safe storage of CO2 and hydrogen without leaks at the end of the huff ‘n’ puff project. This paper also assesses and corroborates the conclusion that "significant improvements in oil recovery can be obtained by injecting gas at larger rates during shorter periods of time (as opposed to injecting gas at smaller rates during longer periods of time)." The same conclusion holds true for methane, CO2, hydrogen and rich gas injection.
The novelty of this work is demonstrating the efficiency of CCUS and huff ‘n’ puff gas injection when geologic containment exists in the shale reservoir. It is a solution where everyone benefits and allows to significantly increase oil recoveries, while providing safe storage of CO2 and H2 without any leaks.