Simultaneous enhanced oil recovery, CCUS and UHUS in shale oil reservoirs

Abstract

The objective of this paper is to put forward some ideas related to CO2 and H2 utilization and storage while simultaneously conducting huff and puff (H&P) gas injection to increase oil recovery. The discussed utilization (U) and storage (S) are important parts of carbon capture, utilization and storage (CCUS). However, the CO2 capture (C) is beyond the scope of this study. Underground hydrogen storage (UHS) has been studied in the past. However, this is the first paper that investigates the possibility of H&P H2 injection in shale oil reservoirs. Hence, for simplicity we are introducing the acronym UHUS to signify underground hydrogen utilization and storage. It is anticipated that the simultaneous underground utilization and storage of CO2 and H2 will contribute to achieving the goal of net zero emissions.The paper involves the analysis of a real H&P CH4 injection pilot well in the Eagle Ford shale of Texas. The procedure includes history matching the primary and H&P history of the pilot well, and then forecasting oil recovery if the H&P is continued with CH4, or if the H&P is switched to CO2 or H2 in the reservoir simulator. The success of this method relies on geologic containment, which occurs when significant hydrocarbon volumes remain over geologic time in the same general location where they were generated. The Eagle Ford shale exemplifies this phenomenon, with hydrocarbons showing an inverted distribution - oil at the top, condensate in the middle, and dry gas at the bottom of the structure. Geologic containment enables the implementation of H&P CH4, CO2 or H2 injection and simultaneous storage of any of the injection fluids in the shale reservoir with negligible risk of unwanted leakage.The results demonstrate that H&P CH4, CO2 or H2 gas injection can considerably boost oil recovery to 25–30% of the original oil in place (OOIP), depending on the injected gas, as compared to only 5–10% with primary recovery methods. The advantages of H&P gas injection described in this paper also have potential application in other shale reservoirs with an inverted distribution of oil, condensate and dry gas, such as the Duvernay shale in Canada, the La Luna shale in Colombia and Venezuela and the Vaca Muerta shale in Argentina. Geologic containment ensures safe and appropriate storage of CO2 and H2 with negligible possibilities of leakage at the conclusion of the H&P project. Additionally, this paper also supports a previous conclusion by Olusola et al. (2021) indicating that gas injection at higher rates for shorter durations of time (as opposed to smaller gas injection rates for longer periods of time) can result in substantial improvements in oil recovery. This finding holds true for CH4, CO2 and H2 injection.The novelty of this research is demonstrating the effectiveness of combining H&P CO2 or H2 injection with the underground storage of such fluids in shale reservoirs characterized by geologic containment. This combination provides a win-win situation, as it not only enhances oil recoveries significantly, but also allows for safe storage of CO2 and H2 with negligible possibilities of potential leaks.