Analytical modeling of flow regimes during cyclic CO2 injection in hydraulically fractured tight reservoirs for enhanced oil recovery

This paper presents several analytical models for the pressure distribution in hydraulically fractured reservoirs depleted by horizontal wells with the aid of cyclic CO2 injection. The objective is to eliminate uncertainties in predicting reservoir performance after the enhancement by CO2 injection and develop accurate tools for designing CO2 injection projects. This paper's primary purpose is to present novel analytical models for flow regimes and validate them. The proposed models are unique because they are derived without using an approximated approach, they consider multiphase flow and can be utilized for injection applications. Although CO2-injection has been a favorable enhanced oil recovery (EOR) approach in the petroleum industry, some studies reported its negative impact due to the premature decline in production. Additionally, few researchers have linked the cyclic injection with the flow response inside the formation. This paper presents three flow regimes (hydraulic fracture regime, bilinear flow regime, and formation linear-flow regime) that develop during production and injection in unconventional reservoirs. The analytical solutions that encompass the non-approximated trilinear pressure transient model for hydraulically fractured reservoirs are developed. The models are solved by one of the state-of-the-art computational tools. The solutions are used to characterize the analytical models for the three aforementioned flow regimes. Then, the numerical solution is designed to validate the analytical models. The results show a good agreement between analytical and numerical solutions. The hydraulic fracture linear flow regime and bilinear flow regime occur at the early and intermediate well production stage. These flow regimes indicate the end of the CO2 injection into the fractures and the stimulated reservoir volume, respectively. Thus, knowing the period for the CO2 injection and the hydraulic fracture characteristics will facilitate the optimization of the CO2 injection process in tight formations depleted by multiple hydraulic fractures.

Automated summary

This paper introduces analytical models for pressure distribution in hydraulically fractured reservoirs depleted by horizontal wells with cyclic CO2 injection, aiming to eliminate uncertainties and develop accurate tools for CO2 injection projects. The unique models, derived without approximate methods, consider multiphase flow and can be applied for injection purposes. The study validates the novel flow regime models and emphasizes the importance of understanding CO2 injection timing and hydraulic fracture characteristics in optimizing tight formation CO2 injection processes.