Analytical Modeling of Flow Regimes During Cyclic CO2 Injection in Hydraulically Fractured Tight Reservoirs for EOR

Summary This paper presents several analytical models for the pressure distribution in hydraulically fractured reservoirs depleted by horizontal wells with the aid of the cyclic CO2 injection. The objective is eliminating the uncertainties in predicting reservoir performance after the enhancement by CO2 injection and developing accurate tools for designing the CO2 injection projects. 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. Therefore, it is essential to learn how the CO2 injection process can be optimized in the hydraulically fractured reservoirs to increase production. The analytical solutions presented here reveal three flow regimes (hydraulic fracture regime, bilinear flow regime, and formation linear flow regime) that develop during production and injection in unconventional shale reservoirs. Then the numerical solution is designed to validate those analytical models. The results show that the hydraulic fracture flow regime and bilinear flow regime occur at the early and intermediate well production stage. These indicate the end of circulation of the CO2 injection into the fractures and the stimulated reservoir volume, respectively.