Compositional modeling of fracture-to-fracture miscible gas injection in an oil-rich shale

The ultra-low permeability of shale makes injection from a well to other wells difficult. A novel scheme was proposed in a recent patent (Dombrowski et al., 2015) where gas is injected into a hydraulic fracture along a horizontal well and production occurs from an adjacent fracture, intersecting the same well. Compositional reservoir modeling was performed to investigate the effectiveness of the proposed gas injection scheme. The computational domain consists of two hydrofrac half-stages along a horizontal well. The results show 15.7% and 12.5% OOIP incremental recovery over 5000 days of CO2 injection for the base models with the matrix permeability of 10 μD and 1 μD, respectively, demonstrating that the gas injection scheme has the potential to vastly improve oil recovery in oil-rich shale formations. The effects of reservoir properties and injection conditions on oil recovery were investigated by changing the injection pressure, reservoir heterogeneity, distribution of natural fractures, hydrofrac spacing, size of pore space, and compositions of the injection gas. Most of them affect the oil recovery significantly. Recovery by miscible hydrocarbon gas injection is comparable to CO2; so it should be considered as an alternative.