The current technique to produce shale oil is to use horizontal wells with multi-stage stimulation. However, the primary oil recovery factor is only a few percent. The low recovery and the abundance of shale reservoirs provide a huge potential for enhanced oil recovery.
Well productivity in shale oil and gas reservoirs primarily depends upon the size of fracture network and the stimulated reservoir volume (SRV) which provides highly conductive conduits to communicate the matrix with the wellbore. The natural fracture complexity is critical to the well production performance and it also provides an avenue for injected fluids to displace the oils. However, the disadvantage of flooding in fractured reservoirs is that the injected fluids may break through to production wells via the fracture network. Therefore, a preferred method is to use cyclic gas injection to overcome this problem.
In this paper, we use a numerical simulation approach to evaluate the EOR potential in fractured shale oil reservoirs by cyclic gas injection. Simulation results indicate that the stimulated fracture network contributes significantly to the well productivity via its large contact volume with the matrix, which prominently enhances the macroscopic sweep efficiency in secondary cyclic gas injection. In our previous simulation work, the EOR potential was evaluated from planar traverse fractures. In this paper, we examine the EOR potential by including the effect of fracture networks. Therefore, a higher oil recovery potential is demonstrated. The impacts of fracture spacing density and stress dependent fracture conductivity on the ultimate oil recovery are also investigated. In a case where the fracture network spacing is 100 ft and the fracture network is 100% stimulated, it can achieve more than 60% of incremental oil recovery. The results presented in this paper demonstrate an EOR potential by cyclic gas injection in fractured shale oil reservoirs.
This paper builds upon and extends our earlier work that investigated the impact of the planar fractures have on the enhanced oil recovery by cyclic gas injection (Wan et al. 2013). We investigated the impact of different well operating schedules (injection time and production time in each cycle), degree of in-situ miscibility between solvent with oil and propped planar hydraulic fractures spacing on the ultimate oil recovery. The previous work mainly focused on examining the effects of planar hydraulic fractures on the well primary production and secondary production performance without taking into account of the contribution from fracture network. In this work, the effects of fracture-network spacing, the size of SRV and fracture conductivity on well performance in shale oil reservoirs are examined.