Enhanced-Oil-Recovery Potential for Lean-Gas Reinjection in Zipper Fractures in Liquid-Rich Basins

Abstract

Summary Production from liquid-rich shale has become an important contributor to US production, but recovery factors are low. Enhanced-oil-recovery (EOR) methods require injectivity and interwell communication on reasonable time scales. Herein, we investigate the development of fracture interference for the application of recycled-lean-gas injection to displace reservoir fluids between zipper fractures in liquid-rich shales. In condensate systems, the liquids produced from miscible displacement could be extracted at the surface and the gas reinjected. In unconventional oil systems, immiscible displacement would occur with arrest in the oil-rate decline upon the onset of pressure support until immiscible front breakthrough, although this may never occur in a reasonable time. In either case, the time for interference is critical in assessment of process feasibility. Using superposition plus existing analytical solutions to the diffusivity equation for arbitrarily oriented line sources/sinks for pressure and new extensions for the pressure logarithmic temporal derivative, we analyze the time for interfracture-communication development (i.e., interference) and productivity index (PI) for both classical biwing fractures in a zipper configuration and complex-fracture networks. As a novel contribution, we demonstrate the ability to map both pressure and pressure temporal derivative as a function of time and space for production and/or injection from parallel motherbores under the infinite-conductivity wellbore and fracture assumption. The infinite-conductivity assumption could be relaxed later for more-general cases. We present the results in terms of geometrical-spacing requirement for both horizontal wells and stimulation treatments to achieve reasonable time frames for interfracture communication and sweep for parameters typical of various shale plays. Results can be used to determine whether spacing currently considered for primary production is sufficient for direct implementation of EOR or if current practice should be modified with EOR in the field-development plan.