Impact of micro- and macro-scale consistent flows on well performance in fractured shale gas reservoirs

Abstract

Shale gas revolution comes from the skillful combination of horizontal drilling and hydraulic fracturing technology that can create a fractured gas reservoir for gas production. The well performance in the fractured shale gas reservoir is significantly impacted by the complicated gas flow regimes in both fracture network and shale matrix. The consistency between the macro-flow in fracture network and the micro-flow in shale matrix determines the gas production curve, thus being a key issue to gas well design. This paper proposes a numerical model to investigate the impact of micro- and macro-scale consistent gas flows on well performance in fractured shale gas reservoirs. In this numerical model, the macro-scale gas flow follows the Darcy law in the fracture network and the micro-flow in the shale matrix is described by a diffusion-controlled gas transport model. Two apparent diffusion coefficients or models are then obtained. They incorporate viscous flow with slip boundary, molecular diffusion (i.e. molecular self-diffusion), Knudsen diffusion, and surface diffusion in the adsorption layer. The performances of these two diffusion models for the gas transport within shale matrix are investigated and compared with two apparent permeability models proposed by Singh and Javadpour (2013) and Darabi et al. (2012). Furthermore, the pressure-dependent anisotropy of fracture permeability and compressibility is incorporated into the numerical model. This numerical model is verified by an analytical solution and history matching for a Barnett shale gas well. Finally, a fractured gas reservoir with different scenarios is numerically simulated and the shapes of production curves are analyzed through parametric study. It is found that the enhancement of gas recovery efficiency and the life of a shale gas well can be effectively designed if the consistency of micro- and macro-flows can be well designed.