Optimization of hydraulic fracture-network parameters based on production simulation in shale gas reservoirs

摘要

This paper presents a dual-porosity composite model to represent the shale gas reservoir with a stimulated reservoir volume (SRV) and a dual porosity / dual permeability continuum model with consideration of Knudsen diffusion, surface diffusion , vi scous flow, adsorption and desorption to describe the special flow mechanisms of shale gas in matrix porosity .The SRV domain is regarded as an enhanced permeability zone. The stress sensitivity effect of natural fracture system is also incorporated in the mathematical model . Galerkin finite element has been used to approximate solution of seepage differential equations of natural fracture system and matrix system with only taking two-dimensional flow field into account. The finite element equation s for natural fracture system and matrix system based on triangular element were derived . The method for handl ing the boundary condition was given. Pressure equations of fracture and matrix systems were sovled sequentially to model shale-gas production performance. The impact of different values of SRV and fracture permeability and microscopic transport mechanisms on production were quantitatively analysed. The results indicate that the SRV and fracture permeability in stimulated area has the most significant impact on production. While adsorption and desorption , natural fracture permeability in unstimulated area, Knudsen diffusion, surface diffusion have less effect on cumulative gas production but with 36%, 24.5%, 15%, 8.3% cumulative production increase respectively for the reported simulation parameters and a 4.5% production loss for stress sensitivity effect of natural fracture .