A semi-analytical pressure model of horizontal well with complex networks in heterogeneous reservoirs

Abstract

The tight reservoirs have been successfully developed by horizontal wells with massive hydraulic fractures. The inherent heterogeneity along the wellbore, complex fracture networks generated due to the pre-existing natural fracture and stress isotropy, the difference of reservoir properties between the stimulated reservoir volume (SRV) and the unstimulated region all bring huge challenges in predicting pressure and rate transient responses. Previous study always simplified the whole reservoir as homogeneous or radial composite region, and treated the complex networks as orthogonal fracture networks. In the light of this situation, by using the source function, boundary element method and composite reservoir model, a rigorous semi-analytical model for a horizontal well with complex fracture networks in heterogeneous reservoirs was presented in this paper. A previous semi-analytical model and numerical model established by commercial simulator were both used to verify the feasibility of the proposed model. The effects of critical parameters on the transient pressure behaviors are discussed. The results show that heterogeneity of the reservoir has a significant influence on pressure behavior. The sensitivity analysis of fracture number, fracture geometry, storage coefficient and inter-porosity factor of SRV, reservoir sizes and relative position between SRV and the outer boundaries are conducted to further understand the transient pressure behaviors of volume fractured horizontal well. In this paper, both the heterogeneity along the horizontal well in the SRV and the heterogeneity between the SRV and the unstimulated region is brought into consideration. In addition, the complex fracture geometry is also captured. Therefore, our model can be capable of studying the transient pressure behaviors of volume fractured horizontal wells in heterogeneous reservoir. The research results provided by this work have some significance for well test interpretation of tight reservoirs.