Impact of cross-flow on well production in shale reservoir considering vertical variation of reservoir and fracture properties: Model and field application

Abstract

Shale is a highly vertical heterogeneous formation due to the complex sedimentary environment. Unfortunately, available models to predict the well production rely on the over-simplified assumption that ignores the effect of vertical heterogeneity and cross-flow on well production. This work aims to propose a simple-yet-rigorous oil flow model considering the vertical heterogeneity in shale formation. The stimulated reservoir volume (SRV) near well is characterized by a Vertical Heterogeneous Cross-flow Model (VHCM). The drainage volume is divided into several layers, and the diffusivity equation of each segment is derived separately. Thus, three dimensions of flow are considered simultaneously. The VHCM is analytically solved in Laplace domain and inversed to real domain numerically. Then the proposed model is verified against the fine-grid numerical results. Based on the VHCM, the flow characteristics in shale formation considering the effects of vertical heterogeneity and cross-flow are systemically investigated. The result shows that the adoption of a vertical homogeneous model will lead to the overestimation of reservoir properties and using the Vertical Heterogeneous No-cross-flow Model (VHNM) will lead to the underestimation of reservoir properties in shale formation. In addition, thin interbedded structures and stratified sandstone in shale are beneficial for well production. Compared with the traditional vertical homogeneous model, the VHCM captures the variation of reservoir and fracture properties in shale reservoirs, and the results better match the field data.