Discrete fracture networks modeling of shale gas production and revisit rate transient analysis in heterogeneous fractured reservoirs

Horizontal wells with multiple hydraulic fractures are necessary stimulation technique for economically developing tight and shale gas reservoirs. In such reservoirs, the conventional well-test techniques are not suitable because of ultralow formation permeability. Rate transient analysis (RTA) is the widely used tool for analyzing these reservoirs for the purpose of reserves estimation, hydraulic fracture stimulation optimization, and development planning. However, the conventional rate transient analysis is based on the models that were derived from idealistic assumptions for homogenous reservoirs. In this article, we first review the industry's common practice for rate transient analysis and discuss why the idealized conceptual model may not be adequate for analyzing production data from shale gas reservoirs. Then, a unified shale gas reservoir model based on Discrete Fracture Networks (DFN) is presented to investigate how each mechanism influences shale gas production and the corresponding rate transient behavior. It is found that shale gas production and rate transient behavior are significantly impacted by reservoir heterogeneity, fracture networks, non-Darcy flow, gas adsorption and completion efficiency. Short early-time linear flow with long transitional flow period is an indication of either existence of abundant complex fracture networks or heterogeneous completion with unevenly distributed hydraulic fractures. Consider the nature of non-unique results of RTA, information from other independent sources is required to achieve a consistent and holistic interpretation.