It is critical to smoothly and efficiently couple fracture complexities from fracture model with reservoir model in shale reservoirs with complex natural fractures. In this study, an efficient EDFM (embedded discrete fracture model) method was applied and tested. First, the fracture complexities were simulated using a complex fracture propagation model with the effect of natural fractures. Two scenarios with low and high horizontal stress difference were simulated and investigated. After that, the complex non-planar and planar hydraulic fractures, activated and non-activated natural fractures were directly transferred to a shale-gas reservoir model with simple structured grids using the EDFM method, which does not need unstructured grids and local grid refinement. The impacts of different fracture complexities between two scenarios on 10-year shale gas recovery were simulated and compared. The simulation results show that the scenario with low horizontal stress difference is easier to generate complex non-planar hydraulic fractures and produce higher well productivity than the scenario with high horizontal stress difference. The relative difference of 10-year cumulative gas production is about 24% in this case study. In addition, the effects of fracture complexities on drainage area, drainage volume, and drainage efficiency at different production times can be clearly visualized and compared.

1. Introduction

In shale oil and gas reservoirs with low permeability and porosity, the horizontal drilling with multi-stage hydraulic fracturing remains the most widely used technology to make well production economical. As the dominant and high permeable pathways for fluids flow from the shale matrix to the horizontal wellbore, different configurations of complex hydraulic and natural fractures can significantly impact the well productivity. Many advanced hydraulic fracture diagnostic techniques such as microseismic, DTS (distributed temperature sensing), and DAS (distributed acoustic sensing) indicate that the real fracture geometries along the horizontal wellbore are created in a more complex way rather than a simple way (Raterman et al., 2017; Gale et al., 2018; Stegent and Candler, 2018). Meanwhile, the activation of pre-existed natural fractures in shale reservoirs makes it more complicated to accurately capture the actual fracture geometry.

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