History-matching shale reservoir production with a multi-scale, non-uniform fracture network

Numerical simulations of oil/gas production from shale reservoirs often suffer from uncertainties in the description of the fracture system. An integrated stimulation-production framework (referred as the GEOS-TOUGH simulation framework) was developed to enable the use of realistic, non-uniform hydraulic fractures in multi-phase flow simulation. In this work, the GEOS-TOUGH model is further improved by designing a non-uniform secondary fracture model. In this model, the secondary fractures are densely placed parallel to the main hydraulic fracture. The aperture of the secondary fractures is decreasing as the distance from the well increases. The characteristics of the secondary fractures are quantified using four parameters, which are tuned to match the production history at two wells of the Hydraulic Fracturing Test Site (HFTS) in Texas, USA. The simulation results show that the secondary fractures are crucial for reservoir production as more than 60% of the hydrocarbons are produced via the secondary fractures. The non-uniform aperture of the secondary fractures have strong influence on oil/gas production because it leads to rapid depressurization and the associated gas exsolution near the horizontal well. With the inclusion of non-uniform secondary fractures and the fracture closure process, the cumulative production of oil and gas can be qualitatively matched with a forward model alone by manual calibration. This study advances knowledge in multiphase production processes and emphasizes the important role of the multiscale fracture network (interconnected non-uniform hydraulic fractures and secondary fractures) in multiphase production. The findings of this study can be used to improve the physical description of the fracture system in reservoir models, which could enhance the applicability and predictability of history matching.