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Hydraulic fractures and natural fractures constitute the gas flow channels of fractured horizontal wells in shale gas reservoirs. Their shape and structural characteristics determine the production of horizontal wells and reservoir pressure propagation. To study the influence of hydraulic fractures and natural fractures on reservoir production performance at different degrees of complexity, a method was proposed to construct and simulate hydraulic fractures and natural fractures with complex shapes based on an embedded discrete fracture model, and the finite volume method was used to solve the model. On this basis, the effects of hydraulic fracture complexity and natural fracture connectivity on the production performance of fractured horizontal wells are analyzed. The results show that when the natural fracture orientation is perpendicular to the pressure wave propagation direction, the natural fracture will form a local shielding effect on the pressure propagation. Better natural fracture connectivity leads to better seepage capacity of the complex fracture network. Under the same conditions, hydraulic fracture complexity is more controllable than natural fracture connectivity, and the contribution of hydraulic fracture complexity to horizontal well production is underestimated. Increasing the complexity of hydraulic fracture is the key to improve the effect of hydraulic fracturing. Combining ant body technology and microseismic monitoring data, the method proposed in this paper is applied in the Longmaxi shale formation to obtain the history matching with the gas well production data and predict the estimated ultimate recovery.

Unmodified original shale gas reservoirs have been demonstrated to have extremely low permeability, and the long horizontal drilling and hydraulic fracturing techniques are widely used to obtain economic gas production. However, these techniques can result in a nonlinear flow of fluids during transport through the multi-scale pore system and the complex fracture network around the horizontal well, as well as a two-phase gas-water flow during shale production. To solve these issues, in this paper, first, the complex fracture network around the horizontal well is characterized using the discrete main hydraulic fractures combined with composite regions with different properties. Then, the dual porosity media and discrete-fracture model are implemented to describe the nonlinear flow behavior in the multi-scale pore system, and a wellbore pressure drop model is established to characterize the transient two-phase gas–liquid flow in the different sections of the fractured horizontal well. Finally, the coupled reservoir wellbore flow model is fully implicitly solved using the control volume finite element method and unstructured tetrahedral grids. The results of the simulation model of a multi-stage fractured horizontal well in the shale of the Longmaxi Formation will help field engineers deeply understand gas and water production performance and the dynamics of wellbore and reservoir pressure, as well as optimize development schemes.

The production performances of a well with a shale gas reservoir displaying a complex fracture network are simulated. In particular, a micro-seismic cloud diagram is used to describe the fracture network, and accordingly, a production model is introduced based on a multi-scale flow mechanism. A finite volume method is then exploited for the integration of the model equations. The effects of apparent permeability, conductivity, Langmuir volume, and bottom hole pressure on gas well production are studied accordingly. The simulation results show that ignoring the micro-scale flow mechanism of the shale gas leads to underestimating the well gas production. It is shown that after ten years of production, the cumulative gas production difference between the two scenarios with and without considering the micro-scale flow mechanisms is 19.5%. The greater the fracture conductivity, the higher the initial gas production of the gas well and the cumulative gas production. The larger the Langmuir volume, the higher the gas production rate and the cumulative gas production. With the reduction of the bottom hole pressure, the cumulative gas production increases, but the growth rate gradually decreases.

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