Abstract
As hydraulic fracturing is a fluid-rock coupling process, the permeability of the hydraulic-stimulated fracture network in the initial stage has great effects on the propagation of the hydraulic fracture network in the following stages. In this work, the permeability of the hydraulic-stimulated fracture network in shale gas reservoirs is investigated by a newly-proposed model based on the displacement discontinuity method. The permeability of the fracture network relies heavily on fracture apertures, which can be calculated with high precision by the displacement discontinuity method. The hydraulic fracturing processes are simulated based on the natural fracture networks reconstructed from the shale samples in the Longmaxi formation of China. The flow fields are simulated and the permeability is calculated based on the fracture configurations and fracture apertures after hydraulic fracturing treatment. It is found that the anisotropy of the permeability is very strong, and the permeability curves have similar shapes. Therefore, a fitting equation of the permeability curve is given for convenient use in the future. The permeability curves under different fluid pressures and crustal stress directions are obtained. The results show that the permeability anisotropy is stronger when the fluid pressure is higher. Moreover, the permeability anisotropy reaches the minimum value when the maximum principle stress direction is perpendicular to the main natural fracture direction. The investigation on the permeability is useful for answering how the reservoirs are hydraulically stimulated and is useful for predicting the propagation behaviors of the hydraulic fracture network in shale gas reservoirs.
Highlights
The prediction of the propagation behaviors of the complex fracture network is an essential requirement for the hydraulic fracturing design of shale gas reservoirs
The permeability of the hydraulically‐stimulated fracture network in shale gas reservoirs is investigated by a numerical model based on the displacement discontinuity method
The permeability of the hydraulically-stimulated fracture network in shale gas hydraulic fracturing processes under different fluid net pressures and crustal stress conditions are reservoirs is investigated by a numerical model based on the displacement discontinuity method
Summary
The prediction of the propagation behaviors of the complex fracture network is an essential requirement for the hydraulic fracturing design of shale gas reservoirs. Many techniques have been used to investigate the propagation behaviors of the fracture network during fracturing treatment. Micro seismic events have been used to diagnose the location and the mechanism of the propagation of hydraulic fractures. The details of the fracture network cannot be measured completely by the observation methods. Aside from the observation methods, laboratory experiments have been implemented to investigate how hydraulic fractures propagate under different conditions [1,2,3]. It is difficult to observe the propagation of the complex fracture network and to know how laboratory experiments are related to reservoir scale [4]. Comparing with the observation methods and the laboratory experiments, numerical modelling is much more flexible
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