Investigation of shale hydraulic fracturing propagation laws based on extended finite element analysis

Abstract:

Hydraulic fracturing is an effective technical method to exploit subsurface shale gas resources. To investigate the law of fracture propagation in shale hydraulic fracturing can provide proper guidance for high-efficient exploitation of shale gas. By using the extended finite element module of ABAQUS which is a large finite element software to investigate the influence of the position， azimuth and number of the initial fractures in homogeneous shale， and the structural direction， internal dip angle and lithology of the bedding shale on hydraulic fracture propagation at different ground stress deviations. The results show that for vertical hydraulic fractures， with the increase of the horizontal principal stress， the fracture is more difficult to propagate， the fracture propagation length decreases， and the initiation pressure increases. At the same injection volume， the length of hydraulic fractures formed by simultaneous initiation at both ends of the initial fracture is larger than that formed only on one side. When the initial fracture is located in the middle of shale with a direction of 45°， the fracture will deflect to the direction of the maximum horizontal principal stress， and the degree of deflection increases with the maximum horizontal principal stress. In the process of time-sharing multi-cluster fracturing， the propagation of fractures will interfere with each other， and it will greatly affect the attitude of fracture propagation and initiation pressure， but it has little influence on the fracture width at the injection point. For shale with horizontal and vertical bedding structures， hydraulic fracture deflection will be deflected to different degrees when the internal dip angle of bedding is changed， and the deflection degree of hydraulic fractures decreases with the increase of the internal dip angle of bedding. For shale with structural bedding in the direction of 45°， the deflection degree of hydraulic fractures increases successively in sandstone， coal rock and mudstone， and the fracture migration ratio increases with the maximum horizontal principal stress.

Key words:shale gas;hydraulic fracturing;XFEM;ground stress deviation;bedding;laws of fracture propagation