| dc.description.abstract | In unconventional shale formations where the horizontal bedding planes and laminations prevalently exist, the height propagation of a vertical hydraulic fracture is not only affected by the conventional factors such as the treating pressure, in-situ stress, fracture toughness, Young’s modulus, Poisson ratio, fracturing fluid density and viscosity, but can also be strongly affected by the horizontal bedding interfaces. Quantifying the hydraulic fracture propagation path and fracture geometries becomes much challenging with the existence of close-spacing bedding interfaces in the laminated formations.
In this work, a comprehensive and non-intrusive hydraulic fracture height growth model is developed considering the combined effect of the formation rock properties and the horizontal weak interfaces. The impact of the rock properties on the fracture height containment is computed by the theory of the linear elastic fracture mechanics, where an equilibrium height status is obtained simultaneously at both upper and lower fracture tips. Meanwhile, the shear slippage of the weak bedding layers is modeled by an efficient 2D higher order displacement discontinuity method based on the joint element (JE-HDDM), and the effectiveness on the hydraulic fracture height is quantified by correcting the stress intensity factors at the hydraulic fracture tips.
Numerical studies based on the Permian Basin Wolfcamp formation using our model demonstrates that the shear slippage of the beddings can significantly slow down the hydraulic fracture height growth and that the shear fracture toughness of the bedding layers and the spacing between the laminations have considerable impact on the effectiveness of the shear slippage on the fracture height growth.
The non-intrusive hydraulic fracture height model is incorporated into an in-house cell based P3D hydraulic fracture simulator, which uses plane strain deformation in each vertical cross-section coupled with a 2D fluid flow. The numerical results show that the weak interfaces have considerable impact on the fracture height, lateral length, and width distribution. With the existence of the weak interfaces, the hydraulic fracture height is reduced, which results in a longer fracture lateral length, together with a reduction of the overall width values. Sensitivity analysis shows that the spacing between the weak interfaces and interfacial shear toughness have significant impact on the fracture geometry and width values. In multi-fracture propagation case, the impact of the weak interfaces on the outer fractures results in a reduction in average height and overall width distribution and an increase of the lateral length. For inner fractures, the impact of weak interfaces varies by the cluster spacing.
The proposed workflow effectively captures the mechanism of the horizontal weak interfaces on the hydraulic fracture height growth and the lateral propagation. The numerical studies provide more understanding on the fracture propagation in the laminated shale reservoirs. The new P3D hydraulic fracture simulator can be used as an effective tool for fracturing job design in shale formations. | |
