Shale gas is one of the fastest-growing natural gas resources in the United States, accounting for almost 80% of dry natural gas production, according to the U.S. Energy Information Administration. To produce shale gas, hydraulic fracturing of the reservoir is the preferred method of access. Pressurized fluids are injected to stimulate or fracture the shale and release natural gas. Technological advances, including various simulation methods, have aided increased shale gas production. However, fractures continue to be a problem. One solution, the discrete element method, shows promise for overcoming shortcomings in dealing with the fracture propagation between boreholes by using micromechanical analysis. DEM can easily simulate the hydraulic fracturing process, replicate laboratory results, and clearly display the microscopic changes in fracture.
Researchers employed two improvements on the algorithm of the traditional DEM pipe domain model. First, they calculated the volume of fracturing domain using the surrounding particles and the influence of domain volume on the pressure inside the domain, which allowed them to identify the relationship between aperture and normal stress. In their research, “Effects of In Situ Stress and Multiborehole Cluster on Hydraulic Fracturing of Shale Gas Reservoir from Multiscale Perspective,” authors Riu Sun and Jianguo Wang applied their algorithm to numerically study the effects of different in situ stresses and multiborehole clusters on the hydraulic fracturing of shale gas reservoir from a multiscale perspective. Read their full results to gain insight on fracture network development and best practices for applying hydraulic fracturing. The full paper is in the Journal of Energy Engineering at https://doi.org/10.1061/JLEED9.EYENG-5226. The abstract is below.
Abstract
Hydraulic fracturing through a multiborehole cluster is a crucial technology for the enhancement of shale gas reservoir production. However, the impact of borehole interference and in situ stress on hydraulic fracturing is still unclear. This study developed a multiscale hydraulic coupling model by improving the algorithm of the traditional pipe domain model within discrete element method and the initiation and propagation of hydraulic fractures under in situ stress and three multi-borehole clusters were numerically studied. Numerical results indicate that fracture development is initially governed by bedding planes, followed by the maximum principal stress. Tensile fractures account for over 80% of the observed fractures. As the lateral pressure coefficient decreases from 1, the proportion of tensile fractures decreases, while shear fractures become more prominent. The circumferential stress primarily influences fracture propagation, while radial stress plays a key role in governing fracture connectivity. During hydraulic fracturing of multiborehole clusters, the vicinity of the boreholes is prone to stability loss, and the stress shadow significantly affects the generation of fracture network. These results can deepen our understanding on the fracture network development and provide a guidance for the application of hydraulic fracturing technology.
Learn more in the ASCE Library: https://doi.org/10.1061/JLEED9.EYENG-5226.
