Abstract
Numerical simulation is very useful for understanding the hydraulic fracturing mechanism. In this paper, we simulate the hydraulic fracturing using the distinct element approach, to investigate the effect of some critical parameters on hydraulic fracturing characteristics. The breakdown pressure obtained by the distinct element approach is consistent with the analytical solution. This indicates that the distinct element approach is feasible on modeling the hydraulic fracturing. We independently examine the influence of in-situ stress ratio, injection rate and fluid viscosity on hydraulic fracturing. We further emphasize the relationship between these three factors and their contributions to the hydraulic fracturing. With the increase of stress ratio, the fracture aperture increases almost linearly; with the increase of injection rate and fluid viscosity, the fracture aperture and breakdown pressure increase obviously. A low value of product of injection rate and fluid viscosity (i.e., Qμ) will lead to narrow fracture aperture, low breakdown pressure, and complex or dispersional hydraulic fractures. A high value of Qμ would lead wide fracture aperture, high breakdown pressure, and simple hydraulic fractures (e.g., straight or wing shape). With low viscosity fluid, the hydraulic fracture geometry is not sensitive to stress ratio, and thus becomes a complex fracture network.
Highlights
Hydraulic fracturing technology is widely used in the unconventional energy field [1,2,3]
The in-situ stress ratio, injection rate, and fluid viscosity all have a crucial effect on the hydraulic fracturing results
Some researchers [7,8,9] have investigated the influence of injection rate on hydraulic fractures through laboratory experiments, which indicated that under the same experimental conditions, with the increase of injection rate, the branches of the hydraulic fracture would decrease, and the complex fracture network turns into a single straight fracture
Summary
Hydraulic fracturing technology is widely used in the unconventional energy field [1,2,3]. The in-situ stress ratio, injection rate, and fluid viscosity all have a crucial effect on the hydraulic fracturing results. Wangen [29] established a two-dimensional numerical model based on the finite element method and further analyzed the bottom-hole pressure and the number of failed elements under different permeability conditions. Using the finite difference software Flac3D , Zhou and Hou [32] established a model in which the leak-off could be simulated in both rock matrix and fractures They verify the modeling approach by comparing the borehole pressure between numerical and laboratory results. Based on our numerical model, the influence of stress ratio, injection rate, and fluid viscosity on hydraulic fracturing are independently investgated by tuning one while retaining the other parameters.
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