Abstract
Unconventional oil and gas are important resources of future energy supply, and shale gas is the focus of the development of unconventional resources. Shale is a special kind rock of porous medium, and an orderly structure of beddings aligned in the horizontal direction where causing the strong elastic anisotropy of shale is easy. A new model has been established to calculate the fracture initiation pressure with the consideration of mechanical characteristics of shale and the anisotropic tensile strength when judging rock failure. The fracture initiation model established in this paper accurately reflects the stress anisotropy and matches well with the actual situation in porous media. Through the sensitivity analysis, the results show that σv/σH, Ev/EH, υv/υH, m/s, and A/B have a certain impact on the tangential stress when the circumferential angle changes, and there is a positive relationship between the initiation pressure and the above sensitive factors except for A/B. The results can provide a valuable and effective guidance for the prediction of fracture initiation pressure and fracture propagation mechanism under special stratum conditions of shale.
Highlights
Unconventional oil and gas are important resources of future energy supply
Shale gas can only be profitable by hydraulic fracturing of horizontal wells with the current volume fracturing techniques
Fracture initiation of horizontal well hydraulic fracturing is a technical difficulty related to fracturing technology
Summary
Unconventional oil and gas are important resources of future energy supply. And shale gas is the focus of the development of unconventional resources. Based on the hydroshearing concept, they established generic models to estimate the location of the shearing onset, the required injection pressure, and the overall shearing growth direction during enhanced geothermal system hydraulic stimulation They adopt the Coulomb failure criterion to define the shear strength of a single rock joint but neglected the cohesion of fracture. Considering the elastic mechanics anisotropy difference of shale, the sensitivity analysis of perforation parameters on the fracture initiation pressure and location of the horizontal well was proposed With both the numerical simulations and experiments, Huang et al [25] discussed the initiation mechanisms of natural fractures during hydraulic fracturing. The influence of the anisotropy should be considered when calculating the effective stress distribution around the borehole and confirming the tensile strength of the rock
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