KEY MECHANICAL PROBLEMS OF WELL DRILLING AND COMPLETION AND HYDRAULIC FRACTURE IN HIGHLY EFFICIENT EXTRACTION OF SHALE GAS

The key mechanical problems of well drilling and completion, and hydraulic fracture network reformation are studied in the highly efficient extraction of shale gas. The anisotropic constitution, strength and fracture toughness of poroelastic medium in shale are demonstrated. The micro-homogenous and micro-isotropic assumptions are discussed, and the material constants measurement of the transversely isotropic poroelastic rock is analyzed. The fracture propagation in the weak plane model with the maximum energy release rate criterion is discussed. The time-related shear failure models of borehole wall stability in the poroelastic medium are discussed during well drilling and completion. Eight failure modes of the well drilling problem are discussed, and the allowable borehole pressures are given with explicit expressions. The technologies of hydraulic fracture network reformation for horizontal wells are shown, including the experimental method of hydraulic fracture in a large physical model, the numerical simulation based on the extended finite element method and finite volume method for fluid/solid/fracture coupling during fracking process, and a field application of hydraulic fracturing on site in Sichuan-Chongqing region. Based on the data-driving method, a prediction model of shale gas recovery ratio is developed, and the effectiveness of the extreme gradient boosting method for the small dataset is discussed,.