Research And Application Of Horizontal Well Segmental Fracturing Induced Stress Field

Nowadays unconventional oil and gas resources including tight oil, tight gas and shale gas become increasingly important, horizontal well staged fracturing technology is the key to the effective development of unconventional reservoirs technology. In order to accurately understand the change of stress field around the wellbore in the process of staged fracturing in horizontal wells, and guide the research of the fracture initiation and extension mechanism. An artificial fractures stress interference model has been established based on homogeneous and isotropic two-dimensional artificial fracture model. In use of displacement discontinuity method, this model considers unequal crack half-length, unequal crack spacing and arbitrary inclination between cracks and horizontal wellbore, with considering the influence of the wellbore pressure, in-situ stress, fracturing fluid seepage effect, thermal stress and perforation, a calculation model of stress field for horizontal well staged fracturing was established. On the basis of the model, from the perspective of reducing the fracture pressure, a preferred method of breaking point was established by analyzing fracture pressure variation under multiple fractures induced stress field combined with the rock fracture criterion, and by analyzing the stress field variation around the wellbore under the crack interference, feasibility of complex fractures for fi-actured reseroir was studied combined with conditions of complex cracks. There are some of the major results through the research:(1) A crack induced stress field model was established by the use of displacement discontinuity theory, it is able to solve the problems of induced stress field around the horizontal wellbore, which cannot be resolved by the conventional analytical method, at the same time it is able to analyze induced stress caused by irregular cracks.(2) For horizontal well staged fracturing, the crack-induced stress field makes the horizontal wellbore stress field more complex, the facture initiation and morphology under those stress fields is more complex, so fracturing optimization design must take into account this factor.(3) The induced stress caused by open cracks in certain crack spacing will lead to an increase of the fracture pressure of subsequent cracks, which increases the difficulty of fracturing operations, and induced stress may reduce fracture pressure when crack spacing exceeds a certain distance, which is instructive in preferring the breaking point and thus optimizes the perforation position from the perspective of reducing the fracture pressure.(4) Cracks induced stress field will affect principal stress difference around the wellbore, thereby affecting subsequent crack extension process. The degree of interference between the cracks can increase by optimizing perforation, fracture parameters and other factors, increasing the feasibility of complex cracks.The study has a certain significance for clear understanding of multiple fractures stress interference theory and the change of stress field around the wellbore in the process of staged fracturing in horizontal wells under crack stress interference, while providing guidance to fracturing design.