The developed analytical model for fracture initiation pressure estimation is described. The model is based on solving the problems of stress tensor transformation, estimation of stress distributions around the boreholes, direction cosines estimation, transforming stress tensor between cylindrical and Cartesian coordinate systems. In the work, the stress state of natural fractures only intersecting the well trajectory is calculated. As criteria for crack initiation, the shear fracture criterion and the tensile fracture criterion are used. The calculation results showed that when the well pressure changes, the stress state at the point of intersection of the fracture and the well changes, including the fracture initiation criterion. A study was made to estimate the influence of the following factors on the magnitude of the fracture initiation pressure: the orientation of the wellbore relative to the main stresses and fracture geometry. Combinations of fracture initiation parameters are determined. The developed technique allows to determine the bottomhole pressure boundaries to prevent fracture initiation near the wellbore. The technique allows to determine the necessary pressure during the drilling or wellkilling operations. On the other hand, it is possible to estimate the bottomhole pressure at which natural fractures will be initiated to assess the risks of hydraulic fracturing, as well as to prevent early water breakthroughs from water-injection wells. Further steps to improve the technique include a more detailed sensitivity analysis of the developed analytical model, estimation of the fracture initiation pressure located at a small distance from the well (without well and fracture intersection), estimation of the fracture initiation pressure in the case of perforation, verification of the results in the field using hydrodynamic tests, as well as geophysical studies.
References
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