| Hydraulic fracturing stimulation of natural fractured reservoir shows that the fracture propagation is very complicated due to the effects of geological structure. Accurately predicting and calculating the initiation pressure is a crucial step to make sure the success of hydraulic fracturing design. Currently, predictive calculation of initiation pressure is for sandstone homogeneous formations; however, that for fractured reservoir which has rich natural fractures and perforations has been lacked all the time. This article based on the rock mechanics, elastic mechanics and space analyze geometry considering the hydraulic fracture may initiate along rock body and along natural fracture, this paper deeply analyzed and discussed the initiation pressure calculation model and vary law of horizontal perforated well for fractured reservoir, mainly including:(1) Considering the perforation hole as a small borehole well and connecting to the horizontal well, this paper analyzes the horizontal wellbore stress distribution, establishes the mathematical model for horizontal well perforation stress distribution, and calculates principle stress distribution of horizontal well perforation.(2) Based on rock mechanics and space analytic geometry coordinate transformation principle, this paper analyzes the position relationship between natural fracture surface and perforation surface stress field based on the elastic mechanics and space coordinate transform theory. Then, three different initiation pressure computing model were established, such as along the rock body initiation pressure and along the natural fracture initiation pressure.(3) Based on the initiation pressure calculation model and method, this paper analyzes the influence of perforation angle, wellbore azimuth, natural fracture mechanics characteristics and natural fracture strike and dip angle etc factors on the initiation pressure of initiating along rock body and along the nature fractures. |
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