Effect of Natural Fractures on Hydraulic Fracture Initiation in Cased Perforated Boreholes

Hydraulic fracturing is a significant stimulation technology and method to enhance hydrocarbon recovery from low-permeability reservoirs. Accurate prediction of initiation pressure is a crucial step to make sure the success of hydraulic fracturing. Currently, predictive calculation of initiation pressure is for homogeneous formations; however, in fractured formations that has been a very complex issue all along. This paper assumes that natural fractures intersect with perforations, the tensile failure criteria is adopted and the calculation model of initiation pressure is presented for perforated wells of fractured formations considering that hydraulic fracture initiates from rock body of perforations surface or along natural fractures. The calculation results show that many factors have significant influence on the initiation pressure: the strike and dip of natural fractures, the intersecting position of natural fractures and perforations, the perforation orientation around borehole and the geostress orientation. The research results also suggest that not only the initiation pressure may sharply fall but also the initiation pressure difference for different orientation perforations may significantly become smaller due to the effect of natural fractures which will lead to hydraulic fractures’ simultaneous initiation and propagation from different orientation perforations, so that complex near-wellbore multiple fractures develop. The comparative analysis of the actual and the calculation initiation pressure proves the accuracy and reliability of the calculation model. The established calculation model in this paper achieves the quantitative calculation of initiation pressure and simultaneously provides the theoretical basis to explain the physical phenomena of near-wellbore multiple fractures propagation for perforated wells of fractured formations.

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Metoda frakcjonowania hydraulicznego jest stosowana do odzyskiwania związków węglowodorowych a więc na przykład w technologii odzyskiwania gazu łupkowego. W artykule zaprezentowano model matematyczny tej technologii.