Study Of The Linear Elastic Fracture Mechanics In Hydraulic Fracturing For Unconventional Reservoirs

Hydraulic fracturing is one of the most effective stimulation methods to develop unconventional reservoirs.While the linear elastic fracture mechanics is considered as the key factor in hydraulic fracturing simulation,as it controls the process of fracture opening and propagation,and widely used in various models.To accurately predict the opening and propagation of hydraulic fracture using the linear elastic fracture mechanics based models,we combined the stress field analysis,calculation of fracture process zone and singularity dominated zone to investigate the applicability of the linear elastic fracture mechanics in hydraulic fracturing modelling.In the study,the fracture process zone and the singularity dominated zone are defined based on the calculations of the stress fields near the fracture tip and various failure criteria.The applicability of the linear elastic fracture mechanics is obtained according to the comparison of the fracture process zone and the singularity dominated zone.In order to give a general study,this study considers different faulting conditions and reservoir pressures to mimic the natural environments of different reservoirs.Based on the above calculations,sensitive analysis is conducted to investigate the influences of the principal stress,reservoir pressure,fracture length,tensile strength and shear strength on the precision of linear elastic fracture mechanics based models.It is observed that the principal stress and fracture pressure turn to be the most dominating factors and corresponding suggestions are given for the usage of the linear elastic fracture mechanics for hydraulic fracturing modelling.For the calculations of the full stress field around the fracture tip,Fourier series is used to represent the irregular overpressure distribution around the fracture length and the Gauss-Laguerre method is used to calculate the stress field numerically.The presented work can be used to study the damage mechanism around the fracture tip under similar condition for improved modelling of hydraulic fracturing.The conclusions add to our understanding of the LEFM and its proper application for unconventional reservoir stimulation.