Study On Fracture Propagation Based On Maximum Energy Release Rate Theory

Hydraulic fracturing is the most common and effective reservoir stimulation technology in oil and gas development.Hydraulic fracturing usually leads to complex fracture geometry morphology.The interaction between hydraulic fractures and natural fractures is the key factor determining the complexity of the fracture.At present,it is generally considered that natural fractures are interfaces with a certain friction coefficient,however,natural fractures in real reservoir are weak planes with a certain cement strength.Therefore,it is more accurate and appropriate to study the interactions between hydraulic fractures and structural weak planes by energy release rate theory.Firstly,the energy release rate of branch fractures is calculated via continuity hypothesis based on the linear elastic fracture mechanics,and the fracture propagation model based on the maximum energy release rate theory is established combined with the discontinuous fracture toughness model.Considering the influence of non-singular terms in Williams expansion,the calculation model of fracture propagation path is established by maximum tensile stress criterion,and analyzed the influence of T stress on pure mode I and compound mode I-II fracture propagation.Then,considering the influence of the far-field stress on the fracture stress field,the limitation of the influence of the stress difference on the fracture propagation is corrected,and a more accurate and reasonable fracture propagation criterion is established.Analyzed the influence of approximation angle,far-field stress difference,net pressure,plastic zone radius at fracture tip and inclination angle on fracture propagation path.Finally,true triaxial fracturing simulation experiment was carried out,and analyzed the effect of different stress conditions and approximation angles on the hydraulic fracture propagation law and the fracture morphology.The accuracy of the theoretical model is verified by comparing the experimental simulation results with the complex fracture morphology obtained by the theoretical model.This paper begins with the fracture stress field,analyzed the mechanisms of fracture propagation under far-field stress and revealed the law of interaction between the hydraulic fractures and the weak planes,which is of great guiding significance for predicting complex fracture morphology and evaluating fracturing effects in construction field.