Predicting hydraulic fracture propagation based on maximum energy release rate theory with consideration of T-stress

Abstract

The interaction between hydraulic and natural fractures is a key factor in determining hydraulic fracture complexity. Based on the theory of linear elastic fracture mechanics and the fracture toughness discontinuity model, the maximum energy release rate (MERR) theory-based fracture propagation model with consideration of T-stress is discussed in this paper. A calculation model of fracture propagation orientation is established via the maximum circumferential stress criterion based on the influence of non-singular terms in the Williams expansion, and the influence of transverse stress (T stress) on the fracture propagation orientation is analyzed. Within considering the influence of the far-field stress, the limitation of the influence of the traditional MERR theory on the fracture propagation is modified, and a more reasonable criterion is established to reflect the influence of the stress difference on fracture propagation. In addition, the influences of the approaching angle, stress difference, net pressure, fracture tip plastic zone radius, and dip angle on fracture propagation is analyzed. Results show that when the T-stress is compressive stress or the T-stress is tensile stress and Bδ < 0.375, the propagation orientation remains 0° for pure Mode I fractures. As for mixed Mode I-II fractures, the deflection angle increases with an increase in T stress, and that the existence of negative T stress can restrain the fracture deflection. Under the conditions of low approaching angle, low horizontal stress difference, high net pressure, and high dip angle, hydraulic fractures are more prone to deflection along the weak plane. The modified theoretical model is verified by laboratory fracturing experiments. This study reveals the interaction between hydraulic fractures and weak planes, and can provide guidance for predicting complex fracture geometry in field constructions.