Abstract
Structural planes (such as joints, natural fractures, and faults) that are extensively developed in unconventional reservoirs significantly control the propagation morphology of hydraulic fractures. To fully stimulate the reservoir and enhance ultimate recovery, it is necessary to accurately predict the morphology of the hydraulic fracture network and clarify the mechanical response characteristics of structural planes when hydraulic fractures intersect with them. Based on the theory of linear elastic fracture mechanics, this paper proposes a new criterion for predicting the intersection behavior between hydraulic fractures and structural planes under non-orthogonal conditions. This criterion comprehensively considers the coupling effects of fluid flow, stress shadow, poroelastic response, and the influence of plastic yielding at the fracture tip. Through comparative verification with published theories, laboratory experiments, and numerical simulation results, the findings demonstrate that the new criterion exhibits good reliability under both toughness-dominated and viscosity-dominated fracture propagation modes. Sensitivity analyses were conducted on key parameters in rock mechanics and fracturing operations under different dominant modes. The results indicate that structural plane parameters are the primary controlling factors governing intersection behavior in both dominant modes. In the toughness-dominated mode, short propagation fracture length, high friction coefficient, and high cohesion are conducive to hydraulic fractures crossing structural planes; in the viscosity-dominated mode, high injection rate, low-viscosity fracturing fluid, short propagation fracture length, high friction coefficient, high cohesion, and high fracture toughness are conducive to hydraulic fractures crossing structural planes. Furthermore, the study reveals the significant influence of intersection angle on intersection behavior: when the intersection angle exceeds the critical transition angle, high stress difference promotes hydraulic fractures crossing structural planes; conversely, high stress difference inhibits intersection behavior, and hydraulic fractures are blocked by structural planes or propagate along them. The research findings provide important theoretical basis for the optimization design of hydraulic fracturing in unconventional reservoirs and facilitate rapid characterization of propagation features in complex hydraulic fracture networks.
Full Text
Criterion for Hydraulic Fracture-Discontinuity Intersection Behavior in Toughness- and Viscosity-Dominated Regimes
Liu Tong¹, Wei Xiaochen¹, Liu Xiangjun¹
(1. School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500)
Abstract
Structural discontinuities (such as joints, natural fractures, and faults) that are widely developed in unconventional reservoirs significantly control hydraulic fracture propagation patterns. To fully stimulate reservoirs and enhance ultimate recovery, it is necessary to accurately predict hydraulic fracture network patterns and clarify the mechanical response characteristics of discontinuities when hydraulic fractures intersect them. This paper proposes a new criterion for predicting hydraulic fracture-discontinuity intersection behavior under non-orthogonal conditions based on linear elastic fracture mechanics theory. The criterion comprehensively considers the coupling effects of fluid flow, stress shadow, poroelastic response, and the influence of plastic yielding at the fracture tip.
Through comparative validation with published theories, laboratory experiments, and numerical simulation results, the findings demonstrate that the new criterion exhibits good reliability under both toughness-dominated and viscosity-dominated fracture propagation regimes. Sensitivity analyses were conducted for key parameters in rock mechanics and fracturing operations under different dominant regimes. The results indicate that discontinuity parameters are the primary controlling factors governing intersection behavior in both regimes. In the toughness-dominated regime, short propagation fracture length, high friction coefficient, and high cohesion favor hydraulic fracture crossing through discontinuities; in the viscosity-dominated regime, high injection rate, low-viscosity fracturing fluid, short propagation fracture length, high friction coefficient, high cohesion, and high fracture toughness favor hydraulic fracture crossing through discontinuities. Furthermore, the study reveals the significant influence of intersection angle on intersection behavior: when the intersection angle exceeds the critical transition angle, high stress difference promotes hydraulic fracture crossing through discontinuities; conversely, high stress difference inhibits intersection behavior, causing the hydraulic fracture to be arrested by or propagate along the discontinuity.
The research findings provide important theoretical foundations for optimizing hydraulic fracturing design in unconventional reservoirs and facilitate rapid characterization of complex hydraulic fracture network propagation features.
Keywords: Hydraulic fracturing; Fracture mechanics; Intersection criterion; Toughness-dominated regime; Viscosity-dominated regime