Investigating the interaction of hydraulic fracture with pre-existing joints based on lattice spring modeling

Pre-existing joints have a significant influence on the geometry of the fracture network induced by hydraulic fracturing. Understanding the interaction between hydraulic fractures (HF) and pre-existing joints is of great importance to optimize the design of hydraulic fracturing operations in many applications. A three-dimensional hydro-mechanical coupled lattice-spring code was employed to investigate the interaction mechanisms under different pre-existing fracture shear strength (cohesion and friction angle), in-situ stress, angle of approach, and varying treatment parameters (fluid viscosity and injection rate). Simulation results indicate that hydraulic fractures tend to cross pre-existing joints for high magnitudes of assumed of fracture cohesion, friction angle, stress difference, approach angle, fluid viscosity, and injection rate. Three basic model hydraulic fracture-joint relationships were noted which were termed zero-joint crossing, 1-joint crossing and 2-joint crossing. For varied assumed shear strength, in-situ stress, approach angle and treatment parameters, the contribution of tensile-failure in intact rock and shear-failure on pre-existing joints tends to be enhanced or reduced, which controls the dominant observed interaction behavior (slip or crossing) as well as the variation in the resulting stimulated reservoir area.