Abstract
This paper investigates a hydraulic fracture development and its potential impact in terms of elastic stress perturbations and fracture triggering. The hydraulic fracture is simulated during fluid injection with a fully coupled hydromechanical 3D discrete-element method in a homogeneous granite without (i.e. intact rock) and with pre-existing fractures. The results of the models show how pre-existing fractures affect the growth rate, the accumulation of the displacement and interaction between hydraulic and mechanically-induced fractures. In the intact rock model, a circular hydraulic fracture grows normal to the minimum principal stress due to successive tensile failures. The measured length of the hydraulic fracture increases as a fractional power of time for a constant injection rate and the maximum aperture is positively correlated to the length. Stress perturbations observed in the model promote tensile and shear failure at the hydraulic fracture tips, but inhibit failure near the fracture walls. We expect microseismicity to be concentrated near the fracture tip, with a more linear shape, assuming negligible pore pressure diffusion. Similar hydraulic fracture behavior is observed in a model with preexisting fractures disconnected to the fluid injection. Conversely, fluid leakage occurs in a model with connected natural fractures. This strongly impacts the growth of the hydraulic fracture, with a fracture length increasing linearly with time, and a very limited fracture aperture that is essentially constant over time. In this case we describe a significant reduction of the elastic stress perturbation and a more elliptically microseismic cloud is expected to grow away from injection point. Such typical signatures can be used for interpretation of ongoing rock deformation in natural hydraulic fracture treatments. These results confirm analytic expectations and give insights into rock deformation occurring in natural hydraulic fracturing.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call