Natural hydraulic fractures develop in rock formations due to fluid pressure and expand when surrounding rock cannot resist the growing pressure. These tensile cracks affect igneous dike formations as well as geothermal systems and oil and gas reservoirs. In some cases, this improves the rock permeability; in others, it hampers fluid flow. In the worst-case scenario, overpressure can result in formations exploding. Researchers Cexuan Liu and Fengshou Zhang wanted to better understand the predicted growth of a natural hydraulic fracture. They introduce a detailed model for an NHF in overpressurized porous rock, offering valuable insights into fracture propagation and fluid flow behavior in their paper “Growth Rate of Natural Hydraulic Fracture” for the Journal of Engineering Mechanics.
The authors took two approaches to address more complex fluid diffusion patterns. Their analysis indicates that one-dimensional diffusion also works for long-term NHF propagation; revealing a transition from two-dimensional back to 1D. Learn more about pore pressure–driven fracture behaviors in geological media and how they could help develop enhanced modeling techniques at https://ascelibrary.org/doi/10.1061/JENMDT.EMENG-8483. The abstract is below.
Abstract
Natural hydraulic fractures (NHFs) are tensile fractures that form in fluid-saturated rocks when in-situ pore pressure exceeds the minimum compressive stress. Their propagation is controlled by the inflow of pore fluid, which depends on both pore pressure diffusion in the surrounding rock and the evolving fracture size. However, the long-term growth behavior of NHFs remains an open question. This study demonstrates that, after an initial transient phase triggered by a perturbation that caused the fracture to grow, an NHF attains a steady-state propagation rate. An explicit expression for this rate is derived, linking it to the rock poromechanical properties and to the difference between in-situ pore pressure and minimum compressive stress. This result is achieved by recognizing that over time, fracture growth outpaces diffusion, effectively confining pore pressure evolution to a one-dimensional diffusion process within thin layers adjacent to the fracture plane.
Learn how you can leverage the researchers’ findings into rock fracturing in the ASCE Library: https://ascelibrary.org/doi/10.1061/JENMDT.EMENG-8483.
