Investigation on the effect of pore pressure gradient on fracture propagation in rock materials

Abstract

When rock is subjected to internal hydraulic pressure and external mechanical loading, the fluid flow properties will be altered by newly induced fractures. In turn, the fluid flow driven by pore pressure gradient can influence the fracturing behaviour. To better capture the complex hydraulic fractures in rock materials, a ‘pinch-off’ breaking test is numerically conducted to illustrate the tensile failure of a rock specimen within a uniform pore pressure field. A double-notched specimen, with water pressure in one notch while keeping another one open to the atmosphere, is numerically extended to investigate how the water flow direction or the pore pressure gradient will influence the fracturing behaviour. The simulation results indicate that both pore pressure magnitude and the orientation and distribution of pore pressure gradient surrounding the fracture tip can affect fracturing process and macroscopic strength behaviour of rock materials.

Keywords:

• Tensile fracture
• Numerical simulation
• Pore pressure gradient
• Rock
• Damage evolution

Acknowledgements

The work shown in this paper was supported by grants from National Natural Science Foundation of China (grant no. 51479024) and the National Basic Research Programme of China (grant nos. 2011CB013503 and 2014CB047103). The authors are grateful for these supports.