Fluid-Driven Fracturing of Rock Mass: A Review: Fid-Bau Portal

Fluid-Driven Fracturing of Rock Mass: A Review

Sircar, Subhadeep / Maji, V. B.

The fluid-driven fracturing of the rock mass is a complex process. It has many applications, from Hydraulic Fracturing in the oil and natural gas industry to Hydro-Geology and Dam failure analysis. The deformation of saturated rock mass is a hydromechanically coupled process involving the measurement of pore fluid pressure and the deformation of the rock skeleton. The pore fluid pressure and the deformation of the rock skeleton are coupled, and they relate to each other through the governing differential equations. Fracture behavior in such coupled medium with fluid pressure needs special attention to the fluid surface load and the traction separation laws. This article reviews the existing work on fluid-driven fracturing and the critical theories pertaining to understand the process. The linear elastic fracture mechanics concepts, together with cohesive zone models, are discussed, and a review of their suitability for modeling the rock fracturing process is presented. From different laboratory and field tests, it has been found that the subsurface rock behavior is time dependent, especially if the rock is saturated. The time dependency of bulk rock mass during fracking is not fully understood. Time dependency is mainly due to fluid consolidation and the rock skeleton viscoelastic behavior. This article also gives a brief review of the viscoelastic constitutive models, which can be useful while modeling the bulk rock behavior as time-dependent material. The most commonly adopted finite element formulations for a saturated rock mass are highlighted. The rock mass is assumed to be tight with very low permeability, and therefore, the fluid velocity with respect to the rock skeleton is mainly ignored within the rock. Deformation of the rock matrix and pore pressure degrees of freedom are only to be considered. Various techniques adopted for the fluid flow simulation inside the fracture are also discussed. Different analytical closed-form solutions and their assumed fracture geometries are presented. Various existing finite element techniques for simulating fluid-driven fracturing are also highlighted.