Modeling Three-Dimensional Fluid-Driven Propagation of Multiple Fractures using TOUGH-FEMM

Abstract

：In this paper, a new numerical simulation tool named TOUGH-FEMM is presented and applied to model three-dimensional (3D) hydraulic fracturing in porous rock. The fluid flow in both fractures and porous rock is modeled using TOUGH2, which is a well-established code for analysis of multiphase and multi-component fluid flow. Rock deformations associated with fracture propagation are modeled using finite element-meshfree method (FEMM). FEMM is an approach to simulate fracture propagation without remeshing, in which the fracture path does not need to be predetermined. Fracture mechanics with mixed-mode stress intensity factors are employed to detect fracture instability and determine the direction of fracture propagation. TOUGH-FEMM is verified for modeling fluid-driven fracture propagation in 3D through a number of simulation examples, including modeling of hydraulic fracturing laboratory experiments and by comparison to independent numerical simulation results for multiple interacting hydraulic fractures at ten to hundred meter scale.

Special Issue “Hydraulic Fracturing in Hard Rock”

“…Different regimes are identified controlling the direction of fracture propagation by the degree of material anisotropy rather than the stress anisotropy. Tang et al (2019) use the numerical tool TOUGH-FEMM to model three-dimensional fluid-driven propagation of multiple fractures. Rock deformations associated with fracture propagation are modeled using the finite element-mesh-free method (FEMM).…”

A three‐dimensional heat transfer and thermal cracking model considering the effect of cracks on heat transfer

“…where n 1 ð Þ i is the outward normal unit vector of the triangular face opposite to node 1 and S (1) is the area of the triangular face opposite to node 1.…”

“…The proposed 3D thermo-mechanical coupling model not only considers the thermal deformation and thermal stress caused by the temperature change but also considers the effect of crack initiation and propagation on the temperature field. The entire calculation process can be divided into four main steps: (1) The temperature distribution of the system is analyzed based on the 3D heat transfer model; (2) the thermal stress caused by the temperature change is calculated; (3) the temperature-induced thermal stress is applied to the system equation, the mechanical fracture calculation is performed, and the fracture network is updated; and (4) the heat exchange coefficient of the newly generated broken joint element is multiplied by a reduction factor r T , which will be used as the input for the thermal transfer calculation at the next time step. According to above four steps, the thermo-mechanical coupling analysis is completed in a one-time step, and the thermal cracking of rock can be simulated, as shown in Figure 10.…”

“…If the stress concentration exceeds the tensile strength of the rock, thermal cracking will occur, and a fracture network will eventually form. Unlike hydraulic fracturing, which often generates cracks that extend along a certain direction, thermal cracking creates a fracture network, which can increase both the fracture length and fracture density simultaneously. Therefore, thermal cracking has significant application prospects for increasing the permeability of reservoirs.…”

Stability of the formation interface under the impact of hydraulic fracture propagation in the vicinity of the formation interface

“…Many unconventional hydrocarbon reservoirs occur in formations with clear interfaces, such as stratified formations and formations interlaced with sand-mud beddings. A formation interface complicates the mechanism of hydraulic fracture propagation, owing to the difference in pressure, rock material properties, interfacial strength, interfacial morphology, and rock failure behavior between the two sides of the formation interface (Guo et al 2017;Li et al 2018;Lu et al 2015;Tang et al 2019). When hydraulic fractures extend to the vicinity of the formation interface but do not contact the formation interface, it can be considered that the hydraulic fractures are propagated in a homogeneous medium.…”