Numerical Simulation of Shale Reservoir Fluid-Driven Fracture Network Morphology Based on Global CZM

Abstract

There are a large number of natural fractures in shale reservoirs, which create great challenges to hydraulic fracturing. Activating the natural fractures in reservoirs can form a complex fracture network, enhance fracturing effects, and increase shale gas production. Reservoir geological conditions (low in situ stress, natural fracture distribution, and cement strength) and operation parameters (fracturing fluid viscosity and injection rate) have an important influence on fracture network propagation. In this article, a two-dimensional hydraulic fracturing fluid-mechanic coupling numerical model for shale reservoirs with natural fractures was established. Based on the global cohesive zone model, the influence of geological conditions and operation parameters on the propagation of the hydraulic fracture network and fracturing process is investigated. The numerical simulation results show that when the horizontal in situ stress difference, approach angle, and cement strength are low, it is easier to form a complex fracture network. Research on the construction parameters indicated that when the viscosity of the fracturing fluid is low, it is easier to form a complex network of fractures, but the length of the fractures is shorter; in contrast, the fractures are straight and long. In addition, increasing the injection rate is beneficial for increasing the complexity of the fracture network while increasing the initiation pressure and width of the principal fracture reduces the risk of sand plugging. This article also proposes an optimization solution for hydraulic fracturing operations based on numerical simulation results.

A comprehensive review of numerical simulation methods for hydraulic fracturing

“…The fracture advances in the path of least resistance, with a continuous rise in exerted pressure. Generally, two types of fluid flow occur in the fracture: flow along the fracture length and flow normal to the fracture length 38 . The average flow corresponds to leakoff in the hydraulic fractures, as depicted by the red arrows in Figure 1.…”

“…Generally, two types of fluid flow occur in the fracture: flow along the fracture length and flow normal to the fracture length. 38 The average flow corresponds to leakoff in the hydraulic fractures, as depicted by the red arrows in Figure 1. The fluid-filled zone indicates a specific stage in CZM where traction exceeds the critical threshold, triggering fracture development.…”

Numerical simulation of hydraulic fracture propagation in fractured reservoir using global cohesive zone method

“…Afterward, the propagation path of a large-scale complex fracture network was successfully simulated [23][24][25][26][27][28] by inserting zero-thickness cohesive elements around the solid element. Researchers have utilized the global cohesive zone model to conduct a series of studies on geological and operation parameters for hydraulic fracturing, such as in situ stress conditions, fluid injection rate, fluid viscosity, natural fractures geometry parameter, and strength parameter [29][30][31]. Natural fracture physical and mechanical properties can be described by the three types of parameters, namely, geometry (e.g., crack length and dip angle), strength (e.g., crack friction coefficient or bonding strength), and deformation parameters (e.g., crack normal and shear stiffness).…”