ABSTRACT: Geomechanical discrete fracture networks (DFNs) are grown using a 3D finite element-based fracture mechanics simulator. The influence of the fracture growth rate exponent (ß) on the resulting fracture geometry and hydraulic properties of networks is investigated. Previous work has found that has a complex relationship with the final geometry of geomechanically-grown 2D DFNs. Realistic features evolve during the growth of DFNs as a result of the orientation of the principal stress axis and fracture interaction. High values of cause interaction effects to be more pronounced, and irregular shaped fractures to be more common. Low values of are found to produce networks with a balance between selective growth on preferentially oriented and interacting fractures, and significant increases in fracture surface area with computation time. The permeability of DFNs is significantly influenced by anisotropy, which develops in the axes perpendicular to the principal stress direction. For fracture networks with different values, permeabilities along the principal axes are similar for the same total fracture void space.

ABSTRACT: Accurate modeling of naturally fracture reservoirs requires a comprehensive understanding of fracture network geometry in three-dimensional space. This is a significant challenge to the realistic construction of discrete fracture network (DFN) models since these reservoirs are often controlled by subseismic-scale fractures whose characteristics are difficult to define. We present results from natural fracture network characterization and parametric DFN modeling within the Horn River Basin that emphasize the major challenges to accurate DFN construction. Fracture network parameters that were found to have the largest impact on model results included fracture stratigraphy, intensity, and orientation dispersion. These results provide insight into the challenges of sparse well samples when attempting to accurately characterize natural fracture geometry. Furthermore, this study highlights the fundamental considerations that are necessary for realistic modeling of naturally fractured reservoirs.

ABSTRACT: Aimed at supporting the hydraulic fracturing experiments in EGS Collab project, a three-dimensional (3D) quasistatic discrete element model (DEM) incorporating hydro-thermo-mechanical (HTM) coupling effects has been developed and applied to simulate the hydraulic fracture propagation under the influence of stress alterations due to the drift evacuation and its longer-term cooling effects. The induced stresses are modeled by developing a 3D quasi-static DEM model and validated against that from commercial finite element model package. It is observed that the fracture starts from a more-or-less penny-shaped crack and then becomes less symmetric with a preferred growth direction toward the drift which the stress nearby is less compressive. Sensitivity studies are then performed to understand how the operational parameters, such as injection rate, impact the fracture size, geometry and aperture distribution. The containment mechanism of propagating fracture by production wells is also investigated, and the simulation results clearly indicate the risk of hydraulic fracture intersecting the drift is minimum when producing wells exist in the neighborhood.

ABSTRACT: Well tests are a fundamental characterization tool for oil and gas reservoirs and for groundwater investigations. Several common geometric models exist within conventional well testing practice. These models are based on porous continua. In particular, two dimensional radial flow has been used as an indicator of porous medium flow. On the other hand the infinite conductivity hydraulic fracture model of Gringarten, which has a one-dimensional flow geometry (all flowlines parallel), has been used as an indicator of fracture flow. The main point of this paper is that the geometric models of well tests are not unique to fractured or porous media. Discrete fracture network models are useful to show that well test responses associated with porous media can also be produced in discrete fracture networks. Two dimensional flow behavior may be produced by a space filling fracture network in a layered system. One-dimensional flow is easily produced where there is a strong single fracture set orientation, and three-dimensional flow can be developed from a layered system with out of plane faults.

ABSTRACT: Advances in multistage fracturing combined with horizontal drilling have made this technique the driving force for the recent spectacular success in shale gas development and production. In this paper, a hierarchical approach integrating discrete fracture networks with multi-continuum concept is proposed to model various coupling mechanisms of gas nonlinear transport in shale. The hybrid model is composed of three continuum layers: organic matter, inorganic matter and micro-fractures in matrix which are treated as a continuum medium, and the discrete fractures are embedded into the micro-fracture-continuum. The extended finite element method is employed to decouple the mesh conformity between the mesh of media and the discrete fractures. The results of long-term well-performance dynamics are used to show the power and flexibility for simulating the multi-continuum/discrete-fracture interactions during gas transport in shale. The effects of fracture geometry and coupling flow mechanisms on gas production are also analyzed in this paper.

ABSTRACT: Micro discrete fracture networks (µDFN) have been embedded into Grain Boundary Models (GBM) within UDEC to simulate laboratory tests on a series of progressively larger in size numerical specimens. The initial GBMs simulating the intact rock consist of Voronoi blocks to capture the fracturing of the intact material. The µDFNs were generated separately from the GBMs in SR2 to create pre-existing “defects”. These geometries were created stochastically with fracture orientation, mean length and areal intensity (P21) serving as input parameters for the generation process. Following the generation of the µDFN geometries, the fracture networks were incorporated into the GBMs to create synthetic rock mass (SRM) models. This type of model is able to capture the behaviour of “flawed” rock samples as the defects are explicitly modelled. A sensitivity analysis is undertaken to examine the effect of micro-defect intensity on the UCS and modulus of deformation under an assumption of a constant crack length. Preliminary results highlight the impact of pre-existing defects and their geometrical configuration on the rock block strength.