Modeling of transport processes through large-scale discrete fracture networks using conforming meshes and open-source software

Abstract

Most industrial and field studies of transport processes in Discrete Fracture Networks (DFNs) involve strong simplifying assumptions, especially at the meshing stage. High-accuracy simulations are therefore required for validating these simplified models and their domain of validity. The present paper proposes an efficient workflow based on open-source software to obtain transport simulations. High-quality computational meshes for DFNs are first generated using the conforming meshing approach FraC. Then, a tracer transport model implemented in the open-source code DuMux is used for simulating tracer transport driven by the advection-dispersion equation. We adopt the box method, a vertex-centered finite volume scheme for spatial discretization, which ensures concentration continuity and mass conservation at intersections between fractures. Numerical results on simple networks for validation purposes and on complex realistic DFNs are presented. An a-posteriori convergence study of the discretization method shows an order of convergence O(h) for tracer concentration with h the mesh size.

Performance of horizontal wells in composite tight gas reservoirs considering stress sensitivity

“…In recent years, numerical simulation attracts researchers' attention. It is able to consider more complicate situation of unconventional reservoirs using meshed numerical models (Wu et al, 2014;Noetinger, 2015;Ngo et al, 2017;Ding et al, 2018). However, analytical and semianalytical methods still need to be valued for their fast and low-cost advantages.…”

FraC: A new conforming mesh method for discrete fracture networks

“…In this section, we consider a synthetic DFN, which was also studied by a number of authors (e.g. Khvoenkova and Delorme, 2011;Delorme et al, 2016;Ngo et al, 2017). The network consists of 33 dish-shaped fractures inside a 3m  3m  3m cube.…”

“…The main idea is that major workload will be spent on generating DFN meshes rather than in the development of specific numerical approaches (Adler et al 2012). Recent studies dealt with conform mesh approaches (Hyman et al, 2014(Hyman et al, , 2015Huang et al, 2016;Fourno et al, 2016;Ngo et al 2017). CPU time for DFN mesh generation may be considerably reduced in line with progress in computer sciences and information technology.…”

“…At this stage, an octree-like approach (Khvoenkova and Delorme, 2011;Hyman et al, 2014) is used to improve the computational efficiency. This approach works well if the size of the fractures is almost of the same order of magnitude (Ngo et al, 2017…”

Comparison of the response to geometrical complexity of methods for unstationary simulations in discrete fracture networks with conforming, polygonal, and non-matching grids

“…To be specific, the edges of the computational elements have to match at the intersections. This approach, called conforming-mesh discretization, may suffer, for example, when intersections lines are very close to each other; see [26,42,43,49,50]. To partially overcome these problems, a possibility is to consider the class of polytopal methods, like mimetic finite difference and polytopic discontinuous Galerkin (DG) that allow grid elements of general shapes.…”