Upscaling permeability for fractured porous rocks and modeling anisotropic flow and heat transport

Chen, Tao; Clauser, Christoph (Thesis advisor); Kolditz, Olaf (Thesis advisor); Marquart, Gabriele (Thesis advisor)

Aachen / E.ON Energy Research Center, RWTH Aachen University (2017, 2018) [Book, Dissertation / PhD Thesis]

Page(s): 1 Online-Ressource (ii, 114 Seiten) : Illustrationen, Diagramme

Abstract

Modeling of fluid flow through fractured porous media is important for groundwater resources management, hydrocarbon and geothermal energy resources exploitation, waste disposal and sequestration. In conventional reservoir modeling, the fractured porous medium is assumed as an equivalent fracture model in which averaged equivalent fracture permeability is used. However, it is not yet known how best to incorporate the permeability of fractured porous media at a fine scale into conventional reservoir simulators at a coarse scale, i.e., upscaling permeability. Furthermore, modeling anisotropic flow in equivalent fracture models often assumes that the permeability tensor is diagonal, which means that its principle directions are always aligned with the coordinate axes. However, the equivalent fracture permeability is usually a full tensor. In this thesis, a new method, the multiple boundary method, is developed to determine equivalent permeability of fractured porous media. Inspired by the previous flow-based upscaling methods, I use a multi-boundary integration approach to compute flow rates within fractures. The method is verified by upscaling an arbitrarily oriented fracture which is crossing a Cartesian grid. The method is applied for a long fracture and a fracture network with different matrix permeability in two dimensions. The multiple boundary method is extended in three-dimensional fractured porous rocks and is compared with the Oda upscaling method and the volume averaging method for computing equivalent permeability. The main objective is to illustrate the differences quantitatively and discuss their advantages and drawbacks by considering such aspects as: (1) fracture size, (2) fracture orientation, (3) fracture intersection, and (4) fracture tortuosity. Additionally, the multiple boundary method is applied for three-dimensional stochastic discrete fracture networks and is compared with the other two methods. I first build a computational framework for the flow-based upscaling in which the permeability of the fractures and the rock matrix can be considered. Then I analyze the frequency distribution of the equivalent permeability and the errors between the equivalent fracture model and the discrete fracture model when solving a flow problem. Finally, I use the mimetic finite difference method (mFD) for discretizing the flow equation in a hydrothermal reservoir simulation code, SHEMAT-Suite, which couples this equation with the heat transport equation. I verify SHEMAT-Suite-mFD against analytical solutions of pumping tests, using both diagonal and full permeability tensors. I compare results from three benchmarks for testing the capability of SHEMAT-Suite-mFD to handle anisotropic flow in porous and fractured media. The benchmarks include coupled flow and heat transport problems, three-dimensional problems, and flow through a fractured porous medium with full equivalent permeability tensors.

Identifier

  • ISBN: 978-3-942789-45-5
  • REPORT NUMBER: RWTH-2017-07054