No abstract

No abstract

No abstract

Multiphase flow in porous media is very important in various scientific and engineering fields. It has been shown that relative permeability plays an important role in determination of flow characteristics for multiphase flow. The accurate prediction of multiphase flow in porous media is hence highly important. In this work, a novel predictive model for relative permeability in porous media is developed based on the fractal theory. The predictions of two-phase relative permeability by the current mathematical models have been validated by comparing with available experimental data. The predictions by the proposed model show the same variation trend with the available experimental data and are in good agreement with the existing experiments. Every parameter in the proposed model has clear physical meaning. The proposed relative permeability is expressed as a function of the immobile liquid film thickness, pore structural parameters (pore fractal dimension D f and tortuosity fractal dimension D T ) and fluid viscosity ratio. The effects of these parameters on relative permeability of porous media are discussed in detail.

Fractures allow crystalline rocks to store and transport fluids, but fracture permeability can also be influenced significantly by the existence or absence of gouge and by stress history. To investigate these issues, we measured the water permeability of macrofractured basalt samples unfilled or infilled with gouge of different grain sizes and thicknesses as a function of hydrostatic stress and also under cyclic stress conditions. In all experiments, permeability decreased with increasing effective pressure, but unfilled fractures exhibited a much greater decrease than gouge‐filled fractures. Macrofractures filled with fine‐grained gouge had the lowest permeabilities and exhibited the smallest change with pressure. By contrast, the permeability changed significantly more in fractures filled with coarser‐grained gouge. During cyclic pressurization, permeability decreased with increasing cycle number until reaching a minimum value after a certain number of cycles. Permeability reduction in unfilled fractures is accommodated by both elastic and inelastic deformation of surface asperities, while measurements of the particle size distribution and compaction in gouge‐filled fractures indicate only inelastic compaction. In fine‐grained gouge this is accommodated by grain rearrangement, while in coarser‐grained gouge it is the result of both grain rearrangement and comminution. Overall, sample permeability is dominated by the gouge permeability, which decreases with increasing thickness and is also sensitive to the grain size and its distribution. Our results imply that there is a crossover depth in the crust below which the permeability of well‐mated fractures (e.g., joints) becomes lower than that of gouge‐filled fractures (e.g., shear faults).

No abstract

Permeability is one of the key factors involved in the optimization of oil and gas production in fractured porous media. Understanding the loss in permeability influenced by the fracture system due to the increasing effective stress aids to improve recovery in tight reservoirs. Specifically, the impacts on permeability loss caused by different fracture parameters are not yet clearly understood. The principal aim of this paper is to develop a reasonable and meaningful quantitative model that manifests the controls on the permeability of fracture systems with different extents of fracture penetration. The stress-dependent permeability of a fracture system was studied through physical tests and numerical simulation with the finite element method (FEM). In addition, to extend capability beyond the existing model, a theoretical stress-dependent permeability model is proposed with fracture penetration extent as an influencing factor. The results presented include (1) a friendly agreement between the predicted permeability reduction under different stress conditions and the practical experimental data; (2) rock permeability of cores with fractures first reduces dramatically due to the closure of the fractures, then the permeability decreases gradually with the increase in effective stress; and (3) fracture penetration extent is one of the main factors in permeability stress sensitivity. The sensitivity is more influenced by fracture systems with a larger fracture penetration extent, whereas matrix compaction is the leading influencing factor in permeability stress sensitivity for fracture systems with smaller fracture penetration extents.

Fractured reservoirs' media consists of matrix and effective fractures. The fracture distribution is complex and variable in these reservoirs with strong characters of anisotropy of reservoirs. This paper introduces a simple, fast and accurate method to test 2D tensor permeability of fractured anisotropy media. Combining numerical simulation results and experiment results, 2D tensor permeability is derived and the variation mechanism of 2D tensor permeability in fractured anisotropic media has been revealed. According to the polar form of elliptic equation, permeability elliptic is derived. With ellipsoidal permeability, the change law of permeability value in principal direction is studied. 3D permeability tensor model for fractured media is proposed on basis of the coordinate transformation principle. Based on the quantitative characterization of 3D tensor permeability and Gangi's permeability stress sensitivity model, a stress-dependent 3D permeability tensor mathematical model for fractured media is established. The method provides a theoretical basis for the determination of percolation parameters in fractured reservoirs, and the results are significant in understanding the fluid flow in fractured anisotropic media.