Study of dynamic models for coal gas dynamics (part 1)

Permeability and capillarity

915120 Effect of transverse dispersion on solute transport in soils Leij, F J; Dane, J H J Hy&ol V122. Nl/4, Jan 1991. P407-422

See also: 915200, 915273, 915360 915116 Mercury intrusion and permeability of Louiseviile clay Lapierre, C; Leroueil, S; Locat, J Can Geotech J V27. N6, Dee 1990, P761-773 Several theories have been put forward to correlate pore size distribution and permeability of soils. Permeability and mercury porosimetry tests were carried out on a grey marine plastic Champlain Sea clay from Louiseville, Quebec. Both intact specimens and those remoulded after compression strains from O-42% were tested. For intact and remoulded conditions, a relation was found between pore size parameters and permeability. However, no unique relation covering these tests and those previously reported is found, and thus mercury porosimetry cannot be used to estimate permeability of soils in general. 915117 Layered permeable systems Schoenberg, M Geophys Prospect V39, N2, Feb 1991, P219-240 Permeability is a tensor property of porous media, and is generally anisotropic. A theoretical model is proposed which allows simple computation of the anisotropic permeability of a layered medium knowing the properties of each layer. Components of parallel sets of flow channels and barriers can be added or removed in any order, although for the case of intersecting sets of channels or barriers it is necessary to specify whether the channel or barrier is introduced first. Exact analogues are found in heat or electrical current flow. 915118 Analytical expressions for the permeability of random twodimensional Poisson fracture networks based on lattice percolation and equivalent media theories Hestir, K; Long, J C S J Geophys Res V95, NB13, Dee 1990, P21565-21581 Requirements of continuum assumptions, infinite and perfectly connected fractures, are not found in real rock masses, where fractures occur at all scales and are erratically and sparsely connected. The representative elementary volume may not exist if the scale of observable features continues to increase with scale of observation. The theoretical aspects are studied using a 2-dimensional Poisson network model of fractures as essentially conducting pipes, each equally conductive and with location and orientation independent of each other fracture. Permeability of partially connected networks is studied as a function of degree of interconnectivity and scale of measurement. 915119 Evduation of in situ permeability testing methods Femuik, N; Haug, M J Geotech Engng Div ASCE V117. N2, Feb 1991, P297-311 A program to evaluate the accuracy and efficiency of sealed single-ring and double-ring infiltrometers and air entry permeameters is described. The theoretical basis of the methods and experimental techniques are outlined. Full scale tests wete carried out on a residual soil-liner test pad and on a prototype liner of Ottawa sand and bentonite. Triaxial permeability tests on cored and remoulded samples were used for purpose of comparison. Good agreement between triaxial and field tests is possible, but care must be taken when setting up the field apparatus to ensure accurate and repeatable results. 0

A two dimensional transport model, with emphasis on the contribution of transverse dispersion to transport, is presented. A finite element code (Huyacorn et al, 1984) solves flow and transport problems in isotropic media using the Galerkin method. Three problems are addressed. The first considers one dimensional flow parallel to the interface of two layers with different pore water flow velocity. The other two examine transport of a pollutant from point and diffuse sources respectively, located at the soil surface. 915121 Statistical properties of immiscible fluid displacement in bona/site correlated network models of porous media Maier, R; Laidlaw, W G Math Geol V23. NI. Jan 1991. P87-110 An analytic formulation is presented which describes the number of sites (pores) and bonds (throats, necks) which are invadable in a percolation representation of immiscible fluid displacement in a porous medium. Statistical formulation is developed to allow determination of capillary pressures and relative permeabilities from lattice properties, and potentially, therefore, from core properties. Results from the statistical and the more expensive Monte Carlo simulation are in good agreement for both drainage and imbibition. 915122 Numerical simulation of time-dependent methane flow Ediz, I G; Edwards, J S Min Sci Technol VIZ. Nl, Jan 1991, PI-15 A numerical method for solving the gas flow equation for a medium with variable anisotropic permeability is presented. Approximate solutions can be obtained using finite element analysis to give time-dependent gas pressure. It is used with a modified version of the heat flow code PAFEC’75 to model methane pressure distribution around a coal seam for cases of no drainage and floor and roof borehole drainage. 915123 Study of dynamic models for coal gas dynamics (part 1) Sun Peide Min Sci Technol VIZ, Nl. Jan 1991. PI 7-25 Practical measurements of gas flow rate in homogeneous coal do not agree with values computed using Darcy’s Law, and a Power Law (Higuchi) was proposed. This has been extended and partial differential equations for gas flow in homogeneous and heterogeneous coal seams derived. Measured parameters of coal gas dynamics are used to assess the accuracy of the new nonlinear flow models. Predictions are closer to observed behaviour than for other theories. 915124 Mass arrival of reactive solute in single fractures Cvetkovic, V D Water Resonr Res V27. N2. Feb 1991, P177-183 An expression is derived for expected mass arrival at a single fracture, which couples solution advection and diffusion of the solute into the rock matrix. The fracture is conceptualised as a two dimensional porous medium with spatially variable transmissivity. The first two moments of solute arrival time are evaluated by assuming a special case of statistical anisotropy

1991 Pergamon Press plc. Reproduction

not permitted