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Abstract: Numerical Modelling of Displacement Processes in Porous Media

Gunter Fiebig, Bernhard M. Krooss

The slow, capillary-dominated penetration of non-wetting fluids (mercury, gas, oil) into a pore system, e.g. a cap rock can be considered as an invasion percolation process which is controlled by the sizes of the bonds and sites of a network representing the pore space. With increasing pressure the fluid fills an increasing fraction of the pores. Volume flow across the porous medium, i.e. seal failure of a cap rock, will occur when an interconnected pathway along the pore system develops throughout the sample.

Numerical simulations of drainage and imbibition, which include the detection of trapped regions of the displaced fluid, have been performed both on the laboratory scale and for geologic systems. The 3D grids used for the computations represented statistically homogeneous as well as inhomogeneous media assuming different pore size distributions to construct randomly heterogeneous and layered structures. Co-ordination numbers of the pores were varied between values of 6 and 20.

The computations were used to assess the saturation values of the non-wetting and the residual wetting phase, respectively, as a function of increasing entry pressure of the non-wetting fluid. After reaching the percolation threshold, corresponding to seal failure of cap rock systems, the "backbone"., i.e. the transport-relevant fraction of the pore system, is monitored continuously to determine the fraction of the total pore system involved in the fluid transport across the medium and to calculate its hydraulic conductivity. The onset of percolation depends Strongly on the co-ordination number of the grid system and on the existence of spatial correlations.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France