Reservoir Characterization to Inexpensively Evaluate the Exploitation Potential of a Small Morrow Incised Valley-fill Field

Kansas Geological Survey
Open-file Report 2002-9

Core Petrophysical Properties

Relative Permeability

Previous study of Morrow cores from the Stewart field provided oil-water imbibition relative permeability curves. These cores exhibit a generally similar trend in Swi versus ki to the Morrow in the Minneola Unit. Effective water permeabilities at residual oil saturation kew,Sorw range from 0.06 to 0.325, with an average of 0.19.

Modeled Relative Permeability

For the Stewart field Morrow, relative permeability exponents appear to exhibit trends with change in absolute permeability but cannot be defined with confidence. Based on the distribution of these values median values were adopted. The Corey-type equations were used to develop oil-water and gas-oil relative permeability curves for rocks of differing permeability. For each rock the Swi input into the relative permeability equation was predicted using the synthetic capillary pressure curve equations described. Initial values for m, n, and Sorw were 2.8, 3.1, and 37% respectively. Available data indicates that Morrow Sorw averages 37% and is not correlated with permeability. Based on this analysis, Sorw was assumed to be a constant 37% for all permeabilities. Calculated relative permeability and capillary pressure curves for rocks with 3 md, 10 md, 30 md, 100 md, and 300 md. Permeabilities of each gridcell were initially assigned to five basic classes to conform to the five general relative permeability curve types. Greater subdivision was not considered necessary since the five relative permeability curve sets covered the range in Swi and differed in saturation by less than 15% (saturation percent). During history matching the Corey exponent m and n were adjusted for some well locations to provide gas, oil, and water flow rates consistent with observed production.

Modeling Relative Permeability

Since relative permeability end point saturations change with permeability (e.g., “irreducible” water saturation changes with permeability), the relative permeability curves also change with absolute permeability. Relative permeability curves for each layer were predicted using the Corey-type equations below where Swi was obtained from Pc-k relations and the average absolute permeability values for each layer. Exponent m and n values were initially obtained from the measured data above and were modified during simulation to reproduce lease production data.

In reservoir simulation either unique kr curves must be defined for each unique water saturation region or pseudo-kr curves and corresponding pseudo-Sw values used. Since kr was defined by layer and region, it represents a pseudo-relative permeability. Initial pseudo-Swi values were assigned to each layer using Pc-k relations discussed.

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Last updated March 2002