Introduction
Coal density is less than that of conventional reservoir rocks and is highly variable, depending primarily on rank and purity.
The organic components of coal are less dense than the inorganic components of coal. In a general sense, coal density ranges between 1.1 and 2.2 g/cm3. The Gas Research Institute (GRI) suggests higher values are indicative of inorganic content.
Net Pay in a coal seam is often determined from applying a bulk density cut-off to wireline logs, perhaps supplemented by gamma ray, acoustic, or resistivity logs.
All our coal seam GIP calculations are based on in-situ values of coal density and gas content. That is, AFA defines gas content for coalbed gas reservoirs as the in-situ gas volume per unit weight of rock. The unit weight of rock contains both organic and inorganic components within coal and other organic-bearing rock types.
The dry, ash-free basis or the mineral-mineral matter- free bases are useful for comparing gas content or storage capacity estimates obtained from samples of differing composition. We do not use these bases to estimate gas-in-place volumes.
See Also:
References:
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John Seidle, Fundamentals of Coalbed Methane: Reservoir Engineering, 2011, PennWell Corporation.
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Energy & Coal: Coal Formation, Directorate of Turkish Coal Website.
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Coalbed Reservoir Gas-In-Place Analysis, Gas Research Institute (GRI), October 1997