ABSTRACT

Coal is conventionally regarded as a solid fuel, but in fact comprises a complex admixture of volatile and nonvolatile constituents. Volatile components include water, sorbed gases, and oils, all of which compete for accessible sites within the coal structure. Ten core samples from the Fruitland Formation (San Juan Basin, CO), representing three coal intervals from three different wells, were subject to a battery of analyses to assess the influence of

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the volatile components on gas reservoir characteristics. Preliminary results are tentative, owing to the small number of samples analyzed.

Rock-Eval pyrolysis S1 peaks indicate higher concentrations of free hydrocarbons in samples from the lower Fruitland as compared with overlying benches from the same wells. Methylene chloride solvent extracts show little difference in EOM, but indicate higher concentrations of saturated C₁₅₊ (waxy) hydrocarbons in lower Fruitland coals. Petrographically, the oil-enriched coals contain a higher proportion of micrinite.

Equilibrium moisture capacities and CO₂ surface areas are lower in the waxy coals, indicating lower sorbate accessibility. Laboratory desorption tests indicate lower in situ gas concentrations and lower percentages of desorbed CO₂ from the waxy coal. In contrast, experimental high pressure isotherms indicate little difference in methane sorption capacity of waxy versus non-waxy coals. Solvent extraction produces a significant increase in CO₂ and CH₄ sorption capacity in some of the samples, but has little effect on others.

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