Abstract

Mudlogs offer a method of determining the gas content in coals in standard cubic feet of gas (SCF/TON). This paper discusses the following:

1) the theory used to support coal-gas content measurement by mudlogging methods;

2) the methodology and equipment used to determine gas content of coals drilled with mud or air;

3) examples of mudlog derived coal-gas content as compared to canister desorption,

4) computations used determine coal-gas content, and

5) the sources of error and the degree of uncertainty in the measurements.

Coal whole-core desorption data indicate that a preponderance of gas will desorb from coal drill cuttings as they are drilled and circulated to the surface. Calculations needed to determine drill-cutting size and desorption times required to desorb small drill cuttings and a method to determine the amount of coal gas freed using mudlog data will be discussed. Two methods to determine mudlog response to coal gas and the advantages and disadvantages of both techniques will be reviewed.

Examples of air drilled and mud drilled mudlog gas content data will be compared to canister desorption data. An analysis of the sources of error and the common pitfalls of determining gas content from mudlogs will be discussed.