Abstract: Continuous In-Situ Evaluation of Coal Resources and Acid Mine Drainage Potential with Wireline Geochemical Logging
CLAYTON, E. A., and R. E. LEWIS
Schlumberger HydroGeological Technologies, Englewood, CO
C. B. CECIL and F. DULONG
U.S. Geological Survey, Reston, VA
S. L. HERRON and J. A. GRAU
Schlumberger-Doll Research, Ridgefield, CT
In comparison with conventional analytical methods, a single logging pass of a wireline geochemical logging service provides real-time, complete coal characterization for both resource evaluation and acid-base accounting (ABA).
Coal-bearing strata were logged with the ECS (mark of Schlumberger) Elemental Capture Spectrometer sonde, which uses a prompt gamma ray neutron activation spectroscopy probe routinely employed in the oil industry to analyze for Ca, S, Fe, Ti, K, Gd and Si. Processing was modified to include coal, based on a spectral hydrogen measurement sensitive to coal content. The result is a continuous log of coal, calcite, pyrite, clay and quartz weight concentrations that can be used to characterize the depth, thickness, net footage, S and mineral content of coal seams, as well as the parameters required for ABA.
ABA is an accepted methodology for evaluating a coal property's potential to generate acidmine drainage. ABA consists of a series of equations in which S and calcite content in the overburden are equated based on the chemical reactions governing acid generation. The ECS log provides a continuous measure of both S and calcite content for a discrete, cumulative ABA evaluation.
Comparison of ECS measurements from two boreholes at selected study sites in the West Virginia bituminous coal field with chemical analyses of a total of 1603 ft of equivalent core samples indicates that the ECS sonde provides accurate elemental concentration and lithology logs of coalbearing strata. The calcite means for the ECS and core analyses in the deeper well are 4.36 and 5.06 weight %, respectively; the S means are 0.23 and 0.25 weight %, respectively.
AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio