Coal Resource Classification System of the U.S. Geological Survey

By Gordon H. Wood, Jr., Thomas M. Kehn, M. Devereux Carter, and William C. Culbertson

GEOLOGICAL SURVEY CIRCULAR 891

CONTENTS

1. Introduction
2. History of the classification system
3. Coal resource classification system
4. Glossary of coal classification system and supplementary terms
5. Criteria for coal resource classification
6. Applications of criteria
7. Specific criteria
8. Guidelines for estimating coal resources
9. General guidelines for classification of coal resources
10. Specific Instructions
    1. Rank of coal
    2. Overburden
    3. Thickness of coal categories
    4. Size of unit area
    5. Major categories of resources
    6. Coal bed maps
    7. Thickness of coal measurements
    8. Distribution of coal bed thickness measurements
    9. Measurement of areas
    10. Weight of coal per unit volume
    11. Calculation of coal resources
    12. Rounding of tonnage estimates
    13. Estimation of resources in the vicinity of where a coal bed bifurcates into two or more tongues
11. Estimation of hypothetical resources
    1. Extrapolated bed map method
    2. Extrapolated coal zone method
12. Examples illustrating the basic geometric principles of constructing coal resource bed maps
13. Geophysical logs as a source of coal bed data
    1. Electric logs
       • SP log
       • Normal and lateral logs
       • Focusing-electrode and induction logs
       • Discussion of electric logs
    2. Gamma ray log
    3. Density log
    4. Neutron log
    5. Acoustic velocity log
    6. Measurement of the coal bed thickness
    7. Composition and rank of coal
    8. Stratigraphy and structure
    9. Summary
14. Intended audience
15. References

ILLUSTRATIONS

1. Format and classification of coal resources by reserves and subeconomic resources categories
2. Format and classification of coal resources by reserve and inferred reserve bases and subeconomic and inferred subeconomic resources categories
3. Flow chart showing hierarchy of coal resources and criteria for distinguishing resource categories
4. Diagram showing reliability categories based solely on distance from points of measurement
5. Coal fields of the conterminous United States
6. Coal fields of Alaska
7. Coal regions of the conterminous United States
8. Coal provinces of the conterminous United States
9. Determination of areas of reliability using coal thickness data only at points of measurement along outcrop line
10. Determination of areas of reliability from points of measurement on the outcrop line, supplemented by mine and drill-hole data
11. Determination of areas of reliability using coal thickness measurements taken along a continuously exposed, strip-mined bed, supplemented by drill-hole data
12. Determination of minimum thickness isoline
13. Determination of areas of reliability and overburden thickness
14. A ridge with construction of 14-inch minimum thickness limit
15. Same ridge as figure 14 with areas of reliability, coal thickness isopachs, and overburden contour
16. A simple valley reentrant with construction of 14-inch minimum thickness limit
17. Areas of reliability, overburden contours, and coal thickness isopachs to accompany figure 16.
18. A valley and ridge with part of coal bed less than minimum thickness but within determined 14-inch limit as illustrated in figure 16
19. Areas of reliability, overburden contours, and coal thickness isopachs to accompany figure 18
20. Coal categories in plane of coal bed, a structure section, and coal categories as viewed projected to the ground surface from plane of coal bed
21. Areas of resource categories for a flatlying coal bed based on data only from underground mined areas and drill holes
22. A small coal basin divided into areas of coal resource categories
23. A large, simple coal basin divided into areas of coal resource categories
24. Suggested form for recording coal resource data and calculated tonnage estimates
25. Suggested format for tabulating data and calculating tonnages
26. Early conventional electric log (1957) of the Owanah Kendrick No. 1 well, Big Horn County, Montana
27. Induction and conductivity geophysical logs (1960) of the Hose-Austin Drilling Company from Bone Brothers No. 1 well, Rosebud County, Montana
28. Examples of oil- and gas-well geophysical logs from western Kentucky that can be used for coal bed correlations and coal resource evaluations
29. SP, gamma ray, acoustic velocity, normal resistivity, and induction conductivity logs (1971) from Davis Oil Grady Fed No. 1-2 well, Sweetwater County, Wyoming
30. SP, gamma ray, density, dual induction-lateral log, and neutron logs (1978) from Getty Tri-County No. 1 well, Rosebud County, Montana
31. Five geophysical logs of a coal exploration drill hole showing response to coal and limestone

TABLES

1. Classification of coals by rank
2. Average specific gravity and average weight of unbroken coal per unit volume of different ranks
3. Summary of coal resource criteria
4. Areas of reliability from figure 13 listed by overburden and coal thickness categories, and by counties
5. Areas of reliability from figure 15 listed in proper overburden and coal thickness categories
6. Areas of resource categories from figure 17 listed in proper reliability and thickness of coal and overburden categories
7. Areas of resource categories from figure 19 listed in proper reliability and thickness of coal and overburden categories

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