subsurface geology and coal resources of the pennsylvanian system ...

50 ILLINOIS BASIN COAL RESOURCES
Location
T. R.
TABLE 5.-DEPTHS OF POSSIBLY WORKABLE COAL BEDS IN CLAY COUNTY
(In feet)
I I I
Coal No. "7"
Coal No. 6 Coal No. 5
surface. The actual coal thickness has not
been satisfactorily ascertained in any of the
control wells because of insufficient differentiation
of the drilling time for the roof
shale and the coal. In two of the control
wells (Nos. 195 and 377), in which the
drilling time is slightly differentiated, however,
coal thicknesses of at least 2 to 3 feet
are indicated. Estimates of coal thicknesses
based on the examination of 406 electric
logs, by means of the conservative method
used for coal No. 6, indicate that the coal
reaches thicknesses from 3 to 4 feet in
widely scattered limited areas of the county,
as in the Iola, Bible Grove, and Sailor
Springs Consolidated oil pools. The electric
logs show, however, random thinning
of the bed to less than 30 inches for the
coal and roof shale combined, within the
areas of possible workable thickness. Coring
will be required to determine true coal
thicknesses in order to delineate the areal
extent of workable thickness for No. 5
coal bed. Because of great uncertainty in
regard to the thickness of No. 5 bed, no
estimate is made of the quantity of coal
present. Despite the variation in thickness,
it is recommended that the bed be
protected over the entire county for future
possible utilization by means of undergrour,d
gasification.
Tradewater-Caseyville groups.-The occurrence
of four coal beds in the undifferentiated
Tradewater and Caseyville deposits,
which attain local thicknesses of 3 to
6 feet of combined rcof shale and coal,
has been discussed in the section on other
prominent beds. No additional records of
thicker coal beds are available outside the
wells noted there. Reference to their occurrence,
depth, and thickness will be found
in that section and in table 4.
The uncertainty of the coal thickness of
practically all beds of possibly mineable
thickness does not now warrant an estimate
of the total coal reserves of the county.
PROTECTION OF COAL BEDS
No. 6 coal and No. 5 coal are the only
coal beds which should be protected by
means of plugging of abandoned drill holes
in those areas where mineable thicknesses
have been established or estimated. The
structure map of coal No. 6, the map showing
the interval between No. 6 and No. 5
coals, the thickness map of coal No. 6, the
tabulations, and tables 4 and 5 are to be
used as a guide for the proper placing of the
plugs.