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

94 ILLINOIS BASIN COAL RESOURCES
large quantities of coal. Probably damage
to the coal beds will result from penetration
of the beds by numerous drill holes,
particularly where closely spaced in producing
oil pools. Additional loss is inevitable
from the mining processes. It seems
probable that the actual amount of recoverable
coal from these beds cannot be more
than half the amount given above, or 1500
million tons.
Some of the other coal beds, includiiig
"No. 7," "No. 4," "No. 2," the Dekoven,
Curlew, and possibly others higher or lower
in the section, may be of workable thickness
in areas large enough to support mining
operations in Gallatin County. However,
only additional exploration can provide the
data necessary far evaluation of these
possible reserves.
PROTECTION OF COAL BEDS
Workable beds of coal were originally
defined in the Rules and Regulations of the
Oil, Gas, and Coal Conservation Act
(effective July 29, 1911 ) as beds 30 inches
or more thick at a depth of 1000 feet o,r
less, and 36 inches or more thick at a depth
of more than 1000 feet. This order has
been modified to limit workable beds to a
thickness of 30 inches at or above 1000
feet.31 Three beds need protection in this
area: No. 6, No. 5, and the Davis. No
drill hole should be abandoned in this county
unless provision is made fo,r the protection
of these coal beds. With the aid of the
structure contour map, showing the altitude
of No. 6 coal bed above sea level, the depth
to this bed can be calculated from the surface
altitude. The average intervals between
No. 6 bed and No. 5, and No. 6 bed
and the Davis coal bed, for the various
townships in the area mapped, appear in
table 8. In general, No. 6 and No. 5 beds
are separated by about 100 to 110 feet of
strata. To protect these beds, a cement
31 Oil, Gas. and Coal Conservation Act-Rules and Regulations,
Rule 11. p. 12: Illinois Dept. Mines and Minerals,
Division of Oil and Gas Conservation, October IS,
1945 (mimeographed).
plug should extend from 50 feet above to
150 feet below No. 6 coal bed. To protect
the Davis bed, a cement plug should extend
for 100 feet from about 290 feet below No.
6 bed in T. 7 S., and about 315 feet beloiv
No. 6 bed in T. 8 S. Such a plug should
give satisfactory protection for both the
Dekoven and the Davis beds.
Placing o,f plugs at the positions indicated
will provide protection for the three beds
of special importance in the area. Hornever,
this procedure does not release the
operator f ro,m the obligation of protecting
other beds which adjacent diamond drilling
or careful logging of any rotary-drill holes
indicate are of workable thickness. The
present report, particular1.y the cross-sections,
graphic logs, and tabulations, shows
the positions where coal beds are likely to
be penetrated. Care should be exercised
in drilling at these positions so that unusual
thicknesses of coal beds that are generally
thin may be reported.
OIL AND GAS RESOURCES
Structure of the No. 6 coal bed has a
close similarity to the structure of the
upper and middle Mississippian beds which
contain the o'il and gas produced in Gallatin
County. Where these accumulations
are related to structural features of the producing
strata, the structure of No. 6 coal
provides a fairly accurate picture of the
structure of the reservoir formations. However,
this constitutes a post fnctum relationship
which is established a-fter the pools
have been discovered. The relationship
everthe he less is important because it indicates
the value of shallow structure testing to key
beds such as No. 6 coal bed.
The structure map of the No. 6 coal
bed presents the structural features in
sufficient detail to meet the primary objectives
of this study. However, a contour
interval of 25 feet is probably too large to
delineate the smaller structural irregularities
that seem to determine positions of
some of the oil pools in Gallatin County.