The recent impetus to oil prospecting in Illinois

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STATE OF ILLINOIS

HENRY HORNER. Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

JOHN J. HALLIHAN, Director

DIVISION OF THE

STATE GEOLOGICAL SURVEY

M. M. LEIGHTON, Chief
URBANA

CIRCULAR NO. 3 3

THE RECENT IMPETUS TO OIL PROSPECTING

IN ILLINOIS

BY
GEORGE V. COHEE

Reprinted from the Transactions,
Illinois State Academy of Science,
VOL. 30, NO. 2, PP. 226-228, 1938.

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS
1938

(55171;

226 Illinois State Academy of Science Ti~ansactions

The Recent Impetus to Oil Prospecting
in Illinois*

George V. Cohee

Illinois State Geological Survey, Urbana, Illinois

The present "oil boom" in Illinois started with the extensive leasing
program in Marion and Clay counties by the Carter Oil Company during the
latter part of 1935 and the early part of 1936. In a short time many com-
panies and individuals were taking leases in the Illinois Basin. Land was
leased in large blocks for as little as 10 cents a year per acre for a period of
ten years.

In many areas leasing proceeded rapidly and without any attempt to
secure geologic information. The major companies were more fortunate in
that they were able to finance the operation of seismograph parties which
could provide geophysical information bearing upon oil possibilities.

These geophysical methods are especially necessary in examination of
the Illinois basin as so much of the subsurface formation there is completely
hidden by a thick cover of glacial drift. Even where bedrock is exposed by
stream erosion, the formations usually consist of sandstones and shales
which are very difficult to place in their correct stratigraphic position. And
in the deeper part of the basin there has not been enough drilling to yield
detailed subsurface information.

Although the seismograph in many areas has given very satisfactory
results in geophysical prospecting for structures favorable to accumulation
of oil, and much can be said in favor of the results obtained by the torsion
balance, magnetometer, and electrical resistivity in particular kinds of ex-
ploration, still, geophysical surveys are only preliminary steps in the search
for oil: after favorable structures have been located, drilling is necessary to
determine whether or not oil is actually present.

Two methods used in seismographing, this indirect but very important
means for locating oil, are those of refraction and of reflection.

The refraction method which was used in the Gulf Coast region until
1930 for the detection of salt domes, consists of setting off a charge of dyna-
mite with detectors arranged in a circle around the shot point. The radius
of the circle is from 5 to 7 miles. As much as 500 pounds of dynamite is
used for one shot. Velocities of the waves through the rock layers from
the shot point to the detectors are computed. Extremely high velocities be-
tween these points indicate the presence of high velocity beds or salt domes
between the shot point and the detector.

The reflection seismograph method is used in Illinois. It consists of
setting off a charge of explosives at a certain point and having detectors
called geophones placed at an accurately measured distance away from the
shot to receive the ground vibrations. This distance is usually in the
neighborhood of one quarter of a mile. When the detectors are jarred by
the ground vibrations they generate an electric current which is in propor-
tion to the ground vibration. This voltage is stepped up by the vacuum

* Published with the permission of the Chief, Illinois State Geological Survey.

Geology — 1937 Meeting

227

Fig. 1. This diagram shows field procedure in reflection mapping. The surveying
crew determines the position and surface elevation of points where holes are
to be drilled by the drilling crew. Soon after the shot holes are drilled, the
dynamite charges of from 1 to 6 pounds each are set off and the recordings
are made. The diagram shows the path of the vibrations from the shot to the
reflecting limestone layer and to the geophones. (Published in "Seismic ,
Prospecting in Exploration for Oil" (1) by courtesy of the Askania
Corporation.)

228 Illinois State Academy of Science Transactions

tube amplifiers. After sufficient amplification, the electric current goes to
the oscillograph. In one type of oscillograph the vibrating element is a loop
of fine metal ribbon in a magnetic field. The loop tries to rotate when the
current is introduced in the magnet. At the center of the loop a tiny mirror
is fastened upon which a strong beam of light is focused. This beam is then
reflected upon a moving sheet of photographic paper and records all move-
ments of the mirror as a fine black line when the paper is developed.

When the explosive is set off vibrations travel outward in all directions.
Upon reaching thick rock layers, such as the lower Mississippian limestone,
vibrations of less intensity are reflected to the surface. The distance between
the shot point and the detectors is known, the velocity of the vibrations
through the layers of rock down to the reflecting layer is known, the time
elapsed between the shot and the reception of the vibration is recorded on
the photographic film. With these values the depth to the reflecting layer
can be calculated. The depths to certain key horizons in the area covered by
the seismograph survey are plotted on a map and the subsurface contours are
drawn. When the map is completed favorable structures for the accumula-
tion of oil such as domes, anticlines, monoclines, and fault zones are outlined
if present in the area. Figure 1 shows the operation of the seismograph.

At the present time, April, 1937, there are 13 parties in the State. Two
parties are operating in southwestern Indiana. The estimated cost of
operating a party for one month is from 6 to 8 thousand dollars. The party
includes surveying, drilling, shooting, and recording crews and totals twelve
to fourteen men.

To date there have been four new oil fields discovered in Illinois:
Bartelso, May 1936; Patoka, January 1937; Clay City, February 1937; Cisne,
March 1937. The Patoka, Clay City, and Cisne fields were discovered on
structures outlined by the seismograph. The Bartelso structure was de-
scribed and recommended in Bulletin 20A published in 1912 by the Illinois
State Geological Survey. The Patoka structure was shown as a high on
coal No. 6 in State Geological Survey Bulletin 16, published in 1910. The
recent discoveries have caused extensive exploration activities in southern
Illinois. A map showing the area of best oil and gas possibilities in Illinois
was drawn by Dr. A. H. Bell, Head of the Oil and Gas Division of the State
Geological Survey, and exhibited by the Western Society of Engineers in
Chicago, September 1930. The Illinois basin was then considered to be the
most favorable area and is now the center of the recent oil "boom."

The new fields indicate that on similar structures throughout the basin,
production is likely to be obtained. Much leasing and exchange of royalties
have taken place where the recent "finds" have been made. It has been re-
ported that as much as five hundred dollars an acre has been paid land-
owners for one-half of their royalty which is one-eighth of the production.
Oil companies and individuals who formerly were not attracted by the
"play" are now taking leases and becoming interested in the possibilities of
the Illinois basin. It is anticipated that this year will mark the most wide-
spread drilling program Illinois has ever experienced.

The writer is grateful to Dr. A. H. Bell, of the Illinois State Geological
Survey, for helpful suggestions and criticisms of this paper.

REFERENCES

(1) Gabriel, V. Gavrilovich — Seismic Prospecting in Exploration for Oil. Louisi-

ana Conservation Review, "Vol. 5, No. 4 (1937), pp. 4-8.

(2) Eby J. Brian — Geophysics — Its application to petroleum production. The

Petroleum Engineer, Vol. 8, No. 5 (1937), pp. 113-134.

(3) McKinnet, E. G. — Seismographing for oil. The Times Journal Publishing

Company, Oklahoma City (1935).

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