SOCIETY OF PETROLEUM ENGINEERS OF AIME
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PAPER I 3 8 6 - G
NUMBER
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A PREPRINT --- SUBJECT TO CORRECTION
GEOLOGY OF SOUTHWEST TEXAS
By
O. G. McClain
Geologist, Corpus Christi, Tex.
Publication Rights Reserved
This paper is t;o be presented at the "Oil Recovery Symposium on Southwest Texas" sponsored jointly
by the Texas Petroleum Research Committee and the Southwest Section of the Society of Petroleum Engi•
neers of the American Institute of Mining, Metallurgical and Petroleum Engineers in Corpus Christi,
Tex., October 29-30, 1959, and is considered the property of the Society of ,Petroleum Engineers. Per•
mission to publish is hereby restricted to an abstract of not more than 300 words, with no illustra•
tions, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum
Technology or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where
and by whom the paper is presented. Publication elsewhere after publication in Journal of Petroleum
Technology is granted on request, providing proper credit is given that publication and the original
presentation of the paper.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society
of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered
for pUblication in Journal of Petroleum Technology with the paper.
INTRODUCTION
and to the strike. They show coastward dip and
coastward thickening of the formations. Fig.
is approximately strike section along the
8
Since the problems mutually faced by both
a
petroleum geologists and engineers are explora•
tion, development and production of oil and gas,
various aspects of the geology of Southwest
Texas pertinent to these problems are presented
in this paper. Southwest Texas is considered
geographically to occupy Railroad Commission
lower coast showing thickening into the Rio
Grande Embayment.
In
a
larger context, Southwest Texas is
situated on the southwestern flank of large
a
basin, the central part of which is now occupied
by the Gulf of Mexico. The long axis of this
basin is near the shore of and parallel with the
present Texas coast line. Strikewise along this
southwest flank there are alternating areas
Districts
2 and 4 and the southeastern portion
of District 1. Structure, stratigraphy and
sedimentation are of critical interest to
petroleum geologists and petroleum engineers.
These will be sketched in broad outline so as
to provide a framework and pertinent detail
then added.
that have received
a preponderance of sediments,
having had relative subsidence to accommodate
a
them and intervening areas of relative stability
which have generally thinner sedimentary sections
The Rio Grande Embayment, with the present day
Rio Grande River being near or shortly to the
south of its axiS, has received an added thick•
ness of sediments. During times of advance of
the sea it was deeper than the adjacent areas,
so that rivers brought more sediments into it
and deposited them farther inland. During times
of re'cession the area remained relatively low
and the rivers continued to flow into and across
it, depositing great quantities of sediments.
STRUCTURE
Fig.
1 is an outline map of Southwest Texas
on which the following data are noted:
Railroad Commission Districts
L
The paths of four cross sections.
The producing trends.
2 and 4
L
part of
2.
and
3·
The Vicksburg Flexure.
4.
To understand the structure and stratigraphy
of Southwest Texas series of cross sections are
through are regional
cross sections approximately norm&l to the coast
Illustrations at end of paper.
By contrast the San Marcos Arch with its
axis approximately along the path of Cross Sec•
tion "A-B-C", Fig. 1, was a relatively stable
a
most helpful. Fig.
2
7
area. Regional contours swing coastward in
a
gentle arch and then turn inland as the East