PETROLEUM RESOURCES—-LEVORSEN 
ing emphasis (fig. 9) and which is 
repeated in many forms in countless 
oil and gas fields. Whether it is an oil 
filed in the small sand lens in Kansas 
or Alberta, the porous limestone reefs 
of West Texas or Mexico, the dolo- 
mite grading into limestone in Indiana 
and Ohio, the rapid lateral change of 
a sand to shale in California, or the 
wedges bounded by unconformities as 
East Texas, the principle is the same— 
an up-dip wedging out of porosity and 
permeability in the reservoir rock. 
This principle applies not only to indi- 
vidual fields, but also to many prov- 
inces. Such a province may be 
SURFACE 
Tert. | | 
wes 
15 MILES 
253 
ena, which as yet has not been tested, 
occurs in the southeastern States of 
Mississippi, Alabama, and Florida 
where the wedge edge of the Lower 
Cretaceous and Jurassic rocks crosses 
first the southwest-plunging Appa- 
lachian arch and again the Florida 
uplift (fig. 10). These two rock series 
occur below the Upper Cretaceous in 
East ‘Texas, southern Arkansas, and 
northern Louisiana and contain the 
reservoir rocks of more than 125 oil 
and gas fields (fig. 11). This wedge is 
expanding at a rate of 100 feet per mile 
down the dip and somewhere in 
Mississippi and Alabama it crosses 
— After W.S.Morris 
| 
FicurE 9.—Generalized west-east cross section of the East Texas oil field. The wedge shape 
of the producing formation is repeated in various ways in many oil and gas fields. 
looked upon as a large-scale version of 
the up-dip wedge of permeability in 
which the oil and gas are first accum- 
ulated in the regional trap and later 
localized into pools by minor deforma- 
tions and local stratigraphic variations. 
Whether the stratigraphic variation is 
on the scale of either a single pool or a 
province, it has the advantage of being 
the earliest trap in the geologic life of 
the reservoir rock, and consequently 
having had more time in which to 
accumulate oil and gas. As a conse- 
quence, any up-dip wedge edge of 
permeability in a potentially produc- 
ing formation is significant. 
One of the largest of these phenom- 
the southwestern extension of the 
Appalachian arch setting up a poten- 
tial trap area of thousands of square 
miles. Farther southeast in Florida 
it crosses the southern extension of the 
Florida arch where production has 
already been found in Cretaceous rocks 
(fig. 12). Here again there is a poten- 
tial trap area of thousands of square 
miles in a group of rocks which have 
produced fields like Smackover, Ro- 
dessa, and Schuler along the same 
trend. Drilling will be deep, it is true, 
probably beyond 15,000 feet and even 
as deep as 20,000 feet. No one can 
even guess in advance of drilling what 
structure, stratigraphic sequences, or 
