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DEPARTMENT OF THE INTERIOR

Boy O. West, Secretary

U. S. GEOLOGICAL SURVEY 

George OtisKSmith, Dfreetor

Professional Paper 154—E

OIL SHALE IN A PRODUCING OIL FIELD IN CALIFORNIA

BY

H, W. HOOTS

Published March 20,1929

Shorter contributions to jfeiteral geology, 1928

~" (Pages 1T1-178)

ETN1TED STATES 

PRINTING 

WASHINGTON
\

CONTENTS

General features._____________________________________________________________________________________________ 171

Microscopic character and richness-____________________________________________________________________________ 171

Age of the oil shale___________________________________________________________-_________-___-____-_____^______ 172

Stratigraphic relation of oil shale to oil-producing zone_--_---_-_--_-_----________--___---_-_-_-_-_--_--_---_______ 172

Significance of the stratigraphic relation.____________________________________________________-_____---_______ ?.-__ 172

ILLUSTRATION

Page 

PLATE 17. A, Photomicrograph of a thin section of oil shale from Wheeler Ridge, Calif.; B, north-south section across axial

part of Wheeler Ridge anticline, Calif., showing stratigraphic relation of oil shale to beds producing oil^_ 172
OIL SHALE IN A PRODUCING OIL FIELD IN CALIFORNIA

By H. W. HOOTS

General features.—A considerable thickness of oil 

shale has been penetrated by a well drilled in the 

southwest corner of sec. 22, T. 11 N., R. 20 W., 

on the north flank of Wheeler Ridge, at the south end 

of San Joaquin Valley, Calif. This shale is similar to 

oil shale found in some of our Rocky Mountain 

States in that it contains no free oil but includes much 

detrital carbonaceous material, which when heated 

yields oil. Nearly continuous cores of this shale and 

associated fine sandstone and sandy shale were taken 

from depths of 1,869 to 4,090 feet, a range that 

represents a stratigraphic thickness of about 1,400 

feet. The cores were 4 inches in diameter. In 1924, 

just before the well was abandoned, the writer was 

permitted by officials of the Midland Oilfields Co. 

(Ltd.), of Fellows, Calif., to sample these cores for 

later examination.

Shale in some of the samples taken is dark brownish 

gray to black, has the appearance of hard rubber, 

and is finely laminated throughout. Dark carbonaceous laminae alternate with others of light buff-gray 

color, which are commonly calcareous. Small calcareous nodules from one-eighth to one-half inch in 

diameter are abundant in some of the samples. In 

other samples, not so rich in hydrocarbons, shale 

either alternates with laminae and thin beds of fine 

gray sand or is splotched irregularly with J^-inch to 

J^-inch patche's of sand not so fine in texture.

The dense brown rubberlike appearance of some of 

the shale suggested its bituminous character. Upon 

heating small crushed samples in test tubes it was 

found that different quantities of dark-brown oil were 

driven off, and that some samples, it was estimated, 

yielded as much as 25 per cent by volume of volatile hydrocarbons that condensed to oil. None of the 

samples, when crushed and subjected to the solvent 

action of carbon tetrachloride, ether, or chloroform, 

were found to contain free oil. Miss Taisia Stadnichenko, of the National Research Council, made 

additional tests with various solvents and obtained the 

same results. These tests, however, were applied io 

•only about a dozen small samples taken from the 

1,400 feet of shale penetrated by the well, and they 

do not prove that free oil is not associated with 

bituminous material in much of the shale. Free oil 

and oil residues are known to be associated with 

bituminous shale in other parts of California.

Microscopic character and richness.—An accurate 

statement of the character and richness of the entire

100368°—29

rock thickness penetrated by this well can not be given. 

Cores were taken from only part of the well. At the 

time of sampling the presence of oil shale was not suspected, and the 82 collected samples, an average of one 

sample for every 27 feet of depth, may not contain 

representatives olthe best oil shale penetrated by the 

drill.

Thin sections were made from some of the samples 

that appeared richest and were submitted to David. 

White for examination. His statements concerning 

the character and content of these shales appear 

below.

The carbonaceous shales found at different depths-in the well 

have been examined by means of thin sections cut both vertical 

and parallel to the bedding. All these sections show much crganie matter, including a rather largp amount of debris that 

consists largely of the outer coats of algae, which were more or 

less cutinized or fatty, together with a few spores of different 

kinds and some miscellaneous debris. In general aspect, chara^' 

ter, and arrangement of debris and "ulmic" colloidal matter rJl 

the specimens belong to the normal laminated type of oil shal% 

whether it be as old as the Devonian or as young as the Tertiar;\ 

In short, these shales are charactertistic bituminous or oil 

shales, in which, in general, only the somewhat decay-resistant 

organic structures are preserved.

Estimation from the thin sections of the possible, yield of tl •? 

shale is difficult, but I am inclined to[ hazard the forecast that 

shale like the thin layers from which some of the sections we~e 

cut would probably yield as much as 30 gallons of distillate to

the ton of rock. /

In addition to the algae, spores, and other organic 

remains noted by Mr. White, some thin sections show 

distinct outlines of calcareous Foraminifera, which, 

according to D. D. Hughes,1 belong to the genera 

Bolivina, Bvlimina,, and Buliminella. Dr. Paul P. 

Goudkoff 2 found these same forms to be common in 

comminuted samples of cores taken from depths belo^ 

3,040 feet. Higher in the well, between depths of 

1,900 and 3,040 feet, Foraminilera contained in tt^ 

cores, according to Doctor Goudkoff, are entirely 

arenaceous forms. -He found that remains of diatoms 

are either entirely absent or scarce in all samples 

examined. This statement applies equally well to 

thin sections.

^In hand specimens amber-colored fish scales 

noted to be abundant throughout practically all ttis 

cores. In one sample the crushed partial skeleton of a 

fish was preserved along the bedding plane of corrpact, finely laminated dark-brown shale.

* Oral communication.

* Letter dated Dee. 22,1926.

171
172 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19158

Of the available small samples having indications of 

at least moderately high content of carbonaceous 

material, those large enough for partial distillation 

tests were tested by the United States Bureau of Mines. 

Unfortunately, before the distillation tests were made 

the original small samples had been twice reduced in 

size for micropaleontologic studies, and as a result some 

of the best samples, including some of those examined 

by Mr. White and heated in test tubes by the writer 

were too small for distillation tests. Yields of oil 

from the tested samples are listed below.

Results of distillation tests on oil shale from Wheeler Ridge, Calif.

Depth (feet)

2, 646-2, 651

3,040

3, 196

3, 352-3, 358

3, 491-3, 496

3, 536-3, 538

Oil yield

(gallons to

the ton)

3.07

2.04

3.28

4.73

2.40

9.27

Specific gravity of^ oil from last sample, 0.9490. Not sufficient oil produced for complete distillation.

The accompanying photomicrograph (pi. 17, A) of 

one of the thin sections, cut normal to the bedding of a 

small sample taken from a depth between 3,475 and 

3,480 feet, illustrates the microscopic character of 

some of the best samples examined. Dark portions 

of this photograph appear in the thin section as darkbrown lamellae of carbonaceous material, which are 

intercalated with irregular stringers of a pale-brown 

(nearly colorless) substance, some of which is isotropic 

with an index of refraction less than 1.54. This substance is syngenetic and appears to be silica in the 

form of opal and incipient chalcedony. Minute 

grains of quartz and feldspar are abundant, and the 

outline and. inner structure of a foraminifer appear in 

the upper right quadrant of the picture. According 

to W. H. Bradley, of the United States Geological 

Survey, this and other slides appear to compare favorably in content of carbonaceous material to fairly 

good oil shales from the Green River formation of the 

Rocky Mountain region. The previously mentioned 

estimate, based on heating of test-tube portions, that 

some samples yield as much as 25 per cent by volume 

of volatile hydrocarbons that condense to form oil 

(about 30 gallons to the ton of rock) may be considered 

an approximation to the potential oil content of the 

best samples.

Age of the oil shale.—The Midland well was drilled 

on the outcrop of rocks considered as belonging to 

the Pliocene Etchegoin formation. The arenaceous 

Foraminifera found in the upper 1,000 feet of the 

cores, between depths of 2,000 and 3,040 feet, are reported by Doctor Goudkoff to be the same as those 

found in strata mapped by Arnold and Anderson 3 as

3 Arnold, Ralph, and Anderson, Kobert, Geology and oil resurees of the Coalinga 

district, Calif.: U. S. Qeol. Survey Bull. 398, PL 1,1910.

the Santa Margarita formation (upper Miocene) of the 

Pyramid Hills and Big Tar Canyon, in the Coalinga 

district. The calcareous Foraminifera found below 

3,040 feet in depth are considered by Doctor Goudkoff 

to belong to the Maricopa shale (upper and middle 

Miocene). It is fairly certain that most, if not all, of 

the oil shale at Wheeler Ridge is of Miccene age.

Stratigraphic relation of oU shale to o^produeing 

zone.—Many shows of oil and of ail am? gas w«re.obtained in the Midland well, and they were aU eea» 

fined to that portion of the well in which oil shale is 

common. (See pi. 17, E.} This striking relation may 

be due in part to the fact that the Miocene "brown 

shale" strata, in which oil shale occurs are the only 

beds that were cored and examined carefully for oil 

content. Nevertheless it is noteworthy that a column 

of rock containing considerable oil shale also yields 

strong shows of petroleum. This relation is substantiated and becomes even more striking when it is 

noted, as shown in Plate 17, B, that this same stratigraphic interval corresponds to most of the producing 

zone of the Wheeler Ridge oil field, only 1,100 feet 

south of the Midland well.

Significance of the stratigraphic relation.—Has the oil 

now being produced from porous strata hi the Wheeler 

Ridge field been derived from the abundant and varied 

detrital organic material of intercalatec1 oiLshale, or 

has it originated, according to the nwe commonly 

accepted theory for California oil, in deeper and possibly also more distant shale deposits, which may be 

composed largely of diatoms and their remains? The 

available evidence provides no answer to this question. 

According to experiments conducted by McCoy 4 and 

Trager,5 oil shale when subjected to pressure will 

yield free oil; but even though this .fact and the close 

stratigraphic relation between oil shale end petroleum 

production in Wheeler Ridge are certainly suggestive, 

the possibility must be considered that this relation is 

entirely accidental and that the Wheeler Ridge oil 

has been derived from another source. On the assumption that oil shale will yield petroleum under 

natural conditions resulting from deep bfirial and pronounced deformation, it must be conceded, that 

there is field evidence at Wheeler fRidge that supports 

a plausible theory for the origin of oil at this locality—a 

theory that is ideal in simplicity and tl at avoids the 

difficulties encountered by assuming migration of oil 

generated in deeper or more distant strata. Diatoms 

and Foraminifera associated with the oil shale may 

also have contributed oil to intercalated petroliferous • 

beds, but from their apparent scarcity in the oilproducing strata of this area it appears probable that 

they are of minor importance as source material.

Is typical oil shale, such as this at Wheeler Ridge, 

more common in fields that are producing oil than is

* McCoy, A. W., Notes on the principles of oil accumulation: Joiir. Geology, 

vol. 27, pp. 252-262, 1918.

5 Trager, E. A., Kerogen and its relation to the origin of oil: Am- Assee. Petroleum 

Geologists Bull., vol. 8, pp. 301-311,1924.
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 17

A. PHOTOMICROGRAPH OF A THIN SECTION OF OIL SHALE 

FROM WHEELER RIDGE, CALIFORNIA

Standard Oil Co. 

wel Is

IM.

Midland Oilfields Co.,Ltd 

well

Etchegoin formation , 

TP'iocene)

Oil-shale zone 

(good shows of oil ^ 

or oil and gas; 

Miocene)

NORTH-SOUTH SECTION ACROSS AXIAL PART OF WHEELER RIDGE ANTICLINE 

CALIFORNIA, SHOWING STRATIGRAPHIC RELATION OF OIL SHALE TO REDS PRODUCING OIL

OH, SHALE 1ST A PKODTJCING OIL FIELD IN CALIFORNIA 173

now generally recognized? Such oil shale may be of 

common occurrence in Pliocene as well as Miocene 

oil-yielding strata of California.

It will be noted from the photomicrograph (pi. 17, A) 

that unmistakable marine Foraminifera occur embedded within the fine laminations of rich carbonaceous 

material. These fragile forms are unbroken and show 

no evidence of having been reworked; they appear to 

prove that the oil shale is of marine origin. In this 

way the Wheeler Ridge shale is similar to the Devonian 

oil shales of Kentucky and Indiana but differs from the 

extensive Eocene deposits of oil shale in the Rocky 

Mountain region, which, according to Bradley,6 were

• Bradley, W. H., Shore phases of the Green River formation in northern Sweetwater County, Wyo.: U. S. Geol. Survey Prof. Paper 140, pp. 127-128,1926.

formed from organic sediments deposited in large 

inland lakes. . • i

It would appear that if typical oil shale will yield 

petroleum under natural conditions which have prevailed since its deposition, any stratigraphic zone of oil 

shale or other highly organic rock, whether of mr.rine 

or lacustrine origin and even though entirely devoid 

of recognizablefossils, should be considered an adequate 

source for petroleum deposit® in areas where overburden has been great or,where deformation has been 

intense. At Wheeler Ridge the oil-shale beds, together 

with about 4,000 feet of overlying Pliocene sediments, 

have been folded into an asymmetric anticline whose 

limbs dip 20° and 50°.

o