12

thick, and rather continuous in some areas; but in others it appears to have
been removed by erosion at an unconformity at the base of the basal Temblor

sandstone.

The bentonites in the Vallecitos area are believed to be clay alteration

products
the beds
currents,

of volcanic ash.

lenses of a lithologically similar bentonite.

Bedding and orientation of mineral grains locally in
suggest some secondary transportation, probably by submarine turbidity
The origin of the bentonite is believed to be from an eruption of
Eocene volcanoes near the Pinnacles to the west,

Pinnacles volcanoes contain

Table 3 shows a generalized stratigraphic column of the Vallecitos forma-
tions, including the clay minerals identified.

TABLE 3, - Generalized stratigraphic column, showing clays present in
Tertiary and Cretaceous formations in the Vallecitos area

Age Unit Clay minerals present
Pleistocene Landslides and Alluvium Mica clays (illite) Montmoril-
Recent terraces lonite.
Pliocene Etchegoin-Jacalitos(?) Mica clays (illite).
U. Miocene(?) | Oro Loma redbeds and marl, Sepiolite(?) (in marl)
Pliocene undifferentiated (illite).
Lower Miocene | Temblor Mica clays (illite).

Eocene

Kreyenhagen shale

BENTONITE BEDS

Mica clays (illite) (montmo-
rillonite in bentonites),

Domengine Mica clays (illite).
Yokut Kaolin.
Lodo Arroyo Hondo
Sh MBR
Cantua ss Mica clays (illite) minor
MBR amounts of kaolin.
Paleocene Cerros Sh MBR
Moreno Sh -
Panoche Fn Mica clays (illite).

It is important to note that volcanic activity during the time of forma-
tion of sedimentary formations in California may be the source of swelling

clays foundL5/

in some California petroleum-reservoir rocks,

In the Tejon-

Grapevine area of the San Joaquin Valley of California, Morris, Aune, and

Gatesl6

point out that volcanic activity during formation of many of the

petroleum-reservoir-rocks of the Miocene epoch may explain the presence of
swelling clays found in the few important California petroleum reservoirs

15/ Morris, F. C., Aune, Q. A., and Gates, G, L., Clay in Petroleum Reservoir
Its Effect on Permeability With Particular Reference to the

Rocks:

Tejon-Grapevine Area, Kern County, Calif.:

Investigations 5425, 1958, 65 pp.
16/ Work cited in footnote 15.

Bureau of Mines Rept. of


ML

VOLUME,

30-MINUTE FILTRATE

40

30

xy
°

we

INITIAL DRILLING FLUID
POOR DRILLING FLUID
TREATED WITH
4 LB. PER BARREL BENTONITIC CLAY
1.7 LB. PER BARREL SODIUM’ ACID
PYRO PHOSPHATE

!

() 2

SODIUM CHLORIDE CONCENTRATION,

4

FIGURE 13. - Effect of Salt (sodium-chloride) on the Filter Properties
at Room Temperature of aMud Containing California and
Wyoming Bentonite.

duction in the viscosity of the mud,

6
LB. /BBL.

33

responded to treat-
ment with sodium
acid pyrophosphate
to the same degree
as the Wyoming ben-
tonite suspension,
Thus, treatment by
sodium acid pyro-
phosphate is pref-
able for suspen-
sions of these ben-
tonitic clays. The
quebracho treatment
contained sodium
hydroxide, which
apparently in-
creased the viscos-
ity of the benton-
itic-clay suspen-
sions. This also
could increase the
yields of the ben-
tonitic clays and
should be consid-
ered when quebracho
treatment is used,
Also, quebracho
treatment of the
suspensions of ben-
tonitic clays 1, 3,
and 11 improved the
filter properties,
as indicated by the
decrease in the vol-
ume of filtrate from
13 to about 5 ml.,
whereas quebracho
treatment did not
improve the filter
properties of the
Wyoming bentonite
suspension appre-
ciably.

Water used in the solution of chemicals added to the muds will cause a re-

To show the effect of the chemical added,

the viscosity of the muds was measured, and the results are listed in table 9.
Water was added to portions of the untreated muds, and the viscosity of the

diluted muds was recorded in table 9 and in figures 16-18.
listed under the column headed "Blank" and are plotted on figures 16-18 with
dashed lines.

These data are


29

TABLE 6. - Yield density and filter properties of selected
Vallecitos bentonites in saturated salt water

Saturated NaCl solution
Yield, Weight Density] Filtrate
bbl, mud/ton| 1b./ 1b./ volume,

Description of clay sample dry clay ft,3 gal. |ml,/30 min,| pH
A, California bentonitic clays:
Sample 1, - 70-ft. tunnel.. 40 78.8 10.5 130 7.97
Sample la, - 70-ft. tunnel
+ 3 percent Na7C03....... - - - - -
Sample 11........eceeeeeeee 59 77.6 10.4 97 6.11
Sample 16a.........e0eeeeee 25 82.0 11.0 104 7.68
Sample 3......ccsseeeeseeee 38 79.6 10.6 121 -
B,. California dry-lake clay.... 20 84.7 11.3 86 7,80
C. Wyoming bentonite........... 36 79.9 10.7 113 8.32

Treatment of a Poor Drilling Mud

In drilling an oil-well the drilling fluid is composed primarily of a dis-
persed clay from the shale formations penetrated by the bit, For the most part
these native clays lack the essential properties for a satisfactory drilling
mud, and small amounts of bentonitic clays are added to improve the properties
of the hole mud, To test the effectiveness of the Vallecitos bentonites in the
laboratory, a low-quality drilling fluid was prepared from Ventura yellow clay
and water, and different quantities of the bentonitic clay were added to the
poor mud, Ventura yellow clay is similar to other clays frequently penetrated
in California, The improvement in the filter loss from the low-quality mud by
adding different bentonitic clays and Wyoming bentonite is shown in table 7 and
figure 12. The results show that treatment of the mud with 8 percent (by
weight) of Vallecitos bentonitic clay or 4 percent (by weight) Wyoming benton-
ite, decreased the API filtrate from 57 to about 18 ml.

At 200° F, the API filtrate of the poor mud containing 8 percent benton-
itic clay was 36 ml,, and the filtrate from the same drilling fluid, treated
with 4 percent Wyoming bentonite, was 28 ml., compared with 99 ml, from the
poor mud before treatment.

After the addition of California bentonitic clays or Wyoming bentonite
to the mud, chemical treatment often was necessary to reduce the viscosity.
Since Vallecitos bentonite sample 3 and Wyoming bentonite suspensions reacted
similarly to treatment by sodium-acid pyrophosphate (see fig. 18) the mud
samples were treated with 1,65 pounds per barrel of the acid pyrophosphate.
As shown in table 8, the viscosity of a mud treated with 8-percent bentonitic
clay, No, 3, was 210 grams Stormer; and, after treatment of the mud with 4
percent Wyoming bentonite, viscosity was about 135 grams Stormer. In all tests
the mud treated with 8 percent Vallecitos bentonitic clay had a substantially
higher viscosity than the mud treated with 4 percent Wyoming bentonite, even
after chemical treatment.


38

STORMER VISCOSITY AT 600 RPM. AND ROOM TEMPERATURE

oe
8

300

250

DRIVING WEIGHT, GRAMS
= x
& 8

3
°

o
°

--o
CALIF. DRY-LAKE CLA

Y

— ren

~ SS
CALIF. BENTONITIC sek
CLAY

YY NO.3 ~>la9

WYOMING BENTONITE —q>>—P—~> |

\Woatie. sewtonitic

CLAY NO.I6A

3 4

SODIUM ACID PYROPHOSPHATE

5 6

7
CONCENTRATION , LB. /eBL.

FIGURE 18. - Effect of Sodium Acid Pyrophosphate on Viscosity of Drilling
Muds Containing California and Wyoming Bentonite.

TABLE 9. - Effect of viscosity reducers on drilling fluids
containing bentonitic clays

Quantity of Stormer viscosity at 600 Filtrate
material r.p.m, and room temperature | volume
Material | added to Treated drill- Blank room
added to | drilling ing fluids |Driving temp.
Clay-sample |drilling fluid, Driving |Centi-| wt., |Centi-|30 min.,
description fluid 1b./bbl, wt., gm.| poises gm. poises ml, pH
A. California
bentonitic
clays:
1. 70-foot
tunnel..,.|Tetra 0.00 330 81 330 81 - 9.87
Do. sodium 05 330 81 325 79 -
Do. phosphate .10 330 81 320 78 -
Do. -40 320 78 297 71 -
Do. 1.15 270 63 245 56 -
Do. 2.19 205 45 190 40 - -



In recent years very little California high-yield, swelling-type bentonite
has been used in oil-well drilling muds; however, hectorite, which is a magne-
sium and Llithium-rich clay mineral of the montmorillonite group, was used in
recent years for filtering, decolorizing, and producing organic-clay complexes
used in manufacturing paints, Hectorite is produced in Southern California,
Several years ago, large quantities were used in oil-well drilling muds.

California bentonite produced in recent years was as follows:

Quantities of California bentonites
sold or used, in short tons

1954 1955 1956 1957
Filler (other than paper or paint).......| 1,789 1,614 245 647
Oil-well drilling mud...... seeee - - - 50
Chemical..........4.. . 40 411 120 80
BECT. oc eee eee ee eees sees - 218 525 -
Trace minerals. errr) sence wees - - 388 -
Concrete admixture, dams, etc............ - 123 - -
Testing purposes... - 150 -
Enameling.. - - 54
Remainder, 1,576 2,190 3,012
Total... 3,942 3,618 3,843

Many clays, including bentonites used in oil-well drilling muds, have been
discussed by Larsen.10/ He describes the properties of several California
clays that have been used in oil-well drilling muds. He also describes the
function of clays in the successful drilling of oil-wells.

Federal Bureau of Mines Mineral Market Report MMS 2806 shows that, in the
United States, the quantity of bentonite sold or used by producers in 1957 de-
creased 8 percent in quantity, and 3 percent in value from the alltime high
established in 1956.

Thus, the oil industry was the largest user of bentonites. Oil-well drill-
ing muds (40 percent) and filtering and decolorizing of mineral oils and greases
(9.6 percent) consumed 695,817 tons, or one-half, of the total bentonite used
in 1957, Foundry sand used 26 percent, or 376,833 tons, and filtering and de-
colorizing vegetable and animal oils, 4.3 percent, or 62,832 tons, of the total
bentonite production. The remainder, 309,086 tons, or 22 percent of the na-
tional output, went for a variety of uses.

10/ Larsen, Delmar H., Use of Clay in Drilling Fluids: Clays and Clay Tech-
nology Proc., Ist Nat. Conf, on Clays and Clay Technology, California
Division of Mines, Bull, 169, July 1955, pp. 269-281.




44

VALLECITOS PETROLEUM GEOLOGY AND ITS RELATION
TO THE BENTONITES DEPOSITS

In June 1955 Long and Hedges completed a discovery oil well, H and H1A,
in the Vallecitos field, which is only a few miles from the outcrops of the
bentonites. In February 1958 there were 15 producing wells in the field, with
a total production of 1,648 barrels of 35° API oil per day. In 1957 81,008
barrels of oil was produced from the field, from the Yokut sandstone of Eocene
age. A pipeline outlet from the field is contemplated,

Petroleum apparently accumulates as a result of folding and faulting. A
large displacement pre-upper Kreyenhagen fault system, which is exposed in
outcrops in section 14, R, 10 E., T. 16 S., on the north limb of the Vallecitos
syncline and in sections 17 and 20, R. 11 E., T. 17 S., on the south limb of
the syncline, is believed to play an important role in trapping petroleum in
Eocene sands, Likewise, a post-Temblor fault, the trace of which outcrops in
section 6 R, 11 E,, T. 17 S., may play an important part, This latter fault
was not traced into the Etchegoin-Jacalitos formation and may be reflected in
anticlinal warping rather than in faulting in the younger sediments of the
Vallecitos syncline.

Fold structures: generally appear to plunge to the east in the vicinity of
the above-mentioned faults, accumulation is not likely to the west due to the
lack of closure, allowing the oil to escape updip to the surface. Accumulation
is not likely in the Miocene Temblor sands, since these are too close to the
surface. Accumulation in the Eocene Domengine and Yokut sands east of the
above-mentioned pre-upper Kreyenhagen fault would seem likely,

Kreyenhagen bentonites appear on both sides of the Vallecitos syncline.
They should be penetrated by most deep wells in the Vallecitos, This could
not be proved, however, in electric logs or micrologs or from core descriptions
of the Kreyenhagen formation, At the horizons where the bentonites would be
expected, sloughing rather than swelling was indicated on the single microlog
available; however, swelling may have preceded the sloughing. Sloughing was
evident at some other shale horizons also.

From Vallecitos-area drilling reports, no drilling or completion problems

could be related directly to the bentonite clays, as most difficulties seemed
to appear at other stratigraphic horizons.

INT. © BULOFMINES.PGH..PAL 317


16

BLOCK TEMPERATURE, DEGREES CENTIGRADE

100
T

500 700
T T T

300
TT T T

SAMPLE | |
Tr
2
3
°
s
a
SAMPLE 2
SAMPLE 3
SAMPLE 4
SAMPLE 5

L_1_}-J_t i 1 1 | ||

1100}
1

100 300 500 700
BLOCK TEMPERATURE , DEGREES GENTIGRADE

900

1100}

FIGURE 6. - Differential Thermal Analysis Thermograms of Vallecitos

Bentonite Samples 1 Through 5.


34

80
3
no:
70 o os
we
nN ase
any
opr?

60
a
=
ur 50 —
=
>
a
$ &

SZ
u 40 Y
e So,
° \)
a 2,
a x
2
— 30 —-
[4
i
a
z
Ww
5 20 INITIAL DRILLING FL
2 UID
= POOR DRILLING FLUID
= TREATED WITH
t LB. PER BARREL BENTONITIC CLAY
8 7 L8.PER BARREL SODIUM ACID
PYRO PHOSPHATE
10
o
2 4 6

SODIUM CHLORIDE CONCENTRATION, LB. /eaL.

FIGURE 14. - Effect of Salt (sodium chloride) on Filter Properties at 200°

F. of a Mud Containing California and Wyoming Bentonite.


CONTENTS

Summary and introduction...
Acknowledgments...
Properties and uses o eee eer eccccnseee
Bentonite production and consumption in the United States
and in California..
Prices.......e00.
Vallecitos bentonites...,
Location and accessibility............
Physical features and climate.........
Definition of terms.........eeeeeeeeee
Description of Vallecitos bentonites........
Method of sampling clay deposit............
Clay-mineral content ........ ccc eee e eee ee ees

Clay-mineral identification by differential
thermal analysis...... ccc cece cece eee e eee nee

Preparation of samples for determining clay-

mineral CONCENE. .....e cece eee eee ene ences
Results and discussion of thermal studies.
Reference clay minerals........ eeeeee

Properties of drilling fluids containing Vallecitos
bentonite clays.....
Laboratory testing procedure,
Yield and filter properties........
Treatment of a poor drilling mud......
Salt contamination of a poor mud,.......
Chemical treatment of muds containing bentonitic
clays... eeeeeee
Economic evaluation......cceccescceceeccecceecees
Vallecitos petroleum geology and its relation to the
bentonite deposits...



27

could be obtained graphically. From the graph of the viscosity expressed in
centipoises with the corresponding weight of clay in the suspension, the quan-
tity of clay in a 15-centipoise mud was determined,

To determine the yield in salt (NaCl) water, which is similar to solutions
encountered in drilling oil wells, the above procedure was repeated, except
that a saturated sodium chloride solution was used in place of distilled water,

The density of these muds was measured in a "Mudwate" hydrometer.

The filtrate volume was collected from the API filter press operated for
30 minutes at 100 p.s.i. and room temperature, The API filter press consists
of a cylinder 3 inches in diameter and at least 2-1/2 inches high. The bottom
of the cylinder contains a sheet of 9-cm, filter paper and the filtration area
below the mud is 7.1 + 0.1 square inches. Below the support for the filter
paper is a tube through which the filtrate flowed into a graduated cylinder.
The top of the press contains connections through which air at 100 p.s.i. en-
tered the filter press.

Yield and Filter Properties

Outcrop samples of the bentonite deposits were taken from different beds
and different areas along the outcrop, as shown in figures 2 and 3. The re-
sults of the laboratory tests of these samples are shown in table 5. As shown
in table 4, the deposits contain bentonitic clays in three beds in three areas
having average yields of about 50 barrels of 15-centipoise (cps.) mud per ton
of dry clay, These are East area (bed 1), West area (bed 1), Central area (bed
2), and West area (bed 3). Only one or two outcrops were sampled from some of
these sections, but there are several sections where substantial deposits of
bentonite having an average yield of about 50 barrels of 15-cps, mud per ton
of dry clay are indicated. The samples of Wyoming bentonite tested in this
study had a yield of 100 to 120 barrels of 15-cps, mud per ton of dry clay.
Bentonitic clay from the East area (bed 2) and Central area (bed 1) had average
yields of 38 and 33 barrels of mud per ton of dry clay. Sample 15 from the
East area (bed 3) had a yield of 22 barrels of 15-cps. mud per ton of dry clay,
These yields are not as high as those for the clays from most of the other
areas tested,

The filter properties of all suspensions of the bentonitic clays were
good, except for sample 14, East area (bed 3), and one sample from Central
area (bed 1). The average filter loss by the API 30-minute test from 15-cps.
suspensions of all the samples except the foregoing samples was about 13 ml,
The filtrate volume collected from a 15-cps. suspension of Wyoming bentonite
was 12 ml.

The yield of some samples of bentonite were determined in saturated salt
(sodium-chloride) solutions. This part of the study was made because, with
the advent of offshore drilling, the need for clays suitable for use in salt-
water muds assumed new importance. The results of the tests indicate that
yields of the Vallecitos bentonites were slightly better than those obtained
from Wyoming bentonite, The results are listed in table 6.


13

studied, These clays, although constituting only a small part of the host
rock, were shown to be an important factor influencing the fluid~flow proper-
ties of the rocks.

Method of Sampling Clay Deposit

To facilitate testing of the bentonite deposit, samples were collected at
various intervals along the length of the outcrops of the bentonite beds during
the field examination, Samples were sealed in jars to preserve their natural
water content before testing. The location of these samples is shown in figure
4, Samples representing typical strata of the several related geologic forma-
tions were also collected for making clay-mineral determinations for these
strata,

The bentonite samples were collected from clay that appeared to be free of
contaminants foreign to the bentonite deposit, Most of the samples were taken
from a random spot with respect to the width of the bed, Samples were collected
about 1 foot below the surface, usually in wet clay.

Sample 1 was taken from a tunnel cut into one of the extensive bentonite
beds to be sure to avoid contamination by materials at the surface, The tunnel
extended about 70 feet into the bentonite bed, It was estimated to be 35 feet
beneath the surface.

Samples 2-15 were taken from outcrops where the bentonite bed sampled is
thick enough to be minable by open-pit methods, other factors being favorable.
In some areas, such as at the sample 5, 6, 7, and 8 localities, rugged terrain
might preclude an economic mining operation at present,

Sample 16, collected from an outcrop on the north limb of the syncline may
be too thin to be minable by the open-pit method, although this sample was com-
posed of clay with drilling mud properties superior to those of any other sam-
ple taken,

Clay-Mineral Content

The bentonites were examined to determine the clay mineral content, Ben-
tonites are known to contain primarily clay minerals of the montmorillonite
group. The dominant clay minerals in the bentonites from San Benito County
were identified by using three methods: (1) Differential thermal analysis,
(2) X-ray diffraction, and (3) optical and dye-staining. Method 3 was pre-
viously described in detail,1//

The results of these determinations showed that these clays contain pre-
dominantly montmorillonite clay minerals, The differential thermal analysis
data are shown in figures 5 through 11.

17/ Work cited in footnote 15 (p. 12).


BLOCK TEMPERATURE, DEGREES GENTIGRADE

100 300 500 700 900 00
c T T T T T T T T T 1
SAMPLE 14 |
+r
>
3
&
—L
SAMPLE 15
SAMPLE 16
PINNACLES

l | i 1 1 1 l 1 l J

100 300 500 700 ‘900 1100
BLOCK TEMPERATURE , DEGREES CENTIGRADE

FIGURE 9. - Differential Thermal Analysis Thermograms of Vallecitos
Bentonite Samples 14 Through 16 and a Bentonite From
Pinnacles, Calif.

19


BLOGK TEMPERATURE , DEGREES CENTIGRADE

100 300 500 700 900
r T T T T T T T T

100
1

GRUNDITE (susmica)
GOOSE LAKE, ILL.!

keouv-|

GRUNDITE 50%, GOOSE LAKE, ILL.
MONTMORILLONITE 50%, OSAGE , WYO.
i I

TT
>
3
3
&
a
MONTMORILLONITE
OSAGE, WYO
Tr
3
3
3
&
+t
KAOLINITE

DRY BRANCH, GA.!
API NO. 4

k100.uv-}

L L L L 1 1 L Ll
100 300 500
BLOCK TEMPERATURE , DEGREES CENTIGRADE

1 L L J
700 900 100

FIGURE 5. - Differential Thermal Analysis Thermograms of Reference Clay Samples.

15


28

TABLE 4, - Properties of 15-cps. viscosity suspensions of Vallecitos

bentonitic clay from different beds and areas

Bed East Area

Central Area

West Area

1 Av. 3 samples

Yieldl/ - 51 bbl. /ton
Filtrate2/ - 13 ml,/30

Av. 5 samples
Yield - 33 bbl./ton
Filtrate - 14 ml,

Av. 2 samples
Yield - 65 bbl,/ton
Filtrate - 15 ml.

min, 1 of 5 samples had
filtrate over 20 ml.

2 Av. 2 samples
Yield - 38 bbl./ton
Filtrate - 13 ml,

1 sample
Yield - 50 bbl./ton -
Filtrate - 17 ml.

3 2 samples 1 sample
Yield - 56 bbl./ton
Sample 13 Filtrate - 12 ml.

Yield - 22 bb1l./ton
Filtrate - 9 ml.
Sample 14
Yield - 59 bbl./ton
Filtrate - 30 ml.
1/ Yield in barrels of 15-cps, viscosity mud per ton of dry clay determined by
API standard test procedure, API-RP 29, Recommended Practice for Standard
Field Procedure for Testing Drilling Fluids, 4th ed., May 1957.
2/ Filtrate, ml. in 30 minutes, determined by API standard filter test, API-RP
29, 4th ed., May 1957,

TABLE 5. - Yield and filter properties of Vallecitos clay samples studied

Yield, bbl. 15-cps, | API filtrate,
Source of sample Sample description |mud per ton dry clay | ml. 30 minutes
Vallecitos, bed 1 1 (70-ft, tunnel) 53.0 13.0
Do. 2 50.0 13.4
Do. 3 50.0 12.0
Do. 4 37.0 10.8
Do. 5 26.0 13.6
Do. 6 33.5 9.2
Do, 7 37.3 24.3
Do. 8 33.0 10.2
Do. 9 70.0 20.0
Do. 10 59.0 11.0
Vallecitos, bed 2 11 38.0 13.0
Do. 12 49.5 17.4
Vallecitos, bed 3 13 22.0 8.8
Do. 14 59.0 30.0
Do, 15 56.0 12.4
Vallecitos, north
limb of syncline 16 81.0 13.0
Do. 16A 37.3 27.4
Pinnacles Eastern 49.5 11.0
Wyoming bentonite - 110 11.2



10

waters, Below the zone of weathering the bentonite is medium gray, contains
about 30 percent water, and exhibits a blocky fracture pattern, Faint bedding
is often visible.

The bentonite beds occur at numerous stratigraphic horizons in the Eocene
Kreyenhagen shale and are most abundant in that formation on the south limb of
a large overturned syncline.
This syncline finds surface ex-
pression in the Vallecitos,
Since the south limb of the
syncline is overturned, the ben-
tonites likewise are overturned
and dip south, at an angle as
low as 30° in some outcrops,
under the older sediments
making up the Diablo Range,
which in this area is a struc-
tural, as well as a physio-
graphic ridge.

The Kreyenhagen shale, on
the south limb of the Vallecitos
syncline, consists mainly of
diatomaceous, porcelaneous,
platy shales, with thin, argil-
laceous interbeds. The appar-
ent thickness of the formation
ranges in this area from about
3,000 to 10,000 feet, Most of
the variation is in the basal
portion of the formation and
appears to result from relative
vertical movement of opposite
sides of Eocene fault zones.

The lowest bentonite beds
in the formation occur within
a few hundred feet of the strat-
FIGURE 2. - Dry Surface of Vallecitos Bentonite Outcrop, igraphic base. Where displace-
San Benito County, Calif. ment due to faulting has caused
much thicker apparent sedimenta-
tion, the lowest bentonites are found several thousand feet above the base
stratigraphically. The thickness of the Kreyenhagen shale above the lowest
bentonites is fairly constant, This would suggest that major Eocene faulting
in this area ceased before deposition of the bentonites,

The thickest, most widespread bed is near the stratigraphic base of the
Kreyenhagen formation, except as noted above, Typical outcrops are shown in
figure 3, Locally, there may be one clay bed at a lower horizon, The thick
clay bed is generally structurally overturned and, where observed, has a thick~
ness varying between 60 and 120 feet. Part of the variation in thickness may
be due to deformation during folding.


The results of this study indicate that the Vallecitos bentonites are
suitable for use in oil-well drilling muds, although they are not of as good
quality for this purpose as the Wyoming bentonites, Except for samples con-
taining gypsum as an impurity from localized areas, all samples tested exhib-
ited good filter properties, Yield properties are comparable with, or supe-
rior to, those of most other California bentonite deposits of appreciable size.
To prepare a drilling-mud suspension or to treat a poor drilling mud, about
twice as much Vallecitos bentonite as Wyoming was needed, Ground and sacked
Wyoming bentonite in California cost (1958) about $40 per short ton of clay,
including a shipping cost of $23 per ton, Although the quality of the San
Benito bentonite clays is not as good as that of the Wyoming bentonites, the
cost of the San Benito clays delivered in California oilfields is estimated to
be much less than the cost of the clay from Wyoming. The clay deposits outcrop
in an area not far from many California oilfields and irrigation canals,

ACKNOWLEDGMENTS

Grateful acknowledgment is made to the California Division of Mines,
Gordon B. Oakeshott, Chief, and members of his staff for information, particu-
larly geologic information, of the Vallecitos area. Thanks are due the follow-
ing members of the staff for reviewing the manuscript and making helpful sug-
gestions: Charles W. Jennings, George B. Cleveland, and Fred R. Kelly.

Special thanks are extended to C, W. Prewett and Joseph Merrow of the
Shell Oil Co. for information of the Vallecitos area and for reviewing the
manuscript and offering helpful suggestions.

Thanks are given also to A. L. Frye, Waterflood Oil Co., for reviewing
the manuscript and making many helpful suggestions.

PROPERTIES AND USES OF BENTONITES

Bentonites, particularly swelling bentonites, are used by the petroleum
industry for preparing drilling muds, because the addition of smali quantities
of bentonites decreases the filtrate volume of the drilling mud, Bentonites
also supply gel strength and thixotropic properties to drilling muds. These
properties are necessary to suspend drill cuttings, particularly when circula-
tion is stopped, and to prevent the cuttings from settling in the long column of
mud and packing around the drill pipe, possibly resulting in a stuck drill pipe.

The drilling fluid is recognized as a major factor in successful drilling
of deep wells. The proper use of a good drilling md not only prevents costly
delays in drilling caused by lost circulation, stuck pipe, or blowouts but
eliminates the need for costly strings of casing in the hole during drilling.
Thousands of feet of open hole may be maintained without setting pipe in a
hole containing a good mud. The quantity of bentonite used in muds varies
widely and depends on local conditions.

The drilling-mud industry is essentially a development of the last 30
years, When use of the rotary method of drilling increased following the dis-
covery of oil at Spindletop, Tex., in 1901, attention was given the function


25

It generally does not swell appreciably in contact with water, A thermal curve
of clay sample from Dry Branch, Ga. (API reference 4) shows that a single en-
dothermic peak at about 605° C. and an exothermic peak at 975° C, illustrate
the thermal characteristics of this clay group. Thermal curves of individual
members of the group will show that the endothermic peak may occur as low as
550° C. for diaspore and as high as 690° C, for dickite; however, the exother-
mic peak for both of these kaolin members remains very close to the 975-990° C,
range. Because of the degree of crystalline development it was necessary to
use a less sensitive scale (100 microvolts per inch) to record the thermal pat-
tern of kaolin, as compared to a 20-microvolt-per-inch scale for the micas and
montmorillonite clays.

The thermal curves of clays from San Benito County, Calif., shown in
figures 6-11, exhibit characteristics indicating that montmorillonite is pres-
ent in samples 1-16 and is also in the Pinnacles sample. The magnitude of the
thermal reactions of the San Benito clays does not appear to be as great as
those of the reference montmorillonite, indicating that the former clays may
not have the degree of crystalline development or the purity of the reference
clay,

Small amounts of organic matter are indicated by the low exotherm between
250° and 450° C, in the thermal curves for sample 4 (fig. 6); samples 6, 7, and
9 (fig. 7); sample 12 (fig. 8), and samples 14 and 15 (fig. 9). In most in-
stances the quantity of organic matter is not significant and should be ex-
pected to be present in almost any outcrop sample,

Indication of the presence of mica-clay minerals is apparent in the ther-
mal curves by the endotherm between 500° and 600° C. of clay samples 12-14 and
the Pinnacles sample. Only the faintest hint of the presence of mica clays is
indicated by this endotherm in samples 4-6 and 15. These clay samples probably
are of the mixed-layer type. The strongest indication of mica clay was found
in clay sample 13 (fig. 8). The data listed in table 5 show that sample 13 has
the lowest yield, 22 barrels per ton, of any of the clays examined; however,
the filter characteristics of this clay are very good at 8.8 ml. per 30 min-
utes, The thermal curve for clay sample 16 approximates the curve obtained
from the Osage, Wyo., montmorillonite reference clay more closely than any of
the other clay samples.

Table 5 shows that the mud yield for this sample was high, 81 barrels per
ton, and the filter qualities are good also, 13,0 m. per 30 minutes compared
with a yield for Wyoming bentonite of 110 barrels per ton and a filter rate of
11.2 ml. per 30 minutes,

DTA thermograms were made to identify the predominant clays associated
with stratigraphic units present in the Vallecitos area. Thermal curves of
these clays are shown in figures 10 and 11. Mica-clay minerals predominate in
the outcrop sample from the Etchegoin-Jacalitos(?), Upper Miocene(?) marl,
Lower Temblor, and the Upper Panoche. The presence of montmorillonite may be
detected in the thermal curves of each of these samples. Carbonates are evi-
dent in the thermal curve for Upper Miocene(?) marl by the strong endotherms at
780° and 880° C.; these two peaks have been virtually eliminated by treating


22

(Al203), which does not undergo thermal reactions throughout the temperature
range to be studied, The other terminal is placed in the powdered material
being analyzed. This arrangement permits a record to be obtained of the endo-
thermic (heat-absorbing) and exothermic (heat-liberating) effects by measuring
the temperature at which these reactions take place as the unknown and the
standard are heated simultaneously at a constant rate. The temperature-differ-
ence measurement is obtained by using a differential thermocouple, which is two
thermocouples connected in series opposition. For a given clay mineral the
endothermic and exothermic reactions take place at the same relative tempera-
ture; therefore, once a thermogram has been obtained from a known clay mineral
it may be used for identification purposes by comparison with thermograms of
unknown clay minerals.

The clay-mineral groups montmorillonite, micas (illites), and kaolin yield
different enough thermograms to make the method particularly useful for clay
identification, Identification of pure clay minerals from thermal curves is
relatively simple; clay samples that contain components and impurities can be
identified in more complex mixtures. Some investigators19/ have reported semi-
quantitative application of differential thermal analysis for determining the
degree of purity of a particular clay mineral.

The temperature of the furnace is raised at a uniform rate of 10° C. per
minute up to a maximum of 1,100° C., by means of a commercial electronic pro-
gram temperature controller. This equipment also may be used to control the
cooling rate of the furnace, so that reversible reactions may be studied.

Thermocouple terminals are connected to the basic recorder unit, so that
the differential potential between the unknown and the reference material is
plotted on the x-axis and the block temperature is plotted along the y-axis.
Before the differential potential is received by the recording potentiometer it
is passed through a d.c. preamplifier equipped with a scale multiplier to ob-
tain necessary sensitivity. This feature permits adjustment of full-scale de-
flection from +25-microvolts to +l-millivolt, Exothermic peaks are plotted
upward and endothermic peaks downward from the neutral axis.

The pure nickel sample holder was made from a design recommended by Pask
and Warner .20. Approximately 0.8 gram of clay is required for each analysis.
Platinum and platinum-10 percent rhodium, 32-gage wire was used in all thermo-
couple circuits.

Thermal patterns of clay reference materials are illustrated in figure 5.
Thermal patterns of 17 outcrop samples of clays from the Vallecitos area of San
Benito County, Calif., are shown in figures 6 through 11.

19/ van der Murel, H. W., Quantitative Differential Thermal Analysis of Clay
and Other Minerals: Am, Mineral., vol. 41, No. 3 and 4, 1956, pp.
222-244,

20/ Pask, Joseph A,, and Warner, Maurice F,, Differential Thermal Analysis
Methods and Techniques: Am. Ceram, Soc. Bull., vol. 33, No. 6, June
15, 1954, pp. 168-175.


dii

TABLES

Page

Bentonite sold or used by producers in the United

States, 1955-57, by States... ..... cece eee eee cece eens 5
Bentonite sold or used in the United States in 1957,

by kinds and USCS. ...ceeeecceeercscccsccevevcseveees 7
Generalized stratigraphic column, showing clays

present in Tertiary and Cretaceous formations in

the Vallecitos area..... cece cece eeeceeeeeeceeeeees 12
Properties of 15-cps., viscosity suspensions of

Vallecitos bentonitic clay from different beds

ANd ATCAS LL eee eee cece cere cece eceeceteetseeecesces 28
Yields and filter properties of Vallecitos clay

samples studied....... rrr
Yield density and filter properties of selected

Vallecitos bentonites in saturated salt water....... 29
Effect of clays on filtrate volume and viscosity

Of A POOT MUG... . reece rece cer ece ee cceweececseeees 30
Effect of salt (sodium chloride) on drilling fluid

containing bentonitic clayS..........0008 eeeeceees 32
Effect of viscosity reducers on drilling fluids

containing bentonitic clays... ..... cc cseee reese eeeee 38

28



ii

10.

ll.

12.

13,

14,

15.

16.

17.

18.

ILLUSTRATIONS

Location of Vallecitos bentonite deposits relative
to California oilfields... seen eeees
Dry surface of Vallecitos bentonite outcrop, San
Benito County, Calif... cc cece cece eee cece ences
View of Vallecitos bentonite outcrop.... oe ecccee
Location of outcrop-sample sites in Vallecitos
bentonite deposits, San Benito County, Calif..... .
Differential thermal analysis thermograms of
reference clay SampleS.....ccccecccccscevcccccecee
Differential thermal analysis thermograms of
Vallecitos bentonite samples 1-5.........
Differential thermal analysis thermograms o
Vallecitos bentonite samples 6-10............eee0e
Differential thermal analysis thermograms of
Vallecitos bentonite samples 11-13.............04-
Differential thermal analysis thermograms of
Vallecitos bentonite samples 14-16 and a bentonite
from Pinnacles, Calif....ccccc cece eee c cece ee eeeee
Differential thermal analysis thermograms of samples
from Etchegoin, Upper Miocene(?) marl untreated,
Upper Miocene(?) marl treated, and Lower Temblor
formations in Vallecitos........ ccc cece cece ee eeeee
Differential thermal analysis thermograms of samples
from Yokut and Upper Panoche formations in
Vallecitos...ceceescc cece cneeecenreeeseeeeeescees
Effect of California and Wyoming bentonites on
filter properties of a poor drilling mud..........
Effect of salt (sodium chloride) on the filter
properties at room temperature of a mud con-
taining California and Wyoming bentonites.........
Effect of salt (sodium chloride) on the filter
properties at 200° F, of a mud containing
California and Wyoming bentonites..... see eeees
Viscosity changes resulting from the addition of
salt (sodium chloride) to drilling muds con-
taining California and Wyoming bentonites.........
Effect of tetrasodium pyrophosphate on the vis-
cosity of drilling muds containing California
and Wyoming bentonites.......ceceeeee cece cee eeeee
Effect of quebracho on viscosity of drilling muds
containing California and Wyoming bentonites......
Effect of sodium acid pyrophosphate on the vis-
cosity of drilling muds containing California
and Wyoming bentonites...........006 ecw cece eee eee

15
16
17

18

19

20

21

31

33

34

35

36

37

38


11

This thick bentonite bed is continuous along the strike for about 13 miles
or more, except where offset by faults or covered by Quaternary landslides.
There is another rather continuous bentonite bed about a 100 feet strati-
graphically above this bed. Locally the intermediate shales may be missing,
and the two beds may be combined into one. This upper bed is somewhat less
continuous than the main bentonite bed,

FIGURE 3. - View of Vallecitos Bentonite Outcrop.

Above these beds and below the uppermost bentonite are at least two hori-
zons of discontinuous bentonite beds or series of lenses, They are usually
thin and rather impure, contain associated gypsum, and where seen were con-
sidered noncommercial.

The uppermost bentonite bed lies directly beneath the contact between the
Kreyenhagen and Temblor formations, It is fairly pure, up to 60 feet or more


EVALUATION OF A CALIFORNIA BENTONITIC CLAY
FOR USE IN OIL-WELL DRILLING MUDS-Y

by

Quintin A. Aune,2/ W. Hodge Caraway,2/ Frank C, Morris, ~/
and George L. Gates2/

SUMMARY AND INTRODUCTION

This report presents the results of a field and laboratory study by the
Federal Bureau of Mines, in cooperation with the California Division of Mines,
of the swelling-type bentonite deposits in the Vallecitos area in San Benito
County, Calif. The purpose of the study was to learn if these large deposits
contain bentonite of sufficient quality and quantity to be of economic value
as an oil-well drilling mud additive,

Large amounts of bentonitic clays are used by the petroleum industry as
well as the steel industry in California, Additional amounts may be required
in the near future as a concrete or earth-fill admixture in constructing dams
and canals in the California Central Valley. Depletion of some local clay de-
posits and loss of others to military installation areas have given new empha-
sis to the need for developing new bentonite deposits in California.

Geologically, bentonites and swelling-type clays in oil-bearing sand-
stones are often related. In the case of extensive bentonite deposits in the
Vallecitos district in southern San Benito County, it was deemed desirable to
determine both the potential economic value of the bentonites and the relation-
ship of these clays to petroleum reservoir sands and source rocks in adjacent
areas, Well-log records have shown that bentonite beds of the Kreyenhagen
shale occur in the San Joaquin Valley in the Coalinga area,

The total tonnage of minable bentonite in the Vallecitos area is estimated
to be of the order of 2,500,000 tons. The actual available tonnage depends on
cutoff points, nature of impurities present, overburden to ore ratio, and
applied mining method.

1/ Work on manuscript completed October 17, 1958,

2/ Former Bureau of Mines mining geologist; now with California Division of
Mines, San Francisco, Calif.

3/ Petroleum engineer, Bureau of Mines, Region II, San Francisco, Calif.

4/ Former Bureau of Mines valuation engineer (Gas and Petroleum); now with
U.S. Treasury, San Francisco, Calif.


BLOGK TEMPERATURE , DEGREES CENTIGRADE
100 300 $00 700 900

f T T T T T T T T T T

SAMPLE 6

SAMPLE 7

SAMPLE 8

SAMPLE 9

SAMPLE 10

l L 1 1 l 1 L L i

1100
}

100 300 500 700 900
BLOGK | TEMPERATURE , DEGREES CENTIGRADE

|
1100

FIGURE 7. - Differential Thermal Analysis Thermograms of Vallecitos
Bentonite Samples 6 Through 10.

17


Bureau of Mines
Report of Investigations 5487

EVALUATION OF A CALIFORNIA BENTONITIC CLAY
FOR USE IN OIL-WELL DRILLING MUDS

By QUINTIN A. AUNE, W. HODGE CARAWAY,
FRANK C. MORRIS, AND GEORGE L. GATES

rose etree o
i] c

aaa

GEOLOGY _
CIBRARY

United States Department of the Interior — 1959
metadc38676


40

TABLE 9, - Effect of viscosity reducers on drilling fluids
containing bentonitic clays (Con,)

Quantity of Stormer viscosity at 600 Filtrate
material r.p.m, and room temperature | volume
Material | added to Treated drill- Blank room
added to | drilling ing fluids |Driving temp.

Clay-sample | drilling fluid, Driving |Centi-| wt., |Centi-|30 min.,
description fluid lb./bbl. lwt., gm. |poises fm. poises ml. pH
A. Continued
Sample 16A..|Tetra 0.00 200 43 200 43 - 9.42

Do, sodium .06 94 13 200 43 -

Do, phosphate 12 99 14 198 43 -

Do. +23 99 14 196 42 -

Do. 46 94 13 190 40 -

Do, 91 94 13 182 38 -

Do. 1.34 89 12 172 35 -

Do. 2.53 84 11 150 29 -

Do. 2.20 74 9 | 110 18 [2/244 |7.75

Do, 2 parts .00 285 67 285 67 -

Do, quebracho .23 140 26 283 67 -

Do. with 1 46 130 24 282 67 -

Do, part NaOH 91 125 22 280 66 -

Do. 3.56 125 22 264 61 -

Do, 9.95 135 25 229 51 -

Do. 7.27 84 12 110 18 |1/24.0 |9.75

Do, Sodium 00 285 67 285 67 -

Do. acid wll 110 18 283 67 -

Do. pyro- 21 105 17 281 66 -

Do, phosphate 83 100 16 270 63 -

Do. 2.40 100 16 246 56 -

Do. 4.56 95 14 217 48 -

Do, 3.33 79 10 110 18 |2/30.4 |5.47
Sample 3....|Tetra 00 280 66 280 66 - 8.35

Do. sodium .06 250 57 275 65 -

Do. phosphate wll 240 55 272 64

Do. 44 260 60 266 62

Do. 86 290 69 234 53 7

Do, 2.40 210 46 184 39 -

Do. 2.10 - - - - |4/10.2 | -

Do, 2 parts .00 320 78 320 78 -

Do, quebracho «25 300 72 315 76 -

Do. with 1 251 290 69 311 75 -

Do. part NaOH 1.01 310 75 303 73 -

Do. 3.92 335 82 269 63 -

Do. 5.76 325 79 247 57 -

See footnote at end of table.



Adding a swelling clay to muds causes an increase in viscosity, which may be
lowered by adding certain chemicals, such as complex phosphates, In contrast,
the addition of nonswelling clays causes a relatively slight increase in vis-
cosity. Also, large quantities of the nonswelling clays may be added to a mud
to increase the density of the mud without the necessity of adding relatively
expensive barites,

Bentonites also are used in foundries to add strength to the molding
sands.

Bentonites are used to clarify solutions. Small quantities of materials
that discolor some solutions may be removed by filtering the solution through
clay, which adsorbs the discoloring material. The adsorption apparently de-
pends on a large surface area, Finely divided clays have large surface areas,
A cube 1 cm, on an edge subdivided into 1 times 1012 cubes 0.001 mm. on an edge
has a total surface of 6 square meters or 64.6 square feet, Clays frequently
have been defined, from the size viewpoint, as particles smaller than 0.004 m,

Bentonite is being studied for use in fighting forest fires, The
California Forest and Range Experiment Station, U.S. Forest Service, and the
California State Division of Forestry are conducting a cooperative study of the
effectiveness of bentonite slurries in forest-fire fighting. Preliminary re-
sults indicate that the use of aircraft to spray the slurry over an area ahead
of the fire may be effective in controlling forest fires.

In engineering practice bentonites are used to control the permeability of
linings and groutings. Mielenz and King// describe the use of bentonite in
linings to reduce the loss of water through canal walls. They report that ben-
tonite lining may be applied in several ways, The linings, usually 2 to 3
inches thick, require adequate cover for protection against drying and conse-
quent cracking, curbing, and erosion, Cracking as a result of syneresis might
occur in membrane linings, The admixture of bentonite with granular material
increases the shrinkage limit and thus prevents the formation of penetrating
cracks, >

Another method of applying the bentonite to canal walls, particularly in
canals with considerable leakage, is to add ground bentonite directly to the
canal water, The flow of water to the leaks carries the bentonite to the holes
through which the water is escaping. The bentonite particles plug the small
holes and greatly reduce the loss of water from the canals,

Permeability of linings can be changed by ion exchange through continued

contact with saline waters. In 1941 Lee8/ showed that seepage from a lagoon on

i/ Mielenz, Richard C., and King, Myrle E., Physical-Chemical Properties and
Engineering Performance of Clays: Clays and Clay Technology Proc., lst
Nat. Conf. on Clays and Clay Technology, California Division of Mines,
Bull. 169, July 1955, p. 221.

8/ Lee, C. H., Sealing the Lagoon Lining on Treasure Island With Salt:
Trans, Am, Soc, Civil Eng., vol. 106, 1941, pp. 577-607.


of the mud as a carrier of the cuttings from the bit. Sticky surface clays
from areas near the drill site frequently were used to make mud. Not long
thereafter the commercial drilling-mud industry was started to supply clays as
suspending agents in addition to barites and hematite as weighting materials,
Chemical methods for controlling the properties of drilling muds were developed
in the early thirties, As Gray? pointed out, the list of commercial mud mate-
rials has continued to increase until mud suppliers in 1958 listed 25 to 50
products. In 1957, 53,000 wells were drilled in the United States, and the
total expenditure for materials used in drilling fluids approached $150,000,000.
The average depth was 4,122 feet. In the last 5 years, however, the number of
wells drilled to depths below 15,000 feet has increased. In 1957, 199 wells,
drilled to depths below 15,000 feet, had an average mud cost of $121,000, which
was 16 percent of the total cost.6/ Deeper wells require careful control of
the quality of the md. Larger volumes of mud also are required.

At the well the mud engineer must control the viscosity, density, and gel
properties so that the md may attain its essential functions,

The primary function of the drilling fluid is to remove the cuttings from
the hole, A second important function of the drilling fluid is to keep natu-
rally occurring fluids in the formations from entering the borehole, Blowouts
caused by uncontrolled flow of gas, oil, or salt water into the hole are pre-
vented by keeping the weight of the mud column in the hole in excess of the
fluid pressure in the formation.

Considerable heat is developed by the cutting action of the bit on the
rock, and the drilling fluid must carry this heat away so that the hardened
metal cutting surfaces of the bit may retain the necessary hardness.

Another important function of drilling fluid is to seal porous formations
penetrated by the bit to minimize the flow of mud or mud filtrate from the
borehole into the formation pore space, Where the openings in the rocks are
too small for the clay particles and other mud solids to enter, only water from
the mud enters the pores, and solids filter out on the walls of the hole, form-
ing a filter cake, The permeability of this filter cake determines the rate of
flow of water from the mud into the porous formations.

Bentonite, when added to heavy muds in small quantities, provides enough
gel and viscosity to keep the weighting material, generally barites, in
suspension,

Although swelling-type bentonites are used in most drilling muds, some
nonswelling clays are used in the shallower holes, The nonswelling bentonites
require comparatively larger quantities of clay to improve the filter proper-
ties to desirable ranges. Consequently the nonswelling clays sell for a lower
price. The nonswelling clays have one advantage over the swelling clays.

5/ Gray, George R., Chemicals in Oil-Well Drilling Fluids: Am, Chem. Soc,
Meeting, San Francisco, Calif., April 1958, preprint.

6/ Adams, Ernestine, Deep Wells Increase 28 Percent: Petrol. Eng., vol. 30,
No, 3, March 1958, pp, B-21 - B-30.


36

STORMER VISCOSITY AT 600 RRM. AND ROOM TEMPERATURE

ORIVING WEIGHT, GRAMS

400,

350
300
250
ENTONITIC
CLAY NO.3
200,
“A
-)
150 i
WYOMING BENTONITE
100
CALIF. BENTONITIG CLAY NO.I6A
50
BLANK ~---—
° |
6 2 3 4

TETRA SODIUM PYROPHOSPHATE
CONCENTRATION LB. /BBL.

FIGURE 16. - Effect of Tetrasodium Pyrophosphate on Viscosity of
Drilling Muds Containing California and Wyoming
Bentonite.


24

were made in a nitrogen atmosphere. In some instances the exotherm due to or-
ganic matter shows up because of insufficient nitrogen surrounding the sample
block in the furnace,

Thermal curves of clays in the montmorillonite group are similar to the
patterns of the mica-clay minerals. Both clay minerals have a 2:1 lattice type
of structure composition; thermal patterns, consisting of three endothermic
peaks, followed by an exothermic peak, are characteristic of clay minerals with
this type of structure. Montmorillonite from Osage, Wyo., has a classical DTA
curve characteristic of this clay-mineral group (see fig. 5). This curve has
endothermic peaks near 180°, 725°, and 900° C., followed by an exothermic peak
at about 950° C, The first endothermic reaction for both the mica and the
montmorillonite clays is thought to be the result of evaporation of mechani-
cally held water, This reaction is of greater magnitude for the latter clay
than for any of the other clay minerals, Water of crystallization is driven
off at the second peak.

The position of the second peak for a montmorillonite-clay mineral may
range from 670° to 720° C.; however, the position of the peak usually is con-
sidered sufficient to distinguish montmorillonite-clay minerals from mica-clay
minerals, The second endothermic peak for the latter group of clay minerals is
usually found below 600° C,.; this second endothermic peak generally is found at
a higher temperature for montmorillonite-clay minerals; an exception to this is
nontronite, which may have a second endothermic peak as low as 500° C,23/

Mixtures of montmorillonite and the mica-clay minerals as a mixed-layer
complex are a common occurrence, It is well recognized that a relatively pure
sample of either clay mineral is difficult to find in nature and the ratio of
one layer type to the other may vary greatly throughout a given clay deposit.
Because the ratio of one clay to the other is difficult to measure, a 50-per-
cent-by-weight mixture was prepared of two reference clays to obtain a DTA
curve with both clays present in sufficient quantity to illustrate the charac-
ter of this mixed-layer complex. Often one clay may be interlayered with
another to such a slight extent that its presence cannot be detected by DTA.
It is apparent from the thermal curve of the mixture that the second endother-
mic peak of each clay mineral has been shifted to a lower temperature by ap-
proximately 20° C, in comparison with the occurrence of this peak in the clean
clay samples, Furthermore, the magnitude of the second endothermic reaction
of the mica clay (grundite) in the mixture at 540° C. is considerably less
than half the magnitude for this endothermic reaction shown in the DTA curve of
the reference clay sample at 570° C, However, the second peak for montmoril-
lonite at 690° C. in the mixture does approximate half the magnitude of this
reaction at 720° C. in the reference clay-sample curve, Such characteristics
of DTA thermograms of clay mixtures suggest that considerable caution must be
used when estimating the composition of a mixture from thermal curves,

Kaolinite has received the attention of a number of researchers, and much
more is known about its composition and character than of the mica-group or
montmorillonite-group clay minerals. Kaolin has a 1:1 lattice-type structure.

23/ Work cited in footnote 21 (p. 23), pp. 25-38.


TABLE 9, - Effect of viscosity reducers on drilling fluids
containing bentonitic clays (Con.)

41

Quantity of Stormer viscosity at 600 Filtrate
material r.p.m, and room temperature | volume
Material | added to Treated drill- Blank room
added to | drilling ing fluids |Driving temp,
Clay-sample | drilling fluid, Driving |Centi-| wt., |Centi-|30 min.,
description fluid lb./bbl. |wt., gm. |poises gm. poises| ml, pH
A, Continued
Sample 3.... 10.89 300 72 205 45 -
Do. 8.85 - - - - | 44.9 J9.57
Do. Sodium -00 300 72 300 72 -
Do. acid 12 240 55 298 71 -
Do. pyro- 324 220 49 293 70 -
Do. phosphate 93 195 42 269 63 -
Do. 1.82 175 36 244 56 -
Do. 5.05 140 26 180 38 -
Do. 7.17 120 21 151 29
Do. 6.23 - - - - |A/10.5 |5.07
B, California|Tetra .00 300 63 300 63 -
dry-lake |sodium 05 290 61 290 61 -
clay phosphate .10 270 56 288 60 -
Do. 41 250 50 263 54 -
Do, 1.18 210 39 220 42 -
Do, 2.24 170 28 186 32 -
Do. 1.8 100 16 | 110 18 |L/10.2 | -
Do, 2 parts 00 190 33 190 33 - 9,25
Do. quebracho ~20 180 31 189 33 -
Do. with 1 239 185 32 188 33 -
Do. part NaOH 78 190 33 187 33 -
Do. 1.55 175 29 184 32 -
Do. 3.05 175 29 178 30 -
Do. 4.51 180 31 172 29 -
Do. 8.62 350 77 158 25 -
Do. 12.39 1,100 - 144 21 13.8 -
Do. Sodium .00 280 58 280 58 -
Do. acid 14 230 44 275 57 -
Do. pyro- 227 215 40 271 56
Do. phosphate 54 200 36 263 54
Do. 2.04 190 33 227 44 -
Do, 5.28 180 31 185 32 -
Do. 4.48 - - - - |2/13.6 [6.15

See footnote at end of table.



23

Preparation of Samples for Determining Clay-Mineral Content

A method of preparing samples is needed so that the analysis is performed
on a representative sample and not on a particular size fraction; therefore
about 50 grams of clay was selected for analysis, The sample was ground in a
mortar and pestle until the entire sample passed a 100-mesh screen, This pow-
dered sample was set aside for identification by differential thermal analysis
(DTA) .

Quantitative estimation of the minerals in a clay sample has been at-
tempted, based upon a comparison of the amplitude of the peaks of DTA curves
of clay references with the peak amplitude of DTA pattern of the outcrop clay
samples, In each instance comparisons also are made of the areas between the
curve and the neutral axis of the DTA patterns of reference clays and the un-
known clay sample being analyzed, The shape of the DTA pattern and the inten-
sity of the thermal reactions are influenced strongly by differences in par-
ticle size, crystallite sizes, the degree of development of crystallinity of
the clays, and ion substitution in the structure of the clay. Heats of trans-
formation may deviate from one clay sample to another, even though both samples
are members of the same clay-mineral group. Consequently estimates of the
purity or composition of a given clay sample are doubtful when they are based
upon differential thermal analysis and should not be considered beyond the
order of semiquantitative accuracy.

Results and Discussion of Thermal Studies

Reference Clay Minerals

Grundite from Goose Lake, I1l., was selected as a reference clay, repre-
sentative of the mica-clay group, Many investigators have studied the charac-
teristics of this group of clays, and consequently a number of terms are used
in reference to it, such as submica group, hydrous micas, and illite.2l/ This
clay-mineral group is perhaps the most complex of the natural clays, and it is
of considerable importance because of its wide occurrence, The thermal analy-
sis curve of grundite in figure 5 is typical for this clay; three endothermic
reactions are apparent, with peaks at 135°, 570°, and about 860° C. The last
of these reactions is followed almost immediately by a small exothermic reac-
tion at 980° C, This pattern agrees with those published by other investi-
gators 22:

The endothermic reactions are plotted downward, and the exothermic reac-
tions are plotted upward from the neutral axis. Oxidation of organic matter
associated with clays often causes an exothermic peak between block tempera-
tures of 250° and 550° C. This exothermic reaction may blank out endothermic
reactions needed to identify a clay; to alleviate this condition many DTA's

21/ Grim, Ralph E., Modern Concepts of Clay Materials: Jour. Geol., vol. 50,
No, 3, April-May 1942, pp. 225-275.

22/ Kerr, Paul F., and others, Differential Thermal Analyses of Reference
Clay Mineral Specimens: Preliminary Rept. No. 3, API Research Proj.
49, Columbia Univ., N. ¥., 1951, pp. 38-41.




14

R.10 E. RAVE. RE, RA2E,

TABS,

PANOCHE

McDonald
Ranch

Syncline
Divide 2,000 ft.

Ranch

13.4

Approximate

Thickness,
Feet

API
Filtrate Vol.

BbI /Ton/| MI/30 Minutes
Sample No.
G E UPPER BESO 3 ————
MIDDLE BEDZ eeeeeees Sogig__t
LOWER BED | oma 62500
° y2 ami

R.10 E. RWI EL

FIGURE 4. - Location of Outcrop-Sample Sites in Vallecitos Bentonite Deposits, San Benito County, Calif.

TITS,


31

60

piers DRY-LAKE CLAY
50

2 | CALIFORNIA BENTONITIC CLAY NO.|
1

40 D0. NO.

\ Do. NO.6A

Do. NO.3

ow
°

WYOMING BENTON

nm
co}
q
y

30-MINUTE FILTRATE VOLUME,

3

° I 2 3 4 5 6 7 8
CLAY ADDED TO POOR ORILLING FLUID, PERCENT

FIGURE 12. - Effect of California and Wyoming Bentonites on Filter
Properties of a Poor Drilling Mud.

Salt Contamination of a Poor Mud

Frequently while an oil well is being drilled the mud will become con-
taminated with sodium chloride from salt water in the formation, Table 8 and
figures 13-15 show the effect of different amounts of sodium chloride on the
filter properties and viscosity of a drilling mud treated previously with
California bentonitic clays, The filtrate volumes at 200° F. from this md
treated with 8 percent California bentonite and with 4 percent Wyoming


32

bentonite were 39 and 28 ml., respectively. After contamination with 5.3
pounds of sodium chloride per barrel of mud, the filtrate volumes increased
to 49 and 51 ml., respectively.

TABLE 8, - Effect of salt (sodium chloride) on drilling
fluids containing bentonitic clays

Quantity Stormer viscos-
of clay |Sodium chlo-|Filtrate volume,|ity, 600 r.p.m.,
Description of clay added, ride con- ml./30 min. room temp,
sample added to percent | centration,| Room Driving | Centi-
poor mudl/ by weight] 1b./bbl. temp. | 200° F. |wt., gm.| poises
A. California benton-
itic clays:
Sample 1 - 70
foot tunnel..... 8 0.00 17 31 200 43
Do. 8 5.31 - 46 490 129
Sample 11........ 8 00 7 39 240 55
Do. 8 5.31 26 - 570 153
Sample l6a....... 8 00 26 55 130 24
Do. 8 5.31 - - 240 55
Sample 3......... 4 .00 27 59 110 18
Do. 4 1.11 27 53 150 29
Do, 4 2.46 31 65 165 33
Do, 4 5.31 33 73 185 39
Do. 8 00 19 39 210 46
Do. 8 5.31 25 49 460 120
B, Wyoming bentonite. 2 .00 28 56 110 18
Do. 2 5.31 - 72 240 55
Do. 4 00 18 28 135 25
Do. 4 1.11 17 31 190 40
Do, 4 2.46 21 39 250 57
Do. 4 5.31 27 51 305 73

1/ The poor mud used in these tests contained 30 percent Ventura yellow
clay, 70 percent water, and 1,65 1b. per bbl. of sodium acid
pyrophosphate,

Chemical Treatment of Muds Containing Bentonitic Clays

Figures 16-18, and table 9 show the effects of chemical treatment on the
viscosities of suspensions of several of the bentonitic clays and Wyoming ben-
tonite. The viscosity of suspensions of all of the bentonitic clays, includ-
ing Wyoming bentonite, did not respond to treatment by quebracho or sodium
tetraphyrophosphate. The viscosity of the bentonitic clay sample 3 suspension


20

BLOGK TEMPERATURE, DEGREES GENTIGRADE
100 300 500 700 900

I T T T T T T T T T T

ETCHEGOIN

MONTEREY MARL
|

MONTEREY MARL
{acio TREATED) = |

LOWER TEMBLOR

l | L [ 1 1 1 l | 1

100 300 500 700 ‘900
BLOCK TEMPERATURE , DEGREES CENTIGRADE

i
100

FIGURE 10. - Differential Thermal Analysis Thermograms of Samples From
Etchegoin, Upper Miocene(?) Marl Untreated, Upper Miocene(?)
Marl Treated, and Lower Temblor Formations in Vallecitos.


The Library of Congress has cataloged this publication as follows:

Aune, Quintin A .
Evaluation of a California bentonitic clay for use in oil-
well drilling muds, by Quintin A. Aune ,and others. Wash-
ington, U. S. Dept. of the Interior, Bureau of Mines, 1959.

lil, 44 p. illus. maps, tables. 27 cm. (U.S. Bureau of Mines.
Report of investigations, 5487)

Bibliographical footnotes.

1, Bentonite. 2. Clay — California — San Benito Co. 3. Oil well
drilling fluids. 1. Title. (Series)

[TN23.U43 no. 5487] Int 59-107

U.S. Dept. of the Interior. Library
for Library of Congress



TABLE 9. - Effect of viscosity reducers on drilling fluids

containing bentonitic clays (Con.)

39

Quantity of Stormer viscosity at 600 Filtrate
material r.p.m, and room temperature | volume
Material | added to Treated drill- Blank room
added to | drilling | __ing fluids |Driving temp,
Clay-sample | drilling fluid, Driving |Centi-} wt., |Centi-|30 min.,
description fluid lb./bbl. _|wt., gm.|poises gm. poises| ml, pH
A, Continued |
1. 70-foot
tunnel....|2 parts 0.0 325 79 325 79 -
Do, quebracho 2 320 78 321 78 -
Do. with 1 4 315 77 319 78 -
Do. part NaOH 1.7 300 72 301 72 -
Do, 4.8 255 59 260 60 -
Do, 9.2 240 55 212 47 4.9 -
Do, Sodium 0 325 79 325 79 -
Do. acid al 315 77 320 78 -
Do, pyro- 2 305 73 317 77 -
Do. phosphate 4 285 67 310 75 -
Do. 1.6 225 50 265 63 -
Do. 4.5 170 35 189 40 -
Do, 3.6 96 15 | 110 18 |2/10.2 [5.22
Sample 11.,.|Tetra 00 240 55 240 55 - 6.43
Do. sodium .08 200 41 232 52 -
Do. phosphate .16 180 34 227 51 -
Do. 33 195 39 216 48 -
Do. 264 320 74 200 43 -
Do. 1.25 1,100 - - - -
Do. 1.1 400 | 102 | 110 18 | 1/9.0 | -
Do, 2 parts .00 400 102 400 102 -
Do. quebracho ~22 350 87 370 93 -
Do, with 1 44 370 93 355 88
Do, part NaOH 88 480 126 388 83
Do, 1.75 710 - 306 74 -
Do. 1.35 240 | 55 | 110 18 | 4/6.0 |8.79
Do. Sodium .00 400 102 400 102 -
Do. acid +20 310 75 343 85 -
Do. pyro- 41 280 66 325 79 -
Do. phosphate 1.59 250 57 249 57 -
Do. 4.47 210 46 183 38 -
Do. 6.31 185 | 39 | 110 18 | 2/7.0 |a.21

See footnote at end of table,



STORMER VISCOSITY AT 600RPM. AND ROOM TEMPERATURE

400

350

300

GRAMS
~
a
fo}

np
°
fs)

150

DRIVING WEIGHT,

100

50

37

>1100 GRAMS AT 12.4 LB. /BBL.

f

T T
CALIF. DRY-LAKE
st sOGLAY
ENTONITIG CLAY NOJ3y
. -
_
‘4 WYOMING BENTONITE
. —
I~. oe Z|
“Dae —f-4 |
| ~e—_[ ~~ 7 --t2~ e
Toh aed
> go fae
Norse we
pa
~-_] wee
4  |*
to. ro —o- ]
“XSTMCALIF. BENTONITIC GLAY NO.I6A
BLANK ~----
re) 2 4 6 8 10 12

QUEBRACHO CONCENTRATION, LB/®BL.

FIGURE 17. - Effect of Quebracho on Viscosity of Drilling Muds Containing
California and Wyoming Bentonite.


TABLE 2. - Bentonite sold or used in the United States in 1957,
by kinds and uses, in short tons

Quantity,
Use in industry short tons | Percent
Oil-well drilling mds............ eeeee 556,889 38.3
Foundry sand.........ccees ec eeeeee eacee 376,833 25.9
Filtering and decolorizing (raw and activated earths)

Mineral oils and greases........... nee 138,940 9.5
Vegetable or animal oils and fats . 62,832 4.3
Other filtering and clarifying.. . 6,865 4
Insecticides and fungicides..... . 18,743 1.2
Absorbent uses..... eeasccces . 14,120 9
Chemicals, eee wees . 8,488 5
EXpOrts......seeeee eee cee ences . 74,212 5.1
Portland and other hydraulic cements, . 3,125 2
Fillers... rr rrr rr . 2,852 al
Art pottery, owerpots, and glaze slips . 105 .0
Enameling.......ee.e05 eevee eee eee . 54 0
Other uses, eee ceeeee . 187, 377 12.9
Total,.... eererree eee : 1,451,435 99.3

Prices

Bentonite production and prices have increased generally in the last 25
years with industrial expansion and growth of population. As reported in
Bureau of Mines Minerals Yearbook preprint (1957)11/ and Mineral Market Report
MMS 2803, 1,451,445 short tons of bentonite valued at $17,830,645 was sold or
used by producers in the United States in 1957.

The price of bentonite was listed in the Chemical and Engineering News,
December 29, 1958, as $14 per ton f.0.b. plant for 200-mesh-size material in
bags.

The railroad freight rate for a March 1959 shipment of Wyoming bentonite
from Osage, Wyo., to Los Angeles or San Francisco was $1,15 per 100 pounds or
$23.00 per short ton, if shipped in an 80,000-pound car. If shipment was in a
60,000-pound car, the rate was $32.20 per short ton. The LCL (Less than Car-
load Lot) rate was $4.03 per 100 pounds. If the clay was sacked it could be
shipped by truck from Osage, Wyo,, to Los Angeles, or San Francisco for $3.71
per 100 pounds or $74.20 per short ton.

VALLECITOS BENTONITES

Location and Accessibility

These bentonite deposits outcrop along the southern border of the
Vallecitos in the west-central part of California, as shown in figure 1, The

11/ Gunsallus, Brooke L,, and Brett, Betty Ann, Clays: Preprint From Bureau
of Mines Yearbook 1957, pp. 7-8.


Panoche Creek, The north-facing slopes on which the bentonite deposits lie
are covered by a fairly thick stand of chaparrel, scrub oak, and related
brush,

The climate of the north-facing slopes is semiarid, The annual precipi-
tation is about 10-12 inches, mostly occurring in the winter months, The
average daily temperatures during July and August approach 100° F, A minimum
of 30° is not uncommon in December and January, A northwesterly breeze blows
throughout much of the year,

Definition of Terms

The following related terms used frequently in this report are defined as
follows:

BENTONITE - a rock, It is the claylike alteration product of a volcanic
ash;12/ is composed primarily of the clay minerals of the montmorillonite
group.

MONTMORILLONITE - used both as a group name for all clay minerals with an
expanding Lattice except vermiculite and also as a specific mineral name ,13/

VOLCANIC ASH - a volcanic ejecta consisting of particles smaller than 4
mm, in diameter ,14/

CLAY - a fine-grained, natural, earthy material, which develops plastic-
ity when mixed with a limited amount of water, It is composed primarily of
aluminum silicates, The word "clay" is employed as a size term, Use of clay
as a size term is considered undesirable in this study because the clay size
range - generally particles less than 4 microns in diameter - is shared by
numerous other materials,

Description of Vallecitos Bentonites

The Vallecitos bentonites appear to be derived mainly from acidic vitric
and crystalline volcanic ash, Some remnant glass shards, as well as feldspar
laths, suggest the volcanic origin of the clay. The bentonites are gray,
white-weathering clays occurring in massive outcrops and are subject to fre-
quent landslides. The surface weathered zone has a crackly appearance, as
shown in figure 2, The surface clays, to a depth of approximately 1 foot, may
be subject to contamination by gypsum carried in solution by surface runoff

12/ Davis, C. W., Vacher, H. C., and Conly, John E., Bentonite: Its Proper-
ties, Mining, Preparation, and Utilization: Bureau of Mines Tech,
Paper, 609, 1940, p. 1.

13/ Grim, Ralph E., Clay Mineralogy: McGraw-Hill Book Co., Inc., New York,
N. Y., 1953, p. 34.

14/ Williams, Turner, and Gilbert. Petrography: W. H. Freeman & Co., San
Francisco, Calif., 1954, p. 149.


EVALUATION OF A CALIFORNIA BENTONITIC CLAY
FOR USE IN OIL-WELL DRILLING MUDS

BY QUINTIN A, AUNE, W. HODGE CARAWAY,
FRANK C. MORRIS, AND GEORGE L, GATES

* «© «* + «# « « « «+ Report of Investigations 5487

UNITED STATES DEPARTMENT OF THE INTERIOR
Fred A. Seaton, Secretary
BUREAU OF MINES.
Marling J. Ankeny, Director

1959


30

TABLE 7. - Effect of clays on filtrate volume and viscosity of a poor mud2/
Quantity] Quantity of | Filtrate vol- Stormer viscos-
of clay | sodium acid |ume, ml./30 min, | ity, 600 r.p.m.,
Description of clay | added, pyrophos~ Room room temp,
sample added to percent |phates added, |temp., Driving |Centi-
poor mud by weight| 1b./bbl. °F. 200° F. |wt., gm.|poises
A, Vallecitos benton-
itic clays:
1. 70-ft. tunnel (0) 0.00 - - 99 15
Do. 0 1.65 57 99 84 ll
Do. 2 .00 - - 185 39
Do. 2 1.65 44 54 110 18
Do, 4 .00 - - 340 84
Do. 4 1.65 32 39 160 32
Do. 8 00 - - - 1/
Do. 8 1.65 17 31 200 43
Sample No. 11.... 2 .00 - - 145 29
Do, 2 1.65 44 66 105 17
Do. 4 .00 - - 265 61
Do. 4 1.65 - 47 140 26
Do. 8 .00 - - - L/
Do, 8 1.65 17 39 240 54
Sample No, 16A... 2 .00 - - 145 29
Do. 2 1.65 43 80 110° 18
Do. 4 00 - - 225 50
Do, 4 1.65 33 72 125 22
Do. 8 .00 - - 245 56
Do. 8 1.65 26 55 130 24
Sample No. 3..... 4 00 - - 195 42
Do. 4 1.65 27 59 110 18
Do. 8 .00 - - - L/
Do, 8 1.65 19 39 210 46
B, California dry-
lake clay........ 2 .00 - - - -
Do. 2 1.65 51 - - -
Do. 4 -00 - - - -
Do. 4 1.65 48 - - -
Do. 8 .00 - - 190 40
Do. 8 1.65 - 73 130 24
C,. Wyoming bentonite, 2 .00 - - - -
Do, 2 1.65 28 56 110 18
Do. 4 -00 - - 270 63
Do. 4 1.65 18 28 135 25

1/ The viscosity of the mud was too high to measure,
2/ The poor mud in these tests contained 30-percent Ventura yellow clay and
70 percent water.


18

BLOCK TEMPERATURE, DEGREES GENTIGRADE A

100 300 500 700 900 4100
T T T T T

t

SAMPLE II |
+
LL

SAMPLE 12 |

SAMPLE 13

1 1 1
100, 300 500 700 ‘900 T109|
BLOGK TEMPERATURE, DEGREES GENTIGRADE

FIGURE 8. - Differential Thermal Analysis Thermograms of Vallecitos
Bentonite Samples 11 Through 13.




42

TABLE 9, - Effect of viscosity reducers on drilling fluids
containing bentonitic clays (Con.)

Quantity of Stormer viscosity at 600 Filtrate
material r.p.m, and room temperature volume
Material | added to Treated drill- Blank room
added to | drilling ing fluids [Driving temp.
Clay-sample | drilling fluid, Driving |Centi-| wt., |Centi-|30 min,,
description fluid 1b./bbl. lwt., gm. |poises gm. poises| ml, pH
C, Wyoming Tetra 0.00 380 97 380 97 - 9.29
bentonite| sodium 13 340 84 362 91 -

Do. phosphate «25 320 78 350 87 -

Do. 50 290 69 328 80 -

Do. .97 240 55 290 69 -

Do, 1.86 190 40 233 53 -

Do. 3.44 150 29 172 35 - -

Do, 2 parts 00 380 97 380 97 -

Do, quebracho .20 350 87 374 94 -

Do. with 1 -40 340 84 371 93 -

Do. part NaOH 80 330 81 364 91 -

Do. 1.60 300 72 347 86 -

Do. 4.70 240 55 297 71 -

Do, 12.7 250 57 209 46 16.6 -

Do, Sodium -00 260 60 260 60 -

Do, acid .10 250 57 258 60 -

Do, pyro- .20 240 55 254 58 -

Do, phosphate 40 225 50 250 57 -

Do, 1.60 180 38 221 49 -

Do. 4.40 140 26 172 35 -

Do. 3.50 a4 | 13 | 110 18 /i3.5 [+

1/ In this determination the drilling fluid was diluted with water to the
final clay concentration in the yield test, so that the filtrate volumes
are comparable with similar data in table 5,

ECONOMIC EVALUATION

The following economic evaluation of the Vallecitos bentonite deposits
was made on five factors: (1) Quality of the bentonite, (2) nearness to mar-
kets, (3) ease of mining, (4) size of reserves, and (5) response of clay to
chemical treatment.

1. The results of laboratory tests show that the samples of Vallecitos
bentonites were of good quality for use in oil-well drilling muds or possibly
other applications requiring a swelling-type bentonite. The yield of a 15-cps.
mud from samples of bentonites from the Vallecitos was approximately half that
from Wyoming bentonite. As an additive to drilling muds, twice as much
Vallecitos bentonite was required to improve the filter properties of a mud
as was required to attain an equivalent improvement by the addition of Wyoming


26

the clay with hydrochloric acid (see thermal curve for Monterey-shale acid-
treated, fig. 10). The strong exotherm at 830° C. is strongly indicative of
the clay mineral sepiolite, a magnesium silicate complex; however, it is known
that the DTA's of chlorite mineral also exhibit this strong exotherm at 830° C,
The thermal curve obtained for the Yokut formation definitely indicates kaolin.
The weak exotherm at 960° C, may be due to lack of crystalline development in
this particular sample.

The results of study of the clay-size fraction from these clays utilizing
X-ray diffraction and optical methods confirmed the findings obtained by the
DTA,

PROPERTIES OF DRILLING FLUIDS CONTAINING VALLECITOS BENTONITIC CLAYS

Laboratory Testing Procedure

The procedure followed in determining the properties of the clays studied
in this investigation was based approximately upon the American Petroleum In-
stitute (API) code, Recommended Practice for Standard Field Procedure for Test-
ing Drilling Fluids, API-RP 29, 4th edition, May 1957.

The sand content of the clay samples was determined by mixing a weighed
quantity of clay with water and washing the suspension through a 200-mesh
screen, The sand retained on the screen was dried, weighed, and expressed as
a percent of the original weight of clay.

The moisture content of the clay samples was determined by drying the sam-
ples in a 220° F. oven overnight and dividing the loss in weight by the initial
weight of the sample,

The density of the clay samples was measured with a Le Chatelier flask
cont;ining toluene. The flask and toluene were held in a constant-temperature
bath until the initial volume was constant, The finely divided clay was added
to the flask until the level of the suspension was well up into the graduated
neck of the flask, The final volume of the suspension was observed after the
flask had been carefully rolled and tapped until no more bubbles of air ap-
peared, Then the flask was replaced in the bath until the final volume became
constant, The difference between the final and initial liquid levels in the
flask is the volume of the clay sample added to the flask, The density of the
clay sample is the weight of the sample divided by the volume of the clay added
to the flask,

To determine the yield of the clays expressed as barrels of 15-centipoise-
viscosity mud per ton of dry clay, the clay samples were mixed with distilled
water in a high-speed mixer and allowed to hydrate for at least 72 hours.

After the hydration period the mud was mixed thoroughly, and the viscosity
measured with a Stormer viscosimeter, recording the driving weight in grams
required to rotate the cylinder at a rate of 600 r.p.m, at room termperature
(about 72° F.). Distilled water was added to the mud in small increments, and
the viscosity of the diluted muds was measured so that the yield of the clay


VISCOSITY AT 600 RPM. AND ROOM TEMPERATURE

STORMER

DRIVING WEIGHT GRAMS

35

40
300 wie <<
wie
3
wwe
we
e
200
7 cLAY NO.3 x
100
INITIAL DRILLING FLUID
POOR DRILLING FLUID
TREATED WITH
4 LB. PER BARREL BENTONITIC CLAY
1.7 L8. PER BARREL SODIUM ACID
PYRO PHOSPHATE
fe) 1
0 2 4

6
SODIUM CHLORIDE CONCENTRATION, LB. /2BL.

FIGURE 15. - Viscosity Changes Resulting From Addition of Salt (sodium
chloride) to Drilling Muds Containing California and Wyoming

Bentonite.


BLOCK TEMPERATURE, DEGREES CENTIGRADE
190 300 500
i T T

700
T T T T

YOKUT

Tr
2
=}
°
a
tL

UPPER PANOCHE

L

300.

4 L L 1 L i i 1 L !
TOO 300 500 700 300 Tog
BLOCK TEMPERATURE , DEGREES GENTIGRADE
FIGURE 11. - Differential Thermal Analysis Thermograms of Samples From

Yokut and Upper Panoche Formations in Vallecitos.

Clay-Mineral Identification by Differential Thermal Analysis

analytical methodl8/

Differential thermal analysis of powdered materials such as clays is an

in which a dual-terminal thermocouple is used.

One ter-

minal is placed in an inert reference material, such as calcined alpha alumina

18/ Spiel, Sidney, Berkelhamer, L. H., Pask, J. A., Davies, Ben.

Differential

Thermal Analysis - Its Application to Clays and Other Aluminous Minerals
Bureau of Mines Tech, Paper 664, 1945, p. 81.

21


Treasure Island, in San Francisco Bay, was reduced by flooding the lining with
sea water, thereby changing the clay to a sodium-type clay before fresh water
was put into the lagoon, The seepage rate, at completion of the operation, was
found to be 0,10 inch per day in contrast to 0.90 inch per day before treatment,

BENTONITE PRODUCTION AND CONSUMPTION IN THE
UNITED STATES AND IN CALIFORNIA

Bentonite occurs in nearly every State west of the Mississippi River, as
well as in many eastern States, but commercial production is limited to a few
areas,

Over half of the domestic bentonite is produced?/ in the Wyoming-South
Dakota area, mainly from a large district in the Black Hills region of north-
eastern Wyoming and adjacent portions of western South Dakota and from a
smaller district near Greybull, Wyo. The bentonite produced in this area is
desirable in oil-well drilling muds and foundry sands.

Fifteen States reported bentonite production in 1957, compared with 14 in
1956, and 13 in 1955,

According to Bureau of Mines Mineral Market Report MMS 2803, the three
largest producing States and their portion of the total United States produc-
tion of bentonite in 1957 were: Wyoming, 57 percent (54 percent in 1956, 56
percent in 1955, 58 percent in 1954, and 53 percent in 1953); Mississippi, 15
percent (14 percent in 1956, and 15 percent in 1955, 1954, and 1953); and
Texas, 9 percent (10 percent in 1956 and 1955, 8 percent in 1954, and 4 percent
in 1953), Production statistics for Arizona, one of the large producers, can-
not be published, as they would disclose individual company operations,

TABLE.1, - Bentonite sold or used by producers in the
United States, 1955-57, by States

1955 1956 1957
Short Short Short
State tons Value tons Value tons Value
Arizona....... 124,872| $674,309 qa/) (Q/) a/) ay)
California.... 3,942 66,192 3,618 $70, 328 3,843 -
Colorado,,.... 207 931 - - 20 80
Idaho......... - - 120 1, 200 185 3,700
Mississippi... 226,852] 2,558,399] 219,216] 2,360,031] 220,313] 2,372,249
Nevada........ 442 4,420 a/) qQ/) @/) Q/)
Texas...... 155,128] 1,461,873] 160,723| 1,182,620] 126,635 963,147
Utah....... 2,520 30, 200 2,741 34,700 2,300 29,800
Washington, - - 300 3,000 165 990
Wyoming... 825,810 |10,721,577| 847,266 |11,624,185| 822,163|11,724,855
Other States2/ 140,432] 1,701,114 | 336,626 | 3,138,743 261,018] 2,433,312
Total...... | 1,480, 205 [17, 219,015 |1, 570,610 |18, 414, 807 [1, 451, 445 |17, 830,645

1/ Included with "other States."

2/ Includes States indicated by footnote 1 and Louisiana, Montana, North
Dakota, Oklahoma, and South Dakota.

97 Gunsallus, Brooke L., Clays; Chap. in Mineral Facts and Problems: Bureau
of Mines Bull. 556, 1956, pp. 196-198.


43

bentonite; however, in salt-water muds, which are important in some offshore
drilling programs, Vallecitos bentonites were superior to Wyoming bentonite.

2. The Vallecitos bentonite deposits are a short distance west of the
San Joaquin Valley, a major petroleum productive area in California, The Los
Angeles Basin area (another region of considerable drilling activity) is south
and east of the Vallecitos. Local drilling activity exists in the Vallecitos
and other parts of the Coast Range.

Of possibly greater importance is utilization of bentonites as an admix-
ture to concrete, and as a seal for irrigation canals in the San Joaquin and
Sacramento Valleys to reduce water loss by seepage. There has been no exten-
sive study of the use of bentonites in the latter field. Yet the use of ben-
tonite admixtures in canal linings in place of concrete might reduce the cost
of construction by a very large percentage and make economic canal construction
that is otherwise uneconomic, This use should be given special attention and
study, since the Vallecitos deposits are close to the San Joaquin Valley, where
much future construction is contemplated, and are not far from the proposed
San Luis Reservoir site.

3, Most of the deposits occur as steeply dipping beds in a rugged ter-
rain, In many places the outcrop slope is near the angle of repose; that is,
any sizable excavation would create a slope too steep to maintain itself and
would result in landsliding and destruction of the quarry. These are limiting
factors. The clays can be mined only in areas where the nature of the terrain
will permit; where overburden, especially from landslide material, is not too
great; and where beds are wide enough to permit an open-pit or trench operation
of economic proportions, It is assumed that the cost of underground mining
would be prohibitive.

4. Because the bentonites are extensive and the main beds are continuous,
and of fairly constant width, a sizable tonnage of reserves exists, in spite of
the foregoing limiting factors, Minable reserves of bentonite having an aver-
age yield of 50 barrels of 15-cps. mud per ton of dry clay and an average 30-
minute filtrate volume of 13 ml. would total about 1,250,000 tons. This figure
was obtained by computing a theoretical tonnage considering the observed thick-
ness and quality of the deposits and dividing this figure by four to make al-
lowance for areas of inaccessibility and contamination by landslides and other
impurities. A similar volume of additional minable reserves of bentonite
having an average yield of 33 barrels and an average filtrate volume of 13 ml.
exists,

5. The oil-well drilling muds containing Vallecitos bentonites responded
well to the addition of phosphates and quebracho. The viscosity of muds con-
taining Vallecitos bentonites was reduced by adding small quantities of the
complex phosphates. Quebracho was effective in improving the filter properties
of muds containing Vallecitos bentonites. In contrast, the filter properties
of the muds containing Wyoming bentonite were not improved by adding quebracho,




Vallecitos is a structural valley on the north flank of the Diablo Range north

of the mercury mining camp of New Idria.

VA
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unre ,
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ay
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\ VALLEGITOS ‘JOAQUIN neu
‘yg, BENTONITES . aS
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Se “ions VALLEY famen
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Se i %
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SAN ARDO Rey V7 Q
Scale <
10 Qo 10 20 30 MI. a

FIGURE 1. - Location of Vallecitos Bentonite Deposits Relative
to California Oilfields.

California.
San Joaquin Valley.

Physical Features and Climate

The bentonites outcrop along a belt

stretching 2 to 13
miles northwest of
New Idria. The
nearest towns are
Mendota, Coalinga,
and King City, all
about 50 miles by
road, to the north-
east, southeast,
and southwest, re-
spectively. The
nearest railroads
accessible by me-
dium-duty highway
are at Firebaugh on
the Southern Pacific
line, about 58 miles
to the northeast,
and at Hollister
on a Southern
Pacific branch line
about 62 miles to
the northwest,

The deposits
are favorably situ-
ated with respect
to oil-well drilling
in the Vallecitos
area a few miles to
the north. They are
also relatively ac-
cessible to most
San Joaquin Valley
and Central Coast
Range oilfields of

Access is good to proposed canal sites along the west side of the

The bentonite beds lie in a maturely dissected area in the northeast foot-

hills of the Diablo Range.

Topography is relatively rugged.

Ridges crossed

by the bentonite beds lie 250-750 feet above canyons crossed by the clay beds.
Landslides are common in the area, and often are related to the bentonite beds.

The deposits are crossed by several short creeks that flow north into
Pimental, Griswold, Larious, and San Carlos Creeks, all of which drain into