Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HYDROCARBON GELS UBEFUL IN FORMATION FRACTURING
This invention relates to improved hydrocarbon gels which
find use in petroleum producing formation fracturing. In
particular it relates to the use of a defined class of
gelling agents for hydrocarbons which provide excellent
results in such fracturing.
The gelling agents are combinations of ferric salts; low
molecular weight amines, and selected orthophosphate
esters with or without optional surfactants.
The development of the,use of gelled hydrocarbons as
fracturing fluids is reviewed by Weldon M. Harms in a
chapter entitled "Application of Chemistry in Oil and Gas
Well Fracturing", at pages 59-60 of the book "Oil-Field
Chemistry (ACS Symposium #396 - 1988)" published by the
American Chemical Society in 1989. The basic technique
of formation fracturing involves the injection of a
fracturing fluid down the well bore, which is usually
cemented in place and at least 0.3 mile long, and then
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through horizontal holes in the steel pipe, or casing, of
the well, to obtain access to the subterranean formation.
The fracturing fluid is under high pressure and must be
able to survive the severe shear forces caused when flow
is forced through the casing perforations of perhaps ; to
inch in diameter, as well as the shear forces
encountered at the leading edge of the fracture.
Whatever chemical additives are used to influence
viscosity, induce gel formation, stabilize against
resident chemicals, pH or temperature conditions in the
formation, inhibit scale formation or corrosion, or
inhibit paraffin deposition, for example, must also be
able to withstand the shear forces and other inhospitable
conditions of use. Most commonly available liquids
typically are viscosified before they are particularly
effective in carrying the large quantities of proppants
widely used in the fracturing process.
When hydrocarbons are used in the fracturing process,
they are commonly treated to increase their viscosity.
As reviewed by Harms, an early viscosifying agent was
napalm, an aluminum soap of fatty acids. Aluminum salts
of orthophosphate esters were introduced in the late
1960's, followed by the suggestion of the use of Fe304
for combination with the orthophosphate esters, in Monroe
US Patent 3,505,374. While many other combinations of
metals and other materials have been suggested as
viscosifying agents, aluminum crosslinked orthophosphate
esters are still, according to Harms, the most widely
used.
The aluminum compounds present problems, however,
particularly where any significant amount of water is
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present. They generally will not satisfactorily perform
the desired crosslinking function in the presence of more
than about 1200 ppm of water, nor where the pH is outside
a relatively narrow range. Moreover, an inadvertent
N5 excess of aluminum compound treatment is detrimental to
the desired performance because the aluminum compound
itself adversely affects the pH. The iron provided by
ferric salts as in the present invention, on the
contrary, permits operation in wider pH ranges.
l0
In describing a gel which can be used as a pig in a
pipeline, Jaggard et al in US Patent 4, 003, 393 recite the
possibility of iron as one of a number of metals to
combine with a class of aliphatic substituted
15 orthophosphoric esters. No other qualifiers are used to
describe the iron, however.
In US Patent 4,153,649, Griffin proposes reacting a
pentavalent phosphorous compound with a class of hydroxy
20 ethers before employing the metal salt. Among the metal
salts he uses is ferric nitrate, but he further requires
a "separate source of base" to be used with the hydroxy
ether modified phosphates, as spelled out in column 4,
lines 55-58 and column 11, lines 37-68.
Monroe, in US Patent 3,505,3?4, uses a gelling agent for
hydrocarbons characterized as a ferroso-ferric salt of an
alkyl oleyl diester of orthophosphoric mono acid. The
iron compound is further described as magnetite, or
Fe30Q. He suggests this combination for fracturing
' subterranean oil-bearing formations, but says none of the
"other oxidized forms of iron including ferrous and
ferric oxides and hydroxides, chlorides, sulfates and
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4
Nitrates" (col 3, lines 2-4) yielded a gel as obtained with
the magnetite.
Burnham, in US Patent 4,200,540, describes a large class of
phosphates and phosphate esters which he mixes with aluminum
slats, aluminates and aluminum metal. He chooses combinations
of the materials as a function of various down-hole
temperatures. No mention is made of iron salts; the reference
is cited mainly for its comprehensive description of the
phosphates deemed to be useful. See also Burnham's US Patent
4,316,810.
We have found that ferric salts can be very advantageous used
in the gelling of hydrocarbons, particularly for use in
formation fracturing, rather than aluminum compounds, for
combination with orthophosphate esters.
According to one aspect of the present invention there is
provided composition for fracturing formations comprising a
hydrocarbon fracturing fluid and (a) about 0.3% to about 1.5%
by weight of a phosphate ester of the formula HP04RR', where R
is an alkyl, aryl, alkoxy, or alkaryl group having from 6 to 18
carbon atoms and R1 is hydrogen or an aryl, alkaryl, alkoxy, or
alkyl group having from 1 to 18 carbon atoms, (b) a ferric salt
in an amount sufficient to form a gel with said hydrocarbon
fluid and said phosphate ester, (c) a low molecular weight
amine of the formula H3"N (CmH2",R) n where n is an integer from 1
to 3, each m is independently an integer from 2 - 6, and R is H
or OH in an amount from about one-fourth molar equivalent to
about one and one-half molar equivalent of the phosphate ester,
and (d) up to
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4a
about 10% surfactant with the proviso that component (c) does
not include triethanolamine or triethylamine.
According to a further aspect of the present invention there is
provided method of making a viscous hydrocarbon fracturing
fluid comprising blending (a) a mixture of a phosphate ester,
potassium hydroxide and a solvent with (b) a co-reacted mixture
of an iron salt and a low molecular weight amine, in a
hydrocarbon fracturing fluid wherein the fracturing fluid
further comprises up to about 10% surfactant.
In one embodiment, the low molecular weight amine is present in
an amount from one-half molar equivalent to one molar
equivalent of the phosphate ester.
In another embodiment the molar ratio of iron salt to amine is
0.1:1 to 1.5:1.
The ferric salt has the advantage that it can be used in the
presence of large amounts of water, such as up to 20%. One of
the advantages of fracturing with hydrocarbon gels is that some
formations may tend to imbibe large quantities of water, while
others are water-sensitive and will swell inordinately if water
is introduced; our invention permits one to use a hydrocarbon
gel in areas where water may cause trouble not only with the
formation itself, but with the fracturing agent or the gelling
agent. Also, it is not adversely affected by commonly used
alcohols, such as methanol and isopropanol. In addition, it can
be used in broad ranges of pH, yet the linkages it forms can
still
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be broken with gel breaking additives conventionally used
for that purpose. In addition, ferric salts such as
ferric sulfate crosslink rapidly and can be made to link
even more rapidly with the use of surfactants and/or
alkaline or caustic agents such as potassium hydroxide.
This application is directed specifically to
combinations of the ferric salts, particularly ferric
sulfate, with low molecular weight amines such as
triethylamine and triethanolamine, referred to herein
sometimes interchangeably as TEA. Other low molecular
weight amines useful in our invention are within the
generic description found elsewhere herein and
include monoisopropanol, butyl amine, and hexyl
amine.
When dissolved in a hydrocarbon such as gasoline, diesel
oil, crude oil, or kerosene, the ferric salt in
combination with orthophosphate esters as defined below
will cause the hydrocarbon to gel. The gel is generally
stable to heat, and the degree of gelling can be
controlled by the concentration of orthophosphate ester
in the fluid.
The phosphate ester which we use is advantageously added
f first and mixed with the Diesel fuel or other hydrocarbon
to be used as the fracturing agent, generally in amounts
from about 0.3% to about 1.5% by weight, based on the
total. Then the ferric salt is added in amounts to
provide preferably about one mole of ferric iron for each
mole of phosphate or phosphate ester. In this manner,
the process materials can be prepared more or less
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continuously, as opposed to the batch approach sometimes
used in the past. More broadly we may use any amount of
ferric salt which is effective to make a gel with the
phosphate ester. This will be accomplished at about 0.1
to about 1.5 mole of ferric iron for each mole of
phosphate ester, preferably 0.8:1 to 1.2:1.
A low molecular weight amine is also employed. The low
molecular weight amine is preferably one of the formula
l0 N (CHZCHzR) 3 where R is H or OH, but may be any amine of
the formula H3_"N(CmH2mR)" where m is an integer from 2 -
6, and n is an integer from 1 - 3, the alkylene group
represented by CmH2m may be linear or branched. Further
examples of such compounds are diisopropylamine,
triisobutylamine, and pentylamine.
The low molecular weight amine is advantageously first
mixed with the ferric salt in a molar ratio of ferric
salt to amine of about 0.25:1 to about 6:1. This is
accomplished by thorough blending.
We have also found that surfactants have the effect of
decreasing the time for crosslinking. Generally, in the
absence of a surfactant, our combination of materials
will crosslink in about two minutes at room temperature;
when a surfactant is used also, this time is
significantly reduced, and in the presence of our
preferred class of surfactants, it is reduced to the
neighborhood of twenty seconds, as determined by
viscosity tests. About 0.1°~ to about 10% (based on the
gelling agent) of surfactant is frequently advantageous
also.
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-'
The phosphate derivatives we use are described in the
literature as orthophosphate esters. They are similar to '
those used by Burnham in US Patents 4,200,540 and
4,316,810, Griffin in US Patents 4,174,283 and 4,153,649,
and Harris et al in US Patent 4,622,155, having the
structural formula O
II
HO---P---OR
OR'
where R is a straight or, branched chain alkyl, aryl,
alkoxy, or alkaryl group having about 6 to about 18
carbon atoms and R' is hydrogen or an aryl, alkaryl,
alkoxy, or alkyl group having up to about 18 carbon
atoms. This structural formula will be referred to
elsewhere herein as HPO,RR'.
In the fracturing fluid, the iron from the ferric sulfate
or other ferric salt forms linkages with the available
oxygen, generally in more than one phosphate group, thus
forming small chains which cause the hydrocarbon to gel.
It has been demonstrated in the laboratory that our
invention may be used to form hydrocarbon gels, and that
the gels can be broken in a manner familiar to persons
who work with hydrocarbon gels in the field such as by
the addition of common alkaline materials. In the
following examples, and in the results reported in Tables
I - IV, the procedure was to employ a laboratory Waring
blender with a voltage regulator set at 25. 300 ml of
Diesel oil was placed in the blender and the power turned
on. The phosphate ester preparation was first added and
after it was blended, the ferric salt solution was
introduced by pipette. Ttie time was recorded from the
* Trade-mark
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_g_
initial introduction of the ferric compound to the gel
point, determined by a concave shape of the material in
the blender. Blending was continued to determine the
time required to reach maximum gel, which was estimated
to be the first sign of conversion of the shape of the
material to convex instead of concave. The blending was
then stopped and the material transferred to a sample
container, observing the consistency of the gel.
Brookfield viscosity readings were then taken as shown in
the Table I.
In the examples below, Composition M is about two-thirds
phosphate ester of the above formula HPOeRR', together
with 10% triethanolamine, and solvent. Composition L
contains about two-thirds phosphate ester HPO,RR',
together with 10% triethylamine, and high f lash aliphatic
solvent. Composition K is two-thirds of the same
phosphate ester and 15.5g 45°sKOH, also with a solvent.
Composition F contains about 27% ferric sulfate, together
with ethylene glycol, mixed surfactants, 10%
triethanolamine, and water. In each case, the amounts of
composition M shown were added first to the Diesel oil
and blended; then the amount shown of Composition F was
added and blended. Results are presented in Table I.
Table I
Ex M F X-linkInvers Snindl5min30min 60min
1 3m1 3m13m120 30 sec #3 2500- 3890
sec
2 3m1 3m1 20 30 sec #3 2300- 3460
sec
3 3m1 3m1 25 35 sec #3 2375- 3400
sec
3 0 4 3m1 3m1 30 60 sec #4 636011000 13800
sec
5 3m1 3m1 30 55 sec #4 732012300 13500
sec
6 3m1 3m1 45 none at 180
sec sec
7 2m1 2m1 60 150 sec #4 - - -
sec
8 3m1* 3m1 20 55 sec #3 10000'- 13000'
sec
3 5 9 6m1* 3m1 15 30 sec #4 - - 21500'
sec
10 2m15 3m1 20 35 sec #4 13650'- 13850'
sec
* CompositionL usedinstead M
of
$ CompositionK usedinstead M ' rotati t 10
of
on a
rpm
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Persons skilled in the art will recognize from Table I
that the formulations make excellent gels.
In a separate experiment, it was shown that the order of
addition of the phosphate ester solution (sometimes
herein called the gellant) and the ferric sulfate
component (activator) is not important. In this
experiment, 6.168 deionized water and 1.3g ferric sulfate
were added to 85.95g Diesel oil and mixed with the
blender; then 0.4 ml of phosphate esters of the formula
HPO4RR' was added and inversion took place in about one
minute.
The data in Table II demonstrate that our hydrocarbon gel
former will operate in the presence of significant
amounts of water; indeed the viscosity increases with
increasing amounts of water. In this experiment, an
initial mixture was made as above with 4g of gellant and
lOg of activator in about 250g of Diesel oil. Water was
then added incrementally and the viscosity measured
immediately.
Table II
Cumulative Viscosity
Water, % ( 511 sec-1 )
0.65% lcp
1.27% 6cp
2.16% l2cp
2.78% l9cp
3.50% 26cp
4.18% 29cp
5.06% 30cp
6.17%
7.58%
8.38%
10.41%
14.78%
20.2 %
* Dial bouncing and unreadable; excellent lipping gel observed.
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Additional tests were made as shown in Table III, which
records the viscosities achieved by various combinations
within our invention.
Table III
ml M ml F cps ml other comment
3 3 13,800
3 3 13,500
2 2 (bouncing dial)
a 3 13,000
b 3 21,500 6TEA*
c 3 13,900 2KOH
3 3 15,000
3 3 16,000
d 3 5,800 low acid value PE
a 3 9,400 high acid value PE
f 3 20,800 KOH
g 3 11,300 '~KOH
3 3 7,000 ~KOH
3 3 8,600 no TEA in F
3 3 8,700 KOH in M; no TEA
in F
3 3 14,500 KOH in M; no TEA
3 3 13,400
3 3 - 4400 cps @ 20 rpm
i 3 9, 300
j 3 20,400
2 ml 3 12,700
2 ml 1.5 8,300
k 1.5 10,000
1 1.5 12,500 2 ph est; KOH; 1.5
Fe
3 3 14,700
m 3 20,000
3 3 23,000 0.258 NaZCO,
n 3 21,000
0 3 18,400 0.25g Na~C03
3 3 19,500 0.5g CaClZ
p 3 13,800 0.5g CaCl,
2 3 7,000
q 3 11,600
r 3 12, 100
3 3 10,500
3 3 10,500 Fe Citrate
3 3 9,700
3 3 6,800 Fe Citrate
a 3 8,200
v 3 18, 400 NaiCO,
w 3 21, 000 Na~CO,
x 3 10,000
y 3 11,000
as 2 6, 700
bb 1 780
cc 4 12,300
dd 3 13,000
ee 4 12,200
ff 5 12,000
gg 6 11,500
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hh 7 12,300
ii 9 11,500
jj 11 11,400
kk 13 13,300
I1 17 11,800
mm 3 10,900
nn 3 14,700
00 2 14,900
pp 4 14,900
qq 6 12, 500
rr 8 12,700
ss 11 10,400
tt 15 7,600
In Table II, the following notes apply to the column
headed "ml Other":
a triethylamine with phosphate ester of M -- 3 ml
b triethylamine with phosphate ester of M -- 6 ml
c KOH with phosphate ester of M -- 2 ml
d triethanolamine with varied phosphate ester -- 3
ml
a triethanolamine with varied phosphate ester -- 3
ml
f KOH with phosphate ester of M -- 3 ml
g same as f with half as much KOH -- 3 ml
h same as g with half as much KOH -- 3 ml
i, m, n, o, p KOH with phosphate ester of M -- 3
ml
k, 1 KOH with phosphate ester of M -- 2 ml
q, r, s KOH with varied phosphate ester -- 2 ml
t,u,v,w,x,y ml
no alkali;
phosphate
ester
of M
-- 3
as 3 ml non-neut phosphate ester; 2m1 F
bb 3 ml non-neut phosphate ester; 1 ml F
cc 3 ml non-neut phosphate ester; 4 ml F
dd 3 ml KOH-treated phosphate ester; 3 ml F
ee 3 ml KOH-treated phosphate ester; 4 ml F
ff 3 ml KOH-treated phosphate ester; 5 ml F
gg 3 ml KOH-treated phosphate ester; 6 ml F
hh 3 ml KOH-treated phosphate ester; 7 ml F
ii 3 ml KOH-treated phosphate ester; 9 ml F
jj 3 ml KOH-treated phosphate ester; 11 ml F
kk 3 ml KOH-treated phosphate ester; 13 ml F
11 3 ml KOH-treated phosphate ester; 17 ml F
mm 3 ml non-neut phosphate ester; 3 ml F
nn 3 ml non-neut phosphate ester; 2 ml F
00 3 ml M; 4 ml F
pp 3 ml M; 6 ml F
qq 3 ml M; 8 ml F
rr 3 ml M; 11 ml F
ss 3 ml M; 15 ml F
* 6 ml of triethanolamine instead of 3 ml
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From the above table III, it is apparent that a broad
range of ferric salts, neutralizing agents, and other
additives such as breakers, and other materials are not
detrimental to the gelling abilities of our invention.
In addition, it may be seen that triethanolamine and
triethylamine are useful in concentrations of about one-
half molar equivalent (3m1 in the above table) to about
1 molar equivalent ( 6m1 ) with respect to the phosphate
ester. We may use the low molecular weight amines in
amounts from about one-fourth molar equivalent to about
1.5 molar equivalent or more.
In the following Table IV, ferric salts as shown were
used in combination with a standard 3 ml concentration of
phosphate ester solution, some with KOH and some without,
in 300 ml oil. The viscosity was measured with a #4
spindle at 10 rpm unless otherwise noted.
Table IV
Iron ml Fe Viscosity Comment
salt
Fe Citrate 3 6,800
Fe Citrate 1 8,800
Fe Citrate 3 16,700
Fe Citrate 3 7,000+
Fe Citrate 2 8,000
Fe Citrate 2.5 3,300 #3 spndl; lOrpm
Fe Citrate 2.5 3,200 "
Fe Citrate 2.5 3,200 "
Fe Citrate 2.5 2,700 "
Fe Amm Sulf 1 13,000
Fe Amm Sulf 1 3,500 (20 rpm)
Fe Amm Sulf 1.5 14,700
Fe Amm Sulf 1.5 15,000
Fe Chloride 3 6,200
Fe Chloride 2 7,600
Fe Sulfate 1 9,700
Fe Sulfate 1.5 14,000
Fe Sulfate 1 7,000
Fe Amm Citrate 3 12,000
Fe Gluconate 3 4,600
Additional ts and demonstrations were made on
tes
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combinations of ferric sulfate and low molecular weight
amines. In the runs shown in Table V, Fann~'viscosity
readings were taken on various gellant preparations
including low molecular weight amines. For Table V, a
solution (TC-23C) of 67% phosphate ester, 15% KOH and 18%
solvent was prepared; this was mixed with a composition
(TC-23E) comprising 54.4% ferric sulfate (40% solution)
15.9% triethanolamine, 18.7% ethylene glycol, 3% ammonium
cumene sulfate, a surfacant (ACS) and 8% water. The
shear rate in the Fann viscosimeter was maintained at
100~ 0.1. The temperature was elevated as shown in the
table. The gel achieved a remarkably stable viscosity
after about 30 minutes of shear.
Table V
ELAPSED SHEAR
TIME STRESS VISCOSITY ~.F
Min. LB(100F' (cP~
0 70.1 0 71
3 123.8 348 94
8 133.7 376 181
13 124.4 350 224
18 100.7 283 251
23 89.5 252 268
28 81.5 229 279
33 77.1 217 288
38 76.0 214 295
41 75.1 211 299
46 74.6 210 301
51 75.1 211 301
55 74.6 210 300
60 74.6 210 300
65 74.8 210 299
69 75.1 211 299
74 74.8 210 299
79 74.9 210 299
99 74.9 211 299
Table VI shows results using the same materials, in which
the pressure was maintained at 240 psig (~ 2) throughout.
The shear rate was 100 ~ 0.1 as in Table V.
* Trade-mark
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Table VI
ELAPSED SHEAR
TIME STRESS VISCOSITY ~.F
Min. LH/100F2 (cP)
0 77.1 0 109
4 120.6 339 144
9 126.9 357 168
14 138.1 388 185
I9 150.9 424 196
24 157.8 444 203
29 157.2 442 210
34 152.0 427 216
39 145.4 409 222
44.5 139.4 392 227
47.5 136.4 384 229
52.5 133.9 377 230
57.5 130.8 368 231
61.5 111.6 314 231
2 0 66.5 86.8 244 230
A third series of results was obtained on the same
preparation, as shown in Table VII:
Table VII
ELAPSED SHEAR
TIME STRESS VISCOSITY TEMP.F PRESS
Min. LB/100FZ (cP) (psig)
0 77.4 0 81 259
3 0 1 144.5 406 90 259
11 174.5 491 136 261
21 214.8 604 155 263
31 213.6 601 I68 264
24 201.5 567 177 265
3 5 29 197.2 554 179 266
58 196.7 553 180 266
68 198.7 559 179 267
86 200.5 563 179 268
109 200.8 564 180 269
40
These also were highly stable after a prolonged period.
In Table VIII, a gellant was prepared by mixing two
components - the first was 67% phosphate ester, 6% KOH,
and 27% solvent; the second was 54.4% ferric sulfate,
45 20.9% triethanolamine, 18.7% ethylene glycol, 3% ammonium
cumene sulfate (a surfactant) and 3% water. These two
components were mixed into Diesel oil at a concentration
of 2 components of 1%. The resulting gelled hydrocarbon
was tested in the Fann (model 50j , viscometer in a manner
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similar to the above. For the series reported in Table
VIII, the pressure increased gradually from 259 to 267
psig.
Table VIII
ELAPSED SHEAR
TIME STRESS VISCOSITY ~,~F
Min. LB/100FZ ~~p~
0 70.6 0 130
5 191.1 538 151
10 194.7 547 160
35 197.6 555 167
201.2 566 172
202.8 570 177
15 28 202.2 569 I79
33 199.2 560 181
38 194.5 547 182
55 182.2 512 181
100 173.4 488 179
20
The same compos itions used for run again
Table VIII were
for the results in Table IX. In this case, pressure
the
was maintained at 244-245 psig.
Table I%
25
ELAPSED SHEAR
TIME STRESS VISCOSITY ~,~F
Min. LB/100F~ ~~p~
0 74.2 0 105
1 172.0 484 129
5 159.8 449 183
9 124.9 351 218
16 92.6 260 255
24 78.2 220 277
32 74.8 210 290
38 73.9 208 298
46 73.9 208 300
52 73.9 208 300
56 73.9 208 300
4 0 82 73.8 208 299
112 73.8 208 299
The same compositions used for Tables VIII and IX were
used for Table X. In Table X, the pressure dropped
gradually from 240 psig to 237 psig. As in all Tables V
- IX, the shear rate was maintained at 100 ~ 0.1.
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Table g
ELAPSED SHEAR
TIME STRESS V I SCOS ITY ~. F
Min. LB/100Fz (cP)
0 72.3 0 103
4 179.0 503 143
8 172.0 484 164 -
12 162.3 456 179
16 149.2 420 190
136.4 384 198
24 124.2 349 206
28 114.7 322 212
32 105.2 296 ' 21g
15 36 102.0 287 219
40 96.4 271 223
44 92.6 260 228
48 91.3 257 231
52 90.0 253 233
2 0 56 90.1 253 233
60 89.8 252 233
77 92.8 261 233
92 94.8 267 229
107 96.3 271 229
122 98.0 276 229
Excellent gels have also been made using the techniques
recited below:
In this procedure, 55g ferric sulfate was blended with
llg monoisopropyl amine CH3
HZN-CH3
CH3
for a period of about an hour, then blended into Diesel
oil containing a previously prepared mixture consisting
of 67% phosphate ester, 15% KOH, and 18% solvent. The
ferric sulfate - containing blend and the phosphate ester
blend each comprised about 0.5 percent of the final
fracturing fluid. The fracturing fluid was found to make
a good gel overnight. A similar experiment substituting
monobutyl amine provided an excellent gel overnight.
