GELLED AQUEOUS INORGANIC ACID SOLUTIONS AND METHODS OF USING THE SAME

MODES D'EMPLOI DE SOLUTIONS AQUEUSES, GELIFIEES D'ACIDES INORGANIQUES

English Abstract

Abstract of the Disclosure
Gelled aqueous inorganic acid solutions and
methods of treating subterranean well formations
using such solutions comprising water, at least one
water soluble inorganic acid and a gelling agent
comprised of a solution of a water soluble organic
solvent and an ethoxylated fatty amine or a mixture
of such amines.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A gelled aqueous inorganic acid solution comprising
water, at least one water soluble inorganic acid and a
gelling agent, said gelling agent being comprised of a
water soluble organic solvent selected from the group
consisting of alkanols having in the range of from about
1 to 5 carbon atoms per molecule, ketones having in the
range of about 3 to 6 carbon atoms per molecule, poly-
hydroxy compounds having in the range of about 2 to 6
carbon atoms per molecule, ethers having in the range
of about 2 to 6 carbon atoms per molecule, compounds
containing both ether and alcohol functions having in
the range of about 4 to 8 carbon atoms per molecule,
esters having in the range of about 2 to 6 carbon atoms
per molecule, lactones having in the range of about 3 to
5 carbon atoms per molecule and mixtures of two or more
of the foregoing compounds, and a mixture of ethoxylated
fatty amines dissolved in said water soluble organic
solvent having the general formula:
<IMG>
wherein:
R is selected from saturated and unsaturated aliphatic
groups having in the range of from about 8 to
about 22 carbon atoms and mixtures thereof, and
x and y each have a value in the range of from 0 to
about 10.
27

2. The gelled aqueous inorganic acid solution of claim 1
wherein the average sum of the values of x and y in said
mixture of ethoxylated fatty amines is in the range of
from about 1.8 to about 2.2.
3. The gelled aqueous inorganic acid solution of claim 2
wherein said gelling agent is present in said acid
solution in an amount in the range of from about 0.1% to
about 10% gelling agent by weight of said acid solution.
4. The gelled aqueous inorganic acid solution of claim 3
wherein R is selected from the group consisting of satur-
ated and unsaturated aliphatic groups having in the range
of from about 16 to about 18 carbon atoms and mixtures
thereof, and wherein the average sum of the values of x
and y in said mixture of ethoxylated fatty amines is equal
to 2.
5. The gelled aqueous inorganic acid solution of claim 2
wherein said ethoxylated fatty amines are present in said
gelling agent in an amount in the range of from about 10%
to about 80% by weight of said gelling agent.
6. The gelled aqueous inorganic acid solution of claim 4
wherein said water soluble organic solvent is an alkanol
selected from the group consisting of methanol, ethanol,
isopropanol, t-butanol and mixtures thereof, and said
ethyoxylated fatty amines are present in said gelling
agent in an amount of about 50% by weight of said gelling
agent.
7. The gelled aqueous inorganic acid solution of claim 2
wherein said water soluble inorganic acid is hydrochloric
acid.
8. A gelled aqueous inorganic acid solution comprising
water, an inorganic acid and a gelling agent, said gelling
28

agent being comprised of a water soluble organic solvent
selected from the group consisting of alkanols having in
the range of from about 1 to 5 carbon atoms per molecule,
ketones having in the range of about 3 to 6 carbon atoms
per molecule, polyhydroxy compounds having in the range of
about 2 to 6 carbon atoms per molecule, ethers having in
the range of about 2 to 6 carbon atoms per molecule,
compounds containing both ether and alcohol functions
having in the range of about 4 to 8 carbon atoms per
molecule, esters having in the range of about 2 to 6
carbon atoms per molecule, lactones having in the range of
about 3 to 5 carbon atoms per molecule and mixtures of two
or more of the foregoing compounds, and an ethoxylated
fatty amine dissolved in said water soluble organic
solvent having the general formula:
<IMG>
wherein:
R is selected from the group consisting of saturated
and unsaturated aliphatic groups and mixtures
thereof having in the range of from about 14 to
about 18 carbon atoms.
9. The gelled aqueous inorganic acid solution of claim 8
wherein R is selected from the group consisting of
saturated and unsaturated aliphatic groups and mixtures
thereof having in the range of from about 16 to about 18
carbon atoms.
10. The gelled aqueous inorganic acid solution of claim 9
wherein said water soluble organic solvent is an alkanol
selected from the group consisting of methanol, ethanol,
isopropanol, t-butanol and mixtures thereof.
29

11. The gelled aqueous inorganic acid solution of claim 9
wherein said ethoxylated fatty amine is present in said
gelling agent in an amount in the range of from about 10%
to about 80% by weight of said gelling agent.
12. The gelled aqueous inorganic acid solution of claim 9
wherein said water soluble inorganic solvent is methanol
and said ethoxylated fatty amine is present in said gelling
agent in an amount of about 50% by weight of said gelling
agent.
13. The gelled aqueous inorganic acid solution of claim 12
wherein said gelling agent is present in said acid solution
in an amount in the range of from about 0.1% to about 10%
by weight of said acid solution.
14. A method of treating a subterranean well formation
comprising the steps of:
combining a gelling agent with an aqueous inorganic
acid solution in an amount in the range of from about 0.1
to about 10% by weight of said solution whereby the
viscosity of said solution is increased, said gelling
agent being comprised of a water soluble organic solvent
selected from the group consisting of alkanols having in
the range of from about 1 to 5 carbon atoms per molecule,
ketones having in the range of about 3 to 6 carbon atoms
per molecule, polyhydroxy compounds having in the range
of about 2 to 6 carbon atoms per molecule, ethers having
in the range of about 2 to 6 carbon atoms per molecule,
compounds containing both ether and alcohol functions
having in the range of about 4 to 8 carbon atoms per
molecule, esters having in the range of about 2 to 6
carbon atoms per molecule, lactones having in the range of
about 3 to 5 carbon atoms per molecule and mixtures of two

or more of the foregoing compounds, and a mixture of
ethoxylated fatty amines dissolved in said water soluble
organic solvent having the general formula:
<IMG>
wherein:
R is selected from saturated and unsaturated aliphatic
groups having in the range of from about 8 to
about 22 carbon atoms and mixtures thereof and
x and y each have a value in the range of from 0 to
about 10 with the average sum of the values of x
and y in said mixture being in the range of from
about 1.8 to about 2.2; and
introducing said solution into said subterranean
formation.
15. The method of claim 14 wherein R is selected from the
group consisting of saturated and unsaturated aliphatic
groups having in the range of from about 14 to about 18
carbon atoms and mixtures thereof, and wherein the average
sum of the values of x and y in said mixture of ethoxy-
lated fatty amines is equal to 2.
16. The method of claim 15 wherein said ethoxylated fatty
amines are present in said gelling agent in an amount in
the range of from about 10% to about 80% by weight of said
gelling agent.
17. The method of claim 16 wherein said water soluble
organic solvent is an alkanol selected from the group
consisting of methanol, ethanol, isopropanol, t-butanol
and mixtures thereof and said ethoxylated fatty amine is
present in said gelling agent in an amount of about 50%
by weight of said gelling agent.
31

18. The method of claim 14 wherein said inorganic acid is
hydrochloric acid.
19. The method of claim 14 wherein said aqueous inorganic
acid solution is an aqueous hydrochloric acid solution
having a hydrochloric acid concentration of above about
22% by weight of said solution.
20. The method of claim 15 wherein said aqueous inorganic
acid solution is an aqueous hydrochloric acid solution
having a hydrochloric acid concentration of below about
22% by weight of said solution.
21. The method of claim 20 which is further characterized
to include the step of combining calcium chloride with
said aqueous hydrochloric acid solution in an amount in
the range of from about 1% to about 10% by weight of said
solution.
32

Description

3~6
Acidizing and fracturing procedures usiny aqueous
acid solutions are commonly carried out in subterranean
well forma~ions to accomplish a number of purposes, one
of which is to facilita~e the increase in the recovery
o hydrocarbons therefrom. In acidizing procedures, aqueous
acid solutions are introduced into wel1 ormations under
pressure so that the acid solutions flow into the pore
spaces of khe formations and react with materials con-
tained therein whereby the pore spaces are enlarged and
the permeability of the formations increased. In fracture
acidizing procedures, one or more fractures are produced
in the formations and the acid solutions are introduced
into the fractures to etch flow channels therein and/or
to enlarge the pore spaces in the fracture faces and in
the formations.
Increasing the viscosity o~ an aqueous acid solution,
hereinafter referred to as "gelling," by the inclusion of
certain swellable materials or gelling agents therein has
been accomplished heretofore. In acidizing and/or frac-
ture acidizing subterranean formations, gelled aqueous
acid solutions are useful in preventing the acid from be-
coming prematurely spent and inactive. In addition, gelling
of the acid solutions enables the development of wider
fractures so that live acid can be forced further into the
formation f:rom the well bore. Furthermore, increasing the
'
. . ,

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viscosities o ~he acid solutions a-lso permits better
fluid loss control.
Gelled aqueous acid solutions have utilit~ in indus~
trial applications other than in the treatment of subterran-
ean well ~ormations such as in the cleaning of industrial
equipment.
Gelling agents such as hydratable gums and cellulose
derivatives have been utilized to increase the viscosity
o aqueous acid solutions. However, the gels produced
using such gelling agents gene~ally have limited stabilit~
at high temperatures in the presence of acid. Other gell-
ing agents which increase the viscosity o aqueous acid
solutions have been developed and used, but they are often
difficult to disperse and usually require considerable
mixing or agitation to develop full viscosity. Still other
prior art gelling agents can form an undesirable precipitate
during the dissolution of formation materials such as lime-
; stone or dolomite, which precipitate can remain in the
formation to thereby damage it by decreasing the perme-
ability thereof.
By the present i~vention, a gelling agent for increas-
ing the viscosity of aqueous acid solutions, the resulting
gelled aqueous acid solutions and methods of using such
gelled aqueous acid solutions are provided. The gelling
agent of the present invention can be easily dispersed into
_3_

3~
an aqueous acid solution and only a small quantity of it
is required to rapidly increase the viscosity of the acid
solution with a minimum of mixing and agitation. The
resulting gelled aqueous acid solutions of the present
invention have. excellent stability over a broad temperature
range; they are relatively non-damaging to subterranean
formations treated therewith; and, upon becoming spent in
subterranean formations, and, without the inc].usion of
chemical breakers or special additives kherein, they break
to low viscosity liquids haviny excellent fines suspension
properties.
The present invention relates to a gelled aqueous
inorganic acid solution comprising water, at least one
water soluble inorganic acid and a gelling agent, said
gelling agent being comprised of a water soluble organic
solvent selected from the group consisting of alkanols
having in the range of from about 1 to 5 carbon atoms per
molecule, ketones having in the range of about 3 to 6
carbon atoms per molecule, polyhydroxy compounds having
in the range of about 2 to 6 carbon atoms per molecule,
ethers having in the range of about 2 to 6 carbon atoms
per molecule, compounds containing both ether and alcohol
functions having in the range of about 4 to 8 carbon atoms
per molecule, esters having in the range of about 2 to 6
carbon atoms per molecule, lactones having in the range
of about 3 to 5 carbon atoms per molecule and mixtures of
two or more of the foregoing compounds, and a mixture of
ethoxylated fatty amines dissolved in said water soluble
organic solvent having the general formula:
--4--
A

))XH
R - N
\ (CH2CH20)yH (1)
wherein:
R is selected from saturated and unsaturated aliphatic
groups having in the range of from about 8 to about 22
carbon atoms, and mixtures thereof, and x and y each have
a value in the range of from about O to about 10. The
preferred ethoxylated fatty amines and mixtures thereoE
useful herein are those wherein the average sum of the
values of x and y in the amines used is in the range of
from about 1.8 to about 2.2.
-4a-
~A

3~
Mixtures of ethoxylated tertiary fatty amines derived
from fats and oils such as coconut oil, soy bean oil, and
tallow are particularly suitable or use in accordance with
the present invention.
A preferred mixture of ethoxylated fatty amines for
use in this invention is a mixture of amines of the general
formula:
~(CH2CM20) xH
~ N\
\(CH2CH2O)yH (2,
wherein:
R is selected from the group consisting of saturaked
and unsaturated aliphatic groups having in the range of rom
abo~lt 14 to about 18 carbon atoms and mixtures of such
groups; and
wherein the average sum of the values of x and y in the
mixture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y each have
a value of 1 (oné).
Examples of such amines are those derived from fatty
acids of the type hexadecyl, tallow, soya and oleyl, either
saturated or unsaturated and either as pure components or
mixtures.
A var:iety of organic solvents can be utilized in mak-
ing the ge:Lling agents so long as such solvents are capable

of dissolving the ethoxylated fatty amines and are also
water soluble. Examples of such water soluble organic
solvents include alkanols having in the range of about 1
to 5 carbon atoms per molecule, such as methanol, ethanol,
5i isopropanol and t-butanol; ketones having in the xange of
about 3 to 6 carbon atoms per molecule~ such as acetone
and methylethyl ketone polyhydroxy compounds having in
the range of about 2 to 6 carbon a~oms per molecule, such
as ethylene glycol and glycerine; ethers having in the range
of about 2 to 6 carbon atoms per molecule, such as dioxane
and tetrahydrofuran; compounds containing both ether and
alcohol functions having in the range o-f about 4 to 8 car-
bon atoms per molecule, such as diethylene glycol and tri-
ethylene glycol; organic acids having in the range of about
1 to 10 carbon atoms per molecule, such as formic acid,
malonic acid, acetic acid, gluconic acid, levuiinic acid
. ~ and propionic acid; esters having in the range of about 2
: to 6 carbon atoms per molecule, such as methyl formate,
dimethyl oxylate and dimethyl malonate; and lactones having
in the range of about 3 to 5 carbon atoms per molecule, such
as beta-propyl lactone and gamma-butyl lactone. Due to the
desirably low freezing point and/or high flash point (tag
closed cup) of the resulting yelling agent the organic acids
are preerxed with acetic acid being the most prefeLred.
The water soluble organic solvent useful herein is
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3~- ~
preferably in liquid phase at the temperature at which it
is mixed with thé ethoxylated fatty amine. Furthermore,
mixtures of the organic solvents can be used. An example
is a mixture of me~hanol and gluconic acid.
The gelling agents useful herein can be pxepared by
mixing the water soluble organic solvents with the ethoxy-
lated fatty amines for a period of time suf~icient to com-
pletely dissolve the amines in the solvents. The quantity
of ethoxylated amines dissolved in the organic solvent
range in an amount of from about 10 ko about 80, preferably
from about 50 to about 60 percent amine by weight o~ the
gelling agent.
As mentioned above, the organic solvents can be used
singly, or in mixtures of solvents of the same chemical
class (acids with acids, ketones with ketones and the like)
or in mixtures of solvents of di~ferent chemical classes
(acids with alcohols, ethers with ketones and the like). A
preferred organic solvent is a mixture of chemicals of dif-
ferent chemical classes wherein at least one of the classes
is an organic acid.
The ethoxylated fatty amines useful herein are very
difficult to dissolve directly in aqueous inorganic acid
solutions. However, the gelling agent of this invention,
comprising a solution of the amines dissolved in a wa-ter
soluble organic solvent, such as acetic acid, readily dis-
solves in an aqueous inorganic acid solution and substan-
tially Lmmediately increases the viscosity of the acid
solution.
The gelling agents of the present invention cause an

3~$
increase in the viscosity of aqueous inorganic acid solu-
tions having acid concentrations in the range from about
1 to abou~ 25 percent active acid by weight of the solu-
tions. However, acid solutio.ns having acid concentrations
of greater than abouk 25 percent can be mixed with the
gelling agents of this invention and such acid solutions,
upon being reacted, will begin to exhibit a noticeable
increase in viscosity w~en the acid concentration, due to
the reaction, is diminished to a value of about 25 percent.
Such increase in viscosity continues with continued decrease
in acid concentration until the acid concentration reaches
a value in the range of from about 10 percent to about 15
percent. To this extent then, this invention features a
delayed gelling characteristic.
The gelling agents of this invention will cause the
viscosity of aqueous inorganic acid solutions having acid
concentrations in the range of from about 1 to about 10
percent, and more particularly in the range of from about
1 to about 5 percent, to rapidly increase providing that the
presence of dissolved salts in the acid solution is very low
and preferably absent. In this connection, the presence of
dissolved salts in the gelled acids of this invention cause
the gels to break when the acid concentration is less than
about 10 percent and particularly when the acid concentration
is less than about 5 percent. This~breaking feature, as will
--8--

be further explained below, can be of particular value when
the acid gels of this invention are used to acid treat sub-
terranean formations.
.
The gelling agents are particulaxly useful in increas-
ing the viscosity o~ aqueous inorganic acid solutions such
as hydrochloric acid solutions, sul~uric acid solutions,
phosphoric acid solutions, hydrofluoric acid solutions and
solutions containing mixtures of such acids.
In preparing a gelled aqueous acid solution of this
invention, the acid or mixture of acids utilized can be,
and is preferably, diluted with water to obtain an aqueous
inorganic acid solution of desired acid concentration. A
gelling agent of the present invention, i.e., an ethoxylated
fatty amine or mixture of such amines of the type described
above dissolved in a water soluble organic solvent, is pre-
ferably comb~ned with the aqueous acid solution in an amount
in the range of from about 0.1 to about 10, and more prefer-
ably in the range of from about 2 to 6, percent gelling
agent by weight of the aqueous acid solution. The acid solu-
tion and gelling agent are agitated or mixed for a short
period of time whereupon the viscosity o the aqueous acid
solution is increased. More specifically, some increase in
viscosity is obtained when as little as 0.1 percent gelling
agent is combined with the aqueous acid solution, and
greater amounts of the gelling agent bring about increased
_9_
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3~i6
viscosity. When the gelling agent is combined with the
aqueous acid solution in an amount of about lO percent
by weight of the solution, viscosities of about 150 centi-
poises can be obtained.
Greater viscosity increase can be obtained through use
of gelling agent amounts in excess of lO percent. Thus,
l~ percent is not a limit on the capability of the gelling
agent to increase the viscosity of acid, but is viewed as
a working guide in view of current process economics and
the practical capabilities of currently known liquid hand-
ling and pumping equipment.
A gelled aqueous acid solution of this invention is
comprised of water, a water soluble inorganic acid or mix-
ture of such acids, and a gelling agent comprised of a
solution of a water soluble organic solvent and an ethoxy-
lated fatty amine having the general formula:
. ~cH2cH2o)xH
; R N\
~ C~2CH2O)yH (3)
wherein:
R is selected from saturated and unsaturated aliphatic
groups having in the range of from about 8 to about 22 car-
bon atoms, and mixtures thereof, and x and y each have a
value in the range of from about 0 to about 10.
A preferred selled aqueous acid solution of this inven-
tion is comprised of an inorganic aqueous acid solution
'.
,
-10-

3~g~
comprising water and a water soluble inorganic acid or
mixture of such acids, and a gelling agent comprised o
a solutlon of a water soluble organic solvent and a mix-
ture of ethoxylated fatty amines having the general
fo~mula:
(C}I;~CH20) xH
R----W ~
. ~ CH2CH20)~H (4)
wherein:
R is selected from saturated and unsaturated aliphatic
groups having in the range of from about 14 to about 18 car-
bon atoms and mixtures of such groups; and x and y each have
a value in the range of from 0 to about 10 with the average
sum of the values of x and y in the mixture being in the
range of fl-om about 1.8 to about 2.2.
The most preferred gelled aqueous acid solution of
this invention is comprised o an aqueous acid solution
comprising water and an inorganic water soluble acid or a
mixture of such acids, and a gelliny agent present in the
aqueous acid solution in an amount in the range of from
about 1 to about 10 percent gelling agent by weight of
the acid so:Lution. The gelling agent is comprised of a
solution of a water soluble organic solvent, and a mixture
of ethoxylated fatty amines present in the gelling agent
in an amount of from about 10 to about 80 percent amines

3~
by weight of the gelling agent. The ethoxylated fatty
amines have the general formula:
~c~l~cH2o) xH
R - N \
~ CH2CH20)yH (5)
wherein:
R is selected from the group consisting of saturated
and unsaturated aliphatic groups having in the range of
from about 16 to about 18 carbon atoms and mixtures of such
groups; and
the average sum of the values of x and y in said mix-
ture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y in formula
(S) each have a value of one (1).
The gelled aqueous acid solutions of this invention
are stable over a wide temperature range and therefore will
not chemically degrade with time, even at a temperature as
high as 250F. It must be understood, however, that the
gelled acids of this invention, like other liquids, do
experiénce viscosity change with temperature change. Thus,
for example, with increasing temperaturel the viscosity of
these gels declines, but is regained upon decrease of tem-
perature. Thus, gels made according to this invention have
long storage life.
While the gelled aqueous acid solutions of this inven~
tion have a variety of uses, they are particularly suitable
-12- .

3~;~
for carrying out acid treatments in subterranean well
formations for increasing the production of hydrocaxbon
fluids therefrom. When the gelled aqueous acid solutions
are intraduced into subterranean well formation, the acid
spends by reacting with materials in the formakion, e.g.,
lLmestone and/or dolomite, whereby salts (e.g., chlorides
when HCl i5 used~ are formed. ~he formation of salts in
the spent acid solution causes the viscosity of the solu-
tion ko decrease. That is, as the acid spends and salks
form, the viscosity of the spent acid solution begins to
decrease when acid concentration is in the range of about
10 to 15 percent. Thus, chemicals known in the art as
"breakers" are not required when the gelled acid solutions
of this invention are used to acid treat subterranean well
formations. The spent acid solutions, after breaking, have
viscosities in the range of from about 5 to about 15 centi-
poises and have excellent particle suspension properties
which facilitates the efficient clean-up of a treated forma-
tion.
In using the gelled aqueous acid solutions for carrying
out acidizing treatments in a subterranean well formation,
an aqueous acid solution of desired acid strength is first
prepared. For example, in carrying out acidizing or acid
fracturing treatments in limestone or dolomite formations,
aqueous hydrochloric acid solutions in concentrations in
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the range of from about 3~ to about 28% by weight are
often utilized. After the particular aqueous acid solu-
tion to be used has been prepared and diluted to the
desired strength, the gelliny agent o the present inven-
tion is combined therewith, pre~erably in an amount in
the range of from about 0.1 to about 10 percent by weight
of the acid solution whereby the viscosity of the solution
is increased. Other conventional well ormation treating
additives, such as corrosion inhibitors, non-emulsifying
agents, fluid loss additives, etc., can also be combined
with the solution. The resultant gelled aqueous acid
solution is introduced into the formation to carry out
an acidizing or acid fracturing treatment therein. After
the a~ueous acid solution has become spent by reaction
with materials in the formation and thereby broken to a
low viscosity fluid, it is produced from the formation and
the formation is cleaned up using conventional clean-up
procedures followed by placing the formation on production.
When a gelled aqueous hydrochloric acid solution of
this invention having an initial acid concentration of be'ow
about 22 percent by weight of solution spends on limestone
or dolomite to thus form calcium chloride and magnesium
chloride and cools, some water and the gelling agent can
separate out of the solution as a thick viscous phase.
Separation does not occur when the initial hydrochloric
- -14-

3~
acid concentration is above about 22 percent by weight. In
order to prevent separation in spent solutions when acid
concentrations below about 22 percent by weight are utilized,
calcium chloride can be added to the aqueous hydrochloric
acid solution prior to gelling in an amount such that after
reaction, the spent solution contains a calcium chloride
concentration equivalent to a spent 22 percent by weight
hyd.rochloric acid solution. The amount of calcium chloride
required generally falls within the range of from about 1
percent to about 10 percent by wei~ht o~ the spent solution.
That is, when a gelled aqueous hydrochloric acid solution
having an acid concentration of above about 22 percent by
weight of the solution is utilized in the treatment of sub-
terranean well formations containing calcium, n4 calcium
- 15 chloride is added to the live solution. When a gelled
aqueous hydrochloric acid solution at a concentration of
20 percent by weight of solution is utilized, about 308
pounds of calcium chloride per 1000 gallons o~ aqueous
acid solution are added thereto which prevents separation
at low temperatures (150F and below). When a gelled
aqueous hydrochloric acid solution having a concentration
of 15 percent by weight is utilized, about 1040 pounds o~
calcium chloride per 1000 gallons of acid solu-tion are com-
bined therewith to prevent such separation.
The following examples are gi~en in order to further
-15-

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.
illustrate the gelling agent and gelled aqueous acid solu-
tions of the present invention.
Example 1
Gelling agents o the present invention are prepared
S using various mixtures of ethoxylated fatty amines dissolved
in glacial acetic acid. The gelling agents are added to
aqueous acid solutions containing 15 percent by weight hydro-
chloric acid, and the viscosities of the resultant gels
determined. The viscosities of the gels are apparent visco-
sities measured on a Model 35 FANN viscometer, no. 1 spring,
standard bob and sleeve, at room temperature (72 - 76F) and
at 300 rpm. The results of these tests are given in Table I
below.
~,
:
-16-

l~D~3~$
TABLE I - VISCOSITIES OF GELLED AQUEOUS
HYDROCHLORIC ACID SOLUTIONS USING VARIOUS GELL~N~ AGENT~ .
Ethoxylated Average Concentratlon Concentratlon Vlscoslty
Fatty Amine Moles of o~ Amines Con- of Gelling of Gelled
S Fatty Acid Ethylen~ tained in Gel- Agent inAqueous
Origin Oxide ling Agent, % Hydrochloric HCl
Per Mole ~y Welght of Acid Solution,
- of Amine Acetic Acid- Solution, cp
.. , Amine % by Weight
Solution
,
Coconut
(Mixture of
Chains Hav-
i~g 8, 10,
12, 14, 16
and 18 Car-
bon Atoms) 2 33.3 9 3
Coconut
(Mixture of
Chains Hav-
ing 8, 10,
12, 14, l~
and 18 Car-
bon Atoms) 5 33.3 9 3
Soya (Mix-
ture of
Chains Hav-
ing 14, 16
and 18 Car-
bon Atoms) 2 33.3 9 77
Soya (Mix-
ture of
Chains Hav-
ing 14, 16
and 18
Carbon
Atoms) 5 33.3 9 3
Tallow
(Mixture
of Chains
Having
14, 16
and 18
Carbon
Atoms) 2 33.3 9 55
Oleyl (18
: Carbon
Atoms) 2 33.3 9 82
Palmityl
'(16 Car-
bon Atoms) 2 50 6 52
.
-17-

t~ 3.~6
From Table I it can be seen that gelling agents con-
taining ethoxylated fatty am:ines derived from coconut,
soya, tallow, oleic, and palmitic fatty acids increase the
viscosit,y,of aqueous hydroch:Loric acid solutions.
The results provided in Table I also make it clear
that ethoxylated ~atty amines having an average of 2 moles
of ethylene oxide per mole of amine and containing hydrocar-
bon chain lengths of 14 to 18 carbon atoms significantly
increase the viscosity of aqueous hydrochloric acid solutions~
Example 2
A gelling agent is prepared by dissolving 3 grams o~
ethoxylated soya amines having an average of 2 moles of
ethylene oxide per mole of amine in 6 mls. (about 7 grams)
of glacial acetic acid. The approximate composition of a
commercial mixture of fatty acids from which the soya amine,
is derived is as follows:
Acid % By Weight
myristic (C14) 0 to 1%
palmitic (C16) 6 to 10%
steariC (C18) 2 to 4%
oleiC (C18) 21 to 29% .
linoleiC (C18) ' S0 to 59%
linoleniC (C18) 4 to 8%
The gelling agent is combined with 125 mls. (about 134
grams) of an aqueous hydrochloric acid solution containing
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,.

D~3~fEi
15 percent by weight hydrochloric acid. After mixing, the
aqueous hydrochloric acid solution has an apparent visco-
sity of 95 centipoises measured on a Model 35 FANN visco-
meter, no. 1 spring, standard bob and sleeve at room
temperature (72 - 76F) and 300 rpm.
Example 3
Gelling agents are prepared by dissolving 5 grams of
ethoxylated tallow amines having an average ethylene oxide
content of 2 moles per mole o amine with vaxious organic
solvents. The gelling agents are then each added in amounts
of 10 mls. to 200 mls. of an aqueous acid solution prepared
by combining 126.8 mls. of tap water with 73.2 mls. o~ a
hydrochloric acid solution containing 37.5 percent by
weight hydrochloric acid to thus produce 200 mls. of 15
percent HCl so,lution which weighed 215 grams. The solu-
tion also contains 25 grams of calcium chloride and 0.4
ml. of a hydrochloric acid corrosion inhibitor. After mix-
ing the gelling agents with the acid solutions, the apparent
viscosities of the resulting gelled aqueous hydrochloric acid
solutions are determined using a Model 35 FANN viscometer,
no. 1 spring, standard bob and sleeve at 80F and 300 rpm.
The results o these tests are shown in Table II below.
--19--

r!~
TABLE II - VISCOSITIES OF GELLED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS USING GELLING AGENTS CONTAINING VARIOUS ORGANIC ACIDS
Quantity of Organic Quantity Degree of Viscosity
Ethoxylated Solvent of Difficulty of Gelled
Tallow Organic in Dissolv- Aqueous
Amines, ml Solvent, ing Amines Hydrochloric
(grams) ml in Solvent Acid
(grams) Used solutions
( 5 ) Propionic 5 (5.0) Easily 51
acid dissolved
( 5 ) Acetic 5 (5.2) Very easily 70
acid dissolved
5 ( 5 ) Formic S (5.9) Dif~icult 88
Acid - 88~
; 15 5 ( 5 ) Acetone 5 (3.9) Easily 67
dissolved
( 5 ) Ethylene 5 (5.5) Easily 75
Glycol dissolved
~.
Gelling agents are prepared by dissolving ethoxylated
tallow amines~having an average of 2 moles of ethylene
oxide per mole of amine in various organic acids in amounts
of 50 percent by weight of amine-acid solution. Each of the
gelling agents are combined with aqueous hydrochloric acid
solutions in amounts of 5 percent gelling agent by weight of
the acid solutions, and the viscosities of the resulting
gelled aqueous acid solutions are determined at various tem-
peratures. Each of the aqueous acid solutions contain 15
percent hydrochloric acid by weight, 12.5 grams of calcium
chloride per 100 cc of acid solution, and 0.2 percent by
weight of a hydrochloric acid corrosion inhibitor.
, -20-

~'~'J1~3~l~
TABLE III - VISCOSITIES OF GELLED HYDROCHLORIC ACID SOLUTIONS
AT VARIOUS ~EMPERATUES USING GELLING AGENTS
CONTAINING VARIOtJS ORGANIC ACIDS
.
Organic Viscosities of Gelled Aqueous ~ICl Solutions, cp
Acid
.
90~F 100F 110F 120F 130F 140F 150F 160F 170F 180F
Formic 70 66 61 55 48.5 40 30 23.5 19 16
Acetic 67 61 54 46 :35 29 23 19 14.S 10.5
Prop-41.5 30 21.5 16 13 10.5 8 6 4.5 3.5
ionic
As illustrated in Tables II and III above, gelling agents
wherein formic acid is used as the amine solvent achieve the
highest apparent viscosity in hydrochloric acid solutions. How-
ever, because the dissolution of ethoxylated ~atty amines in
formic acid is difficult, acetic acid is preferred for use in
accordance with this invention.
. .:,", .
~ Fxample 5
A gelling agent is prepared by dissolving ethoxylated
tallow amines having an average ethylene oxide content of 2
moles per mole of amine in acetic acid in an amount of 50
percent by weight of the amine-acid solution. Various amounts
of the gelling agent are combined with aqueous hydrochloric
acid solutions containing 15 percent by weight hydrochloric
acid and 0.4 percent by weight hydrochloric acid corrosion
inhibitor. The apparent viscosities of the resulting gelled
aqueous hydroc:hloric acid solutions are determined at var~
ious temperatures using a Model 35 FANN viscometer, no. l

3r~
spring, standard bob and sleeve at 300 rpmO The results
of these tests are given in Table IV below.
TABLE IV - VISCOSITIES OF GELhED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS AT VARIOUS TEMPERATUES USING VARIOUS
QUANTITIES OF GELLING AGENT
Percent Viscosities of Gelled Aqueous ~Cl Solutions, cp
Gelling
Agent By ~
Weight of
Acid Solu- 90F100F 110F 120F130F 140F 150F160F
kion
~~
2 l98.5 4 32.5
3 37.535 31.5 27 2l 15.5 6 2.5
4 48.545 40 31.524 18 14 10
S 68.565 50 38 31 24 19 14
From Table IV it can be seen that by increasing the
amount of gelling agent combined with an aqueous solution,
the viscosity of the resultant gelled solution is increased.
Example 6
A gelling agent is prepared by dissolving ethoxylated
tallow amines having an ethylene oxide content of 2 moles
per mole of amine in glacial acetic acid in an amount of
50 percent by weight o the resulting solution. A portion
of the gelling agent is combined with an aqueous hydrochloric
25 acid solution in an amount of 5 percent by weight of the
acid solution. The acid solution contains 15 percent by
weight of hydrochloric acid, 12.5 grams of calcium chloride

3~;$
per 100 cc o~ the solution and 0.2 percent by weight of a
hydrochloric acid corrosion inhibitor. The resulting gelled
aqueous hydrochloric acid solution is spent to 10.3 percent
by weight live hydrochloric acid b~ reacting the solution
with lim,estone. Viscosities of the spent solution are
determined at various temperatures using a Model 35 FANN
viscometer, no. 1 spring, standard bob and sleeve at 300
rpm. The results of these tests are given in Table V.
TABLE V - VISCOSITIES OF GELLED 15~ BY WEIGHT
AQUEOUS HYDROCHLORIC ACID SOLUTION AT VARIOUS TEMPERATURES
AFTER BEING SPENT TO 10.3% BY WEIGHT LIVE ACI~
__ _ _
Temperature, F Viscosity, cp
,
8~ 70
loo ?
110 ' 5
120 3-5
130 , 2
From Table V it can be seen that when a gelled 15
percent by weight hydrochloric acid solution is spent to
a live acid concentration of 10.3 percent by weight, the
acid solution is broken to a ~iscosity of less than about
10 cp at a temperature o~ 100F.
.
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, .. . ...... . ..

3~;
Example 7
A gelling agent is prepared as described in Example 6
and is combined with an aqueous hydrochloric acid solution
in an amount of 5 percent hy weight of acid solution. The
hydrochIoric acid solution contains 28 percent by weight
hydrochloric acid and 0.5 percent by weight acid corrosion
inhibitor. The resulting ge].led aqueous hydrochloric acid
solution is spent by reaction with limestone to various live
acid concentrations, and the viscosities of such partially
spent solutions are determined at various temperatures using
a Model 35 FANN viscometer, no. l spring, standard bob and
sleeve at 300 rpm. The results o these tests are shown
in Table VI below.
TABLE VI - VISCOSITIES OF GELLED 28% BY WEIGHT A~UEOUS
HYDROCHLORIC ACID SOLUTIONS AT VARIOUS TE~PERATURES
AFTER BEING SPENT TO VARIOUS LIVE ACID CONCENTRATIONS
Spent
Solution Viscosities of Spent Acid Solutions, cp
Live Acid
Concentra-
tion, %
By Weight 90F 100F 110F 120F 130F 140F 150F 160F
____ .
19.919,5 20 20 19 lB 16.5 15 13
15.97066.5 60 51 40 30 5 3
10.345 8.5 6 5 4 3 ~ 1.5
6.2 6 ~
From Table VI it can be seen that when a gelled a~ueous
hydrochloric acid solution of this invention containing 28
-2~-

3~i~
percent by weight hydrochloric acid is spent to a live
acid concentration below abol~t 16 percent by weight, such
spent solution is broken to a viscosity below about 5 cp
at 150F~
:'
. Example 8
A gelling agent of the present invention is prepared
by dissolving ethoxylated tallow amines haviny an ethylene
oxide content of 2 moles per mole of amine in glacial
acetic acid in an amount of 50 percent by weight of the solu-
tion. Portions of the gelling agent are added to aqueous
hydrochloric acid solutions, and the resulting gelled hydro-
chloric acid solutions are spent by reaction with limestone.
The apparent viscosities of the spent solutions are measured
on a Model 35 FANN viscometer, no. 1 spring, standard bob
and sleeve at 300 rpm. the particle or fines suspending
properties of the spent acid solutions are determined by
placing 2 grams of fines in 100 ml portions of the spent
solutions, mixing the solutions and then allowing the fines
to settle in the solutions for 6 hours. The fines remaining
suspended in the solutions after the 6-hour periods are
determined by collecting the fines by centrifugation, wash-
ing, drying and wei~hing. The results of these tests are
given in Table VII below.
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D~3~
TABLE VII - FIME SUSPENSION ABILITY OF
SPENT GELLED AQUEOUS ACID SOLUTIONS
Gelled Aqueous Acid Solution Solution
~ _ Live
, Acid Acid Suspended
Caicium Corro Concen- Viscosity Fines in
. Chloride, sion tration O Spent Spent Acid
Grams/ Inhi- Gell:ing After Acid Solution
HCl, l00 cc bitor, Agen1: Spending, After A~ter 6
by Acid ~ By % By % HCl By Solution, Hours, mg/
Weight Solution Weight Weight Wei~ht cp l00 cc
15 12.5 0.2 5 l.5 l0 (74F)206
20 3.7 0.2 5 1.2 5 (80F)279
28 0 0.2 5 1.4 7.S (64F) 330
Deionized water only 5
_ _ _ , _
.
From Table VI it can be seen tha~. the spent gelled
aqueous aci~ solutions of this lnvention have excellent
. fines suspension capability.
,
~:
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