Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to the acicl treatment of
subterranean earth formations, and more particularly to the
acid treatment of siliceous subterranean formations surround-
ing oil wells, gas wells, water injection wells and similar
boreholes.
~ cid treatment or "acidizing" is a well-known
expedient employed for rejuvenating oil-producing and gas-
producing formations and to facilitate the ease with which
fluid such as water, brine or yas can be injected into sub-
1~ terranean formations surrounding a wellbore. Acidizing ofsiliceous formations, e.g. sandstone, shale, serpentines, etc.,
has met with some favorable results when the formation is
treated with hydrogen fluoride. Various modifications of this
hydrogen fluoride acidizing have been disclosed in the prior
art. These modifications have mainly consisted of the use of
various mixtures of h~drogen fluoride and various other mineral
acids such as orthophosphoric acid, fluorophosphoric acid,
sulfuric acid, hydrochloric acid, etc. Although such mixtures
are generally effective, experience has shown that many forma-
tions do not respond to the acid treatment.
In general, hydrocarbon-bearing siliceous formations
are of a heterogeneous nature and contain a variety of inor-
ganic materials. In addition the pores of the formation may
contain objectional deposits of organic matter such as viscous
crude oil, waxes, asphaltenes and resin precipitates of petro-
leum origin. Conventionally, before the acidizing treatment is
begun this undesirable organic matter must be removed. Solvents
such as carbon disulfide, carbon tetrachloride, or an aromatic
hydrocarbon are first injected into the formation surrounding
the well. This solvent treatment is repeated several t:imes
.~
~ .
--1--
until the pores of the formation are relatively free of the
organic material to insure a proper acidizing environment in
the formation.
Another problem common to all methods of acidizing
is the production of precipitates within the formation
interstices through the action of the acid-treating reagent
or its byproducts on some precipitate-forming constituent of
the formation. This generally occurs when the acidizing fluid
is spent and precipitates in a form which plugs the pores of
the producing formation. As noted above, acidizing techniques
have previously employed mixtures of phosphoric acid, generally
referred to as orkhophosphoric acid, with other mineral acids.
~owever, the orthophosphates of pol~valent or heavy metals
are all virtually insoluble in water. For example, calcium and
magnesium compounds are found in all producing formations, and
when attacked by phosphoric acid mixtures form insoluble phos-
phates. The calcium and magnesium phosphates are especially .
difficult to remove and re~uire expensive procedures to revita-
lize a producing formation. Therefore, there exists a need
for a composition which will provide a "one shot" acidizing
treatment which removes objectionable deposits of organic
material, eliminating the need for a separate solvent treatment
step, along with an acidic-treating reagent that does not form
precipitates within the formation.
Accordingly, a principal object of this invention `
is to provide a novel composition and method for increasing the
permeability of siliceous subterranean formations.
Another object is to provide a composition and
method which remove both acid-soluble and oil-soluble compo-
nents from the formation.
A further object is to provide a composition whlch
does not form undesirable precipitates on reac-tion with the
formation.
Other objects, advantages and ~eatures of the inven-
tion will become apparent ~rom the following description and
appended claims.
This invention provides a substantially anhydrous
emulsion comprising (1) about 5 to 95 parts by weight of an
acid component comprising (a) about 50 to 99 parts by weight
of polyphosphoric acid having about S to 86 weight percent of
the total P2O5 present as polymeric P2O5, (b) about 1 to 25
parts by weight of hydrofluoric acid, and (c) 0 to about 50
parts by weight of a catalyst selected from ~he group consis-
ting of (A) strong mineral acids selected from the group con-
sisting of sulfuric, nitric, perchloric and hydrochloric acids
and mixtures thereof; (b) carboxylic acids selected from the
group consisting of formic, acetic, chloracetic, peracetic,
trichloracetic, citric, oxalic and maleic acids; and (C)
oxidizing agents selected from the group consisting of hydro-
gen peroxide, potassium chromate, potassium permanganate and
chromic acid; (2) about 5 to 95 parts by weight of an organic
solvent component; (3) about 0.01 to 3.0 parts by weight of an
anionic or nonionic surfactant component; and wherein -the
H2O/P2O5 mole ratio of the overall emulsion is less than 3.4.
An em~odiment of the invention provides a substan-
tially anhydrous emulsion comprising: (1) about 25 to 75 parts
by weight of an acid component comprising (a) about 60 to 95
parts by weight of polyphosphoric acid having about ~0 to 75
weight percent of the total P2O5 present as polymeric P~O5,
~,~, I
(b) about 2 to 8 parts by weight of hydrofluoric acid and (c)
about 2 to 40 parts by weight of a catalyst selected from the
group consisting of (A~ strong mineral acids selected from the
group consisting of sulfuric, nitric, perchloric and hydrochloric
acids and mixtures thereof; (B~ carboxylic acids selected from
the group consisting of formic, acetic, chloracetic, peracetic,
trichloracetic, citric, oxalic and maleic acids; and (C) oxidi-
zing agents selected from the group consisting of hydrogen
peroxide, potassium chromate, potassium permanganate and chromic
acid; (2) about 25 to 75 parts by weight of an organic solvent
composition comprising (a) about 40 to 65 parts by weight of
a normally li~uid aliphatic hydrocarbon distillate boiling in
the range of about 120~ to 550 F., (b) about 10 to 30 parts
by weight of a normally liquid aromatic hydrocarbon, (c) about 1
to 5 parts by weight of an ether of an aliphatic alcohol, and (d)
about 2 to 10 parts by weight of a lower alkyl monohydric alco-
hol; (3) about 0.1 to 1.0 parts by weight of an anionic or
nonionic surfactant component; and wherein the H2O/P2O5 mole
ratio of the overall emulsion is between 2.2 and 2.8.
This invention further provides the method for in-
creasing the permeability of a siliceous subterranean geological
formation penetrated by a well which comprises lntroducing --
through said well and into the formation surrounding said well
a substantially anhydrous emulsion comprising: (1) about 5 to 95
parts by weight of an acid component comprising (a) about 50 to
99 parts by weight polyphosphoric acid, said polyphosphoric acid
containiny about 5 to 86 weight percent of the total P2O5 present
as polymeric P2O5, (b~ about 1 to 25 par~s by weight of hydro-
fluoric acid, and (c) 0 to about 50 parts by weight of a catalyst
selected from the group consisting of (A~ strong mineral acids
selected from the group consisting of sulfuric, nitric, per-
chloric and hydrochloric acids and mi~tures thereof; (~)
, -4-
organic carboxylic acids selected from the group consisting of
formic, acetic, chloroacetic, peracetic, trichloracetic, citric,
oxalic and maleic acids; and (C~ oxidizing agents selected ~rom
the group consisting of hydrogen peroxide, potassium chromateg
potassium permanganate and chromic acid; (2) about 5 to 95
parts by weight of an organic solvent compo:nent; (3) about
0.01 to 3.0 parts by weight of an anionic or nonionic surfac-
tant; and in which the ~I2O/P2O5 mo:Le ratio is less than 3.4
in the overall acid emulsion.
A further embodiment of the invention provides a
siliceous subterranean geological formation penetrated by a well
bore which comprises introducing into the formation a highly
viscous, substantially anhydrous, liquid-acid-mixture composi-
tion, comprising: (1) about 25 to 75 parts by weight of an acid
component comprising (a) about 60 to 95 parts by weight polyphos-
phoric acid, said polyphosphoric acid containing abou-t 40 to 75
weight percent of the total P2O5 present as polymeric P2O5,
(b) about 2 to 8 parts by weight of hydrofluoric acid, and
(c) about 2 to 40 parts by weight of a catalyst selected from
the group consisting of (A) strong mineral acids selected from
the group consisting of sulfuric, nitric, perchloric and hydro-
chloric acids and mixtures thereof; (B) organic carboxylic acids
selected from the group consisting of formic, acetic, chloracetic,
peracetic, trichloracetic, citric, oxalic and maleic acids;
and (C) oxidizing agents selected from the group consisting -
of hydrogen peroxide, potassium chromate, potassium permanganate
and chromic acid; (2) about 25 to 75 parts by weight of an
organic solvent composition comprising (a) about 40 to 65
parts by weight o a normally li~uid aliphatic hydrocarbon
distillate boiling in the range o about 120 to 550Q F.,
(b) about 10 to 30 parts by weight o a normall~ liquid
aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an
-4a-
~5~
ether of an aliphatic polyhydric alcohol, and (~) about 2 to
10 parts by weight of a lower monohydric a].cohol, and (3~ about
0.1 to 1.0 parts by weight o~ an anionic or nonionic surfactant,
and in which the ~O~P2O5 mole ratio in the overall emulsion
composition is between 2.2 and 2~.
A still further embodiment of the invention provides a
method for increasing the permeability of a mixed subterranean
geological formation penetrated by a well bore which comprises
introducing into the formation a highly viscous, substantially
anhydrous, liquid-acid-mixture composition, comprising: (1) about
5 to 75 parts by weight o~ an acid component compxising (a) about
50 to 99 parts by weight polyphosphoric acid, said polyphosphoric
acid containing about 5 to 86 weight percent of the total P2O5
present as polymeric P205, (b) about 1 to about 25 parts by ~eight
of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a
catalyst selected from the group consisting of (A) strong mineral
acids selected from the group consisting of sulfuric, nitric, per-
chloric and hydrochloric acids and mixtures thereof; (B) organic
carboxylic acids selected from the group consisting of formic,
acetic, chloracetic, peracetic, trichloracetic, citric, oxalic
and maleic acids; and (C) oxidizing agents selected from the
group consisting of hydrogen peroxide, potassium chromate, potas-
sium permanganate and chromic acid; (2) about 25 to 95 parts by
weight of an organic solvent component; and (3) about 0.01 to
3.0 parts by weight of an anionic or nonionic suxfactant compo-
nent, and wherein the H2O/P2OS mole ratio is from 2.1 to 3.4 in
the overall acid emulsion.
A still ~urther embodiment of the invention provides
a method for increasing the permeability of a mixed subterranean
geological formation penetrated by a well bore which comprises
introducing into the formation a highly viscous~ substantially
anhydrous, liquid-acid-mixture composition, compxising~
j"~
about 20 to 50 parts by weight of an acid component comprising
(a) about 60 to 95 parts by weight pol~phosphoric acid, said
polyphosphoric acid containing about 40 to 75 weight percent
of the total P2O5 present as polymeric P2O5, (b) about 2 to
8 parts by weight of hydrofluoric acid, and ~c) about 2 to 40
parts by weight of a catalyst selected from the group consisting
of (A) strong mineral acids selected from the group consisting
of sulfuric, nitric, perchloric and hydrochloric acids and mix-
tures thereof; (B) organic carboxylic acids selected from the
group consisting of formic, acetic, chloracetic, peracetic, tri-
chloracetic, citric, oxalic and maleic acids; and (C) o~idizin~
agents selected from the group consisting of hydrogen peroxide,
potassium chromate, potassium permanganate and chromic acid; (2)
about 50 to 80 parts by weight of an organic solvent composition
comprising (a) about 40 to 65 parts by weight of a normally
liquid aliphatic hydrocarbon distillate boiling in the range
of about 120 to 550~ F., (b) about 10 to 30 parts by weight of
a normally liquid aromatic hydrocarbon, (c) about l to 5 parts
by weight of an ether of an aliphatic polyhydric alcohol, and
(d) about 2 to 10 parts by weight of a lower al~yl monohydric
alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic
or nonion.ic surfactant, and which the H2O/P2O5 mole ratio in the
overall emulsion composition is between 2.1 and 3.4c
The invention relates to a non-a~ueous emulsion
composition for increasing the permeability of siliceous
subterranean geological formations, and to a method of acidizing
which dissolves organic materials and avoids the formation of
insoluble inorganic precipitates and many of the other difficul-
ties encountered in prior art acidizing methods. The invention
3~ involves the injection into the formation of a novel, non-
~. -4c-
aqueous emulsion comprising a substantially anhydrous liquid
polyphosphoric acid-based mixture, an organic solvent composi-
tion, and a surface-active agent or surfactant. The acid com~ .
ponent of the emulsion comprise:s about 5 to 95 parts by weight
of a substantially anhydrous liquid polyphosphoric acid-based :;
mixture comprising ~a) about 50 to 99 parts by weight polyphos-
phoric acid with about 5 to 86 weight percent of the total P2O5 -
present as polymeric P2O5, (b) about 1 to 25 parts by weight
hydrofluoric acid, and (c) optionally, 0 to about 50 parts by
weight of a catalyst selected from the group consisting of strong
mineral acids, carboxylic acids, oxidizing compounds, and mix- ~ -
tures thereof, in which the H2O/P2O5 mole ratio in the overall
emulsion composition is less than 3.4. The emulsion also contains
about 5 to 95 parts by weight of an organic solvent composition
selected from the group consisting of polar solvents, hydrocar-
bon solvents, and mixtures thereof; and about 0.01 to 3.0 parts
by weight of a surfactant selected from the group consisting of
anionic surfactants and nonionic surfactants.
This novel, non-aqueous emulsion composition can be
utilized in both matrix acidizing and acid fracturing well
stimulation pxocedures, and also has utility in many varied
applications such as gas drying, extracting metals from ores,
metal treatment, removing scale deposits from steam boilers and
pipes, and particularly in methods where solvent treatment is
desired along wtih acidizing action.
The drawing is a graph illustrating the relationship
of the polymeric P2O5 content of the polyphosphoric acid ingre-
dient of the emulsion composition as a function of the mole
ratiO of H2O/P2O5~
The novel, non-aqueous acid emulsion of the pre.sent
invention comprises an acid component, an organic solvent com-
ponent and a surfactant capable of forming either an acid-in-
solvent emulsion or a solvent-in-acid emulsion. The composition
of the non-aqueous polyphosphoric acid-based emulsion employed
in carrying out this invention will depend upon its ultimate use.
Compositions of non-aqueous acid emulsions comprising a mixture
of about 5 to 95 parts by weight of the acid component; about 5
to 95 parts by weight o~ the organic solvent component; and about
0.01 to 3.0 parts by weight of an anionic or nonionic surfactant
are encompassed by the invention.
10The non-aqueous acid emulsion compositions are pre-
pared by: (1) adding the surfactant to the solvent component
with moderate stirring, and ~2) adding this surfactant-solvent
mixture to the acid component with moderate stirring to form
the emulsion. The rate of addition of the surfactant-solvent
mixture is critical and should be slow enough so as not to
break the emulsion already formed. In an alternate method the
surfactant is added to the acid component with moderate stir-
ring and then the solvent component is blended into this acid ~-
mixture. The rate of addition of components must also be con
trolled to avoid breaking the emulsion. These methods provide
stable emulsions which can be either solvent external-acid
internal or acid external-solvent internal. It is generally
preferred to use the solvent external-acid internal type emul-
sion in treating formations. When this type of emulsion enters
a formation pore the solvent first contacts and dissolves any
organic material present, thus expo~ing the siliceous formation
to the acid.
The general reactions involved in the attack of the
substantially anhydrous liquid polyphosphoric-based acid emul-
sions of this invention upon siliceous compounds are expressedby the following equation:
--6--
4P27 + sio2~ ~0_ -o-p-o~; + 2~1 ~ siF4~ ~P2O7+ ~2
O O
In the first step of the reaction, a phosphosilicate
complex is formed. Under anhydrous conditions the soluble phos
phosilicate complex then reacts with hydrofluoric acid to pro-
duce a gas, silicon tetrafluoride, and to regenerate polyphos-
phoric acid and water. The overall concept of this invention ; ?
is that the acid componen-t rapidly dissolves the silica and
complexes other metals such as aluminum, iron, cobalt, nickel,
copper, zinc, and the like. Polyphosphoric acid mixtures hav-
ing a mole ratio of water to phosphorus pentoxide (H2O/P2O5)
of between about 2.1 to 3.~, and particularly between about
2.2 and 2.8, form soluble complexes with most cations. Further-
more, the polyphosphate complexes are stable after neutraliza-
tion. The in situ formation of gaseous silicon tetrafluoride
provides the additional benefit of sweeping and carrying undis-
solved particles of debris through the ormation without plug-
ging or bridging. Excess polyphosphoric acid is required to
remove the ambient and produced water in order to keep the
system in an anhydrous condition, i.e., maintaining the mole
ratio of water to phosphorus pentoxide in the overall acid
mixture below 3.4 and in emulsion form.
In the treatment of subterranean formations, a novel,
non-aqueous emulsion composition is injected into a well and
into contact with a siliceous subterranean formation containing
a solid or semi-solid accumulation o~ hydrocarbons withln the
formation pores. This novel, non-aqueous emulsion composition
constitutes a "one shot" treatment with the solvent component
removing the undesirable hydrocarbon accumulations from the
pores of the formation, thus preconditioning the formation ~or
the attack o~ the acid component of the emulsion. The emulsion
is stable at temperatures existing in the wlell but subject to
being broken by either contacting the pore-plugging hydrocar-
bons or reacting with the silica formation.
In accordance with this invention, the exact emulsion
used will depend largely upon the particular type of formation
to be acidized. In predominantly siliceous geological forma-
tions containing sandstone, shale or other siliceous rock com-
positions, the acid component comprises about 5 to 95 parts by
weight of a mixture comprising about 50 to 99 parts by weight
polyphosphoric acid with about 5 to ~6 weight percent o-f the
total P2O5 present as polymeric P2O5, about 1 to 25 parts by
weight of hydrofluoric acid, and optionally up to about 50 parts
by weight of a catalyst selected from the group consisting of
strong mineral acids, organic carboxylic acids and o~idizing
compounds, where the H2O/P2O5 mole ratio in the overall emulsion
composition is between about 2.1 and 3.~. The solvent component
constitutes about 5 to 95 parts by weight of a solvent blend
comprising (a) about 35 to 80 parts by weight of a normally
liquid aliphatic hydrocarbon distillate boiling within the range
of about 120 F. to 550 F., (b) abou~ 4 to 40 parts by weight
of a normally liquid aromatic hydrocarbon, (c) about 0.5 to 6
parts by weight of an ether of an aliphati~ polyhydric alcohol,
and (d) about 1 to 12 parts by weight of a lower alkyl monohy-
dric alcohol. The emulsion also contains about 0.01 to 3.0
parts by weight of an anionic or nonionic surfactant.
The preferred substantially anhydrous acid emulsions
employed in treating siliceous formations comprise: (l) about
'~'s ~
~ ~5~3 ~
25 to 75 parts by weight of an acid component comprising (a~
about 60 to 95 parts by weight polyphosphoric acid having
about 40 to 75 weight percent of the total P2O5 present as
polymeric P2O5, (b) about 2 to 8 parts by weight of hydro-
fluoric acid, and tc) optionally, 2 to 40 parts by weight of
a catalyst selected from strong mineral acids, carboxylic acids,
and oxidizing compounds; (2) about 25 to 75 parts by weight of
a solvent component comprising (a) about 40 to 65 parts by - ;.
weight of a normally liquid aliphatic hydrocarbon distillate
boiling wtihin the range of 120 F. to 550 F., (b) about 10
to 30 parts by weight of a normally liquid aromatic hydrocarbon,
(c) about 1 to 5 parts by weight of an ether of an aliphatic ~ ;
polyhydric alcohol and (d) about 2 to 10 parts by weight of an
alkyl monohydric alcohol; and (3) about 0.1 to 1.0 parts by
weight of an anionic or nonionic surfactant, and in which the
~2O/P2O5 mole ratio in the overall emulsion composition is
between 2.2 and 2.8.
In mixed formations, i.e., formations containing cal-
careous materials in admixture with siliceous materials, parti-
cularly those formations containing less than 15 percent cal-
careous material, it i~ preferred that the substantially anhy-
drous liquid acid emulsion composition also contains hydro-
chloric acid to aid in dissolving the calcareous materials.
However, it is also preferred that these emulsions contain less
acid component than those previously described for use with
predominantly siliceous formations. In treating mixed forma-
tions there is more danger of a plugging material being pre-
cipitated when the acid spenas on the formation than in treat-
ing predominantly siliceous formations.
The compositions employed in treating mixed forma-
tions broadly comprise the same ingredients and proportions as
are utilized in treating siliceous formations except that the
, ~ i
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~56~3
.
acid component is present in about 5 to 75 parts by weight and
the solvent component is present in about 25 to 95 parts by
weight. Similarly, the preferred compositions for use in
treating mixed formations comprise the same ingredients and
proportions as are preferred for treating siliceous formations
except that the acid component is present in about 20 to ~0
parts by weight and the solvent component is present in about
50 to 30 parts by weight.
The hydrofluoric acid component may be prepared
in si~tu by adding crystalline ammonium bifluoride to hydro-
chloric acid. The hydrogen chloride reacts with the bifluoride
salt to form hydrogen fluoride. The more salt added, the
greater will be the hydrogen fluoride concentration and the
lower will be the hydrogen chloride concentration. Other pre-
parative methods, including the mi~ing o hydrofluoria and
hydrochloric acid solutions, can be employed. The use of such
mixed acids is generally preferred.
The major ingredient of the acid component in the
emulsion composition is polyphosphoric acid. Polyphosphoric
acid is a generic term used to defined the phosphoric acids
havin~ less water of constitution than orthophosphoric acid.
Orthophosphoric acid contains one atom of phosphorus per
molecule and has a theoretical mole ratio of water to phos-
phorus pentoxide of 3.0 or greater. Polyphosphoric acids have
two or more atoms of phosphorus in a theoretical mole ratio of
water to phosphorus pentoxide of less than 3. Polyphosphoric
acid has two general forms, the acyclic and cyclic. The latter
is commonly referred to as metaphosphoric acid. In the acyclic
form, which is derived by limited molecular dehydration of
orthophosphoric acid, the individual chains of phosphorus and
oxygen atoms have termirlal ends and a theoretical mole ratio of
--1 0--
. ,: :,
water to phosphorus pentoxide of between 2 and 3. In metaphos~
phoric acid, which is derived from the acyclic form by continued
molecular dehydration, the chain is endless, forming ring struc-
tures. Metaphosphoric acids have theoretical mole ratios of
water to phosphorus pentoxide of 2 or less. However, in some
cases it is preferred that the concentration or dehydration of
the orthophosphoric acid is stopped before the meta species
begin to form. The reason is that the acyclic form of polyphos-
phoric acid is a much better complexing agent for aluminum and
transition metals like iron, cobalt, nickel, copper, zinc, etc.
Therefore, in geological formations which contain substantial
amounts of compounds of the aforementioned metals, a polyphos-
phoric acid-based acidizing mixture with little or no meta poly-
phosphoric acid present would be most effective. Thus, the pre-
ferred acid compositions exhibit H2V/P2O5 mole ratios above about
The substantially anhydrous polyphosphoric acid com-
ponent of the acid emulsion of this invention may be prepared
from either furnace acid or wet process acid. The various com-
ponents are introduced into a suitable vessel with agitation orstirring preferably in a closed vessel or system. Open vessels
are provided with a cooling means to avoid fuming vapors which
are generated by the exothermal mixing of the acid components.
The composition of this invention can be obtained by any suit-
able method depending on the source materials used. For example,
a dilute wet-process phosphoric acid is processed to polyphos-
phoric acid by the addition of dilute, concentrated, or fuming
sulfuric acid followed by concentration of the mixture through
any suitable step, such as evaporation of water or by the addi-
tion of anhydrous phosphorus pentoxide and anhydrous hydro-
fluoric acid. When a polyphosphoric acid having an H2O/P2O5
mole ratio of less than 2.6 is used, it is preferred to add
concentrated (98~ strength) sulfuric acid to avoid dilution
of the P205 content. On the other hand, fu~ing sulfuric acid,
sulfur trioxide, and/or hydrofluoric acid can be added to poly-
phosphoric acid to obtain the proper percent of the other acids
in the mixture. It i9 noted from the drawing that poly acid
begins to form in the equilibrated acid at a mole ratio of
water to P2O5 of about 3.6, i.e., an acid containing ahout 95
weight percent orthophosphoric acid and still containing about
5 weight pexcent of uncombined water. Although this composi-
tion has some free water, the acid is herein referred to as a
substantially anhydrous acid since it is anhydrous in a sense
that it has reached its maximum concentration of orthophos- -
phoric acid and further concentration increases the poly acid
content.
The total P2O5 content of the non-aqueous polyphos-
phoric based acid emulsion is determined by diluting a repre-
sentative sample with water, adding perchloric and nitric acids
and boiling the mixture to convert all forms of phosphoric acid
to orthophosphoric acid. Samples are then passed over a cation
exchange resin to replace the metal cations with hydrogen as
these cations will interfere with subsequent analyses. The ion-
exchanged sample is thereafter titrated with a strong base
through two break-points, the first of which corresponds to
the neutralization of the strong acids present, hydrochloric, ;~
nitric, etc., and the most strongly ionized hydrogen of the
orthophosphoric acid. The second break-point in the titration
curve occurs at a pH of about 9.5 to 10 and corresponds to
neutralization of the second less strongly ionized hydrogen of
the orthophosphoric acid. The difference in titer between
these break-points corresponds to the total phosphate present
which is reported as total P2O5.
5~
The water content of the acid existing as water of
constitution and water of dilution is determined by placing a
weighted portion of the acid in a crucible with zinc oxide in
excess of that needed to react with the acid. The crucible is
then weighed, dried at 100 C. for one hour and placed in an
oven at 500 C. for an hour. The loss in weight corresponds to
the total water present in the acid mixture.
To determine the amount of orthophosphoric acid pre-
sent, various analytical techniques can be employed. Regard-
less of the analytical method employed, prior thereto, the acidsample is prepared by dilution with water, and then acidifica-
tion with concentraked sulfuric or nitric acid, followed by
further dilution. Care should be ta]cen to avoid elevated tem-
peratures and the sample preparation should be done in an ice
bath to avoid hydrolysis of the polyphosphoric acid. The
resultant solution is passed over a strong acid, cation-exchange
resin, e.g., Amberlite IR-120~I resin*, to remove -the metallic
cation impurities which interfere with subsequent analyses.
Immediately after passage over the resin, the acid should be
neutralized to a pH of about 3.5 to about 6.0 to reduce the
tendency of polyphosphoric acid to hydrolyze. The acid is
thereafter titrated to the break-point, ~alling at a pH
between 9.5 and 10 corresponding to the neutralization of the
second, ionized hydrogen of the orthophosphoric acid. There-
after, an excess of a silver nitrate solution is added to pre-
cipitate silver orthophosphate and release the third, very
weakly ionized hydrogen ion o~ the orthophosphoric acid. The
resultant solution is then titrated to determine the amlount of
hydrogen ion released in the silver precipitation, and this
titer value corresponds to the amount of orthophosphoric acid
present in the sample which is reported on a P2O5 basis.
*Trademark
G~3
The amount of phosphorus pentoxide existing in the
form of polyphosphoric acid can be determined by the difference
between the total P2O5 present and that existing as orthophos-
phoric acid. When, however, the polyphosphoric acid is present
in low concentrations, constituting 5 percent or less of the
total P2O5 content, it is preferred to analyze for the polyphos-
phoric acid directly by an anion exchange chromatography method
such as described by Peters and Rieman in Analytica _himica
Octa, 14, page 131 and by Weiner in Journal_Amer can Oil Chemist
Society, 34, page 124.
Catalytic agents which can be used to catalyze the
above-described general reaction are strong mineral acids,
organic carboxylic acids and oxidizing compounds. These
cataly~ts can be employed in concentration ranges of 0 to about
50 parts by weight and preferably in the range of about 2 to
40 parts by weight.
Strong mineral acids such as sulfuric, nitric, per-
chloric and hydrochloric acids or mixtures thereof can be used.
One drawback with using sulfuric acid as a catalyst in acid mix-
tures for treating hydrocarbon formations is the possibility ofsludge ~ormation due to sulfuric acid attack on formation hydro-
carbons. However, for the other utilities mentioned above, sul-
furic acid is preferred for, in addition to the catalytic effect,
it aids in dehydration and depresses the freeæing point of poly-
phosphoric acid to yield a final product having a freezing point
of less than about 30 F., thereb~ insuring that the mixture is
liquid at ambient temperatures. Furthermore, sulfuric acid has
an additional and surprising effect on the viscosity of the
phosphoric acid for it reduces the acid viscosity by 50 to 75
percent at concentrations of about 20 to 40 weight percent
based on 100-percent-strength sulfuric acid, thereby allowing
the use of a polyphosphoric acid with a lower mole ratio of
-14-
water to phosphorus pentoxide.
Suitable organic carboxylic acids useful as catal~sts
in the above-described reaction are those that form water-
soluble or acid-soluble salts of alkali metals and alkaline
earth metals. For example, formic, acetic, chloroacetic, pera-
cetic, trichloroacetic, citric, oxalic and maleic acids can be
used.
lypical oxidizing compounds which can be employed
accoxding to this invention include hydrogen peroxide, potas-
sium chromate, potassium permanganate and chromic acid.
The organic solvent component can be a hydrocarbon
solvent, halogenated hydrocarbon, or a polar solvent or mixture~
thereof.
Hydrocarbon solvents such as petroleum solvents, petro-
leum ether, petroleum naphtha, gasoline, petroleum spirit, var
nish makers' and painters' naphtha, mineral spirit, kerosene,
turbine fuel, high solvency petroleum naphthas, butanes,
2,2-dimethyl-butane, n-hexane, isohexane, n-heptane, isooctane,
isoheptane, pentene-l, pentene-2, mixed pentenes, isoheptene,
isooctenes, naphthas, benzene, toluene, toluene substitutes,
~ylene, solvent naphthas, ethylbenzene, diethylbenzene, iso-
propylbenzene, amyl-benzene, diamylbenzene, triamylbenzene,
tetraamylbenzene, dikeryl-benzene-12, amyltoluene, cyclohexane,
methylcyclohexane, tetrahydronaphthalene, decahydronaphthalene~
diphenyl, coal-tar creosote, turpentine, terpene solvents,
dipentene, pinene, p-cymene, p-menthane, pine oils, tall oils
and crude oils are suitable.
~ lalogenated hydrocarbons such as methyl bromide,
methyl chloride, dichloromerthane, chloroform, carbon tetra-
chloride, ethyl chloride, ethylene dibromide, ethylene chlorobromide, ethylene dichloride, dichloroethylene, B-txichloro-
ethane, trichloroethylene, trichloroethane, te-trabromoethane,
1,1,2,2-tetrachloroethane, tetrachloroethylene, pentachloro-
ethane, hexachloroethane, isopropyl chloride, allyl chloride,
propylene dichloride, mixed amyl chloride, n-amyl chloride,
dichloropentanes, n-hexyl chloride, monochlorohydrin, dichloro-
hydrin, epichlorohydrin, glycerol alpha-monochlorohydrin,
glycerol alpha, gamma dichlorohydrins, monobromobenzenes, dibro-
mobenzene, monochlorobenzene, o-dichlorobenzene, trichloro- ~.
benzene, a-chloronaphthalene, monoamyl chloronaphthalene, diamyl
chloronaphthalene, dichloroethyl ether, dichlorodiiospropyl
ether, triglycol dichloride, halowax oils, dichlorodifluoro-
methane, difluorochloroethane, fluorodichloromethane, fluoro-
trichloromethane, trifluorotrichloroethane, dichlorotetra-
chloroethane and ethylidene fluoride can be used.
Polar solvents and mixtures thereof which can be
employed include alcohols, ketones, ethers and esters. Alcohols
such as methanol, ethanol, n-propyl alcohol, isopropanol,
n-butanol, isobutyl alcohol, sec-butanol, tert-butanol, fusel
oil, amyl alcohol, pentasol, n-amyl alcohol, sec-amyl alcohol,
sec-n-amyl alcohol, methyl amyl alcohol, 2-ethylbutyl alcohol,
heptanol 2, heptanol-3, 2-ethylhexanol, capryl alcohol, nonyl
alcohol, nonyl alcohol derivatives, diisobutyl carbinol,
n-decanol, undecanol, trimethyl-nonyl alcohol, tetradecanol,
heptadecanol, phenol, benzyl alcohol, cyclohexanol, methyl-
cyclohexanol, trimethylcyclohexanol, 4-tertamyl cyclohexyl
alcohol, 4-tert-amyl cyclohexyl alcohol, dimethyl tolyl carhinol,
furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol,
propylene glycol, diethylene glycol, dipropylene glycol, tri-
methyl glycol, triethylene glycol, polyethylene glycols, poly-
propylene glycol 150, 2-methy:1.-2,4-pentane-diol, glycerol,
terpene alcohol, alphaterpineol, fenchyl alcohol and hydroabietyl
alcohols are useful.
-16-
Ketones such as acetone, methyl acetone, methyl ethyl
ketone, methyl n~propyl ketone, methyl isobutyl ketone, methyl
n-amyl ketone, ethyl butyl ketone, di-n-propyl ketone, methyl
hexyl ketone, diisobutyl ketone, diacetone alcohol r acetonyl
acetone~ mesityl oxide, cyclohexanone, methyl cyclohexanone,
isophorone, and fenchone are suitable.
Ethers including ethyl ether, isopropyl ether,
n-butyl ether, diamyl ether, n-hexyl ether, ethylene glycol
monomethyl ether, "Cellosolve"*, ethylene glycol mono-n-butyl-
ether, ethylene glycol monophenyl ether, ethylene glycol mono-
benzyl ether, "Dowanol" 4**, "Dowanol" 3**, diethylene glycol
monomethyl ether, diethylene glycol monoethyl ether, diethylene
glycol monobutyl ether, "Dowanol" 2**, diethyl acetal, 1,2-pro-
pylene oxide, l,~dioxane, methylal, 2-methyl furan tetrahydro-
furane, 2,3-dihydropyran, pentamethylene oxide, trioxane, ter-
pinyl methyl ether, terpinyl ethylene glycol ether, dichloro-
ethyl ether, triglycol dichloride, glyceryl ~-monoethyl ether,
glyceryl ~-y-dimethyl ether, glyceryl ~-mono-n-butyl ether,
glyceryl ~-monoisoamyl ether, and glyceryl ~-Y diisoamyl ether
can be used.
Examples of esters which can be employed include
methyl acetate, ethyl acetate, n-propyl acetate, isopropyl
acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate,
amyl acetate, sec-amyl acetate, pentacetate, methyl amyl acetate,
2-ethyl butyl acetate, cyclohexyl acetate, methyl cyclohexanyl
acetate, ethylene ylycol monoacetate, glycol diacetate, ethylene
glycol monoacetate, glycol diacetate, ethylene glycol monomethyl
e~her acetate, ethylene glycol monoethyl ether acetate, methoxy
butyl ~cetate, methyl propionate, ethyl propionate, n-bu-tyl
* A trademark of Union Carbide Corporation.
** A trademark of The Dow Chemical Company.
propionate, amyl propionate, ethy]. butyrate, methyl butyrate,
n-butyl hutyrate, ethyl hydroxy-iso-butyra-te, diethyl carbonate,
diethyl oxalate, dibutyl oxalate, diamyl oxalate, methyl formate,
ethyl formate, butyl formate, amyl formate, methyl lactate, .
ethyl lactate, butyl lactate, amyl formate and ethyl silicate.
The surface-active agents or surfactants which can
be employed in the practice of this invent:Lon are anionic sur-
factants, nonionic surfactants and combinations thereof. Suit-
able anionic surfactants are sulfonates characterized by the
following generalized formula:
MSO3R ;
organo-sulfates characterized by the following generalized
formula:
MSO4R ;
organo-phosphates characterized by the following generalized
formula: ~
/ R :`
M2PO4R and MPO4
~ R
wherein M is a cation, exemplary of which are hydrogen and
alkali metals, such as sodium,potassium and lithium, and
wherein R is a lipophilic organic group containing up to 200
carbon atoms, and usually containing from about 6 to 100 car-
bon atoms, and which may also contain some hydrophilic func-
tional groups, exemplary of which are alkyl, aryl, alkylaryl,
alkenyl, alkenylaryl, alkylester, alkylpolyester, alkylether,
alkylarylpolyether, cycloalkyl, naphyl, alkylmercaptyl, anthryl
and alkylanthryl groups; and animal fat, vegetable oil, fatty
acid and rosin derivatives.
Exemplary of the surface-active agents that can be
employed in the practice of this invention are commercial
surfactants, listed in Table 1.
-18-
::., .:
TABLE 1
Company Trademark Chemical
NONIONIC ETHERS
Wyandotte Chemical Pluronic L/62* Po:Lyoxyethylene, poly-
Corp. oxypropylene
Wyandotte Chemical Pluronic L/64* Polyoxyethylene, poly-
Corp. oxypropylene
Rohm & Haas Triton X-35* Octylphenoxy, polyoxy-
ethylene ethanol
Rohm ~ Haas Triton X-45* Octylphenoxy, poly-
ethylene ethanol
Rohm & HaasTriton X-100* Octy]phenoxy, polyoxy-
ethylene ethanol
Rohm & HassTriton X-165* Octylphenoxy, polyoxy-
ethylene ethanol
Rohm & HaasTriton X-305* Octylphenoxy, polyoxy~
ethylene ethanol
Retzloff Chemical Retzonal NP-100* Alkylphenoxy, polyoxy-
ethylene ethanol
Thompson-IIaywardT-mulz 391* Alkylphenoxy, polyoxy-
ethylene ethanol
Trylon ChemicalsEmgard 2030* Alkylphenoxy~ polyoxy-
ethylene ethanol
NONIONIC ESTERS
Armour Ind. Chem. Ethofat 0/15* Polyethoxylated fatty
acids
Armour Ind. Chem. Ethofat C/15* Polyethoxylated fatcy
acids
Atlas Chemical Ind. Span 20* Sorbitan monolaurate
*Trademark
Compan~ Trademark Chemical
Atlas Chemical Ind. Span 60* Sorbitan monostearate
Atlas Chemical Ind. Tween 85* Polyoxyethylene sorbitan
trioleate
Baker Castor Oil Co. Surfactol* Glycerol monoricinoleate
Baker Castor Oil Co. Surfactol 365* Ethoxylated castor oil
ANIONIC SULFONATES
General Aniline & Igepon AC-78* Coconut oil acid, esters
Film Corp. of sodium isethionate
General Aniline & Igepon TN-74* Sodium N-methyl-N-palmi-
Film Corp. toyl taurate
General Aniline & Igepon TE-42* Sodium N-methyl-N-tallow
Film Corp. acid taurate
~merican Cyanamid Aerosol OT* Dioctylester sodium sul-
fosuccinic acid
Mona Ind. Inc. Monawet DC-70* Dioctylester sodium sul-
fosuccinic acid
Calif. Chem. Ornite No. S* Alkylaryl sodium sulfo-
nate
Monsanto Co. Santonerse D* Alkylaryl sodium sulfo-
nate ;
ANIONIC SU~FATES
EoI~ duPont Dupanol C* Sodium lauryl sulfate
de Nemours & Co.
E.I. duPont Dupanol L-144* Sodium alkylaryl sulfate
de Nemours & Co.
ANIONIC PHOSPHATES
General Aniline ~ Gafac PE-510* Free acid of a complex
Film Corp. organic phosphate ester
General Aniline & Gafac RE-610* Free acid of a complex
Film Corp. organic phosphate ester
*Trademark
-20-
~i6~3
Company Trademark Chernical
General Aniline & Gafac MC-~70* Sodium salt of a complex
Film Corp. organic phosphate ester
ANIONIC MISClE~LLANEOUS
~ercules Inc. Dresinate 731* Sodium soap of a modified
rosin
Other additives such as acid inhibitors are not
normally required in the emulsion. For example, at temperatures
below 160 F. acid inhibitors are not necessary. However, if
additi~es are employed, they should be compatible with the acid
mixture. Suitable inhibitors useful above this temperature may
include inorganic arsenic compounds and acetylenic alcohols,
thiophenols, heterocyclic nitrogen compounds, substituted
thioureas, rosin amine derivatives, quaternary ammonium compounds
and similar organic agents.
The substantially anhydrous liquid phosphoric acid- -
based emulsions of this invention can be used in both matrix
acidizing and fracture acidizing. In matrix acidizing, the
method of this invention is carried out by injecting the acid
solution to be used into the producing formation surrounding
the well. The injection pressure is kept below that necessary
to fracture the formation so that penetration of the acid into
the formation matrix occurs. The injection rate selected should 3
be generally sufficient to keep the pressure below that neces-
sary to fracture the formation. The acid component of the
invention has a high solubility for siliceous formations result-
ing in products which are either solubilized or chelated in the
form of low viscosity solutions. After the acid component has ~;
remained in contact with the exposed formation surfaces for a
time sufficient to react therewith and to enlarge the ~ormation
passages, the low viscosity reaction effluent is flushed from
' :~
the formation. Generally a spacer fluid, such as a low-boiling,
low aromatic-containing aliphatic hydrocarbon, e.g., diesel oil,
turbine fuel, etc., is injected followed by the injection of an
after-flush fluid such as filtered crude oil, low calcium-con-
taining water, etc. Injection of the afterflush fluid displaced
the spacer fluid and the low viscosity reaction effluent and is
continued until the desired quantity is introduced. The well
may be returned to production as soon after the after-flush has
been injected as is practicable.
The acid emulsions of this invention exhibit high
viscosities under most reservoir conditions and are particularly
useful in fracture acidi~ing; which treatment, due to much lPwer
fluid loss, promotes the formation oE larger fractures and
greater penetration than do the conventional fracturing tech-
ni~ues. ~dditional benefits derived from the high viscosity
characteristics of the acid mixtures of this invention is that
gelling agents need not be added to the acidizing mixture, and
the use of diverting agents in the acidizing operation may be
avoided. Conventional fracture acidizing equipment may be used
in this operation. As mentioned above, because of the high
viscosity characteristics, the acid emulsions of this invention
can function as both the fracturing fluid and the acidizing
reagent. Conventional propping agents can be used. In some
instances, it is desirable to employ a graded sand of uniform
spherical granular configuration such as 20-40 mesh silica sand. ~ -
This sand is retained within the fractured crevices after the
acid mixture has been flushed therefrom and functions as a
propping agent to retain the formation in a fractured condition.
The use of the acid emulsion of -this invention results
in a greater increase in the permeability of the siliceous for-
mation than if a slug of the acid component is either preceded
-22-
-
or followed by a slug of the solvent component. The emulsion
is composed primarily of an intimate mixture of an acid phase
and a solvent phase. When the emulsion contacts the formation
each pore invaded by the emulsion will be exposed to acid and
solvent at the same time. This insures maximum unplugging and
enlargement of the affected pores. If the acid component and
solvent component are injected as alternate slugs, they do not
necessarily enter the same formation pores due to their differ-
ing viscosities and wetting characteristics, and certainly are
not available for permeability increasing action at the same
time. Thus, the overall increase in permeability of the forma-
tion is not as great as when the acid emulsion is used.
The acid emulsion is also effective in fingering into
the formation for only a short distance and then diverting
itself to form other short fingers. The acid emulsion is
initially quite viscous. As the emulsion comes into contact
with formation rock for the first time, the surfactant emulsi-
fying agent tends to partially adsorb on the formation rock.
This sharply lowers the viscosity of that leading portion of
the acid emulsion which is depleted in surfactant and allows
this portion to penetrate or finger into the forrnation rock
more easily~ However, as soon as a Einger has formed, the
next portion of acid emulsion entering the finger encounters
formation rock onto which surfactant has already been adsorbed.
Thus, this next portion of acid emulsion retains its high vis-
cosity since its surfactant concentration is not depleted. This
plugs the finger, discourages its further lengthening, and
diverts the acid emulsion into fresh formation which has not
previously been exposed to the acid emulsion.
The invention is further described by the following
examples which are illustrative of specific modes of practicing
the inven-tion as defined by the appended claims.
~
EXAMPLE 1
The substantially anhydrous acid emulsion of the
present invention is prepared by adding 9.E~ gallons of
Surfactol 395*, an ethox~lated castor oil, to 3,022 gallons `~
of an organic solvent admixture in a suitahle mixing tank.
The organic solvent is an admixture of 76.0 weight percent of
~et A, an aviation turbine fuel meeting AST~ standard specifi-
cation D-1655 entitled "Standard Specification for Aviation
Turbine Fuels, ASTM Standards, American Society for Testing
Materials, part 17, November, 1971, pages 554-556, which speci-
fication is herein incorporated by reference, 21.0 weight per- .
cent of toluene, 1.1 weight percent of ethylene glycol mono-
butyl ether, and 1.9 weight perc~nt oE isopropanol. Next, this
solvent-surfactant mixture is added, with moderate stirring, to
900 gallons of an acid mixture comprising 82 weight percent of
polyphosphoric acid ~83 weight percent P2O5, 95 weight percent
polymeric P2O5), 7 weight percent of hydrofluoric acid (70%
concentration) and 11 weight percent of hydrochloric acid (37~
concentration) in a stainless steel mixing tank equipped with a
stirrer and a circulating water jacket. The rate of addition is
controlled to prevent breaking the emulsion already formed.
This emulsion contains 60 weight percent of the organic solvent
component, 0.25 weight percent of the surfactant component, and
40 weight percent of the acid component; and the ~20/P~O5 mole
ratio of the overall emulsion is 2.7. The emulsion, thus pre-
pared, is shipped to the well site.
EXAMPLE_2
A gravel-packed well completed in a sandstone forma-
tion designed for the production of 200 barrels of high vis-
cosity crude petroleum would produce only 10 percent of design
* A trademark of Baker Castor Oil Co.
-24-
5 ~ 3
capacity. After the production is stopped, the well is treated
in accordance with the invention by inject:ing a Eirst slug of
4,000 gallons of the emulsion described in Example 1 at a
maximum differential pressure of 150 psi. Nex-t a second slug of
3,000 gallons of the same emulsion is injected at a rate of l/2
to 2 barrels per minute and at pressures below the fracturing
pressure. After the acid treatment is complete, 200 barrels of
turbine fuel ~et A, followed by lO0 barrels of filtered brine,
are injected as an aEterflush. This stimulation treatment
results in an immediate increase in petroleum production of 160
barrels per day.
EXAMPLE 3
This example illustrates the use of the method of
the invention in fracture-acidizing a subterranean oil-producing
formation. A production well is completed in a sandstone forma-
tion with perfoxations in the interval between 2,722 and 3,075
feet, and begins producing only l barrel of oil and 4~ barrels
of water per day. Following the preparation of the emulsion
described in Example l, injection operations are commenced.
The emulsion is injected into the well unti] ahout 6,000 gallons
have been introduced. The pressure initially increases and then
falls off, indica~ing that the formation has bro]cen down and
that the fracture has been initiated. This initial volume of
acid emulsion is followed immediately with 3,000 gallons of
40-gravity lease crude containing about 4 pounds per gallon of
small, solid particles of sand suspended therein as a propping
agent. An additional volume of 3,000 gallons oE the acid emul-
sion is then injected. The second and third stages of the frac-
turing operation are performed using the emulsion compositions
and volumes employed in the first stage.
The injection rate of the emulsion fracturing fluid
is ~etween about lO and 16 barrels per minu-te, and the wellhead
pressure ranges from about 4,700 to 5,500 psi Eor the first
'f~ ;6~3
stage, and between about 5,000 and 6,000 psi for the second and
third stages.
Following the treatment, the well is shut in over-
night. When the well is returned to production, it initially
flows at the rate of 345 barrels of oil and 330 barrels of
water per day. A week after the acid emulsion treatment, the
average production is 360 barrels of oil and 263 barrels of
water per day.
While particular embodiments of the invention have
been described, it will be understood, of course, that the
invention is not limited thereto since many modiEications can
be made and it is intended to include within the invention
such modifications as are within the scope o~ the claims.
The invention having thus been described, we claim:
-26-
