U.S. patent application number 13/533031 was filed with the patent office on 2012-12-27 for method of removing inorganic scales.
This patent application is currently assigned to Baker Hughes Incorporated. Invention is credited to Ahmed Mohamed Mohamed Gomaa, Qi Qu.
Application Number | 20120325485 13/533031 |
Document ID | / |
Family ID | 47360746 |
Filed Date | 2012-12-27 |
United States Patent
Application |
20120325485 |
Kind Code |
A1 |
Qu; Qi ; et al. |
December 27, 2012 |
METHOD OF REMOVING INORGANIC SCALES
Abstract
The productivity of hydrocarbons from hydrocarbon-bearing
calcareous or siliceous formations is enhanced by contacting the
formation with a well treatment composition which contains a
hydrofluoric acid source, a phosphonate acid, ester or salt
thereof, a quaternary ammonium salt and an organosilane and,
optionally, a boron-containing compound.
Inventors: |
Qu; Qi; (Spring, TX)
; Gomaa; Ahmed Mohamed Mohamed; (Tomball, TX) |
Assignee: |
Baker Hughes Incorporated
|
Family ID: |
47360746 |
Appl. No.: |
13/533031 |
Filed: |
June 26, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12861390 |
Aug 23, 2010 |
8211836 |
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13533031 |
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11901578 |
Sep 18, 2007 |
7781381 |
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12861390 |
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Current U.S.
Class: |
166/312 |
Current CPC
Class: |
C09K 8/78 20130101; C09K
8/528 20130101 |
Class at
Publication: |
166/312 |
International
Class: |
E21B 37/06 20060101
E21B037/06 |
Claims
1. A method for enhancing the productivity of a hydrocarbon-bearing
calcareous or siliceous formation comprising: (A) pumping into the
wellbore penetrating the formation a well treatment composition
comprising: a) a phosphonate acid, ester or salt thereof, wherein
the phosphonate is of the formula: ##STR00010## wherein R1, R2 and
R3 are independently selected from hydrogen, alkyl, aryl,
phosphonic, phosphonate, phosphate, aminophosphonic acid,
aminophosphonate, acyl, amine, hydroxy or carboxyl groups or R4 and
R5 are independently selected from hydrogen, sodium, potassium,
ammonium or an organic radical; (b) a hydrofluoric acid source; (c)
a quaternary ammonium salt; and (d) an organosilane; and (B)
preventing the formation or inhibiting the formation of inorganic
fluoride scales in the wellbore and/or formation.
2. The method of claim 1, wherein the pH of the well treatment
composition is between from about 0 to about 3.
3. The method of claim 1, wherein the amount of quaternary ammonium
salt in the aqueous well treating composition is between from about
0.01 to about 10 percent by volume based on the total volume of the
well treatment composition.
4. The method of claim 1, wherein the amount of the organosilane in
the well treatment composition is between from about 0.01 to about
10 percent by volume based on the total volume of the well
treatment composition.
5. The method of claim 1, wherein the inorganic or siliceous scales
are selected from the group consisting of calcium fluoride,
magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate
and fluoroaluminate.
6. The method of claim 1, wherein the amount of phosphonate acid,
ester or salt thereof in the aqueous well treating composition is
between from about 0.1 to about 10 percent by volume based on the
total volume of (a) and (b) and water.
7. The method of claim 1, wherein the aqueous well treating
composition further comprises a boron containing compound selected
from the group consisting of (i.) fluoroboric acid and/or (ii.)
boron compounds capable of forming a BF.sub.4.sup.- complex when
exposed to F.sub.4.sup.- or a hydrofluoric acid source and further
comprising forming a BF.sub.4.sup.- complex.
8. The method of claim 7, wherein the boron containing compound is
of the formula R.sub.6R.sub.7R.sub.8BO.sub.3 wherein each of
R.sub.6, R.sub.7 and R.sub.8 are independently hydrogen or a
unsubstituted or substituted alkyl or alkylene group.
9. The method of claim 7, wherein the boron containing compound is
of the formula: ##STR00011## wherein each of R.sub.9, R.sub.10,
R.sub.11, R.sub.12, R.sub.13, R.sub.14, R.sub.15 and R.sub.16 is
independently selected from hydrogen or a substituted or
unsubstituted alkyl or alkenyl group.
10. The method of claim 7, wherein the amount of boron containing
compound in the aqueous well treatment composition is that
sufficient to render between from about 0.5 to about 10 g
BF.sub.4.sup.- complex per 100 cc of (a), (b) and water.
11. The method of claim 1, wherein the aqueous well treatment
composition is introduced into the wellbore during a fracturing,
remedial workover or matrix acidizing operation.
12. The method of claim 1, wherein the quaternary ammonium salt is
represented by the formula:
N(R.sup.6)(R.sup.7)(R.sup.8)(R.sup.9)Y.sup.- wherein each of
R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are selected from the group
consisting of hydrogen, a C.sub.1-C.sub.6 alkyl group or a
hydroxyalkyl group, provided not all of R.sup.6, R.sup.7, R.sup.8
and R.sup.9 are hydrogen; and Y.sup.- is a halide, perchlorate,
thiocyanate, cyanate, a C.sub.1-C.sub.6 carboxylate, an alkyl
sulfate, methanesulfonate, BX.sub.4.sup.-, PF.sub.6.sup.-,
AsF.sub.6.sup.-, SbF.sub.6.sup.-, NO.sub.2.sup.-, NO.sub.3.sup.- or
SO.sub.4.sup.-.
13. The method of claim 12, wherein Y is --Cl.
14. The method of claim 12, wherein the cation of the quaternary
ammonium salt is N,N,N-trimethylethanolammonium.
15. The method of claim 1, wherein the quaternary ammonium salt has
repeating units selected from the group consisting of: ##STR00012##
wherein R and R.sup.3 are independently selected from the group
consisting of an alkylene group having from about 2 to about 4
carbon atoms; R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.7,
R.sup.83n d R.sup.9 are independently selected from the group
consisting of methyl or ethyl; R.sup.6 is selected from the group
consisting of an unsubstituted alkylene group having from about 2
to 4 carbon atoms and a substituted alkylene group having from
about 2 to about 4 carbon atoms and containing a hydroxy group; X
is an anion selected from the group consisting of a halogen, methyl
sulfate, sulfate, and nitrate; v represents the valency of the
anion represented by X; and, s is an integer equal to the number of
said anions required to maintain electronic neutrality.
16. The method of claim 15, wherein the quaternary ammonium salt is
of the formula: ##STR00013##
17. The method of claim 1, wherein the organosilane is at least one
of the following: (a) a silane-based compound of the formula:
##STR00014## wherein X is a halogen, R.sub.1 is an organic radical
having from 1 to about 50 carbon atoms, and R.sub.2 and R.sub.3 are
the same or different halogens or organic radicals having from 1 to
about 50 carbon atoms; (b) a silane-based compound of the formula
R--Si(OR').sub.3 wherein R is branched or linear aliphatic carbon
chain that is saturated or unsaturated, and that has from about 1
to about 10 carbon atoms; and wherein each R' is independently
branched or linear carbon chain that is saturated or unsaturated,
and that has from about 1 to about 4 carbon atoms; or (c) a
siloxane-based compound of the formula:
R--Si(OR').sub.2--O--Si(OR'').sub.2--R wherein R is a branched or
linear aliphatic carbon chain that is saturated or unsaturated, and
that has from about 1 to about 10 carbon atoms; and wherein each R'
and each R'' is independently a branched or linear carbon chain
that may be saturated or unsaturated and that has from about 1 to
about 4 carbon atoms.
18. The method of claim 17, wherein the organosilane is an
aminoalkyl siloxane.
19. A method of preventing and/or inhibiting the swelling of clay
within a subterranean formation penetrated by a wellbore which
comprises: (A) pumping into the wellbore an aqueous well treatment
composition comprising: a) a phosphonate acid, ester or salt
thereof, wherein the phosphonate is of the formula: ##STR00015##
wherein R1, R2 and R3 are independently selected from hydrogen,
alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic
acid, aminophosphonate, acyl, amine, hydroxy or carboxyl groups and
R4 and R5 are independently selected from hydrogen, sodium,
potassium, ammonium or an organic radical; (c) a hydrofluoric acid
source; (d) a quaternary ammonium salt; and (e) an organosilane;
and (B) minimizing or eliminating the amount of clay swelled in the
formation.
20. The method of claim 19, wherein the pH of the well treatment
composition is between from about 0 to about 3, the amount of
quaternary ammonium salt in the aqueous well treating composition
is between from about 0.01 to about 10 percent by volume based on
the total volume of the well treatment composition, and the amount
of the organosilane in the well treatment composition is between
from about 0.01 to about 10 percent by volume based on the total
volume of the well treatment composition.
21. The method of claim 19 wherein the aqueous well treating
composition further comprises a boron containing compound selected
from the group consisting of (i.) fluoroboric acid and/or (ii.)
boron compounds capable of forming a BF.sub.4.sup.- complex when
exposed to F.sub.4.sup.- or a hydrofluoric acid source and further
comprising forming a BF.sub.4.sup.- complex.
22. The method of claim 19, wherein the quaternary ammonium salt is
represented by the formula:
N(R.sup.6)(R.sup.7)(R.sup.8)(R.sup.9)Y.sup.- wherein R.sup.6,
R.sup.7, R.sup.8 and R.sup.9 are independently a C.sub.1-C.sub.6
alkyl group or a hydroxyalkyl group wherein the alkyl group is
preferably a C.sub.1-C.sub.6 alkyl; and Y.sup.- is a halide,
perchlorate, thiocyanate, cyanate, a C.sub.1-C.sub.6 carboxylate,
an alkyl sulfate, methanesulfonate, BX.sub.4.sup.-, PF.sub.6.sup.-,
AsF.sub.6.sup.-, SbF.sub.6.sup.-, NO.sub.2.sup.-, NO.sub.3.sup.- or
SO.sub.4.sup.-.
23. The method of claim 22, wherein Y is --Cl.
24. The method of claim 22, wherein the cation of the quaternary
ammonium salt is N,N,N-trimethylethanolammonium.
25. The method of claim 19, wherein the quaternary ammonium salt
has repeating units selected from the group consisting of:
##STR00016## wherein R and R.sup.3 are independently selected from
the group consisting of an alkylene group having from about 2 to
about 4 carbon atoms; R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.7,
R.sup.8, and R.sup.9 are independently selected from the group
consisting of methyl or ethyl; R.sup.6 is selected from the group
consisting of an unsubstituted alkylene group having from about 2
to 4 carbon atoms and a substituted alkylene group having from
about 2 to about 4 carbon atoms and containing a hydroxy group; X
is an anion selected from the group consisting of a halogen, methyl
sulfate, sulfate, and nitrate; v represents the valency of the
anion represented by X; and, s is an integer equal to the number of
said anions required to maintain electronic neutrality.
26. The method of claim 25, wherein the quaternary ammonium salt is
of the formula: ##STR00017##
27. The method of claim 19, wherein the organosilane is at least
one of the following: (a) a silane-based compound of the formula:
##STR00018## wherein X is a halogen, R.sub.1 is an organic radical
having from 1 to about 50 carbon atoms, and R.sub.2 and R.sub.3 are
the same or different halogens or organic radicals having from 1 to
about 50 carbon atoms; (b) a silane-based compound of the formula
R--Si(OR').sub.3 wherein R is branched or linear aliphatic carbon
chain that is saturated or unsaturated, and that has from about 1
to about 10 carbon atoms; and wherein each R' is independently
branched or linear carbon chain that is saturated or unsaturated,
and that has from about 1 to about 4 carbon atoms; or (c) a
siloxane-based compound of the formula:
R--Si(OR').sub.2--O--Si(OR'').sub.2--R wherein R is a branched or
linear aliphatic carbon chain that is saturated or unsaturated, and
that has from about 1 to about 10 carbon atoms; and wherein each R'
and each R'' is independently a branched or linear carbon chain
that may be saturated or unsaturated and that has from about 1 to
about 4 carbon atoms.
28. The method of claim 27, wherein the organosilane is an
aminoalkyl siloxane.
29. A method of removing calcium fluoride, magnesium fluoride,
sodium fluorosilicate, potassium fluorosilicate and/or
fluoroaluminate scales from hydrocarbon-producing wellbores and
minimizing or eliminating the swelling of clay within a
subterranean formation penetrated by the wellbore, the method
comprising: (A) pumping into the wellbore a well treatment
composition having a pH between from about 0 to about 3.0 and
comprising: a) a phosphonate acid, ester or salt thereof, wherein
the phosphonate is of the formula: ##STR00019## wherein R1, R2 and
R3 are independently selected from hydrogen, alkyl, aryl,
phosphonic, phosphonate, phosphate, aminophosphonic acid,
aminophosphonate, acyl, amine, hydroxy or carboxyl groups and R4
and R5 are independently selected from hydrogen, sodium, potassium,
ammonium or an organic radical; (b) a hydrofluoric acid source; (c)
a quaternary ammonium salt of the formula:
N(R.sup.6)(R.sup.7)(R.sup.8)(R.sup.9)Y.sup.- wherein R.sup.6,
R.sup.7, R.sup.8 and R.sup.9 are independently a C.sub.1-C.sub.6
alkyl group or a hydroxyalkyl group wherein the alkyl group is
preferably a C.sub.1-C.sub.6 alkyl; and (d) an aminoalkyl siloxane;
and (B) removing inorganic or siliceous scales from the wellbore
wherein the amount of quaternary ammonium salt and the amount of
the organosilane in the well treatment composition is each between
from about 0.01 to about 10 percent by volume based on the total
volume of the well treatment composition.
30. The method of claim 29, wherein the cation of the quaternary
ammonium salt is N,N,N-trimethylethanolammonium.
31. The method of claim 29 wherein the aqueous well treating
composition further comprises a boron containing compound selected
from the group consisting of (i.) fluoroboric acid and/or (ii.)
boron compounds capable of forming a BF.sub.4.sup.- complex when
exposed to F.sub.4.sup.- or a hydrofluoric acid source and further
comprising forming a BF.sub.4.sup.- complex.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/861,390 which is a continuation of U.S.
patent application Ser. No. 11/901,578, filed on Sep. 18, 2007, now
U.S. Pat. No. 7,781,381.
FIELD OF THE INVENTION
[0002] The invention relates to a method of enhancing the
productivity of a hydrocarbon bearing siliceous or calcareous
formation by use of a well treatment composition which contains a
phosphonate acid, ester or salt, a hydrofluoric acid source, a
quaternary ammonium salt and an organosilane.
BACKGROUND OF THE INVENTION
[0003] In the course of drilling, or during production or workover,
the vast majority of oil and gas wells are exposed to conditions
that ultimately lead to formation damage. Formation damage limits
the productive (or injective) capacity of the well. The reduction
in well performance is generally due to changes in near-wellbore
permeability which may be caused by a number of factors, such as
rock crushing, invasion of drill solids, swelling of pore-lining
clays, migration of mobile fines and changes in wettability.
[0004] For instance, the swelling and migration of formation clay
particles is often increased when formation clays are disturbed by
foreign substances, such as aqueous well treatment fluids. The
swelling and migration of formation clay reduces the permeability
of the formation by obstructing the formation capillaries,
resulting in a loss of formation permeability and significant
reduction in the flow rate of hydrocarbons. Typically, the use of
clay stabilizers is required during treatment operations in order
to control any change or movement of the clay. In addition to
inhibiting the swelling and/or migration of clay, such additives
are useful in the control of fines generation which further
contribute to a reduction in permeability.
[0005] It is known that permeability impairment may also be
improved by injecting acid formulations containing HF into the
formation. Such methods are known to improve production from both
subterranean calcareous and siliceous formations. Most sandstone
formation are composed of over 70% sand quartz, i.e. silica, bonded
together by various amount of cementing material including
carbonate, dolomite and silicates. Suitable silicates include clays
and feldspars. A common method of treating sandstone formations
involves introducing hydrofluoric acid into the wellbore and
allowing the hydrofluoric acid to react with the surrounding
formation. Hydrofluoric acid exhibits high reactivity towards
siliceous minerals, such as clays and quartz fines. For instance,
hydrofluoric acid reacts very quickly with authigenic clays, such
as smectite, kaolinite, illite and chlorite, especially at
temperatures above 150.degree. F. As such, hydrofluoric acid is
capable of attacking and dissolving siliceous minerals.
[0006] Upon contact of hydrofluoric acid with metallic ions present
in the formation, such as sodium, potassium, calcium and magnesium,
undesirable precipitation reactions occur. For example, during the
treatment of calcareous or siliceous formations containing
carbonate or dolomite, calcium or magnesium fluoride scales often
form as a result of precipitation. Such scales tend to plug the
pore spaces and reduce the porosity and permeability of the
formation.
[0007] Alternative methods of treating calcareous or siliceous
formations with hydrofluoric acid have been sought wherein the
formation of undesirable scales is prevented or inhibited while
minimizing or preventing the swelling and migration of formation
clay particles and the generation of fines.
SUMMARY OF THE INVENTION
[0008] Subterranean sandstone or siliceous formations and
calcareous formations penetrated by oil, gas or geothermal wells
may be treated with an aqueous well treatment composition
containing a hydrofluoric acid source in combination with an
organosilane, a quaternary ammonium salt and a phosphonate acid,
ester or salt. The well treatment composition may further contain a
boron containing compound for forming a BF.sub.4 complex.
[0009] The aqueous well treatment composition aids in the
inhibition of inorganic scales and in most instances the prevention
of formation of the undesirable scales. Additionally, it will
minimize corrosion potential on downhole metal tubulars. Such
compositions have been shown to increase the permeability of the
formation being treated by inhibiting or preventing the formation
of undesirable inorganic scales, such as calcium fluoride,
magnesium fluoride, potassium fluorosilicate, sodium
fluorosilicate, fluoroaluminate, etc. As a result, production from
the formation is increased or improved.
[0010] While the hydrofluoric acid source may be hydrofluoric acid,
it more typically is prepared in-situ in the aqueous system by the
reaction of hydrochloric acid and ammonium bifluoride or ammonium
fluoride. In the current invention, an excess of ammonium
bifluoride or ammonium fluoride is used such that all of the
hydrochloric acid is consumed in the production of hydrofluoric
acid, leaving a small amount of unconverted ammonium bifluoride or
ammonium fluoride.
[0011] When present, the boron containing compound is preferably
fluoroboric acid or a boron compound which is capable of being
hydrolyzed to form a BF.sub.4.sup.- complex when exposed to F.sup.-
or a hydrofluoric acid source.
[0012] The phosphonate of the well treatment composition is
preferably a phosphonate acid, ester or salt thereof, such as those
of the formula:
##STR00001##
wherein R1, R2 and R3 are independently selected from hydrogen,
alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic,
aminophosphonate, acyl, amine, hydroxy or carboxyl groups and salts
thereof and R4 and R5 are independently selected from hydrogen,
sodium, potassium, ammonium or an organic radical.
[0013] The presence of the combination of the organosilane and the
quaternary ammonium salt in the well treatment composition further
provides for greater control of clay migration and inhibits or
prevents swelling. Further, the presence of the combination of the
organosilane and the quaternary ammonium salt inhibits or prevents
formation fines from becoming dispersed in the well treatment
composition. In addition, this combination aids in the inhibition
and thus the control of scale formation.
[0014] The pH of the well treatment composition is typically
maintained at a range of from about 0 to about 3.0.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The permeability of sandstone or siliceous formations and
calcareous formations is increased during acid treatment of the
well by including in an aqueous well treatment composition a
synergistic amount of an organosilane and a quaternary ammonium
salt. The aqueous well treatment composition further contains a
hydrofluoric acid source and a phosphonate compound.
[0016] The combination of the organosilane and the quaternary
ammonium salt acts synergistically to control the swelling and
migration of clay within the formation and to minimize the
generation of fines. In particular, the effect imparted by the
combination of the quaternary ammonium salt and the organosilane is
substantially greater than the effect imparted by either component
when used individually in an otherwise identical well treatment
composition. The combination of the quaternary ammonium salt and
organosilane acts to retain the naturally occurring clay platelets
in the formation in position by controlling the charge and
electrolytic characteristics of the treatment fluid and thus
substantially reduces or eliminates clay and formation fines from
becoming dispersed and plugging the formation matrix.
[0017] The aqueous well treatment composition may further contain a
boron containing compound. When present, the boron containing
compound principally functions to inhibit or prevent the formation
of fluoride scales or to remove such scales from wellbores, screens
or other equipment and/or pipelines.
[0018] In a preferred embodiment, the boron containing compound is
fluoroboric acid or tetrafluoroboric acid of the formula
BF.sub.4.sup.-H.sup.+.
[0019] The boron containing compound may further be an acid soluble
boric acid and/or an organic boron containing compound, including
those which are capable of forming a BF.sup.- complex when
hydrolyzed and exposed to F.sup.- or HF containing solution. The
reaction, where the boron containing compound is boric acid, may be
represented by the equation:
4HF+H.sub.3BO.sub.3.fwdarw.BF.sub.4.sup.-+H.sub.3O.sup.++2H.sub.2O
(I).
[0020] The formation of BF.sub.4.sup.- controls the concentration
of active HF at any given time. Borate esters further acid
hydrolyze to boric acid which tender the BF.sub.4.sup.- complex, as
set forth by equation (I) above. Hydrolysis may not occur, however,
until higher than ambient temperatures are reached. For instance,
hydrolysis may not occur until formation temperature is reached or
sufficient heat is generated from the acid reaction.
[0021] Suitable boron containing compounds include boric acid,
H.sub.3BO.sub.3 as well as esters of boric acid. Preferred as the
boron containing compounds are those of the formula
R.sub.6R.sub.7R.sub.8BO.sub.3 wherein each of R.sub.6, R.sub.7 and
R.sub.8 are independently hydrogen or an unsubstituted or
substituted alkyl or alkylene group, and is preferably
independently selected from hydrogen or C.sub.1-C.sub.4 alkyl
group, optionally substituted with one or more --OH groups.
Preferred boron compounds include tributyl borate which is very
moisture sensitive.
[0022] Also preferred are tetraborates, such as sodium tetraborate.
Boric oxide, B.sub.2O.sub.3, metaboric acid and HBO.sub.2 are
further preferred since they easily hydrolyze to boric acid,
B(OH).sub.3.
[0023] Boric acid reacts rapidly with polyols, glycerol
.alpha.-hydroxycarboxylic acids, cis-1,2-diols, cis-1,3-diosl,
o-quinols, o-catechol and mannitol to form ether type complexes.
For instance, three molecules of water are generated with mannitol
and the last proton, H.sup.+, is associated with the molecule which
can be quantitatively titrated with NaOH. In the presence of HF,
such compounds would readily form the BF.sub.4.sup.- complex.
[0024] Further preferred boron containing compounds are cyclic
borate esters, such as those of the formula:
##STR00002##
wherein each of R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13,
R.sub.14, R.sub.15 and R.sub.16 is independently selected from
hydrogen or a substituted or unsubstituted alkyl or alkenyl group,
and is preferably independently selected from hydrogen or a
C.sub.1-C.sub.4 alkyl group, optionally substituted with one or
more --OH groups or OR.sub.13 (which can readily cleave to form the
desired BF.sub.4.sup.- complex), wherein R.sub.13 is a
C.sub.1-C.sub.9 alkyl or aryl group. Suitable esters include those
formed with salicyclic acid or acetic acid. Other cyclic borates
include CH.sub.3B.sub.3O.sub.3 which hydrolyze rapidly in
water.
[0025] The presence of BF.sub.4.sup.- controls the concentration of
active HF at any given time. As a result, the formation of calcium
and magnesium fluoride, sodium or potassium fluorosilicate, or
fluoroaluminate scales is prevented or inhibited.
[0026] Typically, the amount of boron containing compound in the
well treating composition is that sufficient to impart to the
composition between from about 0.5 to about 10 g of BF.sub.4.sup.-
complex per 100 cc of phosphonate, hydrofluoric acid source and
water.
[0027] The hydrofluoric acid source, useful in the formation of the
BF.sub.4.sup.- complex may be hydrofluoric acid. More typically,
however, the hydrofluoric acid source is the combination of a
mineral acid and ammonium bifluoride or ammonium fluoride. Reaction
of the acid with the ammonium bifluoride or ammonium fluoride
renders HF. The use of the combination of acid and ammonium
bifluoride or ammonium fluoride and boric acid to control hydrogen
fluoride significantly slows the hydrofluoric acid reaction
rate.
[0028] Preferred as the acid is hydrochloric acid, though other
acids such as citric, chloroacetic, methanesulfonic, sulfuric,
sulfamic, nitric, acetic, lactic, fumaric and formic acid may also
be used. Preferred organic acids include citric acid, acetic acid
and formic acid. A retarder may also be used, such as an aluminum
salt.
[0029] In the reaction, ammonium bifluoride or ammonium fluoride
hydrolyzes and is converted to hydrofluoric acid. When ammonium
bifluoride or ammonium fluoride is used as a source of hydrofluoric
acid, typically less acid is present than is necessary to hydrolyze
all of the ammonium bifluoride or ammonium fluoride. Thus, there
remains some unconverted ammonium bifluoride or ammonium fluoride
in the composition.
[0030] The hydrofluoric acid source of the aqueous well treatment
composition generally provides between from about 0.25 to about 10,
typically between from about 1.0 to about 6.0, weight percent of
hydrofluoric acid to the well treatment composition (based on the
total weight of the well treatment composition).
[0031] When present, the well treatment composition may further
contain between from about 1 to about 50 weight percent of organic
acid, preferably about 10 weight percent based on the total weight
of the well treatment composition.
[0032] The phosphonate compound principally functions as a
stabilizer. The phosphonate compound may be a polyphosphonic acid
and their salts and esters and is preferably a phosphonate acid,
salt or ester thereof. Preferred are phosphonate materials of the
formula:
##STR00003##
wherein R1, R2 and R3 are independently selected from hydrogen,
alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic,
aminophosphonate, acyl, amine, hydroxy or carboxyl groups and salts
thereof and R4 and R5 are independently selected from hydrogen,
sodium, potassium, ammonium or an organic radical. Preferred
organic radicals are C.sub.nH.sub.2n+1 wherein n is between from 1
to about 5.
[0033] Preferred as R1, R2 and R3 are aminophosphonate and
aminophosphonic groups which may optionally be substituted with
alkyl, phosphonic, aminophosphonic, phosphate and phosphonate
groups.
[0034] Examples of preferred phosphonate acids, esters or salts
include aminotri (methylene phosphonic acid) and its pentasodium
salt, 1-hydroxyethylidene-1,1-diphosphonic acid and its tetrasodium
salt, hexamethylenediaminetetra (methylene phosphonic acid) and its
hexapotassium salt, and diethylenetriaminepenta (methylene
phosphonic acid) and its hexasodium salt. Among the commercial
phosphonate materials, preferred is
1-hydroxyethylidene-1,1-diphosphonic acid, available as DEQUEST
2010 and diethylenediamine penta (methylene phosphonic) acid,
commercially as DEQUEST 2060S, both available from Solutia, Inc. in
60% strength. In general, the phosphonic acids are more preferred
over the salt derivatives.
[0035] Thus, in formula (III) above, both R4 and R5 are more
desirably --H versus the stated salt derivatives. Also preferred
are those phosphonic acid salts which generate the corresponding
phosphonic acid in-situ in the presence of a slight amount of
strong acid, such as HCl.
[0036] The amount of phosphonate in the well treatment composition
is generally between from about 0.1 to about 10, preferably from
about 0.25 to about 6, more preferably from about 0.5 to about 3,
percent by volume based on the total volume of water, phosphonate
and hydrofluoric acid source.
[0037] The organosilanes for use herein contain a Si--C bond and
includes polysiloxanes.
[0038] Among the organosilanes especially suitable for use in this
invention are those organosilane halides of the formula:
##STR00004##
wherein X is a halogen, R.sub.1 is an organic radical having from 1
to 50 carbon atoms, and R.sub.2 and R.sub.3 are the same or
different halogens as X or organic radicals of R.sub.1. Preferably,
X is a halogen selected from the group consisting of chlorine,
bromine and iodine with chlorine being preferred, R.sub.1 is an
alkyl, alkenyl, alkoxide or aryl group having from 1 to 18 carbon
atoms and R.sub.2 and R.sub.3 are the same or different halogens,
or alkyl, alkenyl, alkoxide or aryl group having from 1 to 18
carbon atoms.
[0039] Suitable specific organosilane halides include
methyldiethylchlorosilane, dimethyldichlorosilane,
methyltrichlorosilane, dimethyldibromosilane, diethyldiiodosilane,
dipropyldichlorosilane, dipropyldibromosilane,
butyltrichlorosilane, phenyltribromosilane, diphenyldichlorosilane,
tolyltribromosilane, methylphenyldichlorosilane,
propyldimethoxychlorosilane and the like as well as organosilane
alkoxides and amino silanes.
[0040] Among the organosilane alkoxides suitable for use in this
invention are those having the formula:
##STR00005##
wherein R.sub.4, R.sub.5, and R.sub.6 are independently selected
from hydrogen and organic radicals having from 1 to 50 carbon
atoms, provided not all of R.sub.4, R.sub.5, and R.sub.6 are
hydrogen, and R.sub.7 is an organic radical having from 1 to 50
carbon atoms. Preferably, R.sub.4, R.sub.5, and R.sub.6 are
independently selected from hydrogen, amine, alkyl, alkenyl, aryl,
or carbhydryloxy groups having from 1 to 18 carbon atoms, with at
least one of the R.sub.4, R.sub.5, and R.sub.6 groups not being
hydrogen, and R.sub.7 is selected from amine, alkyl, alkenyl, and
aryl groups having from 1 to 18 carbon atoms. When R.sub.4,
R.sub.5, and R.sub.6 are carbhydryloxy groups, alkoxy groups are
preferred.
[0041] In another embodiment, the organosilane may be of the
formula:
R--Si(OR').sub.3 (VI)
wherein in one embodiment R is branched or linear aliphatic carbon
chain that may be saturated or unsaturated (e.g., containing one or
more double and/or triple bonds), and which may have from about 1
to about 10 carbon atoms, alternatively from about 1 to about 5
carbon atoms, and further alternatively about 3 carbon atoms; and
wherein each R' is independently branched or linear carbon chain
that may be saturated or unsaturated (e.g., containing one or more
double and/or triple bonds), and which may have from about 1 to
about 4 carbon atoms, alternatively from about 1 to about 2 carbon
atoms, and further alternatively about 2 carbon atoms; it being
understood that each R' group may be the same or different
structure than one or both of the other R' groups. In another
embodiment, R may be further characterized as alkanyl or alkenyl
carbon chain having the above-properties. In other embodiments, R
may be characterized as an aromatic carbon chain or alicyclic
carbon chain.
[0042] In a further embodiment, one or more of the carbon chains R
and/or R' may be optionally and independently derivatized, e.g.,
the R carbon chain and/or one or more of the R' carbon chains may
each contain one or more amino functional groups, one or more
halogen groups (e.g., tetrachlorosilane, methyltrichlorosilane,
etc.), two or more isocyanate functional groups, two or more epoxy
groups, etc.
[0043] In one exemplary embodiment, a silane may include an
amino-functional silane-based compound such as aminoalkyl siloxanes
like gamma-aminopropyltriethoxy silane, a isocyanate-functional
silane-based compound such as gamma isocyanatopropyltriethoxy
silane and mixtures thereof.
[0044] Specific examples of commercially available silane-based
products available from liquid isobuytlisopropyldimethoxysilane,
liquid diisopropylmethoxysilane, liquid diisobutyldimethoxysilane,
liquid dicyclopentyldimethoxysilane,
gamma-aminopropyltriethoxysilane epoxy functional silanes.
[0045] In another embodiment, the silane may include one or more
siloxane-based compounds having the following chemical formula:
R--Si(OR').sub.2--O--Si(OR'').sub.2--R (VII)
wherein in one embodiment R is a branched or linear aliphatic
carbon chain that may be saturated or unsaturated (e.g., containing
one or more double and/or triple bonds), and which may have from
about 1 to about 10 carbon atoms, alternatively from about 1 to
about 5 carbon atoms, and further alternatively about 3 carbon
atoms; wherein each R' and each R'' is independently a branched or
linear carbon chain that may be saturated or unsaturated (e.g.,
containing one or more double and/or triple bonds), and which may
have from about 1 to about 4 carbon atoms, alternatively from about
1 to about 2 carbon atoms, and further alternatively about 2 carbon
atoms; it being understood that one R' may be the same or different
than the other R' group, that one R'' may be the same or different
than the other R'' group, and that one or both R' groups may be the
same or different than one or both R'' groups. In another
embodiment, R may be further characterized as alkanyl or alkenyl
carbon chain having the above-properties. In other embodiments, R
may be characterized as an aromatic carbon chain or alicyclic
carbon chain. In a further embodiment, one or more of the carbon
chains R and/or R' may be optionally and independently derivatized,
e.g., the R carbon chain and/or one or more of the R' and/or R''
carbon chains may each contain one or more amino functional groups,
two or more isocyanate functional groups, two or more epoxy groups,
etc.
[0046] Specific examples of siloxane-based compounds include, but
are not limited to, an aqueous solution of aminoalkyl siloxane
available from Baker Hughes Incorporated as FSA-1.
[0047] Further, suitable specific organosilane alkoxides and amino
silanes include methyltriethoxysilane, dimethyldiethoxysilane,
methyltrimethoxysilane, divinyldimethoxysilane,
divinyldi-2-methoxyethoxy silane, di(3-glycidoxypropyl)
dimethoxysilane, vinyltriethoxysilane,
vinyltris-2-methoxyethoxysilane, 3-glycidoxypropyltrimethoxysilane,
3-methacryloxypropyltrimethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
N-2-aminoethyl-3-propylmethyldimethoxysilane, N-2-amino
ethyl-3-propyltrimethoxysilane, N-2-amino
ethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,
tetraethoxysilane and the like.
[0048] Generally, the amount of organosilane in the aqueous well
treatment composition is between from about 0.01 to about 10
percent, preferably from about 0.1 to about 5 percent, by volume
based on the total volume amount of the well treatment composition.
The amount of the ammonium salt in the aqueous well treatment
composition is between from about 0.01 to about 10 percent,
preferably from about 0.1 to about 5 percent by volume based on the
total volume amount of the well treatment composition. In a
preferred embodiment, the volumetric ratio of the organosilane to
quaternary ammonium salt is between from about 0.001 to about 1000,
most preferably from about 0.02 to about 50.
[0049] The ammonium salt is preferably a quaternary ammonium salt
represented by the formula:
N(R.sup.6)(R.sup.7)(R.sup.8)(R.sup.9)Y.sup.- (VIII)
wherein R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are independently
hydrogen, a C.sub.1-C.sub.20 alkyl group (preferably a
C.sub.1-C.sub.6 alkyl group), a hydroxyalkyl group wherein the
alkyl group is preferably a C.sub.1-C.sub.10 alkyl and more
preferably a C.sub.1-C.sub.6 alkyl or a radical of the
structure:
##STR00006##
wherein m is from 0 to about 10, p is form 1 to about 5, R.sup.10
is hydrogen or methyl, provided that (i) the total number of
carbons in the radical of formula (IX) do not exceed 20 and not all
of R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are hydrogen. In one
embodiment, each R.sup.6, R.sup.7 and R.sup.8 is a hydroxyalkyl,
such as 2-hydroxyethyl, and R.sup.9 is an alkyl group, such as
methyl. In another embodiment, each of R.sup.6, R.sup.7 and R.sup.8
are alkyl and R.sup.9 is a hydroxyalkyl, such as 2-hydroxyethyl. In
another preferred embodiment, each of R.sup.6, R.sup.7, R.sup.8 and
R.sup.9 are an alkyl group. The anion, Y.sup.-, is a salt,
preferably a halide, X, perchlorate, thiocyanate, cyanate, a
C.sub.1-C.sub.6 carboxylate, an alkyl sulfate, methanesulfonate,
BX.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, SbF.sub.6.sup.-,
NO.sub.2.sup.-, NO.sub.3.sup.- or SO.sub.4.sup.-. In a preferred
embodiment, X is a halide, such as chloride. Such salts are set
forth in U.S. Pat. No. 5,342,530, herein incorporated by
reference.
[0050] Further, acceptable salts include polycationic polymers
having a molecular weight up to about 300,000, for instance from
50,000 to 300,000 and having the repeating units represented by the
formulae:
##STR00007##
as well as compounds of the formula:
##STR00008##
wherein R and R.sup.3 are independently selected from the group
consisting of an alkylene group having from about 2 to about 4
carbon atoms; R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.7, R.sup.8,
and R.sup.9 are independently selected from the group consisting of
methyl and ethyl; R.sup.6 is selected from the group consisting of
an unsubstituted alkylene group having from about 2 to 4 carbon
atoms and a substituted alkylene group having from about 2 to about
4 carbon atoms and containing a hydroxy group; X is an anion
selected from the group consisting of a halogen, methyl sulfate,
sulfate, and nitrate; v represents the valency of the anion
represented by X; and, s is an integer equal to the number of said
anions required to maintain electronic neutrality. In a preferred
embodiment, R and R.sup.3 are preferably independently selected
from the group consisting of ethylene, trimethylene,
tetramethylene, or 2-methyltrimethylene; R.sup.6 is preferably
selected from the group consisting of 2-hydroxytrimethylene,
2-hydroxytetramethylene, and 3-hydroxytetramethylene; R.sup.1 and
R.sup.2 are preferably methyl; R.sup.4 and R.sup.5 are preferably
ethyl; R.sup.7, R.sup.8 and R.sup.9 are preferably methyl; and X is
preferably selected from the group consisting of a halogen such as
chloride, bromide, and iodide, methyl sulfate and sulfate, most
preferably halogen. Preferred are those compounds of the
formula:
##STR00009##
Such polycationic ammonium salts are disclosed in U.S. Pat. Nos.
4,447,342 and 4,536,305, both of which are herein incorporated by
reference.
[0051] In a preferred embodiment, the ammonium salt is a quaternary
ammonium salt like choline chloride and preferably contains the
N,N,N-trimethylethanolammonium cation. Such quaternary ammonium
salts include Claytreat-3C clay stabilizer (CT-3C) or Claymaster-5C
both by Baker Hughes Inc.
[0052] The pH of the well treatment composition is typically
maintained at a range of 0 to about 3.0. Enough acid should be used
to maintain the pH of the aqueous HF solution and to hydrolyze
ammonium fluoride or bifluoride, if it is used. Maintenance of the
desired pH range aids in the inhibition of inorganic scales and in
most instances the prevention of formation of such scales. In
addition, maintenance of the pH range maximizes the effect of the
organosilane and the quaternary ammonium salt on the inhibition and
control of fines and swellable clay.
[0053] Other materials commonly added to acid treatment solutions
may also optionally be added to the well treatment composition
herein. For example, the composition may include or have added
thereto corrosion inhibitors, surfactants, iron control agents,
non-emulsifiers, foaming agents, water-wetting surfactants,
anti-sludge agents, mutual solvents or alcohols (such as methanol
or isopropanol), gelling agents, bactericides, or fluid loss
control agents. The amount of such additives, when employed, is
typically between from about 0.1 to about 2 weight percent. When
mutual solvents or alcohols are employed, they are typically used
in amounts between from about 1 to about 20 weight percent of the
well treatment composition.
[0054] The well treatment composition is introduced into the
formation at the location where treatment is desired. The well
treatment composition may be applied after treatment of the
formation with a pre-flush.
[0055] The well treatment composition of the invention enhances the
production of hydrocarbons from hydrocarbon bearing calcareous or
siliceous formations. The treatment method is especially effective
if applied prior to gravel packing or fracturing.
[0056] The well treatment composition may easily be applied in the
stimulation of sandstone formations containing calcareous materials
and calcareous formations such as carbonate or dolomite. In
addition to its use in matrix acidizing, it may be used in acid
fracturing as well as pre-fracturing treatment on sandstone,
carbonate and dolomite formations. They may also be used for
remedial workovers of wells to keep silicates in suspension and to
remove clay, fine and sand deposits as well as inorganic scales
from downhole screens and from drilling fluid damage. The well
treatment composition is capable of dissolving carbonates, as well
as siliceous minerals, while minimizing the formation of calcium
fluoride and magnesium fluoride or sodium or potassium
fluorosilicate or fluoroaluminate.
[0057] Such well treatments may be simplified by use of the well
treatment composition defined herein since the need to pump
multiple fluids in a carefully choreographed sequence is
eliminated. Further, acid placement and distribution is improved
and equipment requirements are reduced, e.g., in terms of tankage,
etc. Use of the well treatment composition improves logistics,
reduces costs, along with improved results, while simultaneously
rendering treatments which are easier to implement and control at
the field level.
[0058] The well treatment composition may further be employed in
the remediation of oil and gas and geothermal wells by preventing
and/or inhibiting the formation of unwanted deposits on the
surfaces of the wellbore, downhole assembly, sand control screens,
production equipment and pipelines. Such unwanted deposits form
and/or accumulate in the wellbore, production equipment, recovery
equipment and well casing. Such accumulated deposits affect
productivity and are typically removed prior to cementing or the
introduction of completion fluids into the wellbore. Remediation
treatment fluids are further typically used to remove such
undesired deposits prior to the introduction of stimulation fluids
or to restore well productivity from the undesired deposits. In a
preferred embodiment, the invention is used to remove siliceous or
calcareous deposits inside well tubulars. The well treatment
composition may also be used to treat pipelines from undesired
deposits.
[0059] In well remediation applications, the well treatment
composition is preferably injected directly into the wellbore
through the production tubing or through the use of coiled tubing
or similar delivery mechanisms. Once downhole, the composition
remedies damage caused during well treating such as, for instance,
by stimulation fluids and drilling fluid muds, by dispersing and
removing siliceous materials from the formation and wellbore.
[0060] The following examples are illustrative of some of the
embodiments of the present invention. Other embodiments within the
scope of the claims herein will be apparent to one skilled in the
art from consideration of the description set forth herein. It is
intended that the specification, together with the examples, be
considered exemplary only, with the scope and spirit of the
invention being indicated by the claims which follow.
[0061] All percentages set forth in the Examples are given in terms
of volume percent except as may otherwise be indicated.
EXAMPLES
Examples 1-6
[0062] Analytical grade carbonate powder was exposed to an aqueous
hydrofluoric acid solution at 70.degree. F. The un-dissolved solid
or precipitate was analyzed by X-ray diffraction technique (XRD).
Table 1 presents the results of these tests wherein pH A represents
the pH at the beginning of the testing and pH B represents the pH
at the end of the testing.
TABLE-US-00001 TABLE 1 Ex. CaCO.sub.3 No. Composition pH A pH B
added Comments Comp. HF acid 2.2 2.2 0.4 g/100 cc All carbonate Ex.
1 dissolved and CaF.sub.2 precipitate formed within 5 minutes.
Comp. HF acid 1.9 1.9 0.4 g/100 cc All carbonate Ex. 2 3% Dequest
dissolved and 2010 CaF.sub.2 precipitate formed within 5 minutes.
Comp. HF acid 2.2 >4.0 0.4 g/100 cc All carbonate Ex. 3 2.8
g/100 cc dissolved and Boric acid CaF.sub.2 precipitate formed
within 5 minutes. 4 HF acid 1.6 1.6 0.4 g/100 cc All carbonate 3%
Dequest dissolved and 2010 no precipitate 2.8 g/100 cc formed over
4 Boric acid hours. 5 HF acid 1.6 1.6 1.0 g/100 cc All carbonate 3%
Dequest dissolved and 2060S no precipitate 4.2 g/100 cc formed over
24 Boric acid hours. 6 HF acid 1.6 1.6 1.0 g/100 cc All carbonate
1.5% Dequest dissolved and 2010 no precipitate 1.5% Dequest formed
over 24 2060S hours. 4.2 g/100 cc Boric acid
Example 7
[0063] The dissolution effect of the compositions of Examples 1-6
was illustrated on a formation containing calcareous minerals as
follows. A composition consisting of 75 wt. % quartz, 5 wt. %
kaolinite, 10 wt. % potassium-feldspar and 10 wt. % calcium
carbonate (powder) was prepared. The composition was tested for its
solubility in a HF acid at 150.degree. F. over 4 and 24 hrs. After
solubility testing, the un-dissolved solid or precipitate was
analyzed. The experimental conditions and results are set forth in
Tables 2-5. Table 2 represents the 4 hour solubility testing of the
formation composition at 150.degree. F. Tables 3-5 represent the 4
and 24 hour solubility testing of the formation composition at
150.degree. F.
TABLE-US-00002 TABLE 2 HF acid HF acid 3% Dequest 3% Dequest HF
acid HF acid 2010 HF acid 2060S 3% Dequest 2.8 g/100 cc 2.8 g/100
cc 3% Dequest 2.8 g/100 cc Acid 2010 Boric acid Boric acid 2060S
Boric acid pH 1.9/1.9 2.2/5.5 1.6/1.9 1.6/1.6 1.0/1.3 before/after
Solubility, % 14.9 4.4 14.4 14.7 9.6 Quartz 87 79 91 89 88
Plagioclase nd 1 1 nd 1 K-feldspar 4 7 6 2 6 Kaolinite nd 2 nd nd 2
Calcite 1 1 1 tr 1 CaF.sub.2 7 9 <0.5 8 1 K.sub.2SiF.sub.6 tr nd
nd nd nd Notes: nd--not detected and tr--trace.
TABLE-US-00003 TABLE 3 HF acid HF acid 7.5% Dequest 2010 7.5%
Dequest 2010 22.5% Dequest 2060S Acid 22.5% Dequest 2060S 2.8 g/100
cc Boric acid Time, Hrs 4 24 4 24 pH before/after 1.6/1.6 1.6/1.6
1.3/1.6 1.3/1.6 Solubility, % 13.4 20.8 11.9 12.2 Quartz 89 91 90
91 Plagioclase nd nd 1 1 K-feldspar 3 nd 6 6 Kaolinite nd nd 1 nd
Calcite tr nd 1 1 CaF.sub.2 7 8 nd nd K.sub.2SiF.sub.6 tr tr nd nd
Notes: nd--not detected and tr--trace.
TABLE-US-00004 TABLE 4 HF acid HF acid 1.5% Dequest 2010 1.5%
Dequest 2010 1.5% Dequest 2060S Acid 1.5% Dequest 2060S 2.8 g/100
cc Boric acid Time, Hrs 4 24 4 24 pH before/after 1.9/1.6 1.9/1.6
1.3/1.6 1.3/1.6 Solubility, % 13.8 24.6 12.0 15.4 Quartz 90 90 90
92 Plagioclase nd nd 1 tr K-feldspar 2 nd 6 6 Kaolinite nd nd 1 nd
Calcite tr nd tr tr CaF.sub.2 7 9 1 1 K.sub.2SiF.sub.6 tr tr nd nd
Notes: nd--not detected and tr--trace.
TABLE-US-00005 TABLE 5 3% HF HF acid 22.5% Dequest 2010 22.5%
Dequest 2010 7.5% Dequest 2060S Acid 7.5% Dequest 2060S 2.8 g/100
cc Boric acid Time, Hrs 4 24 4 24 pH before/after 1.6/1.6 1.6/1.6
1.3/1.6 1.3/1.6 Solubility, % 13.9 22.8 12.1 15.3 Quartz 89 89 90
90 Plagioclase nd Nd 1 1 K-feldspar 2 Tr 5 5 Kaolinite nd Nd tr nd
Calcite tr Nd 1 1 CaF.sub.2 8 10 2 2 K.sub.2SiF.sub.6 tr Tr nd nd
Notes: nd--not detected and tr--trace.
[0064] Tables 2-5 demonstrate that the well treatment compositions
defined herein can control or minimize the formation of inorganic
fluoride scales, such as calcium fluoride, in the hydrofluoric
acid.
Example 8
[0065] A coreflood study was conducted using a Bandera Sandstone
core at 180.degree. F. The composition of Bandera Sandstone is set
forth in Table 6:
TABLE-US-00006 TABLE 6 Mineral Composition Wt % Quartz 61 Feldspar
15 Dolomite 5 Illite 12 Kaolinite 4 Chlorite 2
Table 7 shows the composition of acids systems used in the
coreflood experiment wherein HV represents an
organophosphonate.
TABLE-US-00007 TABLE 7 Pre-Flush acid Main acid Post-Flush acid
System system system HF, wt % -- 3 -- HCl, wt % 10 2 10 HV, gpt --
60 -- Iron control agent, gpt -- 10 -- Corrosion inhibitor, gpt 2 2
2 Acetic acid, wt % -- 3 -- Boric Acid, ppt -- 60 --
Five fluid stages were injected in the following sequence: [0066]
1. 5 wt % NH.sub.4Cl solution to measure initial core permeability.
[0067] 2. 4 pore volumes (PV) of Pre-Flush acid system. [0068] 3. 4
PV of Main acid system. [0069] 4. 4 PV of Post-Flush acid system.
[0070] 5. 5 wt % NH.sub.4Cl solution to measure initial core
permeability. The results of two coreflood experiments are shown in
Table 8. All acid solutions injected in the second experiment
contained the combination of 3 gpt of a quaternary ammonium salt,
commercially available as Claymaster-5C from Baker Hughes Inc., and
5 gpt of an aminoalkyl siloxane, commercially available as FSA-1
from Baker Hughes Inc. while in the first experiment none of the
acid solutions contained Claymaster-5C and FSA-1. A significant
increase in permeability was observed when the acid solution was
prepared with the addition of Claymaster-5C and FSA-1.
TABLE-US-00008 [0070] TABLE 8 Measure Measure initial Acid system
final Permeability permeability Pre- Post- permeability
enhancement, No. with flush Main flush with % A 5 wt % 0 gpt of 5
wt % -10.9 NH4Cl Claymaster-5C, NH.sub.4Cl 0 gpt of FSA-1 B 5 wt %
3 gpt of 5 wt % 42 NH4Cl Claymaster-5C, NH.sub.4Cl 5 gpt of
FSA-1
Test A.
[0071] The pressure drop across the core is a function of
cumulative injected pore volumes during the five fluid stage
injections. Initially a NH.sub.4Cl solution was injected at a rate
of 5 ml/min for 1 PV then reduced to 2 ml/min to calculate an
accurate average value of initial permeability. All acid stages
were injected at a rate of 2 ml/min and did not contain the
combination of Claymaster-5C and FSA-1. An increase in the pressure
drop across the core during the injection of the pre-flushed stage
(which mainly 10 wt % HCl) was observed. Also, during the injection
of main acid the pressure drop across the core initially decreased
then increased again as evidence of damage occurring during the
main acid injection. At the end of the experiment NH.sub.4Cl
solution was injected at a rate of 2 ml/min and then increased to 5
ml/min to calculate an accurate average value of final
permeability. A -10.9% permeability enhancement was observed
Test B.
[0072] Initially a NH.sub.4Cl solution was injected at a rate of 5
ml/min then reduced to 2 ml/min to calculate an accurate average
value of initial permeability. All acid stages were injected at a
rate of 2 ml/min and contained the combination of 3 gpt of
Claymaster-5C and 5 gpt of FSA-1. An increase in the pressure drop
across the core during the injection of the pre-flushed stage
(mainly 10 wt % HCl) was observed. However, no increase in pressure
drop was observed across the core during the injection of main
acid. This illustrates that the combination of Claymaster-5C and
FSA-1 enhanced the permeability of the core during main acid
injection. Finally, a NH.sub.4Cl solution was injected at a rate of
2 ml/min and then increased to 5 ml/min to calculate an accurate
average value of final permeability. A 42% permeability enhancement
was observed.
Example 9
[0073] A coreflood study was conducted using a Bandera Sandstone
core at 180.degree. F. wherein the Bandera Sandstone had the
composition illustrated in Table 6 above. Table 9 sets forth the
composition of the acid system:
TABLE-US-00009 TABLE 9 Pre-Flush acid Main acid Post-Flush acid
System system system HF, wt % -- 3 -- HCl, wt % 15 1 15 HV, gpt --
30 -- Iron control agent, gpt -- 10 -- Corrosion inhibitor, gpt 2 2
2 Acetic acid, wt % -- -- -- Boric Acid, ppt -- -- --
Five fluid stages were injected in the following sequence: [0074]
1. 5 wt % NH.sub.4Cl solution to measure initial core permeability.
[0075] 2. 6 PV of Pre-Flush acid system. [0076] 3. 12 PV of Main
acid system. [0077] 4. 6 PV of Post-Flush acid system. [0078] 5. 5
wt % NH.sub.4Cl solution to measure initial core permeability. The
results of a coreflood experiment are shown in Table 10.
TABLE-US-00010 [0078] TABLE 10 Measure Measure initial Acid system
final permeability Pre- Post- permeability Permeability with flush
Main flush with enhancement, % 5 wt % NH4Cl 3 gpt of 5 wt % 95
Claymaster-5C, NH.sub.4Cl 5 gpt of FSA-1
The main acid used had less amount of phosphonate acid, no boric
acid and no acetic acid, as shown in Table 10. However, all acid
systems contained the combination of Claymaster-5C (3 gpt) and
FSA-1 (5 gpt). A 95% increase in core permeability was
observed.
[0079] The pressure drop across the core was a function of
cumulative injected pore volume during the five fluid stage
injections. Initially a NH.sub.4Cl solution was injected at a rate
of 5 ml/min then reduced to 2 ml/min to calculate an accurate
average value of initial permeability. All acid stages, set forth
in Table 9, were injected at a rate of 2 ml/min and contained the
combination of 3 gpt of Claymaster-5C and 5 gpt of FSA-1. An
increase in the pressure drop across the core during the injection
of the pre-flush stage, principally 15 wt % HCl, was observed.
Also, no increase in pressure drop across the core was observed
during the injection of the main acid which had less amount of
phosphonate acid, no boric acid and no acetic acid. This
illustrates that the combination of Claymaster-5C and FSA-1
enhanced the permeability of the core during the main acid
injection. Finally, a NH.sub.4Cl solution was injected at rate of 2
ml/min then increased to 5 ml/min to calculate an accurate average
value of final permeability. A 95% permeability enhancement was
observed.
Example 10
[0080] A coreflood study was conducted using Bandera Sandstone core
at 180.degree. F., wherein the Bandera Sandstone had the
composition illustrated in Table 6. The composition of the acid
system is set forth in Table 11:
TABLE-US-00011 TABLE 11 Main acid system HF, wt % 2.6 HCl, wt % 6
HV, gpt 53 Iron control agent, gpt 10 Corrosion inhibitor, gpt 2
Acetic acid, wt % 2.6 Boric Acid, ppt 53
[0081] Three fluid stages were injected in the following
sequence:
1. 5 wt % NH4Cl solution to measure initial core permeability. 2.
16 PV of main acid system. 4. 5 wt % NH.sub.4Cl solution to measure
initial core permeability. No pre-flush or post-flush acid stages
were injected. The main acid used contained the combination of
Claymaster-5C (3 gpt) and FSA-1 (5 gpt). A 86% increase in core
permeability was observed as illustrated in Table 12.
TABLE-US-00012 TABLE 12 Main Acid system (no Measure Pre-Flush
Measure initial stage acid and final Permeability permeability no
Post-flush permeability enhancement, with stage acid) with % 5 wt %
NH4Cl 3 gpt of 5 wt % NH.sub.4Cl 86 Clay master-5C, 5 gpt of
FSA-1
Example 11
[0082] A coreflood study was conducted using Berea Sandstone core
at 180.degree. F. having the composition set forth in Table 13:
TABLE-US-00013 TABLE 13 Mineral Composition Wt % Quartz 87 Feldspar
3 Dolomite 1 Calcite 2 Illite 1 Kaolinite 5 Chlorite 2
The acid system is set forth in Table 11. Three fluid stages were
injected in the following sequence: 1. 5 wt % NH4Cl solution to
measure initial core permeability. 2. 4 PV of Main acid system. 3.
5 wt % NH4Cl solution to measure initial core permeability. No
pre-flush or post-flush acid stages were injected. The main acid
contained the combination of Claymaster-5C (3 gpt) and FSA-1 (5
gpt). A 82% increase in core permeability was observed as set forth
in Table 14.
TABLE-US-00014 TABLE 14 Main Acid system (no Measure Pre-Flush
Measure initial stage acid and final Permeability permeability no
Post-flush permeability enhancement, with stage acid) with % 5 wt %
NH4Cl 3 gpt of 5 wt % NH.sub.4Cl 82 Clay master-5C, 5 gpt of
FSA-1
[0083] From the foregoing, it will be observed that numerous
variations and modifications may be effected without departing from
the true spirit and scope of the novel concepts of the
invention.
* * * * *