U.S. patent application number 12/786096 was filed with the patent office on 2011-11-24 for disposable downhole tool.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Tianping Huang.
Application Number | 20110284232 12/786096 |
Document ID | / |
Family ID | 44971497 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110284232 |
Kind Code |
A1 |
Huang; Tianping |
November 24, 2011 |
Disposable Downhole Tool
Abstract
A disposable downhole tool is disclosed. The tool is suitable
for use as a frac tool. The tool includes a housing having an inner
wall surface defining a bore. The tool also includes a valve
structure disposed within the bore, the valve structure comprising
a disposable plug seat, the disposable plug seat comprising a first
natural material. The disposable tool may also include a disposable
plug in fluid sealing engagement with the seat, the plug comprising
a second natural material, the plug and the plug seat comprising a
plug valve. The first and second natural materials may include
sedimentary rock, such as various forms of limestone, including
Carrara marble or Indiana limestone.
Inventors: |
Huang; Tianping; (Spring,
TX) |
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
44971497 |
Appl. No.: |
12/786096 |
Filed: |
May 24, 2010 |
Current U.S.
Class: |
166/317 ;
977/775 |
Current CPC
Class: |
E21B 34/06 20130101;
E21B 21/103 20130101; E21B 34/14 20130101; E21B 2200/06 20200501;
E21B 43/26 20130101 |
Class at
Publication: |
166/317 ;
977/775 |
International
Class: |
E21B 34/00 20060101
E21B034/00 |
Claims
1. A disposable downhole tool, comprising: a housing having an
inner wall surface defining a bore; a valve structure disposed
within the bore, the valve structure comprising a disposable plug
seat, the disposable plug seat comprising a first natural
material.
2. The disposable tool of claim 1 further comprising a disposable
plug in fluid sealing engagement with the seat, the plug comprising
a second natural material, the plug and the plug seat comprising a
plug valve.
3. The disposable tool of claim 2, wherein the plug seat comprises
a ball seat and the plug comprises a ball.
4. The disposable tool of claim 1, wherein the first natural
material comprises a sedimentary rock.
5. The disposable tool of claim 4, wherein the sedimentary rock
comprises limestone.
6. The disposable tool of claim 5, wherein the limestone comprises
calcite.
7. The disposable tool of claim 6, wherein the first natural
material comprises, by weight, at least 70 percent calcite.
8. The disposable tool of claim 4, wherein the sedimentary rock
comprises Carrara marble or Indiana limestone.
9. The disposable tool of claim 1, wherein a surface of the natural
material is treated with a sealer.
10. The disposable tool of claim 9, wherein the sealer comprises a
slurry comprising nanoparticles.
11. The disposable tool of claim 2, wherein one of the first
natural material or the second natural material comprises a
sedimentary rock.
12. The disposable tool of claim 11, wherein the sedimentary rock
comprises limestone.
13. The disposable tool of claim 12, wherein the limestone
comprises calcite.
14. The disposable tool of claim 13, wherein the first natural
material comprises, by weight, at least 70 percent calcite.
15. The disposable tool of claim 11, wherein the sedimentary rock
comprises Carrara marble or Indiana limestone.
16. The disposable tool of claim 11, wherein a surface of the first
natural material or a surface of the second natural material is
treated with a sealer.
17. The disposable tool of claim 16, wherein the sealer comprises a
slurry comprising nanoparticles.
18. The disposable tool of claim 1, wherein the valve structure
comprises a sleeve disposed within the bore.
19. The disposable tool of claim 1, wherein the sleeve comprises a
slidable sleeve.
20. The disposable tool of claim 19 further comprising a return
member, the return member comprising a third natural material.
21. The disposable tool of claim 20, wherein the third natural
material comprises limestone.
22. The disposable tool of claim 2, wherein the first natural
material and the second natural material have a solubility greater
than 70% in a dissolution fluid.
23. The disposable tool of claim 22, wherein the dissolution fluid
comprises an organic or inorganic acid.
24. The disposable tool of claim 23, wherein the acid comprises a
dicarboxylic acid.
25. The disposable tool of claim 24, wherein the acid comprises
dicarboxylic acid comprises oxalic acid, malonic acid, succinic
acid, glutaric acid, adipic acid, pimelic acid, or a combination
thereof.
26. The disposable tool of claim 23, wherein the acid comprises
hydrochloric acid, sulfuric acid, hydrofluoric acid, formic acid,
acetic acid, fluoroboric acid, phosphoric acid, citric acid,
sulfonic acid, glycolic acid, ethylenediaminetetraacetic acid
(EDTA), disodium EDTA, hydroxyethylethylenediaminetriacetic acid,
docosatetraenoic acid, nitrilotriacetic acid,
hydroxyaminocarboxylic acid, diethylenetriaminepentaacetic acid,
hydroxyethyliminodiacetic acid, polyaspartic acid, or a combination
thereof.
27. A disposable downhole tool, comprising: a disposable plug that
is seatable against a disposable plug seat of a disposable valve
structure, the disposable plug comprising a natural material.
28. The disposable tool of claim 28, wherein the natural material
comprises a sedimentary rock.
29. The disposable tool of claim 29, wherein the sedimentary rock
comprises limestone.
Description
BACKGROUND
[0001] In the well completion and production arts, production
systems that enable operators to pinpoint fluid placement and
volume during openhole fracturing (frac) operations are very
desirable. These systems are used to establish openhole isolation
between zones, zone lobes, or fault lines, so fracture fluid may be
delivered where it is needed, for maximum effect. The systems are
designed to incorporate short-radius open-hole packers and frac
sleeves to isolate intervals of an underground fluid production
section for targeted fracturing treatment placement. The result is
greater control of the frac treatment and a greater chance of
fracturing the entire length of the lateral and increasing
production.
[0002] Such systems may be advantageously deployed as a one-trip
installation and set in place by the application of hydraulic
pressure. Isolation and casing packers may be set against a ball
seat in the shoe of the liner. The drill rig can then be moved to
another location and the desired frac treatment may be performed by
the application of hydraulic pressure by pumping when ready.
[0003] Frac treatment is performed by providing fluidic access
through openings in the tubular string in a generally radial
direction. Such openings allow fluid communication between the ID
of the flow channel and an annulus created between the tubular
string and a borehole wall (casing or openhole). Openable and
closable valves are employed in concert with such openings to
selectively promote and prevent the fluid movement noted above.
[0004] One frac sleeve arrangement employed in these systems is a
slidable frac sleeve. A slidable frac sleeve employs a housing
having an opening, a slidable sleeve translatable relative to the
housing to either misalign entirely with the opening or to align a
port with the opening, and a spring to bias the sleeve to a
selected position (open or closed). The sleeve employs a plug valve
that is configured to receive a plug to close the valve; the plug
valve may include a ball seat in the sleeve that is configured to
receive a corresponding ball that is configured to be seated in the
ball seat for closing the valve. The systems typically employ a
plurality of plug valves that are sized with successively smaller
valve openings proceeding inwardly from the surface along the
length of the production string.
[0005] In use, successively larger plugs (e.g. balls) are dropped
into the string, each configured to engage a corresponding valve
seat, closing their respective valves and opening the corresponding
frac sleeves at various locations along the production string.
Desired fracture volumes can be displaced with timing of the ball
releases to accurately place frac fluid in each desired interval of
the production string.
[0006] It has previously been the practice to remove the balls and
ball seats in the sleeves after the frac operations. This has
included flowing the balls back to the surface by high production
rate flows and by drilling out the ball seats to recover a
full-open string inside or inner diameter (ID). While effective,
such ball removal and drilling operations represent additional
drill string operations that require additional equipment and time
on the drill rig.
[0007] Therefore, it is desirable to provide frac tools that
incorporate plug valves, such as ball valves, that may be removed
to recover the full ID of the drill string without drilling.
BRIEF DESCRIPTION
[0008] In an exemplary embodiment, a disposable downhole tool is
disclosed that includes a housing having an inner wall surface
defining a bore. The disposable downhole tool also includes a valve
structure disposed within the bore, the valve structure comprising
a disposable plug seat, the disposable plug seat comprising a
natural material.
[0009] In another exemplary embodiment, a disposable downhole tool
is disclosed that includes a disposable plug that is seatable
against a disposable plug seat of a disposable valve structure, the
disposable plug comprising a natural material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring now to the drawings wherein like elements are
numbered alike in the several Figures:
[0011] FIG. 1 is a cross-sectional view of an exemplary embodiment
of a frac tool, including a disposable valve structure and sleeve,
in a first position, as disclosed herein;
[0012] FIG. 2 is view of the frac tool of FIG. 1, together with a
partial cross-sectional view of an exemplary embodiment of a
disposable plug, forming an exemplary embodiment of a disposable
plug valve, in a second position;
[0013] FIG. 3 is a view of the frac tool of FIG. 2 in a third
position; and
[0014] FIG. 4 is a view of the frac tool of FIG. 2 in a fourth
position.
DETAILED DESCRIPTION
[0015] Referring to FIGS. 1-4, an exemplary embodiment of a
downhole frac tool 30 is disclosed. The frac tool 30 includes an
outer housing 32 that includes an inner wall surface 34 defining a
bore 38. Frac tool 30 also includes a valve structure 50 disposed
within the bore 38. The valve structure 50 is used to provide a
disposable valve 53 that is configured to selectively control the
flow (F) of a frac fluid 55 within frac tool 30 as shown in FIG. 2,
particularly to selectively direct flow F of frac fluid 55 from the
frac tool 30 into a surrounding earth formation in conjunction with
frac operations. Valve structure 50 includes a disposable plug seat
59 for seating a disposable plug 62 in sealing engagement with
therewith. Disposable plug seat 59 may include all manner of
suitable disposable plug seats 59 for seating various forms
disposable plugs 62, such as disposable balls 63, to form various
disposable plug valves 53. In one exemplary embodiment, disposable
plug seat 59 may include a disposable ball seat 60, such as a
frustoconical ball seat 60, as illustrated in FIGS. 1-3. While
illustrated herein as having a frustoconical form comprising a
flat, planar, inwardly-tapering ball seat 60, disposable plug seat
59 may have any suitable plug seat form, including various curved,
planar, inwardly-tapering surface forms (not shown). Disposable
plug seat 59 and disposable plug 62 together may be used as a
disposable plug valve 53.
[0016] Disposable valve structure 50, including disposable plug
seat 59, includes a first natural material 61 that is dissolvable
in a suitable dissolution fluid 80 as described herein, which may
include naturally occurring downhole fluids, or a fluid introduced
into the downhole environment in conjunction with frac or other
drill string operations, or various acid fluid treatments
introduced into the drill string, as described herein. Valve
structure 50 and disposable plug seat 59 may be made either
partially or completely of first natural material 61. First natural
material 61 may include any suitable natural material, including
any suitable form thereof. In an exemplary embodiment, first
natural material 61 may include a sedimentary rock, including
various forms of limestone. More particularly, the limestone may
include calcite, and may also be formed predominantly from calcite.
This includes the use of a first natural material 61 that includes,
by weight, greater than 70 percent calcite. For example, first
natural material 61 may include forms of limestone such as Carrara
marble that is readily available in Europe or Indiana limestone
that is readily available in the US. First natural material 61 may
have an acid solubility greater than 70% and permeability of less
than 10 millidarcy (mD). For example, Indiana limestone has a
solubility of about 99.01% in 15% by volume hydrochloric acid and
98.86 in 10% by volume of dibasic acid, and a dissolution rate on
the order of 0.5 grams per square centimeter per minute at ambient
temperature. It also has a permeability of less than 3 mD. Indiana
limestone is generally composed of greater than 98% calcite, which
has high acid solubility. Additionally, the compressive Young's
modulus of Indiana limestone is approximately 30,600 MPa with no
dependence on confining pressure, which is comparable to that of
high strength concrete. Limestone with similar properties is also
readily available in other countries and on other continents.
[0017] The permeability of first natural material 61, as well as
the other natural materials described herein, may also be reduced
by filling the limestone matrix with another acid-soluble
substance, such as a nanoparticle slurry, as a sealer. For example,
as an option, a nanoparticle slurry may be used to fill in the
limestone matrix to make the sealing surfaces, such as the surfaces
of plug seat 59 and disposable plug 62, less permeable, thereby
enhancing the seal formed between them. The nanoparticles may have
relatively large surface charges per volume, thereby permitting the
crystal particles to bond, associate, link, connect, group, or
otherwise relate together to further reduce the permeability of the
matrix of the natural materials to which they are applied.
Exemplary acid-soluble nanoparticle slurries include, in
non-limiting embodiments, ConFINE.TM., available from Baker Hughes,
or a high-concentration slurry of approximately 35 nm magnesium
oxide (MgO) particles in an appropriate fluid base, such as a
diluent or solvent as described herein.
[0018] Disposable plug 62, including disposable ball 63, includes a
second natural material 65 that is dissolvable in a suitable
dissolution fluid 80 as described herein, which may include a
naturally occurring downhole fluid, or a fluid introduced into the
downhole environment in conjunction with frac or other drill string
operations, or a predetermined dissolution fluid, including various
acid treatments that may be introduced into the drill string as
described herein. Disposable plug 62, including disposable ball 63,
may be made either partially or completely of a second natural
material 65. Second natural material 65 may include the same
materials identified for use as first natural material 61. Second
natural material 65 may be selected to be the same as first natural
material 61, or may be selected to be a different natural material.
Second natural material 65 may be selected so that it has the same
dissolution rate in a given dissolution fluid 80 as first natural
material 61, or may be selected to have a different dissolution
rate. The selection of different first natural material 61 and
second natural material 65 enables predetermined and selective
dissolution of, for example, disposable plug 62 prior to disposable
valve structure 50, or vice versa.
[0019] Valve structure 50 and valve 53 may be used in various frac
tools 30, including various forms of slidable disposable sleeves
51. Frac tools, including slidable disposable sleeves 51 may also
include or work in conjunction with other disposable components 69,
such as disposable return member 70, including disposable return
sleeve 71. Disposable components 69, such as disposable return
member 70, including disposable return sleeve 71, includes a third
natural material 67 that is dissolvable in a suitable dissolution
fluid 80 as described herein, including naturally occurring
downhole fluids or a fluid introduced into the downhole environment
in conjunction with frac or other drill string operations, or
dissolution fluid, including various acid treatments introduced
into the drill string, as described herein. Disposable components
69, such as disposable return member 70, including disposable
return sleeve 71, may be made either partially or completely of
third natural material 67. Third natural material 67 may include
the same materials identified for use as first natural material 61
or second natural material 65. Third natural material 67 may be
selected to be the same as first natural material 61 or second
natural material 65, or any combination thereof, or may be selected
to be a different material than first natural material 61 or second
natural material 65, or any combination thereof, or any combination
of the same or different materials. Third natural material 67 may
be selected so that it has the same dissolution rate in a given
dissolution fluid 80 as first natural material 61 or second natural
material 65, or these materials may be selected to have a different
dissolution rate. The selection of different first natural material
61, second natural material 65 or third natural material 67 enable
predetermined and selective dissolution of, for example, disposable
component 69 prior to disposable plug 62 or disposable valve
structure 50, in any combination.
[0020] Referring now to FIGS. 1-3, frac tool 30 includes outer
housing 32 having inner wall surface 34, outer wall surface 36,
bore 38, first or frac port, 40, and second or production port 42.
First or frac port 40 may also include a first fluid flow control
member or device shown as a screen 41 that allows frac fluid 55 to
flow out into earth formation 100 through first port 40, but
prevents certain sized particulate matter from flowing back into
housing 32 and bore 38 from earth formation 100 through first port
40. Second port 42 may include a second fluid flow control member
or device shown as screen 43 that allows liquids to flow through
second port 42, but prevents certain sized particulate matter from
flowing through second port 42. Either of first port 40 or second
port 42 may also include a fluid flow control member such as a
choke (not shown), that is capable of controlling the pressure drop
and flow rate through the port.
[0021] Disposable sleeve 51 is in slidable engagement with inner
wall surface 34. Disposable sleeve 51 includes bore 52 and
retaining member 48 shown as a flange 49 that is disposed within
recess 39 in inner wall surface 34. Disposable sleeve 51 also
includes sleeve port 54 and an actuator for moving disposable
sleeve 51 from the desired run-in position (FIG. 1) to the first
operational position (FIG. 2) where frac fluid 55 and plug 62 are
introduced to frac tool 30 and disposable sleeve 51. The actuator
may be any device or method known to persons of ordinary skill in
the art, including action of pressurized frac fluid 55 against
disposable plug 62 to seat plug 62 against disposable plug seat 59.
As shown in FIGS. 1-3, the actuator is a disposable plug seat 59
such as disposable ball seat 60 capable of receiving disposable
plug 62 such as disposable ball 63. Although FIGS. 1-3 show
disposable ball seat 60 and disposable ball 63, it is to be
understood that the disposable plug seat 59 is not required to be a
disposable ball seat 60 and the disposable plug 62 is not required
to a disposable ball 63. Instead, the disposable plug seat 59 can
have any other shape desired or necessary for receiving a
reciprocally or complementary shaped disposable plug 62. Disposable
sleeve 51 may include dynamic seals 56 (numbered only in FIG. 1) to
assist sleeve 51 in sliding along inner wall surface 34 and to
reduce the likelihood of leaks between inner wall surface 34 and
the outer wall surface of sleeve 51.
[0022] Also disposed along inner wall surface 34 is disposable
return member 70. Disposable return member 70 comprises a
disposable return sleeve 71 having bore 73 and disposable bias
member 74. Although disposable bias member 74 is shown as an
elastic member such as a spring in FIGS. 1-3, it is to be
understood that disposable bias member 74 can be another elastic
device that is capable of being biased to exert a force upward
against sleeve 51 when sleeve 51 is in the first operational
position (FIG. 2). Suitable elastic members for utilization as
biased member 74 include Belleville springs (also known as
Belleville washers), capillary springs, and deformable elastomers
and polymers. Disposable bias member 74 may be rendered disposable
by appropriate selection of the material of bias member 74 and
dissolution fluid 80 so that member has a high solubility in the
fluid. Return sleeve 71 is in slidable engagement with inner wall
surface 34. As shown in FIGS. 1-3, inner wall surface 34 includes
shoulders 33 and 35 and return sleeve 71 comprises a head portion
75 and a stem portion 76. Dynamic seals 77 (numbered only in FIG.
1) disposed on return sleeve 71 assist return sleeve 71 in sliding
along inner wall surface 34 and to reduce the likelihood of leaks
between inner wall surface 34 and the outer wall surface of return
sleeve 71. Head portion 75 and shoulder 33 form chamber 37 in which
biased member 74 is disposed. Shoulder 35 provides a stop to
prevent sliding of return sleeve 71 at a predetermined location
along inner wall surface 34. Biased member 74 is disposed within
chamber 37 and on shoulder 33 so that biased member 74 can urge
head portion 75 and, thus, return sleeve 71 upward.
[0023] The operation of frac tool 30 is now described with
reference to FIGS. 1-4. As illustrated in FIG. 2, frac fluid 55 and
disposable ball 63 are introduced to bore 38. Disposable ball 63
engages disposable ball seat 60 to restrict fluid flow through bore
52. Fluid pressure, such as may be developed by pumping frac fluid
55 down through bore 38, is exerted onto disposable ball 63 causing
retaining member 53 to release from inner wall surface 34 so that
disposable sleeve 51 is forced downward into disposable return
member 70. Disposable sleeve 51 continues to be forced downward,
energizing biased member 74, until disposable return sleeve 71
engages stop shoulder 35. In this position, sleeve port 54 is
aligned with first port 40 of housing 32 and, thus, frac tool 30 is
in the first operational position as shown in FIG. 2. Accordingly,
pressurized frac fluid 55 can be pumped from bore 38, through
sleeve port 54, through first port 40, and into the well or well
formation to fracture the formation.
[0024] As shown in FIG. 3, after sufficient frac fluid 55 is
injected into the well or openhole formation, it may be desirable
to assess production by moving disposable sleeve 51 to a second
operational position, as illustrated in FIG. 3, where production
inflow Fp through second port 42, or ports 42, from the surrounding
earth formation 100 may be assessed. Ball 63 is removed from ball
seat 60 through any method known to persons skilled in the art. For
example, disposable ball 63 may be removed from ball seat 60 by
increasing the fluid pressure of the frac fluid 55 being pumped
downward through bore 38 until disposable ball 63 is forced through
ball seat 60 so that it can fall to the bottom of the well.
Alternatively, disposable ball 63 may be removed from ball seat 60
by decreasing the fluid pressure of the fracturing fluid being
pumped downward through bore 38 so that ball 63 can float back to
the surface of the well. Still alternately, ball 63 may be selected
so that it may be preferentially dissolved either completely or
partially sufficiently to pass through ball seat 60 and fall to a
location lower in the well, including to the bottom of the
well.
[0025] Reduction of the fluid pressure of the frac fluid 55 in
conjunction with removal of ball 63 allows energized biased member
74 to overcome the downward force of the frac fluid 55. When the
upward force of biased member 74 overcomes the downward force of
the frac fluid 55, disposable return member 70 begins to move
upward and, thus, forces disposable sleeve 51 upward from the first
operational position (FIG. 2) to the second operational position
(FIG. 3). In this position, sleeve port 54 is aligned with second
port 42 of housing 32 and, thus, frac tool 30 is in the second
operational position as shown in FIG. 3 where production flow Fp
into housing 32 and bore 38 through second port 42 is possible.
Accordingly, return fluids 57, such as oil, gas, and water, are
permitted to flow from the well or well formation and into bore 38
so that the return fluids 57 can be collected at the surface of the
well.
[0026] Movement of frac tool 30 from the first operational position
(FIG. 2) to the second operational position (FIG. 3) did not
require any well intervention using another tool or device. All
that was required was the reduction of fluid pressure forcing
disposable sleeve 51 into disposable return member 70 either to
facilitate both removal of the restriction in bore 52 and movement
of disposable sleeve 51 from the first operational position (FIG.
2) to the second operational position (FIG. 3), or to facilitate
movement of disposable sleeve 51 from the first operational
position (FIG. 2) to the second operational position (FIG. 3) after
the restriction in bore 52 has been removed by other
non-intervention means, e.g., forcing disposable ball 63 through
ball seat 60, allowing it to float to the surface or dissolving it
by introduction of an appropriate dissolution fluid 80. In an
additional embodiment, bore 52 can remain restricted during
production operations, i.e., when frac tool 30 is in the second
operational position.
[0027] In the embodiments discussed herein with respect FIGS. 1-3,
upward, toward the surface of the well (not shown), is toward the
top of FIGS. 1-3, and downward or downhole (the direction going
away from the surface of the well) is toward the bottom of FIGS.
1-3. In other words, "upward" and "downward" are used with respect
to FIGS. 1-3 as describing the vertical orientation illustrated in
FIGS. 1-3. However, it is to be understood that frac tool 30 may be
disposed within a horizontal or other deviated well so that
"upward" and "downward" are not necessarily oriented
vertically.
[0028] As shown in FIG. 4, after injection of frac fluid 55 into
the well or openhole formation and assessment of return fluid 57
production has indicated a desired flow F.sub.P, and there is no
longer a need to use frac tool 30, particularly disposable plug
valve 53, portions of the tool, including disposable valve
structure 50, disposable plug 62 and other disposable components,
such as disposable return member 70, may be disposed of to recover
the full diameter of housing 32 and bore 38, thereby removing the
restrictions therein associated with these portions of frac tool 30
and a fourth position of the tool. The disposable portions of frac
tool 30 may be removed from housing 32 by dissolution using a
predetermined dissolution fluid 80. Dissolution fluid 80 may be any
fluid suitable for use as a downhole fluid that is configured to
dissolve first natural material 61, second natural material 65 or
third natural material 67, or any combination thereof that is
desired. In an exemplary embodiment, dissolution fluid 80 may
include an acid fluid, including an inorganic acid, organic acid or
a combination thereof. As used herein, an acid fluid may include
various liquid inorganic or organic acids, or combinations thereof,
and may also include an acid precursor, or combination of
precursors, in any material state or form that may be used to form
an acidic dissolution fluid 80, including various anhydrous or
other materials that may be hydrolyzed to form a desired acid fluid
as dissolution fluid 80.
[0029] In one example, an inorganic acid dissolution fluid 80 may
include hydrochloric acid (HCl) or a hydrochloric acid mixture,
including a mixture of hydrofluoric acid and hydrochloric acid.
This includes conventional wellbore inorganic acidizing fluids that
include hydrochloric acid, including those having a high acid
strength. Further exemplary inorganic acid fluids which may be used
include, but are not limited to, sulfuric, hydrofluoric,
fluoroboric or phosphoric acid, or a combination of the above
inorganic acids.
[0030] In another example, an organic acid dissolution fluid 80 may
include an organic acid fluid system and method for matrix
acidization of subterranean formations penetrated by a wellbore,
including acidization at temperatures in excess of about
200.degree. F. (92.degree. C.). One suitable organic acid fluid
contains at least one water-soluble dicarboxylic acid. In one
non-limiting embodiment of an organic acid fluid, the dicarboxylic
acid is of relatively low molecular weight, that is, has a formula
weight of 175 or less. Suitable dicarboxylic acids therefore
include, but are not necessarily limited to, oxalic (ethanedioic),
malonic (propanedioic), succinic (butanedioic), glutaric
(pentanedioic), adipic acid (hexanedioic), or pimelic
(heptanedioic) acid, or combinations thereof, including mixtures
thereof. In another embodiment, the dicarboxylic acids are selected
from the group consisting of succinic, glutaric and adipic acid,
and mixtures thereof. In a non-limiting embodiment, the organic
acid fluid may include a dibasic acid comprising 51-61 weight
percent glutaric acid, 18-28 weight percent succinic acid, and
15-25 weight percent adipic acid. Interestingly, glutaric, succinic
and adipic acid have been used as components for corrosion
inhibitors for ferrous metals. Further exemplary inorganic acids
which may be used include, but are not limited to, formic, acetic,
citric, sulfonic, glycolic acid, or combinations of the above
organic acids. Dissolution fluid 80 also include other suitable
acid fluids, including various acidic chelating agents, such as,
for example, ethylenediaminetetraacetic acid (EDTA), disodium EDTA
(Na.sub.2EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA),
docosatetraenoic acid (DTA), nitrilotriacetic acid (NTA),
hydroxyaminopolycarboxylic acid (HACA),
diethylenetriaminepentaacetic acid (DTPA),
hydroxyethyliminodiacetic acid (HEIDA), or polyaspartic acid (PASP)
and the like, or combinations thereof.
[0031] In addition to dissolution of the disposable elements of
frac tool 30 described herein, the organic acid fluid systems of
the invention can also effectively generate wormholes to stimulate
production in subterranean carbonate formations and dissolve
carbonate scale, and these organic acids mixed with hydrofluoric
acid can effectively remove fines to recover production in
sandstone formations at elevated temperatures. These organic acid
fluids have very low corrosion on the tubing, casing and downhole
equipment.
[0032] Based on the properties of glutaric, succinic and adipic
acid, this composition of dicarboxylic acids and other combinations
of dicarboxylic acids (or dicarboxylic acids used alone) can be
used as acid compositions to stimulate high temperature wells in
addition to dissolution of frac tool 30. This organic acid system,
which is advantageously highly biodegradable, can also successfully
remove the calcium carbonate scale and fines to stimulate
production. Core flood testing demonstrates that this organic acid
system can effectively remove calcium carbonate scales and fines at
temperatures up to 400.degree. F. (204.degree. C.). In addition to
its reactivity, the acid system, when combined with corrosion
inhibitor, exhibits very low corrosion at high temperatures. These
acid fluid systems may be used for successive removal of plugging
fines from screens, such as screens 43 in addition to dissolution
of the disposable elements of frac tool 30.
[0033] In some non-limiting embodiments, hydrofluoric acid may be
used together with the dicarboxylic acids. Hydrofluoric acid may be
used to aid in dissolving silicates. Alternatively, a substance
that hydrolyzes to hydrofluoric acid may be used. Suitable
substances include, but are not necessarily limited to, ammonium
bifluoride and ammonium fluoride, alkali metal fluorides and
bifluorides (where the alkali metal is typically sodium, potassium
or the like) as well as transition metal fluorides (for instance
hexafluorotitanate salts and the like) and mixtures thereof.
[0034] Suitable solvents or diluents for the acids described
include, but are not necessarily limited to, water, methanol,
isopropyl alcohol, alcohol ethers or aromatic solvents, or
combinations thereof, including mixtures thereof. In one exemplary
embodiment, the composition has an absence of monocarboxylic acids
and/or an absence of tricarboxylic acids. Alternatively, in another
exemplary embodiment, the acid composition has an absence of
quaternary ammonium compounds and/or an absence of
sulfur-containing corrosion inhibitor activator (e.g. thioglycolic
acid, alkali metal sulfonate, etc.).
[0035] While one or more embodiments have been shown and described,
modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustrations and not limitation.
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