Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND ACIDIZING TOOL FOR DEEP ACID STIMULATION USING
ULTRASOUND
TECHNICAL FIELD OF THE INVENTION
[0001] The field of invention relates to a method and device for improving the
effectiveness
of a matrix acidizing technique by increasing the depth of penetration of the
acid throughout
a subterranean carbonate formation.
BACKGROUND OF THE INVENTION
[0002] It is a common practice to acidize subterranean formations in order to
increase the
permeability thereof. For example, in the petroleum industry, acidizing fluid
can be injected
into a well in order to increase the permeability of a surrounding hydrocarbon
bearing
formation, thereby facilitating the flow of hydrocarbonaceous fluids into the
well from the
formation. Such acidizing techniques may be carried out as "matrix acidizing"
procedures or
as "acid-fracturing" procedures.
[0003] In acid fracturing, the acidizing fluid is disposed within the well
under sufficient
pressure to cause fractures to form within the formation. An increase in
permeability;
therefore, is effected by the fractures formed, as well as by the chemical
reaction of the acid
within the formation.
[0004] In matrix acidizing, the acidizing fluid is passed into the formation
from the well at a
pressure below the fracturing pressure of the formation. In this case, the
permeability increase
is caused primarily by the chemical reaction of the acid within the formation
with little or no
permeability increase being due to mechanical disruptions within the formation
as in
fracturing.
[0005] In most cases, acidizing procedures are carried out in calcareous
formations such as
dolomites, limestones, dolomitic sandstones, and the like. However, a common
difficulty
encountered in acidizing these types of formations is presented by the rapid
reaction rate of
the acidizing fluid with those portions of the formation with which it first
comes into contact.
This is particularly serious in matrix acidizing procedures. As the acidizing
fluid is forced
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from the well into the formation, the acid reacts rapidly with the calcareous
material
immediately adjacent to the well. Thus, the acid becomes spent before it can
penetrate a
significant distance into the formation. For example, in matrix acidizing of a
limestone
formation, it is common to achieve maximum penetration with a live acid to a
depth of only a
few inches to a foot from the face of the wellbore. This, of course, severely
limits the
increase in productivity or injectivity of the well.
100061 Various methods have been attempted to reduce the reaction rate of the
acid with the
rock formation. For example, others have tried adding reaction inhibitors to
the acid
formulation. Additionally, other work has focused on ways to reduce the local
temperature in
order to slow down the reaction rate. However, all of these types of solutions
suffer serious
drawbacks by increasing the cost and complexity of the matrix acidizing
operation.
Therefore, it would be advantageous to have a method and a device that
provided for an
improved deep acid stimulation over those known heretofore.
SUMMARY OF INVENTION
100071 The methods and device provides for matrix acidizing aimed at reaching
deeper
stimulation zones in the underground formation. The method uses ultrasound
energy to push
the stimulating acid deeper into the underground formation.
100081 A method for performing a deep acid stimulation of a zone to be treated
in an
underground formation utilizes an acidizing tool. The method includes the step
of
introducing the acidizing tool into a well bore. The well bore is operable to
permit access to
the underground formation. The well bore is also defined by a well bore wall.
The acidizing
tool is operable to introduce an acid formulation onto the well bore wall. The
acidizing tool
is also operable to introduce ultrasound energy into the underground
formation. The method
includes the step of introducing the acid formulation onto the well bore wall
at the treatment
zone. The acid formulation includes an acid. The introduction of the acid
formulation is
such that the acid diffuses into the underground formation at the treatment
zone to an initial
acid penetration depth. The method includes the step of introducing ultrasound
energy into
the underground formation at the treatment zone. The acid diffuses into the
underground
formation at the treatment zone to a subsequent acid penetration depth. The
subsequent acid
penetration depth is deeper into the underground formation than the initial
acid penetration
depth.
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100091 A method of stress fracturing a portion of an underground formation
includes the step
of introducing the acidizing tool into a well bore such that it is positioned
proximate to a
focused treatment point. The focused treatment point is associated with a
portion of the
underground formation under stress. The acidizing tool is operable to direct
the acid
formulation and the ultrasound energy at the focused treatment point. The
method includes
the step of introducing at the same time the acid formulation and the
ultrasound energy at the
focused treatment point. The simultaneous introduction diffases acid from the
acid
formulation into the portion of the underground formation under stress. The
acid formulation
is introduced at a pressure less than the fracture gradient pressure stressed
underground
formation. The diffused acid creates weakened acidized spots in the
underground formation
under stress. The weakened acidized spots in combination with the stress on
the underground
formation causes oriented stress-induced fractures to form that are fluidly
coupled with the
well bore.
100101 An acidizing tool for use in a well bore traversing through an
underground formation
includes an acid delivery system operable to introduce an acid formulation
onto a well bore
wall of the well bore. The acidizing tool also includes an ultrasonic
transmitter operable to
introduce ultrasound energy into the underground formation.
BRIEF DESCRIPTION OF THE DRAWINGS
100111 These and other features, aspects, and advantages of the present
invention are better
understood with regard to the following Detailed Description of the Preferred
Embodiments,
appended Claims, and accompanying Figures, where:
100121 Figures IA-C show an embodiment of the method of using an embodiment of
the
acidizing tool in a cross-sectional view of a pre-formed well bore;
100131 Figure 2 show an embodiment of the method of using an embodiment of the
acidizing
tool in a cross-sectional view of a pre-formed well bore;
100141 Figure 3 shows a cross-sectional view of an embodiment of the acidizing
tool;
100151 Figure 4 shows a cross-sectional view of an embodiment of the acidizing
tool;
100161 Figure 5 shows the histogram depth analysis for both before and after
acid
formulation exposure on a first core plug; and
100171 Figure 6 shows the histogram depth analysis for both before and after
acid
formulation and ultrasound energy exposure on a second core plug.
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1.00181 In the accompanying l'igures, similar components or features, or both,
may have the
same or a similar reference label.
DETAILED DESCRIPTION
100191 The Specification, which includes the Summary of Invention, Brief
Description of the
Drawings and the Detailed Description of the Preferred Embodiments, and the
appended
Claims refer to particular features (including process or method steps) of the
invention.
Those of skill in the art understand that the invention includes all possible
combinations and
uses of particular features described in the Specification. Those of skill in
the art understand
that the invention is not limited to or by the description of embodiments
given in the
Specification. The inventive subject matter is not restricted except only in
the spirit of the
Specification and appended Claims.
100201 Those of skill in the art also understand that the terminology used for
describing
particular embodiments does not limit the scope or breadth of the invention.
In interpreting
the Specification and appended Claims, all terms should be interpreted in the
broadest
possible manner consistent with the context of each term. All technical and
scientific terms
used in the Specification and appended Claims have the same meaning as
commonly
understood by one of ordinary skill in the art to which this invention belongs
unless defined
otherwise.
100211 As used in the Specification and appended Claims, the singular forms
"a", "an", and
"the" include plural references unless the context clearly indicates
otherwise. The verb
"comprises" and its conjugated forms should be interpreted as referring to
elements,
components or steps in a non-exclusive manner. The referenced elements,
components or
steps may be present, utilized or combined with other elements, components or
steps not
expressly referenced. The verb "couple" and its conjugated forms means to
complete any
type of required junction, including electrical, mechanical or fluid, to form
a singular object
from. two or more previously non-joined objects. If a first device couples to
a second device,
the connection can occur either directly or through a common connector.
"Optionally" and
its various forms means that the subsequently described event or circumstance
may or may
not occur. The description includes instances where the event or circumstance
occurs and
instances where it does not occur. "Operable" and its various forms means fit
for its proper
functioning and able to be used for its intended use.
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100221 Spatial terms describe the relative position of an object or a group of
objects relative
to another object or group of objects. The spatial relationships apply along
vertical and
horizontal axes. Orientation and relational words including "taphole" and
"downhole";
"above" and "below"; "up" and "down" and other like terms are for descriptive
convenience
and are not limiting unless otherwise indicated.
100231 Where the Specification or the appended Claims provide a range of
values, it is
understood that the interval encompasses each intervening value between the
upper limit and
the lower limit as well as the upper limit and the lower limit. The invention
encompasses and
bounds smaller ranges of the interval subject to any specific exclusion
provided.
100241 Where the Specification and appended Claims reference a method
comprising two or
more defined steps, the defined steps can be carried out in any order or
simultaneously except
where the context excludes that possibility.
Figures 1A-C
100251 Figures 1A-C show an embodiment of the method of using an embodiment of
the
acidizing tool in a cross-sectional view of a pre-formed well bore traversing
an underground
formation.
100261 Figure 1A shows underground formation 10 containing treatment zone 15,
which is a
portion of underground formation 10 to be treated. Underground formation 10
and treatment
zone 15 are accessible through. well bore 20. Well bore 20 extends from the
surface
downward to treatment zone 15 and is defined by well bore wall 22. Treatment
zone 15
interfaces with well bore 20 at well bore wall 22 and extends radially from
well bore 20.
Treatment 'Dane 15 has uphole bound 24, which is the uphole-most portion of
treatment zone
15 accessible through well bore 20, and downhole bound 26, which is the
downhole-most
portion of treatment zone 15 accessible through well bore 20.
100271 In Fig. 1A, acidizing tool 30 is introduced (arrow 32) into well bore
20 such that it is
positioned proximate to uphole bound 24 of treatment zone 15. .Acidizing tool
10 is
introduced coupled to coiled tubing 34. Coiled tubing is operable to supply
acid formulation
and power from the surface to acidizing tool 30. Acid formulation is
introduced to treatment
zone 15 through acid delivery system 36, which includes acid flow channels 38,
which are
operable to direct the acid formulation onto well bore wall 22 in treatment
zone is.
100281 An embodiment of the method includes where the treatment zone of the
underground
fortnation is made of carbonate rock.
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100291 Fig. 1B shows acidizing tool 30 introducing acid formulation (jets 40)
to treatment
zone 15 through acid flow channels 38. Acidizing tool 30 distributes acid
formulation 40
radially onto well bore wall 22 from. uphole bound 24 to downhole bound 26 of
treatment
zone 15. Acid formulation 40 coats well bore wall 22 where distributed, which
allows the
acid from acid formulation 40 to diffuse and penetrate into treatment zone 15,
forming acid
treated portion 42 of treatment zone 15. The acid penetrates into treatment
zone 15 to initial
acid penetration depth 44, which is the depth into underground formation 10 as
measured
from well bore wall 22. Fig. 1B shows acid formulation 40 introduction while
acidizing tool
30 is being further introduced into well bore 20.
100301 The acid formulation includes an acid. Diluted hydrochloric and
sulfuric acids are
useful examples of acids solutions for the acid formulation. An embodiment of
the method
includes using a weak acid as the acid in the formulation. Weak acids are
acids that do not
fully disassociate in the presence of water. Acetic acid, formic acid,
fluoroboric acid and
ethylenediaminetetraacetic acid (EDIA.) are examples of useful weak acids.
Weak acids are
considered useful in that their reaction is not instantaneous and total with
the minerals present
in the formation upon contact but rather measured through known reaction
constants,
permitting application of ultrasound energy. A.n embodiment of the method
includes where
the acid has a pH value in a range of from about 2 to about 5.
100311 The acid formulation as part of an applied gel or foam can prolong
contact with the
well bore wall. The gel or foam can also reduce the amount of the acid
formulation that
directly contacts the well bore wall, which increases the amount of unreacted
acid
formulation available for driving into the treatment zone using ultrasound
energy. The foam
or gel can also improve the locating of the acid formulation as the foam or
gel adheres to the
well bore wall proximate to where it is distributed. An embodiment of the
method includes
where the acid formulation is part of a eel that is operable to physically
adhere to the well
bore wall. An embodiment of the method includes where the acid formulation is
part of a
foam that is operable to physically adhere to the well bore wall. Pressurized
gases, including
nitrogen, air and carbon dioxide, are useful for creating a foam to carry the
acid formulation.
100321 Acidizing tool 30 also includes ultrasonic transmitter 50 (shown
internally). Fig. 1C
shows acidizing tool 30 introducing ultrasound energy (arrows 52) to treatment
zone using
ultrasonic transmitter 50. Acidizing tool 30 transmits ultrasound energy 52
radially into
treatment zone 15 from uphole bound 24 to downhole bound 26 of treatment zone
15.
Ultrasound energy 52 radiates through acid treated portion 42 of treatment
zone 15.
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Ultrasound energy 52 pushes the acid in acid treated portion 42 deeper into
treatment zone
15, forming ultrasonic treated portion 54 of treated zone 15. The acid
penetrates deeper into
treatment zone 15 to subsequent acid penetration depth 56, which is the depth
into
underground formation 10 as measured from well bore wall 22. Subsequent acid
penetration
depth 56 is a greater value (that is, deeper into underground formation 10
from well bore wall
22) than initial acid penetration depth 44. Fig. IC shows ultrasound energy 52
introduction
while acidizing tool 30 is being extracted from well bore 20, which allows
acidizing tool 30
to reach the position proximate to uphole bound 24.
100331 The ultrasonic transmitter can introduce the ultrasonic energy into the
underground
formation at a range of frequencies and a range of intensities based upon the
concentration,
types, and amount of acid formulation used. An embodiment of the method
includes
introducing ultrasound energy at a frequency in a range of from about 10
IdloHertz (kHz) to
about 1 megahertz (MHz). An embodiment of the method includes introducing
ultrasound
energy at an intensity of sonication in a range of from about 1 Watt per
square centimeter to
about 10 (Wicm2).
100341 The acid formulation and the ultrasound energy are directed by the
acidizing tool in
the same general direction to promote the dispersion of acid deep into the
underground
formation. A.n embodiment of the method includes where both the acid
formulation and the
ultrasound energy are introduced radially from the acidizing tool. This
permits total coverage
of the underground formation from the well bore. An embodiment of the method
includes
where both the acid formulation and the ultrasound energy are introduced to a
focused
treatment point.
100351 The acid in the acid formulation reacts with the mineral constituents
of the
underground formation. A useful acid formulation is one where the acid has a
reaction rate
with the mineral constituents of the underground formation that is lower than
the rate of
diffusion thought the underground formation. Using a weak acid can prevent all
the acid
being consumed upon introduction to the well bore wall surface. Also,
incorporating the acid
formulation into a gel or a foam can also prevent a majority of the acid from
being consumed
upon initial application to the well bore wall. This permits maximizing the
distance of
diffusion through the underground formation, which improves the quality of
formation
stimulation per treatment, instead of simply acidizing the surface of the well
bore wall with
the entire amount of applied acid. An embodiment of the method includes where
a
significant portion of the acid does not react with the underground formation
until the acid is
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diffused into the underground formation by the introduction of the ultrasonic
energy. In an
embodiment of the method, a "significant portion" means at least 50% of the
acid introduced
with the acid formulation. In an embodiment, a significant portion means at
least 60% of the
acid introduced. In an embodiment, a significant portion means at least 70% of
the acid
introduced. In an embodiment, a significant portion means at least 80% of the
acid
introduced. In an embodiment, a significant portion means at least 90% of the
acid
introduced. In an embodiment, a significant portion means at least 95% of the
acid
introduced.
100361 The difference in depth between initial acid penetration depth and the
subsequent acid
penetration depth depends on several factors, including the intensity of
sonication and
frequency of the ultrasonic energy, time between application of the acid
formulation and
application of ultrasonic energy, time of exposure to ultrasonic energy, the
acid composition,
and the composition of the underground formation. An embodiment of the method
includes
where the difference in depth between the initial acid penetration depth and
the subsequent
acid penetration depth, as measured from the well bore wall, is at least 50%
greater. An
embodiment of the method includes where the difference in depth between the
initial acid
penetration depth and the subsequent acid penetration depth, as measured from
the well bore
wall, is in a range of from about 50% to about 90% greater.
100371 The method of treatment does not require introduction of the acid
formulation in
excess of the fracture gradient pressure of the underground formation.
Although potentially
useful as a hydraulic fracturing or "fracking" fluid, the acid firmulation
useful for deep acid
stimulation is operable to permit diffusion of the acid into the underground
formation through
the well bore wall using fluid transport and diffusion mechanics. An
embodiment of the
method includes introducing the acid formulation at a pressure less than the
fracture gradient
pressure value of the underground formation.
100381 An embodiment of the method includes not introducing an externally
supplied
surfactant.
Figure 2
100391 Figure 2 show an embodiment of the method of using an embodiment of the
acidizing
tool in a cross-sectional view of a pre-formed well bore traversing an
underground formation
similar to Figures 1A-C. Acidizing tool 130 introduces acid formulation (jets
140) to
treatment zone 115 through acid flow channels 138. Acid flow channels 138 are
located in a
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downholc position along acidizing tool 130. Acidizing tool 130 distributes
acid formulation
140 from uphole bound 124 to downhole bound 126 of treatment zone 15. The acid
from
acid formulation 40 diffuses and penetrates into treatment zone 115, forming
acid treated
portion 142. The acid penetrates into treatment zone 115 to initial acid
penetration depth
144.
100401 Simultaneously, acidizing tool 130 introducing ultrasound energy
(arrows 152) to
treatment zone 115 using ultrasonic transmitter 150 (shown internal).
Ultrasonic transmitter
150 is located uphole of acid flow channels 138. Acidizing tool 130 is
introduced such that
for a fixed position in treatment zone 115 well bore wall 122 is exposed to
acid formulation
140 before introduced to ultrasound energy 152. Acidizing tool 130 transmits
ultrasound
energy 152 from uphole bound 124 to downhole bound 126. Ultrasound energy 152
radiates
through acid treated portion 142, pushing the acid in acid treated portion 142
deeper into
treatment zone 115 to form ultrasonic treated portion 154. The acid penetrates
deeper into
treatment zone 115 to subsequent acid penetration depth 156. Subsequent acid
penetration
depth 156 is greater than initial acid penetration depth 144.
Figure 3
100411 Figure 3 shows a cross-sectional view of an embodiment of the acidizing
tool.
Acidizing tool 230 has an acid delivery system 236 with a plurality of acid
flow channels
238. Acid flow channels 238 are such that they are operable to introduce acid
formulation
(jets 240) onto focused treatment point 260. Acidizing tool 230 also has
ultrasonic
transmitter 250 positioned such that it is operable to introduce ultrasound
energy (arrows
252) onto focused treatment point 260. The embodiment of the acidizing tool
permits
simultaneous introduction of acid formulation 240 and ultrasound energy 252
onto focused
treatment point 260, driving acid deep into underground formation 210.
Acidizing tool 230 is
shown coupled to the surface with coiled tubing 234, which supplies acid
formulation, and
power conduit 262, which supplies electrical power.
100421 An embodiment of the method of deep acid stimulation includes where the
acidizing
tool both introduces the acid formulation and the ultrasonic energy
simultaneously by
directing both towards a focused treatment point. The focused treatment point
is a point on
or a short length along the well bore wall.
100431 Introducing the acid formulation and the ultrasonic energy
simultaneously at a
focused treatment point using such an embodiment of the acidizing tool is
useful for creating
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oriented fracturing within a portion of the underground formation under
stress. The acidizing
tool is introduced into the well bore such that it is located proximate to the
focused treatment
point. The focused treatment point is associated with the portion of the
underground
formation under stress.
100441 Simultaneous introduction of both the acid formulation and ultrasonic
energy at the
focused treatment point diffuses the acid deep into the underground formation
at that
location. The acid formulation introduction does not require exceeding the
fracture gradient
of the portion of the underground formation under stress. The acid inside the
underground
formation reacts with the formation and causes weakened acidized spots to
form.
100451 Although shown in Figures 1-3 as applying the acid formulation and
ultrasonic energy
such that the applied acid is driven into the formation in a direction
perpendicular to the
orientation of the well bore, the methods of deep acid penetration and
inducing stress-induced
fractures are not limited merely to angles perpendicular to the well bore. In
instances where
the orientation of underground formation does not lend itself to deep acid
penetration at a 90
degree angle relative to the well bore, as often is the case in vertical or
deviated directional
wells applying acid formulation and ultrasonic energy into thin bands of
productive
formation, the ultrasonic transmitter is operable for positioning, either
remotely or pre-
positioned before introduction into the well bore, such that the ultrasonic
energy directs the
applied acid formulation into the underground formation in a non-perpendicular
angle to the
orientation of the well bore. For example, Figure 3 could show acidizing tool
230 having a
first ultrasonic transmitter 250 positioned such that its ultrasound energy
252 is directed at an
obtuse angle relative to the orientation of the well bore and a second
ultrasonic transmitter
250 oriented such that transmitted ultrasound energy 252 is directed at an
acute angle relative
to the orientation of the well bore.
100461 The creation of weakened acidized spots within the underground
formation in
conjunction with the stress in the formation causes stress-induced fracturing
of the portion of
the underground formation under stress. The stress-induced fractures are
oriented fluid flow
channels that not only fluidly connect with the well bore but also run deep
into the
underground formation. In an embodiment of the method the stress-induced
fractures fluidly
connect with the weaken acidized spots. Such oriented stress-induced fractures
are fluid
cannels useful for additional operations.
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1.00471 Introducing hydraulic fracturing fluid into the oriented stress-
induced fractures at
pressures greater than the fracture gradient of the underground formation can
widen the
fractures and open up previously tight underground formations to exploitation,
but in a
predictable and controllable manner versus simply hydraulically fracturing the
underground
formation.
Figure 4
100481 Figure 4 shows a cross-sectional view of an embodiment of the acidizing
tool.
Acidizing tool 330 includes first acid delivery system 370 and first
ultrasonic transmitter 372
coupled in series with second acid delivery system 374 and second ultrasonic
transmitter 376.
Acid formulation is distributed from the surface through coiled tubing 334.
Both first acid
delivery system 370 and second acid delivery system 374 fluidly couple to
coiled tubing 334
and to one another. Power conduit 362 transmits power from the surface to both
first
ultrasonic transmitter 372 and second ultrasonic transmitter 376, which
electrically couple
together in series. Acidizing tool 330 permits greater acid formulation and
ultrasonic energy
distribution in a single pass through well bore 320.
Supplemental Equipment
100491 Embodiments include many additional standard components or equipment
that
enables and makes operable the described apparatus, process, method and
system.
100501 Operation, control and performance of portions of or entire steps of a
process or
method can occur through human interaction, pre-programmed computer control
and
response systems, or combinations thereof.
Experiment
100511 Examples of specific embodiments facilitate a better understanding of
deep acid
stimulation method. in no way should the Examples limit or define the scope of
the
invention.
100521 Two similar carbonate core plugs having similar physical and
permeability properties
are used in order to test the effect of ultrasound waves on acid penetration
depth. Both
carbonate core plugs are cylindrical in form with opposing flat faces and are
35 millimeters
(mm) in length from face-to-face. The first core plug has an initial
permeability value of 6
milliDarcy (mD). The second core plug has an initial permeability value of 8
mD. Each core
11
=
TM
plug is prepared by wrapping the side of the cylinder in TEFLON (E. I. du Pont
de Nemours
and Co.; Wilmington, Del.) but keeping the faces exposed.
[0053] The acid formulation for the experiment is a composition of a 5 wt.%
aqueous acetic
acid solution. The acid formulation is maintained at 25EC and is not stirred
to maintain
static conditions.
100541 Both the first and second core plugs are partially immersed in a bath
containing the
acid formulation such that one face of the plug is in fluid contact with the
acid formulation.
The first plug is maintained in its position for two hours without any
additional changes to its
environment. The second plug followed the same procedure except that the bath
containing
the acid formulation and the second plug is exposed to ultrasound energy from
an ultrasound
source for the two-hour acid formulation exposure period. The ultrasound
source directs
ultrasound energy (at 300 kHz) at the face of the second cylinder immersed in
the acid
formulation.
100551 After the two hour acid fommlation immersion period, the acid
penetration distance in
both the first and second plugs is determined using computerized tomography
(CT) analysis.
A CT scanner performs a scan on the two carbonate plugs at 5 mm intervals
starting from the
fluid-exposed face of the core plug to the non-exposed face. The CT scanner
scans both core
plugs before treatment to establish a baseline for comparison. For each core
plug, 7 CT
"slices" along the length of the first and second core plugs both before and
after testing help
to create histograms that are useful in determining the effects of ultrasound
energy
introduction on acid penetration depth.
100561 Figure 5 shows the histogram depth analysis for both before and after
acid
formulation exposure on the first core plug. Figure 6 shows the histogram
depth analysis for
both before and after acid formulation and ultrasound energy exposure on the
second core
plug.
[0057] Histogram analysis shows that both the first and second core plugs
reacted with the
acetic acid in the acid formulation. A downward shift in the CT distribution
values produced
by the CT analysis reflects a change in overall density of the core plug at
that distance from
the face exposed to the acid. The downward shift reflects that the acid
dissolved mineral
content from within the core plug and lowered its overall density. At
distances where no
downward shift in CT distribution occurred indicates that the acid did not
penetrate to that
depth and dissolve minerals from the core plug.
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1.00581 The histogram analysis of the first core plug indicates that the acid
penetrated the core
plug to a depth no greater than 23 mm from the exposed face. Beyond this
distance, there no
difference in the CT distribution values before or after treatment of the
first core plug,
indicating that acid did not penetrate any further into the first core plug.
100591 The histogram analysis of the second core plug indicates that the acid
penetrated the
core plug to a depth of almost 35 mm from the exposed face. Compared to the
first core
plug, the effect of introducing ultrasound energy into the core plug during
acid formulation
treatment increased the acid penetration distance by at least 50%. The
experiment shows that
the use of ultrasound improves acid penetration depth.
13
