U.S. patent application number 12/901695 was filed with the patent office on 2011-05-05 for method for forming an isolating plug.
This patent application is currently assigned to Schlumberger Technology Corporation. Invention is credited to Vadim Kamil'evich Khlestkin, Konstantin Igorevich Popov.
Application Number | 20110100625 12/901695 |
Document ID | / |
Family ID | 43924165 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100625 |
Kind Code |
A1 |
Popov; Konstantin Igorevich ;
et al. |
May 5, 2011 |
METHOD FOR FORMING AN ISOLATING PLUG
Abstract
The invention relates to methods for isolating near-wellbore
zones and fractures and can be used for plugging fractures in the
near-wellbore zone during the removal of the fracturing fluid, as
well as for plugging different kinds of fractures and branches in
the casing. The method for forming an isolating-plug includes the
injection of a slurry containing dispersed fibers into a well and
subsequent formation of a plug to isolate the relevant section of
the well and to prevent the fluid penetration. The slurry is
admixed with amphiphilic substances, and the fibers used are
capable of adsorbing the amphiphilic substances on their
surface.
Inventors: |
Popov; Konstantin Igorevich;
(Dubna, RU) ; Khlestkin; Vadim Kamil'evich;
(Novosibirsk, RU) |
Assignee: |
Schlumberger Technology
Corporation
Cambridge
MA
|
Family ID: |
43924165 |
Appl. No.: |
12/901695 |
Filed: |
October 11, 2010 |
Current U.S.
Class: |
166/293 |
Current CPC
Class: |
E21B 33/13 20130101;
C09K 2208/08 20130101; C09K 8/516 20130101 |
Class at
Publication: |
166/293 |
International
Class: |
E21B 33/13 20060101
E21B033/13 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2009 |
RU |
2009137265 |
Claims
1. A method for forming an isolating plug, which includes the
injection of a slurry containing dispersed fibers into a well and
subsequent formation of a plug to isolate a relevant section of the
well and to prevent a fluid penetration, wherein the slurry is
admixed with amphiphilic substances, and the fibers used are
capable of adsorbing the amphiphilic substances on their
surface.
2. A method for forming an isolating plug according to claim 1,
wherein the fiber material is selected from the group which
includes PET fibers, polylactic acid, polyglycol acid, polyether,
cotton, silica glass fiber, polyamide, protein,
phenol-formaldehyde, polycarbonate, polyanhydride, epoxy resin.
3. A method for forming an isolating plug according to claim 1,
wherein the amphiphilic substances are added to the slurry during
the preparation of the slurry.
4. A method for forming an isolating plug according to claim 1,
wherein the amphiphilic substances are injected into the well
before the slurry injection, or in parallel with the slurry
injection, or after the slurry injection.
5. A method for forming an isolating plug according to claim 1,
wherein surfactants are used as amphiphilic substances.
6. A method for forming an isolating plug according to claim 1,
wherein quaternized ammonium salts are used as amphiphilic
substances.
7. A method for forming an isolating plug according to claim 1,
wherein benzoic acid is used as amphiphilic substances.
8. A method for forming an isolating plug according to claim 1,
wherein diblock copolymers with a polyelectrolyte block are used as
amphiphilic substances.
9. A method for forming an isolating plug according to claim 1,
wherein the amphiphilic substances are added to the slurry in the
capsular form to be subsequently released at the plug formation
place under the influence of the environmental conditions, such as
temperature, or pressure, or flow, or chemical dissolution.
10. A method for forming an isolating plug according to claim 1,
wherein the amphiphilic substances used are destroyed under the
influence of the environmental conditions, such as the temperature,
the flow, or due to chemical reactions.
11. A method for forming an isolating plug according to claim 1,
wherein the amphiphilic substances are added by injecting
precursors into the well in parallel with the slurry injection,
which precursors will be transformed into amphiphilic substances at
the plug formation place under the influence of the environmental
conditions, such as the temperature or the flow.
12. A method for forming an isolating plug according to claim 1,
wherein esters, antihydrides, heterocyclic acetates, amines, amides
and other chemically unstable groups are used as precursors.
Description
FIELD OF INVENTION
[0001] The invention relates to the oil and gas production
industry, in particular, to methods for isolating near-wellbore
zones and fractures, and can be used for plugging fractures in the
near-wellbore zone during the removal of the fracturing fluid, as
well as for plugging different kinds of fractures and branches in
the casing.
BACKGROUND OF THE INVENTION
[0002] The hydraulic fracturing is the main tool used for
increasing the productive capacity of a well through creation or
expansion of channels from the wellbore to the producing formation.
This operation is generally accomplished by injecting a fracturing
fluid into the wellbore which intersects an underground deposit,
and by exposing the strata to the fluid pressure action. In order
to increase the oil and gas production rates, it is necessary to
solve the problem of how to remove the fracturing fluid and to plug
the near-wellbore zones and fractures. A few methods are used for
solving this problem, and these methods are usually based on
addition of solid inclusions to fracturing-fluid solutions. The
formation of an isolating plug starts from the formation of a
bridge (so-called "bridging") which is nothing but a cluster of
solid inclusions stably captured from the solution on the fracture
surface. At the same time, the fluid keeps on flowing through the
fixed agglomerate of solid inclusions. As a result, the
solids-containing solution (the slurry) is filtered, which
gradually increases the density of the solids arrested and reduces
the penetrability of the resulting structure and completely stops
the flow. For example, U.S. Pat. No. 7,036,588 describes the use of
ceramic particles and starch buildups for fluid loss control
purposes; U.S. Pat. No. 7,318,481 describes shape-memory foams
which are used as a withdrawal agent; International Application No.
WO2007066254 describes the reversible plugging of a fracture or a
well with a decomposable material. U.S. Pat. No. 7,331,391
describes the use of water-soluble fibers for drilling-mud loss
control purposes.
[0003] RU Patent No. 2330931 describes a method for forming an
isolating plug, which includes the injection of a slurry containing
dispersed fibers into the well and subsequent formation of a plug
to isolate the relevant section of the well. When the slurry is
injected, the device used in this patent accumulates fibers, thus
forming an impermeable plug in the wellbore. Depending on the fiber
material selected, it is possible to obtain a temporary or
permanent plug. This method has a number of limitations on use,
namely: relative design complexity and the fact that the plug is
formed in the wellbore, which makes the access to the well areas
behind the packer (access to the well end) difficult or
impossible.
[0004] A high fiber concentration is required for successful
formation of a plug from fibers. Such an approach encounters a
number of problems, namely: financial expenses related to the
production/purchase/transportation of large amounts of fibers, and
expenses related to the expansion of injection equipment
capacities. At the same time, the equipment (pumps, mixers, etc.)
may fail if used for processing a high fiber concentration.
SUMMARY OF THE INVENTION
[0005] The technical result achieved with the implementation of the
invention consists in providing efficient isolation of fractures in
the near-wellbore zone, while reducing the fiber concentration and
preventing the pumps and other equipment from fouling.
[0006] To achieve the said technical result, we suggest a method
for forming an isolating plug, which includes the injection of a
slurry containing dispersed fibers into a well and subsequent
formation of a plug to isolate the relevant section of the well and
to prevent the fluid penetration. The slurry is admixed with
amphiphilic substances, and the fibers used are capable of
adsorbing the amphiphilic substances on their surface.
[0007] When adsorbed on the fiber surface directly upstream of the
isolation zone, the amphiphilic substances change the affinity of
fibers to solvent and lead, as a consequence, to the formation of
agglomerates from fibers. The agglomerates are bigger in size than
the fibers, which results in the formation of a plug. The initial
fiber concentration is low enough to ensure that the equipment will
operate without failures.
[0008] Vice versa, the amphiphilic substances promote a uniform
distribution of hydrophobic fibers in the original fluid. After the
decomposition of amphiphilic substances upstream of the isolation
zone, this distribution will be disturbed, resulting in the
formation of fiber agglomerates and then a plug.
[0009] The amphiphilic substances can be added to the slurry during
the preparation of the slurry.
[0010] The amphiphilic substances can be injected into the well in
parallel with the slurry injection, before the slurry injection or
after the slurry injection.
[0011] It is possible to use surfactants as amphiphilic
substances.
[0012] It is possible to use quaternized ammonium salts as
amphiphilic substances.
[0013] It is possible to use benzoic acid as amphiphilic
substances.
[0014] It is possible to use diblock copolymers with a
polyelectrolyte block as amphiphilic substances.
[0015] The amphiphilic substances can be added to the slurry in the
capsular form and can be subsequently released at the plug
formation point under the influence of the environmental
conditions, such as the temperature, the pressure, the rate of
shear in the flow, or chemical dissolution. Capsular amphiphilic
substances are described in such patents as EP Patent No. 0107086,
U.S. Pat. No. 5,480,577, etc.
[0016] The amphiphilic substances can decompose under the influence
of the environmental conditions, such as the temperature, the rate
of shear in the flow, or due to chemical reactions.
[0017] The amphiphilic substances can be added by injecting their
precursors into the well, which precursors will be transformed into
amphiphilic substances under the influence of the environmental
conditions, such as the temperature or the flow. It is possible to
use esters, antihydrides, heterocyclic acetates, amines, amides,
and other chemically unstable substances forming amphiphilic
substances as a result of a chemical reaction, as precursors.
[0018] The amphiphilic substances, their precursors, and the
chemicals which destruct the precursors or the capsules containing
amphiphilic substances can be injected upstream of the isolation
zone through coil tubing.
[0019] It is possible to use PET fibers, polylactic acid,
polyglycol acid, polyether, cotton, silica glass fiber, polyamide,
protein, phenol-formaldehyde, polycarbonate, polyanhydride, epoxy
resin as the fiber material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] In this invention, the coagulating properties of the fibers
are controlled by adding amphiphilic molecules with charged or
polarized groups. In case that fibers have a partially
uncompensated charge on their surface, the charged or polarized
groups will allow the molecules to adhere to (to be adsorbed on)
the fiber surface, while the amphiphilicity of the molecules will
ensure that the surface properties (hydrophobic/hydrophilic
properties) of the fibers will be controlled. It is a well-known
fact that hydrophilic particles coagulate in oil (a non-polar
medium) and that hydrophobic particles coagulate in water (a polar
medium). This results from the fact that the particles tend to
reduce the area of unfavourable contacts with the environment. The
main idea of the invention is to coat each fiber in the slurry with
amphiphilic molecules, which will change the energy of the
fiber-to-fiber contact and the fiber-to-fluid contact, making the
former more favourable. As a result, the fibers will start
aggregating in order to increase the number of more favourable
contacts, thus making the slurry less homogeneous.
[0021] The bridging ability of the slurry injected with fiber
aggregates will be better than that of a homogeneous slurry at the
same fiber concentration.
[0022] Let us consider the embodiment where surfactants are used as
amphiphilic substances. The method for forming an isolating plug is
implemented as follows. The slurry is injected into a well and
contains dispersed fibers which adsorb amphiphilic substances on
their surface. It is possible to use PET fibers, polylactic acid,
polyglycol acid, cotton, silica glass fiber, polyamide, protein,
phenol-formaldehyde, polycarbonate, polyanhydride, epoxy resin as
the fiber material.
[0023] In parallel, the surfactants are injected. The fiber
aggregation process presented herein and promoted by the
surfactants has a simple physical explanation. Let us consider an
undiluted slurry of fibers. The fibers come in mechanical contact
with each other in such a slurry. Let us assume that each fiber has
an uncompensated positive or negative charge on its surface (the
nature of this charge can be of any kind, e.g. polarization of
fiber-forming molecules). Let us assume that the suspending fluid
is polar (e.g. water) and that the fibers in this system are weakly
hydrophilic. Due to the presence of an uncompensated like charge on
the fiber surface, they will be pushed away from each other. In
order to initiate the coagulation and the formation of aggregates
in such a system, it is necessary to add cationic or anionic
surfactant molecules (the sign of the charged groups should be
selected in such a way as to be opposite to the sign of the fiber
surface charge). Due to electrostatic interactions, such
surfactants are adsorbed with charged heads on the surface of the
oppositely charged fiber, thus creating a crown of hydrophobic
(non-polar) tails around it. As a result, the fibers coated with
surfactants become hydrophobic (an evaluation of adhesion forces
between the fibers and of the impact of certain surfactants on the
adhesion forces is given in the following paper: E. A. Amelina, I.
V. Videnskii, N. I. Ivanova, V. V. Pelekh, N. V. Altukhova, and E.
D. Shchukin, Colloid Journal, vol. 63, No. 1, 2001, pp. 124-126).
By using a great number of different surfactants (and even a
greater number of possible amphiphilic molecules in the general
case) at different concentrations, it is possible to obtain an
immensely wide range of values for the hydrophobic properties of
the fibers.
[0024] In order to determine the optimum concentration of the
surfactant molecules, it is necessary to take the following
conditions into account: [0025] 1) The number of the molecules
should be great enough to coat the entire surface of the fibers.
[0026] 2) The concentration should not exceed the critical micelle
concentration (CMC) for these surfactants so that no
self-transformation of the surfactants into micelles could take
place.
[0027] In case of cylindrical fibers, the concentration of the
surfactant molecules can be evaluated by the following formula:
m S = 4 M N A S 0 .rho. d m f ##EQU00001## C S = 4 M N A S 0 .rho.
d C f ##EQU00001.2##
[0028] where M is the molar weight of the surfactant molecules,
N.sub.A is Avogadro's number, S.sub.0 is the surface area of the
surfactant molecule's head, d is the fiber diameter, .rho. is the
fiber material density. C.sub.f, m.sub.f and C.sub.s, m.sub.s are
the concentrations and weights of the fibers and of the surfactant
molecules, respectively.
Example 1
[0029] Let us consider polylactic acid fibers having the following
parameters: .rho.=1.25 g/cm.sup.3, So=25 A.sup.2, d=12 .mu.m, l=6
mm. For similar fibers: m.sub.s.about.10.sup.-3 m.sub.f and
C.sub.s.about.10.sup.-3 C.sub.f.
[0030] Similar fibers contain a low uncompensated negative charge
on their surface due to the polarization of the ester group. The
fibers were suspended in a linear guar solution (at a concentration
of 3.6 g/L), the fiber concentration was equal to 4.8 g/L.
Trimethyl tetradecyl ammonium bromide at a concentration of 54.6
mg/L was added as a cationic surfactant to a similar slurry. After
it had been mixed for 10 minutes in a mixer the propeller of which
was rotating at 1,500 rpm, the presence of aggregates was detected
in this slurry, as opposed to an equivalent slurry without
surfactants added. The average aggregate size was equal to 25
mm.
[0031] Amphiphilic substances can be added by injecting precursors
into the well in parallel with the slurry injection, which
precursors will be transformed into amphiphilic substances at the
plug formation point under the influence of the environmental
conditions. It allows you to inject a slurry containing
homogeneously distributed fibers and to prevent the pumps from
fouling and the wellbore from plugging near the surface, but to
plug the fracture or the specified section of the wellbore below
the ground. There are a few possibilities to achieve the described
approach.
[0032] For example, precursor molecules of cationic/anionic
surfactants (which contain no charge) are injected together with
the slurry at the initial stage.
[0033] The precursor groups undergo a number of chemical
transformations near the perforation or in the fracture, which
results in the generation of a charge on the surfactant molecules'
polar (hydrophilic) groups.
[0034] The precursor groups may include esters, antihydrides,
heterocyclic acetates, amines, amides and other chemically unstable
groups.
[0035] The following factors may be responsible for the
transformation of the precursors: the temperature below the ground,
the rock surface properties, the flow velocity, acids/bases (in
case of hydrolysis or protonation), alkylating agents or other
chemicals. The sign of the resulting charge of a portion of the
surfactant molecules must be opposite to the sign of the fiber
surface, which results in favourable contact between the surfactant
molecules and the fibers and in subsequent coagulation of the
fibers.
[0036] It is also possible to use capsular surfactant molecules
with charged groups. In this case, the surfactant molecules are
released from capsules under the influence of the temperature, the
flow, the pressure, or the chemical dissolution of the capsules.
The released surfactant molecules behave just as described
above.
[0037] It is possible that the surfactant molecules will reduce the
interactions (attractions) between the fibers in the slurry. In
this case, the slurry is more homogeneous and can be injected more
easily into the well. If a certain number of the surfactant
molecules are removed from the system, the slurry will become less
homogeneous and will have a greater tendency to plug the well.
[0038] A similar approach can be implemented with decomposable
surfactants. In this situation, a so-called double layer will be
formed on the fiber surface due to a high concentration of the
surfactant molecules. Having been adsorbed on the fiber surface due
to electrostatic interactions, the surfactant molecules with
charged groups (the sign of this charge is opposite to that of the
fiber surface charge) form an internal layer. The surfactant
molecules left in the solution in order to minimize the number of
unfavourable contacts between the non-polar groups and the polar
fluid (or vice versa) will form an external portion of the layer,
with the polar heads being directed outwards. As a result, the
fibers surrounded by the double layer will be hydrophilic, which
promotes a better dispersion of the fibers in the slurry. The
surfactant molecules in the external layer will decompose under the
relevant conditions. After the decomposition, the fibers will
become hydrophobic and will start aggregating.
[0039] The surfactants which decompose below the ground can
contain, as hydrophilic heads, the following decomposable chemical
groups: esters, amides, anhydrides, quaternized ammonium salts,
amines, etc.
[0040] The surfactants which decompose below the ground can
contain, as hydrophobic tails, the following decomposable chemical
groups: groups containing double bonds, alcohols, disulfides, aza
groups, esters, amides, amines, etc. The decomposition can be
caused by the hydrolysis or oxidation, the presence of acids or
bases, the presence of other chemicals, the action of temperature
or flow.
[0041] Decomposable surfactants are described, for instance, in the
following papers: Rairkar Maithili E.; Diaz M. Elena; Torriggiani
Mauro; Cerro Ramon L.; Harris J. Milton; Rogers Sarah E.; Eastoe
Julian; Gomez Del Rio Javier A.; Hayes Douglas G.; Colloids and
surfaces. A, Physicochemical and engineering aspects ISSN
0927-7757; 2007, vol. 301, no. 1-3, pp. 394-403, or International
Application No. WO2006120422.
[0042] The described methods can be used with any amphiphilic
substances. For example, it is possible to use quaternized ammonium
salts the amphiphilic chains of which are shorter than those of the
surfactant molecules but are long enough to provide the hydrophobic
properties. Another example is benzoic acid having a charged
carboxyl group and an aromatic hydrophobic fragment. Such
substances can also be delayed-action or decomposable ones. Also,
it is possible to use diblock copolymers with a polyelectrolyte
block.
* * * * *