U.S. patent application number 12/082478 was filed with the patent office on 2008-10-30 for method and apparatus for hydraulic treatment of a wellbore.
This patent application is currently assigned to NCS Oilfield Services Canada Inc.. Invention is credited to Clayton Plucheck, Marty Stromquist.
Application Number | 20080264636 12/082478 |
Document ID | / |
Family ID | 39855409 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264636 |
Kind Code |
A1 |
Stromquist; Marty ; et
al. |
October 30, 2008 |
Method and apparatus for hydraulic treatment of a wellbore
Abstract
A method and apparatus for applying hydraulic treatment and
diversion treatment to a wellbore are described. The method
involves isolating a wellbore segment using hydraulic seals;
applying fluid treatment and perforation diverters within the
isolated segment; and scraping a portion of the wellbore after
termination of treatment to remove any lodged perforation diverters
from the wellbore. A collection chamber may also be provided for
collecting used diverters for return to surface following
treatment. In one embodiment, diverters used and collected within a
first segment may be reused during treatment of a successive
wellbore segment.
Inventors: |
Stromquist; Marty; (Calgary,
CA) ; Plucheck; Clayton; (Tomball, TX) |
Correspondence
Address: |
BROWNSTEIN HYATT FARBER SCHRECK, LLP
410 SEVENTEENTH STREET, SUITE 2200
DENVER
CO
80202
US
|
Assignee: |
NCS Oilfield Services Canada
Inc.
Calgary
CA
|
Family ID: |
39855409 |
Appl. No.: |
12/082478 |
Filed: |
April 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60911844 |
Apr 13, 2007 |
|
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|
Current U.S.
Class: |
166/281 ;
166/120 |
Current CPC
Class: |
E21B 33/138 20130101;
E21B 43/25 20130101 |
Class at
Publication: |
166/281 ;
166/120 |
International
Class: |
E21B 33/124 20060101
E21B033/124 |
Claims
1. A method for applying hydraulic treatment to a wellbore
comprising the steps of: reversibly setting hydraulic seals against
a wellbore above and below a first wellbore segment of interest to
isolate said first wellbore segment; delivering hydraulic treatment
to the isolated wellbore segment; delivering perforation diverters
to the isolated wellbore segment; terminating the delivery of
hydraulic treatment to the isolated segment; unsetting the
hydraulic seals from the wellbore; and scraping the wellbore
segment to dislodge perforation diverters therefrom.
2. The method as in claim 1 further comprising the step of
collecting deployed perforation diverters from the wellbore.
3. The method as in claim 1 wherein the hydraulic seals are packer
assemblies.
4. The method as in claim 1 wherein the hydraulic seals are
pressure actuated sealing members.
5. The method as in claim 1 wherein the wellbore segment of
interest bears two or more perforations.
6. The method as in claim 1 wherein the hydraulic treatment is
fracturing fluid, acidizing or energizing treatment, proppants, or
cleaning fluid.
7. The apparatus as in claim 6 wherein the hydraulic treatment is
in liquid state, gaseous state, or a combination of liquid and
gaseous state.
8. The method as in claim 7 wherein the hydraulic treatment further
includes solids, waxes, biodegradables, or other particles
suspended therewithin.
9. The method as in claim 1 wherein the perforation diverters are
delivered to the isolated wellbore segment during delivery of the
hydraulic treatment fluid.
10. The method as in claim 1 wherein the perforation diverters are
ball sealers.
11. The method as in claim 10 wherein the ball sealers are formed
from polymeric or elastomeric materials, biodegradable material,
ceramics, composites, or wax.
12. The method as in claim 1 wherein the number of perforation
diverters deployed within the segment is less than or equal to the
number of perforations within the segment.
13. The method as in claim 1 wherein the number of perforation
diverters deployed within the segment is greater than the number of
perforations within the segment.
14. The method as in claim 1 wherein scraping is performed by
abrading the wellbore with a scraper.
15. The method as in claim 14 wherein the perforation diverter is a
ball diverter and wherein the scraper is a rigid cup-shaped scraper
for dislodging ball diverters from the wellbore.
16. The method as in claim 14 wherein the perforation diverter is
gel or foam and wherein the scraper is a wire brush for scrubbing
the gel or foam from the wellbore.
17. The method as in claim 14 wherein a diverter collection chamber
is operatively attached to the scraper for collecting used
perforation diverters from the wellbore segment.
18. The method as in claim 1 further comprising the steps of:
reversibly setting the hydraulic seals against the wellbore above
and below a second wellbore segment of interest to isolate said
second wellbore segment; applying hydraulic treatment to the
isolated second segment; deploying perforation diverters within the
isolated second segment; terminating the application of treatment
fluid to the isolated segment; unsetting the hydraulic seals from
the wellbore; and scraping the second wellbore segment to dislodge
perforation diverters therefrom.
19. The method as in claim 18 wherein one or more of the
perforation diverters deployed within the first isolated segment is
collected and then redeployed within the second isolated
segment.
20. The method as in claim 18 wherein the first and second segments
are within the same wellbore.
21. The method as in claim 18 wherein the first and second segments
are within independent wellbores.
22. An apparatus for use in hydraulic treatment of a wellbore, the
apparatus comprising: upper and lower sealing assemblies for
reversibly setting at least two hydraulic seals within a wellbore
to isolate a portion of the wellbore between the seals; a hydraulic
treatment assembly for applying a hydraulic treatment within the
isolated portion of the wellbore; a diversion assembly operatively
attached to the hydraulic treatment assembly for delivering
perforation diverters to the isolated portion of the wellbore
during hydraulic treatment; and a scraper assembly for scraping
lodged perforation diverters from the wellbore segment.
23. The apparatus as in claim 22 wherein the upper and lower
sealing assemblies comprise pressure-activated sealing members for
sealing against the wellbore.
24. The apparatus as in claim 22 wherein the scraper assembly
includes at least one scraper extending outwardly towards the
wellbore to a radial distance less than or equal to the wellbore
drift diameter.
25. The apparatus as in claim 22 wherein the scraper is helically
disposed about the longitudinal axis of the apparatus.
26. The apparatus as in claim 22 wherein two or more scrapers are
arranged radially about the apparatus.
27. The apparatus as in claim 22, further comprising a collection
assembly associated with the scraper assembly for collecting
deployed perforation diverters within the wellbore.
28. The apparatus as in claim 27 wherein the collection assembly
includes a collection chamber having a collection port adjacent the
scraper assembly such that scraping action directs used perforation
diverters into the collection chamber through the collection
port.
29. The apparatus as in claim 28 wherein the hydraulic treatment
assembly is continuous with the collection chamber such that when
hydraulic treatment fluid is applied to the isolated wellbore
segment, at least a portion of the treatment fluid passes through
the collection chamber to cause perforation diverters within the
collection chamber to be expelled therefrom and delivered to the
isolated wellbore segment through the collection port.
30. A diverter scraping and collection assembly for use in removing
lodged perforation diverters from a wellbore, the assembly
comprising: a tubular body for suspension within a wellbore; a
scraping member extending radially from the tubular body for
scraping a wellbore surface to remove lodged diverters therefrom; a
collection chamber operatively attached to the tubular housing for
collecting perforation diverters from the wellbore; and a diverter
collection port adjacent the scraper and continuous with the
collection chamber for directing dislodged perforation diverters to
the collection chamber.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C. 119(e)
to U.S. provisional application No. 60/911,844, entitled "METHOD
AND APPARATUS FOR HYDRAULIC TREATMENT OF A WELLBORE" filed Apr. 13,
2007, the disclosure of which is hereby incorporated by reference
in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the application
of hydraulic treatment to perforated wellbores. More particularly,
the present invention relates to a method for delivering,
distributing, and removing ball diverters within a wellbore to
improve the effectiveness of the hydraulic treatment.
BACKGROUND OF THE INVENTION
[0003] Oil and gas companies are continually seeking strategies to
improve recovery from existing under-producing reserves, while also
conducting new exploration to locate additional potential
resources. Horizontal drilling and solvent or steam-assisted
drainage methods have improved production in certain applications,
while further applications have derived benefit from the
development of new perforation, fractionation, and other
stimulation treatments.
[0004] Notably, hydraulic fracturing and stimulation treatment of
cased wellbores has been improved by the use of diversion
techniques, in which patent perforations along the wellbore are
temporarily sealed or blocked by chemical or mechanical means such
as diversion balls, foam, gels, filter cake formation, and/or
straddle packers to allow the treatment to open blocked or damaged
perforations that may otherwise remain untreated and
underproductive. Although such diversion techniques have generally
improved recovery, chemical diversion is expensive and mechanical
diverters pose other logistical difficulties such as the retrieval
of used ball diverters from the well.
[0005] The most common method of mechanical diversion involves the
use of rubber or polymeric ball sealers, which are released
downhole under pressure proximal to a patent perforation to lodge a
ball sealer therewithin. The number of locations requiring sealing,
number of ball sealers to apply, and time for treatment are
determined prior to application of the ball sealers, and the
pressure is monitored during treatment to confirm fracturing of all
desired perforations. When the pressure rises rapidly without
dissipating, it is assumed that all available perforations have
been opened and blocked with ball sealers (known as bailout). At
this point the treatment is terminated and the well is prepared for
production. The operator may use a casing scraper to remove any
lodged ball sealers from the casing, which are collected in the
production fluid or simply permitted to drop downhole.
[0006] As current methods of hydraulic treatment and diversion are
generally applied to the entire wellbore at once, it is difficult
to apply treatment to specific wellbore portions, and similarly, to
ensure that each perforation has received the appropriate degree of
treatment. Moreover, when ball sealers are used to divert hydraulic
treatment, the balls may become lodged within a perforation,
jamming or damaging tools, requiring additional runs of downhole
equipment to dislodge the ball diverters or otherwise facilitate
tool retrieval.
[0007] Some of the problems encountered with the use of ball
sealers have been addressed by the development of high and low
density ball sealers as well as tools to apply both types of balls
to appropriate downhole locations. For example, U.S. Pat. No.
4,194,561, U.S. Pat. No. 4,287,952, and Canadian Patent CA 1210686
describe the general use of high and low density ball sealers.
[0008] Further, U.S. Pat. No. 7,059,407 describes an assembly for
sequential perforation and fluid treatment of multiple wellbore
segments without interruption to first remove perforating equipment
from the wellbore. Although the assembly allows hydraulic treatment
of specific wellbore segments, it does not provide a means to use
ball sealers for diversion of fluid treatment within a wellbore
segment.
[0009] U.S. Pat. No. 7,134,505 describes a tubing string assembly
that includes a number of segments, each bearing packer elements
and fluid ports such that several segments of a wellbore may be
isolated simultaneously and fluid treatment may be applied to each
segment independently.
[0010] U.S. Pat. No. 4,881,599 describes a tool for delivering
fluid treatment and ball diverters to specific locations along a
wellbore. The tool includes a packer, swivel, tubing tail with a
centralizer, ball ejection port, and two circulating-washer cups.
The system may be used to treat a series of locations along the
wellbore, thereby minimizing the number of downhole trips made by
the tool.
[0011] US published patent application 2006/0108117 describes a
downhole cleaning tool deployed on a slickline or wireline, for
removing debris from a well tubular. The tool is manipulated by
jarring action at the surface, which moves brushes, scrapers, and
wipers into and out of contact with downhole surfaces to be
cleaned. Debris is caught by a debris catcher or is carried to the
surface during production.
[0012] Although progress has been made in simplifying methods for
effective fluid treatment of a wellbore, planning and proper
execution of these treatments remains unpredictable and costly,
with tools often becoming jammed downhole. It is, therefore,
desirable to provide methods to simplify the process of hydraulic
wellbore treatment.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to obviate or
mitigate at least one disadvantage of previous wellbore fluid
treatment methods and devices.
[0014] In accordance with a first aspect of the invention, there is
provided a method for applying hydraulic treatment to a wellbore
comprising the steps of: reversibly setting hydraulic seals against
a wellbore above and below a first wellbore segment of interest to
isolate said first wellbore segment; delivering hydraulic treatment
to the isolated wellbore segment; delivering perforation diverters
to the isolated wellbore segment; terminating the delivery of
treatment fluid to the isolated segment; unsetting the hydraulic
seals from the wellbore; and scraping the wellbore segment to
dislodge perforation diverters therefrom. The method may further
comprise the step of collecting deployed perforation diverters from
the wellbore.
[0015] In a suitable embodiment, the hydraulic seals are pressure
actuated sealing members. Further the hydraulic treatment may be
fracturing fluid, acidizing or energizing treatment, proppants, or
cleaning fluid and is applied in liquid state, gaseous state, or a
combination of liquid and gaseous state and may further bear
solids, waxes, biodegradables, or other particles suspended
therewithin.
[0016] In an additional embodiment, the wellbore segment of
interest bears two or more perforations, and perforation diverters
are preferably delivered during hydraulic treatment of the
segment.
[0017] In a further embodiment, the number of perforation diverters
delivered to a particular segment is less than or equal to the
number of perforations within the segment. In another embodiment,
the number of perforation diverters delivered within the segment is
greater than the number of perforations within the segment.
[0018] The perforation diverters for use in accordance with the
invention are preferably ball sealers, which may be formed from
polymeric or elastomeric materials, biodegradables, ceramics,
composites or wax.
[0019] In a suitable embodiment of the invention, the step of
scraping is performed by abrading the wellbore with a scraper. A
diverter collection chamber may be operatively attached to the
scraper for collecting used perforation diverters from the wellbore
segment.
[0020] Alternatively, and particularly in treating uncased
wellbores, the perforation diverters may include chemical diversion
by gel or foam. In such embodiments, the gel or foam may be scraped
from the wellbore using a wire brush scraper or other suitable
scraping tool.
[0021] In a further embodiment, the method steps are repeated to
isolate and treat a number of segments within the same wellbore. In
such embodiment, deployed perforation diverters may be collected
from each wellbore segment and returned to surface following
treatment of all segments of interest. In a further embodiment, the
perforation diverters delivered to one segment may be collected and
redelivered downhole during the treatment of further wellbore
segments by a tool specifically designed for this purpose.
Accordingly, the method may further comprise the steps of:
reversibly setting the hydraulic seals against the wellbore above
and below a second wellbore segment of interest to isolate said
second wellbore segment; applying hydraulic treatment to the
isolated second segment; delivering perforation diverters to the
isolated second segment; terminating the application of treatment
fluid to the isolated segment; unsetting the hydraulic seals from
the wellbore; and scraping the second wellbore segment to dislodge
perforation diverters therefrom.
[0022] In an embodiment, one or more of the perforation diverters
deployed within the first isolated segment is collected and then
redeployed within the second isolated segment.
[0023] In accordance with a second aspect of the invention, there
is provided an apparatus for use in hydraulic treatment of a
wellbore, the apparatus comprising: upper and lower sealing
assemblies for reversibly setting at least two hydraulic seals
within a wellbore to isolate a portion of the wellbore between the
seals; a hydraulic treatment assembly for applying a hydraulic
treatment within the isolated portion of the wellbore; a diversion
assembly operatively attached to the hydraulic treatment assembly
for deploying perforation diverters within the isolated portion of
the wellbore during hydraulic treatment; and a scraper assembly for
scraping lodged perforation diverters from the wellbore
segment.
[0024] In an embodiment, the upper and lower sealing assemblies
include pressure-activated sealing members for sealing against the
wellbore.
[0025] In another embodiment, the scraper assembly includes at
least one scraper extending outwardly towards the wellbore to a
radial distance less than or equal to the wellbore drift diameter.
The scraper may be helically disposed about the longitudinal axis
of the apparatus. Alternatively, two or more scrapers may be
arranged radially about the apparatus.
[0026] A collection assembly may be associated with the scraper
assembly for collecting deployed perforation diverters within the
wellbore. The collection assembly may include a collection chamber
having a collection port adjacent the scraper assembly such that
scraping action directs used perforation diverters into the
collection chamber through the collection port.
[0027] In a suitable embodiment, the hydraulic treatment assembly
is continuous with the collection chamber such that when hydraulic
treatment fluid is applied to the isolated wellbore segment, at
least a portion of the treatment fluid passes through the
collection chamber to cause perforation diverters within the
collection chamber to be deployed to the isolated wellbore segment
through the collection port.
[0028] In accordance with a third aspect of the invention, there is
provided a diverter scraping and collection assembly for use in
removing lodged perforation diverters from a wellbore, the assembly
comprising: a tubular body for suspension within a wellbore; a
scraping member extending radially from the tubular body for
scraping a wellbore surface to remove lodged diverters therefrom; a
collection chamber operatively attached to the tubular housing for
collecting perforation diverters from the wellbore; and a diverter
collection port adjacent the scraper and continuous with the
collection chamber for directing dislodged perforation diverters to
the collection chamber.
[0029] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figures,
wherein:
[0031] FIG. 1 is a schematic diagram of a method in accordance with
an embodiment of the invention;
[0032] FIG. 2 is a schematic cross-sectional view of a device in
accordance with an embodiment of the invention; and
[0033] FIG. 3 is a perspective view of the device shown in FIG. 2;
and
[0034] FIG. 4 is a schematic cross-sectional view of a device in
accordance with a further embodiment of the invention.
DETAILED DESCRIPTION
[0035] Generally, the present invention provides a method and
apparatus for hydraulic treatment of a wellbore including the use
of perforation diverters to mechanically divert the treatment from
patent perforations along the wellbore during treatment.
Specifically, the method and apparatus of the invention provide a
means for isolating a wellbore segment, delivering hydraulic
treatment and perforation diverters to the segment as necessary,
and scraping lodged diverters from the wellbore. Used diverters may
be collected following scraping and returned to surface for
reuse.
Method Overview
[0036] With reference to FIG. 1, in an embodiment, the method of
the invention generally includes the steps of: setting (100)
hydraulic seals within a wellbore in two or more locations to
isolate a wellbore segment between the seals; delivering (200)
hydraulic treatment and diversion treatment to the isolated
wellbore segment; scraping (300) the wellbore segment to remove any
lodged diverters therefrom; and unsetting (400) the hydraulic seals
from the wellbore. These steps may be repeated at successive
locations along the wellbore without removing equipment from the
wellbore.
[0037] As indicated in FIG. 1, the sequence of steps in the method
may vary depending on the specific formations surrounding the
wellbore and the degree of treatment desired. For example, several
wellbore segments may be isolated and treated in succession without
removing equipment from the wellbore, followed by scraping of the
entire wellbore. Further, the wellbore may be scraped while the
seals remain set rather than after the seals have been removed.
Each step in the method may be performed on several successive
wellbore segments in one trip downhole by an apparatus designed for
this purpose, or in stages using several individual downhole
devices. The apparatus and method described below are intended
primarily for use with cased wellbores, however the method may also
be useful with uncased wells using suitable diversion techniques
such as gel or foam-based diversion, with suitable hydraulic
sealing assemblies, such as inflatable packer assemblies. In such
methods, the scraper may be provided as a wire brush to adequately
remove the gel or foam diverter.
Set Hydraulic Seals
[0038] The step of isolating a portion of the wellbore for specific
and controlled treatment enables various segments of one wellbore
to be treated individually and sequentially, without removing
equipment to surface. Thus, customized treatments may be delivered
at various locations along the wellbore simply by determining
appropriate seal positioning for each treatment location
desired.
[0039] Hydraulic seals are set along the wellbore above and below a
zone of interest, to isolate same from the remainder of the
wellbore. The zone of interest, or isolated segment, is generally a
portion of the wellbore that has been previously perforated and to
which hydraulic treatment such as fracturing or acidizing agents
need be applied. The length of the isolated segment and number of
perforations within the segment may vary depending on the phasing
of the perforations along the wellbore and the characteristics of
the surrounding formation.
[0040] The seals may be provided on a tubing string or other
customizable assembly such that the seals are spaced apart as
necessary to meet the needs for treatment of a particular wellbore.
Suitable seals for use in accordance with the invention include
weight-set, traction, or straddle packers, inflatable sealing
devices, pressure-actuated deformable annular seals, or other known
sealing devices suitable for use within a wellbore. The seals are
preferably composed of elastomeric material suitable for use in the
anticipated downhole temperature and pressure conditions. As such,
it is preferable that the method be carried out using a number of
operatively attachable subunits to enable substitution of
appropriate sealing system subunits suitable for use in a specific
situation.
[0041] Once the seals are set, hydraulic treatment is delivered
specifically to the isolated segment under controlled pressure.
Ball sealers may be similarly delivered as treatment progresses.
When the treatment is terminated and pressure within the isolated
segment dissipates, the seals are unset and may be relocated and
reset to isolate another segment of the wellbore for treatment.
Alternatively, if seals are already appropriately positioned
throughout the wellbore, only the hydraulic treatment and diversion
equipment need be lowered to the next appropriate segment, the
corresponding seals set around the segment, and treatment may again
be initiated.
Hydraulic Treatment and Diversion
[0042] Hydraulic treatments for use with the present method include
any fluid stimulation treatments, whether liquid or gaseous,
including fracturing fluid, proppants, stimulants, acidizing or
energized fluid treatments, cleaning fluids, etc.
[0043] The perforation diverters intended for use with the present
method include any removable mechanical perforation sealer,
preferably ball sealers, which may be composed of biodegradable
materials, polymers, elastomers, encapsulants, wax, or other
suitable material.
[0044] When planning the stimulation treatment, the number and
location of the wellbore segments to be isolated is determined and
the volumes of fluid needed are estimated according to the
operator's desired parameters. Typically, an electric log will be
run downhole prior to perforation (and in some situations prior to
casing) to gather data regarding the characteristics of the
surrounding formation. In addition, valuable information may be
determined by examining cuttings during drilling, and gas detectors
may be placed downhole during drilling to identify gas-bearing
zones within the wellbore. Based on this type of data, the operator
is able to estimate the degree of stimulation treatment required,
and customize the presently described method accordingly.
[0045] When the hydraulic treatment is fracturing fluid, generally
the fluid will first be applied alone to the isolated zone under
pressure to determine whether any of the perforations remain open.
If one or more perforations are open and accept fluid, as
determined by monitoring the pressure as the treatment is applied,
the operator may wish to divert treatment from these open
perforations in order to stimulate any blocked perforations.
Accordingly, perforation diverters may be delivered to the isolated
wellbore segment. Typically, the number of diverters delivered will
be fewer than the total number of perforations in the isolated
segment, however in certain circumstances an excess of diverters
may be used, for example 130% of the number of perforations. The
operator continues to pump fluid into the isolated segment and
carefully monitors the pressure within the segment. A spike in
pressure followed by some degree of dissipation indicates that at
least one new perforation has been fractured, which may be followed
by delivery of further diverters to the segment.
[0046] When it has been determined that the wellbore has been fully
treated, the treatment is terminated and the pressure within the
isolated wellbore segment is released.
Scraping of Wellbore
[0047] When perforation diverters are delivered during hydraulic
treatment of a wellbore segment, the diverters may become lodged
within the perforations, protruding past the estimated drift
diameter of tools used within the wellbore. When this occurs,
downhole tools will contact the lodged diverter and may become
damaged or jammed downhole. To avoid this problem, the method may
include the step of scraping the wellbore to remove the diverters
from the isolated segment.
[0048] Scraping of the wellbore is preferably performed immediately
following cessation of the hydraulic treatment. Any diverters
scraped from the wellbore are preferably collected to surface and
may be redeployed for diversion within another treatment run. The
scraping need not abrade the inner diameter of the wellbore, as
effective removal of lodged perforation diverters may be achieved
by scraping against the protruding portion of the lodged
perforation diverter. Accordingly, it is sufficient to scrape with
a device having a diameter less than or equal to the drift diameter
of the wellbore.
[0049] Scraping of the wellbore may be accomplished by known
methods, or using a tool designed for this purpose. It is
preferable that the scraper be integrated with the hydraulic
treatment delivery assembly to facilitate completion of the process
without running additional tools downhole. The scraper should be
somewhat pliable or deformable so it may be rotated and/or
reciprocated as needed against the wellbore to dislodge diverters
therefrom and avoid becoming jammed or stuck downhole.
Used Diverter Collection
[0050] In addition, the method may include the steps of collecting
and retrieving deployed diverters from the isolated segment rather
than simply allowing the used perforation diverters to flow to the
surface with production fluid or drop downhole. In a preferred
embodiment, the diverters are collected and stored during treatment
of further wellbore segments.
[0051] In certain further contemplated embodiments, used ball
diverters collected within the collection chamber may be
redelivered to further wellbore segments for use in diversion. In
such embodiments, used diverter collection may be a continual
process whereby deployed diverters not functioning to divert
treatment may be collected within the segment during treatment and
redeployed during treatment of the same segment as a cyclical
process to seal new perforations as they are opened during
treatment.
Apparatus
[0052] A suitable apparatus for use in accordance with the
invention includes an upper sealing assembly, a treatment assembly
for delivering hydraulic treatment and diverters to a wellbore
segment, a wellbore scraping assembly, and a lower sealing
assembly. A diverter collection assembly may also be present for
collecting used diverters within the wellbore.
Structure
[0053] With reference to FIGS. 2 and 3, an apparatus in accordance
with an embodiment of the invention is shown in longitudinal cross
section and in perspective view, respectively. The apparatus is
generally composed of a series of threadably attached tubular
components. Upper and lower sealing assemblies 20, 25, each bear
two deformable pressure-actuated sealing members 21, 22 and 26, 27.
The upper sealing assembly is attached to coiled tubing or jointed
pipe through a safety shear sub and tubing connector (not shown) so
the apparatus may be lowered to an appropriate wellbore depth and
safely removed following treatment.
[0054] Disposed between the upper and lower sealing assemblies 20,
25 are the hydraulic treatment and diversion assembly 30, and the
scraping and collection assembly 40. The treatment and diversion
assembly supplies treatment fluid from surface, which is delivered
to the isolated wellbore segment through port 31. Similarly, when
diversion is required, ball diverters may be dropped from surface
and delivered to the isolated wellbore segment along with the
treatment fluid through port 31.
[0055] The scraping and collection assembly 40 bears scraper 41 and
diverter collection port 42, which is continuous with collection
chamber 43. Scraper 41 may be one or more annular rings spaced
along the assembly, or a helical ring extending around the
assembly. Alternatively, the scraper may be provided as a series of
individual scraping blades or wire brushes spaced appropriately
around the assembly. The scraper 41 preferably extends a distance
such that the total diameter of the tool is approximately equal to
the estimated wellbore drift diameter, not permitting sufficient
space between the scraper and the wellbore for passage of a ball
diverter. The scraper is therefore the widest rigid portion of the
apparatus, and is preferably composed of material having suitable
rigidity to effectively remove lodged ball diverters from the
wellbore, while remaining deformable upon application of excessive
force to enable removal of the apparatus from the wellbore should
the scraper become jammed against a foreign object or surface. In
embodiments in which the scraper is helical or segmented, with
individual scrapers disposed about the assembly, the scraper need
not be deformable, as rotation of the tool will allow avoidance of
foreign objects or aberrations along the wellbore. Further, a
second scraper may be present adjacent the upper sealing assembly
20 to allow bidirectional scraping as the apparatus is raised and
lowered to abrade the wellbore.
[0056] The collection port 42 is located just above the scraper 41
to direct used ball diverters into the collection chamber 43 during
scraping. In addition, as ball diverters are delivered to the
isolated wellbore segment through port 31, some will become lodged
within patent perforations along the wellbore, while others may be
suspended within the fluid in the segment and/or fall towards the
bottom of the isolated segment, where they will encounter scraper
41 and be directed to the collection port 42 and into collection
chamber 43. Further, once treatment has been terminated and the
wellbore is scraped, as lodged ball diverters are loosened by
scraper 41, the used ball diverters will similarly be directed to
collection port 42 and into collection chamber 43.
[0057] Apparatus 10 may be customized as necessary for use within a
specific wellbore. Accordingly, it is preferable that the apparatus
be assembled as a series of coupled subunits whereby additional
components may be added or removed as necessary. In certain
applications, a large collection chamber 43 may be required, which
can be accommodated by inserting additional collection subs as
necessary between the scraper 41 and the lower sealing assembly 25.
Further, some applications may require delivery of hydraulic
treatment within compact wellbore segments, while other
applications may permit treatment of lengthy wellbore segments.
This will depend on the preferences of the operator, the phasing of
perforations within the wellbore, and the anticipated treatment
pressure necessary to open perforations within the segment.
Operation
[0058] In use, a wellbore requiring hydraulic treatment is first
analyzed to determine the number and length of wellbore segments to
which hydraulic treatment is to be applied. Preferably, each
segment contains 1 to 400 perforations and is between 0.1 and 20
metres in length. The apparatus shown in FIGS. 2 and 3 may be
customized as necessary by adding or removing components to provide
the appropriate distance between the upper and lower sealing
assemblies, a suitable number and arrangement of sealing elements
and scrapers, and an appropriate size for the collection chamber.
If several segments of the wellbore are to be treated in
succession, the collection chamber (if present) should be large
enough to hold the anticipated total number of ball sealers to be
used in treating all segments, as each segment will be scraped and
balls collected within the collection chamber in series without
removing the apparatus from the wellbore.
[0059] The apparatus is lowered, for example on coiled tubing,
until the sealing systems 20, 25 straddle the lowest wellbore
segment of interest. Treatment fluid is pumped through the coiled
tubing to the segment through fluid port 31, until the pressure
within the wellbore surrounding the apparatus reaches a threshold,
activating the sealing systems 20, 25 to cause sealing members 21,
22, 26, 27 to flex or deform and seal against the wellbore,
isolating the wellbore segment between the sealing systems for
further treatment.
[0060] Treatment fluid is pumped to the isolated segment and the
pressure is monitored. Once satisfactory treatment of patent
perforations is achieved, typically as evidenced by a drop in
pressure, ball sealers are delivered to the isolated segment
through fluid port 31, along with continued treatment fluid. The
ball sealers will seat against patent perforations within the
isolated segment, diverting fluid to the untreated perforations.
This process of applying treatment fluid and ball sealers is
continued until the desired level of treatment is achieved.
[0061] When the operator has determined that treatment of the
isolated segment is complete, the pumping of treatment fluid is
terminated and the system is depressurized to unset the sealing
systems 20, 25. Loose ball sealers will not be able to fall past
the scraper 41, and will be guided into the collection chamber 43
through collection port 42. As the apparatus is raised to become
aligned with the next segment of interest, the scraper will scrape
any lodged ball sealers from the wellbore, which will be similarly
collected within the collection chamber. If the operator determines
that further scraping within the initially treated segment is
necessary, the tool may be raised and lowered in succession to more
thoroughly scrape the wellbore segment. This will be particularly
effective when an upper scraping member is also present adjacent
the upper sealing system.
[0062] Once the apparatus is properly aligned with the next
wellbore segment of interest (ie. with sealing systems 20, 25
straddling the segment), fluid treatment is again initiated to set
the sealing members 21, 22, 26, 27 against the wellbore. Delivery
of treatment fluid and ball sealers proceeds as above, and is
repeated as necessary to similarly treat all segments of the
wellbore. Once all treatments are complete, the apparatus is
brought to surface and the ball sealers are removed from the
collection chamber.
[0063] It is preferable that the lowermost segment of interest
within the wellbore is treated first, and that treatment of
segments proceeds upwards in succession to maximize sealer
collection and minimize the number of trips downhole.
ALTERNATE EMBODIMENTS
[0064] When only one segment is to be treated, or when it is
anticipated that few perforation diverters will be required, the
collection chamber may be absent, with diverters collected within a
cup-shaped scraper. In situations where diverter collection is not
required, the collection chamber may be open at its base or may
include a lower discharge port, dropping perforation diverters
downhole as necessary.
[0065] If desired, the sealing assemblies may be provided
independent from the hydraulic treatment and diversion assembly,
and from the scraping and collection assembly. For example, the
seals could be appropriately positioned for isolation of each
wellbore segment of interest by threading sealing assemblies into a
length of tubing at appropriate distances. The scraping and
collection assembly may be similarly attached at each interval, or
at the bottom of the tubing string, beneath the lowest sealing
assembly. The hydraulic treatment and diversion assembly could then
be lowered within the tubing to each segment successively for
treatment, and when all segments have been isolated and treated,
raising the tubing string will cause the entire wellbore to be
scraped, and diverters collected.
[0066] With reference to FIG. 4, a proposed alternate embodiment of
the invention is shown in which collected perforation diverters may
be reused during further fluid treatment. The apparatus is similar
to that shown in FIGS. 2 and 3, however, treatment assembly 50 is
provided to for delivering fluid treatment and diversion, and for
scraping and collecting used diverters. Perforation diverters are
present within collection chamber 56, and fluid treatment is
applied from surface and passes into fluid channel 55, which
delivers fluid to the wellbore initially through fluid ports 51.
Under higher fluid pressures, treatment fluid will pass into
collection chamber 56 with sufficient force to expel diverters from
the chamber 56 and into the wellbore through ejection and
collection port 52. Diverters will therefore circulate within the
isolated wellbore segment during treatment and become lodged within
patent perforations to divert treatment to the remainder of the
wellbore. Upon termination of fluid treatment, the wellbore is
scraped, returning used diverters to the collection chamber 56 via
ejection/collection port 52. To facilitate collection, the scraper
41 may be angled to direct balls to port 52. Many other
configurations of such a system are possible and will be apparent
to those of skill in the art upon reading the present
disclosure.
[0067] The above-described embodiments of the present invention are
intended to be examples only. Alterations, modifications and
variations may be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
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