U.S. patent application number 11/157423 was filed with the patent office on 2006-12-21 for coiled tubing overbalance stimulation system.
Invention is credited to John Kovacs, Stephen P. Lemp, Abbas Mahdi.
Application Number | 20060283596 11/157423 |
Document ID | / |
Family ID | 37572216 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283596 |
Kind Code |
A1 |
Mahdi; Abbas ; et
al. |
December 21, 2006 |
Coiled tubing overbalance stimulation system
Abstract
Formation zones of interest may be isolated and stimulated by
substantially instantaneously providing a pressure equal to or
greater than the fracture pressure of the targeted zone. A
treatment fluid is accumulated in coiled tubing until the pressure
is equal to or greater than the fracture pressure of the targeted
zone. The accumulated pressurized treatment fluid is released
substantially instantaneously at the targeted formation zone. The
accumulated pressurized treatment fluid may be substantially
simultaneously released with the detonation of a perforation
gun.
Inventors: |
Mahdi; Abbas; (Calgary,
CA) ; Lemp; Stephen P.; (Calgary, CA) ;
Kovacs; John; (Calgary, CA) |
Correspondence
Address: |
SCHLUMBERGER TECHNOLOGY CORPORATION
IP DEPT., WELL STIMULATION
110 SCHLUMBERGER DRIVE, MD1
SUGAR LAND
TX
77478
US
|
Family ID: |
37572216 |
Appl. No.: |
11/157423 |
Filed: |
June 21, 2005 |
Current U.S.
Class: |
166/297 ;
166/305.1; 166/308.1; 166/313 |
Current CPC
Class: |
E21B 43/26 20130101;
E21B 43/14 20130101 |
Class at
Publication: |
166/297 ;
166/305.1; 166/308.1; 166/313 |
International
Class: |
E21B 43/26 20060101
E21B043/26; E21B 43/116 20060101 E21B043/116 |
Claims
1. A method of selectively stimulating a targeted formation zone
from a wellbore surrounded by a formation utilizing coiled tubing
as the conduit for the stimulation, the method comprising the steps
of: positioning an assembly connected to coiled tubing adjacent a
target formation zone; sealing between the coiled tubing and the
formation to isolate the target formation zone from the rest of the
wellbore; accumulating a desired pressure in the coiled tubing with
a treatment fluid, the desired pressure at least equal to the
fracture pressure of the target formation zone; and releasing
substantially instantaneously the accumulated pressure through the
assembly at the target formation zone.
2. The method of claim 1, further including the step of: releasing
the sealing isolating the target formation zone; repositioning the
assembly adjacent a subsequent target formation zone; sealing
between the coiled tubing and the formation to isolate the
subsequent target formation zone from the rest of the wellbore;
accumulating pressure in the coiled tubing at least equal to the
fracture pressure of the subsequent target formation zone; and
releasing substantially instantaneously the accumulated pressure
through the assembly at the subsequent target formation zone.
3. The method of claim 1, wherein the sealing step includes:
setting a sealing element between the coiled tubing and the
formation above the formation zone targeted; and setting a second
sealing element between the coiled tubing and the formation below
the formation zone targeted.
4. The method of claim 2, wherein the sealing step includes:
setting a sealing element between the coiled tubing and the
formation above the formation zone targeted; and setting a second
sealing element between the coiled tubing and the formation below
the formation zone targeted.
5. The method of claim 1, wherein the wellbore adjacent the
formation zone targeted includes casing having a least one
perforation.
6. The method of claim 5, wherein the sealing step includes:
setting a sealing element between the coiled tubing and the
formation above the formation zone targeted; and setting a second
sealing element between the coiled tubing and the formation below
the formation zone targeted.
7. The method of claim 6, wherein the sealing elements comprise
packers.
8. The method of claim 1, wherein the wellbore adjacent the
formation zone targeted includes a slotted liner.
9. The method of claim 8, wherein the sealing step includes:
setting a sealing element between the coiled tubing and the
formation above the formation zone targeted; and setting a second
sealing element between the coiled tubing and the formation below
the formation zone targeted.
10. The method of claim 9, wherein the sealing elements comprise
packers.
11. The method of claim 1, wherein the wellbore adjacent the
formation zone is not cased.
12. The method of claim 11, wherein the sealing step includes:
setting a sealing element between the coiled tubing and the
formation above the formation zone targeted; and setting a second
sealing element between the coiled tubing and the formation below
the formation zone targeted.
13. The method of claim 12, wherein the sealing elements comprise
packers.
14. A method of selectively stimulating a targeted formation zone
from a wellbore utilizing coiled tubing as the conduit for the
stimulation, the method comprising the steps of: positioning an
assembly connected to coiled tubing adjacent a target formation
zone, the assembly including a perforating gun; accumulating a
desired pressure in the coiled tubing with a treatment fluid, the
desired pressure at least equal to the fracture pressure of the
target formation zone; detonating the perforating gun; and
releasing substantially instantaneously the accumulated pressure
through the assembly at the target formation zone.
15. The method of claim 14, wherein the releasing step occurs
substantially simultaneously with the detonation of the perforation
gun.
16. The method of claim 14, wherein the step of accumulating
comprises: injecting a first treatment fluid into the coiled
tubing; and pressurizing the first treatment fluid by a second
treatment fluid in the coiled tubing.
17. The method of claim 15, wherein the step of accumulating
comprises: injecting a first treatment fluid into the coiled
tubing; and accumulating pressure in the coiled tubing by injecting
a second treatment fluid in the coiled tubing.
18. The method of claim 14, wherein the wellbore proximate the
target formation zone is not cased.
19. The method of claim 14, wherein the wellbore adjacent the
formation zone targeted includes a slotted liner.
20. The method of claim 14, wherein the wellbore adjacent the
formation zone targeted includes casing having a least one
perforation.
21. The method of claim 18, wherein: the step of accumulating
comprises injecting a first treatment fluid into the coiled tubing,
and pressurizing the first treatment fluid by a second treatment
fluid in the coiled tubing; and the releasing step occurs
substantially simultaneously with the detonation of the perforation
gun.
22. The method of claim 19, wherein: the step of accumulating
comprises injecting a first treatment fluid into the coiled tubing,
and pressurizing the first treatment fluid by a second treatment
fluid in the coiled tubing; and the releasing step occurs
substantially simultaneously with the detonation of the perforation
gun.
23. The method of claim 18, wherein: the step of accumulating
comprises injecting a first treatment fluid into the coiled tubing,
and pressurizing the first treatment fluid by a second treatment
fluid in the coiled tubing; and the releasing step occurs
substantially simultaneously with the detonation of the perforation
gun.
24. A method of selectively stimulating a targeted formation zone
from an uncased portion of a wellbore utilizing coiled tubing as
the conduit for the stimulation, the method comprising the steps
of: positioning an assembly connected to coiled tubing adjacent a
target formation zone; accumulating a desired pressure in the
coiled tubing with a treatment fluid including an acid, the desired
pressure at least equal to the fracture pressure of the target
formation zone; and releasing substantially instantaneously the
accumulated pressure through the assembly at the target formation
zone.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to stimulating a
well to increase the rate of flow into or out of the surrounding
formation and more particularly to a method and apparatus for
extreme overbalance stimulation of the formation surrounding a well
utilizing coiled tubing.
BACKGROUND
[0002] Well stimulation refers to techniques used for increasing
the productivity of the formations surrounding the well. For
production wells, it is important to increase the rate at which
fluid flows from the formation into the wellbore. For injection
wells, it is often important to increase the rate of injection of
fluid into the surrounding formation.
[0003] The region of the formation proximate the wellbore is very
often the most significant restriction to the well's productivity.
This region is frequently damaged during the drilling of the
wellbore creating resistance to fluid flow through the region. The
resistance to fluid flow near the wellbore is defined by "skin
factor." Skin factors are measured by measuring bottom hole
pressures in a well under differing flow conditions. A positive
skin factor indicates that the region near the wellbore is more
resistive to flow than the formation farther away from the
wellbore. A negative skin factor indicates that the region near the
wellbore is less resistive to fluid flow than the formation farther
away from the wellbore. The resistance to fluid flow can be reduced
by stimulation.
[0004] The two primary methods for treating these damaged regions
or zones to stimulate productivity, include chemical stimulation
and fracturing. In chemical stimulation, fluids such as acids or
other chemicals are injected into the formation to interact with
the rock matrix to increase the permeability of the formation. In
hydraulic fracturing, a fluid under a pressure greater than the
stress of the formation is injected forming fractures in the rock
matrix. Typically, proppant is included in the fracturing fluid so
as to be lodged in the fractures to maintain the created
permeability to fluid when the fracturing pressure ceases. It is
desired at times to combine chemical stimulation with fracturing,
for example with acid fracturing. In certain circumstances
fractures may be created extending hundreds of feet from the
wellbore.
[0005] It is more economical, and at times only necessary, to
create fractures near the wellbore. One method of creating these
near-wellbore fractures is by overbalance stimulation, wherein
pressure greater than the formation's fracture pressure is suddenly
released proximate the formation. Prior art methods have been
utilized, however, these methods are expensive and often
uneconomical and thus not feasible for multi-formation wells. The
prior art systems fail to provide a mechanism for selectively
treating formation zones in uncompleted, open hole, wellbores or
slotted liner completions.
[0006] Therefore, it is a desire to provide an extreme overbalance
stimulation method that addresses the shortcomings of the prior art
devices. It is a still further desire to provide a overbalance
stimulation method that utilizes coiled tubing as the main
treatment string.
SUMMARY OF THE INVENTION
[0007] In view of the foregoing and other considerations, the
present invention relates to an extreme overbalance stimulation
method utilizing coiled tubing as the main treatment string.
[0008] Accordingly, an extreme overbalance stimulation system and
method is provided. An embodiment of the overbalance stimulation
method includes positioning an assembly connected to coiled tubing
adjacent a target formation zone and sealing between the coiled
tubing and the formation to isolate the target formation zone from
the rest of the wellbore. A desired pressure is accumulated in the
coiled tubing with a treatment fluid. The desired pressure is at
least equal to the fracture pressure of the target formation zone.
The accumulated pressure is substantially instantaneously released
through the assembly at the target formation zone.
[0009] In another embodiment, the extreme overbalance stimulation
method includes positioning an assembly connected to coiled tubing
adjacent a target formation zone, wherein the assembly includes a
perforating gun. A desired pressure is accumulated in the coiled
tubing with a treatment fluid. The desired pressure is at least
equal to the fracture pressure of the target formation zone. Upon
detonating the perforating gun the accumulated pressure is
substantially instantaneously released through the assembly at the
target formation zone. Creating a temporary path of least
resistance, ensuring preferential flow toward the targeted zone in
open hole and slotted liner completions.
[0010] The system may include a coiled tubing unit having coiled
tubing adapted for disposing in a wellbore and a pump (or several
pumps) for providing a pressurized treatment fluid in the coiled
tubing. A pressure release device is in fluid connection with the
coiled tubing, the pressure release device being connected to a
port positionable proximate a targeted formation zone. The pressure
release device is operatable between a closed position for
maintaining the pressurized treatment fluid within the coiled
tubing, and an open position for substantially instantaneously
discharging the pressurized treatment fluid through the port. The
system may further include a top sealing element adapted for
sealing between the coiled tubing and the formation, and a bottom
sealing element adapted for sealing between the coiled tubing and
the formation, wherein the bottom sealing element is spaced from
the top sealing element sufficient to isolate the targeted
formation zone from the rest of the wellbore.
[0011] The foregoing has outlined the features and technical
advantages of the present invention in order that the detailed
description of the invention that follows may be better understood.
Additional features and advantages of the invention will be
described hereinafter which form the subject of the claims of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and other features and aspects of the present
invention will be best understood with reference to the following
detailed description of a specific embodiment of the invention,
when read in conjunction with the accompanying drawings,
wherein:
[0013] FIG. 1 is an illustration of an embodiment of the
overbalance stimulation system of the present invention set for
stimulating a first formation zone;
[0014] FIG. 2 is a schematic illustrating the stimulation of the
first formation zone of FIG. 1;
[0015] FIG. 3 is an illustration of the overbalance stimulation
system set for stimulating a subsequent formation zone;
[0016] FIG. 4 is a schematic illustrating the stimulation of the
second formation zone;
[0017] FIG. 5 is an illustration of another embodiment of the
overbalance stimulation system of the present invention; and
[0018] FIG. 6 is an illustration of the step of stimulating a
targeted formation system of the embodiment of FIG. 5.
DETAILED DESCRIPTION
[0019] Refer now to the drawings wherein depicted elements are not
necessarily shown to scale and wherein like or similar elements are
designated by the same reference numeral through the several
views.
[0020] As used herein, the terms "up" and "down"; "upper" and
"lower"; and other like terms indicating relative positions to a
given point or element are utilized to more clearly describe some
elements of the embodiments of the invention. Commonly, these terms
relate to a reference point as the surface from which drilling
operations are initiated as being the top point and the total depth
of the well being the lowest point.
[0021] FIG. 1 is an illustration of an embodiment of an overbalance
stimulation procedure and system using coiled tubing, generally
denoted by the numeral 10. Overbalance stimulation system 10
includes a coiled tubing unit 14 having coiled tubing 16 for
spooling into and out of a wellbore 18 via an injector head 20 (or
other coiled tubing deployment apparatus) through a wellhead 22. A
pump 24 is in fluid communication with coiled tubing 16 for
providing a pressurized treatment fluid described in more detail
below. As well-known in the art, pump 24 is further connected to a
treatment fluid reservoir (not shown) as well as a high pressure
treating line (not shown). The treatment fluid may include,
singularly or in combination, a variety of fluids, including, but
not limited to, gasses, liquids, acids, gels, foams, and slurries.
It should be further recognized that the treatment fluid may carry
a proppant.
[0022] Wellbore 18 may be substantially vertical or at any angle
including horizontal. The earth surrounding the wellbore includes a
formation having one or more formation zones that are targeted to
produce fluid from or inject fluid into. In the present embodiment
three target zones 26a, 26b, and 26c are illustrated. Zones 26 may
include perforations 28, or perforations may be created during the
process of the present invention. Wellbore 18 may include casing
30, include a slotted liner, be an open hole completion, or be a
combination of the aforementioned.
[0023] System 10 further includes a bottom hole assembly (BHA) or
treatment assembly 32 in functional and fluid connection with
coiled tubing 16. Assembly 32 includes a pressure release device
34, a discharge port 36 and an upper and lower sealing element 38,
40.
[0024] Sealing elements 38 and 40 may be packers, cups or any other
elements or mechanisms adapted for isolating a formation zone 26 to
be stimulated from the rest of wellbore 18. Pressure relief device
34 is adapted for maintaining treatment fluid 42 within coiled
tubing 16 under pressure until it is desired to discharge fluid 42
through port 36. Pressure relief device 34 may be, but is not
limited to, valves or frangible discs. Port 36 is positioned
between sealing elements 38, 40.
[0025] FIG. 1 illustrates the system set in wellbore 18 for
stimulating first formation zone 26a. Although first formation zone
26a is illustrated as the lower formation zone, the first formation
zone may be any zone desired to be treated. Coiled tubing 16 is
spooled through injector head 20 and wellhead 22 into wellbore 18
positioning BHA 32 proximate first zone 26a. Sealing elements 38
and 40 are set between coiled tubing 16 and formation 26,
substantially sealing zone 26a from communication with the
remaining portion of wellbore 18. Port 36 is positioned proximate
first formation zone 26a and pressure release device 34 is in the
closed position, preventing fluid flow between coiled tubing 16 and
wellbore 18 through port 36.
[0026] With port 36 of pressure release device 34 in the closed
position, pressure is accumulated in coiled tubing 16. The desired
pressure accumulated is at least equal to and preferably greater
than the fracturing pressure for the targeted zone 26, shown as
zone 26a in FIG. 1. The fracture pressure of the zone varies with
its depth and its geological characteristics. Often, an initial
breakdown pressure greater than the fracture pressure is required
to initiate the fractures. This higher initial breakdown pressure
is due in part to the necessity of overcoming the tensile strength
of the rock. Thus, the desired pressure accumulated may be equal to
or greater than the initial breakdown of the formation of
interest.
[0027] The pressure is accumulated by pumping treatment fluid 42
into coiled tubing 16 via pump 24. As described, treatment fluid 42
may be any fluid necessary and adapted for the fracturing the
formation zone of interest. For example, it may be desired to
utilize nitrogen in a coal seam well. Additionally, it may be
desired to include proppant in treatment fluid 42 to maintain the
fractures when the pressure is released, or follow the initial
extreme overbalance stimulation with a fluid carrying proppant or
other treatment substances.
[0028] FIG. 2 illustrates the step of fracturing zone 26a utilizing
extreme overbalance stimulation. Once the desired stimulation
pressure is accumulated in coiled tubing 16, pressure release
device 34 is activated to the open position in a manner to
substantially instantaneously release the accumulated pressure
through port 36 to act on formation 26a. Pressure release device 34
may be activated by any suitable means. For example, the release
device 34 may be a frangible disc activated by a dropped bar or
ball. Similarly, the release device 34 may be a valve activated
electrically, hydraulically or optically. Any means capable of
activating the pressure release device 34 should be considered to
be within the scope of the present invention.
[0029] The sudden, substantially instantaneous, release of the
accumulated pressure equal to or greater than the fracturing
pressure causes fractures 44 to be formed in zone 26a. Seals 38, 40
isolates treatment fluid 42 and the accumulated pressure at zone
26a. Further pumping of treatment fluid 42 or a subsequent treating
fluid may be pumped after the shock treatment. The overbalance
treatment may be repeated numerous times if a series of shocks are
needed or desired.
[0030] With reference to FIGS. 2 and 3, once stimulation of zone
26a is completed seals 38, 40 are released. Coiled tubing 16 is
then spooled positioning port 36 of pressure release device 34
adjacent to the next formation zone targeted for stimulation, shown
as 26b herein. Seals 38, 40 are set substantially isolating zone
26b from the rest of wellbore 18 and formation 26. With pressure
release device 34 in the closed position, the pressure, via
treatment fluid 42 and pump 24, is accumulated in coiled tubing 16
at a pressure equal to or greater than the fracture pressure of
formation zone 26b.
[0031] Once the desired pressure is accumulated, pressure release
device 34 is activated substantially instantaneously releasing
treatment fluid 42 and the accumulated pressure through port 36 at
zone 26b, as shown in FIG. 4. This sudden release of treatment
fluid 42 under pressure creates fractures 44, or stimulates
pre-existing natural fractures, cleats or other naturally occurring
or man-made pathways in zone 26b. After stimulation of zone 26b,
the extreme overbalance stimulation may be conducted on subsequent
formation zones 26 without requiring the removal of coiled tubing
16 or assembly 32 from wellbore 18. Additionally, the stimulation
of multiple zones does not require the making or breaking of a
jointed tubing string. The present invention utilizes coiled tubing
16 as the conduit for the stimulation.
[0032] FIGS. 5 and 6 are illustrations of another embodiment of the
stimulation system of the present invention, generally denoted by
the numeral 10. Illustrated is a horizontal wellbore 18, having an
open hole section 46, in a carbonate formation. A portion of
wellbore 18 is cased 30 and the well may include jointed tubing 50.
The well is designated for stimulation of the targeted formation
zone 26a. Open hole section 46 may have only one pay zone 26a of
interest, or multiple zones. The prior art stimulation systems
require large amounts of costly treatment fluids and a may require
higher horsepower to stimulate the target zone as well as the
formation surrounding the uncompleted portion of wellbore 18 that
is not of interest.
[0033] Overbalance stimulation system 10 of the present invention
provides a cost effective method for selectively stimulating zone
26a. Bottom hole assembly 32 includes a pressure release device 34
and a perforating gun 48. Assembly 32 is functionally connected and
carried by coiled tubing 16. Assembly 32 is positioned adjacent to
the target zone 26a with the pressure release device 34 in the
closed position maintaining fluid and pressure within coiled tubing
16.
[0034] Pressure is accumulated in coiled tubing 16. The pressure
may be accumulated by first injecting a volume of a first treatment
fluid 42a, such as acid, into coiled tubing 16. Desirably first
treatment fluid is a liquid. A second treatment fluid 42b, is
pumped into coiled tubing 16 to pressurize the treatment fluid.
Desirably, the second treatment fluid is a gas such as, but not
limited to, nitrogen. The desired pressure of treatment fluid 42
may be equal to, or greater than, the fracture pressure of
formation 26a.
[0035] Once the desired pressure of treatment fluid 42 is achieved,
zone 26a may be stimulated. Perforating gun 32 is detonated. The
detonation of gun 32 initiates fractures 44 by creating
perforations. Substantially simultaneous with the detonation of gun
32, treatment fluid 42 is substantially instantaneously released
under pressure at formation 26a, illustrated by the arrows in FIG.
6. The extreme overbalance release of treatment fluid 42 extends
fractures 44 connected to the wellbore through the perforation
tunnels.
[0036] From the foregoing detailed description of specific
embodiments of the invention, it should be apparent that a method
and system for overbalance stimulation with coiled tubing that is
novel and unobvious has been disclosed. Although specific
embodiments of the invention have been disclosed herein in some
detail, this has been done solely for the purposes of describing
various features and aspects of the invention, and is not intended
to be limiting with respect to the scope of the invention. It is
contemplated that various substitutions, alterations, and/or
modifications, including but not limited to those implementation
variations which may have been suggested herein, may be made to the
disclosed embodiments without departing from the spirit and scope
of the invention as defined by the appended claims which
follow.
* * * * *