SUBSEA WELL WO KOVER SYSTEM AND METHOD
Background Setting of the Invention
Subsea wells are usually serviced or worked over with the same type rig or ship used
to drill and complete the well. These rigs are large and expensive, particularly when of the type required for wells in deep water.
The prior art has suggested techniques and equipment for working on subsea wells without the use of large rigs. One approach has been to use coiled tubing to work on the completed well. The coiled tubing can be deployed and used from a relatively small workboat that is substantially less expensive to operate than a conventional drilling or completion rig. Suggested prior art systems for working on subsea wells have also included self- contained, watertight-coiled tubing assemblies that are lowered into the water and positioned at the wellhead of the subsea well. See U.S. Patent Nos. 5,002,130 and 4,899,823. An injector drive assembly secured to the wellhead propels the coiled tubing into and out of the well. It has also been suggested to position the injector drive assembly and the coiled tubing directly into the water without first enclosing the components in a watertight container.
Coiled tubing provides a desirable work string for many simple workover applications in that it is a continuous string that can be stored in a compact coil. A derrick and makeup and handling tools normally required for use with a string of jointed pipe are not required when using a coiled tubing string.
Conventional coiled tubing made of metal, however, suffers from limitations imposed by the requirement to repeatedly straighten and re-bend the pipe while unspooling and spooling the pipe on its storage reel. As compared with jointed pipe of the same dimensions,
coiled tubing is more expensive, shorter lived, limited in pressure handling capabilities and
more, susceptible to wear and corrosion. Deploying and reeling the coiled tubing also requires the use of a curving injector head to straighten the pipe during injection into the well
and to bend the pipe as it is being extracted from the well and coiled back onto the reel.
Summary/of the Invention
A string of pipe formed from individual steel pipe joints secured together at their ends by threaded connectors is positioned and stored in or on the water in the vicinity of a subsea well. The pipe string can be as long as desired for use in deep and ultra-deep water. In the preferred form of the invention, the pipe sections are secured together with flush joint connections so that the resulting pipe string has a uniform outside diameter along most of its length.
The pipe string is formed as an elongate continuous length of pipe that extends away from, or about, the subsea well into the water area between the sea bottom and the water surface. The end of pipe to be inserted into the well is positioned adjacent the subsea well and the opposite end may be located several miles away.
The pipe may extend through the water in a linear, essentially non-curving configuration or may be curved in multiple, extended curving open loops or spiral or helical configurations. The radii of any curves imposed in the pipe string are maintained at values greater than the minimum-bending radius of the pipe. The pipe string is inserted into the subsea well to produce well fluids from the well, place or remove tools, open or close valves, work the well over, and process, inspect and/or perform any other required subsea or down-hole well activity.
"~r- During the initial introduction of the stored pipe into the subsea well, in one form of
the invention, the end of the pipe to be inserted into the well is moved through a guide that redirects the pipe from its substantially horizontal water storage position to a substantially vertical position for introduction into the well. ,The radius of the curve of the guide is
maintained large enough to prevent plastic deformation of the pipe. The guide may include
gripping elements that engage the external surface of the pipe and propel the pipe for
movement into and out of the well.
The non-inserted end of the pipe may be connected by a service line to a surface
support facility such as a floating work vessel or a sea floor supported platform. The service line may be a flexible supply hose, a string of jointed pipe sections or other suitable, elongate, fluid-communicating tubular body. The service line may also include, or may alternatively comprise, an electric slickline, wireline or other equivalent connection.
The pipe string may be stored in open water or may be received within a storage sleeve. In one form of the invention, the storage sleeve is provided with a suitable corrosion inhibiting liquid or other treating material. Seals extending about the annulus between the pipe string and the storage sleeve retain the treating fluid within the sleeve as the pipe is moved into and out of the sleeve.
A work string constructed of individual steel pipe segments secured together with conventional end connectors is significantly less expensive than a coiled tubing string having similar internal dimensions. Storing the string of pipe in a configuration that does not require repeatedly yielding the pipe material reduces the likelihood of fatigue-induced failure in the string. The use of conventional jointed pipe also permits higher operating pressures than those possible with continuous coiled tubing.
While the preferred form of the invention employs individual sections of flush joint pipe to form a pipe string, the present invention anticipates the use of a string of unjointed pipe positioned in the water in a linear or curving configuration having curvatures with radii that are not less than the minimum non-yielding radius of curvature for the pipe.
, In pne broad aspect of the invention, axially extending "unyielded pipe" (that is, pipe
that has not been bent in a curve having a radius smaller than the minimum allowable non- yielding bending radius of the pipe) is positioned with its central axis oriented in a direction
that is not parallel to the central axis of a subsea well that is to be engaged by a string of pipe that includes the unyielded pipe. The unyielded pipe is moved along a curving path and then allowed to straighten to redirect the central axis of the unyielded pipe to. an axially extending orientation substantially parallel with the axis of the subsea well. One end of the pipe string in this parallel orientation is inserted into the well and the pipe string is driven through the well with a propulsion device that is submerged in the body of water overlying the subsea well.
Brief Description of the Drawings
Figure 1 is a vertical elevation, partially in section, illustrating a surface support
facility working on a subsea well using a pipe string of the present invention;
Figure 2 is a vertical 'elevation, partially in section, illustrating a modified form of the invention applying different type work strings of the present invention to a subsea well; Figure 3 is a vertical elevation, partly broken away, illustrating a surface support facility working over a subsea well using a submerged work string carried within a protective sleeve;
Figure 3 A is a vertical section, partially broken- away, illustrating a. sliding seal disposed between the work string and a protective sleeve to retain corrosion inhibiting fluid in the sleeve as the pipe is advanced through the sleeve;
Figure 3B is a vertical section, partially broken away, illustrating a fixed seal at one end of the protective sleeve providing a sliding seal between a surface supply line and the pipe string of the present invention; and '
Figure 4 is a vertical elevation illustrating a modified form of the present invention storing the pipe string of the present invention in multiple curving open loops.
Description of the Illustrated Embodiments
Figure 1 illustrates a support facility indicated as a surface vessel 11 on a surface S of
a body of water W servicing a subsea well 12 at a distant underwater location on a water bottom 13. A pipe work string 14 extends at substantially a diagonal to the horizontal
between the work vessel 11 and the well 12. A controlled buoyancy guide head 16 is anchored above the well 12 with anchoring lines 17 that extend to the water bottom 13. The pipe string 14 extends through the guide 16 and through a pipe drive assembly head 20 secured to the top of the well 12. An RON 25 is used to position and assemble the guide head 16 and drive assembly 20 over the well 12.
As thus illustrated in Figure 1, it will be appreciated that the pipe string 14 includes a section of unyielded pipe 14a having a central axis that extends diagonally in a substantially non-parallel direction relative to a substantially vertically oriented central axis 12a of the subsea well 12. The pipe 14a is reoriented from its non-parallel orientation to its parallel orientation as it passes through the buoyancy guide head 16. In this application, as well as the others illustrated herein, an unyielded pipe section is moved around a curving path such that the central pipe axis becomes parallel with the central axis of the subsea well. The curving path has a radius of curvature that is greater than the niimmum allowable non-yielding bending radius of the pipe material in the curved section whereby the bent or curving pipe section is not yielded as a result of moving over the curving path.
The assembly 20 may be bolted to the wellhead or otherwise suitably secured relative to the wellhead so that the linear driving force exerted by the drive assembly 20 forces the pipe string 14 into the well 12. The drive assembly 20 may be enclosed within a protective housing or may be directly exposed to the seawater.
The buoyancy guide 16 may be constructed in any manner suitable for regulating the
position of the guide in the water relative to the drive assembly 20. Positive flotation or
surface controlled displacement mechanisms may be employed in the buoyancy head 16 to achieve the desired positioning of the head relative to the well 12. The lines 17 may be any suitable line, including flexible or rigid lines, that assist in maintaining the relative lateral placement of the buoyancy guide 16 and the well 12.
A supply line 26 extends between the surface vessel 11 and the well 12 to provide hydraulic power, electric power, and/or data and control signals as required to accomplish the desired workover procedure. The supply line 26 may be a conventional flexible line having one or many conduits or conductors. The supply line 26 may be used to supply the power required to operate the drive assembly 20 and to communicate with the RON 25. Additionally, the supply line 26 may be used to work with the work string 14, circulate fluid or otherwise perform services required in the workover, production and/or servicing of the well 12.
A controlled buoyancy device 27 is used to support the pipe string 14. Multiple such controlled buoyancy devices may be deployed along the length of the pipe string 14 if necessary to maintain a desired orientation of the string in the open water. , The buoyancy devices may also be tethered to the bottom 13 if desired.
A second work string 30 is illustrated extending from the vessel 11 along the surface
S of the water body W. Buoyancy devices 31 support the string on the water surface S. A floating curving guide 32 directs the pipe string 30 vertically down into the water W toward
the subsurface well 12. The lower end (working end) of the string is introduced through the
guide 16 to the drive head 20 to insert the working end of the string into the well 12. The
oppoβite end (topside end) of the string 30 is connected by a flexible line 33 supplied from a
reel 34 to communicate hydraulic fluid or well fluid or working materials between the vessel
11 and the well 12.
As illustrated herein, , it will be understood that an unyielded pipe section 30a of the
pipe string 30 is oriented in a direction that is not substantially parallel with the direction of the centerline 12a of the subsea well 12. When the section 30a is moved through the curving guide 32, the orientation of the central axis of the pipe section 30a is changed to become substantially parallel with the central axis 12a of the well.
The string 30 slides through the flotation devices 31 as it advances into the water W. The lateral positioning of the flotation devices 31 may be remotely controlled by signals sent from the vessel 11 causing the devices to selectively grip or release the pipe as it is being moved. The flotation devices 31 may also have remotely controlled, self-propulsion capabilities to move them along the length of the pipe 30 as required to assist in deploying and retrieving the pipe string.
A third work string 40 is illustrated resting on the bottom of the sea floor 13. The working end of the work string 40 passes through a curving guide 41 that is part of a controlled buoyancy assembly 42. A drive head assembly 43 is included with the controlled buoyancy assembly 42.
An operator in the vessel 11 remotely controls the buoyancy of the assembly 42 as the
ROV 25 moves the assembly into position above the wellhead 12. The flexible line 26 may
be connected to the controlled buoyancy assembly 42 to power and/or transfer fluids or information and/or otherwise communicate with the drive head assembly 43, the working end of the pipe string 40 and/or the well 12.
Figure 2 illustrates a surface support vessel 50 assembling individual joints of pipe 51
and 52 into an elongate string 53 used to work over the well 12. The pipe is being assembled and fed from the ship 50 through a curving guide 55 that directs the pipe vertically down through the water W from the surface S. A work string 56 extends away from the vessel 50
where it is stored on the water surface S resting upon flotation devices 57. The working end of the string 53 is fed into the well through a drive head assembly 60 that is secured to the well 12. The drive head assembly 60 propels the string 53 into and out of the well as required to service, produce or otherwise deal with the well 12 and its contents.
The work string 56 may be drawn onto the vessel 50 and fed through the curving guide 55 to replace or supplement the string 53. A second work string 61 is illustrated submerged below the surface S of the water body W. Controlled buoyancy devices 62 regulate the depth of the string 61 below the water surface. The string 61 slides through the flotation devices 62 as it is being run into or retracted from the well 12. A controlled flotation guide assembly 63 redirects the substantially horizontally disposed pipe string 61 to a vertical position for introduction into the well 12. A flexible supply line 65 provides support and communication for producing and servicing the well and operating the drive assembly 60. A flexible anchor line 66 is used to hold one or more of the flotation devices 62 fixed relative to the sea bottom 13.
Figure 3 illustrates a surface vessel 70 having a flexible supply line 71 connected to the end of a work string 72 that extends through a protective sleeve 75. The internal diameter of the sleeve 75 is sufficiently large to accommodate the pipe string 72 with an additional
annular space 76 between the sleeve and pipe string. A suitable corrosion inhibiting or other
fluid.is disposed within the annular area 76 to minimize corrosion or otherwise process or test
the string 72.
The sleeve 75 is maintained at a desired location' below the surface S of the water by
suitable buoyancy devices 78. The sleeve 75 and enclosed work string 72 extend to the water
body W in an elongate open loop that brings the working end of the work string back to a
curving guide 80 positioned atop the subsea well 12. The guide 80 has a radius of curvature that is greater than the minimum radius of curvature below which the material of the pipe string 72 yields.
A pipe injection drive head 81 is secured to the well 12 for propelling the pipe string 72 into and out of the well. The drive head assembly 81 and guide 80 are supported over the well 12 by struts 85 that are secured to a baseplate 86 at the bottom of the well 12.
The assemblies 81 and 80 may be moved by a line deployed from the vessel 70 and secured to a lifting eye 87 to be moved from one subsea well to another. In performing this
operation, it is only necessary to elevate the assembly sufficiently to clear projections from the sea bottom 13. An ROV is used in the positioning and deployment of the assembly. Figure 3 A illustrates a sliding seal 90 formed internally of the sleeve 75. The seal 90
moves with the pipe 72 in the direction of an arrow 91 through the sleeve 75 as the drive
head assembly 81 advances the pipe 72 into the well 12. The seal sliding through the inside
of- the sleeve 75 traps the corrosion inhibiting fluid in the annular area-76. As the pipe is
advanced into the well 12, and the supply line 71 is pulled through the sleeve 75, the sliding
seal 90 prevents egress of the treating fluid from the sleeve. The supply line 71 includes a
line 91 used to supply fluid to the inside of the pipe string 72 and a return line 92 used to
return displaced fluid in the area 76 back to the support vessel 70.
Figure 3B illustrates a modified form of a seal 95 used to contain the treating fluid
within the annulus 76 of the sleeve 75 as the pipe advances through the sleeve. The seal 95 is
fixed relative to the sleeve 75 and maintains a sliding seal with the external surface of the
supply line 71 as the line 71 follows the advancing work string 72 through the sleeve and to
the subsea well 12. Fluid is supplied to the work string 72 through a conduit 96 and returned
to the vessel through a return line 97.
Figure 4 illustrates a modified form of storing and deploying the work strings of the
present invention from a surface support vessel 100 at the surface S of the body of water W. A pipe string 101 extends in several open loops between free moving forming guides 102 and curving guides 103 and 104. The guides 102 are raised and lowered as the pipe is deployed
or retracted relative to the well The working end of the string 101 is introduced into the well 12 in a manner previously described with reference to the string 14 and the buoyancy guide 16 of Figure 1. The end of the pipe string at the support vessel 100 may be connected to
pumps or other surface control or production devices or means required for working over, producing or otherwise dealing with the well 12.
The means and method for practicing the invention, and the best mode contemplated
for practicing the invention, have been described herein. It is to be understood however, that the foregoing description is illustrative only, and that other means and methods as well as
materials of construction may be employed in the practice of the present invention without
departing from the scope of the invention. Additions, deletions and other modifications in
the specifically described embodiments may be carried out without departing from the scope
of the invention, which is intended to be limited only by the scope of the following appended
claims.