Boring or penetrating the earth – Boring a submerged formation – Boring from nonbuoyant support
Reexamination Certificate
1999-11-02
2001-06-19
Bagnell, David (Department: 3673)
Boring or penetrating the earth
Boring a submerged formation
Boring from nonbuoyant support
C175S080000, C175S082000, C166S277000, C166S380000
Reexamination Certificate
active
06247541
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a method for reclaiming an unused or unusable slot on an offshore platform by replacing the drive pipe originally positioned within said slot and in one aspect relates to replacing an unused drive pipe on an offshore platform by severing and removing the upper portion of the old drive pipe and then using a tethered guide cable to guide a new drive pipe into a position which bypasses the path of the old drive pipe.
2. Background
In producing hydrocarbons from subsea deposits, it is common to drill and complete a plurality of wells from the same offshore structure; i.e. bottom-supported platforms, tethered platforms, etc. In structures of this type, a plurality of “slots” are provided through which individual drive pipes (sometimes called “conductors”) are run through guides on the platform and are driven to refusal or otherwise penetrated to a desired depth into the marine bottom. A well is then drilled and completed through each of the drive pipes by techniques, e.g. directional drilling, well known in the art.
Unfortunately, when a well is being drilled, completed, or produced, the drive pipe in a particular slot may become clogged or damaged below the mud line or the wellbore from the drive pipe may be proceeding along a undesirable path (e.g. intersection with another wellbore). When this happens, an attempt is usually made to salvage the effected slot by clean-out or some other remedial technique. If these measures, usually expensive and time-consuming, are unsuccessful, the slot may have to be abandoned. Also, if a well turns out to be a dry hole or does not produce at an economical rate, the slot will have to be abandoned. Since the number of slots on any particular platform is limited, it is highly desirable to “reuse” a slot rather than abandon it.
One highly successful technique for reclaiming an unused or unusable slot on an offshore platform is that disclosed in U.S. Pat. No. 4,733,732 to Lynch, issued Mar. 29, 1988. The original or “old” drive pipe in the effected slot is first cut or severed below the marine bottom or mudline. The upper portion of the old drive pipe is retrieved to the surface, leaving the lower portion or old stub pipe in place. In the preferred embodiment, a “sub-mudline drive pipe whipstock” (“SDW”) is attached to the lower end of the new drive pipe which, in turn, is then passed or driven downward through the same set of vertically-spaced guides on the platform that were used in positioning the old drive pipe. Thus, as disclosed in U.S. Pat. No. 4,733,732, the SDW is self-aligning onto the old stub pipe where it becomes firmly seated.
Once the SDW is in place on the old stub pipe, continued downward force on the new drive pipe will shear the bolts holding the SDW to the new drive pipe. As the new drive pipe moves downward, it will engage the inclined surface of the whipstock and will be deflected thereby into a new direction. Also, in another modification, the SDW is lowered on the lower end of a drill string which is retrieved to the surface after the SDW is properly positioned on the old stub pipe. While not disclosed in U.S. Pat. No. 4,733,732, the drill pipe may remained connected to the SDW after the SDW is in place and the new drive pipe can be lowered over the drill pipe which, in turn, serves as a guide to insure the path between the surface and the old stub pipe.
While drill pipe is useful as a guide string in relatively shallow water depths, it is impractical, if not impossible, to design a drill pipe and/or drill collar guide string using present technology and commercially-available supplies which would free-stand under its own weight and/or withstand the dynamic conditions of ocean currents and wave action (i.e. column buckle problem) in water depths of about 250 feet or greater. Accordingly, some means is needed to replace drive pipes in water depths which exceed about 250 feet.
SUMMARY OF THE INVENTION
The present invention provides a method for replacing an old drive pipe which extends through a slot on an offshore platform, especially where the platform is positioned in a deep body of water (e.g. 250 feet or more). The old drive pipe is a damaged or otherwise unusable conductor pipe which extends from a deck on the platform, through the body of water, and into the marine bottom to a depth below the mudline. To replace the old drive pipe, it is first cut to provide an upper portion and a stub portion, the latter remaining firmly embedded in said marine bottom. Next, a guide cable is affixed to the stub portion of the old drive pipe so that the guide cable will extend between the stub portion and the deck on the platform. The upper portion is removed from the slot on the platform as the upper portion is retrieved to the surface.
A new drive pipe is then made-up as it is lowered over the guide cable and passes through the same slot as previously occupied by the old drive pipe. The new drive pipe will be guided downward along the guide cable until it reaches the stub portion of said old drive pipe where it is then diverted away from the stub portion of said old drive pipe into a different path from that of said old drive pipe.
More specifically, the present method is carried out by first setting an anchor packer, having a central bore therethrough, in the old drive pipe at a point below the mudline. The old drive pipe is then cut at a point above the anchor packer to thereby provide an upper portion and a stub portion which, in turn, remains firmly embedded in said marine bottom. Next, a retrievable packer, having a central bore therethrough, is set in the upper portion of the old drive pipe near the cut point.
A guide cable assembly, comprised of the necessary length of cable having a shearable tool at the lower end thereof, is releasably connected by a J-slot connector or the like to a work string and is lowered thereby down the old drive pipe. The cable will pass through the central bores of both the retrievable packer and the anchor packer until the releasable connector comes to rest on the retrievable packer. The work string is then released and retrieved to the surface.
The upper portion of the old drive pipe is then raised to the surface. Since the retrievable packer is firmly set in the upper portion of the old drive pipe and the releasable connector on the cable rests on the retrievable packer, they too will be raised as the upper portion of the old drive pipe is raised. This draws the cable back up through the bore in the anchor packer until the shearable tool on the lower end of the cable assembly engages the anchor packer and holds it against further upward movement. At this time, the retrievable packer and the upper end of the cable has reached the surface.
A whipstock assembly having either a stab-in or stab-over connection thereon is releasably connected to the lower end of a new drive pipe by shearable bolts or the like. The drive pipe and the whipstock connection are threaded over the guide cable and are lowered through the same slot as that previously used by the old drive pipe. Make-up of the new drive pipe continues as it is lowered down over said guide cable until the whipstock assembly engages the stub portion of said old drive pipe. Now continued downward force on the new drive pipe will cause the bolts to shear thereby releasing the new drive pipe from the whipstock assembly and causing the new drive pipe to be diverted into a different path from that taken by the old drive pipe.
REFERENCES:
patent: 4249619 (1981-02-01), Burns
patent: 4526232 (1985-07-01), Hughson et al.
patent: 4733732 (1988-03-01), Lynch
Brochure : “Whip Stock”; Petro-Drive, Inc; undated.
Ellis Harvey Andrew
LeJeune George Virgil
Bagnell David
Scott F. Lindsey
Singh Sunil
Sloat Robert E.
Vastar Resources Inc.
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