Wells – Processes – Assembling well part
Reexamination Certificate
2000-12-01
2003-03-18
Tsay, Frank S. (Department: 3672)
Wells
Processes
Assembling well part
C166S050000, C166S055100, C175S004500
Reexamination Certificate
active
06533040
ABSTRACT:
FIELD OF THE INVENTION
In many mature Oil fields, most existing low-productivity wells, also called “stripper wells”, become un-economic when oil prices drop below $14/B, thus causing their premature abandonment and the loss of their remaining Petroleum reserves. To prevent this loss of a precious Natural Resource, it is necessary to boost the wells productivity at low Capital Cost, without any significant increase of the wells Operating Cost.
A proven method of reaching the objective of an increased well productivity is to convert single wells into multi-lateral wells. These drain a larger area of the reservoir, either because the added branch well is drilled into a different layer or because it is highly deviated to reach an un-depleted region of the original productive layer. Various types of downhole sealed connectors have been described and claimed in U.S. Pat. No. 5,462,120, but the present Invention is especially applicable to existing wells equipped with a casing of outside diameter ranging from 7⅝″ to 6.5″ and cemented or not at the lateral kick-off point. The pre-fabricated Assembly is designed so as to minimize the cost of its installation in the existing well, by reducing the required rig time, while providing both a reliable sealed connection of the casing with the branch well liner and full access to the bottom of the casing, below the kick-off point. These two main features are required whenever the existing and branch wells are not at comparable pressures or temperatures, because of reservoir or fluid characteristics, or when the two wells must be operated independently of each other, for instance to convey different fluids, as in the configurations described and claimed in U.S. Pat. No. 5,085,279. These features are not achievable for existing wells of those sizes, using any presently available connecting equipment.
Furthermore, the use of the Assembly, in conjunction with a Combined Apparatus for jet-drilling, and for the liner completion of the branch well through the sealed connection, provides additional cost saving benefits, for which conventional drilling tools of the required small size are not well suited, especially in relatively soft formations.
SUMMARY OF THE INVENTION
The first step required for making a branch lateral connection to an existing cased well is that a window be cut-out in the casing to provide access to drill strings and completion tubulars required for the branch well. Performing this operation with a milling bit at the end of a drill string is a time-consuming task. It also results in an irregular window's edge providing a poor fit with the upper end of the branch well liner hung and sealed in a short connecting tube (called a liner stub).
The generally poor fit obtained between the liner stub and a conventionally milled-out casing window makes the sealed junction of the existing well with the new branch lateral entirely dependent upon the bonds between the steel of the two poorly fitting tubulars and the cement filling the gap between them.
The long-term integrity of such a cement to steel seal is unreliable when the well tubulars are subjected to cyclic stresses resulting from pressure or temperature variations at the junction of casing and liner stub, during operation of the dual well.
In addition to the high window-cutting cost, the conventional use of a succession of many different downhole tools requires many trips of the work string, which increase the total rig time and Capital cost of the work-over beyond the limit of affordability for marginal wells.
The present Invention addresses these problems by the design of a multi-function apparatus to be used in existing cased wells, called a “Liner Stub” Assembly, of outside diameter not exceeding the well casing drift diameter, such that said Assembly, used in the First, Second, Third and Fourth Embodiments of the Invention is designed to be:
1) factory pre-fabricated at low cost, from inexpensive drillable materials (except for the high-strength steel stub), including a housing equipped with an outer retrievable hanger-packer, and presenting an inner cavity containing said liner stub,
2) run-in, with the liner stub in a locked position, at the end of a 5″ or 4.5″ OD work string, oriented and set in the casing, preferably opposite a soft formation, all in a single trip,
In addition, said multi-function Assembly allows:
3) the insertion of the stub in a casing window neatly cut-out, in a very short time, using cordon-type linear explosive shaped charges, all equipped with appropriate cutting liners, disposed in a template also included in the said Assembly, but armed at the well site,
4) the remains of the casing wall left in the window and other large debris to be removed by wireline fishing tools, through the work string and the Assembly housing,
5) a side pocket hole of approximate dimensions sufficient to contain the liner stub to be drilled, prior to the liner stub's full extension from the Assembly's housing cavity through the casing window into said pocket hole, in which a cement slurry is displaced outside the extended liner stub, by conventional means,
6) the liner stub, when un-locked and fully extended into said pocket hole, to be at a prescribed small angle (typically less than one degree) from the axis of said Assembly, by using an associated stub-guiding system, also included in said Assembly,
7) the cordons' sequential detonation, controlled by a surface-triggered firing system, included in said Assembly, to shatter the sand face within the cut-out window, followed by small-size debris removal to the surface by reverse circulation of the casing fluid, using flow channels included outside the housing of said Assembly, which may be used during the period of extension of the liner stub in said side pocket hole, and thereafter, during drilling and completion of the branch well,
8) a soft metal stop-collar, affixed at the annealed upper end of the liner stub during pre-fabrication of said Assembly, to reliably stop the liner stub's extension and to maintain said stub in close contact with the inner surface of the casing, along the window's edge, for re-inforcement of the casing and liner stub at their junction,
9) after full-extension of the stub, and displacement of a slug of cement slurry behind the stub in the hole, the guiding system of the liner stub and charge enclosure debris to be quickly retrieved, by wireline, directly through the work string and Assembly housing, or by drilling-out, using a smaller-diameter drill string, inserted in the work string,
10) secondary explosive charges, affixed to said liner upper end and protected by a drillable pressure-resistant annular enclosure to be independantly detonated by a second surface-triggered firing system, also included in said Assembly, as means of bonding the end of the liner stub and its metal collar to the casing, all along the window's edge to form an explosively-welded, reliably leak-proof, metal seal between the casing and liner stub metals, capable of withstanding considerable stress,
11) All debris from the explosions and some of the stub guiding systems are removed, but most of the Assembly housing in the First and Second Embodiments remains, still supported by the hanger-packer in the casing. It is now used as a guide for the insertion of cleaning, cementation and completion tools into the explosively-welded stub. Conversely, in the Third Embodiment, a cement slurry is squeezed around the windowed part of the casing, after all debris from the cover plate and from the cut casing have been removed through the bent liner stub. The welded and cemented curved liner stub is now ready to serve as a tool guide for drilling, cementation and completion of the branch well and as a sealed anchor for its liner.
After the cement slurry displaced behind the casing and the welded liner stub has set, the cement plug at the bottom of the stub is drilled through, so as to begin drilling and completion of the branch well. This is advantageously done by means
Tsay Frank S.
Wasson George W.
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