Hydraulic and earth engineering – Marine structure or fabrication thereof – With anchoring of structure to marine floor
Reexamination Certificate
2002-08-28
2004-02-17
Lee, Jong-Suk (James) (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
With anchoring of structure to marine floor
C405S227000, C405S228000, C114S296000, C175S007000
Reexamination Certificate
active
06692194
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a substructure device in the shape of a suction substructure and a method for installing it on and in a waterbed as well as use of the suction substructure in connection with installation of conductor casing for one or more wells, preferably petroleum well(s), in which the installation of suction substructure and drilling of wells are performed from e.g. a floating installation.
BACKGROUND OF THE INVENTION
The background of the invention is the disadvantages of installation and costs often experienced with the use of known substructure devices in connection with the drilling of underwater wells.
KNOWN TECHNIQUE
In connection with known technique the work with a new well is normally started by the drilling of a pilot hole from a drilling installation, e.g. a drilling rig, the hole having a diameter of e.g. 36″, down to a suitable depth under the waterbed, typically approx. 70 metres. In the description that follows the waterbed will be referred to as the seabed, even if the above seabed may equally well be the bottom of e.g. a lake, a river, a delta or a swamp area.
After the drilling of the above pilot hole the drilling tools and the drill string are pulled out of the pilot hole. A string composed of several connected conductor casings, i.e. a conductor casing string, is thereupon lowered down into the pilot hole by means of an installation string of drill pipes connected to the conductor casing string. Then floating cement (cement grout) is pumped down through and out of the bottom of the installation string and the conductor casing string, so that the cement grout is displaced up into the tubular space between the pilot hole and the conductor casing string. The conductor casing string must then be held in a preferably vertical position until the cement grout is sufficiently hardened, and thus has achieved a load carrying strength, which is sufficient for supplying the conductor casing string with necessary lateral support during later strains.
To facilitate the installation of the conductor casing, a guide base is connected to the conductor casing string's upper end. Seen from above the guide base normally has a rectangular shape, and each of the four corners of the guide base is fitted with a guide post with the objective of being an anchoring point for an appurtenant guide line. Each of the four guide lines of the guide base runs at all times to the surface. The conductor casing string, the guide base and the guide lines are then lowered down towards the seabed where the conductor casing string is guided into the lead hole, so that the guide base eventually is placed in an upper sedimentary layer in the seabed, and where this layer is normally made up of loosely composed and finely grained sedimentary particles as well as water, a mixture often referred to as mud. In this connection the lead base must be placed as vertically as possible down into the seabed.
After the location of the guide base on and in the seabed and after the cementing of the conductor casing string in the pilot hole has been done, one may, if desired, lower down a drill string, a casing string, a riser string or other necessary equipment, as such equipment is guided into position at the well centre line by means of the above guide lines, connected to the guide base.
As an alternative to the guide base's above guide lines, the guide base may be equipped with a funnel shaped sleeve, which is not described in greater detail, but in which such a sleeve has proved to be more suitable when working with wells at great sea depths.
In the use of known technique a guide base does not function as a load carrying construction in the founding of the well. Such loads typically consist of both pressure and torsion forces created by the weight of a blow out valve, well heads, casing strings in the well and other related equipment, as well as lateral forces caused to the blow out valve and/or the riser string by ocean streams, or as a result of the drift of a floating drilling installation. These loads are taken up by the conductor casing string, which therefore must be dimensioned accordingly, to avoid bending and breaking.
DISADVANTAGE OF KNOWN TECHNIQUE
The known substructure devices are encumbered with some disadvantages concerning strength and costs.
The drilling of a pilot hole as described above, and in which the drilling is done in loosely composed and substantially water filled waterbed sediments, often leads to great washouts of the wall of the pilot hole, and the greatest washouts often take place in the upper part of the lead hole.
By subsequent cementing of the conductor casing string, one will often achieve an unsatisfactory filling of cement grout in the expanded tubular space between the wall of the conductor casing string and the pilot hole. After the cement grout is hardened in the tubular space, this may lead to the load carrying conductor casing string getting an unsatisfactory lateral support for the above loads. Moreover, the hardened cement grout acts as a safety pressure barrier for possible outflows of e.g. gas in underlying shallow layers of the base formations, and an unsatisfactory cementing can weaken or eliminate this pressure barrier. In addition, large amounts of cement grout are required for the cementing of a conductor casing string, and the volume increases according to the degree of washing out that has taken place during the drilling of the pilot hole.
The method of first drilling a pilot hole, for then to cement a conductor casing string, may also lead to an unfortunate or unacceptable vertical deviation on the installed conductor casing string, either due to the pilot hole being drilled obliquely down into the seabed, or because the conductor casing string is not kept sufficiently immobile within an acceptable vertical deviation during the time needed for the cement grout to develop sufficient rigidity for supporting the conductor casing string. The drilling of pilot holes and the following cementing of the conductor casing string is further complicated when in deep water locations. This has to do with both the conductor casing string being affected by ocean streams and as a consequence of possible drift of a floating drilling installation, but also as a consequence of low seabed temperatures, which may lead to an extremely long hardening period for the cement grout.
The method of first drilling a pilot hole for then to cement a conductor casing string is in this context the main problem, and this method is in addition time consuming and expensive as the work i.a. must be performed with a drilling rig.
SUMMARY OF THE INVENTION
The present invention makes available a substructure device in the shape of a suction substructure having the necessary capacities and constructive features making it possible to pre-install the suction substructure, and at least one conductor casing string, using other and possibly smaller vessels than the present installation vessels, i.e. a suitable boat, and by piling technique. Thus, most of the above mentioned disadvantages are reduced or avoided.
How the Object is Achieved
According to the invention suction substructure is used prior to the installation of one or more conductor casing strings for the drilling of one or more underwater wells, preferably petroleum wells. The suction substructure and the conductor casing string(s) is/are installed from an installation device or installation vessel, e.g. a suitable boat, located on the surface, hereinafter only referred to as installation vessel.
The suction substructure is made up of e.g. a cylinder shaped substructure body whose shape has features resembling a cup or a glass, and which consist of an encompassing vertical part, or mantle, and where the substructure body at one end consists of an open part, which part in the operating position constitutes the bottom of the substructure body, and where the substructure body in the other and upper end, with the exception of a preferably circular opening, preferably consists of a closed horizonta
Andrus Sceales Starke & Sawall LLP
Lee Jong-Suk (James)
LandOfFree
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