Hydraulic and earth engineering – Marine structure or fabrication thereof – With horizontally movable work deck
Reexamination Certificate
1998-08-28
2001-01-09
Will, Thomas B. (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
With horizontally movable work deck
C405S196000, C405S203000, C405S208000, C175S005000, C175S008000
Reexamination Certificate
active
06171027
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a drilling rig in the form of a jack-up platform on which a cantilever is mounted so as to be movable at least substantially horizontally and in a first direction, with the cantilever projecting more or less outside the jack-up platform, while a drilling platform is further present on the cantilever, said drilling platform being movable relative to the jack-up platform in a second direction, different herefrom.
BACKGROUND TO PRESENT INVENTION
In the conventional drilling rigs, the cantilever is movable only in its longitudinal direction relative to the jack-up platform, and the drilling platform is movable relative to the cantilever in a direction transverse thereto. Due to the resulting movement of the drilling platform relative to the jack-up platform, the drilling point of the drilling rig can reach any point located in a rectangle of which the lengths of the sides are determined by the travel of the cantilever relative to the jack-up platform and the travel of the drilling platform relative to the cantilever. However, in the transverse direction, the size of this rectangle is limited by the distance between the cantilever beams extending in the longitudinal direction, which beams determine the width of the cantilever. Located under the drilling platform is a grid of drilling points. The drilling platform with the blow-out valve and a part of the equipment, tools and materials for drilling that are further required moves from one drilling well to the other. The transverse movement of the drilling platform is limited by the cantilever beams. As a consequence, the drilling pattern is limited to drillings within said rectangle. To obtain a drilling pattern which is nevertheless acceptable, the cantilever should be of a relatively wide design. If the drilling platform has moved over the maximal distance in the transverse direction, the cantilever beam on the side to which this movement took place is subjected to a considerably heavier load than the other cantilever beam. Because of such asymmetric load on the cantilever beams occurring in practice, these beams should be of a relatively heavy construction. A further drawback of the conventional rigs is that between jack-up platform and cantilever, as well as between cantilever and drilling platform, flexible connections should be provided for pipes, cable work, etc.
SUMMARY AND OBJECTS OF THE INVENTION
The object of the invention is to provide a drilling rig wherein the above-mentioned drawbacks are avoided at least to a considerable extent. To this end, according to the invention, the drilling rig as described in the opening paragraph is characterized in that the drilling platform is fixedly mounted on the cantilever and said cantilever is movable relative to the jack-up platform in both abovementioned directions.
As a result, the drilling point always remains in the same place relative to the cantilever, viz. preferably centrally between the two cantilever beams. This leads to a symmetric load on the cantilever beams and offers the possibility of giving them a lighter construction. Now, the width of the cantilever can be selected independently of the displacement in the transverse direction and can be slighter without the drilling pattern being limited thereby. On the contrary, by increasing the movement possibility of the cantilever in the transverse direction, a larger drilling pattern can be obtained than is possible with the conventional drilling rigs. The construction according to the invention further has the advantage that flexible connections for pipes, cable work, etc. must only be provided between the jack-up platform and cantilever.
Although the cantilever with the drilling platform is movable in two directions by extending the cantilever in its longitudinal direction and rotating it about a fixed point on the jack-up platform, the cantilever is preferably constructed for movement in its longitudinal direction with the cantilever projecting more or less outside the jack-up platform, and in a direction relative to the jack-up platform which is transverse hereto. To enable these movements in an efficient manner, supporting members for the cantilever are present, which supporting members are movable with the cantilever in the transverse direction over rails secured on the jack-up platform, while the cantilever is supported by the supporting members for movement in the longitudinal direction.
In a concrete embodiment, the supporting members are slidable by means of relevant operating cylinders over rails secured on the jack-up platform and extending in the transverse direction, relative to slide members which can be secured on these rails, when they are at least secured thereon.
When the supporting members slide over the rails on the jack-up platform or the rails of the cantilever slide over the supporting members, considerable shearing forces occur. In order to at least partially relieve the parts sliding over each other in this regard, at least the two supporting members that are movable over the rail located closest to the edge of the jack-up platform may comprise friction-reducing means which are operative in the longitudinal direction as well as in the transverse direction, to take up at least a part of the frictional forces between the supporting members and the relevant rail and between the rails of the cantilever and the relevant supporting members. In a concrete embodiment, these friction-reducing means are formed by pairs of rollers which are freely movable between the supporting members and the rails in the direction of the rails and pressed thereagainst. In this regard, it is advantageous when the pressure exerted on the relevant rails by the friction-reducing means is settable.
It may sometimes be desirable to provide the drilling platform on a separate support platform. With the drilling rig according to the prior art, this is possible by providing a separate support construction on the separate support platform, onto which support construction the drilling platform can be slid from the cantilever. In practice, this proves to be a fairly difficult operation. For that reason, according to another aspect of the present invention, coupling means may be present whereby the drilling platform is detachably connected to the cantilever so that it can be positioned on a separate support platform. Due to the movability in height direction of the jack-up platform and the movability of the cantilever, both in the longitudinal direction and in the transverse direction, an accurate positioning of the drilling platform coupled to the cantilever is possible. By moreover constructing the coupling means such that the drilling platform can be hooked on laterally by the cantilever, it becomes possible, after the drilling platform has been placed on the separate support platform by a downward movement of the jack-up platform, to uncouple the drilling platform from the cantilever through a further downward movement of the jack-up platform and, subsequently, a withdrawing movement of the cantilever.
In the drilling rig according to the prior art, the high-pressure dredge pumps associated with such rig are typically arranged on the jack-up platform and relatively costly flexible high-pressure lines are necessary both between the jack-up platform and the cantilever and between the cantilever and the drilling platform.
Because according to the invention, the drilling platform is fixedly connected to the cantilever, one set of flexible high-pressure lines can be replaced by so much cheaper fixed high-pressure lines.
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Lee Jong-Suk
Marine Structure Consultants (MSC) B.V.
Pillsbury Madison & Sutro LLP
Will Thomas B.
LandOfFree
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