Wells – Submerged well – Riser
Patent
1991-06-04
1993-06-22
Melius, Terry Lee
Wells
Submerged well
Riser
166 775, 166 89, E21B 1701
Patent
active
052209610
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an assembly comprising an extension tube and a sleeving conduit.
BACKGROUND OF THE INVENTION
The principle of sleeving the main tube of a riser in offshore drilling is known from the prior art. However, prior art devices are based on the principle of a rigid connection between the sleeving conduit elements providing transmission of a longitudinal force and tightness between the inside and the outside of the sleeving.
Such connections may be produced in the same manner as those ordinarily used for well tubing with a threaded assembly which is fairly time-consuming and difficult to effect, and whose reliability of tightness and mechanical strength over a given time period may be questionable after several assembly and disassembly operations. Specially designed connectors of the riser connector type are difficult to design in view of the small space available and would considerably increase the weight and cost of sleeving.
Because of the principle upon which prior sleevings have been developed, the prior sleeving systems require the use of a sliding seal inserted into the sleeving in order to compensate for the differential longitudinal deformations of the sleeving conduit and the tube under the effect of variations in traction, pressure and temperature. This sliding seal, since it requires a long travel path, may be several meters in length and is difficult to use since the seal is subjected to substantial pressure differentials and especially since the seal would be located at a lower part of the sleeving conduit.
SUMMARY OF THE INVENTION
In offshore drilling, an assembly according to the present invention has a twin objective, namely, decreasing the volume of mud employed, and decreasing the total mass and apparent weight of the extension tube and its contents, thereby allowing the assembly to be used at considerable depths when the mud density is high and the wellhead tensioning capability is limited.
"Extension tube", as used in this text, is understood to be the main conduit of a riser, with the conduit connecting the sea bed to a floating installation at the surface. The conduit may, for example, be a production, a drilling, or an intervention (maintenance) conduit in a well.
The aim underlying the present invention essentially resides in providing an assembly of the aforementioned type which avoids the above mentioned disadvantages.
According to the present invention, the extension tube has several elements adapted to be connected together. When the extension tube is to be use alone, for example, when a large-diameter passage is required, when, for example, drilling holes up to 171/2" in diameter are necessary, these elements of the extension tube are simply connected together.
When the necessary passage diameter is smaller such as, for example, in the small-diameter drilling phases of 121/4" and above, a sleeving conduit is used to obtain the advantages noted above.
According to the invention, the sleeving conduit, having an outside diameter less than an inner diameter of the extension tube, has several elements Each sleeving element and each tube element has means for supporting the former in the latter. Axial locking of a sleeving element to the extension tube is accomplished automatically upon connection of two adjacent sleeving elements of the extension tube which accommodates, with some clearance, the supporting means serving to hold the sleeving elements.
Tightness between the sleeving elements is obtained by virtue of nesting of the sleeving elements.
The assembly according to the invention allows the weight of the sleeving to be transferred to the extension tube in a stepped manner, thereby solving the problems created by differences in expansion between the extension tube and the sleeving conduit by dividing it, for a few centimeters, between each connection. Moreover, the assembly according to the invention is easy and quick to implement, with each conduit element simply being supported by an element of the extension tube. Thus,
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Barge Louis
Guesnon Jean
Institut Francais du Pe'trole
Melius Terry Lee
Tsay Frank S.
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