WO2000049266A1

WO2000049266A1 - Offshore drill deck structure

Info

Publication number: WO2000049266A1
Application number: PCT/EP2000/001327
Authority: WO
Inventors: Anh Son Dang
Original assignee: Sofitech N.V.
Priority date: 1999-02-17
Filing date: 2000-02-16
Publication date: 2000-08-24
Also published as: AU2805500A; GB9903505D0; GB2346840A

Abstract

A floating drilling platform is provided having drill floor with a set-back segment that is designed as pipe rack for vertically stored stands of drillpipes or other well tubulars and a drill floor segment that supports the derrick or mast with reduced size and weight compared to conventional derricks. The drill floor segment is movable with respect to the main deck of the floating platform and the set-back segment, whereas the set-back segment is fixed to a support structure holding both segments above main deck level.

Description

_ i ,_

OFFSHORE DRILL DECK STRUCTURE

This invention relates to a drill deck structure for drilling platforms and to methods of operating such a structure.

BACKGROUND OF THE INVENTION

According to a conventional arrangement for drilling platforms, such as jack-up rigs or barges, the rig structure comprises a floatable main hull, the upper face of which forms the main deck. The main deck serves as a storage area for heavy equipment, such as the blow-out preventer (BOP) and well tubulars, e.g. drill, riser or casing joints.

The well tubulars on the main deck are in general stored flat, i.e. in horizontal orientation. Usually located at an elevated level above the main deck is the drill floor or drill deck. It is mounted on a support structure, which in case of jack-up rigs is known as cantilever. Usually the drill floor or both, cantilever and drill floor can be moved with respect to the hull, such that the well center can by moved along a line or in a plane, respectively.

The drill floor itself supports the derrick or drilling mast and other equipment used during conventional drilling operation. This drilling equipment includes hoisting equipment to handle well tubular at the well center, rotating devices to rotate the drillstring during drilling, a mousehole to hold joints for assembling those joints into stands of well tubulars.

A part of the conventional derrick structure, the so-called setback area, is designed to vertically store stands of well tubulars during various drilling operations. According to normal drilling practice, the well tubulars stored flat as single lengths of pipe (joints) laid out on racks at the main floor. Joints of well tubulars for use during a drilling operations are lifted over a structure connecting the main rig floor with the drill or rig floor, the so-called catwalk, and lowered into the mousehole next to the well center. To add the joint to the drill string, the upper end of the drillstring, consisting of swivel and kelly, is disconnected from the rest of the drill string and moved over to the mousehole. The kelly is then stabbed into the upper end of the joint ("box") and rotated so as to tighten the threaded tool joint. The kelly and the joint of pipe are lifted and moved back over to well center and stabbed into the upper end of the suspended drill string. Again, the threaded connection is tightened by rotating the pipe joint and kelly. In modern offshore and other rig installation a "top drive that attaches to the top of the derrick is used in place of a rotary table to turn the drill string. It is also used to suspend the drill string in the hole. Modern top drives combine the elevators, tongs, swivel, and hook all into one unit.

After connecting the new joint to the drill sting, drilling can resume for the length of the joint. Then the drilling has to stop to add another joint to the drill string repeating the steps described above .

At certain intervals drilling stops. At this point, the drill string is tripped out of the well . To trip out the kelly and swivel is removed from the top of the drill string and placed into another opening in the drill floor, the rathole. Then, drill pipe elevators are used to pull the drill string and break it into stands of pipes or riser joints. During tripping not every single joint of tubular is broken out one at a time. Instead, the drill string is most often pulled as stands, i.e. two, three or more joints at a time. The stands are then stored in vertical pipe racks in the set-back area of the mast or derrick structure. To reassemble the drillstring the breaking- out operation is basically reversed.

It is recognized as one of the problems of existing designs that with ever increasing drilling depth or reach of wells, the number of stands increases. With an increasing number of stands, the set-back area on the rig has to be enlarged. By enlarging the derrick structure and the number of stands the load on drill floor and hence on the support structure or cantilever increases proportionally. As a consequence, the hull size of the jack-up rig or barge has to be expanded to stabilize the rig.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a floatable drilling platform having a hull with a main deck and a support structure for supporting a drill floor above the level of said main deck, said drill floor comprising a first segment with at least one well center, a mast frame structure, well tubular hoisting apparatus and drillstring rotating apparatus; and a second segment with at least one set-back area with a racking frame to vertically store well tubulars and a tubular handling system to handle well tubulars; wherein both segments rest on said support structure above main deck level; wherein the segments are adjacent; wherein the first segment is designed to be moved relatively to said second segment, said support structure and said main deck; and wherein said tubulars handling system is designed to compensate for a change of position between said first and said second segment.

The invention can be seen as "splitting" the known drill floor into a first segment which is designed as pipe rack for vertically stored stands of drillpipes or other well tubulars and a second segment that supports the derrick. As the need to store tubulars within the derrick structure can be significantly reduced if not eliminated, the present invention offers the advantage of providing a lighter structure, referred to as mast. An additional reduction of momentum on the support structure or cantilever is achieved by moving the pipe carrying section closer to the center of gravity of the rig. Or alternatively, by keeping the load on the support structure constant, the lighter mast can be moved further from the center of gravity of the rig while maintaining its stability. As the mast can be built with a smaller base area, the well center can be also moved closer to the edge of the cantilever. As a further consequence, those parts of the support structure or cantilever supporting the mast can be modified in accordance with the lighter load, leading to further weight savings .

It is an important aspect of the invention that the remaining drill floor and the set-back area are at essentially the same level above the main deck, preferably abutting. For jack-up rigs with a cantilever, this level is above the top of the cantilever. Minor differences in the height levels of drill floor and set-back area can be compensated by the pipe handling system. However time in the critical path to the well center is lost, if the pipe handling system has to bridge larger gaps between the two floors .

Thus, by retrofitting existing barges or jack-ups with a split drill floor design in accordance with the present invention, the effective drilling area can be significantly extended. New rig designs can be made smaller and lighter while preserving the area in which wells can be drilled.

These and other features of the invention, preferred embodiments and variants thereof, possible applications and advantages will become appreciated and understood by those skilled in the art from the following detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows basic elements of a known jack-up rig;

FIG. IB shows a topn view of a known jack-up rig;

FIG. 2 shows a side view of the drill floor of known jack-up rig;

FIG. 3A,B show a side and top view of a drill floor arrangement in accordance with the present invention; and

FIG. 4 shows further details of an example in accordance with the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

In FIGs. 1A and IB, a schematic drawing of a jack-up rig 10 is shown as side elevation and top view, respectively.

The rig 10 comprises a main hull 11, which is supported via legs 112. The legs are shown planted with their spud cans 113 in the sea floor, giving the hull a stable support during drilling operations. To move the jack-up rig 10 to a different location, the hull is lowered until it floats on the body of water.

Installations on the main deck 111 of the hull 11 include cranes 114, crew quarters 115 and heli-pad 116 and lifeboat 117. Also found on the main deck 111 are parts of the mud conditioning system 118 used to clean the mud returning from the borehole. Racks 119 for horizontally storing drill, casing or riser pipes are found on the main deck. Number, sizes and arrangement of the shown installations vary. The main deck installation also includes the mud-reconditioning unit 118. Several other installations typically present on the main deck, such engines rooms, tanks, pits and pipes, etc., have been omitted for the sake of clarity.

Above the main deck level there is a movable support structure, the so-called cantilever 12. The cantilever 12 rests on skidding rails 121 that provide a sliding support. Usually hydraulically driven claws are used to move the cantilever back and forth. The skid device enables the operator to move the cantilever and the derrick from the deck to a drilling position over the water. The outer end 122 of the cantilever usually takes the shape of a beam or frame structure to save weight and leave an opening 123 through which drilling operations can be performed. The inner end is used for additional pipe racks 124 to store well tubulars horizontally.

The drill floor 13 is located above the top of the cantilever 12, supported by the cantilever via skidding rails 131. The skidding rails 131 enable a motion of the drill floor 13 relatively to the cantilever. By adding the motions of the drill floor and the cantilever, drilling activity can cover a two- dimensional space, the so-called drilling area. The maximum reach of the two skidding devices determines the size of this area. In turn, the load as exerted by the drill floor installation on the cantilever and by the cantilever on the main hull limit this maximum reach.

Part of the drill floor installation is the derrick structure 132. In addition to its main frame 133, the derrick comprises the drilling winch (not shown) to suspend the drill hook 134 and the other standard parts of the drilling equipment, i.e. swivel, kelly etc. (also not shown) . For the present invention it is important to note that part of the derrick structure is dedicated as set-back area 135 to store well tubulars 136 vertically during the tripping operations. The drill floor has an opening, the so-called well center 137, through which well tubulars are lowered and raised during the various drilling operations .

FIG. 2 shows an enlarged side view of the known derrick and the cantilever. Elements shown in FIGs. 1A and IB, are given the same numerals as used in those figures . Also shown is the pipe racking system, usually comprising one or more fingerboards 138 at various height levels . The drill floor 13 can be moved on the skidding rails 131 via hydraulically operated claws 139 perpendicular to the paper plane, while the cantilever 12 moves on its skidding rails 121 horizontally within the paper plane.

Referring now to FIGs. 3A and 3B, a schematic side and top view of a drill floor structure in accordance with the present invention is shown.

The support structure is similar to the one described above. Resting on skidding rails 321, the cantilever 32 can be moved above the main deck 31. However, the known drill floor is replaced by two separate floors 33, 34.

Of these two segments, the one which supports the mast 332, rests on skidding rails 331, while the other segment 34, supporting the pipe racking system 342, is permanently connected via steel legs 341 to the cantilever 32.

The new mast structure 332 has no set back area reserved to vertically store well tubulars during the drilling operations (particularly during tripping) . For that reason, the term mast has been chosen instead of using the term derrick, which implies the existence of an internal set-back area. Being exclusively dedicated to hoisting and drilling operations, the "footprint" of the new mast 332 and its weight can be significantly reduced. Further weight gains are achieved by adapting the cantilever 30 to the reduced static load exerted by the mast. As shown, a part of the cantilever frame under the drill floor segment 33 can be sacrificed.

The fixed set-back segment 34 carries the pipe racking system 342. The pipe racking system comprises a steel frame 343 including fingerboards 344 to secure the tubulars 345 in a vertical position.

Further included in the racking system is one or more automatic pipe handling systems 346. These systems are commercially available from vendors such as VARCO International Inc. The racking system shown has three pipe handlers 346. The pipe handlers rest on rails 347 to firstly increase the exploitable set back area 348 and, secondly to compensate for the relative motion of the drill floor segment 33 (and mast) . Therefore at any position, the pipe handler 346 can reach the well center 333.

Depending on its design, the pipe handling systems may also compensate for a vertical difference in the height between the drill floor segment 33 and the set-back segment 34. However, it is seen as most advantageous to have both segments abutting as shown in the drawing.

As an alternative variant, the racking system may only use one pipe handler 346 or one pipe handler on each side of the set back area 348. Generally, the number of automatic pipe handling systems 346 deployed depends on size of the racking system, reach of the handling system and other technical and commercial considerations. Whereas using only one pipe handler has safety, weight and cost advantages, the use of more pipe handlers can add speed and redundancy to the system. A lifting device 349 is provided to raise and lower tubulars off and onto the catwalk 324. The catwalk connects the set back segment 34 to the top level of the cantilever 32. Where there is no cantilever, the catwalk leads directly to pipe storage areas on the main deck level .

To assemble tubulars off the well center and, hence, off the so- called critical path, the set-back segment 34 is provided with a mousehole 350 and an automatic device 351 to assemble tubulars 345. This device is known in the industry as "iron roughneck" and commercially available from companies such as VARCO International and Miko Oilfield Supplies Limited. Hence, the shown variant of the invention does not require a mousehole on the drill floor segment 32, further reducing the operations on this floor.

The novel drill floor structure provides extra space on the cantilever. As the set-back segment 33 no longer moves relatively to the cantilever 31, the area under it can be used for further installations. As an example, it might be advantageous to place the entire or parts of the mud conditioning system (shaker) inside the cantilever as shown in FIG 4. It is common practice to place the conditioning system on the main deck, hence the new location clears deck area on the main deck. Alternatives are known where shaker equipment 125 is placed on the edge of the cantilever as shown in FIG. 2.

FIG. 4 shows a mud return line 421 leading to a distributing trough 422 to a first stage of shakers 423 (scalping shakers) . The mud cleared of larger cutting is then guided through further chutes to subsequent conditioning stages, such as shale shakers, degassing or desanding tanks, or into a mud tank.

The invention can also applied to barge-type floating vessels even when those barges have no moveable cantilever but a fixed structure to hold the mast above main deck level and above the drilling area. In this variant, the drill area reduces to a line.

Also it is feasible to use the mast structure to store a small mount of well tubulars, equivalent to keeping a small set-back area on the moveable drill floor segment.

Claims

CI-AIMS

1. A floatable drilling platform having a hull with a main deck and a support structure for supporting a drill floor above the level of said main deck, said drill floor comprising

a first segment with at least one well center, a mast frame structure, well tubular hoisting apparatus and drillstring rotating apparatus; and

a second segment with at least one set-back area with a racking frame to vertically store well tubulars and a tubular handling system to handle well tubulars;

wherein both segments rest on said support structure above main deck level;

wherein the first segment is designed to be moved relatively to said second segment, to said support structure and to said main deck; and

wherein said tubulars handling system is designed to compensate for a change of position between said first and said second segment.

2. The drilling platform of claim 1, wherein the second segment is an elevated, non-moveable part of the support structure.

The drilling platform of claim 1, wherein the second segment comprises a mousehole to assemble stands of well tubulars .

4. The drilling platform of claim 1, wherein the support structure is a cantilever designed to be moved relatively to the main deck.

5. The drilling platform of claim 1, having mud conditioning equipment on the top level of the support structure below the second segment .

6. The drilling platform of claim 1, being a jack-up rig.