SUBSEA COMPLETIONS AND WELL INTERVENTIONS USING A VESSEL OF OPPORTUNITY

Abstract

A system for performing a desired subsea well-servicing operation, comprises a vessel, a service apparatus for performing the desired subsea well-servicing operation, the service apparatus being supported on the vessel; and a support apparatus mounted on the vessel, the support apparatus having first and second modes, wherein in the first mode the support means does not provide access to a well by the service apparatus and wherein in the second mode the support means does provide access to a well by the service apparatus. The vessel may be a vessel of opportunity and the service apparatus may be selected from the group consisting of subsea tree installation apparatus, perforating apparatus, acidizing apparatus, fracturing apparatus, workover apparatus, reservoir stimulation apparatus, wireline apparatus, coiled tubing apparatus, and snubbing apparatus.

Description

FIELD OF THE INVENTION

The invention relates to a system and method for performing subsea completions or interventions without using a drilling rig or drill ship. More particularly, the present invention provides a technique by which equipment needed for subsea well work is provided on a vessel of opportunity, thereby allowing significant cost savings.

BACKGROUND OF THE INVENTION

Drilling of subsea wells for the production of hydrocarbons typically requires the use of an offshore drilling rig or drill ship, which have the capacity to support the heavy operations associated with drilling. Because of their technical sophistication and extreme capabilities, drill ships are expensive to build and currently cost on the order of $500,000 per day to operate. In addition, there are relatively few drill ships available.

Once a well is drilled, various steps may be performed to prepare the well for production. These steps are collectively referred to as completions and/or interventions. Completion is the process of making a well ready for production or injection, and may include casing and tubing installation or subsea tree installations, perforating, acidizing, or fracturing. In addition, it may be desirable to intervene in a well after production has begun. Such post-production activities include workover, reservoir stimulation, and other activities, which may be carried out using wireline, coiled tubing, or snubbing equipment.

Subsea completions are typically carried out using a mobile offshore drilling unit (MODU), or drill ship. Subsea well interventions in deepwater are commonly carried out using medium intervention vessels or MODUs for the heavier intervention processes such as snubbing and workover. Because MODU drilling rigs and drill ships are particularly suited for offshore drilling, they are very expensive and therefore not optimal for completion or workover activities. Therefore, it is desirable to provide a system and apparatus that is capable of performing completion and/or workover activities without requiring the use of an offshore drilling rig or drill ship, and that is low cost and light well intervention equivalent.

SUMMARY OF THE INVENTION

The present invention provides a system and apparatus for completion and/or workover activities without requiring the use of an offshore drilling rig or drill ship. In particular, the present invention comprises the use of modular completion or other equipment in conjunction with a hoist and a vessel of opportunity to reduce the cost of various operations below what would be incurred if the same operations were carried out using a drilling rig or drill ship. In addition, by using modular well-servicing equipment, off-the-shelf hoist technologies, and non-dedicated vessels, the present invention frees up expensive drilling vessels.

In some embodiments, the inventions provides a system for performing a desired subsea well-servicing operation, comprising a vessel, a service apparatus for performing the desired subsea well-servicing operation; and a support apparatus mounted on the vessel and supporting the service apparatus. The support apparatus has first and second modes such that in the first mode the support means does not provide access to a well by the service apparatus and in the second mode the support means does provide access to a well by the service apparatus.

The vessel may be a vessel of opportunity and is preferably not a drill ship. The vessel may be equipped with one or more position-maintaining devices. The service apparatus may be selected from the group consisting of subsea tree installation apparatus, perforating apparatus, acidizing apparatus, fracturing apparatus, workover apparatus, reservoir stimulation apparatus, wireline apparatus, coiled tubing apparatus, and snubbing apparatus.

In other embodiments, the system provides a system for performing a desired subsea well-servicing operation that comprises at least two vessels and a buoyant platform held in place by said vessels, wherein the platform includes a moon-pool extending therethrough and a rig erected over the moon-pool. The vessels may be vessels of opportunity.

As used herein, “well-servicing” is used to refer to any operation that may be performed on an already-constructed offshore well, including pre- and post-production operations, geological and mechanical sidetracks.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed understanding of the invention, reference is made to the accompanying drawings wherein:

FIGS. 1 and 2 are schematic illustrations of a first embodiment of the invention in transport and operation modes, respectively;

FIGS. 3 and 4 are schematic illustrations of a second embodiment of the invention in transport and operation modes, respectively;

FIGS. 5 and 6 are schematic illustrations of a third embodiment of the invention in transport and operation modes, respectively; and

FIG. 7 is a schematic illustration of a fourth embodiment of the invention in operation mode.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring initially to FIGS. 1 and 2, the present invention includes a vessel 10 afloat on the sea surface 20. Vessel 10 is equipped with a rig 30 capable of performing one or more desired well-servicing operations.

The well-servicing operations that can be performed by rig 30 include but are not limited to tubing make-up and running, subsea tree installation, perforation, acidizing, fracturing, workovers, reservoir stimulation, wireline operations, coiled tubing operations, and snubbing.

Vessel 10 can be any vessel that has the capacity to support the desired well-servicing operation. Thus, depending on the operation, suitable vessels of opportunity include but are not limited to barges, including lay barges, bulk carriers, cable ships, container ships, and ice breakers. The variety of vessels that can be used in the present invention increases the number of ships that can be considered for a given operation and eliminates the need for a drill ship or drilling rig, of which there are relatively few. In turn, this reduces the costs associated with subsea interventions and completions.

In some embodiments, vessel 10 may include a support bracket 32 or the like, to which rig 30 may be pivotably mounted. Rig 30 is preferably in a horizontal or near-horizontal position during transport, and is rotated as indicated by arrow 37 in FIG. 1 into a vertical position (FIG. 2) after vessel 10 has arrived at the target location above a well (not shown) on the seafloor. Once rig 30 has been rotated into a vertical position, it may be supported by bracket 32 and by guy wires 38, or any other suitable support mechanism. In the operating position, rig 30 extends off the stern of vessel 10 with sufficient clearance to allow the desired well-servicing operation to be performed. While the rig is shown mounted at the stern of vessel 10, it will be understood that it could alternatively be mounted on a side or at the bow of the vessel if desired. For the well-servicing operation, rig 30 may be outfitted with a hoist 34 and/or various other systems 36 that may be needed to perform the desired operation via riser 40.

In preferred embodiments, vessel 10 is equipped with position-maintaining devices, such as are known in the art, and/or a mooring system. Referring now to FIGS. 3 and 4, an alternative embodiment of the invention is adapted for use with a coiled tubing system 50. Coiled tubing system 50 is preferably mounted on a skid 51 and preferably comprises a coiled tubing injector head 52, reel 54 and supporting equipment 56. As shown in FIG. 4, once vessel 10 has reached the target location above a well (not shown), skid 51 is moved laterally (as indicated by arrow 57) until injector head 52 is clear of the vessel, after which coiled tubing well-servicing can proceed in a conventional manner via riser 40.

Another alternative embodiment of the invention includes a support structure that can be substantially flattened for transport and erected for use once the vessel has arrived at the target location. For example, referring to FIGS. 5 and 6, a structure 60 may include a deck 62 supported on a plurality of legs 64 and supporting well-servicing equipment 66 and optional support equipment 68. Legs 64 are lowered or substantially horizontal during transport. Once the vessel has arrived at the target location, structure 60 is erected as indicated by arrow 67 and legs 64 are rotated and locked in a vertical position for well-servicing, which is carried out via riser 40.

Referring now to FIG. 7, still another embodiment of the invention comprises a buoyant platform 70 that is held in place by two or more vessels 72. Each vessel 72 is connected to platform 70 by at least one line 74, and is preferably equipped with a position-maintaining system (not shown).

Platform 70 preferably includes a moon-pool 76 extending therethrough, which provides protected access to the sea from the surface of the platform. A rig 78 is preferably erected over moon-pool 76. Rig 78 can be transported to the well site aboard platform 70, or may be erected after platform 70 is in position. Rig 78 preferably includes standard rig equipment, including systems necessary for performing the desired operation(s). If desired, addition support systems 80 can be provided on one or more of the vessels 72 and connected to the drilling system by flexible lines 82. Once vessels 72 and platform 70 are in position at the target location, the desired operation can be carried out via riser 40.

In each of the embodiments disclosed herein, the rig and/or well-servicing or well intervention equipment can be commercially available units that are preferably provided in a modular or turn-key state. By way of example only, such equipment may include automated pipe handling systems and containerized drilling rigs, such as are commercially available.

Because the subsea well-servicing equipment used in the present invention is modular and can be readily transported and assembled, and because vessel 10 is a vessel of opportunity, use of a system in accordance with the present invention greatly reduces costs and increases flexibility in subsea well servicing operations.

The present modular subsea completion running equipment can be used in combination with a non-dedicated vessel. The present modules are relatively easy to transport to different ports around the world for use on vessels of opportunity. This in turn frees up extremely expensive drilling vessels so that they can be used for drilling, while the vessels of opportunity, at a much lower day rate, can be prepared for optimum completions. Advantageously, a large percentage of the work required to prepare the vessel can be performed in port.

While the present invention has been disclosed and described in terms of preferred embodiments, it will be understood that various modifications can be made thereto without departing from the scope of the claims, which follow. For instance, the support structure can be any suitable structure, including but not limited to any structure that slides, pivots, or can be assembled in a position such that it overhangs the stern or the side of the vessel so as to provide access to a subsea well.

Claims

1. A system for performing a desired subsea well-servicing operation, comprising:

a vessel;

a service apparatus for performing the desired subsea well-servicing operation, said service apparatus being supported on the vessel; and

a support apparatus mounted on the vessel, said support apparatus having first and second modes, wherein in the first mode the support means does not provide access to a well by the service apparatus and wherein in the second mode the support means does provide access to a well by the service apparatus.

2. The system according to claim 1 wherein the vessel is a vessel of opportunity.

3. The system according to claim 1 wherein the vessel is not a drill ship.

4. The system according to claim 1 wherein in the first mode the support apparatus does not support the service apparatus and in the second mode the support apparatus does support the service apparatus.

5. The system according to claim 1 wherein the support apparatus supports the service apparatus in both the first and second modes.

6. The system according to claim 1 wherein in the first mode the support apparatus does not extend over the stern or the side of the vessel and in the second mode the support apparatus does extend over the stern or the side of the vessel.

7. The system according to claim 1 wherein the service apparatus is selected from the group consisting of subsea tree installation apparatus, perforating apparatus, acidizing apparatus, fracturing apparatus, workover apparatus, reservoir stimulation apparatus, wireline apparatus, coiled tubing apparatus, and snubbing apparatus.

8. The system according to claim 1 wherein the support apparatus comprises a support bracket and the service apparatus comprises a rig pivotably mounted on said bracket, wherein the rig is in a horizontal or near-horizontal position during transport, and is rotated into a vertical position after the vessel is at a desired location, and wherein in the vertical position the rig extends off the stern or side of the vessel with sufficient clearance to allow the desired well-servicing operation to be performed.

9. The system according to claim 1 wherein the support apparatus comprises a skid and the service apparatus comprises a coiled tubing system mounted on the skid, wherein the coiled tubing apparatus comprises a coiled tubing injector head, a reel and supporting equipment, and wherein once the vessel is at a desired location, the skid can be moved laterally until the injector head is clear of the vessel.

10. The system according to claim 1 wherein the support apparatus comprises a structure that can be substantially flattened for transport and erected for use once the vessel has arrived at the target location, wherein the service apparatus is mounted on the structure, and wherein when the structure is erected, the service apparatus extends off the stern or side of the vessel with sufficient clearance to allow the desired well-servicing operation to be performed.

11. The system according to claim 1 wherein the vessel is equipped with a position-maintaining devices.

12. A system for performing a desired subsea well-servicing operation, comprising:

at least two vessels; and

a buoyant platform held in place by said vessels, wherein the platform includes a moon-pool extending therethrough and a rig erected over the moon-pool.

13. The system according to claim 12 wherein the vessels are vessels of opportunity.