Embodiments of the present disclosure relate to the field of offshore drilling operations and, more particularly, to a system and method for rapid disconnection of the drilling riser of a floating drilling platform in the event of oncoming sea ice, icebergs or other hazards.
This section is intended to introduce various aspects of the art, which may be associated with some embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Offshore wells supporting oil and gas activities in arctic regions may be drilled from a bottom-founded platform up to a water depth of about 100 m. Beyond this water depth, a floating vessel or platform is needed to drill such wells. A floating drilling platform connected to the seabed by a conventional drilling riser system is depicted in
As understood by those skilled in the art, while drilling a well, a floating platform 101 is kept on station by a station-keeping system. In the
In arctic offshore areas, ice is expected to drift across the drilling location for a large part of the year, or even throughout the year, imparting heavy ice loads on the drilling platform 101. In severe ice conditions, these loads can frequently exceed the capacity of the platform's mooring system. To ensure that the mooring lines 113 and the drilling riser 121 are not damaged in such conditions, one approach is to safely suspend operations, retrieve the riser and disconnect the mooring buoy, and reconnect them again when the ice conditions improve. While the mooring is disconnected the platform 101 may drift away from the drilling location under the action of the drifting ice. This is depicted in
Because of the expected high number of such disconnections and reconnections, these actions have to be performed rapidly. One known technique for rapid disconnection and reconnection of the mooring system of a platform 101 is to have all mooring lines 113 connected to mooring buoy 111. Such a configuration typically leads to a quick disconnection or reconnection of the platform 101 from its mooring system—typically of the order of a fraction of an hour.
When it is necessary to disconnect the mooring system from the platform 101, the buoy 111 carrying the mooring lines 113 is released from the hull 109 through the operation of locking mechanisms 119. The disconnection operations of such a system require a much shorter time than it would if the mooring lines had to be disconnected individually. The same is true for the reconnection: the buoy 111 is pulled back in position within the hull 109 of the platform 101 and mechanically locked there with locking mechanisms 119. As known by those skilled in the art, the buoy 111 is designed to float after disconnection at a depth sufficient to avoid contact with any ice features drifting overhead, i.e., keels of sea ice ridges or icebergs.
In the case of a drilling platform 101 so equipped with a mooring buoy 111, the marine drilling riser 121 connecting the main body of the platform to the wellhead is routed through an opening in the middle of the mooring buoy 111 called a moon pool 129. This means that before the mooring buoy 111 can be disconnected so that the platform 101 can be relocated, it is necessary to disconnect the riser 121 at the LMRP 125 above the BOP 127 and retrieve the riser to the platform 101 in order to clear the mooring buoy 111, as shown in
Otherwise there would be interference between the drilling riser 121 and the mooring buoy 111, likely to result in damage to both. An example of such an instance is depicted in
It should be noted that unlike compliant non-vertical oil and gas production risers, whose compliance allows them to be connected directly to the buoy and move with the buoy as the latter is dropping in the water column when disconnected, vertical marine drilling risers 121 are normally tensioned using a riser tensioner 133 acting between the deck 107 of the platform 101 and the lower barrel of a telescopic joint (one of top joints 131). Compliance in the tensioned riser 121 would cause it to buckle and be damaged as buoy 111 is dropped, particularly if there is clashing between the buoy 111 and riser 121.
However, pulling the entire drilling riser 121 up to the deck 107 of the platform 101 takes a considerable amount of time, because the riser 121 has to be disassembled joint-by-joint as it is being pulled up and set back on the platform. As an example, in a water depth of 1000 m, it is estimated that the operation of pulling a drilling riser up to the platform would take approximately 20-30 hours, a much longer time than that required to disconnect the mooring buoy under severe ice conditions. A similarly long time would be needed to redeploy the riser 121 after reconnecting the mooring buoy 111. Thus a clear need exists for a method and/or system that would significantly shorten the time needed to ensure no interference between the mooring buoy and the drilling riser during a disconnection operation.
A potential solution for avoiding the need to pull the entire riser 121 up to the main body of the platform 101 and avoiding interference with the mooring buoy 111 during disconnection is to split the riser into a lower part 401 and an upper part 403, as shown in
During a disconnection, the upper part 403 of the riser is disconnected from the lower part 401 and then retrieved and stowed in the platform 101 as depicted in
Further, even if the resting depth of the mooring buoy is above the top of the lower part of the riser, there is potential for interference between the mooring line 113 and the lower part of the riser 401 and/or the buoyancy can 405 during disconnection. The potential interference may occur when the disconnection occurs with the platform 101 at a significant offset from the wellhead. This example is illustrated in
Thus, there is a need for improvement in this field.
The present disclosure provides a system and method for rapid disconnection of a drilling riser.
One embodiment of the present disclosure is a method for disconnecting a drilling riser of a floating drilling platform, the floating drilling platform having a mooring buoy connected to a seabed, the method comprising: disconnecting the drilling riser from a subsea component engaged to the seabed; attaching the mooring buoy to the drilling riser; and releasing the mooring buoy and the attached drilling riser from the drilling platform.
The foregoing has broadly outlined the features of one embodiment of the present disclosure in order that the detailed description that follows may be better understood. Additional features and embodiments will also be described herein.
The present invention and its advantages will be better understood by referring to the following detailed description and the attached drawings.
It should be noted that the figures are merely examples of several embodiments of the present invention and no limitations on the scope of the present invention are intended thereby. Further, the figures are generally not drawn to scale, but are drafted for purposes of convenience and clarity in illustrating various aspects of certain embodiments of the invention.
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity.
Embodiments of the present disclosure provide a solution to the problem of reducing the time needed to retrieve a drilling riser in order to move the drilling platform and avoiding interference between the riser and a mooring buoy when the latter is disconnected from the drilling platform.
The flowchart of
At block 703, a portion of the riser joints comprising the drilling riser are retrieved. In some embodiments, a diverter, flex joint, telescopic joint and/or a plurality of other riser joints may be retrieved. The number of riser joints retrieved may be based on a variety of factors, such as, but not limited to, environmental conditions, ice conditions, the height of the BOP and the mooring system.
At block 705, the remaining riser is clamped to the mooring buoy. A variety of mechanisms may be utilized to attach the drilling riser to the mooring buoy. Two embodiments of the present disclosure are provided herein below. Once the mooring buoy and riser are connected, the mooring buoy and riser combination may be released into the water column (block 707). In one embodiment, the number of joints removed from the riser in block 703 is predicated upon allowing the mooring buoy and riser combination to drop to a depth sufficient to avoid contact with the icebergs or other ice or hazardous features drifting overhead, while also providing sufficient clearance between the lowest part of the riser and any subsea equipment provided near the drill site.
It is important to note that the blocks depicted in
Like
As depicted, a drilling riser 803 connects the platform 101 to the head of a well, which includes BOP 127 positioned at the seabed 117, via a connector included in a LMRP 125. Riser 803 is comprised of several, individual riser joints 805. According to one embodiment of the present disclosure, riser joints 805 may include connection mechanisms which enable a firm engagement between the riser joint 805 and the riser clamp 801 when the riser clamp 801 is deployed or engaged. In one embodiment of the present disclosure, drilling riser 803 is a conventional drilling riser, such as, but not limited to, a top-tensioned drilling riser. In the embodiment depicted in
As described herein, there are conditions in which a drilling platform must move in order to avoid damage due to the action of the ice or other hazards.
Next, the locking mechanisms 119 of the mooring buoy 807 may be released thereby causing the buoy 807 and remaining riser portion 1001 to drop in the water 103.
The time required for disconnection of a marine riser according to embodiments of the present disclosure is the time required to retrieve a plurality joints at the top of the riser plus the time needed to release the buoy. However, the time required when utilizing embodiments of the present disclosure is significantly shorter than the overall time to disconnect and retrieve the entire riser. It is estimated that the time to disconnect the riser at the LMRP, retrieve a plurality of top joints to the platform, clamp the remaining riser portion to the mooring buoy and release the mooring buoy is of the order of 3 hours, much shorter than the estimated 20-hour time needed to disconnect and retrieve the entire riser in a water depth of 1000 m. Without embodiments of the present disclosure, the arrival of ice conditions capable of applying ice loads on the drilling vessel exceeding the mooring capacity would need to be forecasted 17 hours earlier than when embodiments of the present disclosure are utilized. The reduced window falls within existing ice detection, monitoring and forecasting capabilities, while the 20 hour window exceeds such capabilities.
Though not depicted (while maintaining use the reference numerals provided in
According to embodiments of the present disclosure, the mooring buoy is equipped with a clamp system for holding the riser. In some embodiments, the system consists of struts that span from the buoy and attach to the riser.
In order to allow engagement with mating member 1207, riser joint 1209 is equipped with engagement members 1211. In one embodiment, engagement members 1211 are a pair of conical mating surfaces welded to riser joint 1209. In the depicted embodiment, impact pads 1213 are placed on engagement members 1211 in order to dampen the impact between mating member 1207 and engagement members 1211 when they engage after strut 1205 has been deployed. In other embodiment, impact pads may be affixed to the mating member. In one embodiment, strut 1205 is equipped with springs and/or hydraulic cylinders. In one embodiment, the clamp is deployed by releasing the springs and/or operating the hydraulic cylinders within strut 1205.
In the embodiment in which strut 1205 utilizes springs, the springs are compressed in order to put the mating member 1205 in a retracted position. Mating member 1207 is positioned closer to frame 1203 in its retracted position as compared to its deployed position. In the retracted position, mating member 1207 is positioned away from riser joint 1209 in order to allow engagement members 1211 to pass vertically by without any interference.
In one embodiment, when the riser needs to be attached to mooring buoy 801 for disconnection of the latter, the springs of strut 1205 are released and the mating member 1207 engages engagement members 1211 of riser joint 1209, thus firmly attaching the remaining riser to the buoy 807. In other embodiments, the hydraulic cylinders of strut 1205 are operated to move mating member 1207 between a retracted and deployed position. In the
As more clearly demonstrated in
The following lettered paragraphs represent non-exclusive ways of describing embodiments of the present disclosure.
A. A method for disconnecting a drilling riser of a floating drilling platform, the floating drilling platform having a mooring buoy connected to a seabed, the method comprising: disconnecting the drilling riser from a subsea component engaged to the seabed; attaching the mooring buoy to the drilling riser; and releasing the mooring buoy and the attached drilling riser from the drilling platform.
A1. The method of paragraph A1 further comprising retrieving a first number of riser joints, wherein before disconnection from the subsea component the drilling riser is comprised of a second number of riser joints, the first number of riser joints is less than the second number of riser joints.
A2. The method of any preceding paragraph, wherein the subsea component is a blowout preventer.
A3. The method of any preceding paragraph, wherein the mooring buoy is attached to the drilling riser by releasing a compression clamp.
A4. The method of paragraph A3, wherein the compression clamp comprises a strut extending from the mooring buoy to a riser joint and a mating member which engages a pair of conical surfaces affixed to the riser joint when the compression clamp is released.
A5. The method of paragraph A1, A2 or A3, wherein the mooring buoy is attached to the drilling riser by connecting a tension strut to a riser joint and the mooring buoy.
A6. The method of paragraph A5 further comprising adjusting a turnbuckle operatively connected to the tension strut in order to tighten the tension strut.
A7. The method of any preceding paragraph, wherein the mooring buoy has a moon pool and the drilling riser is positioned within the moon pool.
B. A system for disconnecting a drilling riser from a floating drilling platform, the system comprising: a mooring buoy releasably connected to a hull of the floating drilling platform by at least one buoy locking mechanism, the mooring buoy is connected to a seabed by a plurality of mooring lines; and a clamp system attached to an exterior surface of the mooring buoy, wherein the clamp system has a disengaged position which allows the drilling riser to freely move relative to the mooring buoy, the clamp system has an engaged position which prevents the drilling riser to freely move relative to the mooring buoy, the clamp system is constructed and arranged to maintain the engaged position after the mooring buoy has been released from the hull of the floating drilling platform.
B1. The system of paragraph B, wherein the clamp system comprises a compression clamp.
B2. The system of paragraph B1, wherein the compression clamp comprises a strut connected on a first end to a frame which is affixed to the mooring buoy and a mating member attached to a second end of the strut, wherein the mating member is constructed and arranged to engage a pair of conical surfaces affixed to a riser joint when the clamp system is in the engaged position.
B3. The system of paragraph B1, wherein an impact pad is attached to the interior surface of at least one of the conical surfaces.
B4. The system of any preceding paragraph, wherein the strut is hydraulically operated.
B5. The system of any preceding paragraph, wherein the strut is equipped with springs.
B6. The system of paragraph B, wherein the clamp system comprises a buoy attachment affixed to the mooring buoy, a riser attachment affixed to a riser joint, and a tension strut constructed and arranged to attach to the buoy attachment and the riser attachment when the clamp system is in the engaged position.
B7. The system of paragraph B6, wherein the tension strut comprises a turnbuckle operatively connected to the tension strut.
B8. The system of any preceding paragraph, wherein the mooring buoy has a moon pool and the drilling riser is positioned within the moon pool.
It should be understood that the preceding is merely a detailed description of specific embodiments of this invention and that numerous changes, modifications, and alternatives to the disclosed embodiments can be made in accordance with the disclosure here without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents. It is also contemplated that structures and features embodied in the present examples can be altered, rearranged, substituted, deleted, duplicated, combined, or added to each other. The articles “the”, “a” and “an” are not necessarily limited to mean only one, but rather are inclusive and open ended so as to include, optionally, multiple such elements.
This application claims the benefit of U.S. Provisional Patent Application 61/745,128 filed 21 Dec. 2012 entitled SYSTEM AND METHOD RAPID DISCONNECTION OF THE DRILLING RISER OF A FLOATING DRILLING PLATFORM, the entirety of which is incorporated by reference herein.
Filing Document | Filing Date | Country | Kind |
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PCT/US2013/071516 | 11/22/2013 | WO | 00 |
Number | Date | Country | |
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61745128 | Dec 2012 | US |