Off-center running tool for subsea tree

A running tool for lowering a christmas tree to a subsea wellhead. The running tool includes an off center adjustment to compensate for asymmetric weight distribution in the christmas tree. The running tool comprises a main body, latches for coupling the body to the christmas tree, an offset arm connected to the body, and a lift arm (drill pipe adaptor) connected to the lift arm and selectively positioned on the lift arm to offset and compensate for the christmas tree asymmetric weight distribution.

BACKGROUND

1. Field of Invention

The device described herein relates generally to the production of oil and gas. More specifically, the device described herein relates to a running tool with an off center attachment compensating for asymmetric christmas trees.

2. Description of Related Art

Subsea wellhead assemblies are typically used in the production of hydrocarbons extracted from subterranean formations below the seafloor. Subsea wellhead assemblies generally comprise a wellhead housing attached at a wellbore opening, where the wellbore extends through one or more hydrocarbon producing formations. Casing and tubing hangers are landed within the housing for supporting casing and production tubing inserted into the wellbore. The casing lines the wellbore, thereby isolating the wellbore from the surrounding formation. Tubing typically lies concentric within the casing and provides a conduit for producing the hydrocarbons entrained within the formation. Wellhead assemblies also typically include christmas trees connecting to the upper end of the wellhead housing. The christmas trees control and distribute the fluids produced from the wellbore.

The christmas trees are installed onto the wellhead housing by latching a running tool within the tree's main annulus and attaching wire or drill pipe to the running tool for lowering subsea to the wellhead housing. Often the tree's center of gravity is not coincident with the annulus axis; which if uncorrected causes the tree to tilt to prevent properly landing the tree onto the wellhead housing. The asymmetric tree can be balanced with added weights, but weight balancing is limited by the lowering wire and drill pipe structural limits. Additionally, christmas trees are becoming more complex and heavier thereby making weight balancing less desirable. This is exacerbated by subsea well operator using older rigs to install the newer larger and heavier tree systems. As a result the rigs experience difficulty while transferring the trees from supply vessels to the rig.

SUMMARY OF INVENTION

The present disclosure includes a running tool for raising and/or lowering a subsea wellhead member. The running tool may include a tool body having an axis, a latch on the tool body, an offset member attached to the tool body, and a lift arm affixed to the offset member. The lift arm can be selectively offset some distance from the tool axis to accommodate for an asymmetric weight distribution in the subsea wellhead member. The running tool may further comprising a profile on the latch formed for mating engagement with a profile in a bore of the subsea wellhead member. In one embodiment the subsea wellhead member is a christmas tree. The running tool can be lowered on a drill string or a wire connected to the top of the lift arm. The running tool can optionally include a subsea wellhead member pressure testing system. The pressure can be included in an extension disposed on the body bottom and flow nozzles formed on the extension in selective fluid communication with a pressurized fluid source. The pressurized fluid source can communicate to the nozzles via a passage, a fluid line, the lift arm, and drill pipe, where the passage is formed in the body, the fluid line connects the passage to an annulus in the lift arm, and the lift arm annulus openly communicates to an annulus in the drill pipe. The offset member can be an elongate element with its elongate side disposed substantially perpendicular to the body axis. Multiple lift arm attachment locations can be formed along the offset member elongate side.

Also disclosed herein is a running tool for subsea attachment to a subsea wellhead member, the tool comprising, a tool body configured for insertion into a main bore of the subsea wellhead member, the tool body having an axis aligned with the bore axis, a subsea wellhead member latching device attached to the tool body, an elongate offset member attached to the tool body and oriented with its elongate side substantially perpendicular to the tool body axis, and a lift arm mechanically coupled to the offset member selectively positioned along the elongate side of the member based on the center of gravity of the running tool and the subsea wellhead member.

Also included herein is a method of handling a subsea wellhead member, the method includes providing a running tool having a body with an axis, a wellhead member latch on the body, an offset member attached to the body, and a lift arm attached to the offset member, estimating an offset distance from the tool body axis to where the lift arm is attached to the offset member, where attaching the lift arm an offset distance from the tool body axis compensates for asymmetric weight distribution of the subsea wellhead member about its axis, selectively positioning the lift arm on the offset member a distance away from the axis substantially equal to the offset difference, attaching the running tool to the subsea wellhead member, and manipulating the running tool thereby moving the subsea wellhead member with respect to a subsea well to conduct a subsea wellbore operation. The running tool may further comprise a pressure testing system, the method further comprising pressure testing the subsea wellhead member with the pressure testing system. The method can further include deploying a remotely operated vehicle (ROV) proximate to the running tool, and applying pressurized hydraulic fluid to the running tool from the ROV for activating the wellhead member latch.

DETAILED DESCRIPTION OF INVENTION

Disclosed herein is a running tool used in handling subsea wellhead members while submerged subsea, from above the sea surface to the sea floor, or from the sea floor to the sea surface. For the purposes of discussion herein, subsea wellhead members include any wellhead component or any component deployed subsea. Examples include wellbore christmas trees, manifolds, separation devices, and other devices used in subsea hydrocarbon production. The running tool employs an offset compensating for an unequal weight distribution around a subsea wellhead member axis. The offset distance is selectable and can vary based upon the weight distribution of the subsea wellhead member being handled by the running tool.

With reference now toFIG. 1, a perspective view of a front side of an embodiment of a running tool assembly30is provided. The running tool30comprises a main body32, a tool alignment extension38downwardly depending from the body32lower surface, an offset arm60attached on the upper end of the body32, and a lift arm54(drill string adapter). The tool body32as shown is a substantially cylindrical member and configured for insertion into the main bore of a subsea wellhead member. Latching dogs34are provided circumferentially around a portion on the lower end of the body32. The latching dogs34are profiled on their outer surface for mating engagement with similar correspondingly profiled surfaces on the inner circumference of the main bore of a subsea wellhead member.

The tool alignment extension36comprises a substantially cylindrical main body37attached to the lower end of the tool body32and an extension tip38on the lower end of the cylindrical body37. Nozzles40are shown formed through the outer radial surface of the cylindrical main body37. As will be discussed in more detail below, the nozzles40provide a cleaning and pressurizing function. The lower end of the tip38is hemispherically formed for guiding the tool body32into the main bore of a subsea wellhead member.

A substantially planer base plate42is attached to the upper portion of the tool body32and extends largely perpendicular to the tool axis AX. Extending upward from one end of the base plate42is a remote operated vehicle (ROV) panel44. On the panel44are hydraulic connections for supplying hydraulic fluid to the running tool assembly30. The hydraulic fluid may be pressurized and supplied by an ROV. Also included with the panel44are valves actuatable by the ROV, the valves control hydraulic fluid flow to the running tool assembly30via the hydraulic connections. More specifically, a hot stab receptacle48is disposed on a lower end of the panel44. Adjacent the hot stab receptacle48is a parking receptacle50. In the embodiment ofFIG. 1a T-handle52is temporarily inserted into the hot stab receptacle48. As is known, the T-handle52is removable from the hot stab receptacle48by the ROV to allow a hydraulic line connection in the hot stab receptacle48. While a hydraulic line is connected into the hot stab receptacle48, the T-handle52can be parked in the parking receptacle50.

The valves on the upper portion of the panel comprise a lock valve assembly68and a release valve assembly72. Manipulating the lock valve assembly68into the open position supplies pressurized hydraulic fluid to the latching dogs34for extending them into a locking position and attaching to the subsea wellhead member. Similarly, the dogs34can be unlatched or released by operating the release valve assembly72which bleeds the hydraulic fluid from the dogs34. An optional release assembly66is provided with the tool assembly30extending upward from the base plate42onto risers on opposite sides of the offset arm60; a connecting member connects to the terminal ends of the risers. An attachment ring67is provided on the connecting member and for connection and manipulation of the secondary release assembly66.

An optional parking plate56is bolted on the upper portion of the lift arm54. The parking plate56includes an attachment57for connecting unused electrical lines that as a way of stowing them during use of the running tool assembly30. Stowing unused lines or leads on the parking plate56secures the lines and prevents tangling of these lines and protects the lines or other equipment from potential damage. The parking plate56also includes a fixture59for attachment of a hydraulic line (FIG. 5).

With reference now toFIG. 2, the lift arm54is shown attached to the offset arm60by bolts64extending through bolt holes62shown on the lower portion of the lift arm54. The lift arm54is positioned laterally away from the tool body32wherein its axis ALAis an offset distance ODfrom the tool body32axis AX. In one embodiment, the value of the offset distance ODis established to compensate for an asymmetric subsea wellhead member. In one embodiment, an asymmetric subsea wellhead member has an uneven weight distribution with respect to the point where the running tool attaches to the wellhead member. Thus the wellhead member center of gravity is off-center or laterally disposed from the running tool attachment point. For example, when attaching to a wellhead member within its main bore, the attachment point is considered to coincide with the axis of the main bore.FIG. 7schematically depicts force vectors representing the subsea wellhead member weight WCG1and the lifting force LF1applied by the running tool onto the member. The vectors further illustrate an example of the distance between the applied lifting force and the center of gravity. Attaching to the main bore of an asymmetric subsea wellhead member produces a torque or moment arm on the running tool, as signified by the arrow T1.FIG. 8is a schematic comprising force vectors for lifting with a running tool having an offset lifting arm. Force vector LF2denotes the force to lift the running tool and force vector WCG2represents the running tool center of gravity. The distance between the force vectors represents the distance between the lift arm axis and running tool center of gravity. A torque or moment arm results as illustrated by arrow T2.

The subsea wellhead member center of gravity location can be calculated by various known means. Similarly, the location of the combined running tool assembly30with an attached subsea wellhead member center of gravity can also be calculated. Knowing the center of gravity location and associated weight, the offset distance ODcan be calculated to compensate for the aforementioned asymmetric weight distribution. Accounting for or compensating for asymmetric loading creates a second moment arm counter to the moment arm formed between the attachment to the wellhead member bore and its center of gravity. These two moment arms are in opposite directions, and if in the same magnitude, the moment arms will cancel. This can remove weight distribution tilt and thus eliminating the need to add balancing weights.FIG. 9schematically illustrates a lifting force vector LF3, its resulting moment arm TL, the combined weight force WCG3of the running tool and asymmetric wellhead member applied along the combination's center of gravity, and the moment arm TWbetween the weight and its lift point.

As noted above, the nozzles40on the cylindrical portion of the alignment extension36selectively discharge pressurized fluid. In one embodiment, the pressurized fluid is delivered to the running tool30from inside of an attached drill pipe and through the annulus of the lift arm54. Fluid lines58are shown extending from the side of the lift arm54and to the upper portion of the body of the tool32. Passages (not shown) are formed through the tool body and in fluid communication with the nozzles40. Selectively delivering pressurized fluid to the nozzles40through this fluid supply system can be used for clearing debris from adjacent a subsea wellbore member prior to attaching the running tool assembly30to the member. The pressurized fluid can also pressurize the inner workings of a subsea wellbore member for pressure testing the member and confirming member seal integrity. The pressure testing feature of the running tool assembly30is not limited to asymmetrically loaded subsea members, but can be performed on any device deployed using the running tool assembly30. Accordingly, the running tool assembly30can be used for handling subsea wellhead members that are substantially symmetric and do not require an offset. In this situation, the lift54would be attached along or proximate to the running tool assembly30center of gravity.

With reference now toFIG. 3, a full side view of an embodiment of the running tool assembly30is illustrated. This view displays the front of the lock valve assembly68and release valve assembly72. More specifically, disposed within the lock valve assembly68is a lock valve actuator fitting70having a fitting profiled for manipulation manually or with an ROV. Similarly, the release valve assembly72includes a release valve actuator fitting74also profiled for manual or ROV manipulation.FIG. 4is a rear view of an embodiment of the running tool assembly30depicting a side view of an example of the release valve assembly72. Additionally, optional weights46are shown stacked on an edge of the face plate42to provide balancing of the running tool assembly30.

FIG. 6provides in side view an example of deployment or handling of a subsea wellhead member using the running tool assembly30as described herein. In the embodiment shown, the subsea wellhead member comprises a christmas tree78. The christmas tree78has a main bore82formed through the body of the tree78. Dogs34on the running tool assembly30are shown extended outward into latching engagement with a profile80formed on the inner circumference at the bore82. In this example of use, the running tool assembly30is attached to a drill string76on the upper end of the lift arm54. The christmas tree78includes an offset element84on one side, thereby contributing to an asymmetric weight distribution that offsetts the tree78center of gravity from the bore axis AB.

The lift arm has been selectively positioned at an offset distance from the axis of the bore ABto compensate for the asymmetric weight distribution. It should be pointed out that in this configuration the bore axis ABand the tool body axis AXsubstantially coincide. Selectively positioning the lift arm on the offset member60compensates for the tree78asymmetric weight distribution. The compensation eliminates christmas tree78tilting when being handled by the running tool assembly30. Additionally, an ROV90is shown attached to a control line92and with an ROV arm94extending from the ROV90. As is known, the ROV90can be used for manipulating the valve assemblies (68,72) and delivering hydraulic flow through the hot stab48. A wellhead86is shown below the tree78on a sea bed88. Thus, the operation illustrated inFIG. 6can comprise installation of the tree78on the remaining portions of the wellhead assembly, or removal of the tree for maintenance or repair of the tree78. In the embodiment ofFIG. 6, the axis of the lift line ALAis largely aligned with the center of gravity CGof the combination christmas tree78and running tool assembly30.

In one optional mode of operation, the running tool assembly30can be secured within a subsea wellbore member, such as a christmas tree, during assembly of the wellbore member. This may be done with or without a choke module installed in the bore of the member. Accordingly, the running tool assembly30can be left on the wellhead member until assembly of the member is complete and after it has been installed on a subsea wellhead.

One of the many advantages provided by using the device described herein is reduction of counterweights, which eases the difficulty of older rigs handling heavier newer trees mentioned above. The reduced weight enhances rig safety and reduces the time required for landing operations.

It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. For example, in one optional embodiment, the device could be operated by a surface manipulated umbilical without the need for a remotely operated vehicle.