The invention relates to an apparatus for performing a shear connection between a riser and a Lower Marine Riser Package (LMRP) in a well for pro- ducing and/or enhancing the production of oil and/or gas, where the shear connection comprises first receiver means and second receiver means, which first and second receiver means are held together by shearable means that shears when a certain force is exceeded. The invention is intended for drilling operations through a subsea wellhead system located at the seafloor from a floating type drilling vessel in shallow water.

When connecting a riser and a blow out preventer (BOP) system to a subsea wellhead, the common procedure is to connect the lowermost joint of riser to the combined lower marine riser package (LMRP) and blow out preventer (BOP), then sequentially lower the BOP to the seafloor with the riser by sequentially connecting additional riser joints as required. When such an assembly are going to be moved from one well to another for example, the BOP is disconnected from the subsea well and raised together with the riser to the surface of the sea. During the raising of the riser, the riser must be disassembled as it is raised, and when the BOP is recovered together with the lowermost part of the riser, along with conducting routine maintenance the BOP must be tested before using it on another subsea well drilling operation.

When conducting drilling operations from a floating type drilling vessel, a system is required to have functional capability disconnect the riser from the BOP. Such functionality is utilized when an unanticipated situation occurs requiring the vessel and riser to be separated from the well, while retaining the BOP on the well thereby containing the well and preventing uncontrolled flow of the well into the environment. This functionally is provided by a hydraulic connector with the functioning female portion attached to the LMRP and the male mandrel attached to the BOP. If floating drilling operations are conducted from a drilling vessel that is maintained on location through the exclusive use of a thruster propulsion system of the vessel, typically referred to as dynamic positioning (DP), the riser disconnect system must successfully operate in a very short period of time with multiple functions automatically sequenced upon initiation. Such systems are typically referred to as Emergency Disconnect Systems (EDS).

To date, shallow drilling operations have been conducted by bottom supported drilling units of various types or floating drilling rigs maintained on location with redundant chain or steel wire/rope mooring systems. DP floating drilling operations supported by rapid emergency disconnect systems are typically utilized in deeper water depths that exceed the capabilities of more economical bottom supported or moored units. Specialized shallow water applications are possible where moored or bottom supported units are less desirable. As example of such specialized shallow water application would be to conduct drilling operation in close proximity to the arctic sheet ice. Rigs that are not highly specialized and designed to operate within arctic sheet ice conditions must be moved prior to the sheet ice reaching the drilling location. As both bottom supported and moored floating drilling rigs require considerable time to move off location and the movement of the sheet ice is difficult to accurately predict, a DP vessel equipped with a emergency disconnect system has potential of being a preferred option due to the significantly increased seasonal window of allowable operations.

A geometry of a riser tensioning system that accommodates both nominal amounts of vertical and lateral vessel movements additionally governs a maximum excursion a vessel can deviate from location before an emergency disconnect sequence must be completed. Due to this geometry, at shallower water depth an allowable excursion distance becomes smaller. When considering failure of a DP system, this allowable excursion distance also directly equates to a finite period of time. Existing emergency disconnect systems that utilize a series of complex hydraulic sequenced functions do not successfully operate within a time constraints required for shallow water drilling operations.

From WO 2006/033580 A1 a safety joint is known. This safety joint is related to a riser consisting of two telescoping parts that are arranged t break in the event of a predetermined axial tension load. The safety joint further provided with a bending limiter why it is not able to act on torsional or bending forces.

The invention utilizes the mechanical forces exerted by the vessel such as increased tension within the riser, as the vessel exceeds the allowable excursion envelope, to cause the shear connection to release and thereby separate the riser from the LMRP at a predetermined value of force caused by riser tension. The invention eliminates time dependency of the emergency disconnect sequence and enables use of DP vessels for shallow water drill- ing operations.

NOVEL TECHNIQUE

This is achieved by the invention in that the shearable means connects the first and second receiver means which receiver means engages in a plane substantially perpendicular to a longitudinal axis of the riser and the BOP.

In an embodiment the shearable means are positioned substantially parallel to the longitudinal axis of the riser and the BOP. In an embodiment the first receiver means is located at the lowermost end of the riser and the second receiver means is located at the upper part of the of the lower marine riser package (LMRP). In a further embodiment the shearable means can be bolts, bolting the shear connection together. The bolts can be threaded.

In other embodiments the shearable means can be shearable wire members, shearable pins connecting the first and second receiver means through joint bars or the like.

The shear connection can be situated in a first riser connection joint above a typical point of disconnect between the LMRP and BOP. In an embodiment of the invention, subsea control system pods (8, 9) are mounted above a conventional LMPR hydraulic connector but below the shear connection being the lower marine riser package side of the shear connection. When the riser is separated from the BOP using the shear connection point, the hydraulic control pods remain with the BOP system con- nected to the well.

In further an embodiment an intermediate junction point is located on a control cable at a point close to, but above the shear connection, which cable connects the blow out preventer (BOP) with a vessel surface control system.

In another embodiment the control cable can be provided with weak points that will separate through tensile failure without damaging end connection points. The weak points on the control cable can be situated substantially at the same level as the shear connection. I yet an embodiment the weak points are designed such that the necessary load to provide tensile failure of the weak points is less than the load required for the shear connection to separate. In the following different embodiments of the invention is described with reference to the drawings, where figure 1 shows a shear connection where the riser is connected to the lower marine riser package (LMRP), and figure 2 shows the riser and control cables after a disconnection of the shear connection.

Hereafter different embodiments of the invention are described I detail.

The invention shows a shear connection 1 where a riser 2 is connected to a lower marine riser package (LMRP) 3 through first receiver means 4 and second receiver means 5. The first receiver means can be located at the lowermost end of the riser 2 and the second receiver means can be located at the upper part of the lower marine riser package (LMRP) 3. The first and second receiver means 4, 5 are connected or secured to each other by shearable means (not shown). The shearable means can be bolts, bolting the shear connection together. The bolts can be threaded. The shearable means connects the first 4 and second 5 receiver means which receiver means 4, 5 engages in a plane substantially perpendicular to a longitudinal axis of the riser 2 and the lower marine riser package (LMRP) 13. In an embodiment the shearable means are positioned substantially parallel to the longitudinal axis of the riser 2 and the lower marine riser package (LMRP) 13. The receiver means can have different configurations, but will engage to each other in a plane substantial perpendicular to the longitudinal axis of the riser 2 and the lower marine riser package (LMRP) 3.

In an embodiment the receiver means can be provided with flanges and the shearing means can be mounted to secure the flanges to each other.

When joining the receiver means 4, 5 in a plane substantially perpendicular to a longitudinal axis of the riser 2 and the lower marine riser package (LMRP) 13 the shearing means can react on forces relating to torsion, dis- placement and bending of the riser 2 in relation to the LMRP 3.

In other embodiments the shearable means can be shearable wire members, shearable pins connecting the first 4 and second 5 receiver means through joint bars or the like.

The LMRP 3 is connected to a blow out preventer (BOP) 13 by a hydraulic connector 12 through connecting means 6, 7.

The shear connection 1 can be situated in a riser connection joint above a typical point of disconnect between the LMRP 3 and the blow out preventer (BOP) 13.

In an embodiment of the invention, subsea control system pods 8, 9 are mounted above a conventional LMPR hydraulic connector 12 but below the shear connection 1 being the lower marine riser package side 3 of the shear connection 1 . When the riser 2 is separated from the BOP 13 using the shear connection point 1 , the control pods 8, 9, which can be hydraulic, pneumatic or electrical energized remain with the BOP system 13 connected to the well.

In further an embodiment an intermediate junction point 14 is located on a control cable 10, 1 1 at a point close to, but above the shear connection 1 , which cable connects the blow out preventer (BOP) with a vessel surface control system. In an embodiment the system can be provided with more than one intermediate junction point 14 and more than one control cable 10, 1 1 .

In another embodiment the control cable 10, 1 1 can be provided with weak points (not shown) that will separate through tensile failure without damaging end connection points. The weak points on the control cable 10, 1 1 can be situated substantially at the same level as the shear connection 1 .

I yet an embodiment the weak points are designed such that the necessary load to provide tensile failure of the weak points is less than the load required for the shear connection 1 to separate.

When the control pods 8, 9 are disconnected from the riser 2, they contain both stored hydraulic and electrical power sufficient to complete all time dependent ram and valve functioning required to safely secure the wellbore. Modern computerized control systems currently include programming to complete this sequencing automatically in the event of loss of signal from the drilling vessel. When utilized in conjunction with this invention and the riser 2 is separated from the BOP 13 using the instantaneous shear connection 1 , the functioning BOP control pods 8, 9 remain with the BOP 13 allowing the full time dependent hydraulic closure sequence to be conducted after the riser 2 has separated from the BOP 13. In a further embodiment the BOP 13 is installed and retrieved using a heavy lift heave compensated crane located on the drilling vessel (not shown). Eliminating the BOP 13 running and retrieval loads from the riser 2 and shear connection 1 allows the design shear load to be set at a relatively low ten- sion. Additionally the load ratings of the riser 2 and tensioning system designed for alternative deepwater application are only subjected to a small percentage of connected operational loads when used in shallow water. The tension loads under which the shearable means in the shear connection 1 are designed to separate through tensile failure, can be designed and set to a small fraction of the design load of the system. The total load needed to cause the shear connection 1 to separate can therefore be well within the loads created by the vessel if it were to drift off location following a failure of the DP system. In a further embodiment multiplex control and power cables that connect the BOP 13 to a control and power system located on the vessel are additionally connected to an intermediate junction point 14 located above the shear connection 1 . Short length multiplex control cables 10, 1 1 run between this junction point 14 with the ends connected to the BOP control pods 8, 9 are further designed with engineered weak points that will separate through tensile failure without damaging end connection points. The loads required to cause these junction multiplex control cables 10, 1 1 to separate will only be a small fraction of the load required for the shear connection 1 to separate. Upon separation of the jumper section of multiplex cables 10, 1 1 , communication between the control pods 8, 9 and the surface control system is lost automatically initiating the BOP ram and valve sequence cycle required to secure and seal the well.

In a further embodiment the methodology is to restore the system following a loss of station event and riser separation using the shear connection. Following such an event, the short length or riser required for shallow water opera- tion is retrieved to the surface. The lowermost joint, the bottom of which contains the upper connection of the shear connection 1 is additionally retrieved to surface. The shearable means are removed and discarded. Once the issues causing the loss of station event are resolved and the vessel is again positioned on location utilizing the DP system, the lower portion of the shear connection 1 is retrieved with the LMRP 3 utilizing a heavy lift heave compensated crane with the BOP 13 remaining connected to the wellhead and securing the well against flowing. The LMPR 3 is disconnected from the BOP 13 with hydraulic fluid provided from a Remote Operated Vehicle (ROV). Once the LMRP 3 has been recovered to surface, the failed shearable means are removed from an upper flange or second receiver means 5 of the shear connection 1 and discarded. Both sections of the parted multiplex control and power cable 10, 1 1 are removed from each respective terminal and discarded. The first receiver means 4 of the lowermost riser joint 2 is then secured to the LMPR 3 using new shearable means. New jumper multiplex cables 10, 1 1 are installed between the intermediate junction point 14 above the shear connection 1 and each respective control pods 8, 9. The LMRP 3 is then run and connected to the BOP 13 reestablishing the functional subsea drilling system.

In an embodiment where the shearable means is shearable bolts, the head portion of the failed bolts that are mechanically retained within the upper flange of a shearable bolted connection are removed and discarded. Once the issues causing the loss of station event are resolved and the vessel is again positioned on location utilizing the DP system, the lower portion of the shearable bolted connection is retrieved with the LMRP 3 utilizing the heavy lift heave compensated crane with the BOP 13 remaining connected to the wellhead and securing the well against flowing. The LMPR 3 is disconnected from the BOP 13 with hydraulic fluid provided from a Remote Operated Vehi- cle (ROV). Once the LMRP 3 has been recovered to surface, the threaded portion of the failed shearable bolts are removed from the upper flange of the shearable bolted connection and discarded. Both sections of the parted multiplex control and power cable 10, 1 1 are removed from each respective terminal and discarded. The first receiver means 4 of the lowermost riser joint 2 is then bolted to the LMPR 3 using new shearable bolts. New short jumper multiplex cables 10, 1 1 are installed between the intermediate junction point 14 above the shearable bolted connection 1 and each respective control pods 8, 9. The LMRP 3 is then run and connected to the BOP 13 reestablishing the functional subsea drilling system. Although the invention is intended for drilling operations through a subsea wellhead system located at the seafloor from a floating type drilling vessel in shallow water, the invention can be amended to be used in relation to deep sea drilling.