GB2586948A

GB2586948A - Riser monitoring using distributed sensing

Info

Publication number: GB2586948A
Application number: GB1907870.8A
Authority: GB
Inventors: Head Philip
Original assignee: Enteq Upstream PLC
Current assignee: Enteq Upstream PLC
Priority date: 2019-06-03
Filing date: 2019-06-03
Publication date: 2021-03-17
Also published as: GB201907870D0

Abstract

A riser monitoring assembly to monitor and manage a riser extending between subsea well equipment and a floating vessel comprises a first fibre optic cable 30 terminating in an upper communication and sensor pod attached to the upper BOP stack. The communication and sensor pod is in real time communication with a lower communication and sensor pod which is connected to sensors. The fibre optic cable may be a distributed fibre optic sensor. A second fibre optic cable can be positioned at 180 degrees opposite the first fibre optic cable to provide distributed strain measurement of the riser. Standard choke and kill line passages 9, 10 can be used as conduits for the fibre optic monitoring and communication cables 30 providing permanent distributed sensing of the riser. Alternatively, the fibre optic cables can be spaced inside or outside the riser. The lower communication and sensor pod connected to sensors monitor parameters of a flex joint, the internal pressure of the riser, events occurring inside the riser, and the status of well control hardware fitted to the BOP stack. Gyroscope, inclinometer and or accelerometers can be mounted to the lower riser package and adjacent the top of the riser.

Description

Riser monitoring using distributed sensing This invention relates to riser management systems. More particularly, this 5 invention relates to a system, an apparatus, and related methods for sensing riser dynamics.

Brief Description of the Related Art

A problem presented by offshore hydrocarbon drilling and producing operations conducted from a floating platform or vessel is the need to establish a sealed fluid pathway between each borehole or well at the ocean floor and the work deck of the vessel at the ocean surface. This sealed fluid pathway is typically provided by a drilling riser system. Drilling risers, which are utilized for offshore drilling, extend from the drilling rig to a blowout preventer (BOP) and Lower Marine Riser Package (LMRP), which connect to a subsea wellhead. Production risers extend from a surface vessel to a subsea wellhead system.

The drilling riser, for example, is typically installed directly from a drilling derrick on the platform of the vessel by connecting a series of riser joints connected together. After connecting the riser to the subsea wellhead on the seabed, the riser is tensioned by buoyancy cans or deck mounted tensioner systems. The riser is projected up through an opening referred to as a moon pool in the vessel to working equipment and connections proximate an operational floor on the vessel. In drilling operations, the drill string extends through a drilling riser, the drilling riser serving to protect the drill string and to provide a return pathway outside the drill string for drilling fluids.

In producing operations, a production riser is used to provide a pathway for the transmission of oil and gas to the work deck. Basic components of a riser system typically also include a tensioning system designed to provide lateral load resistance while providing a somewhat constant vertical tension. The tension is normally applied to a tensioning ring attached to the top of the riser and below a telescopic joint. A diverter seals around the drill pipe and diverts gas and drilling returns away from the drill floor. A slip or telescopic joint is designed to decouple the vessel and riser from vertical motions and maintain an integral seal for the riser pipe. A ball or flex joint provides a pinned connection to reduce the transmission of bending moments in the riser caused by a misalignment between the joints. Riser connectors are made up of sections typically bolted together with flanged connections, each section being typically from 60-90 feet in length. Each section typically has a central riser pipe that is normally about 18-24 inches in diameter. Buoyancy devices are typically provided to reduce tensioning requirements, mainly in deep water conditions where the top tension required is greater than the available tensioning capacity.

Various subsea equipment is located on the seafloor. The subsea equipment associated with a drilling riser might include a flex/ball joint. the BOP/LMRP. the wellhead, and a wellhead conductor. The BOP/LMRP typically includes valves and sensors controlled by a BOP/LMRP controller which is connected to the surface via an umbilical cord which includes a data conductor. The umbilical cord can be positioned between the BOP/LMRP controller or other subsea equipment and a computer or controller remotely positioned on a deployment platform of the vessel. An umbilical spool can, in turn, be positioned on the deployment platform for readily storing and deploying the umbilical cord.

Other more specialized riser equipment includes a fill-up valve designed to prevent collapse of the riser pipe due to the differential pressure between the inside of the riser pipe and the surrounding water, an instrument riser joint typically used to monitor the tension and bending due to environmental conditions which allows for adjustment in top tension and vessel positioning, vortex suppression equipment which help suppress vortex induced vibrations typically found in conditions of high current and long riser length, and an emergency riser release which provides a specialized riser release system to prevent catastrophic failure typically found in conditions where incorrect vessel positioning or extreme environmental conditions may occur.

IS

The riser has design requirements that include operation and/or survival in extreme conditions in both connected and disconnected modes. Deep water applications, especially, require close attention to the vertical dynamics of the riser. This generally requires an active riser management program. One goal of riser management is to determine the tension/buoyancy requirements and the operating limits based on a combination of the environmental parameters, the vessel capability, the drilling program (for drilling risers), and the operational constraints. Another goal or series of goals for both drilling and production risers is to manage stresses and loading of individual riser sections to provide for fatigue analysis and thus allow the operator to formulate an enhanced inspection, maintenance, and riser section rotation program. The environmental parameters include, among other things, wave height and period, water depth, current, wind, and tides. The vessel capability includes tensioning capacity, physical interface geometry, and vessel motion characteristics in terms of Response Amplitude Operator (RAO). The drilling program includes riser joint configuration, mud weights, and placement of components. The operational constraints to be considered are drilling modes, upper and lower displacements and forces, combined stresses, and tensioner losses.

The normal modes encountered in offshore drilling operations, for example, include normal or drilling mode, suspended or connected and non-drilling, and hang-off or disconnected mode. The drilling mode is that combination of environmental and well conditions in which normal drilling activities can be safely conducted. The connected and non-drilling mode is the mode when only circulating and tripping out drill pipe is conducted. The disconnect mode is when environmental conditions exceed the limits for safe operation in the connected and non-drilling mode and require the riser to be disconnected to prevent possible damage to surface or subsea equipment.

The loading on both drilling and production risers include internal and external hydrostatic pressures generated by the drilling mud and sea water, weights or buoyant forces generated by auxiliary components, and wave and current actions. The hydrodynamic forces generated by the waves can be based on a regular wave or a wave spectrum. The hydrodynamic forces generated by the current are calculated based on Morrison's Equation using the shape, roughness, Reynolds number, Keulegan-Carpenter Number, and orientation of auxiliary equipment. Standard values of drag and inertial coefficients have been developed. Loading on the riser system can additionally be generated by vortex shedding generated by the current, resulting in vortex induced vibration (VIV). VIV can be generated either in-line or cross-flow, and can induce high stresses if the shedding frequency matches the natural frequency of the riser.

Mathematical methods for the solution of the complex loading and motion in the riser are based on static, frequency domain, and time domain solution techniques. The static solution does not take into account any dynamics and is not as accurate for the overall analysis of the riser system, but can provide current and steady state loading information. The frequency domain solution uses linearization techniques to simulate the dynamic portion of the loading and can accurately model the loading, if the dynamics are moderate as compared to the static loading. The time domain can accurately model the dynamic loading and provide the most accurate modelling of both the linear IS and nonlinear conditions. The time domain solution can encompass a direct integration of the nonlinearities in the calculations, and requires a large number of solution iterations. The advent of more powerful computers has resulted in reasonable solution times and has made the time domain solution the most desirable method of solution.

The operational limits are based on providing a combination of tension, vessel location, and operating mode to maintain ball/flex joint angles, material physical property requirements, system component requirements, and prevent system component failure. Obtaining data to provide to the computer systems, however, has proved more problematic. Especially regarding drilling operations, system integration has been difficult due to the insular nature of the different control systems on the drilling rig. The operator interfaces currently in use have inherent accuracy limitations due to low update rates and do not capitalize on the importance of lower flex joint angle ("LFJA")/upper flex joint angle ("UFJA") differential, nor the importance of modelling the dynamic shape of the riser.

Current systems of monitoring ball/flex joint angle values do not provide riser managers sufficient data to properly maintain such operational parameters. Some recent systems include instrument modules that can provide static differential angle of the riser. The systems were, however, originally designed to support drilling operations, not riser management systems, and are not suitable as a basis for riser analysis because they provide only a limited set of measurements, and typically only for the lower flex joint. Current systems generally provide only static accuracy. That is, current systems generally only IS provide a static lower flex joint angle of inclination, values of which are affected by lateral acceleration, and which does not allow for real-time management of the riser system. Further, the inclination is referenced to a coordinate system separately assigned to the individual instrument housing or case, itself, rather than a globally assigned coordinate system. Thus, such systems are difficult to integrate with other more globally based systems.

In an attempt to acquire data on the behaviour of a riser under determined conditions, a more recent French system is being developed which utilizes a series of instrument modules consisting of lateral accelerometers and inclinometers connected along the length of the riser string and to the lower marine riser package to determine the two dimensional deflected shape of the riser. The modules are connected to a computer through a data transmission cable extending the length of the riser string. This system, however, does not provide dynamic angular position and orientation of the riser. The system also apparently only provides two-dimensional (planar) angular measurements.

Further, this system has not been shown to be practical because each module is individually connected to the data transmission cable through individual cable leads along the length of the data transmission cable. Thus, the data transmission cable requires a series of terminators/taps along the length of the cable. If a section of the riser carrying one of the modules is removed, the module will need to be either moved to another section, or the module will need to be disconnected from the data transmission cable and cap added to replace the removed module. In either scenario, the procedure is rather labour-intensive and requires disruption of the drilling operation and/or the management of the riser.

IS

SUMMARY OF THE INVENTION

According to the present invention, there is provided a riser monitoring assembly to monitor and manage a riser extending between subsea well equipment and a floating vessel. Two fibre optic cables set at 180 degrees apart monitor the entire length of the riser. One or both fibres are in real time communication with a communication and sensor pod attached to the upper BOP stack, this is connected to sensors monitoring the key parameters of the flex joint. internal pressure and events inside the riser, the status of all well control hardware fitted to the BOP stack In real time the distributed fibres along the length of the riser can monitor strain and hence induced stress, and in conjunction with the measurements taken at the BOP stack and the vessel position instrumentation, real time riser management is possible.

In view of the foregoing, embodiments of the present invention provide a system, assembly, software, and related methods provide real-time, full-time data obtained through an distribute fibre optic sensor along the entire riser including a measurement instrument module having gyroscopes, inclinometers and accelerometers, mounted in the lower riser package, and adjacent to the top of the riser, and that provide data which is dynamically accurate and which can be used in all riser modes of operation including installation, drilling, non-drilling, production, disconnect, and retrieval, to allow real-time management In addition, other critical parameter can be monitored such as the condition IS inside the riser at the lower riser package, to enhance well control, and all the well control systems can be measured and monitored in real time to ensure if required they will perform at maximum efficiency.

The invention uses the passages created by the choke and kill lines to be conduits for the fibre optic monitoring and communication cables, they could if required provide electrical power to the lower riser telemetry pod if required. As they are separated by an angle typically of 180 degrees they are ideally positioned to provide distributed strain measurement of the riser. If no choke and kill line exists, then the fibres can be mounted either to the inside or outside of the riser using a suitable spacing.

Further, if the vessel is moored to the seabed using mooring lines and anchors, these too could have a fibre optic cable attached to them to provide an accurate understanding of the loads each line is being subjected too, and any creep or slippage of the anchor, so as to enable active mooring management to be implemented, ensuring the rig does not loose time due to the poor performance of the mooring system It is an objective of this invention to convey a permanent distributed sensing system into a choke and kill line of a riser.

It is a further objective of this invention to provide real time telemetry to a lower riser sensing package.

It is a further objective of this invention to provide real time monitoring of the internal section of the riser at the wellhead.

It is a further objective of the invention to provide real time monitoring of the mooring system from anchor to the vessel.

Embodiments of the invention will now he described in detail with reference to the accompanying drawings in which: Figure 1 is a side view illustration of floating drilling vessel, moored to the sea bed and connected to a subsea wellhead via a drilling riser.

Figure 2 is a photo of a drilling riser connection.

Figure 3 is section side view of the upper end of the drilling riser, with a fibre optic cable being installed in the choke line, and an operational fibre optic cable installed in the kill line.

Figure 4 is a side view illustration of a typical subsea wellhead, BOP stack and lower marine riser package, and the relative positions sensor measurement's made and tied back to the marine riser pod Figure 5 is a section side view lower end of the drilling riser, just above the flex joint, detailing the termination of the choke and kill lines.

Figure 6 is a section end view of the choke or kill line, showing the fibre optic cable resting in a helical path in intimate contact with the inside surface.

Figure 7 is a similar view to figure 6, with a different embodiment of the fibre optic cable inside the choke or kill line.

Figure 8 is a similar view to figure 7, with the sensing fibre open flat around a 20 load bearing central member.

Figure 9 is a similar view to figure 8 with a welding tool suspended on the end of the load bearing member (not shown) bonding the flat cable to the inside surface of the choke, kill line or riser itself Figure 10 is a section side view AA of figure 9 Referring to the figure 1, there is shown a floating drilling vessel 1 connected to a subsea wellhead 2 via a marine drilling riser 3 attached to the wellhead via a BOP stack 4 and lower marine package 5. Mooring line 6 attached to the sea bed by anchors 7 hold the floating drilling vessel 1 on station.

Referring to figure 2, there is shown a photo of a typical flange connection type marine riser, the large pipe in the centre 8 being the drilling riser, and the choke line 9 and kill line 10 as an integral part of the riser joint. Each flange is bolted together 11, all three tubes are continuous and aligned along the entire drilling riser length.

Referring to figures 3 to 6, once the riser is fully assembled it extends from the seabed to the vessel. At the seabed end, there consist three sub-assemblies, the permanent wellhead guide base 12, the BOP stack 13, and the lower marine riser package 14 which connects to the riser 15.

On the BOP stack is a lower riser telemetry pod 16 which has bi directional wireless telemetry 17 with the upper riser telemetry pod 18 being part of the lower marine package. Lower riser telemetry pod 16 monitors what the internal pressure of the riser 19 immediately above the wellhead, connector 20, it also monitors the condition, position, and accumulator pressures associated with the lower pipe ram 21, middle pipe ram 22, upper pipe ram 23 and blind ram 24. The upper riser telemetry pod 18 is hard connected to the fibre optic cable and monitors the key parameters such as orientation, angle of inclination, tension and compression forces of the flex joint 25.

Once the drilling riser has been fully assembled. The fibre optic cable 30 can be lowered into the choke 9 and kill line 10. This can be performed with the top of the choke or kill line open to atmosphere, or with pressure control equipment 31 fitted. On the lower end of the fibre optic cable maybe fitted a 5 fibre optic wet connector 32, this can connect to its other mating half 33 at the lowest most end of the choke or kill line. The pig tail 34 from the fibre optic connector 33 goes to the upper riser telemetry pod 18. The fibre optic cable 30 is fully slacked off and rests in a helical path 35 on the inside surface of the choke or kill line, fully supported and providing intimate contact of the fibre to 10 the structure. At the upper end it passes through a conventional pack off 36 and back to its interrogator box (not shown) Figure 7 to 10 show another embodiment of the fibre optic cable, which is lowered into the choke or kill line wrapped around an electrically insulated S tensile carrying member 40 which at its lower most end has a tool 41. Once fully installed in the choke or kill line, a cutter is dropped from surface which results in the fibre optic cable opening out 41 to form a flat construction. The flat construction includes a metal Cost d tube 42 with a gel surrounding the fibre. And two U shaped thin metal continuous strips 43, 44 which are welded 20 to the inner surface of the choke and kill line by a welding wheel 45 of the tool 41. As the wheel rotates it spikes the flat cable and the tip penetrates the metal foil to make a circuit with the inside surface of the choke or kill line, and a low voltage high current discharge creates the weld.

Claims

Claims 1. A riser monitoring assembly to monitor and manage a riser extending between subsea well equipment and a floating vessel comprising a first fibre optic cable terminates in an upper communication and sensor pod attached to the upper BOP stack, the communication and sensor pod being in real time communication with a lower communication and sensor pod connected to sensors.
2. An assembly according to Cost im 1 wherein a second fibre optic cable is provided, the first fibre optic cable and second fibre optic cable set at 180 degrees on opposite sides of the risers to monitor the entire length of the riser.
3. An assembly according to Cost im 1 or 2 wherein the lower communication IS and sensor pod connected to sensors monitoring the key parameters of a flex joint, the internal pressure of the riser and events occurring inside the riser measured by sensors, the status of all well control hardware fitted to the BOP stack in real time.
4. An assembly according to any previous Cost im wherein the first and/or second fibre optic cables are distributed along the length of the riser also monitor strain and hence induced stress, and relay this in real-time
5. An assembly according to any previous Cost im wherein a lower 25 communication and sensor pod is provided, connected by one the first and/or second fibre optic cables to the upper communication and sensor pod.
6. An assembly according to any previous Cost im wherein a gyroscope and/or inclinometer and/or accelerometers, mounted in the lower riser package, and adjacent to the top of the riser, and that provide data which is dynamically accurate and which can be used in all riser modes of operation including installation, drilling, non-drilling, production, disconnect, and retrieval, to allow real-time management
7. An assembly according to any previous Cost im wherein internal pressure at 10 the well head and/or flow is transmitted instantaneously by the the first and/or second fibre optic cables rate to enhance well control.
8. An assembly according to any previous Cost im wherein the first and/or second fibre optic cables is disposed in choke and kill lines to be conduits for IS the fibre optic monitoring and communication cables
9. An assembly according to any previous Cost im wherein electrical power cable to the lower riser communication and sensor pod disposed in the choke and kill lines
10. An assembly according to any previous Cost im wherein there is included a mooring system for mooring a vessel to the seabed using mooring lines and anchors, fibre optic cable disposed along the mooring line and terminating at the anchor, the first and/or second fibre optic cables transmitting sensed data
11. An assembly according to any previous Cost im wherein strain on the first and/or second fibre optic cables is measured.