WO2019094018A1

WO2019094018A1 - Retrievable monitoring system for subsea systems

Info

Publication number: WO2019094018A1
Application number: PCT/US2017/060880
Authority: WO
Inventors: Richard M. Murphy
Original assignee: FMC Technologies Inc
Current assignee: FMC Technologies Inc
Priority date: 2017-11-09
Filing date: 2017-11-09
Publication date: 2019-05-16
Anticipated expiration: 2020-05-09

Abstract

A system for monitoring one or more parameters of a fluid in a component of a subsea system includes a retrievable unit which is removably mounted to a base unit that is connected either directly or indirectly to the component, and a sensor which includes a sensing element that is configured to generate a raw signal which is dependent on a parameter of the fluid and a signal conditioning circuit that is configured to convert the raw signal into a processed data signal which is representative of the parameter. The sensing element is mounted to the component so as to be exposed to the fluid, the signal conditioning circuit is positioned in the retrievable unit, and the sensing element is electrically connected to the signal conditioning circuit through an electrical cable. In this manner, the signal conditioning circuit is retrievable separately from the sensing element.

Description

RETRIEVABLE MONITORING SYSTEM FOR SUBSEA SYSTEMS The present disclosure is directed to a system for monitoring one or more parameters of a fluid, such as pressure and temperature, in a component of a subsea system, such as the Christmas tree component of a subsea hydrocarbon production system. More particularly, the disclosure is directed to a monitoring system which includes a number of sensors, each of which comprises a sensing element that is mounted to the component and a signal conditioning circuit that is located in a separate unit which can be retrieved to the surface should the signal conditioning circuit require repair or replacement.

BACKGROUND OF THE DISCLOSURE

Subsea systems typically include a number of sensors for monitoring certain conditions of the systems. For example, subsea hydrocarbon production systems usually include pressure and temperature sensors for monitoring the pressure and temperature of the production fluid. These sensors are typically self-contained units; that is, they include both a sensing element for generating a raw electrical signal which is dependent on the measured parameter of the fluid and a signal conditioning circuit for converting the raw electrical signal into a processed data signal which is suitable for use by an external data collection or process control system, such as a subsea control module. In certain prior art pressure and temperature sensors, the sensing element is disposed in probe which is configured to be exposed to the fluid to be measured, the proximal end of the probe is connected to a mounting flange, and the signal conditioning circuit is positioned in an electronics housing which is connected to the mounting flange opposite the probe. When used in a subsea hydrocarbon production system, the probe is positioned in a monitoring port in, e.g., the Christmas tree and the flange is bolted to the wall of the tree to secure the sensor in place. In this position, the electronics housing is located adjacent the wall of the tree.

In certain applications, the Christmas tree is insulated to prevent hydrates from forming in the production fluid. Because the electronics housing is located adjacent the wall of the tree, the insulation will usually cover the electronics housing. As a result, the insulation will retain heat in the electronics housing, and this heat may cause premature failure of the signal conditioning circuit. If the signal conditioning circuit should fail, the sensor is rendered inoperable.

Moreover, since the sensor is bolted to the tree, it cannot be retrieved to the surface vessel and repaired or replaced. Consequently, the parameter which the sensor is designed to detect (e.g., pressure or temperature) can no longer be monitored.

SUMMARY OF THE DISCLOSURE

In accordance with the present disclosure, a retrievable monitoring system for monitoring one or more parameters of a fluid in at least a first component of a subsea system is provided which comprises a retrievable unit which is removably mounted to a base unit that is connected either directly or indirectly to the first component; a first sensor which includes a first sensing element and a first signal conditioning circuit, the first sensing element being configured to generate a raw signal which is dependent on a first parameter of the fluid, and the first signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the first parameter; wherein the first sensing element is mounted to the first component so as to be exposed to the fluid, the first signal conditioning circuit is positioned in the retrievable unit, and the first sensing element is electrically connected to the first signal conditioning circuit through a first electrical cable. Accordingly, the first signal conditioning circuit is retrievable separately from the first sensing element.

In accordance with an aspect of the disclosure, the first sensor further comprises a probe within which the first sensing element is disposed, the probe being positioned in a monitoring port in the first component; a flange to which the probe is connected, the flange being mounted to the first component over the monitoring port; and a first electrical connector which is connected to the flange opposite the probe and is electrically connected to the first sensing element. In this embodiment, the first cable may comprise a first end which is connected to the first electrical connector and a second end which is connected to a second electrical connector that is mounted to the base unit. Also, the second electrical connector may be connected to the signal conditioning circuit through a wet mate connector. In addition, the first electrical cable may be run through a small diameter rigid tube. Furthermore, the first cable may comprise a first end which is electrically connected to the sensing element and a second end which is electrically connected to the signal conditioning circuit via a wet mate connector.

In accordance with another aspect, the monitoring system further comprises a second sensor which includes a second sensing element and a second signal conditioning circuit, the second sensing element being configured to generate a raw signal which is dependent on a second parameter of the fluid, and the second signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the second parameter; wherein the second sensing element is mounted to one of the first component or to a second component of the subsea system so as to be exposed to the fluid, the second signal conditioning circuit is positioned in the retrievable unit, and the second sensing element is electrically connected to the second signal conditioning circuit through a second electrical cable. Accordingly, the first and second signal conditioning circuits are retrievable separately from the first and second sensing elements.

In accordance with further aspect of the disclosure, the first and second signal conditioning circuits may be mounted on respective circuit boards.

Alternatively, the first and second signal conditioning circuits may be mounted on a single circuit board.

In accordance with yet another aspect of the disclosure, each of the first and second sensors further comprises a probe within which the sensing element is disposed, the probe being positioned in a corresponding monitoring port in the first or second component; a flange to which the probe is connected, the flange being mounted to the first or second component over the monitoring port; and a first electrical connector which is connected to the flange opposite the probe and is electrically connected to the sensing element. In this embodiment, each of the first and second electrical cables may comprise a first end which is connected to the first electrical connector and a second end which is connected to a respective second electrical connector that is mounted to the base unit. Also, each second electrical connector may be connected to its corresponding signal conditioning circuit via a respective wet mate connector. In addition, each of the first and second electrical cables may be run through a corresponding small diameter rigid tube. Furthermore, each of the first and second electrical cables may comprise a first end which is electrically connected to the sensing element and a second end which is electrically connected to the signal conditioning circuit via a

corresponding wet mate connector.

The present disclosure is also directed to a method for monitoring one or more parameters of a fluid in at least a first component of a subsea system. The method comprises the steps of mounting a first sensing element to the first component so as to expose the first sensing element to the fluid, the first sensing element being configured to generate a raw signal which is dependent on a first parameter of the fluid; positioning a first signal conditioning circuit in a retrievable unit which is removably mounted to a base unit that is connected either directly or indirectly to the first component, the first signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the first parameter; and electrically connecting the first sensing element to the first signal conditioning circuit in a manner which allows the first signal conditioning circuit to be selectively electrically disconnected from the first sensing element. In this manner, the first signal conditioning circuit is retrievable separately from the first sensing element.

In accordance with an aspect of the disclosure, the method further comprises the steps of mounting a second sensing element to one of the first component or to a second component of the subsea system so as to expose the second sensing element to the fluid, the second sensing element being

configured to generate a raw signal which is dependent on a second parameter of the fluid; positioning a second signal conditioning circuit in the retrievable unit, the second signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the second parameter; and electrically connecting the second sensing element to the second signal conditioning circuit in a manner which allows the second signal conditioning circuit to be selectively electrically disconnected from the second sensing element. In this manner, both the first and second signal conditioning circuits are retrievable separately from the first and second sensing elements.

Thus, the condition monitoring system of the present disclosure physically separates the signal conditioning circuit from the sensing element and relocates the signal conditioning circuit to a separate, remote retrievable unit. Hence, the only part of the sensor which is mounted to the component containing the fluid to be sensed is the sensing element. The part of the sensor which converts the raw signal generated by the sensing element into a processed data signal, that is, the signal conditioning circuit, is located remotely from the sensing element in the retrievable unit. Consequently, should the signal conditioning circuit fail, the retrievable unit can be retrieved to, e.g., a surface vessel and the signal conditioning circuit repaired or replaced.

These and other objects and advantages of the present disclosure will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers may be used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross sectional representation of an example of a prior art condition monitoring system shown in conjunction with an exemplary subsea Christmas tree;

Figure 2 is an enlarged cross sectional representation of one of the sensors of the condition monitoring system depicted in Figure 1 ;

Figure 3 is a cross sectional representation of one embodiment of the condition monitoring system of the present disclosure shown in conjunction with an exemplary subsea Christmas tree; and

Figure 4 is an enlarged cross sectional representation of a portion of one of the sensors of the condition monitoring system depicted in Figure 3.

DETAILED DESCRIPTION

The monitoring system disclosed herein is particularly suitable for use with subsea systems. Examples of subsea systems with which the monitoring system may be used include, but are not limited to, subsea hydrocarbon production or processing systems. The monitoring system is designed to monitor one or more parameters of a fluid in at least one component of the subsea system. The components may be those through which the fluid flows or those within which the fluid is contained. In addition, the components may be stand-alone components of the system or components which are connected together to form larger components of the system. Examples of components of a subsea hydrocarbon production system with which the monitoring system disclosed herein may be used include, but are not limited to, wellheads, tubing heads, Christmas trees, flow loops, chokes, and accumulators.

In accordance with one embodiment of the present disclosure, the monitoring system includes a number of sensors for monitoring one or more parameters of the fluid in the component, and a retrievable unit which is removably mounted either directly or indirectly to the component. Each sensor includes a sensing element which is mounted to the component and a signal conditioning circuit which is positioned in the retrievable unit. The sensing element part of the sensor is configured to generate a raw signal which is dependent on a parameter of the fluid, and the signal conditioning circuit part of the sensor is configured to convert the raw signal into a processed data signal which is representative of the parameter of the fluid. Thus, the only part of the sensor which is mounted to the component is the sensing element. The part of the sensor which converts the raw signal generated by the sensing element into a processed data signal, namely, the signal conditioning circuit, is located remotely from the sensing element in the retrievable unit. As a result, should the signal conditioning circuit fail, the retrievable unit can be retrieved to a surface vessel and the signal conditioning circuit repaired or replaced.

A more specific embodiment of a monitoring system in accordance with the present disclosure will be described below. First, though, an example of a prior art monitoring system for a subsea hydrocarbon production system will be described in order to illuminate the features and advantages presented by the monitoring system of the present disclosure.

An example of a prior art monitoring system for a subsea hydrocarbon production system is shown in Figure 1 . In this example, the subsea production system includes a Christmas tree component 10 which is installed at the top of a well bore (not shown). The tree 10 comprises an axial production bore 12 which is connected to the well bore and a lateral production outlet 14 which is connected to the production bore. In the production mode of operation of the tree 10, production fluid in the well bore is communicated through the production bore 12 and the production outlet 14 to a flowline (not shown), which in turn is connected to, e.g., a surface vessel.

Referring also to Figure 2, the prior art monitoring system includes a pressure sensor 16 and a temperature sensor 18, each of which comprises a sensing element 20 which is disposed in a probe 22. The probe 22 is positioned in a corresponding monitoring port 24 which extends through the tree 10 and is fluidly connected to the production bore 12. The probe 22 is connected to a flange 26 which is bolted and sealed to the tree 10 over the monitoring port 24. An electronics housing 28 is connected to the flange 26 opposite the probe 22. The electronics housing 28 contains a signal conditioning circuit 30 which is electrically connected to both the sensing element 20 and an electrical connector 32 that is attached to the housing.

In the prior art pressure and temperature monitoring system shown in Figure 1 , the signal conditioning circuits 30 are electrically connected to an SCM 34 through respective electrical cables which are run through corresponding oil- filled hoses 36. One end of each cable is connected via a first dry mate connector 38 to the electrical connector 32 of a corresponding sensor 16, 18. The opposite end of each cable is connected via a second dry mate connector 40 to a corresponding electrical connector 42 on a stab plate 44 which is connected to the tree 10 and to which the SCM 34 is removably connected. The electrical connectors 42 are in turn connected to the SCM 34 through corresponding wet mate connectors 46.

Each sensing element 20 is configured to generate a raw, normally analog electrical signal which is dependent on the parameter its corresponding sensor 16,18 is designed to sense. In this example, the sensing element 20 for the pressure sensor 16 is designed to sense pressure and the sensing element for the temperature sensor 18 is designed to sense temperature. Pressure sensing elements which are suitable for use with subsea trees typically include an electrical component which is connected to or incorporated into a mechanical component, such as a diaphragm, that is designed to be exposed to the fluid whose pressure is to be monitored. Examples of such pressure sensing elements include thin film strain gauge sensors, silicone piezo resistive sensors, quartz crystal resonator sensors, silicone resonator pressure sensors, and silicone variable capacitive pressure sensors. Temperature sensors which are suitable for use with subsea trees commonly include a material or combination of materials which produces an electrical output that is dependent on temperature. Examples of such temperature sensing elements include thermocouples, silicone piezo resistive sensors, and resistance temperature detectors (RTD's). Some sensing elements, such as silicone piezo resistive sensors, can be used to sense both pressure and temperature.

Each signal conditioning circuit 30 includes a number of components for converting the raw electrical signal generated by its corresponding sensing element 20 into a processed data signal which is representative of the sensed parameter and is suitable for use by a data collection or process control system, such as the SCM 34. Typical functions of the signal conditioning circuit 30 may include amplifying the raw electrical signal, filtering the raw signal to remove its higher frequency components, and, if the raw signal is an analog signal, digitizing the raw signal. Thus, each signal conditioning circuit 30 may include an amplifier, a bandwidth filter and an analog-to-digital converter. Each signal conditioning circuit 30 may also include components for linearizing the raw signal,

compensating the signal for temperature variations (in the case of the pressure sensor 16), and removing offset errors from the signal.

As discussed above, certain components of subsea systems, such as the Christmas trees, are often insulated to prevent hydrates from forming in the production fluid. In the case of the tree 10 shown in Figure 1 , the insulation will normally cover the sensors 16, 18. As a result, the insulation will retain heat in the electronics housing 28, and this heat may cause premature failure of the signal conditioning circuit 30. If the signal conditioning circuit 30 should fail, the sensor 16, 18 is rendered inoperable. Moreover, since the sensor 16, 18 is bolted to the tree 10, it cannot be retrieved to the surface vessel and repaired or replaced. Consequently, the parameter which the sensor is designed to detect (e.g., pressure or temperature) can no longer be monitored.

In accordance with the present disclosure, this problem is overcome by providing a condition monitoring system which includes one or more sensors whose signal conditioning circuits are housed in a separate remote unit that can be retrieved to the surface vessel. This will enable the signal conditioning circuits to be repaired or replaced. As a result, the sensors can remain in service for an extended period of time. Although the condition monitoring system disclosed herein may be used to monitor the parameters of a fluid in any subsea system, for purposes of simplicity it will be described in connection with the Christmas tree component of a subsea hydrocarbon production system, in particular the

Christmas tree 10 described above.

As shown in Figure 3, the condition monitoring system includes a number of sensors for monitoring certain parameters of the fluid in the production bore 12. In the present embodiment, for example, the condition monitoring system includes a pressure sensor 100 and a temperature sensor 102. Referring also to Figure 4, each sensor 100, 102 includes a sensing element 104 which is disposed in a probe 106. The probe 106 is positioned in a corresponding monitoring port 24 which extends through the tree 10 and is fluidly connected to the production bore 12. The probe 106 is connected to a flange 108 which is bolted and sealed to the tree 10 over the monitoring port 24. An electrical connector 1 10 which is electrically connected to the sensing element 104 is mounted to the flange 108 opposite the probe 106.

Each sensing element 104 is configured to generate a raw electrical signal which is dependent on the parameter its corresponding sensor 100, 102 is designed to sense. Thus, the sensing element 104 for the pressure sensor 100 is designed to sense pressure, while the sensing element for the temperature sensor 102 is designed to sense temperature. Examples of sensing elements for detecting pressure and temperature are provided above in connection with the discussion of the sensing elements 20. These sensing elements 104, as well as sensing elements for detecting other conditions of the fluid in the production bore 12, are well known to persons of ordinary skill in the art.

In contrast to the prior art sensors 16, 18 described above, the sensors

100, 102 do not contain a local signal conditioning circuit. Instead, the sensors 100, 102 comprise a remote signal conditioning circuit 1 12 which is housed in a separate retrievable unit 1 14, such as a power control router (PCR). Each sensor 100, 102 may comprise a respective signal conditioning circuit 1 12 mounted on a corresponding circuit board. Alternatively, the sensors 100, 102 may comprise respective signal conditioning circuits 1 12 which are mounted on a common circuit board. The signal conditioning circuits 1 12 are similar in design and operation to the signal conditioning circuits 30 described above. Thus, the signal conditioning circuits 1 12 function to convert the raw electrical signals generated by their respective sensing elements 104 into processed data signals which are representative of the sensed parameters and are suitable for use by a data collection or process control system, such as the SCM 34.

The raw electrical signals generated by the sensing elements 104 are transmitted to their corresponding signal conditioning circuits 1 12 over electrical cables which optimally are run through small diameter rigid tubes 1 16 (which may be fluid filled). One end of each cable is connected via a first dry mate connector 1 18 to the electrical connector 1 10 of a corresponding sensor 100, 102. The opposite end of each cable is connected via a second dry mate connector 120 to a corresponding electrical connector 122 which is mounted to a base unit 124, such as a stab plate. The base unit 24 is connected either directly or indirectly (e.g., via a frame or other component of the subsea system) to the tree 10, and the retrievable unit 1 14 is removably mounted to the base unit. The connectors 122 are in turn connected to the signal conditioning circuits 1 12 through corresponding wet mate connectors 126. The processed signals from the signal conditioning circuits 1 12 may then be transmitted to the SCM 34 over a cable which is run through, e.g., a conventional fluid filled hose 128.

Since the signal conditioning circuits 1 12 are housed in the remote retrievable unit 1 14, they are not exposed to the potentially damaging heat of the well fluid. However, should a signal conditioning circuit 1 12 fail, the retrievable unit 1 14 can be retrieved to the surface vessel using, e.g., an ROV, and the signal conditioning circuit can be repaired or replaced. The retrievable unit 1 14 can then be reinstalled on the base unit 124 to thereby reconnect the sensing elements 104 to the signal conditioning circuits 1 12. In this manner, the sensors 100, 102 will remain operational for the life of the sensing elements 104, which is typically substantially longer than the life of electronic circuits such as the signal conditioning circuits 1 12.

In another embodiment of the present disclosure, the monitoring system includes at least two sensors whose sensing elements are mounted to respective components of the subsea system. Using the subsea hydrocarbon production system as an example, the sensing element of the first sensor may be mounted to the tree 10 and the sensing element of the second sensor may be mounted to a wellhead or tubing spool (not shown) on which the tree is installed. In this manner, the first sensor can monitor, e.g., the pressure of the production fluid in the tree while the second sensor monitors, e.g., the pressure of the fluid in the production casing annulus. Therefore, the monitoring system of the present disclosure is not limited to monitoring the parameters of the fluid in only one component of the subsea system; it may be configured to monitor the parameters of the fluids in two or more components of the subsea system.

It should be recognized that, while the present disclosure has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the disclosure. For example, the various elements shown in the different embodiments may be combined in a manner not illustrated above. Therefore, the following claims are to be construed to cover all equivalents falling within the true scope and spirit of the disclosure.

Claims

What is Claimed is:

1 . A system for monitoring one or more parameters of a fluid in at least a first component of a subsea system, the monitoring system comprising:

a retrievable unit which is removably mounted to a base unit that is connected either directly or indirectly to the first component;

a first sensor which includes a first sensing element and a first signal conditioning circuit, the first sensing element being configured to generate a raw signal which is dependent on a first parameter of the fluid, and the first signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the first parameter;

wherein the first sensing element is mounted to the first component so as to be exposed to the fluid, the first signal conditioning circuit is positioned in the retrievable unit, and the first sensing element is electrically connected to the first signal conditioning circuit through a first electrical cable;

whereby the first signal conditioning circuit is retrievable separately from the first sensing element.

2. The monitoring system of claim 1 , wherein the first sensor further comprises:

a probe within which the first sensing element is disposed, the probe being positioned in a monitoring port in the first component;

a flange to which the probe is connected, the flange being mounted to the first component over the monitoring port; and

a first electrical connector which is connected to the flange opposite the probe and is electrically connected to the first sensing element.

3. The monitoring system of claim 2, wherein the first cable comprises a first end which is connected to the first electrical connector and a second end which is connected to a second electrical connector that is mounted to the base unit.

4. The monitoring system of claim 3, wherein the second electrical connector is connected to the signal conditioning circuit through a wet mate connector.

5. The monitoring system of claim 3, wherein the first electrical cable is run through a small diameter rigid tube.

6. The monitoring system of claim 1 , wherein the first cable comprises a first end which is electrically connected to the sensing element and a second end which is electrically connected to the signal conditioning circuit via a wet mate connector.

7. The monitoring system of claim 1 , further comprising:

a second sensor which includes a second sensing element and a second signal conditioning circuit, the second sensing element being configured to generate a raw signal which is dependent on a second parameter of the fluid, and the second signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the second parameter;

wherein the second sensing element is mounted to one of the first component or to a second component of the subsea system so as to be exposed to the fluid, the second signal conditioning circuit is positioned in the retrievable unit, and the second sensing element is electrically connected to the second signal conditioning circuit through a second electrical cable.

whereby both the first and second signal conditioning circuits are retrievable separately from the first and second sensing elements.

8. The monitoring system of claim 7, wherein the first and second signal conditioning circuits are mounted on respective circuit boards.

9. The monitoring system of claim 7, wherein the first and second signal conditioning circuits are mounted on a single circuit board.

10. The monitoring system of claim 7, wherein each of the first and second sensors further comprises:

a probe within which the sensing element is disposed, the probe being positioned in a corresponding monitoring port in the first or second component;

a flange to which the probe is connected, the flange being mounted to the first or second component over the monitoring port; and

a first electrical connector which is connected to the flange opposite the probe and is electrically connected to the sensing element.

1 1 . The monitoring system of claim 10, wherein each of the first and second electrical cables comprises a first end which is connected to the first electrical connector and a second end which is connected to a respective second electrical connector that is mounted to the base unit.

12. The monitoring system of claim 1 1 , wherein each second electrical connector is connected to its corresponding signal conditioning circuit via a respective wet mate connector.

13. The monitoring system of claim 1 1 , wherein each of the first and second electrical cables are run through a corresponding small diameter rigid tube.

14. The monitoring system of claim 7, wherein each of the first and second electrical cables comprises a first end which is electrically connected to the sensing element and a second end which is electrically connected to the signal conditioning circuit via a corresponding wet mate connector.

15. A method for monitoring one or more parameters of a fluid in at least a first component of a subsea system, the method comprising:

mounting a first sensing element to the first component so as to expose the first sensing element to the fluid, the first sensing element being configured to generate a raw signal which is dependent on a first parameter of the fluid;

positioning a first signal conditioning circuit in a retrievable unit which is removably mounted to a base unit that is connected either directly or indirectly to the first component, the first signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the first parameter; and

electrically connecting the first sensing element to the first signal conditioning circuit in a manner which allows the first signal conditioning circuit to be selectively electrically disconnected from the first sensing element;

wherein the first signal conditioning circuit is retrievable separately from the first sensing element.

16. The method of claim 15, further comprising:

mounting a second sensing element to one of the first component or to a second component of the subsea system so as to expose the second sensing element to the fluid, the second sensing element being configured to generate a raw signal which is dependent on a second parameter of the fluid; positioning a second signal conditioning circuit in the retrievable unit, the second signal conditioning circuit being configured to convert the raw signal into a processed data signal which is representative of the second parameter; and

electrically connecting the second sensing element to the second signal conditioning circuit in a manner which allows the second signal conditioning circuit to be selectively electrically disconnected from the second sensing element;

wherein both the first and second signal conditioning circuits are retrievable separately from the first and second sensing elements.