Abstract:
An optical monitoring system includes a sensor network including a plurality of optical sensors. The optical switch module is disposed on a first side of a pressure barrier, coupled to the sensor network, and operable to select various subsets of the optical sensors responsive to a control signal. The sensor interrogation unit is disposed on a second side of the pressure barrier and operable to generate the control signal and receive an optical signal from a particular subset of the sensor elements selected by the optical switch module. The optical penetrator is coupled to the interrogation unit and the optical switch module and operable to communicate the optical signal through the pressure barrier. The inductive control unit is operable to inductively communicate the control signal and a power signal to the optical switch module through the pressure barrier.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The disclosed subject matter relates generally to subsea hydrocarbon production and, more particularly, to a subsea optical switch. 
         [0002]    In order to control a subsea well, a connection is established between the well and a monitoring and control station. The monitoring and control station may be located on a platform or floating vessel near the subsea installation, or alternatively in a more remote land station. The connection between the control station and the subsea installation is usually established by installing an umbilical between the two points. The umbilical may include hydraulic lines for supplying hydraulic fluid to various hydraulic actuators located on or near the well. The umbilical may also include electrical and or fiber optic lines for supplying electric power and also for communicating control signals and/or well data between the control station and the various monitoring and control devices located on or near the well. 
         [0003]    Hydrocarbon production from the subsea well is controlled by a number of valves that are assembled into a unitary structure generally referred to as a well tree or Christmas tree. Well tree and wellhead systems have the principle functions of providing an interface to the in-well environment, allowing flow regulation and measurement, and permitting intervention on the well or downhole systems during the operational life of the well. The actuation of the valves in the well tree is normally provided using hydraulic fluid to power hydraulic actuators that operate the valves. Hydraulic fluid is normally supplied through an umbilical running from a remote station located on a vessel or platform at the surface. Alternative systems using electrically based actuators are also possible. 
         [0004]    In addition to the flow control valves and actuators, a number of sensors and detectors are commonly employed in subsea systems to monitor the state of the system and the flow of hydrocarbons from the well. Often a number of sensors, detectors and/or actuators are also located downhole. All these devices are controlled and/or monitored by a dedicated control system, which is usually housed in the remote control module. Control signals and well data are also exchanged through the umbilical. 
         [0005]    Conventional well trees typically only have a few sensors designed to provide information on the production process. These sensors fail to provide any information regarding the operation or efficiency of the well tree or wellhead. If a particular sensor fails to operate accurately, it may provide errant information regarding the production process. Uncertainties in the accuracy of the well monitoring and the limited amount of data make it difficult to optimize the production process or to predict impending failures. 
         [0006]    Optoelectronic sensors and communications systems are useful for providing measurements and transmitting data required for subsea hydrocarbon production installations. There are a number of optoelectronic sensing schemes, such as Raman based distributed temperature sensing and arrays of Bragg gratings, that provide multiple sensors or sensing points along a single optical fiber. However not all the sensors required for such subsea installations can be easily accessed. In many instances the use of individual optical fiber devices and sensors at various locations on subsea installations requires direct cabling between the sensor and the Subsea Control Module (SCM) or other subsea hub arrangement. 
         [0007]    A major limitation in deploying optical devices is the cost of the connectors or feed through between the subsea environment and the inside of the SCM. The cost, per sensor, even when using a multi-fiber connector system, is very high. There are also physical limitations on the number of such connectors that can be installed on a typical SCM, which in turn limits the number of sensors that can be deployed on a subsea installation. These cost and physical limitations greatly restrict the use of directly connected optical devices and sensors on subsea hydrocarbon installations. 
         [0008]    This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
         [0010]    One aspect of the disclosed subject matter is seen in an optical monitoring system that includes a sensor network. The sensor network includes a plurality of optical sensors. The optical switch module is disposed on a first side of a pressure barrier, coupled to the sensor network, and operable to select various subsets of the optical sensors responsive to a control signal. The sensor interrogation unit is disposed on a second side of the pressure barrier and operable to generate the control signal and receive an optical signal from a particular subset of the sensor elements selected by the optical switch module. The optical penetrator is coupled to the interrogation unit and the optical switch module and operable to communicate the optical signal through the pressure barrier. The inductive control unit is operable to inductively communicate the control signal and a power signal to the optical switch module through the pressure barrier. 
         [0011]    Another aspect of the disclosed subject matter is seen in a method for monitoring a sensor network including a plurality of optical sensors. The method includes coupling an optical switch module disposed on a first side of a pressure barrier to the sensor network. The optical switch module is operable to select various subsets of the optical sensors responsive to a control signal. A sensor interrogation unit is provided on a second side of the pressure barrier and operable to generate the control signal and receive an optical signal from a particular subset of the sensor elements selected by the optical switch module. An optical penetrator coupled to the interrogation unit and the optical switch module is provided and is operable to communicate the optical signal through the pressure barrier. The control signal and a power signal is inductively communicated to the optical switch module through the pressure barrier. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0012]    The disclosed subject matter will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0013]      FIG. 1  is a simplified diagram of a subsea installation for hydrocarbon production; 
           [0014]      FIG. 2  is a perspective view of an exemplary well tree in the system of  FIG. 1 ; 
           [0015]      FIG. 3  is a view of the well tree of  FIG. 2  illustrating monitoring sensors; 
           [0016]      FIG. 4  is a simplified diagram of an optical routing system that may be used to support monitoring of the well tree of  FIGS. 1-3 ; and 
           [0017]      FIG. 5  is a diagram illustrating an embodiment of a sensor network that may be used in the routing system of  FIG. 4 . 
       
    
    
       [0018]    While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosed subject matter as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    One or more specific embodiments of the disclosed subject matter will be described below. It is specifically intended that the disclosed subject matter not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the disclosed subject matter unless explicitly indicated as being “critical” or “essential.” 
         [0020]    The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the disclosed subject matter with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
         [0021]    Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to  FIG. 1 , the disclosed subject matter shall be described in the context of a subsea installation  100  located on the seabed  110 . The installation  100  includes a schematically depicted well tree  120  mounted on a wellhead  130 . The wellhead  130  is the uppermost part of a well (not shown) that extends down into the sea floor to a subterranean hydrocarbon formation. An umbilical cable  140  for communicating electrical signals, fiber optic signals, and/or hydraulic fluid extends from a vessel  150  to the well tree  120 . In other embodiments, the vessel  150  may be replaced by a floating platform or other such surface structure. In one illustrative embodiment, a flowline  160  also extends between the vessel  150  and the well tree  120  for receiving hydrocarbon production from the well. In some cases, the flowline  160  and a communications line (not shown) may extend to a subsea manifold or to a land based processing facility. A topside control module (TCM)  170  is housed on the vessel  150  to allow oversight and control of the well tree  120  by an operator. A condition monitoring unit  180  is provided for monitoring the operation of the well tree  120 . The operation of the conduction monitoring unit is described in more detail in U.S. patent application Ser. No. 12/204,311, entitled “Optical Sensing System for Wellhead Equipment,” which is incorporated herein by reference in its entirety. 
         [0022]      FIG. 2  illustrates a perspective view of an exemplary well tree  120 . The well tree  120  illustrated in  FIG. 2  is provided for illustrative purposes, as the application of the present subject matter is not limited to a particular well tree design or structure. The well tree  120  includes a frame  200 , a flowline connector  205 , a composite valve block assembly  210 , chokes  215 , a production wing valve  220 , flow loops  225 , hydraulic actuators  230 , a remotely operated vehicle (ROV) panel  235 , a subsea control module (SCM)  240 , and fluid sensors  245 . Within the ROV panel  235 , hydraulic actuator linear overrides  250  and ROV interface buckets  255  are provided for allowing the operation of the actuators  230  or other various valves and components by an ROV (not shown). Although certain embodiments described below employ components that are hydraulically operated, it is contemplated that corresponding electrically operated components may also be used. 
         [0023]    The construct and operation of the components in the well tree  120  are well known to those of ordinary skill in the art, so they are not described in detail herein. Generally, the flow of production fluid (e.g., liquid or gas) through the flowline  160  is controlled by the production wing valve  220  and the chokes  215 , which are positioned by manipulating the hydraulic actuators  230 . The composite valve block assembly  210  provides an interface for the umbilical  140  to allow electrical signals (e.g., power and control) and hydraulic fluid to be communicated between the vessel  150  and the well tree  120 . The flow loops  225  and fluid sensors  245  are provided to allow characteristics of the production fluid to be measured. The subsea control module (SCM)  240  is the control center of the well tree  120 , providing control signals for manipulating the various actuators and exchanging sensor data with the topside control module  170  on the vessel  150 . 
         [0024]    The functionality of the condition monitoring unit  180  may be implemented by the topside control module  170  or the subsea control module  240  (i.e., as indicated by the phantom lines in  FIG. 1 . The condition monitoring unit  180  may be implemented using dedicated hardware in the form of a processor or computer executing software, or the condition monitoring unit  180  may be implemented using software executing on shared computing resources. For example, the condition monitoring unit  180  may be implemented by the same computer that implements the topside control module  170  or the computer that implements the SCM  240 . 
         [0025]    Generally, the condition monitoring unit  180  monitors various parameters associated with the well tree  120  to determine the “health” of the well tree  120 . The health information derived by the well tree  120  includes overall health, component health, component operability, etc. Exemplary parameters that may be monitored include pressure, temperature, flow, vibration, corrosion, displacement, rotation, leak detection, erosion, sand, strain, and production fluid content and composition. To gather data regarding the parameters monitored, various sensors may be employed. 
         [0026]      FIG. 3  illustrates a diagram of the well tree  120  showing various illustrative monitoring points. These monitoring points may be provided through the use of optical sensors as further described in reference to  FIG. 4 . An exemplary, but not exhaustive, list of optical sensors is provided below. Also, various signals associated with the components (e.g., motor current, voltage, vibration, or noise) may also be considered. As shown in  FIG. 3 , a vibration sensor  300  may be provided for detecting vibration in the flowline  160 . Fluid Monitoring sensors  310  may be provided for monitoring characteristics of the production fluid, such as pressure, temperature, oil in water concentration, chemical composition, etc. One or more leak detection sensors  320  may be provided for monitoring connection integrity. Erosion and/or corrosion sensors  330  may be provided in the flow loops  225 . Valve position sensors  340 , choke position sensors  350 , and ROV panel position indicators  360  may be provided for monitoring the actual valve positions. Shear pin failure sensors  370  may be provided for monitoring the hydraulic actuators  230  and linear overrides  250 . Other various component sensors  380  may also be provided for monitoring parameters, such as motor voltage, motor current, pump characteristics, etc. The sensors  300 - 380  may communicate through an optical feedthrough module  390  to the topside control module  170 . 
         [0027]    In general, the optical feedthrough module  390  is housed in a horizontal penetrator and provides an optical path between the well tree  120  and the topside control module  170  and/or the condition monitoring unit  180 . Although a horizontal penetrator is illustrated, it is also contemplated that a vertically oriented penetrator may also be employed. The optical feedthrough module  390  may take on various forms. In one embodiment, the optical feedthrough module  390  includes an optically transmissive window that includes optical repeaters on either side of the window that allow an optical signal to be communicated between entities inside the well tree  120  pressure barrier to entities outside the pressure barrier. In the case of an optical window, no actual opening is defined in the pressure barrier. In another embodiment, the optical feedthrough module  390  may comprise a penetration that breaches the pressure boundary to allow an optical cable to pass through the housing. 
         [0028]    In some embodiments, multiple sensors may be provided for measuring a particular parameter. For example, multiple voltage and current sensors may be provided to allow measurement of standard motor performance voltage and current as well as voltage or current surges, spikes, etc. The duplicate sensors provide both built in redundancy and a means for cross-checking sensor performance. 
         [0029]    Turning now to  FIG. 4 , a simplified diagram of an optical routing system  400  that may be used to support monitoring of the well tree  120  is provided. Although the optical routing system  400  is described as it is implemented for monitoring a well tree  120 , its application is not limited. The optical routing system  400  may be used for virtually any subsea or harsh environment monitoring application where a pressure boundary exists between the sensors and the monitoring electronics. For example, the optical routing system  400  may be used in a subsea production system or other subsea equipment. 
         [0030]    In general, a sensor interrogation unit  405  communicates through a pressure barrier  410  to a sensor network  415  including a plurality of sensor elements  420 . An optical penetrator  425  (e.g., the optical feedthrough  390 ) is provided to bridge the pressure barrier  410 . An optical switch module  430  is provided for interfacing with the sensor network  415  to select particular subsets of the sensor elements  420  to facilitate communication with the sensor interrogation unit  405 . In one embodiment, the sensor interrogation unit  405  is housed in the SCM  240  and communicates with sensor elements  420  disposed throughout the well tree  120  for monitoring various parameters of the well tree  120 . 
         [0031]    The optical switch module  430  may have a variety of constructions, including a micro-electro-mechanical system (MEMS) or an opto-mechanical system. The optical switch module  430  is powered by an inductive control unit  435  that includes a inductive transmitter coil  440  disposed on the side of the pressure barrier  410  including the sensor interrogation unit  405  and a inductive receiver coil  445  disposed on the same side of the pressure barrier as the optical switch module  430 . A variety of modes of operation may be employed for the inductive control unit  435 . For example, the power and control signals may be at different frequencies. The inductive control unit  435  may also contain smoothing and/or surge protection electronics to minimize the potential for damage to electronics of the optical switch module  430  and to provide the appropriate switching signal. The sensor interrogation unit  405  and the inductive receiver coil  445  may receive electrical power from a common source (e.g., through the umbilical  140 ). The inductive control unit  435  allows the optical switch module  430  to be controlled without requiring an additional penetrator through the pressure barrier  410  to power the optical switch module  430 . The inductive coils  440 ,  445  may be disposed close to the optical penetrator  425  or integrated therewith. The wall of the pressure barrier  410  may be modified in the region where the inductive signal transfer occurs to increase the efficiency of the signal transfer. For example, the metal composition thickness, or structure of the pressure barrier  410  may be varied. In one embodiment, the optical switch module  430  may include a battery  432  that provides primary power for positioning the switch, while the inductive control unit  435  is provided for charging the battery  432  and communicating the control signals. 
         [0032]    The arrangement of the sensor elements  420  in the sensor network  415  may vary depending on the particular parameters monitored and any multiplexing scheme employed. There are a number of optoelectronic sensing schemes, such as Raman based distributed temperature sensing or arrays of Bragg gratings, that provide multiple sensors or sensing points along a single optical fiber. The optical switch module  430  enables the sensor interrogation unit  405  to select a single optical fiber for interrogation. In cases where the sensors on each fiber use the same form of identification (e.g., wave division multiplexing (WDM), the sensor interrogation unit  405  may still uniquely identify each sensor based on the position of the optical switch module  430  and the identification data. 
         [0033]    In the embodiment illustrated in  FIG. 4 , multiple sensor elements  420  are each disposed on a optical fiber  450 . Each optical fiber  450  is coupled to an output port  434  of the optical switch module  430 . Alternatively, as shown in  FIG. 5 , the sensor network  415  may include multiplexed sensor elements  420  that are disposed on multiple branches  455  of an optical fiber  460 . The branching arrangement is useful for locating sensor elements  420  at various measurement points on the well tree  120  or other portions of the subsea processing system. 
         [0034]    The optical routing system  400  described herein has numerous advantages. The number of optical sensor elements  420  used for monitoring the well tree  120  or other equipment may be increased significantly without introducing the physical and cost problems associated with additional pressure barrier penetrations. 
         [0035]    The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.