Patent Publication Number: US-9410380-B2

Title: Systems and methods for providing fiber optics in downhole equipment

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to monitoring downhole equipment, and more specifically to systems and methods for installing optical fibers in downhole equipment without the need for splicing the optical fibers between different sections of the equipment. 
     2. Related Art 
     Oil production often requires the use of artificial lift systems to recover oil and other well fluids from wells. These artificial lift systems may include, for example, electric submersible pump (ESP) systems and subsea boosting systems. These systems are typically very expensive to install and operate. A subsea lift system may, for example, cost tens of millions of dollars to install and hundreds of thousands of dollars each day to operate. The costs associated with failures and downtime in these systems are also very high. 
     Because of the high cost of an artificial lift system such as may be installed in subsea applications, it is very important to take steps to ensure that it is as reliable as possible and has the longest possible operational life. One of the things that can be done to improve reliability is to monitor various parameters associated with the system in order to determine the “health” of the system. These parameters may include such things as temperature, pressure, vibration, fluid flow, fluid viscosity, voltage, current, and many others. 
     If the monitored parameters remain within desired operating ranges (a “green” zone), the system may continue to operate without any changes. If the monitored parameters fall outside the desired operating ranges, but are still within acceptable limits (a “yellow” zone), it may be necessary to adjust the operation of the system in some manner. This may include modifying control signals, updating operating parameters within the downhole equipment, and so on. These adjustments are intended to move the operation of the system (as indicated by the monitored parameters) back into the green operating zone. If the adjustments do not cause the parameters to return to the desired operating ranges, this may indicate that it is necessary to perform repair or maintenance on the system. If the monitored parameters fall outside the range of acceptable values (a “red” zone), it may be necessary to discontinue operation of the system, and possibly repair or replace one or more system components. 
     One of the key parameters that may be monitored is the temperature of the system components that are positioned downhole within a well. In some applications, the temperature can be as high as 600° F. High temperatures can be very hard on components such as motor bearings, and even materials such as electrical insulation, which may begin to break down and lose its electrically insulating properties. Conventionally, thermal sensors such as thermocouples were designed into equipment such as ESP motors to provide information on the temperature of the equipment. A thermocouple, however, can only monitor the temperature at a single point, so multiple thermocouples would be required to provide temperature information from different points within the equipment. 
     More recently, optical fibers that incorporate multiple sensors (fiber Bragg gratings) have been incorporated into the designs of equipment such as ESP motors in order to provide temperature information from multiple points within the motors. These types of sensors also have some drawbacks, however. For instance, in some applications, it may be necessary for an ESP motor to be several hundred feet long in order to generate the required horsepower to drive the associated pump. Because it would be very difficult to transport a motor of this size from the factory to the field where it will be installed, it is typically necessary to construct the motor in sections, each of which is less than 40 feet in length. If fiber optic sensors are incorporated into the motor sections, means must be provided to splice together the optical fibers of adjacent motor sections in the field when the motor is assembled and installed in the well. Currently available means to achieve the splices are expensive, slow and difficult to assemble, and too large to be accommodated in downhole motors. 
     It would therefore be desirable to provide means to facilitate the use of fiber optics in downhole equipment such as multi-section ESP motors which reduce or overcome one or more of the problems above. 
     SUMMARY OF THE INVENTION 
     This disclosure is directed to systems and methods for installing an optical fiber in a downhole equipment system having multiple components that are installed in the field. The components are assembled to form a continuous sealed conduit that extends through multiple ones of the components (e.g., motor sections). The conduit is sealed to prevent potentially damaging fluids from leaking into the conduit. After the conduit through the components is formed, an optical fiber is inserted into the conduit so that the fiber spans the connections between the components. Large, costly and time-consuming fiber optic splices between the different components are thereby avoided. 
     The components in which the optical fiber is installed may be, for example, sections of an ESP motor, a pump section, a seal, or some other type of component. A tubular connector may be used to couple the passageways of the different components to form the continuous conduit. The tubular connectors may be designed to extend upward, above the face of a lower motor section in order to allow the motor section to be filled with oil while preventing oil from entering the conduit. The passageways in the different components may have different diameters, or may have tapered openings to prevent the end of the optical fiber from catching on the passageway openings when the optical fiber is inserted into the conduit. The optical fiber may be unspliced, and may incorporate embedded sensors, such as fiber Bragg gratings. 
     Alternative embodiments may include methods for installing optical fibers in downhole equipment. In one embodiment, multiple system components (e.g., motor sections) are provided, where each of the components has a passageway through it to accommodate an optical fiber. A tubular connector is installed at the top of a lower component at the upper end of the passageway through this component. The tubular connector is initially capped to seal off the conduit that includes the passageway. The lower component is filled with oil. After the lower component has been filled with oil, the cap is removed from the tubular connector and an upper component is installed on the top of it. The tubular connector couples the passageways of the upper and lower components to form a single, sealed conduit through both components. An optical fiber is then inserted into the conduit so that it is positioned within both of the components. 
     Numerous other embodiments are also possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
         FIG. 1  is a diagram illustrating an ESP system installed in a well in accordance with one embodiment. 
         FIG. 2  is a diagram illustrating the coupling of two of the motor sections in accordance with one embodiment. 
         FIG. 3  is a detailed view of a coupling between a motor base and motor head in accordance with one embodiment. 
         FIGS. 4A and 4B  are diagrams illustrating insertion of an optical fiber through passageways that have different-diameters ( 4 A) and chamfered/tapered edges ( 4 B). 
         FIG. 5  is a flow diagram illustrating an exemplary method for installing an optical fiber in an ESP motor having multiple sections. 
     
    
    
     While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. Further, the drawings may not be to scale, and may exaggerate one or more components in order to facilitate an understanding of the various features described herein. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting. 
     The increasing costs of installing, maintaining and operating artificial lift systems is increasing the importance of monitoring conditions relating to operation of these systems. One of the operating conditions that is very important in assessing the health of an artificial lift system is the temperature of the system. The operating temperature of the can be measured in various ways. For instance, temperatures at multiple points within the system can be conveniently measured using an optical fiber having embedded sensors. One of the difficulties of using fiber optic sensors, however, is that artificial lift systems often have multiple components that have to be assembled in the field (such as sections of an ESP motor), which conventionally required optical fibers in the different components to be spliced together. These splices were typically time consuming, expensive, and too large for the small diameters of downhole equipment. 
     The present systems and methods reduce or minimize these problems by providing a means to form a conduit through the various system components and then installing a continuous optical fiber in the conduit. The conduit can be formed in a relatively simple and straightforward manner, and the use of a continuous fiber that is installed in the conduit after the system components (e.g., motor sections) are assembled eliminates the need for splices to connect different sections of optical fiber between different system components. The conduit is sealed to prevent hydrogen-containing fluids such as motor oil and well fluid from contacting the optical fiber and degrading the fiber&#39;s performance. The conduit may also include features that facilitate installation of the optical fiber therein. 
     Referring to  FIG. 1 , a diagram illustrating an ESP system installed in a well is shown. ESP system  100  is installed within the bore  110  of a well. The well may be a subsea well or a surface well. In this embodiment, ESP system  100  is suspended in the well from production tubing  120 . ESP system  100  includes a pump  101 , a seal  102  and a motor  103 . A fiber optic cable  104  couples surface equipment (not shown) to ESP system  100 . Fiber optic cable  104  includes an optical fiber and a protective housing that prevents exposure of the optical fiber to well fluids. In this embodiment, fiber optic cable  104  has a sealed connection to the housing of motor  103  and the optical fiber extends into motor  103  so that it can be used to monitor conditions in the motor, such as its temperature. (“Sealed”, as used herein, refers to the sealing of the passageway connections to prevent potentially damaging fluids from entering the passageways and coming into contact with the optical fiber.) 
     In the embodiment of  FIG. 1 , motor  103  is assembled from multiple, separate motor sections. Each of the motor sections is up to about  35  feet in length, which allows them to be transported in standard  40 -foot shipping containers. Each of the motor sections has a tube that extends through it to accommodate an optical fiber having embedded sensors. A coupling is installed between each of the motor sections to provide a sealed connection between the tubes in the different sections, thereby forming a continuous, sealed, protective conduit that extends through the motor. Fiber optic cable  104  (which contains one or more optical fibers) is coupled to the end of this conduit via a sealed connection. A port may be provided at one end of the conduit to provide means to couple the fiber optic cable to the conduit, and means to introduce the optical fiber(s) of the cable into the conduit. The optical fiber from the cable extends into the conduit within the motor or other system components to enable sensing of the temperature or other parameters at multiple points in the motor or other system components. The optical fiber may also be used to communicate information through the system components. The optical fiber is inserted into the conduit after the motor sections and/or other system components are connected, so no splices between system components are required. The optical fiber itself may be spliced before it is inserted into the conduit. 
     It should be noted that, while  FIG. 1  depicts an ESP system in which an optical fiber is installed in the motor (through each of the motor&#39;s different sections), alternative embodiments may form a conduit through any type of system component, including motors, pumps, seals, gauges, and the like. The conduit may span all of the components, or selected ones of the components. 
     Referring to  FIG. 2 , a diagram illustrating the coupling of two of the motor sections in more detail is shown. Each of the motor sections has a body that houses respective sections of the stator and rotor. At the upper end of the body is a motor head, and at the lower end of the body is a motor base.  FIG. 2  depicts the base  210  of an upper motor section coupled to the head  220  of a lower motor section. The remainder of each motor section is not shown. For purposes of clarity, the details of the electrical and mechanical connections are not described herein. 
     The upper motor section has a tube  240  that extends through it. A lower end of tube  240  is connected to a passageway  211  that extends through motor base  210 . Leak proof connector  212  couples tube  240  to passageway  211  and prevents oil in the upper motor section from leaking into the tube or passageway. Motor head  220  likewise has a passageway  221  that extends through it. A tube  250  that extends through the lower motor section is connected to passageway  221  by another leak proof connector  222 . Leak proof connector  222  prevents oil in the lower motor section from leaking into tube  250  or passageway  221 . 
     A tubular connector  230  is installed between motor base  210  and motor head  220  to connect passageway  211  to passageway  221 . Tubular connector  230  is a rigid tubular structure that bridges the gap between motor base  210  and motor head  220 . As will be described in more detail below, tubular connector  230  extends above the top of motor head  220  in order to facilitate assembly of the motor. The ends of tubular connector  230  are sealed against motor base  210  and motor head  220  to prevent motor oil from leaking into passageways  211  and  221 , or tubes  240  and  250 . As will be described in more detail below, an optical fiber is positioned in the conduit formed by the passageways. 
     Referring to  FIG. 3 , a more detailed view of the coupling between the motor base and motor head is shown. In particular, a close-up view of the interface between motor base  210  and motor head  220  is provided. It can be seen in this figure that a lower end of tubular connector  230  fits into a recess in motor head  220 . In this embodiment, tubular connector  230  has a shoulder  236  that limits the depth to which the tubular connector can extend into the recess. A pair of o-ring seats  232  and  233  are provided to accommodate corresponding o-rings. This ensures a seal between tubular connector  230  and motor head  220 , so that oil contained in the motor does not enter the conduit formed by passageways  211 ,  221  and  231 . 
     The upper end of tubular connector  230  fits into a recess in motor base  210 , which is connected (e.g., bolted) to motor head  220 . Tubular connector  230  spans the gap between motor base  210  and motor head  220 , so that a continuous conduit is formed. A pair of o-ring seats  234  and  235  are provided to accommodate corresponding o-rings, which ensures a seal between tubular connector  230  and motor base  210 . As noted above, this prevents oil contained in the motor from entering the conduit formed by the passageways through the motor base, connector and motor head. An optical fiber is positioned in the conduit formed by passageways  211 ,  231  and  221 . The optical fiber is not explicitly depicted in the figure. 
     As shown in  FIG. 3 , passageway  211  in motor base  211  has a diameter d 1 . 
     Passageway  231  in connector  230  has a diameter d 2 , and passageway  221  in motor head  220  has a diameter d 3 . Passageway  211  has the smallest diameter (d 1 ), while passageway  221  has the largest diameter (d 3 ). In other words, d 1 &lt;d 2 &lt;d 3 . The different diameters of the passageways are designed to facilitate installation of an optical fiber in the conduit formed by the passageways. Since each successive diameter (from top to bottom) has a slightly larger diameter, an optical fiber that has been successfully inserted through an upper passageway should easily pass through the following (lower) passageway, which has a slightly larger diameter, with no difficulty. The insertion of the optical fiber through different-diameter passageways is illustrated in  FIG. 4A . 
     It should be noted that the use of different-diameter passageways is not necessary in all embodiments. In some alternative embodiments, the passageways may all have the same diameter. It may be desirable in these embodiments to chamfer or taper the upper ends of the passageways so that the opening of the passageway is wider than the body of the passageway. This helps prevent the optical fiber from getting caught on the edge of the opening to the lower passageway. Chamfered/tapered edges  270  on connector  230  are illustrated in  FIG. 4B . Some embodiments may utilize both different-diameter passageways and tapered/chamfered passageway openings. 
     It can be seen in  FIGS. 2 and 3  that tubular connector  230  is long enough that its upper end ( 239 ) extends upward beyond the upper end ( 225 ) of motor head  220  by a height h. This allows the conduit through tubular connector  230  to be accessible after the lower motor section is filled with oil during the assembly of the motor. Tubular connector  230  is normally capped when the lower motor section is filled with oil in order to prevent the oil from entering the passageway through the connector. After the lower motor section is filled with oil, the cap can be removed, so that the upper motor section can be installed. Tubular connector  230  extends between the upper and lower motor sections when assembled, forming a sealed connection between passageways  211 ,  231  and  221 . 
     Embodiments of the invention may also include methods for installing optical fibers in downhole equipment. Referring to  FIG. 5 , a flow diagram illustrating an exemplary method for installing an optical fiber in an ESP motor having multiple sections is shown. For purposes of clarity, this exemplary method will be described with respect to a two-section motor, although it can be applied to motors having more than two sections. 
     The first step in this method is providing multiple (e.g., two) motor sections, where each of the motor sections has a passageway through it to accommodate an optical fiber therein (step  505 ). It is assumed that the passageway through the lowest section of the motor is terminated or capped at its lower end. A tubular connector is installed at the top of the lower motor section, so that the passageway through the lower motor section and the tubular connector are coupled to form a continuous conduit (step  510 ). The tubular connector is initially capped to seal off this conduit. The installation of the tubular connector may be performed at the factory or in the field. The subsequent steps of the method are performed in the field (at a well location). 
     The lower motor section is then filled with oil (step  515 ). The cap on the tubular connector prevents the oil from entering the conduit, where it could later contact the optical fiber and degrade its sensing and transmission characteristics. The upper end of the tubular connector extends above the upper end of the lower motor section so that after the lower motor section has been filled with oil, the cap can be removed without allowing oil to enter the conduit. When the lower motor section is filled with oil, the cap is removed from the tubular connector and the upper motor section is installed on the top of the lower motor section (step  520 ). When the two motor sections are assembled, the tubular connector couples the passageways in the motor sections to form a single, sealed conduit through both motor sections. 
     The upper motor section has a port at its upper end that allows access to the conduit through the assembled motor sections. An optical fiber is inserted into the conduit (step  525 ). The continuous sealed conduit through the motor sections allows a single optical fiber to be installed in the different motor sections without the need to splice together different segments of optical fibers that are permanently installed in the different motor sections. Likewise, this method (and the corresponding apparatus) avoids the size restrictions, cost and installation time associated with conventional fiber optic splices. 
     While specific embodiments of the present invention have been described Pressure differential above, alternative embodiments may vary from the described embodiments in a number of ways. For example, while the embodiment of  FIGS. 1-3  provides a conduit through which an optical fiber can be installed in multiple sections of an ESP motor, other embodiments may use the same means to install an optical fiber in other downhole system components. These means can be implemented in two or more such components. The installed optical fiber (or fibers) can be used to provide an optical communication channel and/or sensing means. Although the foregoing embodiments utilize a separate tubular connector to couple the passageways of the different motor sections, alternative embodiments may incorporate this connector into one of the motor sections (e.g., into the motor head). Further, while the foregoing embodiments describe a single optical fiber which is inserted into the conduit, alternative embodiments may have more than one optical fiber inserted into the conduit. Other variations will also be apparent to those of skill in the art. 
     The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment. 
     While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed within the following claims.