Abstract:
Method and blowout preventer for sealing a well. The blowout preventer includes a body having first and second chambers, the first chamber extending substantially perpendicular to and intersecting the second chamber; a ram block configured to move within the first chamber to seal a first region of the second chamber from a second region of the second chamber; a rod connected to the ram block and configured to extend along the first chamber; a piston connected to the rod and configured to move along and within the first chamber; a bonnet configured to receive the piston, the bonnet being detachably attached to the body; and an indicator device partially mounted outside the bonnet and configured to indicate a physical position of the ram block within the body.

Description:
BACKGROUND 
     1. Technical Field 
     Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for externally identifying a position of a ram inside a ram blowout preventer. 
     2. Discussion of the Background 
     During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has increased dramatically. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel. 
     The existing technologies for extracting the fossil fuel from offshore fields use a system  10  as shown in  FIG. 1 . More specifically, the system  10  includes a vessel  12  (e.g., oil rig) having a reel  14  that supplies power/communication cords  16  to a controller  18 . The controller  18  is disposed undersea, close to or on the seabed  20 . In this respect, it is noted that the elements shown in  FIG. 1  are not drawn to scale and no dimensions should be inferred from  FIG. 1 . 
       FIG. 1  also shows a wellhead  22  of the subsea well and a drill line  24  that enters the subsea well. At the end of the drill line  24  there is a drill (not shown). Various mechanisms, also not shown, are employed to rotate the drill line  24 , and implicitly the drill, to extend the subsea well. 
     However, during normal drilling operation, unexpected events may occur that could damage the well and/or the equipment used for drilling. One such event is the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure inside the well exceeds the pressure applied to it by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent it, the well and/or the associated equipment may be damaged. Although the above discussion was directed to subsea oil exploration, the same is true for ground oil exploration. 
     Thus, a blowout preventer (BOP) might be installed on top of the well to seal the well in case that one of the above mentioned events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations. Recently, a plurality of BOPS may be installed on top of the well for various reasons.  FIG. 1  shows two BOPS  26  or  28  that are controlled by the controller  18 . 
     A traditional BOP may be one to five meters high and may weight tens of thousands of kilograms. Various components of the BOP need to be replaced from time to time. An example of a BOP  26  is shown in  FIG. 2 . The BOP  26  shown in  FIG. 2  has, among other things, two ram blocks  30  that are supported by respective piston rods  32  and a corresponding locking mechanism  33 , which is configured to lock the rods  32  at desired positions. The two ram blocks  30  are configured to move inside a first chamber  34  (horizontal bore) along a direction parallel to a longitudinal axis X of the piston rods  32 . The ram blocks  30  may severe the drill line  24  or other tools that cross a second chamber  36  (vertical wellbore) of the BOP  26 . First and second chambers are substantially perpendicular to each other. However, after cutting the drill line  24  for a number of times (if a shear ram block is installed), the ram blocks  30  and/or their respective cutting edges need to be verified and sometimes reworked. For this reason, the BOP  26  of  FIG. 2  is provided with a removable bonnet  38 , for each ram block  30 , which can be opened for providing access to the ram blocks.  FIG. 2  shows the bonnet  38  having a hinge  40  that rotatably opens the bonnet  38 . 
       FIG. 3  shows the BOP  26  having the bonnet  38  opened so as to expose the ram block  30 . Thus, as can be seen from  FIGS. 1 to 3 , when the bonnet  38  is closed, the position of the ram block  30  cannot be ascertained. Further, when the BOP is operational, the ram block  30  may have a functional open position and a functional closed position. At least these two positions need to be known by the operator of the BOP. 
     These positions may be detected as disclosed, for example, in Young et al., Position Instrumented Blowout Preventer, U.S. Pat. No. 5,320,325 (herein Young 1), Young et al., Position Instrumented Blowout Preventer, U.S. Pat. No. 5,407,172 (herein Young 2), and Judge et al., RAM BOP Position Sensor, U.S. Patent Application Publication No. 2008/0196888, the entire contents of which are incorporated here by reference. 
     These documents disclose a magnetostrictive device for determining the position of the ram block  30  relative to the body of the BOP  26 . These devices generate a magnetic field that moves with a piston connected to the ram block and disturbs another magnetic field generated by a wire enclosed by a tube. When this disturbance takes place, a magnetic disturbance propagates as an acoustic wave via the tube to a detector. The time necessary by the magnetic disturbance to propagate to the detector may be measured and used to determine the position of the piston relative to the body of the BOP. 
     Other techniques for measuring the position of the piston are known, for example, the use of a linear variable differential transformer (LVDT). LVDT is a type of electrical transformer used for measuring linear displacement. The transformer may have three solenoidal coils placed end-to-end around a tube. The centre coil is the primary, and the two outer coils are the secondaries. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An alternating current is driven through the primary, causing a voltage to be induced in each secondary proportional to its mutual inductance with the primary. 
     As the core moves, these mutual inductances change, causing the voltages induced in the secondaries to change. The coils are connected in reverse series, so that the output voltage is the difference (hence “differential”) between the two secondary voltages. When the core is in its central position, equidistant between the two secondaries, equal but opposite voltages are induced in these two coils, so the output voltage is zero. 
     When the core is displaced in one direction, the voltage in one coil increases as the other decreases, causing the output voltage to increase from zero to a maximum. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero to a maximum, but its phase is opposite to that of the primary. The magnitude of the output voltage is proportional to the distance moved by the core (up to its limit of travel), which is why the device is described as “linear.” The phase of the voltage indicates the direction of the displacement. 
     Because the sliding core does not touch the inside of the tube, it can move without friction, making the LVDT a highly reliable device. The absence of any sliding or rotating contacts allows the LVDT to be completely sealed from its environment. LVDTs are commonly used for position feedback in servomechanisms, and for automated measurement in machine tools and many other industrial and scientific applications. 
     However, these devices require a continuous source of power for measuring and transmitting the signals corresponding to the position of the ram block. Thus, in case of failure to receive electrical power from the power source, e.g., communication lost with the power source, the well operator is left without any indication about the position of the ram block. 
     Alternatively, well control operators rely on flow readings of fluid flow through the ram BOP in order to determine ram functionality. For example, a well control operator may fully open a ram BOP, measure the fluid flow through the ram BOP, and compare the measured fluid flow to an expected fluid flow. The well control operator may also fully close a ram BOP and measure whether any fluid flows through the ram BOP. Based on these readings, the positions of the rams in between the open and closed positions may be extrapolated. However, these techniques introduce a certain amount of uncertainty because the expected flow of fluid through the ram BOP may not be accurate. For example, the composition of the fluids flowing through the BOP may change such that measurements taken may be misleading. 
     Therefore, it is desired to provide a novel BOP for which the position of the ram block can be ascertained by other means than those discussed above. 
     SUMMARY 
     According to one exemplary embodiment, there is a blowout preventer for sealing a well. The blowout preventer includes a body having first and second chambers, the first chamber extending substantially perpendicular to and intersecting the second chamber; a ram block configured to move within the first chamber to seal a first region of the second chamber from a second region of the second chamber; a rod connected to the ram block and configured to extend along the first chamber; a piston connected to the rod and configured to move along and within the first chamber; a bonnet configured to receive the piston, the bonnet being detachably attached to the body; and an indicator device partially mounted outside the bonnet and configured to indicate a physical position of the ram block within the body. 
     According to still another exemplary embodiment, there is an indicator device to be attached to a movable part of a blowout preventer for sealing a well. The indicator device includes a first magnet configured to be attached to a piston within a bonnet of the blowout preventer; an alignment rod configured to be attached to an outside of the bonnet; a second magnet attached to the alignment rod, outside the bonnet, and configured to move along the alignment rod when pushed or pulled by the first magnet; and a scale provided on the outside of the bonnet such that a position of the second magnet relative to the scale is indicative of the position of a ram block inside the blowout preventer. 
     According to yet another exemplary embodiment, there is an indicator device to be attached to a movable part of a blowout preventer for sealing a well. The indicator device includes a tail-rod extension configured to be connected to the movable part of the blowout preventer and configured to move through a bonnet of the blowout preventer; a seal disposed between the tail-rod extension and the bonnet for maintaining a pressure difference between an inside and outside of the bonnet; and a visual indicator provided on the tail-rod extension, outside the bonnet, and configured to indicate a position of the movable part. 
     According to another exemplary embodiment, there is a method for attaching an indicator device to a movable part of a blowout preventer. The method includes forming a hole in a bonnet of the blowout preventer; attaching a rod to the movable part of the blowout preventer such that the rod enters the hole of the bonnet and part of the rod is inside the bonnet and part of the rod is outside the bonnet; disposing a seal between the rod and the bonnet to maintain a pressure difference between an inside and outside of the bonnet; and providing a visual indicator on the part of the rod that is outside the bonnet to indicate a position of the movable part inside the blowout preventer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings: 
         FIG. 1  is a schematic diagram of a conventional offshore rig; 
         FIG. 2  is a schematic diagram of a traditional BOP; 
         FIG. 3  is a schematic diagram of an opened BOP; 
         FIG. 4  is a schematic diagram of a bonnet of a BOP having an indicator device according to an exemplary embodiment; 
         FIG. 5  is a schematic diagram of an indicator device mounted on a bonnet of a BOP according to an exemplary embodiment; 
         FIGS. 6 and 7  are schematic diagrams illustrating possible magnet distributions for an indicator device according to an exemplary embodiment; 
         FIG. 8  is a schematic diagram of a scale of an indicator device according to an exemplary embodiment; 
         FIG. 9  is a schematic diagram of another indicator device according to an exemplary embodiment; 
         FIGS. 10 and 11  are schematic diagrams of a tail-rod indicator device according to an exemplary embodiment; 
         FIGS. 12 and 13  are schematic diagrams of an off-center indicator device according to an exemplary embodiment; 
         FIGS. 14 and 15  are schematic diagrams of a bent indicator device according to an exemplary embodiment; and 
         FIG. 16  is a flow chart illustrating a method for attaching an indicator device to a BOP according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of a ram BOP provided on top of a well head undersea. However, the embodiments to be discussed next are not limited to these systems, but may be applied to other BOPS that may be used, for example, inland. 
     Reference throughout the specification to “an exemplary embodiment” or “another exemplary embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in an exemplary embodiment” or “in another exemplary embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     According to an exemplary embodiment, a new or an existing blowout preventer (BOP) may be configured to provide an external indicator that is indicative of a position of the ram block 
     More specifically, as shown in  FIG. 4 , a bonnet  60  of a BOP is illustrated having an indicator device  62 . The indicator device  62  may include one or more components as discussed next. It is noted that the indicator device  62  has at least some components provided on an outside surface  60   a  of the bonnet  60 .  FIG. 4  shows a scale  64  provided, for example, directly on the outside of the bonnet  60 . A marker  66  moves relative to the scale  64  for indicating the physical position of the ram block inside the body of the blowout preventer. The marker  66  may be attached, for example, to an outside magnet  68 . The external magnet  68  ma move, for example, along an alignment rod  70 . The alignment rod  70  is fixed to the outside of the bonnet  60  by, for example, two supports  71 . Other connections and/or components may be used to indicate the position of the ram block relative to the scale  64  as would be appreciated by those skilled in the art. For example, the marker  66  may be part of the external magnet  68 . The marker  66 , rod  70 , and supports  71  may be made of stainless steel, corrosion resistant materials, plastics, composite materials, etc. 
     According to an exemplary embodiment illustrated in  FIG. 5 , the indicator device  62  may also include an internal magnet  72 . The internal magnet  72  may be disposed in a groove  74  formed in a piston  76 . Piston  76  is connected via a rod  78  to a ram block  80 . It is noted that piston  76  may be provided inside bonnet  60  and piston  76  is configured to move along axis X for actuating or retrieving the ram block  80 . Mechanisms for moving piston  76  inside the bonnet  60  are known in the art and are not repeated herein. In one embodiment, a piston tail  82  may be attached to the piston  76  or rod  78 . 
     In still another exemplary embodiment, a second internal magnet  84  may be provided in a corresponding groove in piston  76 . First and/or second internal magnets  72  and  84  may be configured to fully circle a periphery of the piston  76 . However, according to another exemplary embodiment, the first and/or second internal magnets may only partially extend around the piston  76 . The internal magnet  72  and the external magnet  68  are sized in such a way that a movement of the internal magnet  72  induces a movement of the external magnet  68 . When the second internal magnet  84  is also present, the polarity of the three magnets  68 ,  72  and  84  may be arranged as shown in  FIG. 6  such that both internal magnets  72  and  84  pull or push the external magnet  68 .  FIG. 7  shows another possibility for arranging the polarity of the magnets. Those skilled in the art would recognize that other combinations are also available, e.g., with multiple polarities. 
     Although  FIG. 5  shows the external magnet  68  connected to alignment rod  70  and the alignment rod  70  being supported by two supports  71 , it is noted that other arrangements may be used for providing the external magnet  68  on a sliding path along axis X of the bonnet  60 . For example, only one support  71  may be used instead of two supports  71 . 
     According to an exemplary embodiment shown in  FIG. 8 , the scale  64  is provided on the bonnet  60  either by being engraved on the bonnet  60  or by being attached with bolts to the bonnet or by being painted or by other mechanisms. Irrespective of the method of providing the scale  64  on the bonnet  60 , a closed position C and an open position O may be indicated on the scale. As the scale  64  and the marker  66  are provided on the outside surface  60   a  of the bonnet  60 , the operator of the BOP may visually determine the position of the ram block by monitoring the marker  66 . For example, when the BOP is deployed undersea, a remote operated vehicle (ROV) may be used to carry a camera and directly determine the position of the ram block. This is advantageous when the communication with the BOP fails. Under these circumstances, the operator may send the ROV to quickly identify whether the BOP has closed or not. 
     Returning to  FIG. 5 , two sensors  86  may be added to the bonnet  60  (inside or outside) for detecting a moving direction of the piston  76 . For example, the sensors may be configured to sense the internal magnet  72 . By sensing with two sensors the internal magnet  72 , the movement direction of the piston  76  may be determined, supposing that power is available to the sensors and the communication with the sensors is not lost. Other sensors or devices may be used to determine the movement direction of the piston  76 . 
     According to another exemplary embodiment illustrated in  FIG. 9 , an indicator device  62  may include a tail-rod extension  100  that is configured to be attached to the piston tail  82 . The tail-rod extension  100  may be attached to an existing bolt pattern  102  that is present on the piston tail  82  (e.g., piston tail  82  may have the bolt pattern  102  for receiving a magnetostrictive device (not shown) that is configured to determine a position of the piston  76 ). Alternatively, an existing BOP may be modified to receive the bolt pattern  102 . 
     The tail-rod extension  100  is configured to exit through the bonnet  60  via a hole  104  formed in the bonnet. In order to prevent a fluid from passing from enclosure  106  to the ambient or vice versa, a seal  108  may be provided between the bonnet  60  and the tail-rod extension  100 . The seal  108  may be a static or dynamic seal and may be configured to maintain a pressure difference between an inside and outside of the bonnet. 
     The embodiment illustrated in  FIG. 9  also includes a scale  110  formed (or attached) to the tail-rod extension  100 . The scale  110  is so calibrated to indicate the position of the ram block  80  inside the body of the BOP. In another application, the tail-rod extension  100  may be attached to another moving component of the BOP, off-center to a central axis of the bonnet, as will be discussed later. 
     However, according to another exemplary embodiment illustrated in  FIGS. 10 and 11  another type of marker may be implemented as discussed next. These figures show a BOP  110  having a body  112 . A rod  114  (solid rod, flexible wire, etc.) may be attached to a moving part of the BOP (e.g., piston or tail-rod). Thus, the rod  114  moves unitarily with the moving part of the BOP. A marker  116  may be attached to the rod  114  in such a way that a position of the marker  116  indicates a closed, opened or in between position of the ram block  80 . Both the rod  114  and the marker  116  may be provided in a partially transparent tube  118 . The partially transparent tube may be totally transparent, e.g., made of glass of plastic, or may have a longitudinal strip that is transparent. The tube  118  may be straight as shown in  FIGS. 10-13  or curved as shown in  FIGS. 14 and 15 . If the space available for the BOP is limited, the curved tube  118  of  FIGS. 14 and 15  may be used. In addition, tube  118  may be closed or opened as also shown in  FIGS. 10 and 11 . 
     The marker  116  being disposed outside the BOP  110 , a ROV may be used to directly read the position of marker  116  such that even when the BOP has failed, the position of the ram block  80  may be determined. For this reason, the tube  118  is partially or totally transparent. In this regard,  FIG. 10  shows a situation when the ram block  80  is open and  FIG. 11  shows the ram block being closed. Other mechanical, thermal, etc. means may be used to indicate the position of the ram block  80  as long as a reading of the position is possible from outside the BOP by either direct visual contact or video contact. 
       FIGS. 12 and 13  are similar to  FIGS. 10 and 11  but indicate that the rod  114  and marker  116  are off-center of a central axis X of the bonnet  60 .  FIGS. 14 and 15  illustrate a different embodiment in which the rod  114  is not straight as in  FIGS. 10-13  but is bent when exiting the bonnet  60  in order to reduce a horizontal foot-print of the BOP. In this case, rod  114  is a flexible wire that can easily bend to follow a given profile of tube  118 .  FIGS. 14 and 15  show that the rod  114  is configured to bend when exiting the bonnet  60  and change a motion direction from a first direction (X) to a second direction (Y) that is substantially perpendicular on the first direction. 
     As those skilled in the art would understand, the novel indicator device that has external components that are visible from outside the BOP may be retrofitted to the existing BOP or may be manufactured together with the new BOP. These indicator devices may be used when the BOP has failed, or when the communication with the BOP has failed or is unreliable, or when the operator intends to calibrate the mechanical or electrical devices that produce the position of the ram block, etc. 
     According to an exemplary embodiment illustrated in  FIG. 16 , there is a method for attaching an indicator device to a movable part of a blowout preventer. The method includes a step  1600  of forming a hole in a bonnet of the blowout preventer; a step  1602  of attaching a rod to the movable part of the blowout preventer such that the rod enters the hole of the bonnet and part of the rod is inside the bonnet and part of the rod is outside the bonnet; a step  1604  of disposing a seal between the rod and the bonnet to maintain a pressure difference between an inside and outside of the bonnet; and a step  1606  of providing a visual indicator on the part of the rod that is outside the bonnet that indicates a position of the movable part inside the blowout preventer. 
     The disclosed exemplary embodiments provide an indicator device and a method for indicating a position of a ram block inside a BOP. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
     Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
     This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.