Patent Publication Number: US-8539975-B2

Title: Drill string valve and method

Description:
BACKGROUND 
     1. Technical Field 
     Embodiments of the subject matter disclosed herein generally relate to methods and valves and, more particularly, to mechanisms and techniques for interrupting a flow of liquid through a valve. 
     2. Discussion of the Background 
     During the past years, with the increase in price of fossil fuels, the interest in developing new oil production fields has dramatically increased. 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 oil reserves. One characteristic of the offshore locations is the high pressure to which the drilling equipment is subjected. For example, it is conventional to have parts of the drilling equipment designed to withstand pressures between 5,000 to 30,000 psi. In addition, the materials used for the various components of the drilling equipment are desired to be corrosion resistant and to resist high temperatures. 
     Existing technologies for extracting oil from offshore fields use a system  10  as shown in  FIG. 1 . More specifically, the system  10  includes a vessel (or rig)  12  having a reel  14  that supplies power/communication cables  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 that the drill string  24  is provided inside a riser  40 , that extends from vessel  12  to a BOP  28 . A wellhead  22  of the subsea well is connected to a casing  44 , which is configured to accommodate the drill string  24  that enters the subsea well. At the end of the drill string  24  there is a drill bit (not shown). Various mechanisms, also not shown, are employed to rotate the drill string  24 , and implicitly the drill bit, 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 (mud). 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 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, i.e., 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 are installed on top of the well for various reasons.  FIG. 1  shows two BOPs  26  or  28  that are controlled by the controller  18 . 
     However, ultra-deep water exploration presents a host of other drilling problems, such as substantial lost circulation zones, well control incidents, shallow-water flows, etc. Thus, many of these wells are lost due to significant mechanical drilling problems. These events increase the cost of drilling and reduce the chances that oil would be extracted from those wells, which is undesirable. 
     A new technology for deep water exploration, which is discussed with regard to  FIG. 2 , has been developed in response to these problems. While the traditional technology used single-gradient drilling, the new technology uses dual-gradient drilling for better controlling a bottom hole pressure, i.e., the pressure at the region around the drill bit  30  shown in  FIG. 2 . With the single gradient drilling, the bottom hole pressure is controlled by a mud (dedicated mixture of liquids used in the oil extraction industry) column extending from the bottom of the well  32  to the rig  12 , as shown in  FIG. 2 . However, with the dual gradient drilling, a better pressure control is achieved through a combination of (i) mud from the bottom  32  of the well to a mud lift pump  34  and (ii) mud from the mud lift pump  34  to the rig  12 .  FIG. 2  shows that the new technology employs a mud return line  36  and a seawater power line  38  to the mud lift pump  34  beside the riser  40 . The mud is provided through the drill string  24  to the drill bit  30 . A subsea rotating device  42  is provided close to the BOP  26  to maintain separation between the sea water in the riser above the subsea rotating device  42  and the mud returns below. Thus, the dual gradient drilling system shown in  FIG. 2  provides the mud pumped through the drill string  24  to the drill bit  30  and then pumped back up an annulus between the drill string  24  and the casing  44  by the mud lift pump  34 . 
     The system shown in  FIG. 2 , which needs to balance the different pressures between the mud and the seawater when the mud lift pump  34  is not active, may employ a drill string valve  46 , disposed below BOP  26  and close to drill bit  30 . The unbalanced pressure formed because of the U-tube effect of the mud could reach 5,000 psi, depending on mud weight and water depth. This is a large pressure that would normally destroy valves used in faucets, irrigation systems, blood dialysis and other technical fields that use valves. Due to these large pressures and the erosion problems posed by the saltwater and mud, one skilled in the art would not look or import components from valves used in these other technical fields because these valves are not designed to withstand large undersea pressures. Also, the sealing requirements for the drilling industry make those valves used in the low pressure fields inappropriate for the drilling industry. 
     The conventional drill string valve  46  is placed inside the casing  44 , close to the drill bit  30 . Thus, the drill string valve  46  is a downhole tool and this valve is illustrated in  FIG. 3 . The drill string valve  46  has a sliding valve  50  that is configured to seal a passage  52  from a passage  54  inside spring carrier  48 . The sliding valve  50  achieves the sealing in concert with cone seal  56 . Cone seal  56  may be made of a strong metal and fixed relative to the drill string valve  46 . The sliding valve  50  is movable along an axis Z and is biased by a spring  58 . The sliding valve  50  is closed in a default position. When the mud is pumped from the vessel  12  towards drill bit  30  (along axis Z in  FIG. 2 ), the high pressure of the mud opens up the sliding valve  50  (by pressing down the sliding valve  50 ) and compresses spring  58 . When the pumping from vessel  12  stops, the compressed spring  58  closes the sliding valve  50 , thus closing the drill string valve  46 . 
     A few disadvantages of the drill string valve  46  shown in  FIG. 3  are now discussed. A drill collar of the valve was designed in two sections. The two sections include a lower long collar  62  to house the long coil spring  58  and a short upper collar  64  to house the valve mechanism. This design requires machining drill collars to high-precision, making holding diameters and concentricities, especially in deep bores, a challenge. Because it is a two-piece collar, assembly and disassembly requires the use of heavy “tongs” or iron roughneck to make up and break the drill collar connection. This equipment is not available in the shop and must be made up and broken on the drill floor. 
     A spring package includes the long coil spring  58 , or tandem springs that make up a long spring, and these springs are provided in a spring chamber  66 . Buckling of the long springs  58  has been observed. The buckling increase a friction between the springs and the package as the coils contact with an outer diameter and an inner diameter of the spring chamber  66 . Also, the spring package is open to borehole fluids in this design. Even if the spring area is packed in grease, the grease eventually is replaced with mud during drilling. Thus, the springs are corroded by the borehole fluids, which further increase the friction between the springs and the walls of the spring chambers and also shorten the life of the springs. 
     Another disadvantage of the system shown in  FIG. 3  is related to the way in which the drill string valve  46  is assembled. The coil spring  58  and spring carrier  48  are installed in the long collar  62 , where the spring carrier  48  male thread is screwed into a mating thread  63  at the lower end of the collar. Once installed, the spring carrier  48  is extended out of the top of the lower collar  62 . The spring extension beyond the collar depends on the spring used, but could be up to 12 inches. This extreme condition would have the free length of the spring hanging out 3 inches beyond the spring carrier  48  with no support. The challenge is to handle the heavy upper collar  64 , swallowing an unsupported spring end and having to compress the spring while lining up for engagement with the lower collar thread  65 . The spring induced end load during these maneuvers could reach a few thousand pounds at thread engagement. This is a safety concern for the rig operator because of potential injury to the crew. 
     Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks. 
     SUMMARY 
     According to one exemplary embodiment, there is a drill string valve configured to be attached to a casing for connecting a drill to a rig. The drill string valve includes an elongated housing having an inside cavity, the housing extending along an axis and having a substantially constant outer diameter; a seal element attached to a first end of the elongated housing, the seal element having an outer diameter smaller than an inner diameter of the elongated housing, and the seal element being disposed within the inside cavity such that a flow of liquid through the inside cavity from the first end to a second end of the elongated housing is allowed; a sliding valve disposed within the inside cavity and configured to slide to and from the seal element along the axis such that when the sliding valve contacts the seal element the flow of liquid is suppressed; a biasing cartridge disposed within the inside cavity, between the seal element and the second end of the elongated housing, and configured to apply a first force on the sliding valve such that the sliding valve is contacting the seal element; and a loading mechanism disposed within the inside cavity, between the biasing cartridge and the second end of the elongated housing, and configured to apply a second force on the biasing cartridge. 
     According to another exemplary embodiment, there is a method for preparing a drill string valve to be connected to a casing for connecting a drill to a rig. The method includes a step of connecting a power source to a port of a biasing cartridge of the drill string valve, the drill string valve including (i) an elongated housing having an inside cavity, the housing extending along an axis and having a substantially constant outer diameter, (ii) a seal element attached to a first end of the elongated housing, the seal element having an outer diameter smaller than an inner diameter of the elongated housing, and the seal element being disposed within the inside cavity such that a flow of liquid through the inside cavity from the first end to a second end of the elongated housing is allowed, (iii) a sliding valve disposed within the inside cavity and configured to slide to and from the seal element along the axis such that when the sliding valve contacts the seal element the flow of liquid is suppressed, and (iv) the biasing cartridge disposed within the inside cavity, between the seal element and the second end of the elongated housing and configured to apply a first force on the sliding valve such that the sliding valve is contacting the seal element, and (v) a loading mechanism disposed within the inside cavity, between the biasing cartridge and the second end of the elongated housing, and configured to apply a second force on the biasing cartridge; a step of applying a pressure to the loading mechanism to generate the second force; a step of compressing a wave spring of the biasing cartridge; a step of locking a stop element to maintain the wave spring in a compressed state; and a step of releasing the applied pressure. 
     According to still another exemplary embodiment, there is a drill string valve configured to be attached to a casing for connecting a drill to a rig. The drill string valve includes an elongated housing having an inside cavity, the housing extending along an axis; a motor module disposed within the inside cavity; a seal element connected to the motor module and configured to move within the inside cavity along the axis; a seat disposed within the inside cavity and configured to receive the seal element to interrupt a fluid flow through the drill string valve when the seat touches the seal element; and a control element disposed within the inside cavity and configured to control a closing and opening of the seal element. 
     According to another exemplary embodiment, there is a method for controlling a drill string valve. The method includes a step of receiving from a flow meter unit a flow rate of a fluid through the drill string valve, a step of determining in a processor a position of a seal element that is configured to move to and from a seat to suppress a fluid flow through the drill string valve, and a step of searching a look-up table stored in memory connected to the processor for determining whether a motor has to be activated to close or open the seal element. 
    
    
     
       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 conventional dual-gradient drilling system; 
         FIG. 3  is a schematic diagram of a conventional drill string valve mechanism; 
         FIG. 4  is a schematic diagram of a novel drill string valve according to an exemplary embodiment; 
         FIG. 5  is a more detailed view of a top portion of the drill string valve of  FIG. 4  according to an exemplary embodiment; 
         FIG. 6  is a schematic diagram of a wave spring; 
         FIG. 7  is a more detailed view of a lower portion of the drill string valve of  FIG. 4  according to an exemplary embodiment; 
         FIG. 8  is a flow chart illustrating steps of a method for activating a drill string valve according to an exemplary embodiment; 
         FIG. 9  is a schematic diagram of another novel drill string valve according to an exemplary embodiment; 
         FIG. 10  is schematic diagram of a motor module that is part of the drill string valve of  FIG. 9  according to an exemplary embodiment; and 
         FIG. 11  is a schematic diagram of the drill string valve of  FIG. 9  that illustrates various pressures present in the valve according to an exemplary embodiment; and 
         FIG. 12  is a flow chart illustrating steps of a method for controlling a drill string valve 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 drill string valve. However, the embodiments to be discussed next are not limited to this type of valve, but may be applied to other systems that are configured to interrupt a fluid flow. 
     Reference throughout the specification to “one embodiment” or “an 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 one embodiment” or “in an 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 novel drill string valve has a substantially constant outer diameter, includes a loading mechanism for loading a valve spring of a spring package, the valve spring includes a wave spring, the spring package is immersed in an oil filled chamber and the oil filled chamber pressure is compensated from an annulus pressure. The above noted features are discussed next in more details. It is noted that the following exemplary embodiments may include one or more of these features or other features and no exemplary embodiment should be construed to require all these features or a specific combination of the features noted above. 
     According to an exemplary embodiment,  FIG. 4  shows an overall view of a novel drill string valve  70 . As shown in  FIG. 4 , an outer diameter  72  of the drill string valve  70  has a substantially constant value along an entire length of the drill string valve  70 . The drill string valve  70  has a cone seal  56  attached to a first end  74  of the drill string valve  70 . The cone seal  56  cooperates with a sliding valve  50  for shutting down a liquid flow through the drill string valve  70 . 
     A second end  76  of the drill string valve  70  is configured to have a lower cap  78 . The lower cap  78  seals a cavity  79  of the drill string valve  70  from the mud existent in the casing  44 . Cavity  79  should be understood as extending from the first end  74  to the second end  76 . Cavity  79  includes plural chambers, as will be discussed later. A fluid  80  may flow through a conduit  81 , provided inside the cavity  79  of the drill string valve  70 . The conduit  81  extends inside the cavity  79 , from an upper flow nozzle  82  to a lower flow nozzle  84 . In operation, the drill string valve  70  of this embodiment may be positioned vertically or substantially vertically and it has the first end  74  displaced above the second end  76 , such that mud from the rig enters, in this order, first end  74 , upper flow nozzle  82 , conduit  81 , lower cap  78 , and lower flow nozzle  84 . It is noted that the drill string valve  70  is part of the drill string  24 , thus being provided inside casing  44 . 
     According to an exemplary embodiment, a body of the drill string valve  70  may include three portions, first portion  86 A, second portion  86 B, and third portion  86 C. The first two portions  86 A and  86 B may be connected together via a valve body  92  and the second portion  86 B may be connected to the third portion  86 C via a spring load cartridge  110 . 
       FIG. 4  also shows a biasing cartridge  90  disposed inside the cavity  79  and configured to apply a first force on the sliding valve  50  such that the sliding valve  50  contacts the cone seal  56 . The cone seal  56  may be replaced with a seal having another shape. A threaded stop  100  is provided inside cavity  79 , between the biasing cartridge  90  and the second end  76 . The threaded stop  100  is configured, as will be discussed later, to apply a second force on the biasing cartridge  90 . 
     Sliding valve  50  is configured to slide to and from cone seal  56  along a Z direction, as shown in  FIG. 5 . Sliding valve  50  is activated by actuator  94 , which is configured to move side a biasing chamber  96 . Actuator  94  extends from the biasing chamber  96 , via the valve body  92  towards the cone seal  56  so that a flow diverter  93  may extend in parallel with sliding valve  50 . Flow diverter  93  may direct the flow of fluid  80 , when under a pressure larger than a pressure created by the biasing cartridge  90 , to move the sliding valve  50  downward to an open position. One or more wave springs  98  are also provided in the biasing chamber  96  for providing the first force on the actuator  94 . One end of the biasing chamber  96  is bordered by a valve body  92  and the other end of the biasing chamber  96  is bordered by a spring spacer  99 , as shown in  FIG. 4 . The drill string valve  70  may be included inside a collar  162  (see  FIG. 4 ). 
     In one exemplary embodiment, the wave spring  98  is not a coil spring but rather has one or more of the shapes shown in  FIG. 6 . Thus, according to an exemplary embodiment, the biasing cartridge  90  includes actuator  94 , biasing chamber  96 , and wave spring  98 . Optionally, the biasing cartridge  90  may include a fluid inside the biasing chamber  96 , for example, oil. For confining the fluid inside the biasing chamber  96 , appropriate seals are provided at the ends of the biasing chamber  96  for preventing fluid leaks. 
     When deployed under sea, the sliding valve  50  of the drill string valve  70  is biased by actuator  94  to actively engage cone seal  56 , thus sealing conduit  81 . The bias applied by actuator  94  to sliding valve  50  is a result of the compression of wave spring  98 . As will be discussed next, the wave spring  98  is initially deployed uncompressed inside the drill string valve  70 , in order to avoid possible hazardous conditions. An advantage of the wave spring  98  is its reduced length in comparison to a conventional coil spring for generating a same spring force. 
     The threaded stop  100  configured to load the biasing cartridge  90  is discussed next with regard to  FIG. 7 . Spring spacer  99  separates the biasing cartridge  90  from the threaded stop  100 . 
     According to an exemplary embodiment, the spring load cartridge  110  includes a hydraulic piston  102  and a threaded stop  100 . A port  106  into loading chamber  108  provides access to pump hydraulic fluid into the loading chamber  108  to actuate hydraulic piston  102 . Thus, hydraulic piston  102  moves from right to left in  FIG. 7 , in order to load the wave spring  98 . More specifically, the hydraulic piston  102  contacts spring spacer  99  and presses the spring spacer  99  against wave spring  98 , compressing (loading) the wave spring  98 . In this way, the wave spring  98  may be loaded to a desired predetermined pressure without posing any danger to the safety of the operating personnel as the wave spring  98  is entirely contained inside the biasing chamber  96 . A pressure sensor (not shown) may be included with the hydraulic pump so that a hydraulic fluid pressure in the loading chamber  108  may be correlated to a desired force generated by the wave spring  98  (i.e., a first force). Thus, the applied pressure may be stopped when the wave spring  98  has achieved the desired spring force. A force corresponding to the applied pressure is considered to be a second force. 
     Once the desired first force in the wave spring  98  is achieved, the hydraulic pressure applied to the loading chamber  108  is maintained constant and the threaded stop  100  is advanced toward the spring until the threaded stop  100  picks up the load of the wave spring  98 , i.e., the threaded stop  100  fixes the spring spacer  99 . At this point, the applied hydraulic pressure may be released from the loading chamber  108 . Port  106  may be connected to a pump that pumps, for example, oil for activating the hydraulic piston  102 . Other mechanism for hydraulic piston  102  may be used as would be appreciated by those skilled in the art. 
     The spring load cartridge  110  defines the border for loading chamber  108  and also provides a mating thread to the threaded stop  100 . Once the spring load bias has been set, the lower section  86 C is assembled, and the tool is ready to be installed in its collar. 
     According to an exemplary embodiment, the spring load cartridge  110  breaks the continuity of the external tubes  86 B and  86 C that constitute the outside wall of the drill string valve  70 . In other words, the outside wall of the drill string valve may be made up of plural tubes. For example, the embodiment shown in  FIG. 4  shows three different tubes  86 A,  86 B and  86 C making up the external wall of the drill string valve  70 . More or less tube components may be used depending on the units to be distributed inside the drill string valve  70 . 
     Still with regard to  FIG. 7 , a compensating piston  120  may be provided, according to an exemplary embodiment, inside a compensating chamber  118 , between the spring load cartridge  110  and the lower cap  78 . Although  FIG. 7  shows both reference signs  79  and  118  pointing to the same chamber, as already discussed above, cavity  79  includes plural chambers, among which, the compensating chamber  118 . In other words, cavity  79  extends along the entire drill string valve  70  and includes, at least biasing chamber  96 , loading chamber  108  and compensating chamber  118 . 
     Compensating chamber  118  communicates via a port  122  with an annulus space around the drill string valve  70  for providing annulus pressure  112  inside a chamber  124  of the compensating chamber  118 , between the compensating piston  120  and the lower cap  78 . In this way, the borehole fluids are separated from the clean oil present in the biasing chamber  96  and part of the loading chamber  108 . 
     The next paragraphs summarize some of the features and/or advantages of the exemplary embodiments discussed above. While an exemplary embodiment may include one or more of these features/advantages, there are exemplary embodiments that include none of these features/advantages. The drill string valve body assembly has a constant outer diameter that enables horizontal or vertical insertion into the bore of the drill string valve collar. 
     The drill string valve collar is simple in design with a long counter bore terminating at a shoulder near the bottom and an internal thread near a top for a lock ring. The overall length may be short, for example, 13 ft (4 m). The body may be inserted in the collar and may land on a shoulder at the bottom of the valve. In one application there is no fixed orientation. The drill string valve may be retained and locked in place at the upper end with a threaded lock ring  74  (see  FIG. 5 ). The modular drill string valve body provides for quick turnaround after tripping out. A replacement drill string valve body can quickly be swapped out with the returning body, or if loaded into a standby collar, swapped out with the returning collar. This feature will eliminate the risk of injury during assembly, streamline assembly, and provide accuracy and repeatability of spring settings. 
     The spring is installed in the drill string valve body at its free length (no spring load). A mechanism (loading mechanism) to load the spring is installed below the spring package. The mechanism to load the spring is integral to the drill string valve body, not an auxiliary tool. The remainder of the drill string valve body is assembled after the spring force is set. 
     The type of spring used for the drill string valve has an effective free length that is shorter than the free length of a coil spring, for example, half the free length of a coil spring with the same spring rate. This feature reduces system friction. The spring package, interior dynamic seals, and bearings are immersed in a pressure balanced oil system. The pressure balance is achieved with a port through the collar wall that taps onto the well bore annulus. A mating port in the lower cap of the drill string valve body channels the annulus pressure to a compensating piston separating the borehole fluids from the clean oil system. 
     According to another exemplary embodiment, various analytical tools, for example, sensors, may be provided inside the drill string valve. Such tools may include pressure sensors, load cell sensors, temperature sensors and sensors for determining a position of the sliding valve  50 . This feature would optimize valve operation. As this type of valve opens very quickly, there is desired for the valve to open in a slower, controlled fashion to reduce the effect of pressure shocks on the well formation. Thus, the sensors discussed above may help monitor and control the drill string valve. According to an exemplary embodiment, a processor with memory capabilities may be deployed inside the drill string valve for collecting and processing the data from the above discussed sensors or others known in the art. Such capability may offer extended control of the drill string valve. 
     Analytical tools provide the ability to optimize a given spring for use over a wide range of operation. This will lessen the frequency of exchanging spring hardware during the course of drilling program. Simulation software provides the capability to input changing operating conditions and to determine the effects of them in a time sequence. This capability is desired for custom spring design. 
     This feature includes the addition of downhole diagnostic instrumentation, for example, a data acquisition system may be packaged in an electronics pressure vessel upstream of the drill string valve body. The time synchronized data acquisition may record pressures, acceleration, spring load, valve position, and temperature data. Pressure transducers ports may be positioned upstream and downstream of the valve seat for measuring local static and dynamic pressures. 
     A time synchronized data acquisition unit may be packaged with a linear measurement transducer to record valve position. Data ports may be built into the drill string valve body for data download, real-time data monitoring during lab testing, flow loop testing, and pre-check diagnostics prior to deployment. Hydraulic access ports may also be built into the drill string valve body for lab testing, flow loop testing and pre-deployment checks. 
     According to an exemplary embodiment, steps of a method for activating the drill string valve  70  are illustrated in  FIG. 8 . The method includes a step  800  of connecting a power source to a port of a biasing cartridge of the drill string valve. The drill string valve includes (i) an elongated housing having an inside cavity, the housing extending along an axis and having a substantially constant outer diameter, (ii) a seal element attached to a first end of the elongated housing, the seal element having an outer diameter smaller than an inner diameter of the elongated housing, and the seal element being disposed within the inside cavity such that a flow of liquid through the inside cavity from the first end to a second end of the elongated housing is allowed, (iii) a sliding valve disposed within the inside cavity and configured to slide to and from the seal element along the axis such that when the sliding valve contacts the seal element the flow of liquid is suppressed, (iv) the biasing cartridge disposed within the inside cavity, between the seal element and the second end of the elongated housing and configured to apply a first force on the sliding valve such that the sliding valve is contacting the seal element, and (v) a loading mechanism disposed within the inside cavity, between the biasing cartridge and the second end of the elongated housing, and configured to apply a second force on the biasing cartridge. The method also includes a step  802  of applying a pressure to the loading mechanism to generate the second force, a step  804  of compressing a wave spring of the biasing cartridge, a step  806  of locking a stop element to maintain the wave spring in a compressed state, and a step  808  of releasing the applied pressure. 
     According to another exemplary embodiment, a drill string valve  160 , different from the drill string valve  70  or other valves discussed above is now discussed with regard to  FIG. 9 . The drill string valve of  FIG. 9  has one or more of the following advantages over a conventional valve. The conventional valve opens when the mud pumps are on and closes when the mud pumps are off. A throttling feature based on an amount of openness of the drill string valve provides smooth flow transitions. The conventional design uses a coil spring to close the valve. The spring force at closing was designed to support the weight of the mud column. The force was primarily based on the mud weight and depth of the water as well as other well planning parameters. Since the mud weight and water depth combinations constitute a 3-D matrix, a host of spring package designs are required. 
     The novel drill string valve shown in  FIG. 9  replaces, among others, the spring with a motor-driven valve actuation system having feed-back control. This new valve eliminates pressure bias on the poppet valve so that an actuation rod does not receive a large axial load. An electronic package that controls the opening and closing of the valve may include a microprocessor control with data acquisition. The instrumented drill string valve may include pressure transducers to monitor absolute pressure and differential pressures across the valve opening and an encoder for monitoring poppet position. A lithium battery may provide the necessary power for the electronic package. The drill string valve module may be mounted in a 8 ft (2.5 m) pony collar. 
     According to an exemplary embodiment, the drill string valve  160  includes a collar  162  inside of which various components are provided. For example, a motor module  180  is provided in contact with a poppet  200 . The poppet  200  seals a motor chamber  182 , in which the motor module is fixed, from a communication chamber  210 .  FIG. 9  shows that the motor module  180  includes a motor  184  that is attached to and configured to rotate a ball screw  186 . The ball screw  186  rotates in a ball screw nut  188 . The ball screw nut  188  connects to a guide sleeve  189  that is fixed to an actuation rod  190  for activating poppet  200 . Motor  184 , ball screw  186  and ball screw nut  188  may be distributed inside a metallic cavity  192 , to prevent any liquid passing through the drill string valve  160  from entering the motor module  180 . The motor module  180  may be controlled by a micro-processor  230  with a data acquisition board  220 . A power source for the electronics, sensors and motor may be a battery or a hydraulic source. 
     Actuation of the motor  184  determines the extension or retraction of the ball screw  186  and actuation rod  190 , which determine the movement of poppet  200  towards and away from poppet seat  202 . When the poppet  200  is in contact with the poppet seat  202 , no fluid (or an insignificant amount) passes through the drill string valve  160 . The metallic cavity  192  that accommodates the motor module  180  may be connected to a spider  204 , which is configured to accommodate poppet  200 . As would be recognized by one skilled in the art, appropriate seals are formed around various elements discussed above for preventing fluid entering the motor module. 
     A pressure inside the drill string valve  160 , may be monitored by pressure sensors  222  and  224 . A position of the poppet  200  may be monitored with an appropriate sensor  228 . Such a position sensor  228  and accompanying mechanism may be a LVDT, as described in Young et al., Position Instrumented Blowout Preventer, U.S. Pat. No. 5,320,325, Young et al., Position Instrumented Blowout Preventer, U.S. Pat. No. 5,407,172, and Judge et al., RAM BOP Position Sensor, U.S. Patent Application Publication No. 2008/0196888, the entire contents of which are incorporated herein by reference. 
     Based on the data provided by the pressure sensors  222  and  224 , and optionally by position sensor  228 , the microprocessor  230  may determine when to close or open poppet  200 . The microprocessor  230  may be provided in a custom made chamber in the body of the drill string valve  160 . According to an exemplary embodiment, the microprocessor  230  is configured to adjust the closing of the drill string valve  160  depending whether poppet  200  is completely closed, poppet  200  is starting to open or close, and/or poppet  200  is open. It is noted that a pressure in the annulus (i.e., outside the motor module  180 ) is larger when the drill string valve is closed than when the drill string valve is opened. Thus, based on the pressure measurements and/or position of the poppet, the amount of opening of the poppet  200  may be controlled, thus achieving a feed-back controlled drill string valve. 
     With regard to  FIG. 10 , various pressures inside the drill string valve are illustrated. A pressure at location  300  in the pipe may be different from a pressure at location  310  around actuation rod  190 , which is equalized to an annulus pressure at location  320 . The annular cavity between spider  204  and poppet  200  is filled with a gas  322  at low pressure. The changes in pressure of gas  322  during deployment are insignificant compared to pressure at location  300  and pressure at location  320 . This balanced pressure on both sides of poppet  200  ensures that motor  184  needs to apply a small force for the actuation of rod  190 , comparative to the large pressures existent in the annulus, for displacing poppet  200 . The pressure at location  310  around actuation rod  190  is made equal to annulus pressure  320  by selecting diameters A 1 , A 2 , A 3  and A 4 . Thus, minimal motor torque requirements are needed for a proper functioning of the poppet and the drill string valve  160  works for all depths and mud weights. 
     Next, the operation of the drill string valve is discussed. The drill string valve is a pressure regulating check valve that uses a flow for compensation. The valve has two modes of operation, which are drilling mode with pumps on and non-drilling mode with pumps off. During the drilling mode the drill string valve becomes a flow compensated check valve. During the non-drilling mode, the drill string valve prevents the mud column above the valve from free falling when the mud pumps are turned off. 
     The drill string valve  70  employs a spring to control the valve opening. According to an exemplary embodiment, the design of the valve spring is dependent on the spring load, the spring rate, the flow rate, the mud weight, the back pressure of the bit nozzles, and the flow losses in the well from pipe friction, casing friction, and any downhole tools in the drill string. Because of the array of operating variables the throttling performance of a spring actuated valve is indeterminate. 
     The drill string valve  160  may use a microprocessor and sensor data from on board sensors to control valve position. The drilling mode is determined by measuring the broad band acceleration of the drill string valve. There is a distinctive change in the broad band when the mud pumps are turned off and on. The microprocessor may read acceleration, mud flow rate, valve position, and differential pressures. Before the tool is run, inputs for control and look-up tables for valve opening vs. time are downloaded via a communication device, for example, a computer. The look-up tables are constructed to meet the requirements of the well plan and may vary from application to application. When the microprocessor senses there is broad band response from the accelerometer, the microprocessor begins modulating the valve and controlling the valve opening based at least in part on information in the look-up table. 
       FIG. 11  is a schematic of drill string valve  160  and shows the instrumentation used to control the valve. Flow meter  226  and valve position sensor  228  provide the data to the micro-processor  230  via data acquisition  220 . The micro-processor software algorithm is based on a user-defined relationship between flow rate and valve position (flow rate vs. position). The processor compares the actual valve position with the desired valve position based on real-time flow rate. The processor sends a command to the motor controller board  227  to have the motor  184  reposition the poppet  200 . According to an exemplary embodiment, a look-up table may be stored in a memory (not shown) connected to the micro-processor  230  and includes a flow rate threshold so that for any measured flow rate above the threshold, the micro-processor  230  is configured to close the seal element to suppress the fluid flow. 
     According to an exemplary embodiment, the seal element and the seat of the above discussed embodiments are configured, when closed, to withstand pressures between 5,000 and 30,000 psi and/or to work on the floor of the ocean while exposed to corrosion. 
     According to an exemplary embodiment shown in  FIG. 12 , there is a method for controlling a drill string valve. The method includes a step  1200  of receiving from a flow meter unit a flow rate of a fluid through the drill string valve, a step  1202  of determining in a processor a position of a seal element that is configured to move to and from a seat to suppress a fluid flow through the drill string valve, and a step  1204  of searching a look-up table stored in memory connected to the processor for determining whether a motor has to be activated to close or open the seal element. 
     The disclosed exemplary embodiments provide a system and a method for closing and opening a duct through which a fluid may flow. 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 example are intended to be within the scope of the claims.