Patent Publication Number: US-11391120-B1

Title: Robustness of flapper valve open/close

Description:
BACKGROUND 
     The present disclosure relates generally to equipment and operations performed in conjunction with subterranean wellbores. Example embodiments described herein include flapper valve assemblies that are biased to a closed configuration. 
     Subsurface safety valves are often employed to control fluid flow in a production string or other downhole tubing strings. For example, a subsurface safety valve may be maintained in an open configuration during nominal operations and may be moved to a closed configuration to block the upward flow of formation fluids through the production string should a failure occur, or hazardous condition exist at the surface. A flapper member, or a “flapper,” may be provided that can be pivoted to configure the valve in the open and closed configurations. Hydraulic pressure may be applied to pivot the flapper member to an open position, and when the hydraulic pressure is removed, either manually or automatically in response to a hazardous condition, a biasing member may operate to pivot the flapper member to a closed position. 
     Torsion springs and coiled extension springs are often provided as the biasing member that urges the flapper member to the closed position. These types of springs may have limited torque capacity due to the limited space available in a subsurface valve assembly. With limited torque capacity, these springs may fall to move the flapper member fully to the closed position, which could potentially permit hazardous fluids to escape into the surrounding environment through the partially closed production string. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is described in detail hereinafter, by way of example only, on the basis of examples represented in the accompanying figures, in which: 
         FIG. 1  is a partial, cross-sectional side view of a wellbore system including a valve assembly in accordance with aspects of the present disclosure: 
         FIG. 2A  is a perspective view of a valve assembly, which may be employed in the wellbore system of  FIG. 1 , illustrating a flapper member biased to a closed position with a wire spring extending across a saddle defined in the flapper member; 
         FIG. 2B  is a perspective view of the wire spring of  FIG. 2A ; 
         FIG. 3  is a perspective view of an alternate embodiment of a wire spring including resistance bands thereon, which may be employed in the valve assembly of  FIG. 2A  engaged with the saddle of the flapper member in accordance with aspects of the present disclosure; 
         FIG. 4  is a perspective view of an alternate embodiment of a flapper member including a plurality saddle grooves defined therein, which may be employed in the valve assembly of  FIG. 2A  in engagement with a wire spring in accordance with aspects of the present disclosure; 
         FIG. 5A  is a perspective view of a valve assembly in accordance with aspects of the present disclosure, which may be employed in the wellbore system of  FIG. 1 , illustrating a flapper member biased to a closed position with a pair of opposed wire springs engaged in a pair of blind holes defined in the flapper member; 
         FIG. 5B  is a perspective view of the pair of wire springs of  FIG. 5A  in accordance with aspects of the present disclosure; 
         FIG. 6  is a perspective view of an alternate embodiment of a flapper member that may be employed in the valve assembly of  FIG. 5A , illustrating a pair of blind holes for receiving ends of wire springs in accordance with aspects of the present disclosure; 
         FIGS. 7A and 7B  are perspective and side views of an alternate embodiment of a flapper member including a channel defined therein for receiving free ends of wire springs in accordance with aspects of the present disclosure: 
         FIGS. 8A and 8B  are perspective and end views of an alternate embodiment of a valve assembly in accordance with aspects of the present disclosure, the valve assembly employing the flapper member of  FIGS. 7A and 7B  with wire springs engaged in the channel defined in the flapper member, and 
         FIGS. 9A and 9B  are cross-sectional side views of an alternate embodiment of a valve assembly in closed and open configurations respectively, illustrating a linear spring coupled in a closure mechanism with a linkage member in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes valve assemblies that may be employed in subterranean wellbore systems. In particular, flapper valve assemblies are described that employ wire springs on opposite lateral sides of a flapper member that cooperatively bias the flapper member to a closed position. The wire springs provide sufficient torque to ensure robust operation of the flapper member and permit sufficient fluid flow through the limited available space through the valve assembly. A symmetrical pair of wire springs may be robustly manufactured and individually installed without unnecessary accumulation of manufacturing tolerances or errors to provide predictable torque to the flapper member. The wire springs may be secured in blind holes or other features defined in the flapper member to ensure the springs remain engaged with the flapper member throughout the operation of the valve assembly. 
       FIG. 1  illustrates a wellbore system  10  in accordance with example embodiments of the present disclosure. In wellbore system  10 , a wellbore  12  extends from a surface location “S” through a geologic formation “G” In some embodiments, the surface location “S” may be a terrestrial location as illustrated, and in other embodiments, the surface location “S” may be an offshore seabed without departing from the scope of the disclosure. A casing string  16  may be cemented in the wellbore  12  to provide structural support and prevent collapse of wellbore walls  18 . Aspects of the disclosure may also be practiced in n-cased or open hole portions of the wellbore  12 . The wellbore  12  intersects a hydrocarbon producing formation  20  from which fluids  22  may be produced. A production string  26  extends between the hydrocarbon producing formation  20  and the surface location “S” and provides a conduit for communicating the fluids  22  to the surface location “S.” A wellhead  28  at the surface location “S” includes one or more valves  30  for controlling the flow and distribution of fluids  22  received from the wellbore  12 . 
     The wellbore system  10  further includes a valve assembly  100  disposed at a subterranean location within the wellbore  12 . The valve assembly  100  is interconnected in the production string  26  and may alternatively be coupled within other types of wellbore tubing strings in other embodiments (not shown). The valve assembly  100  may be operated between an open configuration in which the flow of fluids  22  though the production string  26  is permitted and a closed configuration in which the flow of fluids in inhibited. A control line  32  extends from the valve assembly  100  to a controller  33  in the wellhead  28  or another remote location where communication with the valve assembly  100  maybe required. As illustrated, the control line  32  extends within an annulus  34  defined radially between the production string  26  and the casings string  16 . In other embodiments, the control line  32  could alternatively be arranged internal to the production string  26 , or otherwise formed in a sidewall of the production string  26 . 
     The control line  32  may facilitate maintaining the valve assembly  100  in the open configuration in nominal operations and closing the valve assembly  100  in the event of an emergency or hazardous condition at the surface location “S.” For example, the control line  32  may include a hydraulic conduit that provides hydraulic pressure to the valve assembly  100  to maintain the valve assembly  100  in the open configuration. Reduction or elimination of the hydraulic pressure may operate to close the valve assembly  100  in response to instructions from an operator, or automatically in response to a predetermined wellbore condition. 
     Referring to  FIG. 2A , the valve assembly  100  includes a generally tubular body  102  extending along a longitudinal axis A 1 . The tubular body  102  defines a first end  102   a  and a second end  102   b  and may be interconnected in the production string  26  ( FIG. 1 ) such that the first end  102   a  is disposed uphole of the second end  102   b . A flow path  104  is defined along the longitudinal axis A 1  through the production string  26  and the tubular body  102 . A flapper member  106  is pivotably coupled to the second end  102   b  of the tubular body  102  about a pivot axis A 2 . The flapper member  106  is movable between open and closed positions in the valve assembly  100 . Specifically, the flapper member  106  is movable between the closed position illustrated in which the flapper member  106  engages a valve seat  108  obstructing the flow path  104  and an open position (see  FIG. 9B ) in which the flapper member  106  pivots away from the valve seat  108 , such that flow through the valve seat  108  is permitted. In some embodiments, the open position of the flapper member  106  is generally orthogonal to the closed position of the flapper member  106  (see  FIG. 9B ). For example, an axial face  110  of the flapper member  106  may be oriented in oriented in a lateral direction when the flapper member is rotated to the open position about pivot axis A 2 . 
     The flow path  104  extends through a fixed opening  112  defined through the valve seat  108 . As illustrated, the fixed opening  112  is generally circular and centered about the longitudinal axis A 1 . Other geometries for the fixed opening  112  are contemplated within the scope of the disclosure. The flow path  104  extends from the fixed opening  110  along a cylinder  114  defined around the axis A 1  and having a diameter D similar to the diameter D of the fixed opening  112 . Generally, the valve assembly  100  is arranged so that the flow path  104  along the cylinder  114  is unobstructed when the flapper member  106  is in the open position so as not to impede fluid flow therethrough. 
     The valve assembly  100  includes a closure mechanism  116  that imparts a biasing force to the flapper member  106 , thereby urging the flapper member  106  toward the valve seat  108 . 
     The closure mechanism  116  includes a wire spring  120  and a spring support  122  fixedly coupled to the tubular body  102 . The spring support  122  includes a pair of lateral arms  124 ,  126  extending axially from the tubular body  102 . A first end  122   a  of the spring support  122  is coupled to the tubular body  102  by fasteners  128 , which may include screws, pins, threads and the like. A second end  122   b  of the spring support  122  includes a circumferential cross-beam  130  coupling the lateral arms  124 ,  126  to one another. The cross-beam  130  provides rigidity to the spring support  122  and extends circumferentially around the cylinder  114  such that the flow path  104  is not obstructed by the cross-beam  130 . 
     The wire spring  120  is axially constrained between the spring support  122  and a saddle  132  defined in the axial face  110  the flapper member  106 . The saddle  132  is a curved groove extending laterally across the axial face  110  at a radial distance R 1  from the pivot axis A 2 . A first end  120   a  of the wire spring  120  engages the saddle  132  to impart a torque to the flapper member  106  about the pivot axis A 2 . The curved shape of the saddle  132  allows the saddle  132  to maintain engagement with the wire spring  120  as the flapper member  106  pivots about the axis A 2 . At a second end  120   b  of the wire spring  120 , the lateral arms  124 ,  126  of the spring support  122  provide a base against which the wire spring  120  may extend to impart a force to the flapper member  106  to close the valve assembly  100 . Generally, greater radial distances R 1  from the pivot axis A 2  permit the closure mechanism  116  to provide greater torque to flapper member  102 . However, greater radial distances R 1  may also require more complex closure mechanisms and/or closure mechanisms that occupy more of the limited space in a downhole valve assembly. 
     As illustrated in  FIG. 2B , the wire spring  120  is generally constructed from a single wire strand with a generally circular cross section. Wire spring  120  may be constructed as a wireform spring devoid of any coils or cylindrical structures that could intrude into the flow path  104 . The d int springs discussed herein A straight wire segment  134  extends laterally across the wire spring  120  at a first end  120   a  of the wire spring  120 . The straight wire segment  134  rolls within the saddle  132  ( FIG. 2A ) as the flapper member  106  pivots between the open and closed positions. Extending from the straight wire segment  134  are generally symmetrical shoulder curves  136 ,  138  and lateral arms  140 ,  142 . The lateral arms  140 ,  142  are constructed of straight sections  140   a ,  142   a , major curves  140   b ,  142   b , minor curves  140   c ,  142   c  and straight sections  140   d ,  142   d  terminating in respective free ends  144 ,  146  at a second end  120   b  of the wire spring  120 . The major curves  140   b ,  142   b  and minor curves  140   c ,  142   c  of the lateral arms  140 ,  142  provide flexibility to the wire spring  120 , and specifically permit the wire spring  120  to be compressed axially (by approximating the free ends  144 ,  146  with the straight wire segment  134 ). Thus, when the free ends  144 ,  146  are axially restrained by the spring support  122  ( FIG. 2A ), the wire spring  120  may impart an axial force to the flapper member  106  (FIG.  2 A). In some embodiments, the free ends  144 ,  146  may have end caps (not shown) or other features installed thereon to facilitate securing the free ends  1446  to the spring support  122 . 
     The wire spring  120  exhibits a relatively complex geometry in order to provide a sufficient axial force to reliably close the valve member  100  while not intruding into the flow path  104 . For example, the lateral arms  140 ,  142  of the wire spring  120  are not coiled, but are generally defined in a single plane such that the lateral arms  140 ,  142  do not interfere with the pivotal movement of the flapper member  106  or the flow of fluids through the flow path  104 . Wire-form springs such as wire spring  120  are generally constructed with automated presses and hand bending equipment. Wire-form springs are bent to include concavities and other features in their geometry that permit the spring to store energy. This complex geometry may sometimes result in manufacturing difficulties and stacking of tolerances that may cause the wire spring  120  to behave in unexpected ways. For example, if the lateral arms  140 ,  142  are not exactly symmetrical the wire spring  120  may tend to twist. If each of the sections, e.g.,  134 ,  136 ,  138 ,  140 ,  142 , of the wire spring  120  are constructed within a predefined tolerance defined for the particular section, but the cumulative effect of the manufacturing errors result in an accumulation of errors across the entire wire spring  120 , the wire spring may be have erratically, including becoming disengaged from the saddle  132  of the flapper member  106 . 
     Referring to  FIG. 3 , an alternate embodiment of a wire spring  150  includes resistance bands  152  supported on a straight wire segment  154  thereof. The wire spring  150  may be constructed as a wire-form spring in the same general shape as the wire spring  120  ( FIG. 2B ) described above. The resistance bands  152  may be constructed of rubber bands, molded elastomers or other suitable materials for increasing a frictional resistance between the straight wire segment  154  and the saddle  132  of a flapper member  106  ( FIG. 2A ). As illustrated, three laterally spaced resistance bands  152  are provided, and in other embodiments, any number of resistance bands  152  is contemplated. The resistance bands  152  may help to maintain the straight wire segment  154  engaged in the saddle  132 , particularly when the flapper member  106  is an open position within the valve assembly  100 . The high lateral forces provided by the wire spring  150  might otherwise cause the straight wire segment  154  to slip out of the saddle  132  when the flapper member  106  is rotated to the open position where the axial face  110  of the flapper member  106  is oriented in a lateral direction. 
       FIG. 4  illustrates an alternate embodiment of a flapper member  160  including a plurality saddle grooves  162  defined in a saddle  164  thereof. The saddle grooves  162  extend laterally across the saddle  164  and increase frictional resistance between the saddle  164  and a straight wire segment  134  ( FIG. 2B ),  154  ( FIG. 3 ) of a wire spring  120 ,  150 . The flapper member  160  may be installed in place of the flapper member  106  in the valve assembly  100  and may be employed with either of the wire springs  120 ,  150 . 
     Referring to  FIG. 5A , an alternate embodiment of a valve assembly  200  is illustrated that may be employed in the wellbore system  10  of  FIG. 1 . The valve assembly  200  includes a flapper member  202  biased to a closed position with a pair of opposed wire springs  204 ,  206 . The flapper member  202  includes a pair of opposed blind holes  212 ,  214  defined in an outer circumferential surface  216  thereof, and each of the blind holes  212 ,  214  receives a free end  204   a ,  206   a  ( FIG. 5B ) of one of the opposed wire springs  204 ,  206 . The blind holes  212 ,  214  restrain the free ends  204   a ,  206   a  in both axial and radial directions, and are sized to provide rotational freedom of the free ends  204   a ,  206   a  with respect to the flapper member  202  about an axis A 3 . The axis A 3  defined by the blind holes  212 ,  214  is generally parallel to the pivot axis A 4 . In some embodiments, a resistance band (see  FIG. 3 ), end cap or a non-metallic washer may be secured to the wire springs  204 ,  206  adjacent the respective free ends  204   a ,  206   a  to provide a secure fit within the blind holes  212 ,  214 . The resistance bands, end caps or non-metallic washers may discourage the wire springs  204 ,  206  from disengaging the flapper member  202  in operation. 
     The axis A 3  extends through the blind holes  212 ,  214  and is radially spaced from the pivot axis A 4  about which the flapper member  202  pivots. The valve assembly  200  may employ the same generally tubular body  102  and spring support  122  as described above for use with valve assembly  100  ( FIG. 2A ). The flapper member  202  is movable between the closed position illustrated in which the flapper member  202  engages the valve seat  108  and an open position in which the flapper member  202  pivots away from the valve seat  108 . The pair of opposed wire springs  204 ,  206  may be constructed as wire-form springs devoid of any coils or cylindrical structures. The wire springs  204 ,  206  may exhibit mirror symmetry, which permit the wire springs  204 ,  206  to cooperate to impart a biasing force to the flapper member  202 , thereby urging the flapper member  202  toward the valve seat  108  and the closed position. 
     As illustrated in  FIG. 5B , the opposed wire springs  204 ,  206  each include a straight wire segment  222 ,  224  terminating in a respective free end  204   a ,  206   a . The free ends  204   a ,  206   a  may roll within the blind holes  212 ,  214  as the flapper member  202  pivots between the open and closed positions. The opposed wire springs  204 ,  206  may include shoulder curves  218 ,  220  and lateral arms  222 ,  224  that are identical to the  136 ,  138  and lateral arms  140 ,  142  the wire spring  120  ( FIG. 2B ) described above. The pair of opposed wire springs  204 ,  206 , however, are not as susceptible to the manufacturing and operational difficulties of the wire spring  120  described above. 
     The opposed wire springs  204 ,  206  exhibit a simpler geometry than the wire spring  120 , and thus, lower tolerances and higher manufacturing precision may be achieved. Any manufacturing errors will not be accumulated to the same degree, and thus the structural behavior of the pair of opposed wire springs  204 ,  206  may be more predictable and the design may be more readily analyzed, adjusted and scaled for different valve sizes and loading conditions. A higher level of torque may thus be provided to the flapper member  202  to maintain the valve assembly  200  in a closed configuration. Additionally, since the free ends  204   a ,  206   a  may be secured in both axial and radial directions in the blind holes  212 ,  214 , the wire springs  204 ,  206  may not be as susceptible to disengaging the flapper member  202  in operation. 
     Referring now to  FIG. 6 , a flapper member  230  is illustrated, which may be employed in place of flapper member  202  in valve assembly  200  ( FIG. 5A ). The flapper member  230  is devoid of a saddle, which may simplify machining operations in the construction of a valve assembly. Blind holes  232 ,  234  extend from lateral openings  232   a ,  234   a  in an outer circumferential surface  236  of the flapper member  230  to a hole depth HD. In some embodiments, the hole depth HD is selected such that the free ends  204   a ,  206   a  of wire springs  204 ,  206  ( FIG. 5B ) may abut a bottom surface of the blind holes  232 ,  234 . In this manner, a predetermined lateral position of the wire springs  204 ,  206  may be maintained. In other embodiments, the hole depth HD may be selected such that the free ends that the free ends  204   a ,  206   a  do not reach the bottom surface of the blind holes  232 ,  234 . 
     Referring to  FIGS. 7A and 7B , an alternate embodiment of a flapper member  302  is illustrated for use in a valve assembly  300  ( FIG. 8A ). The flapper member  302  includes a channel  304  defined therein for receiving free ends of wire springs  306  ( FIG. 8A ). The channel  304  extends through a central rib  308  of the flapper member  302  that protrudes beyond shoulders  310  on either lateral sides of the central rib.  308 . The channel  304  is generally parallel and radially offset from a pair of pivot holes  312  defining a pivot axis A 5  of the flapper member  302 . An axial force F 1  applied through the channel  304  may cause the flapper member  302  to pivot about the pivot axis A 5 . The channel  304  is elongated in a radial direction, which may facilitate pivoting of the flapper member  302  with the wire springs  306  engaged. 
     Referring to  FIGS. 8A and 8B , valve assembly  300  includes a generally tubular body  314 , which may be interconnected in the production string  26  ( FIG. 1 ), the flapper member  302 , and a closure mechanism  318 . The closure mechanism  318  includes a spring support  320  fixedly coupled to the tubular body  314  and a pair of wire springs  322 ,  324  which may be decoupled from one another. A flow path  326  is defined along a longitudinal axis A 6  through the tubular body  314 , which is closed with the flapper member  302  in the closed position illustrated. The flapper member  302  is pivotably coupled to the spring support  320  such that the flapper member  302  may pivot to an open configuration wherein the flow path  326  is unobstructed. 
     The closure mechanism  318  imparts a biasing force to the flapper member  302 , thereby urging the flapper member  302  to the closed position illustrated. The pair of wire springs  322 ,  324  are engaged with the flapper member  302  such that free ends  322   a ,  324   a  are disposed within the channel  304  and are axially constrained by the central rib  308 . The free ends  322   a ,  324   a  are rotationally free with respect to the flapper member  302  and slidable along the elongated channel  304  as the flapper member  302  pivots. The wire springs  322 ,  324  are illustrated in relaxed configuration where free ends  322   b ,  324   b  are disengaged from the spring support  320 . In the relaxed configuration, when the free ends  322   a .  324   a  at a first end of the wire springs  322 ,  324  are received in the channel  304 , the free ends  322   b ,  324   b  at a second end of the wire springs are displaced axially and laterally with respect to axial holes  338 ,  340  defined in the spring support  320 . In an operational configuration, the free ends  322   b ,  324   b  may be installed in the axial holes  338 ,  340  to preload the wire springs  322 ,  324  between the spring support  320  and the flapper member  302  such that the wire springs  322 ,  324  urge the flapper member to the closed configuration. 
     The spring support  320  extends axially along the longitudinal axis A 6  and includes a pair of lateral arms  330 ,  332  axially spaced from the flapper member  302 . A circumferential cross beam  334  couples the lateral arms  330 ,  332  to one another. The circumferential cross beam  334  extends circumferentially around the flow path  326  between the lateral arms  330 ,  332  such that the flow path  326  is not obstructed. The lateral arms  330 ,  332  each include an axial hole  338 ,  340  defined therein for receiving a free end  322   b ,  324   b  of the wire springs  322 ,  324 . The axial holes  338 ,  340  are positioned such that the wire springs  322 ,  324  may be axially compressed between the lateral arms  330 ,  332  and the flapper member  302  when the free ends  322   b ,  324   b  are received therein. The wire springs  322 ,  324  may also be shaped such that the wire springs  322 ,  324  are laterally compressed between the spring support  320  and the flapper member  302  when the free ends  322   b ,  324   b  are engaged in the axial holes  338 ,  340 . The lateral compression of the springs  322 ,  324  may serve to maintain the free ends  322   a ,  324   a  within the channel  304 . 
     The decoupled wire springs  322 ,  324  may be installed individually by first installing the free ends  322   a ,  324   a  within the channel  304  and subsequently installing the free ends  322   b ,  324   b  in the axial holes  328 . The decoupled wire springs  322 ,  324  may be installed individually without permanently deforming the wire springs  322 ,  324 . A combined spring (not shown) that would be formed if the free ends  322   a .  324   a  were joined would not as readily be installed through the channel  304  without permanently deforming the spring and would not as reliably and predictably provide a closure force to the flapper member  302 . 
     Referring now to  FIGS. 9A and 9B , a valve assembly  400  is illustrated in closed ( FIG. 9A ) and open ( FIG. 9B ) configurations. The valve assembly  400  may be interconnected in the production string  26  ( FIG. 1 ) and generally includes a tubular body  402 , a flapper member  404  and a closure mechanism  406  that biases the flapper member  404  to the closed configuration. 
     The tubular body  402  defines a longitudinal axis A 6  and a flow path  408  extending therethrough. The flapper member  404  pivots about a pivot axis A 7  and engages a valve seat  410  in the closed configuration. One or more lateral openings  412  is defined the flapper member  404  for engaging the closure mechanism  406 . The lateral openings  412  may be defined in an outer circumferential surface of the flapper member  404  (similar to the blind holes of flapper member  230 ,  FIG. 6 ) or in a central rib of the flapper member  404  (similar to the channel  304  of flapper member  302 ,  FIG. 7A ). The lateral openings  412  may be defined at a radial distance R 2  from the pivot axis A 8 . In some embodiments, the radial distance R 2  may be large enough that the lateral openings  412  are defined generally in a center of the flapper member  404  or further from the pivot axis A 8 . 
     The closure mechanism  406  includes a spring support  414  extending axially from the tubular body  402 . The spring support  414  may be fixedly coupled to the tubular body  402  and define a fixed reference support  416  thereon. The spring support  414  may include lateral arms and a circumferential cross-beam similar to the spring support  122  ( FIG. 2A ) or  320  ( FIG. 8A ). In some embodiments, the fixed reference support  416  may include a feature defined on one of the lateral arms similar to the axial holes  328  ( FIG. 8A ). 
     Coupled between the flapper member  404  and the fixed reference support  416 , the closure mechanism  406  includes one or more link members  420 , a hinge  422  and a biasing member  424 . At a first end  420   a  of the one or more link members  420 , the link members  420  are pivotally coupled to the flapper member  404  at the one or more lateral openings  412 . In some embodiments, a pair of opposed lateral openings  412  may receive respective free ends of a pair of individual link members  420  such that the free ends may rotate within the lateral openings  412 . In other embodiments, a link member may be threaded through a channel defined in the flapper member (see  FIG. 7B ). The link members  420  may be generally rigid or may be flexible in operation, and may include any of the wire springs  204 ,  206 ,  306 ,  322 ,  324  described herein. A second end  420   b  of the one or more link members  420  is coupled to the hinge  422 . The hinge  422  may be constructed as disk with a central rotation ring therein. The hinge  422  pivotally couples the one or more link members  420  to the biasing member  424 . The biasing member  424  is supported between the fixed reference support  416  and the hinge  422 , and may include a linear coiled spring, a stack of spring washers or other axially compressible structure. 
     As illustrated in  FIG. 9A , when the valve assembly  400  is in the closed configuration, the biasing member  424  is axially expanded against the fixed reference support  416  to maintain the hinge  422  and the second end  420   b  of the one or more link members  420  at an axially remote location with respect to the fixed reference support  416 . A force F 2  provided by the biasing member  424  is transferred through the one or more link members  420  to the flapper member  404  to maintain the flapper member  404  engaged with a valve seat  426 . When the valve assembly  400  is moved to an open configuration ( FIG. 9B ), for example with a hydraulically actuated flow tube (not shown), the biasing member  424  is axially compressed against the fixed reference support  416 . The hinge  422  and the second end  420   b  of the one or more link members  420  are moved to an axially approximate location with respect to the fixed reference support  416  permitting the flapper member  404  to pivot to a position that is generally orthogonal to the position of the flapper member  404  in the closed configuration. In this orthogonal position, the flapper member  404  does not intrude into the flow path  408  defined by the tubular body and extending into the spring support  414 . 
     The aspects of the disclosure described below are provided to describe a selection of concepts in a simplified form that are described in greater detail above. This section is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     According to a first aspect, the disclosure is direct to a downhole valve assembly. The assembly includes a tubular body defining a longitudinal axis and a flow path therethrough, a flapper member pivotally coupled to tubular body about a pivot axis and movable between a closed position where the flapper member prevents fluid flow through the flow path and an open position where fluid flow through the flow path is permitted, the flapper member including a pair of opposed lateral openings defined therein radially spaced from the pivot axis, a spring support coupled to the tubular body and extending axially along the longitudinal axis and a pair of opposed wire springs each individually coupled between the spring support and the flapper member, the wire springs each including a free end restrained in a respective one of the lateral openings defined in the flapper member. 
     In one or more embodiments, the pair of opposed wire springs are constructed as wire-form springs devoid of coils and cylindrical structures. The pair of opposed wire springs may exhibit mirror symmetry with respect to one another. 
     In some embodiments, the pair of opposed wire springs each include a non-metallic resistance band thereon engaged with the flapper member. In some embodiments, the lateral openings are defied on an outer circumferential surface of the flapper member extending into opposed blind holes, and the free ends of the wire springs may be restrained in the lateral openings each abut a bottom surface of a respective one of the opposed blind holes. In some embodiments, the lateral openings are defined on an elongated channel extending through a central rib of the flapper member. 
     In one or more embodiments, the spring support comprises a pair of lateral arms connected by a circumferential cross-beam, and the each of the pair of opposed wire springs is supported in a hole provided in a respective one of the lateral arms of the spring support. Free ends of the wire springs opposite the free ends restrained in the lateral openings of the flapper member may be axially and laterally spaced from the holes in the spring support when the wire springs are in a relaxed configuration. In some embodiments, the assembly further includes a linear spring and a hinge coupled between the wire springs and the spring support. 
     In another aspect, the disclosure is directed to a wellbore system. The wellbore system includes a tubular string disposed at a downhole location in a wellbore, a tubular body coupled within the tubular string the tubular body defining a longitudinal axis and a flow path therethrough, a flapper member pivotally coupled to tubular body about a pivot axis and movable between a closed position where the flapper member prevents fluid flow through the flow path and an open position where fluid flow through the flow path is permitted, the flapper member including a pair of opposed lateral openings defined therein radially spaced from the pivot axis, a spring support coupled to the tubular body and extending axially along the longitudinal axis, and a pair of opposed wire springs each individually coupled between the spring support and the flapper member, the wire springs each including a free end restrained in a respective one of the lateral openings defied in the flapper member. 
     In some embodiments, the pair of opposed wire springs exhibit mirror symmetry with respect to one another and are constructed as wire-form springs devoid of coils and cylindrical structures. The lateral openings may be defined on an outer circumferential surface of the flapper member extending into opposed blind holes and wherein the free ends abut a bottom surface of a respective one of the opposed blind holes. In some embodiments, the lateral openings are defined on an elongated channel extending through a central rib of the flapper member. 
     In one or more embodiments, the spring support comprises a pair of lateral arms connected by a circumferential cross-beam, and wherein the each of the pair of opposed wire springs is supported in a hole provided in a respective one of the lateral arms of the spring support. Free ends of the wire springs opposite the free ends restrained in the lateral openings of the flapper member may be axially and laterally spaced from the holes in the spring support when the wire springs are in a relaxed configuration. In some embodiments, the system further includes a linear spring and a hinge coupled between the wire springs and the spring support. 
     In another aspect, the disclosure is directed to a method of constructing a downhole valve assembly. The method includes pivotally coupling a flapper member to a tubular body such that the flapper member is movable between a closed position where the flapper member prevents fluid flow through a flow path defined by the tubular body and an open position where fluid flow through the flow path is permitted, securing a spring support to the tubular body, the spring support extending axially from the tubular member and circumferentially around the flow path, restraining free ends of a pair of opposed wire springs in into a respective one of a pair of opposed lateral openings defined in the flapper member and preloading each of the wire springs between the spring support and the flapper member such that the wire springs cooperate to bias the flapper member toward the closed position. 
     In one or more aspects, the method further includes constructing the wire springs as wire-form springs devoid of coils and cylindrical structures such that the wire springs exhibit mirror symmetry with respect to one another. In some embodiments, preloading each of the wire springs comprises installing free ends of the wire springs opposite the free ends restrained in the lateral openings of the flapper member into holes defined in the spring support. 
     The Abstract of the disclosure is solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of technical disclosure, and it represents solely one or more examples. 
     While various examples have been illustrated in detail, the disclosure is not limited to the examples shown. Modifications and adaptations of the above examples may occur to those skilled in the art. Such modifications and adaptations are in the scope of the disclosure.