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CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. provisional patent application Ser. No. 60/505,515, filed Sep. 24, 2003, which is incorporated by reference herein in its entirety. That application is entitled “Tubing Mounted Safety Valve.” 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Inventions  
         [0003]     Embodiments of the present invention are generally related to safety valves. More particularly, embodiments of the invention pertain to subsurface safety valves configured to permit a cementing operation of a wellbore there through.  
         [0004]     2. Description of the Related Art  
         [0005]     Surface-controlled, subsurface safety valves (SCSSVs) are commonly used to shut-in oil and gas wells. Such SCSSVs are typically fitted into a production tubing in a hydrocarbon producing well, and operate to selectively block the flow of formation fluids upwardly through the production tubing should a failure or hazardous condition occur at the well surface.  
         [0006]     SCSSVs are typically configured as rigidly connected to the production tubing (tubing retrievable), or may be installed and retrieved by wireline without disturbing the production tubing (wireline retrievable). During normal production, the subsurface safety valve is maintained in an open position by the application of hydraulic fluid pressure transmitted to an actuating mechanism. The actuating mechanism in one embodiment is charged by application of hydraulic pressure. The hydraulic pressure is commonly a clean oil supplied from a surface fluid reservoir through a control line. A pump at the surface delivers regulated hydraulic fluid under pressure from the surface to the actuating mechanism through the control line. The control line resides within the annular region between the production tubing and the surrounding well casing.  
         [0007]     Where a failure or hazardous condition occurs at the well surface, fluid communication between the surface reservoir and the control line is broke. This, in turn, breaks the application of hydraulic pressure against the actuating mechanism. The actuating mechanism recedes within the valve, allowing the flapper to close against an annular seat quickly and with great force.  
         [0008]     Most surface controlled subsurface safety valves are “normally closed” valves, i.e., the valve is in its closed position when the hydraulic pressure is not present. The hydraulic pressure typically works against a powerful spring and/or gas charge acting through a piston. In many commercially available valve systems, the power spring is overcome by hydraulic pressure acting against the piston, producing longitudinal movement of the piston. The piston, in turn, acts against an elongated “flow tube.” In this manner, the actuating mechanism is a hydraulically actuated and longitudinally movable piston that acts against the flow tube to move it downward within the tubing and across the flapper.  
         [0009]     During well production, the flapper is maintained in the open position by force of the piston acting against the flow tube downhole. Hydraulic fluid is pumped into a variable volume pressure chamber (or cylinder) and acts against a seal area on the piston. The piston, in turn, acts against the flow tube to selectively open the flapper member in the valve. Any loss of hydraulic pressure in the control line causes the piston and actuated flow tube to retract. This, in turn, causes the flapper to rotate about a hinge pin to its valve-closed position. In this manner, the SCSSV is able to provide a shutoff of production flow within the tubing as the hydraulic pressure in the control line is released.  
         [0010]     During well completions, certain cement operations can create a dilemma for the operator. In this respect, the pumping of cement down the production tubing and through the SCSSV presents the risk of damaging the valve. Operative parts of the valve, such as the flow tube or flapper, could become cemented into place and inoperative. At the least, particulates from the cementing fluid could invade chamber areas in the valve and cause the valve to become inoperable.  
         [0011]     In an attempt to overcome this possibility, the voids within the valve have been liberally filled with grease or other heavy viscous material. The viscous material limits displacement of cement into the operating parts of the valve. In addition to grease packing, an isolation sleeve may be used to temporarily straddle the inner diameter of the valve and seal off the polished bore portion along the safety valve. However, this procedure requires additional trips to install the sleeve before cementing, and then later remove the sleeve at completion.  
         [0012]     Therefore, a need exists for an apparatus and improved method for protecting the SCSSV from cement infiltrating the inner mechanisms of the valve during a cementing operation. There is a further need for an improved SCSSV that does not require elastomeric seals to seal off the flow tube or other operative parts of the safety valve during a cement-through operation. Still further, there is a need for an improved SCSSV that isolates certain parts of the valve from cement infiltration during a cement-through operation, without unduly restricting the inner diameter of the safety valve for later operations.  
       SUMMARY OF THE INVENTION  
       [0013]     A subsurface safety valve is first provided. The safety valve has a longitudinal bore there through. The safety valve generally comprises a tubular housing, a tubular isolation sleeve disposed within an inner diameter of the tubular housing, with the isolation sleeve and the tubular body forming an annular area there between, a flow tube movably disposed along a portion of the annular area, and a flapper. The flapper is pivotally movable between an open position and a closed position in response to longitudinal movement of the flow tube in order to selectively open and close the valve. Preferably, the annular area is isolated from an inner diameter of the isolation sleeve. In one embodiment, a seal ring is placed along an outer diameter of the isolation sleeve for sealingly receiving the movable flow tube and for providing the isolation of the annular area. Preferably, the isolation sleeve is stationary.  
         [0014]     In operation, the valve permits fluid to flow through the inner diameter of the isolation sleeve when the flapper is in the open position, but the valve is sealed to fluid flow when the flapper is in the closed position.  
         [0015]     In one embodiment, the safety valve further includes a piston disposed above the flow tube, wherein the piston acts against the flow tube in response to hydraulic pressure in order to move the flow tube longitudinally. Preferably, the valve also includes a biasing member acting against the piston in order to bias the piston and connected flow tube to allow the flapper to close. An example of a biasing member is a spring. The piston may be either a rod piston or a concentric annular piston.  
         [0016]     A method for controlling fluid flow in a wellbore is also provided. In one embodiment, the method includes the steps of placing a safety valve in series with a string of production tubing. The production tubing has a bore there through, and the safety valve may be as described above. The method also includes the steps of running the production tubing and safety valve into the wellbore, placing the flapper in its open position, and pumping cement into the bore of the production tubing and through the safety valve. In one embodiment, the method also includes further pumping cement into an annulus formed between the production tubing and the surrounding wellbore to form a cement column, thereby securing the production tubing in the wellbore, providing fluid communication between the bore of the tubing and a selected formation along the wellbore, and producing the well by allowing hydrocarbons to flow through the production tubing and the opened safety valve. Preferably, the step of providing fluid communication between the bore of the tubing and a selected formation along the wellbore is accomplished through use of a perforating gun.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0018]      FIG. 1  is a cross-sectional view of a wellbore illustrating a production tubing having a safety valve in accordance with an embodiment of the present invention.  
         [0019]      FIG. 2  provides a cross-sectional view of a tubing-retrievable safety valve, in one embodiment. Here, the safety valve is in its open position.  
         [0020]      FIG. 3  is an enlarged cross-sectional view of the safety valve of  FIG. 2 . Again, the flow tube is positioned to maintain the safety valve in its open position.  
         [0021]      FIG. 4  is a cross-sectional view illustrating the tubing-retrievable safety valve of  FIG. 2  in a closed position.  
         [0022]      FIG. 5  is an enlarged cross-sectional view of the safety valve of  FIG. 4 . The flow tube is again positioned to maintain the safety valve in its closed position. 
     
    
     DETAILED DESCRIPTION  
       [0023]     The present invention is generally directed to a tubing-retrievable subsurface safety valve for controlling fluid flow in a wellbore. Various terms as used herein are defined below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term, as reflected in printed publications and issued patents. In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings may be, but are not necessarily, to scale and the proportions of certain parts have been exaggerated to better illustrate details and features described below. One of normal skill in the art of subsurface safety valves will appreciate that the various embodiments of the invention can and may be used in all types of subsurface safety valves, including but not limited to tubing retrievable, wireline retrievable, injection valves, or subsurface controlled valves.  
         [0024]     For ease of explanation, the invention will be described generally in relation to a cased vertical wellbore. It is to be understood; however, that the invention may be employed in an open wellbore, a horizontal wellbore, or a lateral wellbore without departing from principles of the present invention. Furthermore, a land well is shown for the purpose of illustration; however, it is understood that the invention may also be employed in offshore wells or extended reach wells that are drilled on land but completed below an ocean or lake shelf.  
         [0025]      FIG. 1  presents a cross-sectional view of an illustrative wellbore  100 . The wellbore is completed with a string of production tubing  120  therein. The production tubing  120  defines an elongated bore through which fluids may be pumped downward, or pumped or otherwise produced upward. The production tubing  120  includes a safety valve  200  in accordance with an embodiment of the present invention. The safety valve  200  is used for selectively controlling the flow of fluid in the production tubing  120 . The valve  200  may be moved between an open position and closed position by operating a control  150  in communication with the valve  200  through a line  145 . The operation of the valve  200  is described in greater detail below in connection with  FIGS. 2-5 .  
         [0026]     During the completion operation, the wellbore  100  is lined with a string of casing  105 . Thereafter, the production tubing  120  with the safety valve  200  disposed in series is deployed in the wellbore  100  to a predetermined depth. In connection with the completion operation, the production tubing  120  is cemented in situ. To accomplish this, a column of cement is pumped downward through the bore of the production tubing  120 . Cement is urged under pressure through the open safety valve  200 , through the bore of the tubing  120 , and then into an annulus  125  formed between the tubing  120  and the surrounding casing  105 . Preferably, the cement  160  will fill the annulus  125  to a predetermined height, which is proximate to or higher than a desired zone of interest in an adjacent formation  115 .  
         [0027]     After the cement  160  is cured, the formation  115  is opened to the bore of the production tubing  120  at the zone of interest. Typically, perforation guns (not shown) are lowered through the production tubing  120  and the valve  200  to a desired location proximate the formation  115 . Thereafter, the perforation guns are activated to form a plurality of perforations  110 , thereby establishing fluid communication between the formation  115  and the production tubing  120 . The perforation guns can be removed or dropped off into the bottom of the wellbore below the perforations. Hydrocarbons (illustrated by arrows) may subsequently flow into the production tubing  120 , through the open safety valve  200 , through a valve  135  at the surface, and out into a production flow line  130 .  
         [0028]     During this operation, the valve  200  preferably remains in the open position. However, the flow of hydrocarbons may be stopped at any time during the production operation by switching the valve  200  from the open position to the closed position. This may be accomplished either intentionally by having the operator remove the hydraulic pressure applied through the control line  145 , or through a catastrophic event at the surface such as an act of terrorism. The valve  200  is demonstrated in its open and closed positions in connection with  FIGS. 2-5 .  
         [0029]      FIG. 2  presents a cross-sectional view illustrating the safety valve  200  in its open position. A bore  260  in the valve  200  allows fluids such as uncured cement to flow down through the valve  200  during the completion operation. In a similar manner, the open valve  200  allows hydrocarbons to flow up through the valve  200  during a normal production operation.  
         [0030]     The illustrative valve  200  includes a top sub  270  and a bottom sub  275 . The top  270  and bottom  275  subs are threadedly connected in series with the production tubing (shown in  FIG. 1 ). The valve  200  further includes a housing  255  disposed intermediate the top  270  and bottom  275  subs. The housing  255  defines a tubular body that serves as a housing for the valve  200 . The tubular housing  255  preferably includes a chamber  245  in fluid communication with a hydraulic control line  145 . The hydraulic control line  145  carries fluid such as a clean oil from the control reservoir  150  down to the chamber  245 .  
         [0031]     In the arrangement of  FIG. 2 , the chamber  245  is configured to receive a piston  205 . The piston  205  typically defines a small diameter piston which is movable within the chamber  245  between an upper position and a lower position. Movement of the piston  205  is in response to hydraulic pressure from the line  145 . It is within the scope of the present invention, however, to employ other less common actuators such as electric solenoid actuators, motorized gear drives, and gas charged valves (not shown). Any of these known or contemplated means of actuating the subsurface safety valve  200  of the present invention may be employed.  
         [0032]     As illustrated in  FIG. 2 , the valve  200  also may include a biasing member  210 . Preferably, the biasing member  210  defines a spring  210 . The spring  210  resides in the tubular body  255  below the piston  205 . In one optional aspect, the lower portion of the tubular body  255  defines a connected spring housing  256  for receiving the spring  210 . A lower end of the spring  210  abuts a spacer bearing  265  that is adjacent to the spring housing  256 . An upper end of the spring  210  abuts a lower end of the piston  205 . The spring operates in compression to bias the piston  205  upward. Movement of the piston  205  from the upper position to the lower position compresses the biasing member  210  against the spacer bearing  265 . In the arrangement of  FIGS. 2 and 4 , an annular shoulder  206  is provided as a connector between the piston  205  and the spring  210 .  
         [0033]     Disposed below the spacer bearing  265  is a flapper  220 . The flapper  220  is rotationally attached by a pin  230  to a flapper mount  290 . The flapper  220  pivots between an open position and a closed position in response to movement of a flow tube  225 . A shoulder  226  is provided for a connection between the piston  205  and the flow tube  225 . In the open position, a fluid pathway is created through the bore  260 , thereby allowing the flow of fluid through the valve  200 . Conversely, in the closed position, the flapper  220  blocks the fluid pathway through the bore  260 , thereby preventing the flow of fluid through the valve  200 .  
         [0034]     Further illustrated in  FIG. 2 , a lower portion of the flow tube  225  is disposed adjacent the flapper  220 . The flow tube  225  is movable longitudinally along the bore  260  of the housing  255  in response to axial movement of the piston  205 . Axial movement of the flow tube  225 , in turn, causes the flapper  220  to pivot between its open and closed positions. In the open position, the flow tube  225  blocks the movement of the flapper  220 , thereby causing the flapper  220  to be maintained in the open position. In the closed position, the flow tube  225  allows the flapper  220  to rotate on the pin  230  and move to the closed position. It should also be noted that the flow tube  225  substantially eliminates the potential of contaminants, such as cement, from interfering with the critical workings of the valve  200 . However, it is desirable that additional means be provided for preventing contact by cement with the flapper  220  and other parts of the valve  200 , including the flow tube  225  itself. To this end, the valve  200  also includes a sleeve  215  which is disposed adjacent the housing  255 .  
         [0035]     Each of  FIGS. 2-5  shows an isolation sleeve  215  adjacent to the bore  260  of the valve  200 . The sleeve  215  serves to isolate the bore  260  of the valve from at least some operative parts of the valve  200 . The sleeve  215  has an inner diameter and an outer diameter. The inner diameter forms a portion of the bore  260  of the valve, while the outer diameter provides an annular area  240  vis-à-vis the inner diameter of the tubular housing  255 . Preferably, the sleeve  215  is press fit into the housing  255 . An upper portion of the flow tube  225  is movable received within the annular area.  
         [0036]     In one embodiment, a plurality of notches  295  may optionally be radially disposed at the lower end of the flow tube  225 . The notches  295  are constructed and arranged to allow pressure communication between the bore  260  of the valve  200  and the annular area  240  inside the tubular housing  255 . This, in turn, provides pressure balancing and helps prevent burst or collapse of the thin isolation sleeve  215  and the flow tube  235 . Where notches  295  are employed, it is desirable that the notches  295  be small enough to discourage cement or particles from entering the bottom of the flow tube  225 . It is preferred, however, that notches not be employed, but that the flow tube  235  be fabricated from a material sufficient to withstand anticipated burst and collapse pressure differentials between the bore  260  and the annular area  240 . Similarly, it is preferred that the sleeve  215  also be fabricated from a material sufficient to withstand anticipated burst and collapse pressure differentials between the bore  260  and the annular area  240 .  
         [0037]     A seal ring  235  is preferably provided at an interface between the sleeve  215  and the movable flow tube  225 . Preferably, the seal ring  235  is fixed along the outer diameter of the sleeve  215  at a lower end of the sleeve  215 . The seal ring  235  would then be stationary and the flow tube  225  would move through the seal ring  235 . Alternatively, the seal ring  235  is placed in a groove (not shown) in an upper end of the flow tube  225 . In this respect, the movement of the piston  205  in response to the hydraulic pressure in the line  145  would also cause the seal ring  235  and flow tube  225  to move. In so moving, the seal ring  235  would traverse upon the outer diameter of the isolation sleeve  215 .  
         [0038]     Where a seal is provided, the isolation sleeve  215  fluidly seals an inside of the chamber housing  255 . In an alternative embodiment, the sleeve  215  could be machined integral to the housing  255 . The primary reason for the seal ring  235  is to prevent contaminants, such as cement, from entering into the annular area  240  adjacent the piston  205 . Typically, the seal ring  235  creates a fluid seal between the flow tube  225  and the stationary sleeve  215 .  
         [0039]      FIG. 3  presents an enlarged cross-sectional view of a portion of the safety valve  200  of  FIG. 2 . The flow tube  225  is more visible here. Again, the flow tube  225  is positioned to maintain the safety valve  200  in its open position. This position allows cement or other fluids to flow down through the bore  260  during completion operations, and allows hydrocarbons to flow up through the bore  260  during production. In either case, the flow tube  225  also protects various components of the valve  200 , such as the biasing member  210  and the flapper  220 , from cement or contaminants that will flow through the bore  260 . Furthermore, the flow tube  225  in the open position prevents the flapper  220  from moving from the open position to the closed position.  
         [0040]     Typically, the flow tube  225  remains in the open position throughout the completion operation and later production. However, if the flapper  220  is closed during the production operation, it may be reopened by moving the flow tube  225  back to the open position. Generally, the flow tube  225  moves to the open position as the piston  205  moves to the lower position and compresses the biasing member  210  against the spacer bearing  265 . Typically, fluid from the line (not shown) enters the chamber  245 , thereby creating a hydraulic pressure on the piston  205 . As more fluid enters the chamber  245 , the hydraulic pressure continues to increase until the hydraulic pressure on the upper end of the piston  205  becomes greater than the biasing force  210  on the lower end of the piston  205 . At that point, the hydraulic pressure in the chamber  245  causes the piston  205  to move to the lower position. Since the flow tube  225  is operatively attached to the piston  205 , the movement of the piston  205  causes longitudinal movement of the flow tube  225  and the seal ring  235 .  
         [0041]     It is also noted that the flow tube  225  also may aid in providing isolation of fluids from the annular area  240 . In this respect, the bottom of the flow tube  225  is dimensioned to land on a shoulder of the lower sub  275  when the flow tube  225  is moved to the open position (seen in  FIGS. 2 and 3 ). An elastomeric seal member (not shown) may be provided at the bottom of the flow tube  225  to engage the lower sub  275 . Preferably though, a seal member is provided along a shoulder of the sub  275  to meet the bottom of the flow tube  225  in the valve&#39;s  200  open position.  
         [0042]      FIG. 4  is a cross-sectional view illustrating the tubing-retrievable safety valve  200  of  FIG. 2  in its closed position. Generally, in the production operation, fluid flow through the production tubing may be controlled by preventing flow through the valve  200 . More specifically, the flapper  220  seals off the bore  260 , thereby preventing fluid communication through the valve  200 .  
         [0043]     During closure, fluid in the chamber  245  exits into the line  145 , thereby decreasing the hydraulic pressure on the piston  205 . As more fluid exits the chamber  245 , the hydraulic pressure continues to decrease until the hydraulic pressure on the upper end of the piston  205  becomes less than the opposite force on the lower end of the piston  205 . At that point, the force created by the biasing member  210  causes the piston  205  to move to the upper position. Since the flow tube  225  is operatively attached to the piston  205 , the movement of the piston  205  causes the movement of flow tube  225  and the seal ring  235  into the annular area  240  until the flow tube  225  is substantially disposed within the annular area  240 . In this manner, the flow tube  225  is moved to the closed position.  
         [0044]      FIG. 5  is an enlarged cross-sectional view illustrating the flow tube  225  in the closed position. Here, the piston  205  is raised within the chamber  245 . In this respect, the spring  210  of  FIG. 5  is seen expanded vis-à-vis the spring  210  of  FIG. 3 . This indicates that the biasing action of the spring  210  has overcome the piston  205 . As the piston  205  is raised, the connected flow tube  225  is also raised. This moves the lower end of the flow tube  225  out of its position adjacent the flapper  220 . This, in turn, allows the flapper  220  to pivot into its closed position. In this position, the bore  260  of the valve  200  is sealed, thereby preventing fluid communication through the valve  200 . More specifically, flow tube  225  in the closed position no longer blocks the movement of the flapper  220 , thereby allowing the flapper  220  to pivot from the open position to the closed position and seal the bore  260 .  
         [0045]     Although the invention has been described in part by making detailed reference to specific embodiments, such detail is intended to be and will be understood to be instructional rather than restrictive. It should be noted that while embodiments of the invention disclosed herein are described in connection with a subsurface safety valve, the embodiments described herein may be used with any well completion equipment, such as a packer, a sliding sleeve, a landing nipple and the like.  
         [0046]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Summary:
A subsurface safety valve is first provided. The safety valve generally comprises a tubular housing, an isolation sleeve disposed within an inner diameter of the tubular housing, with the isolation sleeve and the tubular body forming an annular area there between, a flow tube movably disposed along a portion of the annular area, and a flapper. The flapper is pivotally movable between an open position and a closed position in response to longitudinal movement of the flow tube in order to open and close the valve. Preferably, the annular area is isolated from an inner diameter of the isolation sleeve in the open position. A method is also provided that allows for a cementing operation to be performed through an open safety valve.