Patent Application
20060169465
Not applicable.
Not applicable.
The present invention relates to fluid loss devices for use in oil wells, and more particularly to flapper valves that may be closed to hold pressure in both directions.
Oil wells are drilled from the surface of the earth down to and through hydrocarbon bearing formations to allow recovery of the hydrocarbons through the well. The wells are often cased down to the producing formation. The well may be cased or lined with a metal liner through the producing formation or may be left in open hole condition in the producing formation, i.e. without a casing or liner. If a well is cased or lined in the producing formation, the casing or liner is typically perforated to allow hydrocarbons to flow from the formation into the well for production.
In many wells, whether cased and perforated or left in open hole condition in the productive formations, particulates, e.g. sand, may flow from the formation with the produced hydrocarbons. The produced sand may erode and otherwise damage metal liners, casing, valves, etc. and must be removed from the produced fluids at the surface and then safely disposed of. To minimize sand production, it is common practice to gravel pack such wells as part of the completion process.
A gravel packing system typically includes a filter element, e.g. a wire wrapped screen, that is positioned in the well near a productive formation, e.g. adjacent perforations. The screen is carried into a well on a work string that includes a packer that seals the annulus between the work string and a cased portion of the well above the productive formation. A slurry of gravel packing liquid and particulates, typically referred to as gravel, may then be flowed down the work string. A cross over device is normally included to direct the slurry flow from inside the work string above the packer to the annulus around the screen below the packer. The screen allows the liquid to flow into the interior of the screen, but blocks the flow of the particulates to fill the annulus around the screen with the particulates, i.e. to gravel pack the annulus. The liquid flows back up the work string to the crossover, where it is directed into the annulus above the packer and may be returned to the surface location of the well.
Gravel packing is normally done in an overbalanced condition, i.e. with the pressure in the well at the screen higher than the natural formation pressure. Borehole fluids therefore tend to flow into the formation. To avoid fluid loss and possible formation damage, a fluid loss device may be included in a gravel packing work string between the screen and the packer. A fluid loss device typically includes some type of valve, e.g. a ball valve or a flapper valve, that may be closed when gravel packing is completed. The valve may be closed when a wash pipe is withdrawn from the assembly after the gravel packing operation. The closed valve isolates the productive formation from borehole pressure and fluids above the valve. This allows the well fluids to be circulated, e.g. to remove any remaining particulates or other treating fluids, without losing fluids into the formation. When production tubing has been installed in the well, the fluid loss valve is typically opened permanently to allow production of hydrocarbons through the valve and up the production tubing.
Such fluid loss devices may also be useful with other well treatment systems and processes. For example, filter cake in an open hole completion may prevent large fluid losses. It is normally desirable to remove the filter cake before producing the well, for example by an acidizing treatment. After the filter cake is removed, fluid losses may be a problem. Therefore, it may be desirable to include a fluid loss device in such treatment systems to limit fluid losses in the productive zone while the well is circulated to remove any treating fluids, e.g. acid, from the well above the producing formation.
Embodiments of the invention provide a fluid loss device including a flapper valve, i.e. a flapper and seat assembly, that provides a seal on one flapper surface when the flapper is closed and resists pressure in either direction. The flapper and seat assembly is spring biased to contact a flapper support above the flapper to resist deformation of the flapper due to a pressure differential from below the flapper. The flapper and seat assembly may be moved by tubing pressure to release an opening prop that opens the flapper.
In one embodiment, the valve seat includes an elastomeric seal element to improve the fluid flow restriction, especially from below to above the flapper.
In one embodiment, the flapper and seat assembly is also biased upward by a pressure differential from below to above the flapper, to thereby increase the flapper to valve seat pressure as the fluid pressure differential increases.
In one embodiment, the opening prop opens a port to equalize pressure across the flapper before the opening prop opens the flapper.
In one embodiment, the a run in prop holds the flapper open during run in and well treatment, and is movable to close the flapper.
In describing the embodiments of the present invention, various elements are referred to by their normal relative positions when used in an oil well. The terms above or up hole mean that an element is closer to the surface location of a well. The terms below or down hole mean that an element is closer to the end of the well farthest from the surface location. In deviated or horizontal wells, the various elements may actually be at the same vertical elevation. Such terms are not meant to limit the orientation in which a device may be operated in a well, but only to help understand the relative positions of elements that make up the device.
In describing a flapper valve, i.e. a flapper and valve seat, references are made to pressures relative to the flapper. The terms pressure from below and pressure from below to above mean that the pressure below the flapper is greater than the pressure above the flapper. The terms pressure from above and pressure from above to below mean that the pressure above the flapper is greater than the pressure below the flapper.
It is understood that a purpose of a fluid loss device is to hold pressure from above and/or below the device. A perfect seal against fluid flow through the device is not essential to effectively holding the pressure. In most formations, the permeability is sufficient that a small fluid leakage past a fluid loss device has essentially no affect on pressure isolation by the device.
Various embodiments of the present invention provide fluid loss devices for use in oil wells having flapper valves that in a closed position holds pressure in both directions with a valve seat on only one side and may be opened by fluid pressure.
A flapper valve assembly 20 is carried within the sleeve 18. The flapper assembly 20 includes a flapper 22, shown in more detail in
An opening prop or sleeve 36 is carried within the lockout sleeve 32. A prop as used herein is any element having a function of holding a flapper in an open position, i.e. resisting forces that tend to close the flapper. A prop may also function to release an open flapper to move into a closed position and/or to move a closed flapper to an open position. The opening prop 36 is releasably connected to the lockout sleeve by shear pins or screws 38. The opening prop is releasably connected to the upper end of lower tubing connector 14 by shear pins or screws 40. A spring 42 is carried in an annulus between opening prop 36 and the lockout sleeve 32. In this run in condition, the spring 42 is compressed between the upper end of lower tubing connector 14 and a ring 44 threaded onto the opening prop 36. The shear pins 38 are carried in the ring 44. While a coil spring 42 is used in this embodiment, it is apparent that other forms of springs may be substituted if desired. For example, a compressed gas cylinder and piston could be used in place of the spring 42.
In this run in condition, the lower end of the opening prop 36 is positioned a short distance above a shoulder 47 near the center of lower tubing connector 14. This short distance is selected to allow the shear pin 40 to be completely sheared when the opening prop 36 is moved down into contact with the shoulder 47. The shear pins 40 are selected to have sufficient strength to hold spring 42 in a compressed state in this run in condition.
In the run in condition, the flapper 22 is held in its open position by a lower portion of a run in prop 46. The run in prop 46 is releasably held in the run in position by shear pins or screws 48 coupled a flapper support 56, shown in more detail in
The run in position of fluid loss device 10 shown in
When the run in prop 46 is moved to the upper position, the flapper 22 is released and a weak spring, not shown, in the hinge 30 swings the flapper 22 down into contact with the valve seat 28 on the upper end of carrier 24. As noted in the background section, well treatments are normally performed in an overbalanced condition. When the flapper 22 closes, the pressure above flapper 22 will normally be greater than the pressure below flapper 22. As shown in
If the pressure above flapper 22 is not sufficient to shear pins 40, a mechanical device may be used to apply downward force on the flapper 22 to shear the pins 40. Since pins 40 are desirable sheared after a shifter tool has moved the run in prop 46 and allowed the flapper 22 to close, the shifter tool itself may be used to apply the force. That is, the shifter tool may be lowered back down on top of the closed flapper 22 with the proper force to shear pins 40 before being removed from the well.
In this embodiment, the fluid pressure below flapper 22 also increases the contact pressure between the flapper 22 and the valve seat 28. The carrier 24 forms an annular piston sliding within the sleeve 18. Pressure differences above and below carrier 24 are isolated by the O-rings 26. As pressure below flapper 22 increases, the upward force produced by the carrier 24 not only increases the force between the flapper 22 and valve seat 28, but also the force between the flapper 22 and the flapper support 56. Thus, the flapper 22 is effectively at least as stiff or rigid with respect to fluid forces from below as the support 56. The result is that the seal between the flapper 22 and seat 28 is maintained despite substantial pressure differential from below to above the flapper 22.
In some cases, the pressure above flapper 22 may cycle several times between being greater, within certain limits, than the pressure below flapper 22 and being less than the pressure below flapper 22. This may occur as a result of changes in the fluid composition above flapper 22, as a result of intentional pressure changes for testing, packer inflation, etc. As such cycles occur, the assembly of flapper 22, carrier 24, lockout sleeve 32, and opening prop 36 will move between the position shown in
As an alternative to using fluid pressure to open the flapper 22, a mechanical device may be lowered down a well to contact the flapper 22 and provide sufficient force to move the device 10 to the configuration shown in
The disclosed embodiment provides an arrangement for equalizing pressure above and below the flapper 22 so that it may be opened by opening prop 36 and spring 42. A port 60 is provided through the wall of the carrier 24. The port 60 is initially closed by a portion of the opening prop 36 and a pair of O-rings 62 as shown in
The pressure equalizing feature provided by the present invention also prevents fluid shock to the producing formation that may occur with prior art flapper valves, e.g. those that are opened suddenly by breaking or shattering the valve. If the valve opens quickly, the high pressure used to open the valve may damage the producing formation or a gravel pack. In the present invention, the pressure equalization provided by fluids flowing through the port 60 and slot 64 occurs over a longer period of time and avoids a sudden pressure shock to the down hole equipment and formation.
The pressure equalizing arrangement also provides another advantage. During the time that the flapper 22 is closed, solid particles may settle out of fluids above the flapper 22 and build up on the upper surface 58 of the flapper 22 and in the hinge 30. Such solids may interfere with opening of flapper 22. The fluids that flow through the port 60 flow from a space 61, the upper end of which is located at the hinge 30. The well fluids therefore flow across the top of the flapper 22 and through the hinge 30. The flow of fluids tends to remove any solids that may have collected on the flapper 22 and particularly on the hinge 30.
Once the fluid loss device 10 has been configured as shown in
With reference to
In
The flapper surface 68 and valve seat surface 70, and optionally the elastomeric seal 72, form an interface form an interface between the flapper 22 and valve seat 28 that is adapted to hold pressure in either direction, i.e. from above and from below the flapper 22. When holding pressure from below, the support 56 prevents deformation of the flapper 22 that may cause leakage, and allows sufficient force to be applied to the interface between the flapper 22 and valve seat 28 to hold pressure from below. The interface may form a fluid tight seal, but in any case holds pressure.
The support 56 has a cylindrical central bore 86, through which the run in prop 46 is initially positioned. The support 56 includes a notch 86 on its outer edge that mates with a key 88, which key also mates with the carrier 24 at the center of hinge 30 to keep the flapper 22 and support 56 in proper angular alignment. Raised support surfaces 90 are provided on two sides of the support 56, each centered at a 90 degree displacement from the notch 86, and therefore centered on the thin edges 84 of the flapper 22. The support surfaces 90 each extend radially about 30 to 90 degrees, and preferably about 60 degrees, about the periphery of the support 56. If desired, the support 56 may also be shaped to contact the raised area 82 between the thin areas 80, but such contact is generally not needed and may complicate the device since one of these areas includes the hinge 30 area. The support surfaces 90 typically do not form a fluid tight seal with the flapper 22 and are not required to be continuous. The support surfaces are shaped, e.g. by machining or casting, to uniformly support portions of the periphery of the upper surface 58 of the flapper 22 each centered on the thin areas 84. The support areas 90 do not need to be smooth and continuous as normally required for a valve seat, but may instead be stippled or otherwise formed of a plurality of discrete contact points as long as they are spaced close enough to provide uniform support to the periphery of the flapper 22. As noted above in the preferred embodiment, when the flapper 22 is closed and forced upward into contact with the support 56, the flapper 22 and support 56 function as one piece effectively having a uniform thickness and stiffness that resists deformation that might otherwise be caused by pressure from below.
In this embodiment, the flapper 22 has an essentially flat lower surface and a curved upper surface. Other flapper shapes are known to those skilled in the art. For example, some flappers are curved on both their lower and upper surfaces and may have uniform thickness. Such a flapper is essentially a portion of a hollow cylinder. Other flappers may be flat on both upper and lower surfaces. It is apparent that in alternate embodiments, any flapper shape may be used, provided that a valve seat is provided that conforms to the lower surface of the flapper and a support is provided that conforms to and supports at least portions of the upper surface of the flapper.
As described above with reference to
A sleeve valve 108 is connected to the lower end of section 102. The valve 108 in this embodiment is formed by an inner valve sleeve 110 that is slidably carried within an outer valve sleeve 109. The outer valve sleeve 109 may be threaded to the lower end of section 102, or if desired could be formed as an integral part with section 102. An O-ring 112 restricts flow of fluids between the exterior of inner sleeve 110 and the inner surface of outer sleeve 109. Side ports 114 near the upper end of inner sleeve 110 allow fluids to flow from a central bore 111 of outer sleeve 109 to a central bore 113 of inner sleeve 110, which is open on its lower end. Above the side ports 114, the inner sleeve 110 is closed by a cap 116. The inner sleeve 110 is held in its run in position relative to the outer sleeve 109 by shear screws or pins 118. The shear pins or screws 118 are selected to shear at a force less than is required to shear the pins or screws 48 that hold the run in prop 46 in its run in position. In the run in position, the valve 108 is open and allows fluids to flow freely between the central bores 107 and 111 above the valve 108 and a central bore 113 of inner sleeve 110 below the valve 108. While valve 108 is a sleeve valve in this embodiment, other forms of valves known in the art, e.g. a ball valve, may be used in place of a sleeve valve if desired.
In an alternate embodiment, the inner sleeve 110 may be held in its run in position relative to the outer sleeve 109 by a spring instead of shear screws or pins 118. For example, a coil spring may be positioned between the shoulder in which shear pins 118 are shown in
An upper choke 120 is connected to the lower end of the inner valve sleeve 110. The choke 120 includes a central bore 122 that allows fluids flowing through the bore 113 of sleeve 110 to continue flowing through the choke 120. The outer diameter of choke 120 is selected to make a close fit with the inner surfaces of the lower connector 14, the opening prop 36, and upper connector 12 of the fluid loss device 10. If desired, elastomeric rings may be carried on the surface of choke 120 to form a fluid tight seal with the lower connector 14, the opening prop 36, and upper connector 12. A shifting tool 124 is connected to the lower end of the choke 120 and includes an open inner bore 126 in fluid communication with the bore 122. The shifting tool 124 includes profiles 128 on its outer surface adapted for engaging the run in prop 46 and moving it as described above to close the flapper 22. A lower choke 130 is connected to the lower end of the shifting tool 124 and includes an open central bore 132 in communication with the bore 126 in the shifting tool 124. The outer diameter of choke 130 is selected to make a close fit with the inner surfaces of the lower connector 14, the opening prop 36, and upper connector 12 of the fluid loss device 10. If desired, elastomeric rings may be carried on the surface of choke 130 to form a fluid tight seal with the lower connector 14, the opening prop 36, and upper connector 12.
While this embodiment includes both an upper choke 120 and a lower choke 130, the two chokes provide a single flow restriction function and may be considered to be a single choke. In some embodiments one or the other may be omitted from the positioning tool 100. For example, it may be desirable to use a longer upper connector 12 and rely on the upper choke 120 restrict fluid flow between the positioning tool and the fluid loss device 10.
In a preferred embodiment, the inner surfaces of the lower connector 14, the opening prop 36, and upper connector 12 of the fluid loss device 10 may be machined or otherwise formed with close tolerances and a smooth surface, and may therefore be referred to as seal bores. Seal bores may be distinguished from the inner surfaces of typical oilfield tubulars that have fairly large diameter tolerances and may have surfaces that are not suitable for forming a fluid tight seal. The preferred seal bores allow the dimensions of chokes 120 and 130 to be selected to form a close fit with the inner surfaces of the lower connector 14, the opening prop 36, and upper connector 12 without unintentional interference between the parts. Such a close fit may substantially block flow between the parts without actual contact being required. The seal bores also allow use of elastomeric seals on the chokes 120 and 130 to form essentially fluid tight seals without damage that might otherwise occur due to sliding contact between the elastomeric seals and the seal bores.
In the run in configuration shown in
The spacing between upper choke 120 and the shifter tool 124 is selected so that when the choke 120 is in the upper connector 12, the shifter tool 124 is in the run in prop 46 and the profiles 128 engage matching profiles in the inner surface of the run in prop 46. As the positioning tool is moved further up it applies force to move the run in prop 46 up to release the flapper 22. However, this force is resisted by the shear screws 48 holding the run in prop 46 in its run in position, and by the shear screws 118 holding the positioning tool 100 valve 108 in its open position. As noted above, the shear screws 118 are selected to shear at a lower force than the shear screws 48. Therefore, as the positioning tool 100 continues to move up, it will first shear the screws 118 and the valve sleeve 110 will move down relative to the sleeve 109, positioning the ports 114 below the O-ring 112 and closing the valve 108. In the alternative embodiment using a spring to hold the valve 108 in its run in open position, the spring will compress at a force less than required to shear screws 48 and the valve 108 will close. With the valve 108 closed, well fluids may no longer flow through the bypass flow path through positioning device 100. Flow around the device 100 is substantially restricted by the close fit of the upper choke 120 and lower choke 130 with inner surfaces of the lower connector 14, the opening prop 36, and upper connector 12.
As the positioning device 100 continues to move upward, the shear screws 48 are sheared and the run in prop 46 is moved by the shifter 124 to its open position shown in
It can be seen that the positioning device 100 operates by diverting or bypassing fluid flow through an inner bypass flow path as a fluid flow restricting device is moved past a flapper valve 20, then closing the inner flow path before closing the flapper 22. The device avoids or reduces pressure differentials that may otherwise occur across the flapper valve 20 both when the flow restricting device passes through the flapper 22 and when the flapper 22 is closed. However, the positioning device 100 is not essential for operation of the fluid loss device 10 and other shifting tools may be used if desired. The desirability of using the positioning device 100 depends primarily on environmental conditions present in a particular well. If a large flow of fluids is being lost into the productive formation, e.g. due to high overbalance pressure and high permeability, the device 100 may avoid problems caused by the flowing fluids. If the overbalance pressure is low and/or the formation has low permeability and/or has a low permeability filter cake layer, there may be little advantage in using the device 100.
It is also apparent that the positioning device 100 may provide an advantage when used to move or shift an element in any down hole device that also includes a pressure actuated element that could be actuated by a pressure differential caused by moving a shifting device into or through the down hole device.
While the present invention has been illustrated and described with reference to particular embodiments, it is apparent that various changes may be made, and parts may be substituted, within the scope of the invention as defined by the appended claims.
This application is related to U.S. patent application Ser. No. ______, [attorney docket 1391-59400] entitled “Positioning Tool With Valved Fluid Diversion Path”, filed on even date herewith.
