A VALVE, A FLOAT SHOE AND A FLOAT COLLAR FOR USE IN THE CONSTRUCTION OF OIL AND GAS WELLS

Abstract: A valve for use in the construction of oil and gas wells, which valve comprises means (12, 15, 24) responsive to hydrostatic pressure to close said valve, and frangible member to maintain said valve in an open position in which fluid can pass through said valve, characterised in that said frangible member comprises a shear ring (16) the arrangement being such that, in use, when said valve is subjected to a predetermined hydrostatic pressure said shear ring will shear and thereby permit said valve to close.

Description: A Valve, a Float Shoe and a Float Collar for use in the Construction of Oil and Gas Wells This invention relates to a valve, a float shoe and a float collar for use in the construction of oil and gas wells . The invention also relates to a method for using the valve in the construction of oil and gas wells . During the construction of oil and gas wells a borehole is drilled to a certain depth. The drill string is then removed and casing inserted. The annular space between the outside of the casing and the wall of the borehole is then conditioned for cementing by pumping conditioning fluid down the casing. The conditioning fluid flows radially outwardly from the bottom of the casing and passes upwardly through the annular space where it entrains debris and carries it to the surface. Finally, cement is pumped downwardly through the casing, squeezes radially outwardly from the bottom of the casing and passes upwardly into the annular space where it sets . Conventionally a valve is fitted on the bottom of the casing or close to the bottom. The valve inhibits fluid entering the casing from the bore but permits fluid to flow from the casing into the borehole. The valve is normally incorporated in a float shoe or a float collar, a float shoe being fitted on the bottom of the casing whilst a float collar is incorporated between two lengths of casing. It will be appreciated that if the borehole contains liquid the presence of the valve reduces the rate at which the casing can be lowered. PCT publication number WO 95/25874 discloses a valve for use in float equipment which valve comprises means responsive to hydrostatic pressure to close said valve, and a frangible member to maintain said valve in an open position in which fluid can pass through said valve. When the hydrostatic pressure reaches a certain level the frangible member breaks thereby permitting the valve to function normally. Conventionally, the frangible member is formed by one or more shear pins. The difficulty with this arrangement is that it is difficult to be sure that the frangible member will fracture at, or close to, the desired hydrostatic pressure. The present invention aims to reduce this problem. Accordingly, there is provided a valve for use in the construction of oil and gas wells, which valve comprises means responsive to hydrostatic pressure to close said valve, and a frangible member to maintain said valve in an open position in which fluid can pass through said valve, characterised in that said frangible member comprises a shear ring, the arrangement being such that, in use, when said valve is subjected to a predetermined hydrostatic pressure said shear ring will shear and thereby permit said valve to close. Other aspects of the invention are set out in Claims 2 to 9. There is also provided a float shoe and a float collar provided with a valve as claimed herein. There is also provided a method for using a valve in the construction of oil and gas wells, the method comprising the steps of lowering a casing string into the wellbore, the casing string comprising a plurality of hollow tubular pieces of casing connected end-to-end, a valve connected to a lowermost end of the lowermost casing, the valve comprising a tubular housing having a valve seat, a valve member slidably mounted in said tubular housing, spring means for biasing said valve member towards a closed position, said valve member comprising a head engageable with said valve seat of said tubular housing to close the valve, selectively releasable apparatus for releasably maintaining the valve in an open position, the selectively releasable apparatus including a shear ring breakable in response to pressure thereon, a slider movable disposed in a slider housing mounted in the tubular housing, a lower end of the slider initially projecting down and out from the slider housing and abutting a top end of the valve member and preventing the valve member from moving, a top end of the slider abutting the shear ring, the slider prevented initially from moving by the shear ring, the slider movable in response to pressure of fluid in the wellbore, liquid in the wellbore flowing into the string of casing through the open valve, and activating the selectively releasable apparatus to close the fill valve by shearing the shear ring by pressure of the fluid on the slider. For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawing which shows a cross-sectional view of a float collar incorporating a valve in accordance with the present invention. Referring to the Figure, there is shown a float collar which is generally identified by reference numeral 1. The float collar 1 comprises a valve 2 mounted in a tubular 3. The valve 2 is held in place by a ring of cement 4. The valve 2 has a housing 5 in which a valve member 6 is movably mounted. The valve member 6 comprises a tubular upper section 7 and a lower section 8 which is similar to that disclosed in PCT publication number WO 95/25873. The lower section 8 is shaped to allow fluid to flow thereabout whilst retaining a valve member 9. A light spring 10 biases the valve member 6 upwardly to a closed position. The housing 5 has a valve seat surface 11 against which the valve head 9 may seat to close off fluid flow through the float collar 1. A slider 12 has a lower end 13 initially positioned in the upper part of the housing 5 and an upper end 14 initially extending through a slider housing 15 and abutting a shear ring 16. The slider housing 15 is secured in the ring of cement 4. The shear ring 16 is held in place on a ledge 17 of the slider housing 15 by an insert 18 that has a threaded exterior that threadedly mates with a threaded interior 19 of the top of the slider housing 15. Movement of the slider 12 is initially prevented by its abutment against the shear ring 16. When the fill valve 2 is open, fluid flows through a central flow bore 20 of the insert 18, through a central flow bore 21 of the slider housing 15; then through the central flow bore 22 of the valve member 6 and out openings or windows 23. A sealed chamber 24 is defined by an exterior surface 25 of the slider 12 and an interior surface 26 of the slider housing 15. A top o-ring 27 in a recess 28 in the slider housing 15 and a bottom o-ring 29 in a recess 30 in the slider 12 seal the chamber 24. Fluid, for example, a gas such as helium, nitrogen or air at a desired pressure is captured in the chamber 24 during its assembly at the surface. In one aspect the fluid is air at atmospheric pressure. During operation of the float collar 1 in a wellbore in which there is wellbore fluid such as mud, a hydrostatic head of pressure occurs. The hydrostatic head of pressure at some point exceeds the pressure of fluid in the chamber 24 which then begins to exert force on the shear ring 16. When this force exceeds the rating of the shear ring 16, (for example, but not limited to, 69, 138, 207, 276, 345 Bar (1000, 2000, 3000, 4000, 5000 psi strength) or more) , the slider 12 breaks the shear ring 16 freeing the valve member 6 for movement to close the valve head 9 thereby preventing fluid flow through the float collar 1 (unless and if the spring force is overcome by pumping fluid on top of the valve member 6 at sufficient pressure) . The slider 12 acts as a piston as the head pressure acts on it, including on the surfaces 31 and 32. This piston effect (due to differential area) is achieved due to the smaller diameter at the interior of the o-ring 27 compared to the larger diameter at the outer surface of the 0-ring 29. In particular, after the shear ring 16 has broken and the valve 9 has closed, a fluid pressure increase from within the tubular 3 above the float collar 1 will force the valve 9 open by acting on the top of the valve 9 and on surface 31 of the slider 12. This will be resisted partially by surface 32 on the slider 12. A hole 33 (one or more may be used) provides a flow path for fluid to flow to the surface 32 and prevents a hydraulic lock between the moving parts. The slider/shear ring mechanism described above may, according to this invention, be used with any known float valve and any known float collar.

Claims: CLAIMS : 1. A valve for use in the construction of oil and gas wells, which valve comprises means (12, 15, 24) responsive to hydrostatic pressure to close said valve, and a frangible member to maintain said valve in an open position in which fluid can pass through said valve, characterised in that said frangible member comprises a shear ring (16) , the arrangement being such that, in use, when said valve is subjected to a predetermined hydrostatic pressure said shear ring will shear and thereby permit said valve to close. 2. A valve as claimed in Claim 1 , wherein said means is, in use, located above a valve head (9) . 3. A valve as claimed in Claim 1 or 2 , wherein said means comprises a slider (12) and a slider housing (15) . 4. A valve as claimed in Claim 3 , wherein said slider (12) and said slider housing (15) define a chamber (24) enclosing a compressible fluid. 5. A valve as claimed in Claim 3 or 4 , wherein said slider (12) and said slider housing (15) are tubular and concentric with each other having a flow path (21) therethrough for the passage of fluids . 6. A valve as claimed in Claim 5, wherein said slider housing (15) comprises a hole (33) therein for the passage of fluid to beneath said slider (12) . 7. A valve as claimed in any of Claims 3 to 6, wherein said shear ring (16) is located above said slider (12) . 8. A valve as claimed in any preceding claim, further comprising a valve head (9) , a valve seat (11) and a spring (10) biasing said valve head (9) towards said valve seat (11) . 9. A valve as claimed in Claim 8, further comprising a valve member (6) substantially concentric with said valve and located between said spring (10) and said valve head 10. A float shoe or a float collar provided with a valve as claimed in any preceding claim. 11. A method for using a valve in the construction of oil and gas wells, the method comprising the steps of lowering a casing string into a wellbore, the casing string comprising a plurality of hollow tubular pieces of casing connected end-to-end, a valve connected to a lowermost end of the lowermost casing, the valve comprising a tubular housing having a valve seat, a valve member slidably mounted in said tubular housing, spring means for biasing said valve member towards a closed position, said valve member comprising a head engageable with said valve seat of said tubular housing to close the valve, selectively releasable apparatus for releasably maintaining the valve in an open position, the selectively releasable apparatus including a shear ring breakable in response to pressure thereon, a slider movable disposed in a slider housing mounted in the tubular housing, a lower end of the slider initially projecting down and out from the slider housing and abutting a top end of the valve member and preventing the valve member from moving, a top end of the slider abutting the shear ring, the slider prevented initially from moving by the shear ring, the slider movable in response to pressure of fluid in the wellbore, liquid in the wellbore flowing into the string of casing through the open valve, and activating the selectively releasable apparatus to close the fill valve by shearing the shear ring by pressure of the fluid on the slider.

Inventors: GIROUX RICHARD LEE, GIROUX, RICHARD, LEE
Applicants: LUCAS BRIAN RONALD, WEATHERFORD LAMB, LUCAS, BRIAN, RONALD, WEATHERFORD/LAMB, INC.
Application year: 1998
Main classification: E21B34
IPC codes: E21B34