Wells – Valves – closures or changeable restrictors – Longitudinally movable operator
Reexamination Certificate
2001-09-11
2004-02-03
Tsay, Frank (Department: 3672)
Wells
Valves, closures or changeable restrictors
Longitudinally movable operator
C166S327000
Reexamination Certificate
active
06684957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus for use in the oil industry, and, more particularly, to a float collar apparatus for use in oil well drilling operations.
2. Description of the Prior Art
Float collars are utilized by the oil well industry with respect to operations for running in and cementing casing liners down a wellbore. An example of a prior art float collar is the Multi-Purpose Float Collar manufactured and sold by Davis-Lynch, Inc. The Multi-Purpose Float Collar comprises a tubular housing having a bore therethrough and two spring-activated flapper valves which are held in an open position by a sliding sleeve installed in the bore of the float collar. Once the sleeve is forced out of the bore of the float collar, the spring-activated flapper valves are free to rotate to their closed positions.
In practice, a float collar, such as the Multi-Purpose Float Collar of Davis-Lynch, Inc., is installed within the lower end of a casing liner prior to running the casing liner down a wellbore. When the spring-activated flapper valves of the float collar are held in an open position by the sliding sleeve, a clear passage is provided through the casing liner. This open position permits drilling fluid to flow freely through the float collar as the casing liner is being run downhole, which helps to reduce surge pressure against the borehole walls and permits the casing liner to be more readily lowered to total depth. Additionally, if a tight hole condition is encountered during running in of the casing liner, drilling fluid can be pumped downward through the casing liner to circulate drilling fluid around the tight hole condition thereby freeing the casing liner.
Once the casing liner is lowered to total depth, the sliding sleeve is of the float collar actuated using a drop ball, which seats in a ball seat which is coupled to the sliding sleeve. The sliding sleeve is held in place by shear pins installed in the lower portion of the sleeve. Pressure is then increased above the drop ball until the shear pins shear, at which time the sleeve is displaced axially out of the float collar. This movement of the sleeve frees the spring-activated flapper valves to rotate to a closed position. In the closed position, the flowpath through the casing is obstructed such that any fluid passing through the casing must overcome the resistance the spring-activated flapper valves to establish communication between the lower end of the casing liner and the annulus between the casing liner and the borehole.
During cementing operations, cement is pumped downward through the casing at sufficiently high pressure to overcome the resistance of the spring-activated flapper valves. Once cement pumping operations cease, the spring-activated flapper valves close and seal the passage through the casing. This prevents the cement from flowing back upward into the casing. This effect is also known in the art as “backflow” or “u-tube” action. Finally, once cementing operations are completed, the entire float collar assembly is drilled out of the casing to reestablish an unobstructed flowpath through the wellbore.
While prior art float collars have produced desirable results for the oil well industry, a feature of prior art float collars which is undesirable is that once cementing operations are complete, prior art float collars require approximately six hours to drill out of the casing liner to reestablish the unobstructed flowpath. This relatively long drill out time is due in large part to the high metal content of components of the float collar. Prior art float collars are fabricated almost entirely of metals, e.g. aluminum. While the use of such metals allows the float collar assembly to be set at pressures up to 3000 psi, the metal components of the float collar assembly become a disadvantage when cementing operations are completed and valuable time and resources must be expended during drilling out the float collar.
Accordingly, it would be desirable to have a float collar which can be drilled out in substantially less time than the prior art float collars. This novel and useful result has been achieved by the present invention.
SUMMARY OF THE OF THE INVENTION
Apparatus in accordance with the present invention comprises a float collar assembly for regulating the passage of fluid through a tubular member. The float collar assembly is positioned within the tubular member cased in cement at the lower end of the tubular member. The float collar assembly comprises an outer housing having an axial bore therethrough and one or more spring-activated flapper valves arranged within the housing. The spring-activated flapper valves are actuated by an internal sleeve which is fabricated from plastic and which is initially held inside the housing by a plurality of shear pins extending into corresponding shear pin recesses formed near the upper end of the sleeve. While the sleeve is located in the housing, the spring-activated flapper valves are secured by the sleeve in an open position. A drop ball seat is integral with the plastic sleeve and is located at the bottom of the sleeve. The seat receives a drop ball thereby creating a seal which blocks fluid flow through the tubular member. Subsequently, fluid pressure is increased above the drop ball seat such that the shear pins are sheared and the internal sleeve is displaced downward from the float collar assembly thereby freeing the spring-activated flapper valves to rotate to a closed position. In the closed position, the spring-activated flapper valves obstruct passage through the tubular member.
While components of prior art float collars are fabricated almost entirely from metal, the float collar apparatus of the present invention is fabricated from a combination of metal and plastic components. This resultant float collar assembly provides a savings in time and resources expended during drilling out of the float collar.
REFERENCES:
patent: 3645495 (1972-02-01), Aymar
patent: 3995692 (1976-12-01), Seitz
patent: 4469174 (1984-09-01), Freeman
patent: 4615394 (1986-10-01), Kuhlman, Jr.
patent: 4729432 (1988-03-01), Helms
patent: 5246069 (1993-09-01), Glaser et al.
patent: 6209663 (2001-04-01), Hosie
patent: 6244342 (2001-06-01), Sullaway et al.
patent: 6401824 (2002-06-01), Musselwhite et al.
Allamon Interests
McConnell R. Perry
O'Neil & McConnell, PLLC
Tsay Frank
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