Reverse cementing float shoe

Details Reverse cementing float shoe Reverse cementing float shoe

2002-10-30

2004-10-12

Walker, Zakiya (Department: 3672)

Wells

Processes

Cementing, plugging or consolidating

C166S242800, C166S328000

Reexamination Certificate

active

06802374

ABSTRACT:

BACKGROUND OF INVENTION
After drilling a borehole in the earth, a “casing” is often placed in the borehole to facilitate the production of oil and gas. The casing is a pipe that extends down the borehole, through which the oil and gas will eventually be extracted. The region between the casing and the borehole itself is known as the annulus. The casing is usually “cemented” into place in the borehole.
In general, when drilling a wellbore, a drilling fluid is pumped down the drill string during drilling. Common uses for drilling fluids include: lubrication and cooling of drill bit cutting surfaces while drilling, transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, and displacing the fluid within the well with another fluid.
One particularly significant function of the drilling fluid is to maintain the downhole hydrostatic pressure and to seal the borehole. It is desirable that the hydrostatic pressure of the drilling fluid exceed the formation pressure to prevent formation fluids from seeping into the borehole before the well is complete. In a downhole environment, drilling fluids often form what is known in the art as a “mud cake,” which is a layer of drilling fluid particulate that forms on the borehole wall and seals the borehole from the formation. When drilling is completed, the borehole remains filled with the drilling fluid.
Traditional cementing is done by lowering the casing into the borehole and pumping a cement slurry down the casing. As the slurry reaches the bottom of the casing, it is pumped out of the casing and into the annulus between the casing and the borehole wall. As the cement slurry flows up the annulus, it displaces any drilling fluid in the borehole. The cementing process is complete when cement slurry reaches the surface, and the annulus is completely filled with the slurry. When the cement hardens, it provides support and sealing between the casing and the borehole wall.
Cementing the casing into place serves several purposes. The cement holds the casing in place and provides support for the borehole to prevent caving of the borehole wall. The cement also isolates the penetrated formations so that there is no cross-flow between formations.
FIG. 1
shows a prior art cementing method. A borehole
101
is drilled into an earth formation
102
. When the drilling is complete, a casing string
103
, with a float shoe
110
, is lowered into the borehole
101
. A cement slurry
106
is pumped down the casing
103
, and the cement slurry
106
exits the casing
103
near the bottom of the well. The float shoe
110
includes a check valve
109
to prevent reverse flow of drilling fluid into the casing
103
while the casing
103
is being run into the borehole
101
and while the cement is setting.
As the cement slurry
106
is pumped into the annulus
104
between the casing
103
and the borehole wall
101
, the slurry
106
displaces any drilling fluid
105
in the annulus
104
. When the cement slurry
106
in the annulus
104
reaches the surface, the slurry is allowed to harden. The arrows in
FIG. 1
show the direction of cement slurry and drilling fluid flow in the casing
106
and annulus
104
.
There are several drawbacks to traditional cementing. When the cement is first pumped into the casing, it falls down the length of the casing. This “free falling” can cause problems, especially in larger size casings. Another problem is that pumping cement down the casing and back up the annulus requires a significant amount of time. As a result, a retarding agent must be added to the slurry so that the cement will not set before the operation is complete.
Another method for cementing a casing in a borehole is called “reverse cementing.” Reverse cementing is a term of art used to describe a method where the cement slurry is pumped down the annulus and eventually into the casing. The cement slurry displaces any drilling fluid as it is pumped down the annulus. The drilling fluid is forced down the annulus, into the casing and then back up to the surface through the casing. Once slurry is pumped into the bottom of the casing, the reverse cementing process is complete.
A typical float shoe used in a reverse cementing process has an open bottom with a check valve to prevent flow into the casing as the casing is run into the borehole. The valve must then be adjusted to allow flow into the casing during the reverse cementing process and then sealed after the process is complete. Because of the changing requirements for the float shoe, the valve must be a complex device.
SUMMARY OF INVENTION
One aspect of the invention relates to a float shoe comprising an upper section having a casing connection at an upper end thereof, and a lower section slidably coupled to the upper section, the lower section comprising a closed lower end having at least one port disposed therein. In some embodiments, the float shoe according to this aspect of the invention includes a plurality of shear pins that, when intact, maintain the upper section and the lower section in an open position. In some other embodiments, the lower section includes a lock ring and the upper section comprises a tapered wicker, the lock ring and the tapered wicker arranged to retain the upper section and the lower section in a closed position.
Another aspect of the invention relates to a method for cementing a casing into a well comprising the steps of inserting a casing having a float shoe on a lower end thereof into a borehole, filling an annulus between a wall of the borehole and the casing with a cement slurry and applying a downward force to the casing sufficient to shear at least one shear member and move the upper and lower sections into a closed position.
Yet another aspect of the invention relates to a float shoe comprising a hollow body having a casing connection at an upper end thereof, a closed end at a bottom end thereof, at least one port disposed in a side thereof that enables flow into the hollow body and a sliding member disposed on an inside of the hollow body and positioned so that fluid can flow through the at least one port when the sliding member is in an open position and so that the at least one port is blocked or closed when the sliding member is in a closed position. The sliding member typically has an annular upper surface, a fluid flow path through the center of the annular upper surface and a closing member that allows flow upward through the fluid flow path and does not allow downward flow through fluid flow path. The closing member is typically positioned to transmit fluid pressure in the casing to a downward force on the sliding member. In some embodiments, the sliding member may be an annular member, and in some other embodiments the closing member may be a ball.
Still another aspect of the invention relates to a method for cementing a casing into a borehole comprising inserting the casing having a float shoe on a lower end thereof into the borehole, filling an annulus between a wall of the borehole and the casing with a cement slurry and pumping a drilling fluid down the casing thereby moving a sliding member disposed in the float shoe into a closed position.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.


REFERENCES:
patent: 5641021 (1997-06-01), Murray et al.
patent: 6390200 (2002-05-01), Allamon et al.

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