Wells – Processes – Placing or shifting well part
Reexamination Certificate
2001-03-14
2002-10-22
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S318000, C166S194000
Reexamination Certificate
active
06467546
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a downhole drop ball sub for use in a wellbore. The present invention is highly suitable for use in a downhole surge pressure reduction system or for other purposes. More particularly the present invention relates to a drop ball sub that may be used in conjunction with a running tool or other wellbore tools to allow launching a ball in the wellbore whose diameter is larger than the internal diameter of the running tool, drill string, tubing string, or any other restrictions found in the wellbore. The embodiment of the system for surge pressure reduction also includes a unique enlarged flow path that permits increased flow to reduce surge pressure and better handle debris.
DESCRIPTION OF THE RELATED ART
One problem frequently encountered in many wellbore operations is the need to overcome the limitation of a restriction in the wellbore that prevents use of a ball below that restriction where the ball has a diameter greater than the restriction. More particularly, one of skill in the art will realize that it has heretofore been impossible to use a ball downhole that has a diameter which is greater than the diameter of the restriction in the wellbore. The term “ball” also includes any other suitable object, e.g. bars, darts, plugs, and the like. Typically a ball is used downhole to activate, seal, or otherwise perform a useful function.
One embodiment or use of the present invention is effective for reducing surge pressure. For a long time prior to the previous invention for reducing surge pressure as taught in U.S. Pat. No. 5,960,881, which is incorporated herein by reference, the oil industry had been aware of the problem created when lowering a first casing string, which may be a casing liner, at a relatively rapid speed in drilling fluid. This rapid lowering of the casing liner results in a corresponding increase or surge in the pressure generated by the drilling fluid due to the relatively small annulus between the casing liner and the surface casing. The formation about the borehole into which the casing liner is lowered is exposed to the surge pressure.
This surge pressure has been problematic to the oil industry in that it has many detrimental effects. Some of these detrimental effects are 1.) loss volume of drilling fluid, which presently costs $40 to $400 a barrel depending on its mixture, that is primarily lost into the earth formation about the borehole, 2.) resultant weakening and/or fracturing of the formation when this surge pressure in the borehole exceeds the formation fracture pressure, particularly in older formations and/or permeable (e.g. sand) formations, 3.) loss of cement to the formation during the cementing of the casing liner in the borehole due to the weakened and, possibly, fractured formations resulting from the surge pressure of the formation, and 4.) differential sticking of the drill string or casing liner being run into a formation during oil operations, that is, when the surge pressure in the borehole is higher than the formation fracture pressure, the loss of drilling fluid to the formation allows the drill string or casing liner to be pushed against the permeable formation downhole and allows it to become stuck to the permeable formation.
This surge pressure problem had been further exacerbated when running tight clearance casing liners or other apparatus in the existing casing. For example, the clearances in recent casing liner runs have been about ½″ to ¼″ in the annulus between the casing liner and existing casing. This small annulus area in these tight clearance casing liner runs have resulted in corresponding higher surge pressures and heightened concerns over their resulting detrimental effects of surge pressure. The most common known response to surge pressures was to decrease the running speed of the drill string supporting the casing liner downhole to maintain the surge pressure at an acceptable level. An acceptable level would be a level at least where the drilling fluid pressure, including the surge pressure, is less than the formation fracture pressure to minimize the above detrimental effects. Any reduction of surge pressure would be beneficial because the more surge pressure is reduced, the faster the drill string or casing liner could be run. Time is money, and the system of U.S. Pat. No. 5,960,881 significantly reduces the number of hours required for running the casing string downhole while still avoiding the detrimental effects discussed above.
However, it would be desirable to provide an even larger flow path to further reduce surge pressure, to allow better debris removal, and to reduce the possibility of plugging the float equipment. In the prior art, running tools have an internal diameter that is limited or restricted to about 3 inches to 3.4 inches. It would be desirable to use a ball in the wellbore having an outer diameter larger than the restriction of the running tool to actuate, for example, a larger valve in the casing liner float collar or shoe below the running tool. Preferably, it would be desirable to be able to use balls at least in the range of 3½ or 4½ inches in outer diameter. However, it would be expensive to redesign the subsea/liner running tools to have a diameter through which such larger drop ball may pass and such redesign could reduce the tensile strength and hence the holding capability of the running tool.
The present invention allows existing systems for running casing liners to use balls having an outer diameter larger than the internal diameter of existing running tools or any other restriction in the running string. Therefore, the need to pay the high cost of redesigning the running tools is avoided while the advantages of using larger drop balls is achieved. The present invention also provides a larger diameter flow path for returns.
More particularly, the present invention provides a means for launching balls having a larger outer diameter than restrictions in the wellbore that can be used to perform useful functions in the wellbore below the restriction.
SUMMARY OF THE INVENTION
A drop ball system is provided for use in a wellbore having a restriction therein with a restriction internal diameter. The drop ball system allows launching a ball whose diameter is larger than the restriction such that the large ball may be utilized below the restriction in the wellbore. The drop ball system may be used with any tool requiring downhole ball activation or where downhole ball activation is desirable. Such applications include but are not limited to use with float equipment, flapper valves, squeeze tools, inflatable packers, running tools, adaptors, and test tools, for zone isolation, squeeze tools, squeeze production, and the like. In one embodiment, the drop ball system may comprise a drop ball housing that is mounted within the wellbore at a position in the wellbore below the restriction. A first ball or large ball is mounted in the drop ball housing which has an outer diameter larger than the restriction internal diameter.
A release element, such as a yieldable seat for the large ball, is provided for supporting the large ball prior to releasing the large ball from the drop ball housing into the wellbore. A second ball or release ball is provided having an outer diameter smaller than the restriction internal diameter. Upon receipt of the release ball in a seat in the housing, the large ball may be released through the release element by increasing the pressure above the release ball. In one preferred embodiment, the release element is a yieldable or breakable seat for the large ball. A moveable member, such as a sliding sleeve, may be mounted in the drop ball housing for engagement with the large ball to apply force to the large ball so as to release the large ball from the drop ball housing.
In one aspect of the invention, a tubing connector is provided on the drop ball housing for mounting the drop ball housing within the wellbore on a tubular element such as onto a string of wellbore tubulars or a con
Allamon Jerry P.
Waggener Kenneth David
Allamon Jerry P.
Bagnell David
Eriksen Clarence E.
Stephenson Daniel P.
Walker Jackson
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