SELF FILLING CASING

Abstract

A method and apparatus for running a casing string into a wellbore. In one embodiment the string includes an impeller at a lower end thereof. As the string is rotated in the wellbore, the rotating impeller urges fluid into the string.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Embodiments of the present invention generally relate to a self filling casing for running into a wellbore prior to cementing.

[0003] 2. Description of the Related Art

[0004] Oil and gas wells are drilled in sections and each section is typically lined with a tubular string or casing. A section of wellbore is drilled, the drill string and drill are removed and a string of casing is run into the wellbore where it is cemented to isolate that section of the well from the formation therearound. In each instance, isolation takes place by filling an annular area between the casing and the wellbore with cement.

[0005] Hydrostatic pressure is the pressure which is exerted on a portion of a column of fluid as a result of the weight of the fluid above it. Because wellbores are filled with fluid, in deeper wells a hydrostatic head of a column of fluid can place enormous pressure on the walls of a wellbore and the formations therein. Running casing strings into a fluid-filled wellbore necessarily means the string must be filled with fluid as it is inserted. The displacement of fluid created by the casing, especially in deep water applications can cause pressure increases in the fluid which in turn can create fluid pressure waves that act upon the formations and can cause damage. The potential for damage increases the faster the string is inserted into the well. Because sections of wellbore needing casing can be over 1,000 feet deep, there is a continuous demand to run casing at greater speeds. In one example, 90 foot lengths of casing are inserted into the wellbore in 90-second intervals as the string is assembled at the surface of the well.

[0006] What is needed is a more effective way to run casing strings into a wellbore without damaging formations due to increases in hydrostatic pressure brought about by the casing string.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0008] FIG. 1 is a partial section view of a bottom end of a casing string with an impeller mounted therein.

[0009] FIG. 2 is a view of the impeller in the casing.

[0010] FIG. 3A is a first view of the casing and impeller in a wellbore.

[0011] FIG. 3B is a second view of the casing and impeller in the wellbore illustrating direction and rotation.

DETAILED DESCRIPTION

[0012] As shown in FIG. 1, an embodiment of the invention comprises a radial impeller/propeller disposed at a lower end of a casing string. In this disclosure, "impeller and "propeller" are used interchangeably and relate to any structure that creates fluid turbulence when rotated. In the embodiment of FIG. 1, the casing 100 includes a reduced inner diameter portion 105 at a lower end. The impeller 200 includes three vanes 205, each of which has a flat portion 210 as well as an angled portion 215. Unlike a typical impeller, the impeller of FIG. 1 has no shaft connected to a central hub for rotation. Instead, the vanes are affixed at their outer edge 220 to an inner diameter of the casing 100 in order to rotationally fix the impeller 200 to the casing 100. In this manner, the casing string becomes the "shaft" and the impeller is capable of circumferential rotation as the casing string upon which it is mounted rotates. The vanes are arranged such that rotation in one direction (e.g. "right-handed") will cause fluid to move into the tubular casing string. An impeller of the type shown in FIG. 1 is described in U.S. Pat. No. 6,595,752 and that patent is incorporated by reference herein in its entirety.

[0013] FIG. 2 is a top view of the impeller and casing and illustrates the 3 vanes 205 with their flat portions 210 as well as gaps 212 that are visible between the vanes when viewed from above. In FIG. 2 the casing/impeller is shown in a wellbore 115 and the rotation of the string is shown by arrow 120. In other arrangements, the impeller could be mounted in a sleeve which is in turn attached to an inner diameter of the casing. In another embodiment, the impeller has a single auger-shaped spiraling vane rather than a plurality of vanes as shown in FIG. 1. In another embodiment, two or more impellers are mounted or stacked in the casing string at various locations. In each case, the impeller assembly is constructed of drillable material permitting the assembly to be drilled up and destroyed prior to another section of wellbore being drilled.

[0014] In operation, the apparatus and method described can be operated in the following steps: As a casing string is assembled at the surface of a well, the bottom most joint of casing includes, in addition to cementing equipment, an impeller. Cementing equipment typically includes centralizers to ensure satisfactory zone isolation and float shoes and collars (float valves) to prevent backflow after the cement has been pumped into place. Using a top drive, the casing is lowered into the wellbore in stands of 90 feet at a rate of about 90 feet/minute. As the string is lowered into the wellbore, it is rotated in a right-hand manner at a speed, in one example, of 15-30 rpm. The rotation of the casing in turn rotates the impeller, thereby urging the wellbore fluid into a lower end of the casing string to fill the string and to reduce pressure surges brought about by the volume and speed of the string. Once the string has reached depth, cementing is performed as usual. In one embodiment, the impeller stays in place as the cement passes through the casing and into an annulus formed between the casing and wellbore. Thereafter, the impeller is destroyed by drilling as a new section of wellbore is formed.

[0015] FIGS. 3A illustrates the impeller/casing string in a wellbore 115. In FIG. 3B, the casing is shown rotating (arrow 120) and being lowered (arrow 125) to urge fluid into the casing string (arrow 130).

[0016] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A wellbore tubular, comprising: a tubular body attachable at a first end to an adjacent tubular member; an impeller disposed in the body, the impeller fixed relative to the body, whereby the impeller rotates as the body rotates.

2. The tubular of claim 1 wherein the impeller includes a plurality of vanes extending from a central hub.

3. The tubular of claim 2, wherein at least one of the vanes is fixed at an outer edge to an inside surface of the body.

4. The tubular of claim 3, wherein the body is located at a lower end of a string of wellbore casing.

5. The tubular of claim 4, wherein the body includes a reduced inside diameter portion adjacent the impeller.

6. The tubular of claim 5, further including a second impeller mounted in the body adjacent the impeller.

7. The tubular of claim 4, further including cement equipment installed in or adjacent the body.

8. The tubular of claim 7, wherein the cement equipment includes at least one of centralizers, float collars and float shoes.

9. A method of running a casing string into a wellbore, comprising: assembling the string, a lower end of which includes a body with an impeller mounted therein for rotation with the string; and running the string into the wellbore while rotating the string, thereby causing the impeller to urge wellbore fluid into the string.

10. The method of claim 9, wherein the impeller has at least 3 vanes and the impeller is rotationally fixed to the body at its outer edges.

11. The method of claim 10, further including circulating cement though the string and into an annular area defined between an outer surface of the string and the wellbore.

12. The method of claim 11, further including destroying the impeller.

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