A method and apparatus for an anchor for use downhole. In one embodiment, the anchor includes an upper portion and a lower portion. In a run-in position, the anchor has a smaller outer diameter and in a set position, the anchor has a larger outer diameter. A slip assembly includes at least one slip, the slip having a longitudinal axis parallel to the longitudinal axis of the anchor and rotatable relative to the anchor along its longitudinal axis.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention generally relate to self-adjusting slips. More particularly, the invention relates to an anchor assembly having slips that are self-adjusting based upon an inner diameter of a surrounding tubular. More particularly still, the invention relates to an anchor assembly for a whipstock used to facilitate the formation of a lateral wellbore, the assembly having self-adjusting slips.

Description of the Related Art

In the recovery of hydrocarbons, including oil and gas, wellbores are drilled into the earth in a manner intended to intersect hydrocarbon-bearing formations. To facilitate recovery and to prevent unwanted migration of material, the wellbores are typically lined with steel tubular (casing) which is cemented in place. From time to time, additional wellbores are needed to access adjacent formations and it is increasingly common for those new wellbores to be formed or “side tracked” from existing wellbores. In these instances, a whipstock having a concave, ramped surface is anchored in the wellbore at a predetermined location and then a bit or mill issued to form a window in the casing. Once the window is formed, the new wellbore is drilled resulting in two wellbores that share a common path to the surface. Successful use of a whipstock depends on the success of the anchoring operation that holds the whipstock in place during the formation of the window and thereafter as tools and work strings are run in and out of the new wellbore. Anchoring requires extendable slips to be placed in contact with the wall of casing. Because the inner diameter of casing can vary and be uneven, there is a need for an anchoring mechanism that can compensate for variations in the inner surface of a tubular string.

SUMMARY OF THE INVENTION

The present invention generally relates to self adjusting slips for use on an anchor in a wellbore.

DETAILED DESCRIPTION

The present invention relates to an adjustable slip for a downhole anchor.

FIG. 1is a perspective view showing an anchor assembly100having aspects of the invention. The assembly comprises an upper portion110and a lower portion120, the lower potion including a slip assembly200. In the embodiment shown, the slip assembly includes a first205and second210slips, each having a number of wickers215to assist in holding the set assembly100in place in the interior of a tubular (not shown). The anchor assembly includes a connection means101for connection to another tool, like a whipstock (not shown) at its upper end. typically, the assembly100is used at a lower end of a whipstock and once the whipstock is at a predetermined depth and orientation in a wellbore, the assembly is used to anchor the whipstock in place where a concave ramped surface of the whipstock then permits a sidetracked wellbore to be formed. In one embodiment, a work string is run into a well with the following components (from bottom up): an anchoring assembly100, a whipstock, and a mill or drill connected with a shearable member to the whipstock. Once the assembly is set in the wellbore, the shearable member is sheared and the work string rotates and advances the mill/drill along the concave ramped surface of the whipstock to form a window in the casing wall.

FIGS. 2 and 3illustrate the anchoring assembly100in unset and set positions, respectfully. To set the assembly, the lower portion120is raised relative to the upper portion110either by fluid pressure or mechanical movement. In one example, the two portions110,120are held in an unset position (FIG. 2) by a shearable member against an upward force of a biasing member, like a spring (not shown). Once the assembly is ready to be set, the shearable member is sheared by fluid force and the spring causes the lower portion120to move upwards along a ramp-shaped portion230of the upper portion, thereby enlarging the outer diameter of the assembly100and placing the slips205,210in contact with the casing wall300on a first side. On an opposite side, the body of the upper portion110of the assembly100is in contact with an opposite wall of the casing300. Additional downward pressure on the upper portion110from above further anchors the assembly100in the wellbore as the upper portion is urged downwards along the surface of the casing wall.FIG. 3shows the assembly100wedged within the inner diameter of the casing300.

FIG. 4is a partially exploded view showing first205and second210slips associated with the slip assembly200. As shown inFIGS. 1-3, the slip assembly is located in the lower portion120of the anchor assembly100. Returning toFIG. 4, each slip205,210is installed in a pocket250having walls255and a floor260. At each end of the pocket is a bearing housing270. Each slip includes a body275with a plurality of wickers280formed on an outer surface thereof. In the embodiment show, the wickers are arranged in rows and columns. At each end of the slip body275is a bearing285that is seated in the bearing housing270. A bearing cover272is installed at each end and serves to fix the slip205,210in its respective pocket250. Each slip is constructed and arranged to rotate about its longitudinal axis and when installed in the pocket250, a gap G is formed between a lower surface206of the slip and the floor260of the pocket to permit rotation (seeFIG. 6A). As shown inFIGS. 4, 5, 6A-7B, the underside of each slip210,215is equipped with metallic centering members290to keep the slip rotationally centered in the pocket250during run-in of the anchoring assembly100. Each centering member290includes two resilient legs292and in the centered position, each leg contacts the floor260of its respective pocket260.

FIGS. 6A and 6Billustrate a slip205(or210) before and after setting against a tubular wall300having a relatively large ID. As shown in the Figures, due to the size of the casing ID, the slip210remains in or near its rotationally centered orientation even after its wickers280are set against the casing wall300. This is true even though the slip is off-set from the centerline of the anchoring tool (seeFIG. 1).

FIGS. 7A and 7Billustrate a slip205before and after setting against a tubular wall300having a relatively small ID. InFIG. 7Athe slip is in its pre-set, rotationally centered position. However, due to the relatively small ID of the surrounding tubular300, as the slip205is set and its wickers280extend to contact the ID of the tubular therearound, a wicker280at one side of the slip touches the tubular wall first, causing the slip210to rotate in a counter clockwise direction211about its longitudinal axis until all of the wickers are in contact with the wall300as shown inFIG. 7B. Visible also inFIG. 7B, one leg292of the centering member290has been lifted off of the pocket floor leaving a gap212.

FIG. 8is a section view taken from above, showing both slips205,210set against a tubular300having a relatively large ID andFIG. 9is a section view taken from above, showing both slips set against a tubular300having a relatively small ID. As shown in each Figure, the wickers280of each slip are in contact with the tubular wall and opposite the slips205,210, the upper portion110of the anchor is set against an opposite wall of the tubular300.

In use, the assembly100operates in the following fashion: A work string including the anchor assembly and typically, other downhole tools, like a whipstock is run into a wellbore lined with a tubular string, like casing300. At a predetermined location and rotational position, the anchor is set by causing a lower portion120to move relative to an upper portion110, thereby increasing an outer diameter of the assembly and bringing at least one slip205into contact with a wall of the surrounding tubular. Thereafter, optionally, the assembly is further set due to downward force on upper portion110from the surface of the well to increase a wedging effect between the assembly100and the wellbore.

Depending on the geometry, surface characteristics, and inner diameter of the tubular around the assembly, the at least one slip205may rotate about a longitudinal axis as it comes into contact with the tubular wall, thereby increasing the surface contact between the wickers280of the slip and the tubular wall.

While the invention is used with a whipstock for sidetracking a wellbore, it could be used with any downhole apparatus wherein there is a need to anchor the apparatus at least temporarily in the wellbore. The assembly is shown with two slips205,210, each of which has a plurality of wickers280arranged along the length and width of the face of the slip. It will be understood however, that the assembly100could include any number of slips, at least some of which are provided with means for rotating along at least one axis relative to at least one portion of the assembly. Also, the assembly100, in the embodiment described is used in a cased or lined wellbore. However, the invention is equally usable in an open wellbore where variations in borehole walls can be overcome with the self-adjusting slips described herein.

Additionally, while the embodiment illustrated and discussed includes a two-part assembly wherein the slips are disposed on one side of the anchor, it will be understood that the invention could be used with other types of anchor bodies. For example, in one alternative embodiment, the slips are disposed in carriers around the perimeter of a conically shaped member. As the cone moves relative to the carriers, the slips are urged outwards, thereby enlarging the outer diameter of the assembly and setting the slips, with their rotational feature, against the wall of the wellbore in a radial fashion.