In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore, for instance adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore.
Expandable tubular elements are finding increasing application in the context of hydrocarbon drilling and production. A main advantage of expandable tubular elements in wellbores relates to the increased available internal diameter downhole for fluid production or for the passage of tools, compared to conventional wellbores with a more traditional nested casing scheme. Generally, an expandable tubular element is installed by lowering the unexpanded tubular element into the wellbore, whereafter an expansion device is pushed, pumped or pulled through the tubular element. The expansion ratio, being the ratio of the diameter after expansion to the diameter before expansion, is determined by the effective diameter of the expander.
When an expandable tubular is run into a wellbore, it must be anchored within the wellbore at the desired depth to prevent movement of the expandable tubular during the expansion process. Anchoring the expandable tubular within the wellbore allows expansion of the length of the expandable tubular into the wellbore by an expander tool. The anchor must provide adequate engagement between the expandable tubular and the inner diameter of the wellbore to stabilize the expandable tubular against rotational and longitudinal axial movement within the wellbore during the expansion process.
The expandable tubular is often run into the wellbore after previous strings of casing are already set within the wellbore. The expandable tubular must be run through the inner diameter of the previous strings of casing to reach the portion of the open hole wellbore slated for isolation, which is located below the previously set strings of casing. Accordingly, the outer diameter of the anchor and the expandable tubular must be smaller than all previous casing strings lining the wellbore in order to run through the liner to the depth at which the open hole wellbore exists.
Additionally, once the expandable tubular reaches the open hole portion of the wellbore below the previous casing or liner, the inner diameter of the open hole portion of the wellbore is often larger than the inner diameter of the previous casing. To hold the expandable tubular in place within the open hole portion of the wellbore, the anchor must have a large enough outer diameter to sufficiently fix the expandable tubular at a position within the open hole wellbore before continuing with the expansion process.
U.S. Pat. No. 7,104,322 discloses a method and apparatus for anchoring an expandable tubular within a wellbore. The apparatus includes a deployment system comprising an inflatable packing element. The packing is arranged inside the liner and is supported on the drill string. When inflated, the packing radially expands an anchoring portion of the expandable tubular. The outside of the anchoring portion engages the wellbore wall and forms an anchor. The remainder of the expandable tubular can subsequently be expanded using an expander tool. The holding power and shape of the anchoring portion may be manipulated by altering the characteristics of the packer such as the shape and wall thickness of the packer.
However, engagement of the tubular with the formation, as disclosed in U.S. Pat. No. 7,104,322, is limited by the amount of expansion of the tubular element, which is typically constrained by the mechanical limits of the expansion device. For instance in cases where the annulus between the unexpanded tubular and the borehole wall is relatively large, the amount of available mechanical expansion may not be sufficient to cause the expanded tubular to engage the borehole wall.
In addition, although the friction between the outside of the tubular and the wellbore wall that keeps the expandable tubular in position may withstand the reactive forces induced on the expandable tubular by a rotational expansion tool, the friction may be insufficient to withstand the reactive force when pulling an expander cone through the expandable tubular. If the friction is insufficient, the expansion tool may move the expandable element in axial direction during expansion, and the unexpanded tubular may obstruct the previous casing. The unexpanded element must then be removed, at considerable costs, or the obstruction may render the wellbore useless, at even greater expense.
Thus, it remains desirable to provide a device that will mechanically engage the borehole wall upon expansion of a tubular, even in instances where the expanded tubular does not itself engage the borehole wall.