High expansion plug with stacked cups

[0001] The field of this invention is high expansion plugs for downhole use and more particularly made of a stack of nested elements that are compressed to grow from a run in size to the sealing dimension.

[0002] In some cases a packer or plug needs to be run into a well through existing tubing and then set in much larger casing. The required expansion in such cases can be as much as about 300%, when comparing the run in diameter to the set diameter.

[0003] In the past, high expansion bridge plugs have employed a cylindrical tube that is longitudinally compressed between anti-extrusion barriers at opposed ends and is anchored to the casing wall. Several U.S. patents of Carisella illustrate this design, such as: U.S. Pat. Nos. 6,311,778, 6,318,461, and 6,164,375. The problem with such designs using a cylindrical sealing element is illustrated in FIG. 1 showing how longitudinal compression creates an undesirable twisting of the element and the resultant formation of spiral leak paths along the outer periphery of the twisted sealing element.

[0004] Other designs developed by Schlumberger show an element that collapses on itself to seal in casing through tubing, as illustrated in U.S. Patent Re 32,831. In a later patent, Schlumberger acknowledges that the design in the '831 patent has limits in high expansion applications and offers up a design with multiple cup shaped seals where each adjacent seal is bigger than the one below it. When exposed to a compressive force, a protective sleeve for run in breaks away and the series of cups are forced inside each other. Further longitudinal compression forces the outer wall of the outermost cup to contact the surrounding casing. The other cups are nested inside the outer cup and allow the longitudinal compressive force to contact the casing wall without buckling inwardly. The patent that shows this system is U.S. Pat. No. 5,010,958. The problem with this system is that the outer cup does all the sealing. If it tears, despite the presence of the protective sleeve or if, for some reason the protective sleeve fails to rip during longitudinal compression, the ability of the unit to seal will be undermined.

[0005] Other patents reveal casing plugs that are not designed to go through tubing. These designs are not intended to grow much from run in to the set position. As a result, these designs do not employ anchors. Instead, they use very long elements made up of cup stacks that are slightly flexed to get sealing contact. These designs are shown in U.S. Pat. Nos. 1,662,336 and 2,217,038, both of which date back to a time well before through tubing operations were in use downhole. Other downhole plugs for applications that are not in through tubing are illustrated in U.S Pat. Nos. 5,293,905, 6,129,118, 6,142,227, and 6,182,755. Other downhole plug designs can be found in U.S. Pat. Nos. 5,775,429, 5,941,313, 6,145,598, and 6,305,477.

[0006] The present invention provides a through tubing plug that sets in casing and can withstand differential pressures in either direction. The sealing element is preferably made from a plurality of nested cups that act together in response to compression to expand as much as 300% or more from the run in dimension. A support system for the elements in the set position, as well as an anchor is provided to hold the set position. Those and other features of the present invention will be more readily appreciated from the description of the preferred embodiment and claims that appear below.

[0007] A through tubing casing plug is disclosed. It features a stack of nested cup shaped elements that initially slope to reduce the run in diameter. The stack is compressed to force the periphery of the nested cups to move outwardly so that the collective outer surfaces of the cups can seal on the casing. The cups have sufficient initial thickness so that they remain intact despite some radial growth resulting from the compression process. In a particular example, the run in dimension is 2.13 inches and the stack expands to seal against casing with an inside diameter of 6.9 inches while holding a differential of 500 pounds per square inch and more.

[0008] FIG. 1 is a section view of a prior art high expansion element in the run in position;

[0009] FIG. 2 is the view of FIG. 1 showing the prior art element twisting as it is compressed;

[0010] FIG. 3 is the prior art element of FIG. 2 after full compression and showing the exterior leak paths;

[0011] FIG. 4 is a schematic depiction of the nested elements of the present invention in the run in position;

[0012] FIG. 5 is the view of FIG. 4 in the set position in casing;

[0013] FIG. 6 is a section view of the entire tool in the run in position;

[0014] FIG. 7 is the tool of FIG. 6 in the set position;

[0015] FIGS. 8-11 illustrate a variety of stacking orientations for the nested elements.

[0016] FIG. 1 shows a cylindrically shaped prior art element 10 around a mandrel 12 during run in. In FIG. 2, element 10 has started to twist under a compressive load, indicated schematically by arrows 14. The exterior surface 16 assumes an undulating shape. In FIG. 3, the element is totally compressed into contact with the inner surface 18 of casing 20. Formed from the fully compressed undulations in FIG. 2 are a series of exterior leak paths 22 shown in FIG. 3 on the exterior surface 16. Thus, in the prior art design, regardless of the contact pressure against exterior surface 16 the leak paths 22 undermined the effectiveness of element 10 in the set position of FIG. 3 due to the leak paths 22.

[0017] The present invention, in the run in position, is shown in detail in FIG. 4. A stack of nested cups 24, 26, 28, and 30 are illustratively shown. Those skilled in the art will appreciate that more or fewer cups can be used within the scope of the invention. While the preferred shape is stated as being a cup, other circular shapes, such as rings that can be similarly mounted, are within the scope of the present invention. A mandrel 32 extends through all the cups 24-30. In the preferred embodiment, the rings 24-30 are identical. Cup 24 will be described in detail as typical of a stack having identical elements in the preferred embodiment shown in FIG. 4. Cup 24 has surface 34 that runs along mandrel 32. Adjacent surface 34 is surface 36 that runs generally perpendicular to mandrel 32. These two surfaces define a transition point between a cylindrical section 35 and a tapered section 37. The presence of these discrete sections helps insure uniform flexing of all the tapered sections together so that the outer surfaces 40, 48, 50, and 52 that define an outer cylindrical shape, grows uniformly minimizing relative lateral shifting among the elements of the stack 54, until contact with the casing 58. From there, inclined surface 38 extends to outer surface 40. From there inclined surface 42 is generally parallel to inclined surface 38 and finally surface 44 is generally parallel to surface 36. When stacked, surface 36 lands on surface 46 of cup 26. Having surface 36 perpendicular to mandrel surface 32 will prevent cup 26 from extruding into the inner diameter of cup 24 as compressive load is applied. Outer surfaces 40, 48, 50, and 52 are preferably in alignment to present a cylindrical shape to the assembled stack 54. Note that the contact between surfaces 36 and 38 on one hand with surfaces 46 and 56 on the other hand helps to hold the relative positions of cups 24 and 26 to maintain the cylindrical outer shape as the stack 54 is compressed. Outer surfaces 40, 48, 50, and 52 are then more likely to make simultaneous and uniform contact with casing 58. When the stack 54 is compressed, the outer cylindrical shape moves out to a dimension of about 300% of its run in dimension or more to make sealing contact with the casing 58, as shown in FIG. 5. Each member of the stack 54 seals on its exterior surface. Any leak paths along the mandrel 32 are stopped by a seal 60 found in each element of the stack 54, as shown in FIGS. 8-11.

[0018] FIGS. 8-11 show some different arrangements of stack 54. FIG. 8 shows uphole end 62 and downhole end 64 with the lowermost elements having pointed tips 66 and 68 pointing uphole. The uppermost elements of the stack have points 70 and 72 looking downhole. In FIG. 9, the lower end of the stack is looking downhole 64 while the upper end of the stack is oriented uphole 62. In FIG. 10 all the elements are oriented downhole 64. In FIG. 11 they are all oriented uphole 62. Other combinations of orientations are contemplated within the scope of the invention.

[0019] FIG. 6 shows the entire tool in the run in position. Beginning at the uphole end, there is an anchor assembly 74 that has a linkage 76 with teeth 78 that grab casing 58 in the set position shown in FIG. 7. On both ends of the stack 54 are petal type retaining members 80 and 82 that collapse on themselves upon compression to provide anti-extrusion barriers for the stack 54. Looking at FIG. 7, it can be seen that the elements of stack 54 which were all oriented downhole during run in have either flattened close to the downhole end or have come close to inverting near the uphole end, when compared to their run in orientation. Each element of stack 54 is energized from the compression into firm contact with casing 58. The resulting undulation when looking at the elements in section after compression increases the available contact force driving the outer edge of each element of the stack 54 into contact with the interior of the casing 58.

[0020] The preferred material of the stack cups is rubber but other materials compatible with the expected differential pressures and operating temperatures can be used. Differential pressures withstood can vary depending on the degree of expansion. For a stack that expands from 2.13 inches to a casing inside diameter of 6.9 inches the expected ability to withstand differential pressures is in excess of 500 pounds per square inch. That level of expansion is in the order of greater than 300%.

[0021] The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.