FIELD OF THE INVENTION
The field of this invention is wiper plugs and more particularly those used in cementing horizontal runs where the plug is centralized as it wipes.
BACKGROUND OF THE INVENTION
Wiper plugs are used in applications such as cementing to clear the inner wall of the string of remnants of the cement that was earlier delivered through the string through a cementing shoe and into a surrounding annular space to seal around the tubular string. The wiper plug design typically features flexible members designed to bend in contact with the inner wall of the string as pressure behind the plug pushes the plug to a stop, which is referred to as bumping the plug. The flexible members can be tapered toward the uphole end to enhance the contact with the inside wall of the string in response to the pressure applied from above to advance the plug. Typically the wipers are made of rubber or some other flexible material compatible with well conditions.
One concern particularly on long horizontal runs is that the rubber ribs will wear on the low side of the wiper plug to an extent that they will not effectively wipe, leaving remnants of cement stringers as the ribs wear. Another design parameter for wiper plugs is that in some applications the plugs need to pass through a restriction so there must be some flexibility in the exterior wiping structure that will allow such restrictions to be cleared without compromising the wiper fins.
In the past bow spring centralizers in combination with a wiper device were used to clean drill strings as shown in U.S. Pat. No. 5,641,018. Wiper darts with a bow spring centralizer between leading and trailing inclined rubber ribs are shown in U.S. Pat. No. 7,228,897; U.S. Pat. No. 7,069,992 and U.S. Pat. No. 7,063,152. Spiral scraping devices mounted to a tubular string for paraffin and the like are shown in U.S. Pat. No. 2,870,845. String mounted wiping devices for cement distribution and casing cleaning in the form of axial blades or spirals are shown in U.S. Pat. No. 3,351,136 and a spiral string centralizer is shown in U.S. Pat. No. 1,959,368. A wiper plug with a leading disc-shaped centralizer is shown in FIG. 5 of U.S. Pat. No. 5,004,048.
The wiper plug of the present invention features spaced centralizers ahead and behind the sealing assembly for the plug. The centralizers combine features of flexibility and a defined height to allow passage through restrictions with enough rigidity to centralize and clean the string as the assembly passes by. The centralizer can be an array of brush bristles having a spiral appearance where the bristles are connected to a common base pushed into a dovetailed groove for mounting. Other arrangements are contemplated where each spiral leading and trailing ends are closed off with flat members that flex. These and other aspects of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while understanding that the full scope of the invention is to be determined by the appended claims.
SUMMARY OF THE INVENTION
A wiper plug has a elastomeric fin assembly straddled by centralizers that have the capacity to flex through restrictions while being strong enough to centralize and scrape a surrounding tubular wall. The centralizers reduce wear on the rib/fin assembly particularly on long horizontal runs. The centralizers can be a continuous spiral or a series of circumferentially offset spiral segments on a common hub. The spiral segments contain brushes extending from a base where the base and the mounting slot have a dovetail relationship for fixation to the wiper plug body. The plug body consist of three separate segments that are threaded together in order to trap the brush segments in the dovetail channels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the spiral segment embodiment of the centralizers;
FIG. 2 is a section view of a complete 360 degree spiral centralizer;
FIG. 3 is a perspective view of the centralizer in FIG. 2;
FIG. 4 is a variation of FIG. 2 showing the mandrel segments;
FIG. 5 shows a mounting detail for brush type centralizers into a dovetail groove;
FIG. 6 is an enlarged view of the circle labeled 6 in FIG. 2 focusing on the mounting of the continuous spiral embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a segmented spiral version of centralizers for a wiper plug 10. Plug 10 has an uphole centralizer assembly 12 and a downhole centralizer assembly 14 that straddle a wiper fin assembly 16. In this embodiment the centralizer assemblies 12 and 14 comprises circumferentially spaced segments 18 that are spirally oriented on a hub or mandrel 20 and 52. The circumferential coverage of each spiral segment 18 varies with its height. The number of segments is variable and their spacing is preferably even so that in an axial direction an end 22 abuts or overlaps an end 24 of the adjacent spiral segment for continuous circumferential for not only centralizing but also for scraping. The segments 18 can be a collection of brush bristles 26 held in a common base 28 as shown in FIG. 5. The base 28 has a dovetail shape to be inserted into a mating shaped slot 30 best shown in FIG. 6. Once fully inserted into slot 30 the mandrel is threaded to the fin section which shoulders against the open end of the dovetail channel, trapping the brush segments in place. Both the tail and nose sections rely on the wiper fin section shouldering against groove opening to keep brushes secured.
Other aspects of the wiper 10 shown in FIG. 1 are grooves 32 and 34 for o-rings that are not shown and a slip assembly 36 all of which go onto a bore in a tubing string or another plug when the wiper 10 bumps. These features are known in current plugs. The wiper fin portion can have one or more ribs 38 that can be perpendicular to the axis of the hub or mandrel 20. Although three are shown other numbers can be used. Alternatively the ribs can be skewed to the axis of hub 20 as in ribs 40 and 42 with or without use of perpendicular ribs 38.
Referring back to the centralizers 12 and 14 in FIG. 1 open gaps 44 and 46 are present at the uphole and downhole ends of the segments 18. The segments 18 have enough flexibility to bend to get through restrictions but at the same time enough structural rigidity to centralize wiper fin assembly 16 particularly in long horizontal runs to avoid it wearing unevenly to the point where the plug 10 can no longer wipe efficiently from uphole. The rigidity of the segments 18 whose ends rub the surrounding tubular wall also helps to wipe the walls clear. This is helpful particularly from the downhole centralizer assembly 14 so that the wiper fin assembly 16 will see less wear otherwise caused by being propelled over cement debris if not dislodged first by the downhole centralizer assembly 14. The use of an uphole and downhole centralizer aids the centralizing function with front and rear support.
FIGS. 2 and 3 show a continuous spirals 70 and 72 for at least 360 degrees and supported off mandrel 74 and 78. Although a single helix is shown multiple nested helixes are also envisioned. Here or with the design using segments 18 the bristle brush design of FIG. 5 can be used or the shape can be a continuous solid shape that is made of a flexible material that can withstand the well conditions long enough to bump the plug. Either way the centralizers present little resistance to subsequent milling out. The flexibility of the helical or segmental designs can be varied not only by the material selection but also the thickness of the solid material or the bristle density. Some materials that can be used are plastics, soft metals or composite materials. The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
Patent Application
20180080304
