Cement wiper plug with size changing feature

Wiper plugs or other shapes are made from shape memory foam in a size large enough to wipe or clean a tubular of a predetermined size. The plug or other shape is then reformed to a smaller dimension above its transition temperature and allowed to cool while holding that shape. The smaller shape allows delivery through a running string that is smaller than the tubular string to be wiped. Preferably before reaching the string to be wiped, the trigger is applied to get the wiper or other shape above its transition temperature where it then reverts to the prior larger dimension for effective wiping of the string that it will next pass through. The trigger can be well fluid temperature or composition, applied heat from the tubular, generated heat within the wiper or other shape, or heat released from agents introduced into the well acting alone or in conjunction with well fluids.

FIELD OF THE INVENTION

The field of the invention is wiper plugs and more particularly plugs that have to be introduced through a smaller string and thereafter wipe in a larger tubular.

BACKGROUND OF THE INVENTION

Cement is used to seal tubulars in boreholes. The cement is pumped through a one way valve at the lower end of the string to be sealed that is also known as a shoe. The pumped cement needs to be displaced from the tubular to the surrounding annulus after it is delivered from the surface. Different wiper plug systems have been devised to push the cement ahead of the plug until the plug is bumped on a landing shoulder in the vicinity of the shoe.

Liner wiper plugs are typically suspended at the top of a liner to be cemented with an open passage through the wiper plug thorough which the cement is delivered. A dart is then landed in the wiper plug and the two travel together to wipe the liner free of cement until the plug is bumped. The plug can have extending fins in parallel rows or it can be a solid block. A one or two plug system can be used and in each case a dart lands in the plug to move the two in tandem. Composite materials have been employed in such plugs to speed up milling that occurs after the plug or plugs are bumped and the cement sets. The normal procedure is to drill out the plug or plugs and the shoe and either extend the well or complete the well.

Because the plug or plugs are initially located in the liner or casing to be cemented, they are already of the appropriate size for the wiping task that needs to be done when they are deployed. However, issues can develop if the wiper is to be delivered through a smaller running string for the liner or casing to be cemented and then still be expected to wipe the inside dimension of the far larger casing or liner. One approach to addressing this problem has been the development of plugs made of compressible foam that can be squeezed into the running string and pushed with pressure to the casing or liner where the expectation is for the foam to then relax and retain its initially larger dimension. While introducing the plug to the larger diameter tube will allow it to regain its former shape, the problem with such foam plugs under differential pressure loading will be that the pressure will again deform the plug by compression to open bypass flow paths around it and thus undermining its ability to serve as an effective wiper plug. The rationale for such plugs is that they can pass restrictions on the way down and in theory still function effectively as a wiper plug after traversing a limited number of obstructions and reforming. Both foam darts and balls made of open cell rubber have been offered by Halliburton with the caveat that they cannot be used in cementing service where there is a series of tight restrictions.

Various attempts have been made to design wipers regardless of shape that can go through an obstruction and then continue to operate, generally in a tubular having the same drift above and below the obstruction. Some examples of such devices can be seen in US Publication 2008/0190613; U.S. Pat. No. 7,673,688 using a foam body and an external screening material; U.S. Pat. No. 5,435,386 showing a cement plug with a rubber mandrel and a foam exterior layer; U.S. Pat. No. 7,096,949 shows a wiper plug with an articulated seal that is actuated with applied differential pressure as illustrated inFIGS. 8aand8b. US Publication 2010/0038086 teaches the use of stimulus responsive materials that can swell or get smaller in a production system to regulate the location of the produced flow into the wellbore using the stimuli that make plugs change dimension.

The present invention seeks to provide a plug that can be delivered in a smaller string to wipe effectively in a larger string. This is accomplished with shape memory foam that is brought past its transition temperature downhole so that it can pass through a running string and then revert to a larger original shape for effective wiping of the string being cemented or undergoing other downhole operations. The stimulus can be using well fluids or applied heat or reactive materials that are held apart for run in and then allowed to contact for an exothermic reaction that triggers the wiper to revert to the larger size suitable for wiping the larger tubular. Those skilled in the art will more fully appreciate the various aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while appreciating that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

Wiper plugs or other shapes are made from shape memory foam in a size large enough to wipe or clean a tubular of a predetermined size. The plug or other shape is then reformed to a smaller dimension above its transition temperature and allowed to cool while holding that shape. The smaller shape allows delivery through a running string that is smaller than the tubular string to be wiped. Upon reaching the string to be wiped, the trigger is applied to get the wiper or other shape above its transition temperature where it then reverts to the prior larger dimension for effective wiping of the string that it will next pass through. The trigger can be well fluid temperature or composition, applied heat from the tubular, generated heat within the wiper or other shape, or heat released from agents introduced into the well acting alone or in conjunction with well fluids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In order to provide some perspective for the invention,FIGS. 1-5will be initially reviewed to illustrate a currently used technique for wiping a string after cement is delivered through a passage in the wiper that is then closed after cement delivery with a dart to allow differential pressure to launch the assembly and wipe the cement from the tubular. InFIG. 1an existing cemented casing10has a liner12run through it and supported in an overlapping manner. Generally a liner hanger (not shown) is placed in the lap area14for support and for sealing between the two tubulars. The wiper plug16is sized for tubular12and is delivered with tubular12on running string18. For run in the wiper16has an open passage20through which the cement will pass as shown inFIG. 3. A smaller wiper22sized for the running string18passes the running string18and lands on wiper16. Together, the wipers16and22travel down the tubular12to wipe it free of cement as illustrated inFIGS. 4 and 5. It should be noted that each wiper is sized for the tubular through which it is expected to wipe. To accomplish this the wiper16is run in with the string12and the dart or wiper22passes only through the running string18before landing in wiper16.

FIGS. 6-10schematically illustrate the present invention. A single plug30passes through the running string32and then into the larger tubular34. As the plug30progresses it pushes out the cement from the running string32and at the transition36the plug is subjected to sufficient heat to get it above its transition temperature so that the shape memory foam core of the plug30swells to raise the outside diameter of the outer fin assembly38as seen in comparingFIG. 8withFIG. 9. InFIG. 10the now enlarged wiper30wipes the cement clear from the tubular34.

FIGS. 11-14illustrate one way this size change takes place. Wiper plug40has chambers42and44separated by a wall46. The core48that defines these chambers is preferably made of shape memory foam and is surrounded by the fin assembly50that is generally made from an elastomer although other materials durable enough to wipe cement without tearing apart can also be used. The fin assembly50grows with the core48as heat is applied to the core48. The heat is generated from a reaction of components that are in chambers42and44when the wall46is undermined by the landing of a dart52.FIG. 14shows the dart52having a point54that penetrated the wall46to allow two materials that react exothermically to mix and generate heat. Thus a single wiper40goes through the running string56to get to the lap region58with tubular60. At that location its dimension is increased with the heat of reaction and it assumes a dimension large enough to wipe the tubular60. Generating the heat with a triggered reaction is but one way that heat is applied to get a wiper past the transition temperature so that it can revert to an originally larger dimension for wiping the larger sized tubular below. There are other ways.

One other way is illustrated inFIGS. 15 and 16in a schematic way. A heater70powered from the surface or locally as schematically represented by a line72can be used to apply heat to the plug74to allow its core to grow to a larger dimension as shown inFIG. 16with the enlarged plug74′. What has happened is that the core76has grown radially and has taken the outer fin assembly78radially outwardly with it. Heat can also be added in other ways such as the temperature of the well fluids themselves or the pumping down of fluids into the wellbore that cause a reaction that generates heat. The wiper body itself can contain a power source such as a battery and a processor to trigger activation of a heater at a certain time or at a predetermined depth to get the wiper to revert to the larger dimension for wiping the larger tubular. Heat can be applied while still in the smaller string or it can be applied after or in the transition to the larger string. The plug74needs to have attained its larger dimension before it is needed to wipe the larger tubular.

While shape memory foam is preferred, other core materials that can change shape with a proper stimulus signal are also envisioned. Shape memory alloy or polymer cores are also contemplated. As another alternative the plug or parts thereof can be made of a swelling material that responds to well fluids that contain hydrocarbons or water to initiate the swelling so as to enlarge the plug for wiping the larger tubular. Elastomers such as rubber can be used. The core and fin structure can be a common material or different materials. The core can be shape memory foam surrounded by a swelling material that is responsive to water or oil based fluids. On the other hand the entire plug can be of a uniform material internally and externally.

FIGS. 17-23illustrate a series of plugs that have a common core100with different exterior wiper assemblies102. Preferably the cores100are shape memory foam that can support differing wiper assemblies102. There can be rounded bumps as inFIG. 21or a single arcuate shape as inFIG. 22. There can be opposed points that are spaced apart as inFIG. 20or generally cylindrical shapes that in cross-section are either rectangular as inFIG. 23or a parallelogram as inFIG. 19. The traditional parallel extending fin design is illustrated inFIGS. 17 and 18and the wiper assembly can also be of the same or a different material than the core material of the cores100. Both can be shape memory foam for example or the wiper assembly can be a flexible elastomer for example. The core100can alternatively be a shape memory alloy or polymer. The wiper assembly102can also have weaker segments that reduce the resistance of the wiper assembly102to growth of the core100when the temperature stimulus is applied.