Wells – Processes – Assembling well part
Reexamination Certificate
2001-05-02
2002-04-23
Bagnell, David (Department: 3672)
Wells
Processes
Assembling well part
C166S120000
Reexamination Certificate
active
06374917
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to inflation elements for use in downhole well tools and, more particularly, to such an element and a method and mold for making the bladder and/or cover portions of such elements where the elastomeric material used to form the bladder and/or cover is processed to impart improved performance characteristics by pre-disposing directional properties via stretching and expansion operations before the tool is run in service.
BACKGROUND OF THE INVENTION
Downhole inflatable tools such as packers, bridge plugs and the like, have been utilized in subterranean wells for many years. Such tools normally include an inflation element that includes an elastomeric bladder concentrically disposed around a central body portion such as a tube or mandrel. A sheath of axially oriented reinforcing slats or ribs is typically disposed around the bladder. One or more elastomeric cover or seal sections are concentrically disposed around at least a portion of the ribs. Reinforcing structures other than slats and ribs are also common among such tools. Fluid under pressure is introduced from the top of the well or from the interior of the well bore into the central body and through radial passages, or around the exterior body to the interior of the bladder, to cause the bladder and, consequentially, the element to expand. The subject invention is applicable to all known downhole inflatable tools that include a bladder and/or one or more covers.
Typically, the upper ends of the inflatable bladder and ribs are secured relative to the body, while the lower ends of the bladder and reinforcing sheath are secured to a seal which is movable relative to the body. The movable seal responds to inflation forces and allows the inflation element to expand without causing damage to any of its component parts.
For inflation elements of this type, the exposed sections of the reinforcing slats or ribs typically operate as anchor sections, while the elastomeric cover elements typically operate as seals. The anchor section(s) and cover element(s) expand until they engage the wall of the well bore to isolate sections of the well bore on opposite sides of the tool from each other.
Ideally, inflation elements should first expand in the center and then uniformly propagate outwardly in both directions so that fluid is not trapped between the outer surface of the element and the well bore. In addition, the outward expansion should be controlled to prevent relatively steep slopes from occurring in the profile of the bladder during inflation. A steep slope in the profile can cause the bladder to stretch in the axial direction and result in unwanted conditions.
Axial stretching of the bladder during inflation can create two deleterious conditions, 1) localized tri-axial strains in the bladder and 2) pinching seals with related folds in the bladder. Alone, either one of these conditions can cause bladder failure. The presence of both conditions is almost certain to cause failure. Failures occur because the physical properties of the elastomeric material composing the bladder are not adequate to survive service conditions, i.e., highly localized tri-axial strains, high fluid pressure pressing the bladder against the edges of the ribs, elevated temperatures, chemically active (sometimes aggressive) inflation and treatment fluids, etc.
These problems are discussed in an article entitled “Design and Testing of a High-Performance Inflatable Packer,” D. M. Eslinger and H. S. Kohli, SPE Pub. 37483 (1997).
FIG. 3
of that article is reproduced as
FIG. 3
of the appended drawings to illustrate the pinching and folding problem. Although several solutions were suggested in the article, including the use of specially developed elastomers, slats in the carcass with specific structural features and software to aid in the design and execution of specific jobs, the problems of folds and bladder failure still remain.
Bladder failure was also discussed in my U.S. Pat. No. 5,495,892, which recognized conditions where the bladder tends to pinch and form a seal on the mandrel (central body) during inflation and obstruct the passage of pressurized fluid. The obstruction problem was solved by providing a concentric tube between the outside of the mandrel and the bladder to facilitate fluid communication along the entire length of the bladder regardless of the presence of pinching seals. However, the concentric tube did not eliminate of the formation of folds and the occurrence of other phenomena that cause bladder failures.
Three other patents of mine, U.S. Pat. Nos. 5,469,919, 5,564,504 and 5,813,459, also discuss pinching seals, bladder folding, rib kinking, and rib cutting of the bladder. These patents describe the use of structural elements along the length of the bladder to cause relatively uniform expansion such that the ratio of the largest diameter of the bladder to the smallest diameter during inflation is always below a pre-determined maximum value. However, although the designs in these patents resulted in elements with more uniform expansion, they did not completely eliminate the occurrence of folds, rib kinking, rib cutting or the occurrence of high tri-axial strains in the bladder.
Another problem caused by folds is that they remain when the bladder is deflated. This causes difficulty when the tool is to be retrieved because the bladder cannot deflate to a size that is equal to or smaller than its original run-in size and the tool might not be retrievable. This problem would eliminate the use of relatively low cost thru-tubing inflatable tools from a great many service jobs, and possibly necessitate an expensive “rig job”, i.e., such as pulling tubing and requiring other expensive support operations.
In addition, a pinching seal can cause an inflation element to inflate only partially, leaving a significant portion of the element not inflated. At the surface, the tool is thought to be completely inflated and surface operations are continued. However, the pinched seal loses its seal within minutes after inflation operations are terminated. This results in loss of inflation pressure, loss of seal between the inflation element and the well bore, loss of anchor between the inflation element and the well bore and failure of the well tool. This type of failure falls under the general category of a “soft set failure”.
SUMMARY OF THE INVENTION
The present invention is directed to a method for solving the problems discussed above, a shaping tool or vessel for use in the method, and a downhole tool with a bladder and/or cover sections that are pre-disposed in accordance with the method, where the bladder and/or cover sections have improved inflation characteristics and their elastomeric components have improved physical properties.
Pre-disposing elastomeric components means to better align the long axes of the molecular chains of the elastomer in a direction transverse to the long axis of the tool before the tool is run downhole so that the inflation profiles of the inflation element during inflation are improved and the physical properties of the elastomeric material composing the bladder and/or covers are improved and impart enhanced integrity of the bladder and/or covers in service.
The preferred method of pre-disposing (i.e., stretching) elastomeric components (bladders and covers) is by inflating the components within a shaping tool or vessel having a deliberate interior profile. The interior profile imparts different magnitudes of expansion along the length of the elastomeric component. Pre-disposing of an inflation element in an optimally designed vessel will facilitate improved expansion profiles throughout inflation of the well tool and will abate the formation of pinching seals and folds in the inflation element. Additionally, pre-disposing elastomeric components increases the tear resistance of the elastomer and thereby, increases the tolerance of bladders to rib kinking, rib cutting and folds.
When an elastomeric component such as a bladder or cover section is stretched via inflation, its lon
Bagnell David
Dougherty Jennifer R.
Fulbright & Jaworski L.L.P.
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