Patent Application
20050110217
The field of this invention is inflatable packers or bridge plugs and more particularly those that retain a seal after inflation despite an element failure or changes in downhole conditions.
Inflatable packers typically comprise a flexible element mounted on a mandrel with one stationary collar and one movable collar at an opposite end. Typically a system of valves is used to get pressurized fluid into the annular space between the mandrel and the element to start the inflation process. The inflation allows the element to expand radially into sealing contact with a surrounding tubular or wellbore, made possible by the movable collar riding up toward the stationary collar, which is usually located near the uphole end. The valve system includes a check valve to hold the applied pressure in the annular space between the mandrel and the element. Other types of inflatables known as External Casing Packers use fixed collars and reinforcement only on the ends of the element.
In the earlier designs, the inflation medium was drilling mud or other liquids. Inflating the element with such liquids had certain drawbacks. One problem was thermal effects that could cause a pressure reduction under the inflated element and a loss of seal. Another drawback was that damage to the element either from installation or during service in the well over a period of time could result in a tear or rupture of the element and a loss of seal as the fluid escaped, either slowly or virtually immediately depending on the nature of the failure in the element. While the valve system had provisions for avoiding overpressure, the risks to the integrity of the element were real and present and resulted in failures.
In an effort to improve inflatable performance, cement slurry was used as the inflation medium. The idea was that the slurry, in a pumpable condition, would be delivered into the annular space between the mandrel and the element and under pressure. The slurry would then set up with the hope that, once set up, the slurry, now in solid form would help to hold the seal of the packer even if the element experienced a failure. However introducing cement slurry created several new problems. First, there were added risks of getting the slurry through the various valves of the inlet assembly without fouling their operation. Second, the use of cement slurry required specialized equipment at the surface. Some applications, particularly offshore, created logistical problems in locating such equipment on platforms and created increased expense due to the logistical issues. Furthermore, when using cement slurry, time was of the essence in spotting and pumping the slurry behind the element. It was also important to quickly remove any excess slurry to avoid having to drill it out if it impeded later operations. As if all these issues were not enough of a concern, there was yet another downside to the use of the cement slurry. The slurry, upon setting, actually reduced in volume. This made the packer more likely to lose its sealing contact after it was set.
The prior art fluid inflatable packers are described in U.S. Pat. Nos. 4,897,139; 4,967,846 and 5,271,469. Cement inflatable packers are described in U.S. Pat. No. 5,738,171.
The present invention addresses the shortcomings of the past systems for inflation of the element and retention of the seal after inflation. The element is inflated with a fluid, as before. However, a layer is inserted in the annular space between the element and the mandrel that, upon contact with the inflating fluid absorbs the inflating fluid and expands so that the expanded volume of the fluid and the expanding layer is preferably as great as the volume of the two layers prior to absorption. The resulting advantage is retention of the seal despite a failure in the element as the expanding layer with the retained fluid provides the continuing sealing force. Furthermore, there is no volume loss after inflation as occurred in the prior design using cement slurry that could undermine the sealing force of the inflated element. Those and other advantages of the present invention will become more readily apparent to those skilled in the art from the description of the preferred embodiment, the drawings and the claims that appear below.
An inflatable that features a swelling layer is disclosed. The swelling layer can be made integral or attached to the element or it can be bonded or otherwise secured to the mandrel. Upon inflation with fluid, the element expands into sealing contact with a surrounding tubular or wellbore. The fluid is absorbed or otherwise interacts with the swelling layer so that, in a preferred embodiment, the total occupied volume of the swelling layer and fluid individually is retained after mixing with the swelling of the layer acting to hold the seal of the inflatable element even if a problem develops in the sealing element.
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In the preferred embodiment the swelling layer 22 or 22′ is EPDM but other materials such as natural rubber or brombutyl rubber. These materials, when exposed to a hydrocarbon as the inflating fluid will swell and retain the inflating fluid and meet the volume requirements described above. As a result, an inflated element will continue to hold a seal after inflation. The swelling action, which goes on over time actually enhances the sealing force to the extent V3 exceeds the sum of V1 and V2. Additionally, if the element 18 or 18′ develops a leak or tear, the sealing force will remain as the inflation fluid will be tied up in the swelled layer 22 or 22′ and preferably the consistency of the swelled layer will be strong enough to hold the damaged element in sealing contact in the wellbore.
Other options for the swelling layer 22 or 22′ include using swelling clay such as bentonite that expands dramatically in the presence of water as the inflation fluid and then hardens. To the extent such a material meets the volume criteria it could be used in an inflatable. The hardened clay could also serve to retain the inflation fluid and could be rigid enough to help retain a seal in the presence of a failure of the element 18 or 18′. Alternatively the swelling layer 22 or 22′ can include a fabric that absorbs liquid and expands dramatically. A combination of the fabric and clay such as bentonite is possible as is the further addition of an EPDM or other material that swells in the presence of oil.
Oil based drilling fluids contain a mixture of oil and water and can be used as the inflation medium. Typically the drilling fluid mixture might be composed of 60% oil and 40% water with solids to increase the density the fluid. If the inflation fluid is a mixture of oil and water then a clay such as bentonite or fabric can swell with the water phase and the EPDM or a rubber can swell with the oil?
Those skilled in the art will now appreciate that the reliability of inflatable packers is improved through the use of a swelling material that ties up the inflation fluid without suffering a net volume loss. Instead, the swelling enhances the sealing grip and helps to retain such grip even if there are changes in thermal conditions downhole or a failure of the element. Various configurations of sealing element and swelling layer may be used. While the preferred material EPDM can be used other swelling materials when exposed to a variety of fluids can be used. Alternatively, materials that swell in response to heat, current, fields of various types or as a result of reactions of various types can also be used. As long as the volume requirements are met and the resulting layer is strong enough to retain the sealing load despite a failure in the element, the material or combination of materials can be used. Ideally, the inflation medium, whether liquid or gas, is retained by the swelling layer despite an element failure.
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:
This application claims the benefit of U.S. Provisional Application No. 60/525,019 filed Nov. 25, 2003.
| Number | Date | Country | |
|---|---|---|---|
| 60525019 | Nov 2003 | US |
