Wells – Packers or plugs – Expanded by confined fluid from central chamber – pump or...
Reexamination Certificate
2003-01-15
2004-08-24
Bagnell, David (Department: 3672)
Wells
Packers or plugs
Expanded by confined fluid from central chamber, pump or...
C166S118000, C166S120000, C166S122000, C166S387000, C277S331000, C277S334000
Reexamination Certificate
active
06779601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to downhole tools for use in a wellbore. More particularly, the invention relates to a downhole tool for sealing a wellbore, such as a hydrocarbon wellbore. More particularly still, the invention relates to an inflatable sealing element for a downhole tool used for sealing a hydrocarbon wellbore.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the formation. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
After a well has been drilled and completed, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. To accomplish this, perforations are shot through the liner string at a depth which equates to the anticipated depth of hydrocarbons. Alternatively, a liner having pre-formed slots may be run into the hole as casing. Alternatively still, a lower portion of the wellbore may remain uncased so that the formation and fluids residing therein remain exposed to the wellbore.
When a wellbore is completed, the wellbore is opened for production. In some instances, a string of production tubing is run into the wellbore to facilitate the flow of hydrocarbons to the surface. In this instance, it is common to deploy one or more packers within the tubing string in order to seal the annular region defined between the tubing and the surrounding string of casing. In this way, a producing zone within the wellbore is isolated.
Various types of packers may be utilized. One common type of packer is an inflatable packer. Inflatable packers employ an elongated bladder that is inflated using a working fluid or well fluids. Inflation may be accomplished either by injecting fluid into the borehole from the surface, or through actuation of a downhole pump.
Inflatable packers are commonly used to seal the annular space around a string of production tubing in order to direct the flow of production fluids up the bore of the tubing and to the surface. However, inflatable packers may be used for many other purposes during the life of a well. For example, an inflatable well packer may be used to seal the annulus between a liner string and a surrounding string of casing during well completion. They may be used to support a column of cement above a lost circulation zone. They may also be used to isolate producing zones from cement contact during a cement squeeze job.
An inflatable packer may also be used to affect a complete seal of a tubular bore at a selected depth in a wellbore. In this instance, the inflatable packer is more commonly known as a bridge plug. In some instances, a bridge plug may be used to permanently plug a well after production operations have ceased. In other instances, a wellbore may be temporarily plugged so that formation treatment operations may be conducted. For example, a bridge plug may be set at a depth below a production zone within the casing. A formation treating operation can then be conducted above the bridge plug by injecting gel and sand, under pressure, into the formation. Still other uses for packers are also known, including dual use as an anchor.
For purposes of this disclosure, the term “bridge plug” will be used to refer to and to include any downhole tool which includes an expandable bladder as part of a sealing element, or “packing element.” This includes devices having a throughbore that would more commonly be considered “packers.”
The bladder in a typical inflatable bridge plug is surrounded by two separate expandable cover portions. The first cover portion is an expandable anchor; the second cover portion is an expandable sealing cover. Together, the bladder and the two surrounding cover portions make up a “packing element.”
First, the expandable anchor portion of a packing element serves to frictionally engage the surrounding case or, as the case may be, the raw borehole. Typically, the anchor portion defines a series of vertically overlaid reinforcing straps that are exposed to the surrounding casing. The straps are aligned along the linear plane of the tool so as to essentially run the length of the packing element. At the same time, the straps are placed radially around the bladder in a tightly overlapping fashion. For this reason, the straps are sometimes referred to as “lapped steel ribs”. The ends of the metal straps are welded together and are secured to end collars. One end collar defines a slidable sub which permits that end to be drawn up as the reinforcing straps are expanded. Upon expansion, the straps engage the surrounding pipe, serving to anchor the bridge plug within the wellbore. Sufficient straps are employed so that as the bladder expands the straps, the straps do not completely separate, but retain the bladder therein.
As an alternative to the use of metal straps, woven or braided steel cable may be used. In the case of a braided cable reinforcement, a closed tube of braided material is secured at opposite ends to packer end collars. A compression assembly is provided between a pair of conical clamping surfaces for securing the cables. In some cases, the end attachment of braided reinforcement is supplemented by injection of an epoxy polymer between the interstices of cable and the conical clamping surfaces.
As noted, the second cover portion of the inflatable bridge plug is the expandable sealing cover. The sealing cover defines a pliable material which surrounds a portion of the reinforcing straps (or other anchor portion). As the bladder and straps are expanded, the sealing cover expands and engages the surrounding pipe in order to effectuate a fluid seal. Thus, the anchor portion and the sealing cover portion of the packing element combine to effectuate a setting and sealing function for the bridge plug.
Inflatable bridge plugs enjoy certain advantages over mechanically set bridge plugs/packers. Primarily, inflatable bridge plugs are advantageous in the context of high expansion operations. In this respect, most inflatable bridge plugs are capable of achieving a higher expansion ratio than mechanically set bridge plugs and packers. Those of ordinary skill in the art will understand that the expansion ratio is defined by the ratio of the inside diameter of the surrounding pipe to the original outside diameter, i.e., running diameter, of the packing element. However, high expansion applications (typically those greater than 2.25:1) place challenges on the designer to balance the anchoring and sealing capabilities of the packing element. In this regard, a trade-off oftentimes occurs in the design of a bridge plug between a high sealing capability and a high anchoring capability. A higher expansion ratio typically affords a greater anchoring capacity for the straps; in contrast, a lower expansion ratio provides for a weaker anchoring contact between the straps and the surrounding pipe.
In an effort to accomplish both a strong anchoring function and a strong sealing function for an inflatable bridge plug, designers have offered various configurations for the packing element. For example, in one arrangement an elongated sealing cover is provided, with the sealing cover being open or “exposed” central to the anchor. In this arrangement, the anchor portion is located in the center of the packing element. However, because the anchor portion is short relative to the sealing cover portion, this arrangement compromises the maximum anchoring capability of the bridge plug. In this respect, due to the shape change that occurs in the element under load, the short anchor in the ce
Hoffman Corey E.
Wilson Paul J.
Bagnell David
Collins Giovanna M.
Moser, Patterson & Sheridan L.L.P.
Weatherford / Lamb, Inc.
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