Wells – Processes – Perforating – weakening – bending or separating pipe at an...
Reexamination Certificate
1999-02-17
2001-04-24
Neuder, William (Department: 3672)
Wells
Processes
Perforating, weakening, bending or separating pipe at an...
C166S055000, C175S004600
Reexamination Certificate
active
06220355
ABSTRACT:
This invention relates to downhole apparatus, and in particular but not exclusively to apparatus for use in sealing and locating a length of tubing within a casing-lined borehole. The invention also relates to a perforating system.
Boreholes drilled to gain access to underground hydrocarbon-bearing formations are typically lined over most of their length by steel casing. If tests are to be carried out on a hydrocarbon-bearing formation, or oil or gas is to be extracted from the formation, test or production tubing is lowered into the borehole, and fluid communication with the surface is achieved through the tubing. Conventionally, the tubing is located relative to the casing, and the annulus between the casing and the tubing sealed, using one or more expandable or inflatable packers. Such packers are set when the tubing is in position in the borehole by, for example, inflating the packers with pressurised well fluid. Such setting operations may be time-consuming and often encounter difficulties. Further, the tubing consists of a plurality of threaded sections and the tubing must be tested for pressure integrity as the sections are made up and lowered into the borehole. Such “completion” testing is achieved by pressurising the tubing using well fluid, which may result in inflation and premature setting of the packers.
It is among the objects of embodiments of the present invention to provide an apparatus and a method for sealing and locating tubing in casing which obviate or mitigate the above-mentioned disadvantages.
The section of casing or liner which intersects the hydrocarbon-bearing formation is initially solid, to prevent the production fluid from flowing into the bore until the production tubing is in place and all of the associated apparatus and systems have been prepared. The liner is perforated by explosive charges or guns, typically spaced individual charges which are lowered into the bore and detonated at an appropriate location. The charges may be lowered into the bore on electric wireline, slickline or coiled tubing. However, as the length of the perforating guns which may be used is limited by the depth of the safety valve in the wellbore, and the length of liner to be perforated is generally longer than this depth, a perforating operation will tend to involve a number of runs and thus is relatively time consuming. Further, it is desirable to carry out “underbalanced” perforating, in which the pressure within the wellbore is lower than the formation pressure such that, following perforation, the debris produced by the perforating operation is washed out of the wellbore by the higher pressure formation fluid. In the absence of such a pressure differential the debris may be pushed into the perforations, restricting the flow of production fluid into the wellbore. When carrying out a perforating operation using wireline, slickline or coiled tubing which requires a number of runs only the first perforating operation may be underbalanced.
Guns have been mounted on the lower end of production tubing, thus reducing the need for separate runs and separate perforating operations. However, the remains of the charges and firing arrangements which occupy the wellbore following the perforating operation reduces the internal area of the tubing, thus reducing the production capability of the well. This debris may be milled out, such that it falls to the bottom of the well. However, to accommodate the debris from several thousand meters of perforating guns requires the drilling of a substantial extra section of bore, which may take several weeks' drilling, adding substantially to the drilling cost for the wellbore.
It is among the objectives of embodiments of the present invention to obviate or mitigate these difficulties.
According to the present invention there is providing perforating apparatus comprising a length of tubing, the wall of the tubing defining a plurality of apertures, and perforating charges being located in the apertures.
The invention also relates to a perforating method utilising such apparatus.
In use, when the charges are detonated, the charges disintegrate to leave the apertures clear and to permit formation fluid to flow through the apertures into the tubing. The use of tubing as a mounting for the charges allows a perforating “gun” of considerable length (typically 4000 to 7000 m) to be provided, such that a wellbore may be perforated in a single operation, facilitating underbalance perforating.
The tubing is preferably mounted on the lower end of a length of production or test tubing such that the formation fluid may flow into the tubing and then directly into the production or test tubing.
Preferably, the charges disintegrate on detonation to form light or small parts which may be swept out of the well by the formation fluid.
Preferably also, following detonation of the charges the flow area of the tubing corresponds to the tubing internal diameter.
Preferably also, each charge is locatable in a respective aperture from the tubing exterior. Each charge may include a cap adapted to engage with the respective aperture.
Preferably also, the charges are linked by explosive transfer means for communicating a detonation signal to each charge. Most preferably, the explosive transfer means extends through the interior of the tubing. The transfer means will typically be in the form of one or more tracks of detonation cord.
Preferably also, the tubing is provided in separable tubing sections, each section carrying a number of charges.
The sections may be connected by any suitable means, but are preferably connected by threaded collars rotatably mounted on the end of one section for engaging a corresponding threaded portion on the end of an adjacent section. Preferably also, the sections are provided with connectors for explosive transfer means for linking the charges in adjacent guns. Most preferably, the connectors include booster and may define female booster connection and receive a respective end of a central male booster connection portion. Most preferably, the male booster connection portion may be located in the female booster connections after the tubing sections have been placed end-to-end.
Preferably also, the apparatus includes firing means for initiating detonation of the charges. The firing means may be activated by one or more of electrical, hydraulic or mechanical means.
Preferably, the firing means is provided in combination with a valve, such as our Full Bore Isolation Valve (FBIV) as described in PCT\GB97\00308, the disclosure of which is incorporated herein by reference. Most preferably, the valve includes a valve portion, preferably a valve seat, which is movable on pressure being bled off above the valve and the valve opening, which movement of the valve seat releases a firing pin actuating arrangement. The firing pin actuating arrangement preferably incorporates a spring tending to bias the firing pin to a firing position, which spring is released by upward movement of the valve seat. Alternatively, the firing pin may itself be hydraulic pressure actuated, and may be initially retained in a primed position by a rupture disc or retainer which is releases the firing pin on application of a predetermined fluid pressure thereto.
Preferably also, a plug is provided at the end of the tubing, which plug is blown from the tube when the charges are detonated.
According to the another aspect of the present invention there is provided apparatus for locating and sealing tubing in a casing-lined borehole, the apparatus comprising:
a length of tubing;
a sleeve mounted on the tubing; and
the sleeve carrying landing means for engaging a restriction in the casing, locking means for locking the sleeve relative to the casing, and sealing means for sealing the sleeve relative to the casing.
In use, the sleeve may serve an equivalent function to a conventional packer, that is locating and sealing the tubing relative to the casing (as used herein, the term “casing” is intended to encompass any liner provided in a borehole). The tubing may be in t
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Neuder William
Ocre (Scotland) Limited
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