Wells – With electrical means – Valve
Reexamination Certificate
2000-01-31
2001-11-20
Bagnell, David (Department: 3672)
Wells
With electrical means
Valve
C166S050000, C166S207000, C166S334400
Reexamination Certificate
active
06318457
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a multilateral well and electrical transmission system.
BACKGROUND OF THE INVENTION
Numerous electrical and non-electrical power and communication systems are known for use in unbranched or multilateral oil and/or gas production wells.
U.S. Pat. Nos. 5,706,892; 5,706,896 and 5,721,538 disclose that a multilateral well may be equipped with a hardwired electrical or with a wireless communication system and that such a wireless system preferably transmits acoustic waves through a string of well tubulars such as the production tubing. Disadvantages of the known system are that installation of a wire tree in a multilateral well is a complex and expensive operation and that a wireless acoustic transmission system will suffer from high transmission losses and background noise. These disadvantages are particularly significant if the well is equipped with an expandable casing and/or production tubing. Around such an expanded well tubular there is hardly any or no annular space left for housing of the electrical cables and as a result of the physical contact between the expanded tubular and the surrounding formation acoustic signals will be dampened to a high extent.
Numerous other hardwired or wireless power transmission and communication systems are known, which have in common that they require complex and expensive equipment and that they are not suitable for use in multilateral wells.
U.S. Pat. No. 4,839,644 and European patent No. 295178 disclose a wireless communication system known as “Tucatran” which generates antenna currents in an unbranched well where the production tubing and surrounding well casing are electrically insulated from each other. The requirement of electrical insulation between the tubing and the casing is often difficult to accomplish in e.g. curved borehole sections and areas where brine is present in the tubing/casing annulus. International patent application WO80/00727 discloses another signal transmission system which utilizes an electrical circuit formed by a production tubing and a surrounding well casing.
U.S. Pat. No. 4,484,627, UK patent application No. 2322740 and International patent applications Nos. PCT/GB79/00158; PCT/GB93/01272 and PCT/EP96/00083 disclose other downhole electric transmission systems which utilize an externally insulated tubing in an unbranched well.
The present invention aims to overcome the disadvantages of the known transmission systems and to provide a downhole power and/or signal transmission system which can be used to transmit electrical power and/or signals throughout a multilateral well system in a safe and reliable manner even if the well comprises expandable well tubulars and without requiring complex wire trees or production tubing that are electrically insulated from the surrounding well casings.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a multilateral well and electric transmission system, which comprises a primary wellbore in which a primary well tubular is arranged and a branch wellbore in which a branch well tubular is arranged, wherein the branch well tubular is connected in an electrically conductive manner to the primary well tubular such that the primary and branch well tubulars form a link for transmission of electrical power and/or signals between the primary and branch wellbore.
Preferably, the primary and branch well tubulars form a link for transmitting low voltage power from a first pole of an electrical power source, which is electrically connected to the primary well tubular, to electrically powered equipment within the branch wellbore which is electrically connected to the branch well tubular. An electrical circuit is created by electrically connecting a second pole of the electrical power source and the branch well tubular(s) to the earth. It is also preferred that said equipment comprises a re-chargeable battery which is trickle-charged by the low voltage electrical power transmitted via the well tubulars.
Suitably low voltage power is transmitted as a direct current (DC) having a voltage of less than 100 V, preferably less than 50 V through the casing or production tubing of the primary well, which is imperfectly insulated to the surrounding earth formation by a surrounding cement or other sealing material, such as an addition curing silicone composition.
At the same time pulsed electromagnetic signals are transmitted which involve changes of voltage level oscillating around the DC voltage level of the well tubular at very low frequency (VLF), between 3 and 20 kHZ, or preferably at extremely low frequency (ELF), between 3 and 300 HZ.
The surface power generator and the downhole equipment or battery may have an electrode which is connected to the earth so that an imperfect electric loop exists between the power generator and the downhole equipment or battery.
It is also preferred that the branch well tubular is a radially expandable tubular which is made of an electrically conductive material and which is radially expanded within the branch well during installation and wherein an electrically conductive receptacle is arranged at or near the branchpoint such that the expanded branch well tubular is pressed into electrical contact with the receptacle as a result of the expansion process.
A particular advantage of the use of expandable tubulars at least in the branch wellbore is that as a result of the radial expansion process a surplus expansion is created in the expanded tubular which will ensure an intimate electrical contact between adjacent well tubulars of which the ends coaxially overlap each other. Such an intimate electrical contact is also made at the branchpoint between the expanded branch well tubular and the receptacle which may be formed by the primary well tubular itself or by a branched bifurcation element.
Suitably the primary and branch well tubulars are made of a formable steel grade and the branch well tubular is expanded during installation such that the expanded branch well tubular has an inner diameter which is at least 0.9 times the inner diameter of the primary well tubular, so that a substantially monobore multilateral well system is created which may have any desired amount of branches and sub-branches.
Preferably the electrically powered downhole well equipment comprises measuring and/or control equipment which is powered by a rechargeable lithium-ion high-temperature or other battery and/or a supercapacitor and/or a downhole energy conversion system such as a piezo-electrical system, turbine or downhole fuel cell and is mounted on an equipment carrier module in the form of a sleeve which is removably secured within the branch well tubular such that one electrode of the battery is electrically connected to the branch well tubular and another electrode of the battery is electrically connected to the subsurface earth formation surrounding the branch wellbore.
Suitably the sleeve spans an inflow area of the branch wellbore where the branch well tubular is perforated, the expandable clamps consist of a pair of expandable packers which seal off an annular space between the branch well tubular and sleeve near each end of the sleeve and wherein the sleeve is provided with one or more fluid inlet ports which can be opened and closed by one or more valves which are powered by the rechargeable battery. The triggering can be done via a downhole or surface actuated control system.
In many lengthy multilateral well systems it is also preferred that at least one of the primary and branch well tubulars is equipped with at least one electrical booster station which station spans an electrically non-conductive section of the well tubular and which station is electrically connected to the electrically conductive parts of the well tubular at both sides of the electrically non-conductive section thereof.
The electrical booster stations may be distributed at regular intervals along the length of the primary and branch wellbores. If an electrical booster station is required at a location where the ends of two adjac
den Boer Johannis Josephus
Fisher Simon Lawrence
Kuperij Anthony Evert
Stewart John Foreman
Bagnell David
Hawkins Jennifer M
Shell Oil Company
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