Patent Grant
8665110
1. Field of the Invention
The present invention relates to a system for transmitting electric power into a bore hole.
2. Description of the Related Art
Such a system is known and described in paper SPE/IADC 52791 of the Society of Petroleum Engineers, entitled “Electric coiled tubing drilling: a smarter CT drilling system” by D. R. Turner et. al. In the known system, an electrically powered bottom hole assembly is connected to an electric coiled tubing that reaches into a bore hole. The electric coiled tubing holds an electric transmission line, for powering a down hole electric DC motor. The peak power output of this motor is 28 HP, corresponding to some 21 kW.
This system is not considered suitable of transmitting much higher electric power at the motor voltage, for instance as high as 100 to 400 kW, since that would require very large cross section cable which would not fit in the coiled tubing. Moreover, such a cable would become so heavy that it would not be able to pull its own weight if it reaches into a typical bore hole suitable for production of hydrocarbons.
According to some embodiments of the invention, the system comprises an electric transmission line extending through the bore hole between an electric power source and a receiving station and voltage converter means for changing the voltage of the electric current supplied to the receiving station, wherein the receiving station includes frequency increasing means for increasing the frequency of the electric current supplied through the electric transmission line, connecting means for supplying the frequency-increased electric current to the voltage converter means, and means for connecting an electric load to the receiving station, that the frequency increasing means is arranged to convert the electric current into three subsignals of increased frequency, each of which is 120.degree. phase-shifted with respect to the other two, and whereby the voltage converter means change the voltage in each said subsignals, and that the frequency increasing means bring the frequency of the electric current to a value in a range of between 10 and 100 kHz.
The invention will now be illustrated by way of example, with reference to the accompanying drawings wherein
In the figures, like parts carry identical reference numerals.
In
The electric power source in
The receiving station 9 comprises frequency increasing means 10, which is electrically connected to voltage converter means 11, here in the form of a coil transformer. The output of the voltage converter means 11 is connected to a load 12.
In practical operation, the system of
The electric transmission line 7 brings the DC electric power into the bore hole. In bore holes for production of hydrocarbon, the distance over which the electric transmission line 7 reaches can be between several hundreds of meters and 10 km. At the destination in the bottom of the bore hole, the electric current reaches the receiving station 9, where it its frequency is increased in frequency increasing means 10, and its voltage is brought back in voltage converter means 11 to typically between 100 and 800 V, preferably between 400 and 800 V, depending on what is required by the nature of load 12.
The frequency preferably lies in a range of between 10 and 100 kHz, in which range there is an optimum compromise between the quality of the frequency increased current and the miniaturisation of the voltage converter means. With a frequency of approximately 25 kHz, the voltage converter means in the form of a coil transformer can comfortably fit in a tube having a diameter of approximately 15 cm. This makes the frequency specifically suitable for application in a bore hole, particularly in a bore hole for production of hydrocarbons.
In the case of
The load can be a desired tool operating at a specified voltage. The presence of the voltage converter means in the receiving station allows for the voltage in the electric transmission line to be relatively high compared to the voltage desired for operating the load, which is beneficial for achieving the high power transmission through a suitable transmission line. Due to the presence of the frequency increasing means in the receiving station, this system makes it possible to combine a relatively low frequency electric current, preferably direct current, in the electric transmission line with a relatively high frequency electric current in the voltage converter means.
At relatively low frequency the reactive power loading in the transmission line is relatively low resulting in a high efficiency of power transmission. The size of typical transformers in inversely proportional to the current frequency, thus increasing the frequency allows for the use of a relatively small sized voltage converter means, such that it can fit in a typical bore hole suitable for production of hydrocarbons.
Preferably the voltage converter means comprises contactless transformer means. Such a contactless transformer may typically comprise inductively coupled primary and secondary coil windings, preferably coupled via a magnetisable core such as an iron core. Such a transformer is ideally suited for high frequency voltage transformation, because the efficiency increases with frequency such that its size can decrease with increasing frequency.
Optionally, the system further comprises frequency decreasing means 30 (
Preferably, if the receiving station 33 comprises frequency decreasing means 30, the frequency decreasing means is then also arranged to convert three subsignals, each of which is 120° phase-shifted with respect to the other two, into one three phase current of reduced frequency.
In some other applications, however, the frequency must be decreased to several Hz or several tens of Hz, in particular 50 Hz or 60 Hz. An example is powering an AC powered electric motor 35.
In other embodiments, the frequency must even be decreased to zero resulting in a DC current. A system for transmitting high power DC current in the bore hole is shown in
Functionally, the receiving station 13 equates to a DC to DC power converter. Examples of suitable DC to DC power converters are shown and described in, for instance, U.S. Pat. No. 5,027,264, an article an article entitled “A three-phase soft-switched high-power-density dc/dc converter for high-power applications” published in IEEE transactions on Industrial Applications, Vol. 27 No. 1 (January/February 1991) by R. W. A. A. De Doncker, D. M. Divan, and M. H. Kheraluwala, and an article entitled “A three-phase series-parallel resonant converter—analysis, design, simulation, and experimental results” published in IEEE transactions on Industrial Applications, Vol. 32 no. 4 (July/August 1999) by A. K. S. Bhat and R. L. Zheng. These DC to DC converters are incorporated by reference. Another example of a DC to DC converter is a three-phase series resonant converter as shown in
The DC to DC converters generally have frequency increasing means composed of full or half bridges with active gate controlled switching devices which can be based on thyristor valves such as metal on semiconductor controlled thyristors (MCT's), or transistor valves such as insulated gate bipolar transistors (IGBT's), metal on semiconductor field effect transistors (MOSFET's). The DC to DC converters further have transformer means for changing the voltage of the increased frequency current, and a current rectifier.
The current rectifier can be based on a bridge of diodes, or active gate controlled switching devices comprising diodes. In the latter case, the DC to DC converter can be operated in two directions, since a bridge based on active gate controlled switching devices function as frequency increasing means in one direction and as current rectifier in the other direction. The advantage of a rectifier based on active gate controlled switching devices is therefore that the down hole power system can also function to transmit electric power out of the bore hole.
In another embodiment, a bore hole is provided with the system in accordance with one of the above described embodiments, and wherein an electric load in the form of a tool is connected to the receiving station for receiving voltage changed electric current. The tool may include one or more of: an electric welding tool, oil-water separator, an induction coil or heating device in general, a perforating tool, a valve system, an electric sparking tool such as an electric spark drilling tool, a motor-driven tool such as a traction device or a drilling assembly, preferably including a drill bit, or an electric submersible pump.
As an alternative to
Among other features that may be included in the drill bit are:
A gripping device for locking the tube once the arms have reached the fully expanded position by hydraulic actuation via the piston and tube. This way the bit is locked in expanded position. At the end of a bit run the bit can be collapsed by pulling the drilling assembly into the casing again. This pulling force should enable shear pins that hold the gripping device to fail so that the tube is released again and the bit opens and the under-reaming arms can move to the retracted position
By virtue of the provision of the support means, the pivot means is relieved from taking the full torque load. It is thereby achieved that the pivot means is less vulnerable to damage due to transmission of high loads, without loosing reliability of switching the drill bit from the retracted to the expanded position and vice versa.
In another embodiment, the invention provides a hydraulic system for driving a pivoting movement of a pivotable tool arm between a radially retracted position and a radially expanded position, the hydraulic system comprising a cylinder and piston means slidably arranged in the cylinder forming a drive chamber on one side of the piston means and a return chamber on the other side of the piston means, the piston means having a forward and a rearward position in the cylinder whereby the piston means is activatable to its rearward position by causing the drive force acting on the piston as a result of pressure in the drive chamber to exceed the return force acting on the piston as a result of pressure in the return chamber, which piston means is coupled to the pivotable tool arm for driving the tool arm from the retracted position to the expanded position when the piston is driven into its rearward position, whereby the piston means is coupled to gate means with is arranged such that the return force acting on the piston as a result of pressure in the return chamber exceeds the drive force acting on the piston as a result of pressure in the drive chamber when the piston means is in or near its forward position whereas the opposite is the case when the piston means is in a position other than in or near its forward position.
When the tool arm is in its retracted position, the piston means can be positioned in or near its forward position where the gate means is switched such as to bias the piston means to its forward position. When the piston means is mechanically moved out of its forward position, the gate means is switched because it is coupled to the piston means, which results in the drive force acting on the piston as a result of pressure in the drive chamber exceeding the return force acting on the piston as a result of pressure in the return chamber. Consequently, the tool arm is pivoted to its expanded position and held in that position by the piston means. The starting situation, whereby the piston means is again biased in its forward position can be restored by mechanically forcing the piston means to its forward position, or by provision of additional gate means for regulating the pressures inside the drive chamber and return chamber such as to move the piston means forward on command.
Such a traction device requires more than 200 kW, or even between 300 and 500 kW, in order to expand a typical casing tubing at an industrially acceptable rate. The receiving station 13 functions in the same way as described above with reference to
For some applications the power transmitted via the system to the destination inside the bore hole lies in a range of 50 to 500 kW, preferably 200 to 500 kW, depending on the type of operation or application. Such high electric power can be transmitted in a cable having only 1.5 mm2 cross sectional area, provided that the voltage is sufficiently high. Preferably, the Ohmic resistance of the cable is less than 14 Ω/km, determined for DC at 20 C.
One example of a suitable cable is a commercially available HNOK cable from the firm Draka, which is a 8-mm diameter steel shielded coaxial power cable with a 1.5 mm2 tin-plated copper central conductor that can conduct a current of 17 A DC. The insulation between the conductor and the steel shielding can support a potential difference of up to 20 kV between the conductor and the shielding. Thus a theoretical maximum power of 340 kW is transmittable using this cable. In practice the power is preferably limited to around 280 kW. A larger diameter core conductor and/or a thicker insulation layer will enable higher powers up to 500 kW.
In one embodiment, bypassing means are provided to feed to or extract from the electric transmission a data signal parallel to the receiving station. This enables utilization of the electric transmission line for carrying a data signal in addition to the high power transmission. Since such data signal does not have to be of high power, it does not need to pass through the receiving station.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03253754 | Jun 2003 | EP | regional |
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| Entry |
|---|
| D.R. Turner et al., “Electric Coiled Tubing Drilling: A Smarter CT Drilling System,” Society of Petroleum Engineers, 1999, SPE/IADC Drilling Conference, pp. 231-243. |
| Rik W.A.A. De Doncker et al., “A Three-Phase Soft-Switched High-Power-Density dc/dc Converter for High Power Applications,” IEEE Transactions on Industry Applications, vol. 27, No. 1, 1991, pp. 63-73. |
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| Number | Date | Country | |
|---|---|---|---|
| 20110170320 A1 | Jul 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11300663 | Dec 2005 | US |
| Child | 12732055 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2004/051096 | Jun 2004 | US |
| Child | 11300663 | US |
