Patent Application
20160060975
This application is a nonprovisional application which claims priority from Norwegian Patent application number 20141049, filed Aug. 28, 2014.
The present invention relates to a downhole drilling device. More particularly the invention relates to a device for downhole drilling comprising a drill bit rotatable via a drill string, a guiding device provided between said drill bit and said drill string, said guiding device being connected to and operable independently from said drill string, and a power source for powering said guiding device.
In downhole drilling devices according to the prior art, power for driving downhole electric components has normally been supplied via wires from the surface or battery packs included in the downhole device. Power may be required for guiding the drill bit in the well while drilling, so as to be able to drill deviated wells. Power transfer via long wires is undesirable because it limits the design options for the drilling device as long power-transferring wires cannot connect to both rotating and non-rotating parts of the drilling device. Power is also lost in the wire during transfer. Power supplied from included battery packs limits the lifetime between runs to pull out and replace the battery packs, and may significantly increase the length and running cost of the device.
Downhole power sources, such as mud generators, have been used for downhole power generation, and mud generators offer the advantage of downhole sustainable power supply. However, such mud generators are typically provided in the hollow rotating drill string, rotating together with the drill string. Existing power transfer devices generally rely on mechanical contact devices, such as slip-ring devices, which are prone to damage, wear and high contact resistance and which become less efficient over time. The consequence of this is high power losses and temperature increases. No robust solution exists for transferring power from the continuously rotating drill string to nonrotating parts of the bottom hole assembly. On the other hand, various forms of accumulators, such as batteries, could be provided on non-rotating parts, but the power from an accumulator is limited as is the space for placing such accumulators downhole.
More specifically, the invention relates to a downhole drilling device. The downhole drilling device may include a drill bit rotatable via a drill string; a guiding device provided between said drill bit and said drill string, said guiding device being connected to and operable independently from said drill string; and a power source for powering said guiding device. The downhole drilling device may further include an inductive coupler having a primary side and a secondary side, said inductive coupler being adapted to transfer power from said power source, connected to the primary side of said inductive coupler, to said guiding device, connected to the secondary side of said inductive coupler. It will thus be possible to transfer power across rotating connections of the drill string, which may significantly simplify drilling device design.
The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The present invention may be used for the transfer of power and/or data between two parts of any drilling tool, where one part is rotating at a different speed relative to the other part. In the following the drilling tool will be exemplified by a directional drilling device, but the invention as such is not limited to a directional drilling device.
In one embodiment the power source may be a downhole power source, such as a mud turbine generator. The drilling device may thus not require transfer of electrical power from the surface, which may further simplify the design of the drilling device. Also a mud turbine generator will typically be installed in the mud path inside the drill string, thus not taking up unnecessarily much space.
In one embodiment said guiding device may be radially displaceable relative to said drill string. The drilling device may thus be suitable for guiding the drill bit by means of “push the bit” technology, wherein the guiding device is radially displaced in the borehole, e.g. towards a liner or the formation itself, so as to push the bit in the opposite direction of the guiding device and thus alter the direction of drilling. Examples of guiding devices wherein eccentric sleeves are used to control the amount and the direction of the displacement of the guiding devices, are disclosed in patent applications WO 2008156375 and WO 2012152914 to which reference is made for an in-depth description of a possible functionality of such guiding devices.
In one embodiment said guiding device may include a first electric actuator for controlling the radial displacement of said guiding device relative to said drill string; and a second electric actuator for controlling the direction of the radial displacement of said guiding device relative to said drill string. This may be done by using said first and second electric actuators for controlling eccentric sleeves as described in the above-reference patent applications. The directional guiding of said drilling device may thus be fully electric, and if combined with the above-mentioned downhole energy source, the drilling device may be fully self-contained with respect to power supply for the guiding device and for any MWD logging tools. The rotation of the drill string itself may be powered and/or executed from the surface, and will be independent of the powering of the guiding device and the other downhole electronics devices.
In one embodiment the downhole power source may be connected to the primary side of said inductive coupler via a rectifier and a power inverter. This may be beneficial as electronics on the primary side of said inductive coupler may require DC input, and thus be powered from the same power source. The rectified signal must then subsequently be inverted or chopped before fed onto the windings of the primary side of said inductive coupler.
In an alternative embodiment an alternating current power source with one or more phases may be connected directly to the primary side of said inductive coupler consisting of one or more coil pairs, which may be beneficial for avoiding switching losses.
In one embodiment said inductive coupler may further be adapted for bi-directional data transfer. This way it will be possible both to communicate instructions to said guiding device and other electronics over the rotating connection, and at the same time communicate from the BHA to the surface, both information about the guiding device and other loggings performed while drilling, as will be known to a person skilled in the art.
In one embodiment one or more coils for bi-directional data transfer may be isolated from one or more coils for power transfer, for instance by providing one or more coils for bi-directional data transfer without magnetic means, such as magnetic cores, of coils for power transfer. This may increase the signal to noise ratio of the data signals. Coils for data transfer may not need to be provided with magnetic means. Factors that may influence the use of magnetic means are isolation of data signals from power signals, frequency used for data transfer, desired bandwidth of communication signals.
In one embodiment said inductive coupler, on its primary side, may be adapted to produce an analogue or digital feedback signal modulated on a transmit coil for coupling a signal proportional to an output voltage in a power coil on the secondary side to the primary side. The voltage feedback may be beneficial for controlling the voltage output on the secondary side, potentially in a closed loop system by modulating the drive on the primary side. In this way it will be possible to keep the voltage on the secondary side within a predefined limit. The modulation may take various forms but will preferably be a pulse width modulation of the primary side.
In one embodiment the output voltage may be controlled by prior knowledge of the input voltage and the system load using modulation of the primary drive signal.
In one embodiment said inductive coupler may include magnetic means, such as cores, formed with anomalies for the determination of relative position and speed of the primary and secondary sides. The anomalies, which may be cavities, will constitute magnetic signatures that may be measured so as to give full control over the relative position, direction and speed of the drilling device according to the invention. For example if there are unevenly spaced anomalies in the magnetic means on the secondary side, a pulse will be created every time the anomaly passes a reference point in the magnetic means on the primary side. The pulses and the time between pulses can be logged, thus enabling the computation of both the direction of rotation and the speed of rotation by simple arithmetic calculations.
In one embodiment one or more coils of said inductive coupler may include U-shaped magnetic means. It has been found, through experiments and modeling, that U-shaped magnetic means may be more efficient than magnetic means with other shapes, such as E-shaped magnetic means which have traditionally been used. In one embodiment at least a part of said inductive coupler may be potted in a resin-based material. The resin-based material may mechanically protect the magnetic means and associated windings by sealing and making it suitable for downhole operations in high temperatures and pressures. The resin-based compound may further be infused with a magnetically permeable material in order to improve/tailor the coupling efficiency between said primary and secondary sides.
In one embodiment a gap between the primary side and the secondary side of said inductive coupler may be less than 1 millimetre and preferably less than 0.5 millimetres. With a too large gap between the primary and secondary side, a lot of efficiency is lost in the transfer. Gaps of less than 0.5 millimetres have been shown to enable more than 90% power transfer. Reasonable, useful efficiencies are also obtained for gaps between 0.5 millimetres and 1 millimetre, whereas gaps up to 1 centimetre has been shown to also provide some power transfer.
In one embodiment the primary side and the secondary side of said inductive coupler may be arranged in a radial configuration. In an alternative embodiment the primary side and the secondary side of said inductive coupler may be arranged in an axial configuration.
There is also described the use of an inductive coupler for transferring power for the guiding of a downhole drilling device. The is also described the use of an inductive coupler for transferring power and data between two parts of a downhole drilling device, where one part is rotating at a different speed relative to the other part.
In the following is described an example of a preferred non-limiting embodiment illustrated in the accompanying drawings, wherein:
The reference numeral 1 indicates a downhole drilling device according to the present invention. The downhole drilling device 1 will typically be a part of a bottom hole assembly constituting the lower portion of an otherwise not shown drill string. The downhole drilling device 1 is, at its lower end, adapted to be connected to a not shown drill bit as will be known to a person skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20141049 | Aug 2014 | NO | national |
