Patent Application
20060000604
This application claims priority from United Kingdom Patent Application No. 0412927.6, filed Jun. 9, 2004.
The present invention generally relates to apparatus and methods for transmitting information using a radio frequency transponder in a turbulent flow environment. More specifically, it relates to such apparatus and methods to carry information through a flow of well bore effluents.
Radio frequency identification (RFID) tags are found in an ever-increasing number of applications within a wide variety of different environments. Within the oilfield such tags can be used to identify equipment and/or transfer information along the well bore. The use of RFID tags in well bore flows poses a number of challenges not encountered in the field of inventory control and device tracking where such tags are commonly applied.
The flow of effluents from the well bore is often turbulent and the effluents may consist of multiple phases such as hydrocarbons, water and gas. RFID tags are convected along in the flow of the produced fluids. At a surface location the tags are energized and read with an appropriate reader antenna. The lack of orientation of a device free to move within the flow, the temperature of the flow, and the metal pipe surrounding the flow are all factors that either alone or jointly prevent the use of most of the known RFID tags. For example, known tags often have simple antennas with a directional characteristics. In conventional inventory control systems it is possible to overcome this problem by controlling the orientation. For most of these known systems it can be assumed that the tag does not change its orientation during the read-out phase, which is typically in the order of 0.05 second at the low frequencies of interest. However as a tag in a turbulent flow will tumble, it may not couple to the field produced by the reader antenna. In a turbulent flow it is likely that the tag changes its orientation during the read-out phase thus losing contact with the reader. While it is possible to shorten the read times by using higher frequencies, such frequencies have a higher attenuation in conductive fluids and are therefore not a practical solution for many oilfield applications.
A number of technologies have been proposed around the idea of sending some object or element up or down the borehole. A raw piece of semiconductor memory onto which data is written by a downhole device has been disclosed for example in GB Patent Application 1 549 307. A more sophisticated and robust vessel containing memory has been disclosed by GB Patent No. 2 352 041 and the co-pending U.S. patent application Ser. No. 10/049,749 assigned to Schlumberger Technology Corporation. Alternatively, even more complex vessels containing a variety of sensors and data storage have been disclosed. Examples of this solution can be found in GB Patent 2 352 042, co-pending U.S. patent application Ser. No. 10/030,587 assigned to Schlumberger Technology Corporation, and PCT Published Application WO 99/66172.
U.S. Pat. No. 6,443,228 discloses the use of flowable devices in well bores to provide communication between surface and downhole instruments, among downhole devices, to establish a communication network in the well bore, to act as a sensor, and to act as power transfer devices. In some embodiments, the upward communication is proposed by writing information on the flowable devices downhole which are bound for the surface.
Co-pending GB Patent Application No. 0229328.0 filed 14 Dec. 2002 (incorporated herein by reference) discloses a well control system enabling the control of various downhole well control functions by instructions from the surface. The well or downhole tool conveyance mechanism can be used without necessarily being equipped with electrical power and control cables extending from the surface and without the use of complex and inherently unreliable mechanical shifting or push/pull techniques requiring downhole movement controlled remotely from the surface. The invention of this co-pending application makes use of a downhole well control apparatus that is responsive to instructions from elements such as fluids or physical objects such as darts and balls that are embedded with tags for identification and for transmission of data or instructions. According to at least one disclosed embodiment, a downhole device may also write information to the element for return to the surface. In these disclosed embodiments, where information is being sent from a downhole location to the surface, information is written to the device (or acquired by the device itself) downhole.
Co-pending published U.S. patent application Ser. No. 20040020643, filed 30 Jul. 2002, under obligation to assign to Schlumberger Technology Corporation (incorporated herein by reference) discloses a well control system enabling the control of various downhole well control functions by instructions from the surface without necessitating the well or downhole tool conveyance mechanism being equipped with electrical power and control cables extending from the surface and without the use of complex and inherently unreliable mechanical shifting or push/pull techniques requiring downhole movement controlled remotely from the surface. The invention of this co-pending application makes use of downhole well control apparatus that is responsive to instructions from elements such as fluids or physical objects such as darts and balls that are embedded with RF tags for identification and for transmission of data or instructions. According to at least one disclosed embodiment, a downhole device may also write information to the element for return to the surface.
Co-pending GB Patent Application Serial No. 0229328.0, filed 14 Dec. 2002, discloses a downhole communication system with a plurality of releasable vessels positioned at downhole locations, the vessels containing signal information affixed to the vessels prior to placement of the vessels downhole, and the signal information indicating the presence of at least one of three or more predetermined downhole conditions. A detecting system is positioned on the surface such that the signal information can be detected on one or more of the vessels. A processing system is located on the surface and is programmed to establish the presence of the predetermined downhole condition based on the signal information. The vessels can carry RFID tags.
In the light of the above prior art, it is seen as an object of the present invention to provide RF based communication devices with improved read-out capabilities for use in turbulent flows. It is seen as a further object of the invention to provide tags that are more stable during a read-out phase.
According to a first aspect of the invention there is provided a system and vessels for communicating information from a downhole location in a hydrocarbon borehole to the surface with one or more releasable vessels positioned at the downhole location, the vessels carrying radio frequency (RF) activated circuitry and conveying signal information indicative of downhole conditions or parameters, and a RF reading system on the surface positioned and adapted to detect presence and/or the signal information of the one or more vessels, the vessels being adapted to maintain RF coupling with the reader in a fluid flow, particularly in a turbulent flow.
In other words the invention provides means to counter or reduce the effect of a turbulent flow on the read-out of RFID tags.
The fluid flow to which the vessels of the invention are best adapted to can be characterized as at least temporarily turbulent. Turbulent is understood to mean a flow beyond its laminar flow range. RF circuitry or tags are incorporated into the vessel, which in turn floats passively within the well bore liquid.
The RF frequency range best suitable for use in conductive water and oil flow is within the lower range of radio frequencies. A preferred range is 40 to 500 kHz. A more preferred range is 80 to 300 kHz.
The vessels, also referred to herein as passive autonomous devices, preferably encapsulate the tag in such a way as to allow its survival in the challenging downhole environment and facilitate the collection of data without interrupting the well bore flow.
For an inductively coupled tag to be read, its antenna must be aligned with the magnetic field produced by the reader. As the device moves in the flow, it experiences torque due to turbulence. This force, acting in ever changing directions and magnitudes, will cause the object to spin randomly, therefore preventing the data being read from the enclosed tag. In order for reading to be possible, the spin must be controlled or, alternatively, the read-out must be less sensitive to the rotation of the tag.
Therefore according to a further aspect of the invention, an RFID tag of the invention may include two, three or more antennas, each antenna generating a preferred spatial direction for coupling to a reader antenna different from the other antennas. Each of the antennas can be regarded as dipole with a respective emission and/or reception characteristic. By orienting the antennas and hence the dipoles in different spatial, preferably orthogonal directions, any rotation of the RFID tag or device is compensated for by a coupling of another antenna to the stationary receiver.
In a preferred embodiment of this aspect of the invention, the antennas are connected by an electronic circuit designed to pass through to the RFID tag the signal from the antenna with the strongest coupling and, hence, best reception from the reader antenna.
In a further preferred variant of this embodiment, the antennas are coupled by half bridge or full bridge rectifiers. The rectifiers can be assembled from passive elements such as diodes, however, an equivalent transistor circuit or more complex electronic circuitry may be used to couple the antennas at the expense of higher power consumption.
According to another aspect of the invention, the carrier of the RFID tag is stabilized in the turbulent flow by establishing a preferred orientation of the device. This is preferably achieved using a carrier or device that assumes a preferred orientation in either the force field generated by the flow itself or by the gravity field.
According to a preferred embodiment of this aspect of the invention the device has a geometry and weight distribution such that a force field like fluid drag or gravity generates a torque that rotates the device into its preferred orientation.
A possible method of achieving this is to ensure the device has a non-uniform density creating a stabilizing torque. If the stabilizing torque is greater than the perturbations due to the turbulence, the orientation of the device can be stabilized in a preferred orientation. The orientation is chosen to optimize the coupling with a reader coil.
A number of different configurations are feasible to achieve this effect, however, in a preferred variant the device is essentially spherical with the centre of mass offset from the geometrical centre of the sphere. The term essentially spherical includes elliptical, oval or similar shapes. However, it was found that the spherical shape is the least sensitive to turbulent effects.
The device is preferably buoyant in the flow into which it is released. More preferable, it has a density of less than 1.1 g/ccm. Even more preferable, it has a density of 0.7 to 1.0 g/ccm. Hence, mean or average density of the device is preferably less than or equal to water. The device can be for example manufactured using fluid-filled capsules of heat and pressure resistant non-conductive material such as glass or epoxy loaded capsules with a small amount of high-density material at an off-centre position.
To withstand the pressure in the well while maintaining sufficient buoyancy, the device preferably includes sections or parts of a castable hardening material, such as epoxy resin, loaded or filled with hollow particles, such as glass micro-bubbles.
According to a further aspect of the invention, the reader antenna is located inside a metal conveyance system. In the case of hydrocarbon exploration and production, the metal conveyance system includes sections of steel pipe at the entry of the well. The antenna preferably includes a solenoid placed at the inner wall of the pipe but isolated from it by a layer of ferrite material.
These and other aspects of the invention will be apparent from the following detailed description of non-limitative examples and drawings.
FIGS. 3A,B show circuit diagrams of the antenna of tags in accordance with an example of the invention;
FIGS. 6A-C are variants of devices or vessels for RFID tags in accordance with examples of the invention; and
FIGS. 7A,B compare the orientations of tags in a turbulent flow.
In
Reader circuit 20 of surface detection system 13 is shown in greater detail in
The coil and capacitor have a calculated Q of 218, which results in a bandwidth of 568 Hz. To dampen the resonance and thus increase the bandwidth, resistor 23 (510 Ohms) is added in series with coil 21 and capacitor network 22. This reduces Q to 11.3 and increases the bandwidth to 10 kHz. Damping resistor 23 is also used to sense the current flow through coil 21. Coil 21 is driven by signal generator 24 and amplifier 25. The tuning of the coil to a specific frequency is best done in-situ on the flow from the well, as the resonance shifts with the fluid in the flow.
A demodulation circuit includes diode detector 26 to half-wave rectify the signal and remove the carrier signal as generated by signal generator 24 and amplifier 25. Diode detector 26 includes a RC network acting as a low pass filter and DC component blocking circuit. The output of diode detector 26 is fed into low path filter and amplifier 27. The low path filter has a corner frequency of 20 kHz. The filtered and amplified signal is then fed into comparator 28 the level of which was set just above background noise. The comparator lifts the signal to TTL levels via a Schmitt gate.
The TTL level data stream is fed into processor board 29 carrying processor and memory together with I/O ports to decode the signal and covert it into machine-readable data. Processor board 29 also controls signal generator 24.
An arrangement to house coil 21 inside a metal section of surface pipe 131 is shown in
It is beneficial to isolate the reader coil from the enclosing pipe to prevent the occurrence of large eddy currents. Thus, part of inner surface 133 of the pipe is sheathed with layer 134 of ferrite. The ferrite material may be chosen from commercially available material, such as manganese-zinc or nickel-zinc. Sheath 134 of ferrite material separates coil 21 from metal pipe section 131 thereby reducing the eddy current losses and radiation emission. In the example shown, concentrically mounted inner pipe 135 protects the coil from being damaged by abrasive material carried along with the fluid flow. Inner pipe 135 is made of reinforced polyetheretherketone (PEEK). Two connectors 136 provide an electrically conductive path to the exterior of pipe 131. Pipe section 131 terminates in flanges 132.
Instead of using a ferrite sheath, pipe section 131 can be made of high-strength, non-conductive materials, in which case reader coil 21 is wound around the exterior of the pipe. Suitable materials for such non-conductive pipe include ceramics and composites like reinforced PEEK.
In operation, coil 21 generates an axial magnetic field. Magnetic fields in diametrical direction, if required, may be generated using an extra layer of conductors (not shown) running in axial direction along the inside of ferrite sheath 134. The magnetic field is to a large extent confined to the interior of pipe 131. Ferrite layer 134 reduces losses of energy in the wall of steel pipe 131 through eddy currents or other residual losses.
Whilst the above configuration improves the reader antenna, it is another aspect of the invention to enhance the read-out by improving the vessel to be less sensitive to the flow turbulence.
In
Two mutually orthogonally oriented antennas 311, 312 are shown in
Using the antenna configuration of
A Monte Carlo simulation illustrated by
Assuming that the antenna is spinning around an axis that is randomly orientated with respect to both the exciting field and one of the antennas, the probability can be estimated for a tag being read as a function of the exciting field. This field is measured in units of the field necessary to read the tag when it's most favorably orientated. The single antenna (curve 51 of
The read-out efficiency of the devices of the present invention in a turbulent flow environment can be further improved by a strong asymmetry that generates a torque on the device itself when placed in a force field.
It is feasible to create such an asymmetry through the outer shape of the device by, for example, stabilizers such as fins and tails. However, for application in well bores and wellbore pipes, deviation from an approximately spherical shape may cause extended devices to get stuck. The invention therefore contemplates a way of rendering a spherical shape such that a preferred orientation in a turbulent flow is accomplished.
In
The thus weighted sphere has an average density of 0.8 g/ccm thus being slightly buoyant in a mixture of oil and water. It has a torque that can be calculated by integration of the density distribution times the distance from the center of the sphere. The stabilizing torque acts to turn the sphere such that the cap 64 of barite is located at the bottom.
The above example of
The above examples of
In the example of
The barite may be replaced by higher density materials such as tungsten oxide (density 7.1 g/ccm).
The devices of
In the example of
In the example of
While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0412927.6 | Jun 2004 | GB | national |
