WO2011066624A1

WO2011066624A1 - Borehole communication in the presence of a drill string

Info

Publication number: WO2011066624A1
Application number: PCT/AU2010/001636
Authority: WO
Inventors: Iain Mclaren Mason
Original assignee: Geosonde Pty Ltd
Priority date: 2009-12-04
Filing date: 2010-12-02
Publication date: 2011-06-09
Also published as: AU2010327324A1; AU2010327324B2

Abstract

Communications along the interior of a drill string are effected, for example while the drillstring is drilling a borehole and is positioned within the borehole. Wireless signals are launched within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide. Adaptive frequency hopping is also applied, in order to identify and utilise spectral regions which propagate most effectively along the interior of the drill string waveguide. This invention recognises that a wireless communications channel within the drillstring may thus be established, even despite propagation mode conversion between narrow and broad sections of the drillstring, multi-mode propagation within broad sections, and single or multi-mode reverberations in each section of the drill string.

Description

BOREHOLE COMMUNICATION IN THE PRESENCE OF A DRILL STRING

Technical Field

The present invention relates to communication within and along a borehole, while a drill-rod used for drilling the borehole remains within the borehole. In particular the present invention relates to techniques and devices to effect guided propagation of communications signals within and along the drill-rod.

Background of the Invention

Drill holes are frequently drilled in mining and in geological exploration. Such holes for example may be around 150mm in diameter or greater, and many hundreds of metres deep or more, and thus require significant resources to drill. To optimise the chances of a successful result while drilling a borehole, drillers are increasingly using sensors mounted at or near the drill bit to provide data to assist navigation of the drill during drilling. However, the very rugged operating conditions within a drill hole make many conventional communication methods impractical. Space is constrained within the borehole, and tens of kilowatts of power are delivered to the rock in front of the drill bit in order to pulverise the rock. Drill-rod assembly practices are well established and offer little room or time for the installation of communication links between drill-bit and driller. Further, the entire drill string rotates at speeds up to 240 rpm or more during drilling. Such conditions during drilling preclude deployment of many electronic instruments and conventional wirelines which might be used to effect communications in less harsh environments. One approach to measurement-while-drilling has been to convey data by "mud pulsing". This involves the down-hole sensor transmitting pressure pulses along a fluid within the borehole. While this technique provides a communication link for measurement-while-drilling while building up a string of drill rods on site without substantially changing drill-string assembly practice, this technique only provides for very low data rates. Moreover, in cases where the drilling fluid is air, mud pulsing is not applicable.

Another proposed approach is the Intellipipe™ of Grant Prideco. This communications system attempts to effect communication from sensors at or near the drill bit to the surface. This is done by providing each hollow drill rod of the drill string with twin tensioned communications wires embedded in the wall of the rod. Coupling between rods is effected by mutual induction between coils that are connected to the embedded communications wires, and set into annular interfaces which are brought into close proximity by the normal action of mechanically connecting the rods. Both the communications wire and the annular interfaces are somewhat protected from the harsh drilling environment by being embedded within the wall of each hollow rod. Consequently, the entire drill string must be custom-fitted with such embedded wire and annular interfaces, which would appear to practically prevent retro-fitting of such a communications channel into existing drill strings. This solution further provides amplifiers or repeaters to boost the signal every few hundred metres to enable data communications to proceed at higher data rates. However such repeaters comprise delicate electronic components and require their own power supply, all of which may be subject to high rates of failure in the harsh drilling environment. Such a technique is of little or no use in RAB drilling, in which drill-rods are coupled and uncoupled up to 70 times or more each day, increasing the chance of grit entering joints and damaging couplings, and in which harsh sand-blasting of drill rods results from the high pressure airflows. US Patent No. 5,831 ,549 provides for a gas-filled tubular waveguide of constant internal diameter D cm to be positioned concentrically inside a drill string. However the extra mechanical steps required to provide this component within the drill string, and the need for the waveguide to contain the gas and exclude drilling fluid which otherwise fills the drill string, adds significant complexity to the drilling process. The TEoi (H01 ) EM mode preferred for its low attenuation rate propagates at frequencies above F=3000/(0.82D) MHz

US Patent No. 3,905,010 provides for bottom-hole sensors to use a well tubing of constant diameter as a waveguide, with a dielectric well fluid such as benzene within the tubing acting in concert with the inner walls of the conducting well tubing as the transmission medium. A well casing is a fixed element which in use does not move or change characteristics. The transmission is tuned to a suitable frequency to give rise to a single electromagnetic mode of propagation, namely TE^. This technique is said to be particularly suited to free flow wells where no sucker rods or pumps are inside the tubing. However, as this technique relies on a borehole casing or tubing as the waveguide, it cannot be deployed until after the borehole is drilled, and then cased, and thus cannot provide measurement-while-drilling. Further, the need for a suitable fluid dielectric to be present within the tubing adds significant complexity. The TE-n mode envisaged in US Patent No. 3,905,010 propagates at frequencies above F~3000/(1.71 D) MHz.

Any discussion of documents, acts, materials, devices, articles or the like included in the present specification is for the purpose of providing a context for the present invention, and is not to be taken as an admission that any such matters form part of the prior art base or were before the priority date of each claim of this application common general knowledge in the field relevant to the present invention.

In this document the term "comprise", and derivatives including "comprises", "comprised" and "comprising", are to be understood to convey inclusion of one or more stated elements, integers or steps, but not the exclusion of any other element, integer or step.

Summary of the Invention

According to a first aspect the present invention provides a method for communicating along a drill string within a borehole, the method comprising:

launching wireless signals within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide; and

utilising adaptive frequency hopping to identify and utilise spectral regions which propagate most effectively along the interior of the drill string waveguide.

According to a second aspect the present invention provides a transmitter for communicating along a drill string within a borehole, the transmitter comprising:

coupling means for launching wireless signals within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide; and an adaptive frequency hopping module operable to identify and utilise spectral regions which propagate most effectively along the interior of the drill string waveguide. According to a third aspect the present invention provides a receiver for receiving communications along a drill string within a borehole, the receiver comprising:

coupling means for capturing wireless signals propagating within the drill string as at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide; and

a frequency hopping module operable to adaptively respond to transmitter selection of spectral regions which propagate most effectively along the interior of the drill string waveguide.

In some embodiments of the invention, adaptive frequency hopping may be effected by use of the protocol of Bluetooth^® version 1 .2, or later. In such embodiments the wireless signals may be in the 2.4 GHz ISM band (2400 - 2483.5 MHz). Alternatively, the wireless signals may be transmitted in a frequency band selected to optimise propagation along a drill string waveguide, such that at least one electromagnetic propagation mode propagates through constrictions of the drill string. The inventors have found that, depending on drill string characteristics and the dielectric fluid within the drill-string, a suitable band may be between substantially 300 MHz and 5.6 GHz. For example, a band centred around 1 .24 GHz may be suitable in some embodiments, involving propagation of only TE-n modes say in air filled 6 ½" tubes. A band centred on 300MHz may suit TE-n propagation in similar or smaller drill rods filled with high permittivity dielectric such as pure water. Alternatively, a band centred around 5.6 GHz or 5.8 GHz may be preferred for other embodiments, and may for example be effected by use of the WiFi communications protocol with adaptive frequency hopping, in drill rods with sections that narrow to about 1 ½" ID, utilising the TE-n mode for single mode propagation through the narrow sections.

Some embodiments of the invention may provide for spectral quality to be assessed by a channel assessment process, to effect adaptive frequency hopping. The channel assessment process may comprise determining a received signal strength indication of signals passed along the drill string waveguide. The channel assessment process may additionally or alternatively comprise determining a packet error rate of signals passed along the drill string waveguide.

The coupling means used to effect coupling of the signal into the drill string waveguide at the transmitter may comprise any suitable coupler, such as a probe coupler, loop coupler, slot coupler, coil coupler, antenna, resonator, Yagi-Uda antenna, double helix conical antenna, double-X Lorraine-Cross Yagi-Uda, or the like. Similarly, the receiver may couple signals out of the drill string waveguide utilising any suitable such type of coupler. A down-hole monopole may be positioned a short distance, of the order of an eighth to a quarter wavelength, above a non-return butterfly valve of the drill, to use the butterfly valve as a passive reflector/director for EM transmission. At least one coupler preferably comprises orthogonally mounted elements or a circularly polarised transmission pattern in order to avoid or minimise the effects of polarisation extinction during each rotation of the drill-string.

A surface coupler may comprise a passive repeater configured to couple signals between the interior of the drill string and a suitable external wireless coupler positioned outside the drill string, the external wireless coupler configured for wireless communication with a nearby active transceiver unit. Such embodiments permit for only passive components to be mounted upon the surface-end of the rotating drill string, with the active transceiver componentry able to be stationary nearby.

The surface coupler is preferably mounted within a top-saver element of the drill, or the like, so as to not interfere with the regular addition or removal of drill rods from the drill-string below the top saver.

A down-hole transceiver is preferably configured to reside in a stabiliser of the drill string. The down-hole transceiver preferably takes an annular form to permit substantially uninterrupted drill string airflow through a hollow core of the unit.

In some embodiments of the invention, down-hole power may be provided to a down- hole transceiver from a twisted butterfly valve configured to rotate about an axis when subjected to drilling air pressure and to produce electrical power from such rotation. Alternative embodiments may provide down-hole power by use of batteries, vibrating piezo-electric devices, alternators driven by the drilling action, air-driven turbines or the like

In some embodiments of the invention there may be narrow sections of the drill string or drill bit, such as the air passages through a tricone or a PCD bit or the passages through the rotary joint at the top of a drill string, that are "cut off"; i.e., are too narrow to allow for the propagation of any mode at the chosen frequency. In such embodiments propagation past such narrow sections may be effected by provision of two quarter wave monopoles, one at each end of the narrow section, connected by a conducting wire extending through the narrow section to effect propagation through the narrow section. In such embodiments matching is preferably provided at each end of the conducting wire, and/or the conducting wire is preferably an integral number of half-wavelengths in length, to minimise reverberation and transmission losses. Embodiments of the present invention may be particularly suited to rotary air blast (RAB) drill strings in which joints between drill rods comprise constrictions which are smoothly or otherwise gradational from the larger inner diameter of the drill rod to the smaller inner diameter of the joint, such that the gradation effects a type of cone antenna for the communications signals launched within the drill string.

Some embodiments of the present invention may further provide for gradations between narrow and wider sections of the tubular waveguide to be shaped, corrugated, coated, stepped circumferentially, roughened, slotted axially or stepped axially in such a way as to maintain control over signal polarization and electromagnetic mode-conversion during the transition of diameter between the sections. Where the inner diameter of the drill strong changes abruptly from a narrow diameter at drill joints to a larger diameter between joints, embodiments the present invention preferably provide for tapering of the inner diameter transition. For example in some embodiments a tapered transition insert may be positioned within the drill rod at the transition. The tapered transition insert may alternatively be provided at the time of manufacture of the drill rods. For example the tapered transition insert may for cost effectiveness be of simple construction comprising a plurality of concentric pipes of increasing diameter, each larger pipe extending a greater distance, and welded together and to the drill rod. In preferred embodiments, sensor components and communications components are fitted into counter-bore relief spaces that lie between drill-string elements. The sensor components and communications components are preferably shaped such that once fitted into such spaces they cause little perturbation of the flow of either fluid (such as compressed air) and/or electromagnetic energy along the drill-string.

In embodiments in which a counter bore relief space exists at the joints between drill rods, a cylindrical insert is preferably provided so as to bridge the counter bore relief space and present a substantially smooth cylindrical waveguide to electromagnetic signals, in order to improve electromagnetic transmission through the joint. Additionally or alternatively, a filler such as epoxy may be provided in the counter bore relief space between drill rods, to capture an inserted conductive pipe section. Such embodiments present the additional benefit of reducing aerodynamic losses caused by the discontinuity of the counter bore relief space, with such losses in RAB drilling sometimes being significant. The outer surface of the cylindrical insert is preferably featured or roughened so as to provide a strong purchase of the pipe section by the filler. Additionally or alternatively the cylindrical section may comprise a stop of greater diameter than the inner diameter of the joint, such that the cylindrical insert when inserted is suitably positioned when the stop abuts the narrowing of the joint.

Some embodiments of the present invention thus provide for electromagnetic data signal propagation along a drill string in a manner which requires little or no modification to existing drill strings, enabling retrofit deployment of such communications techniques. Further, the present invention requires no active components between a down-hole sensor/transmitter and a surface receiver in embodiments where the transmission distance is less than a propagation dependent threshold. For example embodiments applied to RAB or RC drilling to a depth of less than around 100m, as occurs for overburden removal in open cut coal mining in the Bowen Basin of Queensland, Australia, and in other geologically similar environments, may require no repeater.

The down-hole sensor may be proximal to a drill bit of the drill string. The receiver may be at the surface proximal to an entrance to the borehole. The sensor may be a borehole radar to look ahead of the drillbit, such as is disclosed in International Patent Application No. PCT/AU2010/000583, the content of which is incorporated herein by reference. Alternatively the sensor may be a borehole radar to look laterally of the drillbit, a pressure sensor to sense pressure externally of the drill, a pressure sensor to sense pressure within the drill at the drill-bit, a temperature sensor, a resistivity sensor, or other type of sensor. Communicated data may convey range to target, torque, thrust, rpm, rock resistivity, natural gamma, heading, or the like.

The drill string may in some embodiments be of substantially constant internal diameter.

The present invention recognises that during the drilling process the increasing borehole length, the increasing number of drill rods and joints, and changes in the medium being drilled, among other factors, will lead to variations in the propagation conditions of the drill string waveguide. Signal energy carried in the at least one electromagnetic propagation mode present in constrictions of the drill string may be coupled into higher order modes and carried at different speeds through wider parts of the drill string, affecting the signal in a manner akin to multipath interference. Consequently, the present invention provides for the transmitted signal to exploit bandwidth expansion schemes such as adaptive frequency hopping techniques to ensure that spectral regions of least attenuation are substantially continually sought and used for data transmission.

Brief Description of the Drawings

An example of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates the elements of a typical rotary air blast (RAB) drill;

Figure 2 illustrates mounting of a transmitter and antenna in a down-hole drilling sub-adapter in accordance with one embodiment of the invention;

Figure 3 illustrates passage of wave-guided electromagnetic energy between narrow (single-moded) and broader (over-moded) portions of a drill string acting as a cylindrical waveguide in accordance with the present invention;

Figure 4 further illustrates the construction of the lower part of a drillstring; Figure 5 illustrates modifications to optimise mode conversion at constrictions in the waveguide utilised in some embodiments of the invention;

Figure 6 illustrates another embodiment utilising cylindrical waveguide propagation within the body of each drill rod and utilising coaxial wire propagation through portions of drill string joints too narrow to support cylindrical waveguide propagation;

Figure 7 illustrates use of an accelerometer mounted over one leg of the tricone; a Rogowski toroid on one leg; and an air-jet wire to build up cylindrical images of the rock;

Figure 8 illustrates down-hole power generation by a small turbine in an air-jet duct;

Figures 9a and 9b illustrate electromagnetic propagation past a counter bore relief space in the absence and presence, respectively, of a cylindrical pipe insert, in accordance with further embodiments of the invention;

Figure 10 is a spectral plot illustrating the transmission characteristics of one, two, and three 12m drill rods, respectively, in accordance with the present invention;

Figure 1 1 a illustrates mode conversion in a transition from an 80mm ID joint to a 172mm ID drill pipe, and Figure 1 1 b illustrates the effects of interference between co-existing propagation modes, in accordance with the present invention;

Figure 12 illustrates the spectral propagation characteristics within a drill rod, above the TE-n mode cutoff frequency, in accordance with the present invention;

Figure 13a illustrates a CST simulation of a Gaussian pulse of 200MHz bandwidth centred at 2.45GHz, entering a 12m long, 6⁵/₈" ID, 8⁵/₈" OD drill rod through an 80mm joint as TE-n, illustrating the reverberant temporal behaviour of each mode of propagation, and Figure 13b is a CST simulation of reflection |Sn(oo)| & transmission |SI₂((JO)| through the drill rod, in accordance with the present invention;

Figure 14a illustrates an experimental setup used to establish channel conditions within a single drill rod, and Figure 14b illustrates simulated and measured results for |S₂I((JO)| from the single drill rod setup of Fig 14a, in accordance with the present invention;

Figure 15 illustrates the surface transceiver antenna being a Yagi-Uda and being positioned within a top saver, in accordance with another embodiment of the invention; Figure 16 illustrates the surface transceiver antenna being a conical double helix and being positioned within a top saver, in accordance with another embodiment of the invention;

Figure 17 illustrates an alternative embodiment in which a surface antenna is a double-X Lorraine-Cross TE-n Yagi-Uda for insertion into a top-saver of a drill-rig; and Figure 18 illustrates a down-hole transceiver configured to be mounted within a stabilizer of a drill-string, in accordance with a further embodiment of the invention.

Description of the Preferred Embodiments

The elements of an RAB drill string are shown in Fig 1. A rotary head 102 drives a spindle adapter 104 and in turn a plurality of drill rods 106 including starter pipe 108. The leading end of the drill string comprises a sub adapter 1 10 and a rotary tricone bit 1 12. The elements screw together to drive mechanical power and cooling/flushing fluids from the rotary head 102 to the bit 1 12. The tubular sections are linked by -18" long throats that typically taper in diameter from the drill pipe's 6 ½" inner diameter (ID) down to throats of typical internal diameters between 3 ½" and 1 ½". In the case of Australian mine blastholes with rotary-air-blast (RAB) rigs; and exploration boreholes with RAB and RC (reverse circulation) rigs, borehole to surface distances are short (typically <60m). RAB and RC drill strings are typically made up of three to five screwed-together ~12m steel rods 106. The present invention recognises that when the RAB or RC drill rods 106 are screwed together, a surface to downhole data channel is created in the resulting metal walled hollow cylinder, the construction of which importantly does not need to interrupt the drillers in any significant way, which is important if use of the invention is to be accepted. The RAB and/or RC cylindrical rods 106 are usually filled with non-conducting compressed air, i.e. they are gas filled and they are able to support a suite of cylindrical waveguide modes, the propagation characteristics of each being largely determined by the dielectric (usually air), the frequency and the conducting tube's internal diameter D (in cm). To drive electromagnetic signals into the waveguide formed by such drill-strings, in one embodiment shown in Figure 2 a quarter wave monopole 202, which is ~1 ¼" long at 2.4 GHz, and ~½" at 5.8GHz, is mounted in the wall of the internal tube within the sub-adapter 1 10, about ¾" (18mm) from the hinge of the butterfly blow-back preventer above the tricone bit 1 12. The butterfly valve is a typical element in RAB drill strings and the like, and comprises a double disc valve. The hinge of the butterfly valve reflects EM energy from the monopole 202 back up the waveguide within the drillstring. The monopole 202 is coupled to a transceiver in a small insert to the Sub Adapter 1 10 and links through the waveguide to a similar transceiver in the rotary head 102. In this embodiment the Sub-Adapter 1 10 has 1 ½" (38mm) throat or constriction. At 5.8GHz only one EM mode is able to propagate along such a 38mm tube: the TE-n cylindrically guided mode.

As a result, radiation that leaves the monopole 202 stabilizes rapidly into the TE-n mode, and starts to climb the 1 ½" (38mm) diameter air-filled tube inside the drilling

Sub-Adapter 1 10. The Sub-Adapter 1 10 is screwed into a 6½" ID drill pipe 108.

During the expansion from 1 ½" (38mm) to 6½" ID diameter (Fig 3) the TE-n mode in the narrower pipe 1 10 couples significant 5.8 GHz energy into two or three propagating modes of the larger pipe 108. The resulting mixture of modes travels along the wider pipe 108, each with its own frequency dependent characteristic set of group and phase velocities. The modes beat together in space, and time. A typical beat pattern, strobed at t=50ns,is illustrated at the top of Fig 3.

Our view of the drill rods 106, 108 is band-limited, in this case to the WiFi band between 5.75GHz and 5.85 GHz. Further, access normally is limited to the ports at either end. The band-limited impulse response Si₂(t), between port 1 on the left and port 2 on the right of the drill rod 108, is plotted in the centre chart of Fig 3. The modulus of its Fourier transform, |S12(oo)| is plotted in the bottom chart of Fig 3. Attenuation aside, the pipe 108 is transparent over much of the spectrum. However over-moding and reverberation incise or notch |S₁₂| , with the effect that a succession of communication channels around 5MHz wide are blocked by destructive interference between the multiple co-existing reverberating modes. For example, a pair of notches occur at 5.8068 GHz and 5.8089 GHz. The present embodiment thus recognises that the internal "cylinder" modes of standard RAB drill pipes are promising candidates for drill-bit to surface communications. Carrier frequencies of 2.4GHz (Bluetooth) and 5.8GHz (WiFi) dictate joint throat diameters of 3 ¼ " and 1 .5" respectively. Losses in steel drill pipes can be expected to attenuate by perhaps 10-15 dB per 12m drill rod. A 60m deep blast-hole drill string might be expected to attenuate a 5.8GHz 100ns pulse by a tolerable 50-75 dB. However, multipath stop-bands may pose a significant obstacle to the use of the longer 10us pulses generated by WiFi & Bluetooth transceivers. The present invention thus further provides for these stop-bands to be avoided by adaptive channel hopping.

Even though carefully designed tapered transitions may help to funnel EM energy, diameter constriction at the joints makes it difficult to transfer electromagnetic power cleanly between successive drill rods 106. The wide-diameter drill pipe bodies are over-moded. Mode converted energy reverberates axially. A fortunate effect exploited by the present invention in some embodiments is that reverberation is limited by losses in the steel, and multi-mode / multipath interference effects are near-confined to individual drill rods by the fact that the narrow-diameter joints are single-moded over critical spectral bands. The throats therefore will act as mode-selective filters between individual drilling rods. The critical mode-selective pass bands depend upon the diameter of the throat of the joint. Usefully, a 1.75" throat is TE^ single moded around 5.8 GHz; similarly a 3.5" throat is TE^ single-moded around 2.4GHz. Fortunately too, modern data communication protocols such as Bluetooth (2.4 Ghz) and WiFi (2.4 & 5.8 GHz) are able to cope with (limited) multipath reverberation. Thus, constrictions between drill-rods joints can act as useful mode selective filters to enable wideband MWD communications in RAB drilling

Adaptive frequency-hopping in such protocols improves resistance to stop bands, by avoiding using those frequencies in the hopping sequence. AFH thus uses only the "good" frequencies, after assessing and avoiding the "bad" frequency channels. The present invention recognises that, in the field of drill-string communications of the present invention, the location of these stop bands may change due to the changing nature of the drill string, for example as drill rods are added to the string throughout the drilling process. The present invention further recognises that measurement while drilling (MWD) and/or logging-while-drilling (LWD) instruments that perform say navigation "look- ahead" functions or are used for rock evaluation e.g. in seismic-while-drilling (SWD); and those that act as BlueTooth or WiFi transceivers, can in some instances be retrofitted to RAB/RC drill rigs without machining special cavities, by using existing interstices between drilling joints such as "counter-bore relief" spaces, the geometry of such spaces being shown at 402 and 404 at upper and middle right in Figure 4.

Furthermore, it is possible to lodge air-blown turbines either in these spaces 402 or 404, or in specially adapted spaces, for example in air-jet orifices of tricone 1 12, in order to generate the 0.5-5 W electrical power that is typically needed to run down- hole electronic MWD/LWD instruments. Thus, the present embodiment further provides a power supply for down-hole electrically powered components. It is noted that tricone bits 1 12 for RAB drilling are often provided with removable automatic non- return butterfly valves 204 to prevent backflow when drilling underwater. Such butterfly valves typically comprise two substantially planar semi-circular portions which during down-hole airflow hinge to an open position seen in Figure 2, and allow the airflow past. In the absence of airflow and presence of fluid pressure in a direction up the drill string, the two portions hinge to a closed position and prevent fluid ingress into the drill. The present embodiment provides for the two portions of the butterfly valve 204 to be twisted (not shown) in a manner to continue to provide this functionality while additionally creating a rotational force during airflow, by acting as aerofoils. The modified butterfly hinge of this embodiment is rotatably mounted upon a central axis coinciding with the drill-string axis, and when caused to rotate by down-hole air flow about the axis, the rotating hinge drives a generator to produce electrical power to power electrical sensors and transmitters proximal to the down-hole valve.

Moreover, in this embodiment the butterfly valve 204 is positioned approximately one quarter of a wavelength below a monopole 202 used by the down-hole sensor to launch signals up the drill-string, as shown in Figure 2. This relative positioning can improve directionality of the monopole antenna 202 so as to preferentially direct electromagnetic energy upwardly along the interior of the drill-string, as is desired.

Alternative embodiments may provide down-hole power by use of batteries, vibrating piezo-electric devices, alternators driven by the drilling action, air-driven turbines (Fig 8) or the like. The down-hole electronics are in this embodiment constructed in a form that is easily retrofitted onto a RAB rig. Figure 4 illustrates two suitable cavities 402, 404 into which the electronics may suitably be fitted in this embodiment. Figure 5 further illustrates the gradated constriction 502 occurring in a drill string at joints between drill rods106. The present embodiment further provides for these flaring portions of the drill string to be lined with dielectric 504 or provided with annular corrugations 506 or ribs 508 in order to optimise electromagnetic mode coupling between the narrow portion of the joint and the broader portion within each drill rod 106, as shown in Figure 5. The right-most portion of Figure 5 illustrates a simulation of fields within such a gradated constriction.

The present embodiment further provides for the down-hole sensors to include an air pressure gauge. The bearings of tricone bits such as bit 1 12 are lubricated by air. To prolong bit life, manufacturers recommend that the drillers maintain a pressure down- hole, immediately above the cones, of 40psi +/- 2psi. To achieve this, the drillers watch a remote surface gauge connected to the top of the drill string, and keep the reading at ~50psi. Thus, the point at which all RAB drillers make continuous critical process control measurements, is remote. The assumption that 50psi top-hole equates to 40psi at the bearings is only true if the rock is uniform and various other assumptions hold true. The present embodiment thus provides more reliable information regarding the true air pressure at the tricone 1 12 bearings by providing pressure measurements obtained proximal to the tricone bit 1 12 and communicated to the surface in accordance with the present invention. Pitot tubes may also be included in order to monitor gas flow tubes within the drill string.

Figure 6 shows another embodiment of the invention. Figure 6 shows a standard drill string joint by which two drill rods are connected. As mentioned in the preceding, the joint creates a constriction in the hollow waveguide. Depending on the signal frequency and throat diameter, the constriction may not support any propagation mode and may therefore obstruct communications. In this example, the wider pipe either side of the constriction has a 6.6 inch internal diameter. The pipe has a 5 inch taper down to a 3.5 inch internal diameter constriction through the joint, which is 20 inches long. Signals at 1 .24 GHz can propagate in a single TE^ mode through the wide section but are cut off by the constriction. As shown in the lower portion of Figure 6, signal propagation past the constriction can be effected in such scenarios by providing a conducting wire 602 through the constriction. The conducting wire 602 is coupled to the cylindrical waveguide on either side of the joint by way of quarter wave stubs 604 which are quarter wavelength (2 ½ inch) monopoles.

Figure 7 illustrates another embodiment of the invention which may be used in conjunction with the previously described embodiments or separately. In the embodiment of Figure 7 a longitudinal wire 702 is positioned within, and used to pass energy down, a tube that is too narrow to support cylindrical guided propagation at the chosen frequency. The narrow tube in question in Figure 7 is one of the three that are cut into the hub of a tricone bit 1 12, to force air to clear cuttings from the tricone rollers. The wire 702 is connected, in a similar manner to that shown in Fig 6, to a quarter-wave monopole 704 which appears as a vertical stub in Figure 7. The monopole captures 704 signals from the cylindrical waveguide and conveys the field through the narrow tube, to illuminate the hole exterior to the drill, which usually will comprise the drill cuttings. The wire 702 will be held centrally within the narrow tube by the Bernoulli effect arising from the significant air flow. The tricone bit 1 12 typically rotates at 4 revolutions per second, as it cuts downwards at around a meter a minute. As a result, the wire 402 of Figure 7 that protrudes from the host air-hole moves helically. The guided EM reflection from the wire 702 can be plotted in three dimensions, to yield a near three dimensional microwave resistivity image of structures through which the tricone 1 12 passes. In further embodiments of the invention, a surface radar transmitter may inject a radar pulse into the drill-string waveguide, for propagation to the drilling end of the drill-string and reflection off sensor components, with a radar receiver at the surface receiving any reflection. In such embodiments sensor components at the drilling end of the drill- string may be passive, or may operate on very low power, and may merely function to alter the resistivity of a half wave reflector at the drilling end of the drill-string waveguide. The manner in which the surface-originating radar signal reflects off the reflector will influence the signal received by the radar receiver. Thus, information may be retrieved from a passive sensor in this manner. The sensor may for example be a pressure sensor proximal to bearings of a tricone bit, enabling pressure measurements to be obtained which more accurately reflect the actual air pressure in the tricone chamber. As noted previously such measurements are of importance as effective lubrication requires a difference of between 38psi-42 psi between the tricone's air chamber and the exhausts at the ends of the rollers. Additionally or alternatively, the sensor may be a resistivity sensor, for example, of the type shown in Figure 7.

In such embodiments, the broadband radar pulse acts as a spread spectrum signal, at least a portion of which will navigate the waveguide even in the presence of stop bands. Thus, the broadband pulse can be considered to seek out the spectral regions of least attenuation to effect communications along a borehole in the presence of a drill-string. Moreover, such embodiments may be advantageous in conveying information along a drill-string as the received signal arrival time can be known in advance based on the hole depth and drill-string propagation qualities, with such arrival time information assisting data extraction as will be known to a person of skill in the field.

In Figure 8 an air turbine 802 is shown for powering down-hole electronics. Turbine 802 comprises a 2 inch diameter and 2 inch long 6V 3A DC dynamo positioned in an air chamber within the drill bit 1 12 above the rollers. Another option is for a turbine 804 of around 1 inch diameter to be positioned within a tricone air duct or orifice. The air duct which houses the turbine 804 may be enlarged, relative to the other ducts to maintain an equal supply of air through each duct. Figure 9a illustrates a time series of a simulation of electromagnetic propagation past a counter bore relief space 902 in the absence of a cylindrical pipe insert. As can be seen a significant portion (around 50% at 2-4 GHz) of the EM power is reflected due to the counter bore relief space 902. In contrast, in the simulation of Figure 9b in which a cylindrical pipe insert 904 is present and smoothly bridges the counter bore relief space, transmission past the counter bore relief space is significantly improved. The cylindrical insert 904 may be positioned by filling the counter bore relief space 902 with filler, glue or epoxy. Alternatively the cylindrical pipe insert 904 may comprise a stop configured to abut the constriction of the drill string joint so as to suitably position the cylindrical pipe insert 904 across the counter bore relief space 902. Fig 10 shows transmission characteristics (transfer functions |SI₂((JO)|) 1002, 1004 and 1006 of a RAB drill string, built up from one, two, and three standard 12m long RAB drill rods, respectively, showing that wideband communications can be retrofitted simply into blast-hole operations. As can be seen, adding two rods to the first rod adds 25dB of loss. That is, a six rod drill string (usually the longest used in RAB drilling) could incur losses of around 72dB. However, the AFHSS system used is designed to cope with drillbit-to-surface wireless channel losses of up to 108 dB even at 500kb/s, indicating that communications are indeed possible in accordance with the present invention.

Figure 1 1 a illustrates mode conversion arising at a transition from an 80mm joint to a 172mm drill-pipe, the mode conversion mostly being between the TEn mode of the 80mm ID pipe and the TEn and TM₀i modes within the 172 mm ID pipe. The shape of the pipe transition influences the output mode mix that makes up the emerging travelling interference pattern. Figure 1 1 b illustrates how interference arises between the multiple modes shown in the 172mm ID pipe section in Fig 1 1 a.

Fig 12 illustrates the received signal strength measured for propagation through an actual single drill-rod between 2 GHz and 6 GHz, measured with a spectrum analyzer. Propagation ceases as expected when the TE1 1 mode cuts off below 2.1 GHz in the narrower joint throat section of the rod. A recognition of the present invention is that the 2.4-2.5 GHz ISM band fortunately resides above the 2.1 GHz cutoff of the RAB drill rod throat. As can be seen destructive interference, largely between TE-n & TM₀i modes, incises or notches the spectrum. Losses of 10-15dB are seen along this single rod, but a further recognition of this invention is that in the ISM band such losses are tolerable for many drilling applications.

Fig 13a illustrates a CST simulation of a 200MHz BW 2.45GHz Gaussian pulse, entering (at top left of the figure) a drill rod through an 80mm joint, as TE-n moded energy. This converts to TEn+TM₀i moded energy in the 172 mm ID and 1 1 meter long central portion of the drill rod. These modes travel the 1 1 metre length of 172 mm ID rod in 70ns (TE^) & 103ns (TM₀i) respectively. The energy from these modes reconverts into the 80mm bore TE^ mode on the right side of figure 13a, as a 33 ns doublet. This doublet modulates |SI₂((JO)| at ~60MHz. Significant reverberation and multiple transits can be seen within the 172 mm ID pipe in the subsequent time period after 70 ns. Fig 13b is a CST simulation of reflection |Sn(oo)| 1302 & transmission |Si₂(oo)| 1304 in a 12m long, 6¾" ID, 8¾OD steel drill rod, terminated at either end by 80mm ID throats. Destructive interference of dominant modes, mostly but not only TE-n and TM₀i, can create 40dB deep notches, the depths & locations of which will change as drill rods age, as rods are added/removed, as the drilling fluid varies, and as differing formations are penetrated. This again illustrates the need to use adaptive frequency hopping in order to continually avoid spectral notches which exist at varying spectral locations over time.

Figure 14a illustrates an experimental setup used to establish channel conditions within a single drill rod 1402. This experiment obtains the Transfer function |S12(oo)|, for an 80mm ID, 350mm long thin-walled tube. Quarter-wave (30.94mm) monopoles, drive a 6.5m long, 155mm ID galvanized steel "model" drill string, under control of a DNT2400 1404 at each end, with the DNT2400 1404 at the remote end simply returning the same signal back through the pipe 1402. The DNT2400 is a low cost, long range, multi-purpose, multi-function 2.4 GHz frequency hopping OEM RF module. Figure 14b illustrates simulated results for the setup of Fig 14a as continuous lines, obtained by making three sweeps across the band shown with a spectrum analyser. These simulations again show notching in the spectrum arising from destructive multi- mode interference. Figure 14b also illustrates RSS values which were experimentally measured at each of 37 channels within the ISM band (2409-2467 MHz), the RSS values being indicated by squares, and being in close agreement with the simulations.

Therefore, experiments have confirmed that the meter-long joints that link the eleven- meter pipes in a drill-string are single moded carriers of TE-n signals in the ISM band at 2.4GHz. Experiments have also confirmed that the 1 1 m long 172mm ID pipe sections between joints are over-moded, and have further confirmed that destructive interference between modes can cause 40dB notches at varying frequencies in the transfer function. Despite these difficulties, this invention realises that higher modes, rather than single modes, can in fact be exploited to channel wideband data through such a sporadically over-moded waveguide.

Trials of the invention indicate losses of ~12dB per drill rod in the drill-string, such losses being tolerable at blast-hole drilling depths which are short relative to oil-fields. Moreover the present invention exploits the availability of robust, small, intelligent, frequency hopping transceivers with adaptive ability, and recognises that such adaptive frequency hopping enables a channel to be established even despite the multimodal interference and the changing nature of such interference as each drill rod is added to the cascade of over-moded air chambers that make up a blast-hole drill string.

Thus, the present invention recognises that cylindrical air-filled channels inside RAB drill strings can be used without modification to retrofit a rugged, operationally unintrusive wideband communication link from drillbit to driller.

Some preferred embodiments of the invention thus require no wiring along the drillstring in order to effect a borehole communication channel and thus may, in contrast to some previous approaches, be particularly useful in RAB drilling operations or the like in which blast-hole rods are driven at rapid rates, such as a meter a minute, in which drill rods are re- & de-coupled of the order of every 10 minutes, and wear out and are replaced around every 2-3 months.

It is noted that polarisation extinction may occur at times during drilling operation. Indeed, drill strings rotate many times during operation, at speeds up to 240 rpm or more. Polarisation extinction may occur at certain angles, which may be fixed, for example when the rods are screwed together, or may be encountered at certain times during every rotation of the drill string. To avoid loss of transmission arising from polarisation extinction, preferred embodiments of the invention provide for at least one of the down-hole transmitter and surface receiver to be equipped with two or more antennas offset in the azimuthal dimension. For example a surface receiver may be equipped with two antennas, each comprising a TE^ quarter wavelength monopole, spaced apart by 90 degrees in the azimuthal dimension and spaced apart by a quarter wavelength along the axis of the drillstring. Alternatively, one or both transceivers may be coupled to antenna elements, for example double helix conical spirals, that transduce cylindrically polarized wavefields. In these or other embodiments the antenna of the receiver and/or transmitter may comprise Yagi-Uda reflector/director elements.

In further preferred embodiments of the invention, signals may be coupled from internally of a drill string to external receivers by way of a passive relay, the passive relay comprising a monopole or Yagi-Uda antenna or the like internally of the drillstring, with a connector passing from the internal component radially out through the drillstring wall to an external monopole or the like. The external monopole or antenna then excites wireless signals to be detected by a nearby transceiver. In such embodiments, all surface components of the transmission system mounted upon the drillstring, and rotating with the drillstring, can be passive and not require a power source, while the nearby transceiver can be fixedly mounted and not rotate with the drillstring. While the passive relay may result in signal strength losses, of around 15dB in one configuration, such losses may in some embodiments be acceptable and be preferable to the difficulties of mounting active surface components within/upon a rotating drillstring. Figure 15 illustrates another embodiment in which the surface transceiver antenna is positioned within a top saver 1500. The antenna comprises a Yagi-Uda 1502 electrically fed by, and mechanically tethered by, a coaxial cable 1504 extending along and within a water injection pipe 1506. This embodiment recognises that such water injection pipes, which are used in normal RAB drilling to moisten the airflow and reduce dust, present a possible avenue for positioning the surface antenna within the drillstring so as to be able to communicate with down-hole components. It is also recognized that some water-injection pipes are effective conductors, for example because they are steel-reinforced, and that they can, for this reason, act as imperfect coaxial central conductors, and assist in conveying EM energy & data for example up through the motor to the top of the drill string, after the manner illustrated in Fig 15.

Figure 16 illustrates yet another embodiment of the surface antenna, comprising a double-helix conical conductor 1602 with suitable cross-over 1604 at the tip. This antenna 1602 can launch broad-lobed circularly polarized broadband radiation down (below) the apex of the cone, and conversely receive radiation from the same direction, being axially down along the drillstring as is required. Modelling indicates that a six turn conical double helix, in a 80mm tube, will launch near-circularly polarized TE-n modes down the tube with a front-to-back ratio of about 14dB. Moreover, this antenna 1602 is advantageous in requiring only a single hole 1606 to be formed through the wall of the top-saver in order to feed the antenna 1602 from an external passive monopole or Yagi-Uda 1608. At the top of the spiral 1602, at the "feed" point, the inner of one helical coil is soldered/connected to the outer of the second helical coil. A single hole 1606 through the wall of the drillstring or top-saver 1610 represents a minimal retrofit to existing drill hardware, improving the ease of take-up of such embodiments of the present invention.

Figure 17 illustrates an alternative embodiment of a surface antenna, referred to herein as a double-X Lorraine-Cross TE-n Yagi-Uda. This antenna 1700 is formed with and fed from an internal, integral slit balun, the antenna having two orthogonal cross pairs 1710, 1720. Their arms are deliberately of different lengths, and may be curved. This asymmetry is designed to encourage the net TE^ vector to swing in angle over the ISM band, in order to combat polarization extinction by working constructively with frequency hopping. Such an antenna can be fed in through existing surface structures of the drill string , thus requiring no creation of feed holes in the wall of the top-saver or any drill string component.

Fig 18 illustrates a down-hole transceiver 1802 configured for mounting in a stabilizer 1810 of a drill string. Apart from one or more monopoles extending radially inwards from the transceiver to effect communications up the drill string, the transceiver components all reside annularly around the hollow core, to permit air flow to continue substantially unobstructed. These components include batteries for power, an AFHSS controller, radar/sensor controllers, sensor data acquisition processors, and the like, all housed within a sturdy casing to withstand the rigours of the downhole environment.

In the embodiments shown and other embodiments of the present invention, the down- hole sensor with which communications is established may, for example, comprise one or more of: a seismic while drilling sensor utilising acoustic, sonic, and/or ultra-sonic spectra to guide a drill bit to a seismically-defined point of penetration on a target; a resistivity sensor through which to log lithology at or ahead of the drill bit, resistively at DC, inductively at relatively low frequencies, or using dielectric displacement currents, as in an evanescent field radar;

a pressure sensor to aid in controlling the RAB air compressor and matching air flows to the needs of bailing cuttings;

a vertical accelerometer and/or a geophone to observe and control the brittle fracture of hard rock, to monitor the state of individual teeth on the tricone bit rollers, to assess the regrinding and clearance of cuttings, and/or to secure a reference train for seismic-while-drilling operations;

a circumferential accelerometer and/or a geophone to observe and control the torsional shearing of soft rocks and clays;

a natural gamma detector; or

other type of sensor.

Some portions of this detailed description are presented in terms of algorithms and symbolic representations of operations on data bits within a computer. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self- consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner well understood by those skilled in the art. The data structures where data is maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various of the acts and operations described may also be implemented in hardware.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the description, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1 . A method for communicating along a drill string within a borehole, the method comprising:

2. The method of claim 1 wherein the wireless signals are in a frequency band selected to optimise propagation along a drill string waveguide, such that at least one electromagnetic propagation mode propagates through constrictions of the drill string, and such that multi-mode propagation is permitted through wider diameter sections of the drills string.

3. The method of claim 1 or claim 2 wherein the wireless signals are between substantially 300 MHz and 5.8 GHz.

4. The method of claim 3 wherein the wireless signals are in a band centred at substantially 1 .24 GHz and are launched in air filled tubes of substantially 6 ½" ID so as to give rise to a TE-n mode.

5. The method of claim 3 wherein the wireless signals are in a band centred at substantially 300 MHz and are launched in tubes filled with high permittivity dielectric and of substantially 6 ½" ID or less, so as to give rise to a TE-n mode.

6. The method of any one of claims 1 to 3 wherein the adaptive frequency hopping is effected by use of the protocol of Bluetooth^®, version 1 .2 or later, the wireless signals being in the 2.4 GHz ISM band (2400 - 2483.5 MHz).

7. The method of any one of claims 1 to 3 wherein the adaptive frequency hopping is effected by use of the WiFi communications protocol with adaptive frequency hopping, in drill rods with sections that narrow to about 1 ½" ID, utilising a band centred between substantially 5.6 GHz and 5.8 GHz to give rise to a TE-n mode for single mode propagation through narrow sections.

8. The method of any one of claims 1 to 7, further comprising mounting a surface coupler within a top-saver of the drill string.

9. The method of any one of claims 1 to 8, further comprising mounting a surface coupler within a cross-over sub of the drill string.

10. The method of any one of claims 1 to 9, further comprising mounting a down- hole coupler within a stabiliser of the drill string.

1 1. The method of any one of claims 1 to 10, further comprising mounting a down- hole coupler within a drill-bit of the drill string.

12. A transmitter for communicating along a drill string within a borehole, the transmitter comprising:

coupling means for launching wireless signals within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide; and

an adaptive frequency hopping module operable to identify and utilise spectral regions which propagate most effectively along the interior of the drill string waveguide.

13. The transmitter of claim 12 comprising a down-hole coupler, and the transmitter being configured for mounting within a stabiliser of the drill string.

14. The transmitter of claim 12 or 13 comprising a down-hole coupler, and the transmitter being configured for mounting within a drill-bit of the drill string.

15. The transmitter of claim 13 wherein the down-hole coupler comprises a monopole positioned substantially between an eighth and a quarter of a wavelength above a non-return butterfly valve of the drill, so as to use the butterfly valve as a passive reflector/director to direct EM transmission up the drill string.

16. The transmitter of any one of claims 12 to 15, wherein in order to avoid or minimise the effects of polarisation extinction during each rotation of the drill-string, the transmitter comprises at least one of: orthogonally mounted coupler elements; and a coupler having a circularly polarised transmission pattern.

17. A receiver for receiving communications along a drill string within a borehole, the receiver comprising:

18. The receiver of claim 17 wherein the coupling means comprises a double helix conical antenna.

19. The receiver of claim 17 wherein the coupling means comprises a Yagi-Uda antenna.

20. The receiver of claim 19 wherein the coupling means comprises a double-X Lorraine-Cross Yagi-Uda antenna shaped to combat polarisation extinction.

21. The receiver of claim 17 wherein the coupling means comprises at least one of: a probe coupler, a loop coupler, a slot coupler, a coil coupler, an antenna, and a resonator.

22. The receiver of any one of claims 17 to 21 , being a surface receiver, and comprising a passive repeater configured to couple signals between the interior of the drill string and a suitable external wireless coupler positioned outside the drill string, the external wireless coupler being configured for wireless communication with a nearby active transceiver unit.

23. The receiver of any one of claims 17 to 22, wherein in order to avoid or minimise the effects of polarisation extinction during each rotation of the drill-string, the receiver comprises at least one of: orthogonally mounted coupler elements; and a coupler having a circularly polarised transmission pattern.

24. The receiver of any one of claims 17 to 23, wherein the coupling means comprises a surface coupler mounted within a top saver of the drill string.

25. The receiver of any one of claims 17 to 24, wherein the coupling means comprises a surface coupler mounted within a cross-over sub of the drill string.

26. A system for communicating along a drill string within a borehole, the system comprising:

a drill string formed of one or more drill rods;

a surface transceiver having coupling means for launching and/or receiving wireless signals within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide, and having an adaptive frequency hopping module operable to identify and utilise spectral regions which propagate most effectively along the interior of the drill string waveguide; and

a down-hole transceiver having coupling means for launching and/or receiving wireless signals within the drill string in a manner to give rise to at least one electromagnetic propagation mode arising from the drill string functioning as a waveguide, and having an adaptive frequency hopping module operable to cooperate with the adaptive frequency hopping module of the surface transceiver.

27. The system of claim 26 wherein the down-hole transceiver resides in a stabiliser of the drill string.

28. The system of claim 26 wherein the down-hole transceiver resides in a drill-bit of the drill string.

29. The system of claim 27 or claim 28 wherein the down-hole transceiver takes an annular form to permit substantially uninterrupted drill string airflow through a hollow core of the down-hole transceiver.

30. The system of any one of claims 26 to 29 wherein the coupling means of the surface transceiver comprises a double helix conical antenna.

31 . The system of any one of claims 26 to 29 wherein the coupling means of the surface transceiver comprises a Yagi-Uda antenna.

32. The system of any one of claims 26 to 29 wherein the coupling means of the surface transceiver comprises a double-X Lorraine-Cross Yagi-Uda antenna.

33. The system of any one of claims 26 to 29 wherein the surface transceiver further comprises a passive repeater configured to couple signals between the coupling means in the interior of the drill string and a suitable external wireless coupler positioned outside the drill string, the external wireless coupler being configured for wireless communication with a nearby active transceiver unit.

34. The system of any one of claims 26 to 33 wherein the surface transceiver resides in a top saver of the drillstring.

35. The system of any one of claims 26 to 34 wherein the surface transceiver resides in a cross over sub of the drillstring.