WO2016183656A1

WO2016183656A1 - Systems, devices, and methods for detecting coal deposits using electrical measurements

Info

Publication number: WO2016183656A1
Application number: PCT/CA2015/000321
Authority: WO
Inventors: Gianfranco Morelli; Douglas LA BRECQUE; Federico FISCHANGER
Original assignee: Geostudi.Ca Inc.
Priority date: 2015-05-21
Filing date: 2015-05-21
Publication date: 2016-11-24

Abstract

Disclosed are systems, methods, and devices for detecting characteristics of a coal deposit in a formation. There is provided a plurality of electrodes; a signal transmitter that transmits a signal into the formation, by way of a pair of transmitting electrodes; a signal receiver that receives a signal from the formation, by way of a pair of receiving electrodes, the received signal reflective of induced polarization caused by the transmitted signal; and at least one processor configured to: process the received signal to measure an induced polarization response of the coal deposit; and based on the induced polarization response, determine at least one characteristic of the coal deposit, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

Description

SYSTEMS, DEVICES, AND METHODS FOR DETECTING COAL DEPOSITS USING ELECTRICAL MEASUREMENTS

FIELD

[0001] This disclosure relates to geophysical surveying, and more particularly to detection of characteristics coal deposits using electrical measurements.

BACKGROUND

[0002] Coal is deposited in layered sequences along with shale, sandstone, and limestone. In typical coal sequences, the electrical resistivity of the coal is much higher than surrounding subsurface features. So, measurements of electrical resistivity may be used to determine a location, thickness, and continuity of a coal seam. However, certain subsurface features such as, e.g., intrusions and limestone beds, can present electrical resistivity measurements similar to those of coal seams. Accordingly, it may be difficult to distinguish coal seams from such other features.

[0003] Therefore there is a need for improved technology for detecting coal deposits and/or determining characteristics of coal deposits.

SUMMARY

[0004] In accordance with an aspect, there is provided a system for detecting characteristics of a coal deposit in a formation. The system includes a plurality of electrodes; a signal transmitter configured to transmit a signal into the formation, by way of a pair of transmitting electrodes of the plurality of electrodes; a signal receiver configured to receive a signal from the formation, by way of a pair of receiving electrodes of the plurality of electrodes, the received signal reflective of induced polarization caused by the transmitted signal; and at least one processor configured to: process the received signal to measure an induced polarization response of the coal deposit; and based on the induced polarization response, determine at least one characteristic of the coal deposit, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

[0005] In accordance with another aspect, there is provided a method of detecting characteristics of a coal deposit in a formation. The method includes: transmitting a signal into the formation by way of a plurality of transmitting electrodes; receiving a signal from the formation by way of a plurality of receiving electrodes, the processing the received signal to measure an induced polarization response of the coal deposit; and based on the induced polarization response, determining at least one characteristic of the coal deposit, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

[0006] In accordance with another aspect, there is provided a device for detecting characteristics of a coal deposit in a formation. The device includes: a data communication interface configured to receive measurements of an induced polarization response in the formation; and at least one processor in communication with the data communication interface. The at least processor is configured to: process the received measurements to determine at least one characteristic of a coal deposit in the formation, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

[0007] Many further features and combinations thereof concerning embodiments described herein will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE FIGURES

[0008] In the figures,

[0009] FIG. 1 is a high-level block diagram of a system for detecting characteristics of coal deposits, exemplary of an embodiment;

[0010] FIG. 2 is a schematic diagram of a data acquisition subsystem of the system of FIG. 1 , exemplary of an embodiment;

[001 1] FIG. 3 is an overhead map view of the data acquisition subsystem of FIG. 2, exemplary of an embodiment; [0012] FIG. 4 is a plot of an example transmitted current waveform, and an example received voltage waveform, exemplary of an embodiment; [0013] FIG. 5 is a high-level block diagram of a processing subsystem of the system of FIG. 1 , exemplary of an embodiment;

[0014] FIG. 6 is a high-level block diagram of hardware components of the processing subsystem of FIG. 5; [0015] FIG. 7 is a schematic diagram of a data acquisition subsystem of the system of FIG. 1 , exemplary of an embodiment;

[0016] FIG. 8 is a schematic diagram of a data acquisition subsystem of the system of FIG. 1 , exemplary of an embodiment;

[0017] FIG. 9 is a flowchart of exemplary blocks performed at the system of FIG. 1 , exemplary of an embodiment;

[0018] FIG. 10 is an example image showing induced polarization effects in a formation, exemplary of an embodiment.

DETAILED DESCRIPTION

[0019] FIG. 1 illustrates a detection system 100 configured to delineate coal deposits (e.g., a coal seam) in a formation, exemplary of an embodiment.

[0020] As detailed herein, detection system 100 delineates coal deposits by detecting their characteristics using measurements of induced polarization (IP) for coal deposits. As detailed herein, the IP measurements may be time-domain IP measurements or frequency- domain IP measurements. In some embodiments, detection system 100 may be configured to detect characteristics of coal deposits using IP measurements without resistivity measurements. In some embodiments, detection system 100 may be configured to detect characteristics of coal deposits using IP measurements in combination with measurements of resistivity of coal deposits. Detected characteristics may include, for example, quality, size, and location of coal deposits. [0021] As detailed herein, detection system 100 implements the inventors' discovery that coal deposits exhibit a large IP response, which is used to detect the location of coal deposits. Detection system 100 also implement's the inventors' further discovery that the magnitude of an IP response is approximately proportional to coal quality, which is used to detect the quality of coal deposits.

[0022] As illustrated, detection system 100 includes a data acquisition subsystem 1 10 configured to obtain electrical measurements for coal deposits (e.g., IP measurements and resistivity measurements), and a processing subsystem 120 configured to process the electrical measurements to determine the aforementioned characteristics of those coal deposits.

[0023] FIG. 2 illustrates data acquisition subsystem 1 10 deployed to detect characteristics of coal deposits at a formation 2, exemplary of an embodiment.

[0024] As illustrated, data acquisition subsystem 1 10 includes a plurality of cables 1 1. Each cable 1 1 may be a multi-conductor cable allowing for interconnection with a plurality of electrodes (e.g., surface electrodes 13 or underground electrodes 14). In an embodiment, a cable 1 1 may include a bundle of conventional electrical resistance tomography (ERT) conductors.

[0025] At least one cable 1 1 may be interconnected with a plurality of surface electrodes 13, which may be disposed along a ground surface above formation 2. At least one other cable 1 1 may be interconnected with a plurality of underground electrodes 14, which may be disposed underground in formation 2, e.g., when a cable 1 1 is lowered into a borehole 12. While in such locations, electrodes 13 and 14 may transmit signals to and receive signals from formation 2 in manners disclosed herein.

[0026] Each electrode 13/14 may be formed of metal, carbon, or metal/carbon filled composites. An electrode may also be formed of a metal core surrounded by a solution containing dissolved salts of the same metal as the core, which may be referred to as a non- polarizing electrode.

[0027] Boreholes 12 and electrodes 13/14 may be provided to span a surface area and borehole depth corresponding to a desired survey region. The number and/or spacing of boreholes 12, and the number and/or spacing of electrodes 13/14 may be selected according to desired survey characteristics such as, e.g., a desired survey resolution.

[0028] For example, the resolution of detection system 100 varies in an inversely proportional manner with separation between boreholes 12, e.g., such that survey resolution decreases as borehole separation increases and survey resolution increases as borehole separation decreases. Further, survey resolution increases as electrode separation decreases, and decreases as electrode separation increases. Survey resolution may also be impacted by a survey aspect ratio, i.e., the depth of the boreholes to which electrodes 13 are extended divided by borehole separation. In particular, resolution in particular survey regions (e.g., central regions) tends to decrease as the aspect ratio decreases, and tends to increase as the aspect ratio increases.

[0029] For example, electrodes 14 may be provided along cable 1 1 at intervals corresponding to an estimated thickness of a coal seam (e.g., coal seam 17). In one example application, electrodes 14 may be provided along cable at regular intervals of approximately 5 metres. For thicker coal seams, the separation between electrodes 14 may be increased. For thinner coal seams, the separation between electrodes 14 may be decreased.

[0030] For example, separation between electrodes 14 may be decreased by interconnecting additional electrodes 14 to a cable 1 1. Of course, the separation between electrodes 14 may also be decreased while keeping the number of electrodes the same.

[0031 ] Alternatively or additionally, the separation between the boreholes may be reduced to allow fewer electrodes 14 to be used while maintaining the survey resolution.

[0032] Alternatively or additionally, overlapping datasets may be obtained for a cable 1 1 using multiple survey configurations. For example, a first dataset may be collected, and then a second dataset may be collected upon moving a cables upwards (or downwards) in the boreholes by a fraction (e.g., 1/2, 1/3, etc.) of the electrode separation.

[0033] In the depicted embodiment, a cable 1 1 is interconnected with thirty-two electrodes 14. However, in other embodiments, the number of electrodes 14 per cable 1 1 may vary. For example, the number of electrodes may vary according to the size of a survey, the depth of a borehole, the thickness of a coal seam, and the separation between the boreholes.

[0034] Similarly, although a cable 1 1 is interconnected with four electrodes 13 in the depicted embodiment, the number of electrodes 13 per cable 1 1 may vary in other embodiments, e.g., according to the size of the survey, the separation between boreholes, etc.

[0035] As will be appreciated, increasing the number of electrodes 13/14 may increase data acquisition time, and decreasing the number of electrodes 13/14 may decrease data acquisition time. [0036] In other embodiments, detection system 100 may be configured to use only underground electrodes 14 such that electrodes 13 may be omitted. However, configuring detection system 100 with at least one cable 1 1 interconnected with surface electrodes 13 improves survey resolution relative to configurations without surface electrodes 13.

[0037] In accordance with one example application of data acquisition subsystem 1 10, boreholes 12 may be provided at locations 8, 9, 10. The locations of boreholes 12 may be arranged in a triangular pattern, as shown in FIG. 3, which provides an overhead view of the formation of FIG. 2. The locations of boreholes 12 may be selected to be adjacent an expected location of a coal seam, or to intersect an expected location of a coal seam.

[0038] Each of the boreholes 12 may be separated by a suitable distance, e.g., approximately 100 metres. As shown, surface electrodes 13 may be disposed at locations proximate to one or more of the boreholes locations, e.g., in between locations 9 and 10.

[0039] Although three boreholes 12 are shown, in other applications, a greater number or a fewer number of boreholes 12 may be used. For example, although three boreholes 12 may be used to facilitate a three-dimensional interpretation of survey data, two boreholes 12 may be used to facilitate a two-dimensional interpretation, which may be subject to approximations and be less accurate. Further, in other applications, the locations of boreholes 12 may be arranged into other pattern, e.g., along a line, in a rectangular pattern, a circular pattern, a trapezoidal pattern, etc. [0040] As shown, cables 1 1 are interconnected with one or more multiplexers (e.g., multiplexers 24 and 25). The multiplexers may be controlled by an acquisition unit 23 to selectively connect acquisition unit 23 with electrodes 13 and 14, by way of a cables 1 1. As detailed herein, acquisition unit 23 is configured to transmit signals (e.g., current waveforms) into formation 2 by way of a selected pair of electrodes 13/14, and to receive signals (e.g., voltage waveforms) from formation 2 by way of a selected pair of electrodes 13/14. During operation, multiplexers 24/25 may be controlled by acquisition unit 23 to change the combination of electrodes used to transmit/receive signals.

[0041 ] Acquisition unit 23 may be located on the surface. Although, only one acquisition unit 23 is depicted for simplicity, data acquisition subsystem 1 10 may include multiple acquisition units 23. Conveniently, multiple acquisition units 23 may operate in parallel to improve data acquisition throughput, e.g., by simultaneously acquiring data using multiple pairs of transmitting and receiving electrodes.

[0042] Each acquisition unit 23 includes a current source, and is configured to transmit a controlled current waveform into formation 2. This current waveform is transmitted into formation 2 through a pair of transmitting electrodes, as selected by acquisition unit 23 using multiplexer 24/25. The particular current waveform that is transmitted is detailed below, and may depend on whether data acquisition subsystem 1 10 is configured to obtain time-domain IP measurements or frequency-domain IP measurements. [0043] Acquisition unit 23 may select the transmitting electrodes to include surface electrodes 13, underground electrodes 14, or a combination thereof. Further, acquisition unit 23 may select the transmitting electrodes to include underground electrodes 14 from separate boreholes 12. In one example, acquisition unit 23 may select a pair of transmitting electrodes 15 to include two underground electrodes 14 in the same borehole 12. In another example, acquisition unit 23 may select a pair of transmitting electrodes 16 to include two underground electrodes 14 in separate boreholes 12 (e.g., boreholes at locations 8 and 9). In yet another example, acquisition unit 23 may select a pair of transmitting electrodes 33 to include a surface electrode 13 and an underground electrode 14. In a further example, acquisition unit 23 may select a pair of transmitting electrodes 34 to include two surface electrodes 13. [0044] During operation, acquisition unit 23 may select multiple pairs of transmitting electrodes, formed using various combinations of electrodes 13/14. For each pair of transmitting electrodes, a current waveform is transmitted into formation 2.

[0045] Upon transmitting a current waveform into formation 2, a corresponding signal is received from formation 2 at acquisition unit 23, by way of a selected pair of receiving electrodes, as selected by acquisition unit 23 using multiplexer 24/25. A received signal may be reflective of induced polarization in the formation, e.g., of a coal deposit. A received signal may also be reflective of resistivity in the formation, e.g., of a coal deposit. A received signal may be a voltage signal, from which resistivity, induced polarization effects (e.g., chargeability and/or phase) may be determined.

[0046] In a manner similar to selection of transmitting electrodes, acquisition unit 23 may select the receiving electrodes to include surface electrodes 13, underground electrodes 14, or a combination thereof. Acquisition unit 23 may select the receiving electrodes to include underground electrodes 14 from separate boreholes 12. In one example, acquisition unit 23 may select a pair of receiving electrodes 21 to include two underground electrodes 14 in the same borehole 12. In another example, acquisition unit 23 may select a pair of receiving electrodes 20 to include two underground electrodes 14 in separate boreholes 12 (e.g., boreholes at locations 8 and 9). In yet another example, acquisition unit 23 may select a pair of receiving electrodes 22 to include a surface electrode 13 and an underground electrode 14. In a further example, acquisition unit 23 may select a pair of receiving electrodes to include two surface electrodes 13.

[0047] Selection of pairs of transmitting/receiving electrodes may take into account an expected depth of a coal deposit. For example, although some electrical measurements may be made using surface electrodes 13, it may be desirable to use, additionally or alternatively, underground electrodes 14 when the coal deposit is expected to be deeper.

[0048] As noted, acquisition unit 23 may be configured to obtain time-domain induced polarization (TDIP) measurements and/or frequency domain induced polarization (FDIP) measurements. For both TDIP and FDIP, a low frequency electric current is injected into a formation 2 using a pair of transmitting electrodes 13/14. In an embodiment, the current may have a frequency in the audio to sub-audio range, e.g., approximately 0.01 Hz to 1000 Hz. Acquisition unit 23 controls the magnitude and timing of the current, as detailed herein.

[0049] The injected current may create IP effects in formation 2. As used herein, IP effect refers to low frequency / low time-period intrinsic properties of subsurface materials to store and release energy. The IP effect may be measured from a voltage signal received from formation 2, as received at acquisition unit 23.

[0050] FIG. 4 depicts an example current waveform that may be injected into a formation and an example voltage waveform that may be received from the formation, for obtaining TDIP measurements in accordance with an embodiment. When obtaining TDIP measurements, the current waveform may be injected as a series of rectangular pulses, and in particular, a series of repeated positive and negative pulses. In the depicted example, the waveform includes an on-time period, T-i and an off-time period, T₂, which are of equal length. However, ^ and T₂ need not have equal length, and other choices for and T₂ are possible. [0051] Various electrical measurements may be obtained from the voltage waveform that is received from the formation. For example, resistivity may estimated by measuring the electrical potential, V_r, while the transmitted current is turned on. In particular, resistivity may be measured by determining an average voltage over a time window that that begins at time T₃ and extends over a length of T₄. In an embodiment, the sum of the times T₃ and T₄ is less than T-i . T₃ may be chosen to be long enough to minimize inductive and capacitive effects within the transmitting and receiving instruments of acquisition unit 23, the cables 1 1 which connect acquisition unit 23 to electrodes 13/14, and the earth itself.

[0052] As shown, the current waveform does not reach its peak (desired) magnitude instantaneously. In particular, as a result of inductive effects in instruments and cables, the current magnitude increases approximately linearly, over a period ranging from a few microseconds to a few milliseconds, until it reaches the desired magnitude. During this period, time varying voltages in a transmitter conductor of cable 1 1 will capacitively induce potentials through insulation of the transmitting conductor into the receiving conductors in cable 1 1 , which may be referred to as capacitive coupling. In a similar fashion, the current flow within the transmitter conductor in cable 1 1 will inductively induce time varying potentials into both earth itself and receiving conductors in cable 1 1 , which may be referred to as inductive or electromagnetic coupling.

[0053] Measurements of induced polarization are also obtained from the received voltage waveform. When obtaining TDIP measurements, IP effects may be measured during the period T₂ while the transmitted current is turned off. As turning the current off may also create inductive and capacitive effects, the induced voltage V,, is measured during a time window of length T₆ which is after a delay of T₅.

[0054] Inductive and capacitive effects tend to decrease rapidly in time, and IP effects decrease relatively slowly. As such, multiple induced voltage measurements may be obtained using multiple time windows, and the measurements may be compared to determine if T₅ has been selected to be sufficiently large enough such that the induced voltage measurements are substantially free of coupling effects.

[0055] Since voltages induced by IP effects are small compared to the voltages measured during the on-time (resistivity) period, IP effect may be expressed as chargeability in units of millivolts per volt:

Chargeability (mV/V) = 1000 or in units of milliseconds as

Chargeability (milliseconds) = 1000 T₆ [0056] When obtaining FDIP measurements, a different current waveform may injected into the formation. For example, the current waveform may be a sinusoidal waveform having a controlled magnitude. The IP effect may be measured from the amplitude of an induced voltage received from the formation, as well as a phase shift in the induced voltage relative to the injected current. [0057] The current waveform may also be a square wave, which can be considered as a summation of a primary sinusoid and a series of harmonics. The harmonics can be separated from the primary sinusoid by filtering the received signal. FDIP measurements may be collected using a series of waveforms with different primary frequencies, and/or by estimating the phase and amplitude changes of the various harmonics of a square wave. Such measurements provide an estimate of the spectral characteristics of a formation subsurface. The spectra may then be matched to intrinsic properties (e.g., grain size) of the polarizable media in the formation.

[0058] Compared to TDIP measurements, FDIP measurements may be more susceptible to interference from inductive and capacitive effects. Accordingly, it may be more desirable to use TDIP measurements for down-hole surveys (e.g., with a pair of electrodes in a single borehole) and cross-hole surveys (e.g., with a pair of electrodes spanning two boreholes), in which signals transmitted to and received from a formation may be carried in cables 1 1 over long, and closely-spaced conductors. In contrast, it may be more desirable to use FDIP measurements for surface surveys (e.g., using surface electrodes 13), in which signals transmitted to and received from a formation may be relatively short, and transmitting and receiving conductors may be spaced apart from each other. [0059] Electrical measurements, e.g., IP measurements and resistivity measurements, are determined at data acquisition unit 23. A data set may be collected for electrical measurements obtained from various combinations of transmitting electrodes and receiving electrodes, selected in manners described herein. Measurement data may be stored at acquisition unit 23 and later transferred to processing subsystem 120 for processing, e.g., by way of computer-readable media. In an embodiment, measurement data may be transmitted to processing subsystem 120, e.g., by way of a wired or wireless link, or a network of wired and/or wireless links. For example, measurement data may be transmitted to processing subsystem 120 in real-time or near real-time.

[0060] In addition to the measurement data, acquisition unit 23 may also record the time of the measurements, the location of the measurement electrodes, the magnitude and time of the current created by the transmitter, and the estimates of the errors in the measurements. Further, acquisition unit 23 may also record repeated measurements such as reciprocal measurements (i.e., measurements where the transmitting and receiving electrode locations are interchanged) or other redundant measurements that can be used to estimate error levels in the data. All such data may be included in the data sets transferred to processing subsystem 120.

[0061] FIG. 5 illustrates processing subsystem 120, exemplary of an embodiment. As illustrated, processing subsystem 120 includes a data pre-processing module 124, an image module 126, an estimation module 128, and an estimation database 130.

[0062] Pre-processing module 124 receives measurement data 122, which includes electrical measurements obtained for a formation, e.g., resistivity measurements and IP measurements. Measurement data 122 may, for example, be received from data acquisition subsystem 1 10 (FIG. 1 ). Pre-processing module 124 processes measurement data 122 to estimate noise levels, and to remove outliers (e.g., values that differ radically from related data points). Pre-processing module 124 may also perform other types of pre-processing, e.g., clustering, filtering, etc. The pre-processed data is passed to image module 126 and/or estimation module 128.

[0063] Image module 126 processes the data from pre-processing module 124 to generate two or three dimensional images of resistivity and/or IP effects. FIG. 10 is an example three dimensional image showing chargeability in a formation. As illustrated, the location and contours of coal deposits may be seen. The positions of electrodes are shown as lines of circles.

[0064] In an embodiment, image module 126 may generate these images by applying an inversion technique (e.g., a multi-dimensional inversion technique) to create one or more model fitted to the resistivity and/or IP measurements. In an embodiment, image module 126 may be configured to apply an inversion technique adapted from a conventional ERT inversion technique described in William Daily, Abelardo Ramirez, Andrew Binley, and Douglas LaBrecque (2005) 17, "Electrical Resistance Tomography— Theory and Practice", Near-Surface Geophysics: pp. 525-550. Other inversion techniques may also be used such as, e.g., Quasi-Newton approximation, stochastic inversion, decoupled DC resistivity- induced polarization inversion, or the like. [0065] The generated images facilitate identification of certain characteristics of coal deposits in the formation, e.g., faults, washouts, intrusions, or other disruptions in the coal deposits. Such identification may be performed manually or automatically using the generated images. For example, automatic identification of characteristics may be performed by applying various image processing and machine vision techniques known to those of ordinary skill in the art.

[0066] Estimation module 128 processes the data from pre-processing module 124 to estimate characteristics of coal deposits in the formation. Estimation module 128 performs such estimation using data reflective of characteristics of a variety of formation features, as may be stored in estimation database 130. For example, estimation database 130 may store a plurality of records of formation features. These records may, for example, include tabulated values from previous coal sites, which may have similar features as the site at which detection system 100 is deployed. So, the records may include data covering similar coal types and measurement strategies (e.g., TDIP or FDIP, base frequency, window delay, window type, electrode placement, electrode selection). The particular measurement strategy used may affect the magnitude of the IP measurements.

[0067] These records may also include data obtained from on-site calibrations. The records may also include electrical measurements for other subsurface materials (e.g., ash or inorganic materials). [0068] Estimation module 128 generates a measurement signature using the obtained measurement data (as received from pre-processing module 124). The deposit signature includes IP measurements for a given coal deposit. The measurement signature may also include resistivity measurements for that deposit. The measurement signature may also include descriptors of the measurement strategies used. The measurement signature may also include descriptors of the type(s) of coal being characterized. The measurement signature may also include other data in the data sets received from data acquisition subsystem 10.

[0069] Estimation module 128 compares the measurement signature to one or more records stored in estimation database 130 to determine one or more characteristics of the given coal deposit. The characteristics may include the quality of the coal deposit. The characteristics may also include, for example, size and location of the coal deposits.

[0070] In an embodiment, such comparison may take advantage of the inventors' discovery that coal has an intrinsic IP response (e.g., chargeability or phase) for measurement data collected in the low audio to sub-audio range (e.g., approximately 0.01 Hz to 1000 Hz), and that the IP (either FDIP or TDIP) response of coal is substantially higher than background values. In an embodiment, such comparison may take advantage of the inventors' discovery that the IP response of coal is largest for high quality coal and decreases in an approximately linear fashion with increases in ash content. [0071 ] Electrical resistivity is poorly correlated with coal quality. In the depicted embodiment, detecting coal characteristics using IP measurements (instead of or in addition to resistivity measurements) provides an ability to detect coal quality. Further, in the depicted embodiment, detecting coal characteristics using IP measurements may provide more accurate estimates of the location, extent, and quality of coal compared to detecting coal characteristics using resistivity measurements alone.

[0072] Processing subsystem 120 may be embodied in a variety of devices, such as a personal computer, workstation, server, portable computer, mobile device, personal digital assistant, laptop, tablet, smart phone, etc., or a combination of these.

[0073] FIG. 6 is a block diagram depicting hardware components of processing subsystem 120, exemplary of an embodiment. As illustrated, processing subsystem 120 includes at least one processor 130, memory 132, at least one I/O interface 134, and at least one network interface 136.

[0074] Each processor 130 may be any type of processor, such as, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, or any combination thereof.

[0075] Memory 132 may be any type of electronic memory that is located either internally or externally such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDRO ), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. In an embodiment, measurements database 128 (FIG. 5) may reside in memory 132. [0076] Each I/O interfaces 134 enables processing subsystem 120 to communicate with input and output devices, e.g., peripheral devices or external storage devices. Such peripheral devices may include one or more input devices, such as a keyboard, mouse, camera, touch screen and a microphone, and may also include one or more output devices such as a display screen (with three-dimensional capabilities) and a speaker. In an embodiment, an I/O interface 134 may function as a data communication interface allowing processing subsystem 120 to receive measurement data 122, e.g., from computer-readable media.

[0077] Each network interface 136 enables processing subsystem 120 to communicate with other components (e.g., data acquisition subsystem 1 10) to exchange data with other components, and to access and connect to network resources, by way of a network or networks. The network(s) may include any type of network capable of carrying data, including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others, and any combination of these. In an embodiment, network interface 136 may function as a data communication interface allowing processing subsystem 120 to receive measurement data 122, e.g., by way of the above-noted network(s).

[0078] In an embodiment, data acquisition subsystem 100 may include hardware components substantially similar to those shown in FIG. 6.

[0079] FIG. 7 illustrates data acquisition subsystem 1 10' deployed to detect characteristics of coal deposits at a formation 2, exemplary of another embodiment. In this embodiment, a single borehole 29 is used. As depicted, underground electrodes 14 may be provided in the formation below the ground surface by lowering a cable 1 1 into borehole 29. The cable may be provided in a fixed position, or moved as described above.

[0080] Further, surface electrodes 13 may be provided on the surface of the formation. Measurement data may be collected using acquisition unit 23, multiplexer 24, and electrodes 13/14 in manners described above. Collected data may be processed at processing subsystem 120 in manners described above. For example, collected data may be processed using a layered or axi-symmetric inversion technique to provide an estimate of the coal location, thickness, and quality within a few meters or tens of meters of a borehole. In an embodiment, processing subsystem 120 may be configured to apply an axi-symmetric inversion technique adapted from a conventional ERT axi-symmetric inversion technique described in Douglas J. La Brecque, Greg A. Oldenborger, Roger Sharpe, and Michael D. Knoll, (2006), "Axi-Symmetric Inversion of Electrical Resistivity Tomography Data to Monitor the Movement of Fluids Injected in Wells", Symposium on the Application of Geophysics to Engineering and Environmental Problems 2006: pp. 1505-1513. [0081 ] FIG. 8 illustrates data acquisition subsystem 1 10" deployed to detect characteristics of coal deposits at a formation 2, exemplary of another embodiment. In this embodiment, again a single borehole 29 is used. As depicted, underground electrodes 14 may be provided in the formation below the ground surface by lowering a cable 1 1 into borehole 29. A small number of electrodes 14 are placed in borehole 29, e.g., as few as two electrodes 14. Cable 1 1 is attached to a suitable set of draw-works 35 which is configured to spool cable 1 1 at a continuous rate downwards from the top, upwards from the bottom, or both upwards and downward in the borehole. Measurement data may be collected as cable 1 1 is spooled. Collected data may be processed at processing subsystem 120 in manners described above. [0082] In this embodiment, when electrode separation is much smaller than a coal seam thickness, but much larger than the borehole diameter, the IP effects and therefore, the coal seam thickness and coal quality can be estimated from a simple plotting of the recorded values. Otherwise, processing described above may be used to estimate coal characteristics while compensating for borehole influences. [0083] The operation of detection system 100 may be further described with reference to the flowchart of FIG. 9, illustrating blocks 900 and onward performed at detection system 100, exemplary of an embodiment.

[0084] Operation begins with deployment of detection system 100. Data acquisition subsystem 1 10 may be deployed at a formation, e.g., as shown in FIG. 2. Processing subsystem 120 may be deployed at the formation or at a location remote from the formation.

[0085] At block 902, a signal (e.g., a current waveform) is transmitted into the formation by way of a plurality of transmitting electrodes.

[0086] At block 904, a signal (e.g., a voltage waveform) is received from the formation by way of a plurality of receiving electrodes. The received signal is reflective of induced polarization caused by the signal transmitted at block 902 (e.g., of a coal deposit). The received signal may also be reflective of resistivity in the formation (e.g., of a coal deposit).

[0087] Block 902 may be repeated for a plurality of signals, transmitted using various selected combinations of transmitting electrodes. Similarly, block 904 may be repeated for a plurality of received signals, each corresponding to one of the transmitted signals. Each of the received signals may be received using selected combinations of receiving electrodes.

[0088] At block 906, the received signal is processed to measure an induced polarization response (e.g., including chargeability, phase, etc.).

[0089] At block 908, at least one characteristic of the given coal deposit (e.g., size, location, quality, etc.) is determined based on the induced polarization response. For example, a measurement signature may be generated and compared to records of known formation features (e.g., as stored in estimation database 130).

[0090] Although data acquisition subsystem 1 10 and processing subsystems 120 have been described as separate components in the depicted embodiments, in other embodiments, these subsystems may be integrated in a single component. For example, in an embodiment, these subsystems may be implemented using a single device. [0091] The embodiments of the devices, systems and methods described herein may be implemented in a combination of both hardware and software. These embodiments may be implemented on programmable computers, each computer including at least one processor, a data storage system (including volatile memory or non-volatile memory or other data storage elements or a combination thereof), and at least one communication interface.

[0092] Program code is applied to input data to perform the functions described herein and to generate output information. The output information is applied to one or more output devices. In some embodiments, the communication interface may be a network communication interface. In embodiments in which elements may be combined, the communication interface may be a software communication interface, such as those for inter-process communication. In still other embodiments, there may be a combination of communication interfaces implemented as hardware, software, and combination thereof.

[0093] The foregoing discussion provides many example embodiments. Although each embodiment represents a single combination of inventive elements, other examples may include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, other remaining combinations of A, B, C, or D, may also be used.

[0094] The term "connected" or "coupled to" may include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0095] The technical solution of embodiments may be in the form of a software product. The software product may be stored in a non-volatile or non-transitory storage medium, which can be a compact disk read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (personal computer, server, or network device) to execute the methods provided by the embodiments.

[0096] The embodiments described herein are implemented by physical hardware, including computing devices, servers, receivers, transmitters, processors, memory, displays, and networks. The embodiments described herein provide useful physical machines and particularly configured hardware arrangements. The embodiments described herein are directed to electronic machines and methods implemented by electronic machines adapted for processing and transforming electromagnetic signals which represent various types of information. The embodiments described herein pervasively and integrally relate to machines, and their uses; and the embodiments described herein have no meaning or practical applicability outside their use with computer hardware, machines, and various hardware components. Substituting the physical hardware particularly configured to implement various acts for non-physical hardware, using mental steps for example, may substantially affect the way the embodiments work. Such computer hardware limitations are clearly essential elements of the embodiments described herein, and they cannot be omitted or substituted for mental means without having a material effect on the operation and structure of the embodiments described herein. The computer hardware is essential to implement the various embodiments described herein and is not merely used to perform steps expeditiously and in an efficient manner.

[0097] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope as defined by the appended claims.

[0098] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps

[0099] As can be understood, the examples described above and illustrated are intended to be exemplary only.

Claims

WHAT IS CLAIMED IS:

1. A system for detecting characteristics of a coal deposit in a formation, the system comprising: a plurality of electrodes; a signal transmitter configured to transmit a signal into the formation, by way of a pair of transmitting electrodes of the plurality of electrodes; a signal receiver configured to receive a signal from the formation, by way of a pair of receiving electrodes of the plurality of electrodes, the received signal reflective of induced polarization caused by the transmitted signal; and at least one processor configured to: process the received signal to measure an induced polarization response of the coal deposit; and based on the induced polarization response, determine at least one characteristic of the coal deposit, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

2. The system of claim 1 , wherein the plurality of electrodes includes at least one electrode disposed in at least one borehole in the formation.

3. The system of claim 1 , wherein the plurality of electrodes includes at least two electrodes disposed in respective at least two boreholes in the formation.

4. The system of any one of claims 1 to 3, wherein the plurality of electrodes includes at least one electrode disposed at a ground surface of the formation.

5. The system of claim 2, wherein the plurality of electrodes is disposed in a single borehole in the formation.

6. The system of any one of claims 1 to 5, wherein the at least one processor is configured to process the received signal to determine resistivity of the coal deposit, and the at least one characteristic of the coal deposit is determined based on the resistivity and the induced polarization response.

7. The system of any one of claims 1 to 6, wherein the signal transmitter comprises a current source, and the transmitted signal is a current signal.

8. The system of any one of claims 1 to 7, wherein the at least one processor is configured to generate an image by processing the received signal, the image reflective of the measurement of induced polarization in the formation.

9. The system of claim 8, wherein the image is generated using multi-dimensional inversion.

10. The system of any one of claims 1 to 9, wherein the transmitted signal has a frequency between approximately 0.01 Hz to 1000 Hz.

1 1. The system of any one of claims 1 to 10, wherein the induced polarization response comprises a measurement of frequency domain induced polarization.

12. The system of any one of claims 1 to 10, wherein the induced polarization response comprises a measurement of time-domain induced polarization.

13. The system of any one of claims 1 to 12, wherein the induced polarization response comprises a measurement of chargeability.

14. The system of any one of claims 1 to 13, wherein induced polarization response comprises a measurement of phase.

15. The system of any one of claims 1 to 14, further comprising: a cable interconnected to at least one of the plurality of electrodes, the cable configured to lower interconnected electrodes into a borehole in the formation.

16. A method of detecting characteristics of a coal deposit in a formation, the method comprising: transmitting a signal into the formation by way of a plurality of transmitting electrodes; receiving a signal from the formation by way of a plurality of receiving electrodes, the received signal reflective of induced polarization caused by the transmitted signal; processing the received signal to measure an induced polarization response of the coal deposit; and based on the induced polarization response, determining at least one characteristic of the coal deposit, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.

17. The method of claim 16, further comprising disposing at least one electrode of the plurality of electrodes in at least one borehole in the formation.

18. The method of claim 16, further comprising disposing at least two of the plurality of electrodes in respective at least two boreholes in the formation.

19. The method of any one of claims 16 to 18, further comprising disposing at least one of the plurality of electrodes at a ground surface of the formation.

20. The method of claim 17, wherein the plurality of electrodes are disposed in a single borehole in the formation.

21. The method of claim 16, wherein the plurality of electrodes are attached to a cable, and the method further comprises moving the cable during said transmitting and receiving.

22. The method of claim 21 , wherein moving the cable comprises at least one of raising and lowering the cable in a borehole in the formation.

23. A device for detecting characteristics of a coal deposit in a formation, the device comprising: a data communication interface configured to receive measurements of an induced polarization response in the formation; and at least one processor in communication with the data communication interface, the at least processor configured to: process the received measurements to determine at least one characteristic of a coal deposit in the formation, the at least one characteristic comprising at least one of a location, a size, and a quality of the coal deposit.