Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Reexamination Certificate
2002-01-15
2003-07-15
Le, N. (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
C324S338000
Reexamination Certificate
active
06593746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ground-penetrating radars and coal mining, and more particularly to methods and systems for radio-imaging anomalous geology in coal bed deposits.
DESCRIPTION OF THE PRIOR ART
Given the growing need to produce cleaner run-of-mine (ROM) coal, improved information about the seam geology and coal quality in coal mine operations is of great value. The identification of anomalies is important so planning operations keep productivity high and cut cleaner coal. For example, the identification of a paleochannel anomaly before mining began would allow longwall panels to be laid out to avoid crossing it.
A natural coal seam waveguide occurs in layered sedimentary geology because the electrical conductivity of the bounding shale, mudstone, and fire clay, ranges between 0.01 and 0.1 Siemens per meter (S/m) (100 and 10 ohm-meters). Inside, the conductivity of the coal is near 0.0005 S/m (2,000 ohm-meters). The 10:1 conductivity contrast enables the waveguide travel of electromagnetic waves within the coal bed.
The electric field (E
z
) component of a traveling electromagnetic wave (EM) is polarized in a vertical direction and the magnetic field (H
y
) component is polarized horizontally in the seam. The energy in this part of the EM wave travels laterally in the coal seam from the transmitter to the radio imaging receiver. There is a horizontally polarized electric field (E
x
) that has zero value in the center of the seam and reaches maximum value at the sedimentary rock-coal interface. This component is responsible for transmission of the electromagnetic wave signal into the boundary rock layer. The energy in this part of the EM wave travels vertically in the coal deposit.
The magnitude of coal seam radiowave decreases as it travels along the waveguide. The attenuation rate and cylindrical spreading of wave energy in the coal seam are two of the things at work that attenuate the travelling signals. The cylindrical spreading factor is
1
r
,
where r is the distance from the transmitting to receiving antenna. This factor compares with the non-waveguide far-field spherically spreading factor of
1
r
.
Thus, for a given separation of one-hundred meters, the magnitude of the seam EM wave decreases by ten in a waveguide, and by a factor of one-hundred in an unbounded media. So one advantage of sending signals down a seam waveguide is the much greater travel distance. Another advantage is that the traveling electromagnetic wave predominantly stays within the coal seam, the main item of interest.
A coal-seam electromagnetic wave is very sensitive to changes in the waveguide geometry and materials. The radiowave attenuation rate (decibels per 100 feet) and phase shift (electrical degrees per 100 feet) were determined by Dr. David Hill at the National Institute for Science and Technology (NIST). Dr. James Wait was the first to recognize that natural waveguides exist in the earth's crust. Both are Fellows in the Institute of Electrical and Electronic Engineers. The science underlying the traveling of an electromagnetic wave in the coal seam waveguide is well known. The engineering of both the crosshole transmitter and receiver has also been developed to a high degree of performance. The transmitter and receiver are synchronized to enable the measurement of total path phase shift from the transmitter to the receiver location. The total phase shift measurement is a distinguishing factor in the radio imaging-IV instrumentation. Prior art radio imaging instrumentation measures only the change in magnitude of radiowave, e.g., attenuation, when propagating in the coal seam waveguide.
The path length or distance a radio signal travels can be determined from attenuation measurements. In uniform-construction waveguides, the path is a straight line. The straight line path is an assumption used in the Algebraic Reconstruction Technique (ART) tomography algorithm. But radiowaves are refracted near significant geologic anomalies causing the travel path of the radiowave to bend and be longer than in the uniform waveguide case. This bending cannot be accounted for in ART processing and accounts for this distortion in the ART tomography processing algorithm. By measuring the total path phase shift, the bending effect can be accounted for in a new type of tomography reconstruction algorithm called Full-wave Inversion Code (FWIC) radio imaging IV acquires data that can be processed in the Sandia National Laboratories' WAIC algorithm. The effect of attenuation in the waveguide is to reduce the magnitude of the electromagnetic wave along the path.
Under sandstone sedimentary rock, the attenuation rate increases because more of the radio imaging signal travels vertically into the boundary rock, i.e., leaks from the waveguide. If water is injected into the coal, then clay in the coal causes the electrical conductivity to decrease and the attenuation rate/phase shift to increase.
The attenuation rate/phase shift rapidly increases with decreasing seam height. This coal seam thinning can be easily detected with radio imaging. The above graphical presentation of coal seam waveguide attenuation and phase constants represents the science factor in the art and science of interpreting radio imaging tomographic images. Higher attenuation rate zones suggest that either the coal seam boundary rock is changing, the seam is rapidly thinning, or/and water has been injected into the coal seam. Drilling and radar would determine the exact cause of the anomalous seam condition. This advance in the state of the art in mining would reduce both risk and cost in coal extraction.
Faults and dykes cause reflections to occur in the waveguide. The reflections can appear as excess path loss. Total phase shift measurements are useful in detecting reflection anomalies.
The predominating electromagnetic wave propagation mode in layers of coal is a “seam wave”. Such is polarized in the plane of the seam, and has a uniform, polarized electric field orthogonal to the layer. In horizontal lying coal bed layers, the magnetic field will be horizontally polarized with the same field strength across a vertical cross-section. The electric field is vertically polarized. A third electric field is polarized in the horizontal plane and is maximum value at each boundary of the seam.
The horizontal component of the electric field is null near the physical center of the coal seam, albeit if the lower-resistivity boundary layers above and below are about equal in their respective material electrical resistivities.
The present inventor, Larry G. Stolarzyck, has described methods and equipment for imaging coal formations in geologic structures in many United States Patents. Some of those Patents are listed in Table I, and are incorporated herein by reference.
TABLE I
Patent No.
Issued
Title
U.S. Pat. No.
Mar. 18, 1986
Continuous Wave Medium Frequency
04577153
Signal Transmission Survey Procedure
For Imaging Structure In Coal Seams
U.S. Pat. No.
Sep. 01, 1987
Electromagnetic Instruments For
04691166
Imaging Structure In Geologic
Formations
U.S. Pat. No.
May 03, 1988
Method For Constructing Vertical
04742305
Images Of Anomalies In Geological
Formations
U.S. Pat. No.
Jun. 28, 1988
Method For Remote Control Of A Coal
04753484
Shearer
U.S. Pat. No.
Oct. 11, 1988
Radio Communication Systems For
04777652
Underground Mines
U.S. Pat. No.
Nov. 07, 1989
Medium Frequency Mine Communi-
04879755
cation System
U.S. Pat. No.
Nov. 06, 1990
Long Range Multiple Point Wireless
04968978
Control And Monitoring System
U.S. Pat. No.
Feb. 19, 1991
Method And Apparatus For Detecting
04994747
Underground Electrically Conductive
Objects
U.S. Pat. No.
Nov. 19, 1991
Long Feature Vertical Or Horizontal
05066917
Electrical Conductor Detection
Methodology Using Phase Coherent
Electromagnetic Instrumentation
U.S. Pat. No.
Dec. 10, 1991
Method And Apparatus For Measuring
05072172
The Thickness Of A Layer Of Geologic
Material Using A Microstrip Antenna
U.S. Pat. No.
Feb. 11, 1992
Long Range Multiple Point Wireless
05087099
Control And Mo
Aurora Reena
Le N.
Main Richard B.
LandOfFree
Method and system for radio-imaging underground geologic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for radio-imaging underground geologic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for radio-imaging underground geologic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3051724