DE3100460A1 - METHOD FOR SEISMOLOGICALLY DETERMINING THE GEOLOGY OF A FLOE - Google Patents

Description

Applicant: COAL INDUSTRY (PATENTS) LIMITED, Hobart House, Grosvenor Place, London SW 1X 7AE, England

Method for the seismological determination of the geology of a Seams.

DESCRIPTION

The invention relates to a method for determining the geology of a seam by means of a seismic method. The invention is used in the detection and location of defects in the seam by the method and the Measurement operations are carried out in the seam itself.

In particular, the present invention has application to coal seams, but is not to seams of these properties limited and can be applied directly or with modifications to other seams.

About 80 % of the coal mined underground in Great Britain comes from the mining of the track. This mining process is highly capital intensive. It takes several months to build a coal mining front and the cost of capital is substantial. A significant proportion of the UK longwall faces have small but serious geological voids. These imperfections almost inevitably interrupt production. In a large number of cases, unexpected geological errors lead to the premature abandonment of mining fronts. Defects of this type also usually affect the load-bearing capacity and reliability of the hydraulically supported

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Hanging walls. A defect found directly in advance also brings the risk of flooding and / or fire with himself. As a result, it is at most desirable to know the geological structure of a seam before mining. There are a number of techniques for studying underground geology. Direct procedures include drilling Boreholes - both vertically from the surface and horizontally from the coal mining front itself. Indirect or geophysical methods include seismology, geoelectric gravity and those with geophysical Methods related to drilling techniques. Of these known methods, the one carried out from the surface of the earth leads Seismology for the best results in terms of subterranean structures. Big flaws can be detected in this way, but small, but equally significant imperfections are overlooked can. For this reason, seismology has gone underground.

It has been known since about 1963 that the efficiency of the mechanized Mining can be improved by using seismological techniques known from the surface of the earth underground can be applied. In a series of tests carried out in the Saar region, it was clearly shown that a coal seam carries or channeled seismic waves. This has led to the development of an area of seismology which referred to as "in-seam seismology".

The in-seam seismology differs from the usual surface seismology in two main aspects. First are channel waves dispersive. The signal from a quasi-impulsive source, for example a small explosion, is gradually phase encoded as it is propagated. The original sharp signal spreads through the coal as it wanders. Second are the environmental conditions can be described as extremely rough underground. Great Britain has the strictest safety regulations which with regard to the use of underground systems

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be applied. The possibilities of movement are limited. In order to achieve a practical production system, an underground technology must be as simple as can be made possible.

A general method of applying in-seam seismology consists in placing geophones in short horizontal boreholes in the coal seam. Small explosive charges are made one after the other ignited from other wells in the coal seam. The signals received by the geophones are recorded, using a conventional seismic recording system is, for example, a Sercel SN338B, with 12 channels and a recording speed of 0.5 m / sec. A such a system and method for evaluating the results is disclosed in British patent applications 79/36412 and 79/36413 disclosed and described. A disadvantage of this method is that coal production must necessarily be halted while the wells are being drilled and the measurement is carried out. The loss of production can in some cases make up the bulk of the cost of the Display measurement.

The present invention is based on the object of creating an improved method of in-seam seismology, which does not make it necessary to stop coal production while measurements are being taken.

According to the invention, this object is achieved in a method for the seismological determination of the geology of a seam which a sound signal is generated at a part of the seam and the signal or a reflection of the signal with a detector at another part of the seam is detected and the received signal to achieve a recording or map of the seam is processed, essentially solved by the fact that the generated noise signal through the Effect of a cutting or mining process in which the seam is generated.

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The generated noise signal is preferably obtained from the noise generated by a cutting or mining machine which reacts with the mineral in the seam to break the mineral out of the seam. The signal is generally continuous Signal and is preferably interrupted in order to effectively form the signal of a point source which is responsible for the position of the mining machine is characteristic at every point in time during the mining process. It can be alike a multitude successive signals generated at different points during a degradation process can be used and if the one mining operation is done along a straight line, the position of the machine can easily be identified directly a number of consecutively spaced points along the line are related.

The detection device is preferably a geophone or an array of geophones, either in the cutting plane of the machine or along a path at an angle are arranged to the cutting plane, for example in a line or a tunnel in front of the cutting machine. As one Alternatively, a coal seam can have the geophones placed in contact with the hanging wall of the seam behind the cutting machine be.

In the following the invention is exemplified with reference to the drawings illustrated.

In the drawings shows:

1 shows a schematic arrangement of geophones and a cutting machine in a coal seam;

FIG. 2 is a view corresponding to FIG. 1; FIG. and

3 shows a digital signal pattern which is typically generated according to the method of the invention.

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It will be apparent that various types of coal cutters are available on the market, but all of them Machines have violent physical contact with any part of the machine with the mined coal. the existing energy is used in the breaking of coal, in the generation of noise and in the generation of seismic waves destroyed. In the context of the present invention, a coal cutting machine can act as a generator of seismic energy, possibly with a low efficiency. Due to the nature of coal mining, this source is more seismic Waves over the entire mining front.

It is well known that a traveling source with a single detector is equivalent to a single source with a fine grid of detectors is. This procedure, or this equivalence situation, applies to passive solar and air traffic generally confirmed in radar technology with synthetic diaphragms.

These methods use a signal processing technique to transform an effectively long antenna from an actually short one to generate moving antenna. Such a system improves the azimuth resolution and enables focusing on any specified area. In one mode of operation, the transmitter and receiver are in the same place in the Space (what is called the receiver's moving coordinate system). The radar or echo sounder reflection is thereby It is estimated that a matched filter will be applied to the return signal. The filter itself is created by the original signal of the transmitter and this signal can be assumed to be known. The signal processing can therefore take place in the real-time process.

A coal mining cutter can be used in a similar manner. There are a number of differences, however. First of all, the function of the source is seismic, unknown and largely uncontrollable. Further, the movement is not continually. Stopping points across the mining front are frequent.

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Third, the receiver is not attached to the cutting machine. Coupling detectors to the coal is difficult. They can be attached to the coal and run therefore not with the recipient. Fourth, there is no direct need for real-time processing.

The system therefore consists of a few detectors (geophones) G, which are arranged in the coal or its surroundings. the Geophones are coupled to any conventional seismic signal recorder. The seismic observer records the signals received by the geophones for the various positions of the cutting machine. The local The cutting machine's relationship to the mining face must be noted while the seismograms are being drawn up. Since the seismograms are only a few seconds long and the cutting machine itself moves slowly, can these are regarded as being essentially stationary during each recording.

A variety of signal processing methods are possible, depending on the number of seismic signals recorded depends.

With separate reference to Fig. 1, this shows a schematic geometric arrangement of a first processing scheme, which assumes that the coal cutting machine moved in a substantially straight line along a coal mining front, which at its ends by the reference numerals A, B which denote the routes in a mine. It is assumed that at a certain moment the cutting machine ' the position C is located and that with respect to the length of the mining front, the next geophone is G_. Furthermore, Assume that there are enough geophones to confirm the correctness of assuming the distance CG is small compared to the length of the array of geophones. (In Fig. 1 the arrangement of the geophones is schematic. They do not have to be arranged on the dismantling front. They can be attached to the hanging wall.) That of any geophone

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G. signal received at a point i is g. (t, y) when

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at a point in time t the cutting machine is in a position y, which is measured from the reference point A along the y-axis. We define P (x, y) as any point in the mapping space. The delay time T ^ is given by the formula

where L ^ is the distance PG ₁ , M is the distance CP and ν is the speed of the seismic waves. The composite signal g is formed by summing and by varying χ and y.

g (t, y _c ) = ψ _Βι (t - T ₁ , y _c ) ψ S ₁ (t - Vy ₀ )

The summation takes place over all geophone signals with the exception of g ", which corresponds to the geophone that the cutting machine on next lies. This process generates an artificial signal which corresponds to a recording position C. The value g can then be determined by cross-correlation using known techniques with g, where g is the matched filter for the composite signal is. The cross-correlation can be recorded using a range variable. This process is repeated using different positions of the cutting machine and adding up the individual records, in order to generate an overall record.

A second scheme can also be described with reference to FIG. 1. In this case there are only two geophones at the points G ^ and G ₂ , which _{record signals g 1} (^ y ₀ ) ^and g £ ("^ y ₀ ). The signals g ₁ and g ₂ are subjected to the cross-correlation and the Points of the peak values are recorded. This is repeated for different positions of the cutting machine. Corresponding arrival times of the peak values determined by cross-correlation are recorded over positions of the cutting machine. Those signals which are generated by random noises,

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are also distributed according to the random distribution. Those signals that are generated due to seismic waves those along the line A-B of the coal seam v / other lie on a straight line parallel to the y-axis. The signals which are generated due to the reflection of a rectilinear defect lie on a straight line, which in any Angle to the y-axis. These points can be lumped into a straight line by the known method least squares is used. Consequently, there is a specific one for a specific position y of the cutting machine Arrival time T of the peak values from the cross-correlation, which corresponds to the reflection of the defect (if available). The signal g ^ (t) (say) can then use the summation technique as described in UK Patent Applications 79/36412 and 79/36413. The signal gp (t + T) is also subjected to the same procedure (assuming that G “is closer to the cutting machine). the Recording is repeated for all recorded locations of the cutting machine.

In the third scheme, only a single geophone can be used, using the second method described above Can be used when two consecutive recordings with the cutting machine in the same position be performed.

In each of the methods described above, it may actually be necessary to use the signals from previous processing before the techniques described are applied. For example, the distance of the 50 Hz signals in many cases necessary to separate the secondary noise signals from the main signals. Furthermore, if the seismic energy on a bandwidth centered around a trigger frequency may be beneficial, heterodynamize the signals with respect to the baseband and to use a lowpass filter. In addition, the speed may initially be unknown, but it can be determined by optimizing the recording.

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The coal mining process in a particular coal seam will now be described with reference to FIG. The coal seam is determined by the boundaries WXYZ. The coal is mined in longwall dismantling, with the mining front progressing VJY to XZ and with stretches WX and YZ defining stretches separated by 232 meters of coal. Geophones are located at _{points designated G 1} and G ₂ and the geophone signals are recorded when the cutting machine is located at points C ₁ , C ₂ ... C ₁₂ . The raw recording contains 50 Hz signals and a significant proportion of noise signals that were generated by mining machines other than the cutting machine. However, the cutting machine is the only part that moves along the mining front. A typical record obtained on one of the geophones is illustrated in FIG. Each recorded signal is preprocessed by normalization, filtering out the 50 Hz signals by a Gaussian filter in the frequency domain and finally by a low-pass filter in order to reduce the high-frequency noise signals. The preprocessed signals for the various positions of the cutting machine, denoted by C, are then subjected to the cross-correlation on the two geophones and the envelope of the cross-correlation function is calculated in order to determine the maxima. Most correlations have a pronounced maximum. 4 shows the plot of the maximum correlation delay times versus the difference in distance m from the cutting machine to the two geophones. Obviously, an increase in the delay time can be seen with increasing distance 85 Hz produces v / earth.

This shows that it is possible to follow the movement of the cutting machine along the coal mining face by recording the signals at two locations on the geophones. There is thus an identifiable seismic signal generated by the cutting machine.

It is obvious that the invention makes it possible to continue production while the measurement is taking place, whereby production is actually an integral part of measurement. Few geophones are in the area of the coal mining front arranged. The seismic source is the coal cutting machine itself, which moves along the mining front. There is a Number of possible data processing schemes depending on the number depend on the geophones used. Three methods, namely the use of one, two and a few (12) geophones have been explained in more detail in the above description, but it is obvious that the invention does not apply to them Numbers is limited. The invention is based on the cutting machine sending an identifiable seismic signal or generates what has been proven in the present case.

All features and advantages of the invention which emerge from the description, claims and drawings, including Constructive details and spatial arrangements can be used both on their own and in any Combination be essential to the invention.

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Claims (10)

BROSE BROSE ^ge D-8023 Munich Pullach. Wiener Str . IeI <08?> 7 9 <30 Π Tele «5 212 147 bros d: Cables: -Patentibus» Munich Applicant: COAL INDUSTRY (PATENTS) LIMITED, Hobart House, Grosvenor Place, London SW 1 X 7AE, England ^ wW / r- γ Your mark: Day: January 7th, 1981 Ca s e 4177 Date: DBr / hö PATENT CLAIMS (1.) Procedure for the seismological determination of the geology of a seam in which a sound signal is generated at a part of the seam and the signal or a reflection of the signal is detected at another part of the seam and the received signal is processed to make a record of the seam, characterized in that the generated noise signal is generated by the action of mining work on the seam. 2. The method according to claim 1, characterized in that that the noise signal is generated by a cutting or cutting machine (C), which with the in the seam existing mineral reacts to the breakdown of the mineral from the seam. 3. The method according to claim 1 or 2, characterized in that the signal is generated continuously and that the method further includes the step of collecting the signal for only a short period of time, to achieve the effect, the signal as 130051/0404 Identify the signal emanating from a point source which corresponds to the position of the mining machine at any point in time of the degradation process is characteristic. 4. The method according to claim 3 _f, characterized in that the collection of the signals is repeated for different positions of the mining machine. 5. The method according to any one of the preceding claims, characterized in, that a plurality of devices (G) is used to detect the signal. 6. The method according to claim 5 »characterized in that the used devices (G) are arranged at intervals along a mining front, which is driven by the mining machine (C) is dismantled. 7. The method according to claim 5, characterized in that the devices used (G) behind the mining machine and in Contact with a hanging wall previously exposed by the machine (C) are arranged and that the devices (G) in be provided essentially parallel to the direction of movement of the machine (C). 8. The method according to claim 5 »characterized in that the devices (G) arranged in the seam along a line which is at an angle to the line defined by the direction of movement of the machine (C). 9. The method according to any one of claims 1 to 4, characterized in that that a single detection device (G) is arranged to receive the signals from the mining machine, if this is in different positions (C1 ... C12). 10. The method according to any one of the preceding claims, characterized characterized in that from the detected signals any noise or unwanted signals before the processing of the Signals to generate the recording are filtered out. 130051 / (UCU