CN111025392B - Coal rock body fracturing crack real-time rapid monitoring and evaluation method utilizing microseismic signals - Google Patents
Coal rock body fracturing crack real-time rapid monitoring and evaluation method utilizing microseismic signals Download PDFInfo
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Abstract
A method for rapidly monitoring and evaluating a coal rock body fracturing crack in real time by using a microseismic signal comprises the steps of firstly, calculating microseismic waveform characteristic parameters such as channel average waveform number, time window maximum amplitude sum, channel average pulse number, time window waveform average duration, time window waveform average dominant frequency and the like in any time window; on the basis of the above, respectively obtaining
A curve,
A curve,
A curve,
Curves and
and according to the size of the longitudinal coordinate value of the curve and the curve change trend, monitoring and evaluating the initiation, expansion and communication of the main fracture of the coal rock body fracturing and the initiation of the branch fracture without carrying out complicated microseismic positioning and seismic source mechanism inversion calculation.
Description
Technical Field
The invention belongs to the technical field of fracture monitoring, relates to monitoring of coal rock body fractures, and particularly relates to a real-time rapid monitoring and evaluation method of coal rock body fractures by using microseismic signals.
Background
In recent years, the fracturing technology is widely applied to the aspects of oil gas and hot dry rock development, mine dynamic disaster prevention and control and the like. The fracturing technology is characterized in that high-pressure fluid is continuously injected into the coal rock body through a fracturing well or a drilling hole, so that the coal rock is fractured and a fracturing crack is generated; and high-pressure fluid is continuously injected, and the cracks can be expanded towards the inside of the coal rock body to form a crack network system mainly comprising main cracks and wing-shaped branch cracks. The rapid real-time monitoring and evaluation of fracture initiation, expansion and expansion of the fracturing fracture have important significance for improving the fracturing effect, optimizing the fracturing scheme design, preventing and treating fracturing-induced dynamic disasters and the like.
The most common coal rock fracturing monitoring method on site is to monitor and evaluate fracturing fractures by observing a pressure curve, however, the coal rock stratum on site is complex and changeable, the pressure curve can only indicate the pressure in a fracturing pipeline, and the pressure in the fractures and at the tips of the fractures in the fracturing process cannot be truly reflected; and the pressure difference with the fracturing crack and the pressure at the tip of the crack is larger, when the fracturing area has special structures such as a latent fault, a hole, a goaf and the like, a pressure curve can be sharply reduced, but the fracturing crack does not crack or expand at the moment, and misjudgment is easily caused in actual operation. Before and after the on-site coal rock body fracturing, checking holes are usually arranged on the periphery of a fracturing drilling well or a drilling hole, and the fracturing process is monitored by comparing the drilling cutting quantity of the checking holes before and after fracturing, the water content of the coal rock body, the stress and the like. Firstly, the method can only concentrate on a certain point in the potential fracturing influence range, cannot continuously monitor all point positions of the whole fracturing area, and cannot continuously monitor in real time; secondly, the method mainly carries out point evaluation on the fracturing affected zone through stress and water content change, and cannot carry out real-time continuous monitoring on fracture initiation and expansion of the fracturing fracture. The fracturing effect is evaluated by monitoring the change of the oil and gas yield after fracturing, and because oil and gas extraction can be carried out after drainage and exhaust for a certain time after fracturing, the method cannot carry out real-time continuous monitoring on the fracturing process; in addition, the method can only indirectly evaluate the fracturing effect through the oil gas yield change after fracturing, and cannot carry out real-time continuous monitoring evaluation on the fracture initiation and expansion process of the fracturing fracture.
In recent years, microseismic technology is adopted to monitor coal and rock fracturing at home and abroad. At present, the microseismic monitoring technology is mainly used for positioning and monitoring the coal and rock body fracturing process by a seismic source positioning method. However, due to the large computation amount of microseismic positioning, the theoretical and technical requirements on a monitoring and computing system and practitioners are high, the monitoring efficiency is low, the monitoring cost is high, and the real-time monitoring is difficult to realize; more importantly, the positioning result of the micro-seismic source fractured by the coal rock mass only can reflect the form of the fractured crack, and the fracture initiation and expansion processes of the main crack and the branch crack of the fractured crack are difficult to be rapidly monitored in real time.
In summary, a method for rapidly monitoring the fracture initiation and propagation of a coal rock body fracture is urgently needed so as to provide a basis for real-time adjustment of fracture parameters in the fracturing implementation process.
Disclosure of Invention
The invention aims to provide a method for rapidly monitoring and evaluating a coal rock body fracturing crack in real time by using a microseismic signal, which has simple steps and is rapid in real time.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a real-time rapid monitoring and evaluation method for coal rock body fracturing cracks by using microseismic signals comprises the following specific steps:
(1) microseismic signal background noise of coal rock mass fracturing environment and induced original microseismic signal acquisition
N microseismic sensors are arranged at the periphery of a coal rock fracturing well or a fracturing drill hole and are sequentially marked as No. 1,2,3, …, i, … and N microseismic sensors (channels). Before the fracturing operation begins, the background noise of microseismic signals of the fracturing environment in a period of time is collected, and the average value of the absolute value of the amplitude of the background noise is calculated
And frequency distribution rules, providing input data for fracturing to induce effective microseismic signal detection; and starting coal rock mass fracturing, and continuously acquiring original micro-seismic signals induced in the whole coal rock mass fracturing process in real time.
(2) Effective microseismic waveform detection induced by coal rock body fracturing and characteristic parameter extraction thereof
Selecting a reasonable time window (time window for short) according to the actual situation of coal rock mass fracturing, recording the time length (duration for short) of the time window as L, and sequentially dividing original microseismic signals monitored in the whole coal rock mass fracturing process into M (j is 1,2,3, …, M) time windows with the time length of L according to the time sequence;
scanning and detecting the original microseismic signals monitored by each sensor in all time windows by adopting a long-short time window method based on instantaneous frequency and energy, and automatically identifying effective microseismic waveforms (effective microseismic waveform signals) induced in the whole process of coal rock fracturing; on the basis, the arrival time, the ending time, the waveform duration, the maximum amplitude and the main frequency of each effective microseismic waveform are respectively calculated; defining the number of effective microseismic waveforms monitored by each microseismic sensor in the jth (j is 1,2,3, …, M) time window as the waveform number, using letter W to represent the waveform number, and recording the waveform number of the ith microseismic sensor in the jth time window as
On the basis, the number of effective microseismic waveforms monitored by each microseismic sensor in any time window is recorded as the average waveform number of channels in the time window, and the average waveform number is used
Indicating that the average waveform number of the channel in the jth time window is used
It is shown that,
calculated by the following formula:
calculating to obtain each microseismic sensorMaximum amplitude A of the effective microseismic waveform monitored by the devicemax(ii) a Calculating to obtain the duration T of the effective microseismic waveform monitored by each microseismic sensord(ii) a Calculating to obtain the main frequency F of the effective microseismic waveform monitored by each microseismic sensorp(ii) a Averaging absolute values of background noise amplitudes of microseismic signals
As a threshold value, respectively calculating the times of wave crests exceeding the threshold value in the effective microseismic waveform monitored by each microseismic sensor, and defining the times as the pulse number H;
recording the maximum amplitude sum of effective microseismic waveforms monitored by all microseismic sensors in any time window as the maximum amplitude sum of the time window, and using
Indicating that the maximum amplitude sum of the time windows in the jth time window is
It is shown that,
calculated by the following formula:
in the above formula (2), i is 1,2,3, …, N,
representing the maximum amplitude of the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
recording the average pulse number monitored by each microseismic sensor in any time window as the average pulse number of the channel in the time window, and using the average pulse number
Indicates that the channel in the jth time window is averagedFor the number of pulses
It is shown that,
calculated by the following formula:
in the above formula (3), i is 1,2,3, …, N,
representing the number of pulses in the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
recording the average duration of all effective microseismic waveforms monitored by all microseismic sensors in any time window as the average duration of the time window waveform, and using
Indicating that the average duration of the waveform in the jth time window is
It is shown that,
calculated by the following formula:
in the above formula (4), i is 1,2,3, …, N,
representing the k-th effective microseismic waveform of the i-th microseismic sensor in the j-th time windowA duration of time;
recording the average main frequency of all effective microseismic waveforms monitored by all sensors in any time window as the average main frequency of the time window waveform, and using the average main frequency
Indicating that the average dominant frequency of the waveform in the jth time window
It is shown that,
calculated by the following formula:
in the above formula (5), i is 1,2,3, …, N,
representing the dominant frequency of the kth effective microseismic waveform of the ith microseismic sensor in the jth time window.
(3) Real-time rapid monitoring and evaluation of coal rock body fracturing crack based on micro-seismic waveform characteristic parameters
Respectively drawing the average waveform number of the channels
Maximum amplitude sum of time window
Number of channel average pulses
Average duration of time window waveform
Time window waveform average dominant frequency
Graphs of time window number j (which is essentially time) and are separately labeled
A curve,
A curve,
A curve,
Curves and
a curve;
according to
A curve,
A curve,
A curve,
Curves and
and monitoring and evaluating the cracking, expansion, penetration and branch crack initiation of the main crack of the coal rock body fracturing by the size of the longitudinal coordinate value of the curve and the change trend of each curve.
When in use
Curves and
the slope of the curve simultaneously presents a turning point which is obviously increased, an
Curves and
the curve shows local sudden drop, and
when the curve is locally suddenly increased, the fracture initiation of the coal rock fracturing main fracture is shown;
thereafter, when
Curve or line of
The slope of any one of the curves increases; or
The slope of the curve increases and at the same time
When the slope of the curve is reduced, the coal rock mass fracturing is shown to have branch crack initiation;
when the main fracture of the coal rock body fracturing is initiated,
a curve,
Curves and
the curve continues to increase; and the average duration of the time window waveform
The duration is greater than the average duration of the time window waveform of the fracture initiation stage of the main fracture
Namely, it is
Time window waveform average dominant frequency
Time window waveform average main frequency continuously smaller than fracture initiation stage of main fracture
Namely, it is
Indicating that the coal rock fracturing main crack enters a stable expansion stage;
when in use
A curve,
A curve,
The curves are simultaneously subjected to global sudden drop and are dropped to the global minimum value and are continuously positioned at the minimum value; and is
The curve is abruptly increased to a global maximum,
the curve suddenly drops to the global minimum value, which shows that the coal rock fracturing main fracture penetrates through the existing fault, large fracture or roadway section and the like, and the continuous fracturing is meaningless, so that the curve can be used as a microseismic signal precursor characteristic for finishing the fracturing operation.
The coal rock body fracturing fracture is generated under the action of high-pressure fluid. Compared with the microseismic waveform induced by the coal rock body fracture and crack caused by stress without participation of fluid, the microseismic waveform induced by the fracture and crack has unique characteristics in amplitude frequency, time frequency, duration, pulse number and other parameters due to the participation of high-pressure fluid. In addition, a main fracture and a branch fracture can be fractured in the coal rock fracturing process, and different microseismic waveform signals can also be generated when the main fracture and the branch fracture are initiated; the induced microseismic waveform characteristic parameters of the cracks are different at different stages of initiation, expansion, penetration and the like due to stress, fluid pressure, fluid flow state and the like. The invention systematically monitors the initiation, expansion, penetration and the like of the coal-rock body fracturing fracture in real time and rapidly according to the difference characteristics of microseismic waveform parameters induced by the coal-rock body fracturing for the first time, and mainly has the following beneficial effects:
(1) the invention utilizes the microseism waveform characteristic parameters induced by coal rock body fracturing and the change characteristics of the microseism waveform characteristic parameters along with time to realize real-time and rapid monitoring and evaluation of different stages of initiation, expansion, penetration and the like of coal rock body fracturing cracks, and is suitable for monitoring and evaluation technologies of various fracturing cracks of coal rock body hydraulic fracturing, carbon dioxide gas fracturing and the like in the fields of oil gas, mines, dry and hot rocks and the like; in addition, the method can also be applied to monitoring and evaluating coal rock stratum fractures caused by excavation of underground engineering such as mines, tunnels and the like.
(2) The traditional coal rock body fracturing micro-seismic monitoring method needs complex and large-computation-amount computing work such as micro-seismic source positioning, micro-seismic wave velocity imaging, a seismic source mechanism and the like, and the traditional micro-seismic monitoring time cost and the economic cost are very high; in addition, the analysis and interpretation of monitoring results such as microseismic positioning, wave velocity imaging, seismic source mechanisms and the like are obscure and difficult to understand, and the traditional microseismic monitoring has high requirements on professional theories and technologies of related practitioners. The method for rapidly monitoring the coal rock body fracturing fracture in real time by utilizing the micro-seismic waveform signal characteristics has the advantages of small calculated amount, high calculating speed and simple and understandable result analysis and explanation; the method not only greatly reduces the calculation workload, the economic cost and the time cost of microseismic monitoring, but also greatly reduces the difficulty of analyzing and explaining the monitoring result, thereby reducing the professional technical requirements on related operators.
(3) The coal rock body fracturing induced microseismic waveform characteristic parameters and the change characteristics of the characteristic parameters along with time, which are obtained by the invention, can provide reference and comparison for positioning of a fracturing fracture microseismic seismic source, inversion of a seismic source mechanism and the like, and have important significance for real-time adjustment of fracturing parameters in the design and implementation processes of coal rock body fracturing schemes.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic diagram of characteristic parameters of microseismic waveforms induced by coal-rock body fracturing: (a) inducing effective microseismic wave forms by coal rock body fracturing; (b) a spectrogram corresponding to the effective microseismic waveform;
fig. 3 is an effective microseismic waveform induced by coal rock body fracturing monitored by the microseismic sensor No. i (i ═ 8) of the jth (j ═ 29) time window actually monitored in the process of coal mine underground coal rock body drilling fracturing: (a) 9 effective microseismic waveforms induced by coal rock mass drilling fracturing; (b)1# effective microseismic waveform enlarged view; (c) a time-frequency curve corresponding to the 1# effective microseismic waveform;
fig. 4 is a change curve of each microseismic waveform characteristic parameter induced by coal-rock mass fracturing drilling along with a time window sequence number: (a)
curve, (b)
Curve, (c)
Curve (d)
Curve, (e)
Curve line.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
As shown in fig. 1A flow chart of a real-time rapid monitoring and evaluation method for coal rock body fracturing cracks by using microseismic signals. FIG. 2 is a schematic diagram of characteristic parameters of microseismic waveform induced by coal-rock body fracturing, and it can be seen from the diagram that the average value of the absolute values of the amplitudes of the background noise is
The arrival time of effective microseismic wave shape induced by fracturing is taEnd time teThe waveform has a duration of Td＝te-ta(ii) a The pulse number H of the waveform is 12; the maximum amplitude of the waveform is Amax(ii) a The dominant frequency of the waveform is Fp。
Fig. 3 shows effective microseismic waveforms induced by coal rock body fracturing monitored by a microseismic sensor No. i (8) in a jth (j (29)) time window of coal rock body drilling fracturing under a coal mine. As can be seen from fig. 3(a), the time window is 120 seconds long, and the number 8 microseismic sensors in the time window monitor 9 effective microseismic waveforms induced by fracturing. FIG. 3(b) is an enlarged view of the 1# effective microseismic waveform in the time window, FIG. 3(c) is a time-frequency curve corresponding to the 1# effective microseismic waveform, and it can be seen from FIGS. 3(b) and (c) that the average value of the absolute values of the background noise amplitudes is the average value
The background noise frequency is mainly distributed around 15Hz, and the main frequency of the 1# effective microseismic waveform is 109 Hz.
The coal mine underground coal rock mass drilling fracturing micro-seismic monitoring is carried out by arranging 12 micro-seismic sensors in total, namely N is 12; the microseismic sensors are numbered as sensors No. 1-12 in sequence.
According to the coal rock body fracturing crack micro-seismic monitoring process, before the coal rock body drilling and fracturing of the coal mine, micro-seismic signal background noise test is carried out, and the average value of the absolute value of the amplitude of the background noise is calculated
The frequency of the background noise is mainly concentrated on about 15Hz, and the amplitude and the frequency information of the background noise provide input data for detecting effective microseismic signals induced by the coal-rock body fracturingAccordingly.
According to the actual situation of the coal mine underground coal rock body drilling fracturing microseismic monitoring, a reasonable time window is determined, the time duration of the time window L is 2 minutes and 120 seconds, and original microseismic signals monitored by coal rock body fracturing are sequentially divided into M (j is 1,2,3, …, M) time windows with the time duration of L according to the time sequence.
And scanning and detecting microseismic signals monitored by each sensor in all time windows by adopting a long-time window method based on instantaneous frequency and energy, automatically identifying effective microseismic waveforms induced in the whole process of coal rock mass drilling fracturing, and respectively calculating the arrival time, the ending time, the waveform duration, the maximum amplitude and the main frequency of each effective microseismic waveform on the basis. Calculating to obtain the number of effective microseismic waveforms monitored by each microseismic sensor in each time window, namely calculating to obtain the number of effective microseismic waveforms monitored by the ith microseismic sensor in the jth time window, and recording the number as
And setting the average value of the absolute values of the amplitudes of the background noise as a threshold value, and calculating to obtain the pulse number in each effective microseismic waveform duration.
Calculating the average waveform number of the channels in the jth time window according to the following formula
Calculating the sum of the maximum amplitudes of the effective microseismic waveforms monitored by all the sensors in the jth time window according to the following formula, namely the sum of the maximum amplitudes of the instant windows
The average pulse number monitored by each sensor in the jth time window is calculated according to the following formula, namely the average pulse number of the channels
Calculating the average duration of all effective microseismic waveforms monitored by all sensors in the jth time window according to the following formula, namely the average duration of the waveform of the time window
Calculating the average main frequency of all effective microseismic waveforms monitored by all sensors in the jth time window according to the following formula, and calculating the average main frequency of the waveform of the real-time window
Respectively drawing the channel average waveform number according to the calculation results
Maximum amplitude sum of time window
Number of channel average pulses
Average duration of time window waveform
Time window waveform average dominant frequency
The time window number j is plotted and recorded as
A curve,
A curve,
A curve,
Curves and
the curves, the respective graphs are shown in detail in fig. 4.
According to the detailed characteristics of microseismic waveform signals and the change along with time given in figure 1, the fracture initiation, expansion, penetration and branch fracture initiation of the main fracture of the coal rock body fracture are monitored and evaluated, and the specific process and the monitoring and evaluation results are as follows:
(1) in the context of figure 4(a),
the slope of curve OA is gw,1The slope of the curve in the AB section is gw,2The slope of the curve at the BC section is gw,3The slope of the curve in the CD segment is gw,4Slope of curve in DE section is gw,5The slope of the EF-segment curve is gw,6And is and
the slope of each section of the curve satisfies the following condition: gw,5＜gw,6＜gw,1＜gw,2＜gw,3＜gw,4(ii) a In FIG. 4(b)
The slope of curve OA is gH,1The slope of the curve in the AB section is gH,2The slope of the BD segment curve is gH,3Slope of curve in DE section is gH,4The slope of the EF-segment curve is gH,5And is and
the slope of each section of the curve satisfies the following condition: gH,4＜gH,5＜gH,1＜gH,3＜gH,2。
(2) When in use
Curves and
the slope of the curve simultaneously presents a turning point which is obviously increased, an
Curves and
the curve shows local sudden drop, and
when the curve is locally suddenly increased, the fracture initiation of the coal rock fracturing main fracture is shown. As can be seen from fig. 4, in the a-th time window, i.e. at point a on each curve,
curves and
the slope of the curve increases simultaneously, and this time
Curves and
the curve is locally suddenly dropped, and the local sudden drop occurs,
the curve is locally suddenly increased, so that the main fracture of the coal rock drilling fracture is initiated.
(3) After the main crack of the coal rock mass drilling and fracturing is initiated, the main crack is treated
Curve or line of
The slope of any one curve in the curves is increased; or
The slope of the curve increases and at the same time
When the slope of the curve is reduced, the coal rock mass fracturing is shown to have branch crack initiation. As can be seen from FIG. 4, at the b-th time window, i.e., atCurves and
when the point B is on the curve, the point B,
the slope of the curve increases and at the same time
The slope of the curve is reduced, which indicates that the coal rock drilling fracture has branch fracture initiation at the moment. In addition, at the time of the c-th time window,
the slope of the curve increases, and the branch crack initiation occurs again in the coal rock drilling and fracturing process.
(4) When coal is usedAfter the main fracture of the rock mass fracturing is initiated,
a curve,
Curves and
the curve continues to increase; and the average duration of the time window waveform
The duration is greater than the average duration of the time window waveform of the fracture initiation stage of the main fracture
Namely, it is
Time window waveform average dominant frequency
Time window waveform average main frequency continuously smaller than fracture initiation stage of main fracture
Namely, it is
And indicating that the coal rock fracturing main crack enters a stable expansion stage. As can be seen from FIG. 4, the main fracture of the coal rock drilling fracture starts at the a-th time window until the d-th time window, and in the process
A curve,
Curves and
the curve continues to increase; and in the process, the average duration of the time window waveform
Is always longer than the average duration time of the time window waveform of the fracture initiation stage of the main fracture
Namely, it is
Time window waveform average dominant frequency
The average main frequency of the waveform of the time window always smaller than the fracture initiation stage of the main fracture
Namely, it is
This indicates that the coal-rock body borehole fracture main fracture is in a stable propagation stage from the a-th time window to the d-th time window.
(5) When in use
A curve,
A curve,
The curves simultaneously have global sudden drop and drop to a global minimum value, and then continuously fluctuate near the minimum value; and is
The curve abruptly increases to a global maximum, an
The curve suddenly drops to the global minimum value, which shows that the main fracture of the coal rock mass fracturing is through and the fracturing is continued to lose significance, and the curve can be used as the precursor characteristic of the microseismic signal for finishing the fracturing operation. As can be seen from fig. 4, after the d-th time window,
a curve,
A curve,
The curve also shows a sudden sharp decrease and drops to a global minimum in a very short time, i.e. at the e-th time window, and thereafter continues at the minimum until the fracturing is finished; and is
The curve rapidly increases after the d-th time window to the global maximum at the e-th time window,
and the curve rapidly drops to the global minimum value of the time window e after the time window d, which shows that the main fracture of the coal-rock body drilling fracture starts to accelerate and expand after the time window d until the main fracture of the coal-rock body drilling fracture is communicated with the time window e. The coal mine underground field observation also shows that the water spraying phenomenon occurs on the roadway roof around the fracturing drill hole in the e-th time window, which shows that the main fracturing crack of the coal rock body drill hole penetrates through the broken zone of the roadway roof, and simultaneously shows that the monitoring and evaluation method provided by the invention is feasible and has important significance for the real-time adjustment of the fracturing parameters in the design and implementation processes of the coal rock body fracturing scheme.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (1)
1. A real-time rapid monitoring and evaluation method for coal rock body fracturing cracks by using microseismic signals is characterized by comprising the following steps: the method comprises the following specific steps:
(1) microseismic signal background noise of coal rock mass fracturing environment and induced original microseismic signal acquisition
Arranging N microseismic sensors around a coal rock fracturing well or a fracturing drilling hole, sequentially recording as No. 1,2,3, L, i, L and N microseismic sensors, collecting background noise of microseismic signals of a fracturing environment for a period of time before the fracturing operation starts, and calculating to obtain the average value of the absolute value of the amplitude of the background noise
And the frequency distribution rule thereof, and provides input data for the detection of effective microseismic signals induced by fracturing; starting coal rock mass fracturing, and continuously acquiring original micro-seismic signals induced in the whole coal rock mass fracturing process in real time;
(2) effective microseismic waveform detection induced by coal rock body fracturing and characteristic parameter extraction thereof
Selecting a reasonable time window according to the actual situation of coal rock body fracturing, recording the time length of the time window as L, and sequentially dividing the original microseismic signals monitored in the whole coal rock body fracturing process into M (j is 1,2,3, L, M) time windows with the time length of L according to the time sequence;
scanning and detecting original microseismic signals monitored by each sensor in all time windows by adopting a long-time window method based on instantaneous frequency and energy to automatically identify effective microseismic waveforms induced in the whole process of coal rock fracturing, respectively calculating the arrival time, the ending time, the waveform duration, the maximum amplitude and the dominant frequency of each effective microseismic waveform on the basis, defining the number of the effective microseismic waveforms monitored by each microseismic sensor in the jth (j is 1,2,3, L, M) time window as a waveform number, representing the waveform number by using a letter W, and recording the waveform number of the ith microseismic sensor in the jth time window as the waveform number
On the basis, the number of effective microseismic waveforms monitored by each microseismic sensor in the jth time window is recorded as the average waveform number of channels in the jth time window for use
Is shown to be
Calculated by the following formula:
calculating to obtain the maximum amplitude A of the effective microseismic waveform monitored by each microseismic sensormax(ii) a Calculating to obtain the duration T of the effective microseismic waveform monitored by each microseismic sensord(ii) a Calculating to obtain the main frequency F of the effective microseismic waveform monitored by each microseismic sensorp(ii) a Averaging absolute values of background noise amplitudes of microseismic signals
As a threshold value, respectively calculating the times of wave crests exceeding the threshold value in the effective microseismic waveform monitored by each microseismic sensor, and defining the times as the pulse number H;
recording the maximum amplitude sum of effective microseismic waveforms monitored by all microseismic sensors in the jth time window as the maximum amplitude sum of the time window, and using the sum
Is shown to be
Calculated by the following formula:
in the above formula (2), i is 1,2,3, L, N, k is 1,2,3, L,
representing the maximum amplitude of the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
recording the average pulse number monitored by each microseismic sensor in the jth time window as the average pulse number of the channel, and using the average pulse number
Is shown to be
Calculated by the following formula:
in the above formula (3), i is 1,2,3, L, N, k is 1,2,3, L,
representing the number of pulses in the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
recording the average duration of all effective microseismic waveforms monitored by all microseismic sensors in the jth time window as the average duration of the time window waveform, and using the average duration
Is shown to be
Calculated by the following formula:
in the above formula (4), i is 1,2,3, L, N, k is 1,2,3, L,
representing the duration of the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
recording the average main frequency of all effective microseismic waveforms monitored by all microseismic sensors in the jth time window as the average main frequency of the time window waveform, and using the average main frequency
Is shown to be
Calculated by the following formula:
in the above formula (5), i is 1,2,3, L, N, k is 1,2,3, L,
representing the main frequency of the kth effective microseismic waveform of the ith microseismic sensor in the jth time window;
(3) real-time rapid monitoring and evaluation of coal rock body fracturing crack based on micro-seismic waveform characteristic parameters
Respectively drawing the average waveform number of the channels
Maximum amplitude sum of time window
Number of channel average pulses
Average duration of time window waveform
Time window waveform average dominant frequency
The time window number j is plotted and recorded as
A-j curve,
A-j curve,
A-j curve,
The j curve and
-j-curve;
according to
A-j curve,
A-j curve,
A-j curve,
The j curve and
and (3) monitoring and evaluating the fracture initiation, expansion, penetration and branch fracture initiation of the coal rock body fracturing main fracture by the longitudinal coordinate value of the j curve and the variation trend of each curve:
when in use
The j curve and
the slope of the j-curve simultaneously presents a turning point which is significantly increased, and
the j curve and
the curve-j shows a local dip, and
when the curve-j is locally suddenly increased, the fracture initiation of the coal rock fracturing main fracture is indicated;
thereafter, when
The j curve or
-an increase in the slope of any one of the j curves; or
The slope of the-j curve increases and at the same time
When the slope of the-j curve is reduced, indicating that the coal rock mass fracturing has branch crack initiation;
when the main fracture of the coal rock body fracturing is initiated,
a-j curve,
The j curve and
the j curve increases continuously; and the average duration of the time window waveform
The duration is greater than the average duration of the time window waveform of the fracture initiation stage of the main fracture
Namely, it is
Time window waveform average dominant frequency
Time window waveform average main frequency continuously smaller than fracture initiation stage of main fracture
Namely, it is
Indicating that the coal rock fracturing main crack enters a stable expansion stage;
when in use
A-j curve,
A-j curve,
The j curve is simultaneously subjected to global sudden drop and drops to the global minimum value and is continuously positioned at the minimum value; and is
The curve j is abruptly increased to a global maximum,
and (4) suddenly reducing the curve-j to a global minimum value, indicating that the coal rock mass fracturing main fracture penetrates through the existing fault, large fracture or roadway section, continuing fracturing and losing significance, and taking the fracture as a microseismic signal precursor characteristic for finishing fracturing operation.
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| CN111636859B (en) * | 2020-07-09 | 2022-08-16 | 中煤科工集团重庆研究院有限公司 | Coal rock while-drilling self-identification method based on micro-fracture wave detection |
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