RU2795783C1 - Seismic receiver - Google Patents

Abstract

FIELD: seismic data recording systems.

SUBSTANCE: seismic receiver contains a housing in which there are three units of microseismic signal receivers (MSR) orthogonally oriented in the X, Y, Z directions. Each MSR unit includes N geophones, which are connected through the corresponding N instrumental amplifiers to an adder connected through a backward filter, consisting of two series-connected bandpass integrators, configured to operate in the frequency band from the lower cutoff frequency ω₁ to geophone natural frequencyω₀, and a high-pass filter with an A/D converter driver connected to a reference voltage source and to an output connector located on the front panel of the case. A damping ratio equal to one is set on each geophone using a shunt resistor R_d connected in parallel with the geophone. Each geophone contains two pull-up resistors R_p, having a resistance value of 100 kΩ, through which the output signals of each geophone are pulled up to ground potential. Each instrumentation amplifier is an ultra-low noise differential amplifier with a gain of 0 dB. The adder is an analog adder on an operational amplifier. The high pass filter consists of two 2nd order Butterworth high pass filters series-connected. The A/D converter driver is a precision, ultra-low distortion driver that converts a single-ended signal to a balanced signal.

EFFECT: enabling registration of weak seismic signals in a large dynamic range by improving the signal-to-noise ratio and attenuating low-frequency noise in the frequency range below the lower cutoff frequency ω₁.

8 cl, 8 dwg

Description

The invention relates to the field of seismometry in the oil and gas industry and can be used in seismic data recording systems, for example, when conducting surface monitoring of a hydraulic fracturing operation, searching for hydrocarbon deposits, and determining a natural fracturing system.

At present, when solving these problems, it is necessary to use autonomous broadband high-precision seismic receivers, which are located in a compact group.

As a rule, in passive seismological monitoring networks, seismometers are used as seismic receivers, allowing them to operate in the frequency range from 0.5 Hz to 60 Hz.

The organization of a working small-aperture group in this case is not economically feasible due to the high cost of autonomous broadband seismic receivers and the lack of ready-made solutions based on them to provide real-time monitoring.

The high cost of such seismic receivers, the complexity of their installation, subsequent maintenance and protection make such work extremely costly.

At the same time, geophone-based seismic receivers, supplemented with appropriate amplification and correction modules for amplitude-frequency characteristics and filtering, can be used in modern digital seismic data recording systems.

Such seismic receivers make it possible to register seismic signals associated with a hydrocarbon deposit, the development of a hydraulic fracture.

Methods for increasing the frequency range make it possible to create a seismic receiver that covers the required operating frequency range in the low-frequency region, while the upper limit of the frequency range can reach up to 1 kHz, which makes it possible to combine passive and active seismic monitoring methods.

The use of such seismic receivers will increase the density of local seismological networks by reducing the cost of their arrangement and maintenance.

Seismic signal recorders are known that use measuring primary transducers (seismic receivers):

ZET 048-C by ZETLAB

[https://zetlab.com/product-category/izmeritelno oborudovanie/seysmostantsii/];

Baikal-8 manufactured by R-sensors LLC

[http://r-sensors.ru/1_products/Descriptions/BY-8-RU.pdf],;

DELTA-03M manufactured by Logic Systems LLC [http://logsys.ru/index.php?page= 15].

The disadvantages of analogues are:

- the use of primary converters with low levels of the output signal, due to low gain factors;

- the impossibility of maintaining an acceptable signal-to-noise ratio in the case of supplementing the above devices with an amplification stage with a significant gain to use primary converters with a low output signal level;

- insufficiently high signal-to-noise ratio when measuring microseismic signals at frequencies of fractions and a few hertz, in particular for the tasks of searching for hydrocarbons and weak signals of a fractured medium during hydraulic fracturing.

The prototype is a device for correcting the frequency response of a geophone, consisting of two series-connected bandpass integrators configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ (patent RU 111689 U1, IPC G01V 1/00, publication date 12/20/2011).

The main disadvantage of the prototype device is the insufficient signal-to-noise ratio, while, since the bandpass integrator has a constant gain in the frequency range 0 - ω ₁ , and the signal-to-noise ratio in this frequency range is less than one, the signal amplification in this frequency range leads to the amplification of low-frequency noise, and the value of the resistor in the feedback circuit of the bandpass integrator can reach large values, on the order of a megaohm, which is an additional source of thermal noise.

The disadvantages of the prototype device are also:

- low noise immunity, since an unbalanced output signal is used;

- low reliability and mobility of the device in field use, if the geophone is an electrodynamic seismic receiver with a significant inertial mass, which has a low resistance to shock and vibration loads, which leads to low reliability of the total measuring system;

- increased weight and size characteristics and power consumption, if the geophone is an electrochemical (molecular-electronic) converter of mechanical quantities, which has a significant dependence on the ambient temperature, which leads to an uncontrolled deterioration of the signal-to-noise ratio during measurements in the field, and requires the use of temperature control .

Thus, seismic receivers known from the prior art have disadvantages, and their arsenal needs to be expanded to meet the needs of manufacturers and users of seismic data recording systems.

The technical task is to expand the arsenal of seismic receivers by creating a seismic receiver - a mobile broadband device based on geophones, which is a three-coordinate seismic receiver in a single housing, which makes it possible to use it in various operating conditions.

The main technical result is to enable the registration of weak seismic signals in a large dynamic range by improving the signal-to-noise ratio and attenuating low-frequency noise in the frequency range below the lower cutoff frequency ω ₁ .

The technical result is also an increase in the accuracy and reliability of the recorded microseismic signals through the use of geophone grouping, an increase in the noise immunity of the output signal through the use of a symmetrical output signal.

The technical result is achieved by the fact that the seismic receiver, according to the present invention, contains a housing in which three blocks of microseismic signal receivers (PMS) are located, orthogonally oriented in the X, Y, Z directions, while each MSS unit includes N geophones, which, through the corresponding N instrumental amplifiers, are connected to an adder connected through an inverse filter, consisting of two series-connected bandpass integrators, configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ , and a high-frequency filter with a driver analog-to-digital converter connected to the reference voltage source and to the output connector located on the front panel of the housing.

And also by the fact that each geophone has a damping coefficient equal to one with the help of a shunt resistor R _d connected in parallel to the geophone, the resistance value of which is determined from the relation

where h _m - mechanical damping, R _c - resistance of the geophone coil, m - mass of the moving part of the geophone, ω ₀ - natural frequency of the geophone, G - sensitivity of the geophone in open circuit.

And also by the fact that each geophone contains two pull-up resistors R _p having a resistance value of 100 kOhm, through which the output signals of each geophone are pulled up to ground potential.

And also because each instrumentation amplifier is a differential ultra-low noise amplifier with a gain of 0 dB.

And also by the fact that the adder is an analog adder on an operational amplifier, and the output signal V _sum at the output of the adder is determined from the relationship:

where V _l , V ₂ ,… V _N are the output voltages from each geophone, and the ratio of resistor values R _ƒ and R _a sets the required gain of the total signal.

And also by the fact that the transfer characteristic in the frequency band ω ₀ - ω ₁ of the first bandpass integrator is determined from the relationship:

where V _int1 is the output signal of the first bandpass integrator; V _sum is the output signal from the adder, and the transfer characteristic in the frequency band ω ₀ - ω ₁ of the second bandpass integrator is determined from the relationship:

where V _int2 is the output signal from the second bandpass integrator, V _int1 is the output signal from the first bandpass integrator.

And also by the fact that the high-pass filter consists of two series-connected Butterworth high-pass filters of the 2nd order, while the transfer characteristic of the first Butterworth high-pass filter of the 2nd order is determined from the relation

where V _int2 is the output signal from the second bandpass integrator; V _hpƒ1 is the output signal of the first 2nd order Butterworth high-pass filter, and the transfer characteristic of the second 2nd order Butterworth high-pass filter is determined from the relationship:

where V _hpƒ2 is the output of the second 2nd order Butterworth high pass filter, V _hvƒ1 is the output of the first 2nd order Butterworth high pass filter.

Also, the A/D converter driver is a precision, ultra-low distortion driver that converts a single-ended signal to a balanced signal.

Figures 1, 2, 3 and 4 present, respectively, an enlarged block diagram of the proposed seismic receiver, functional block diagrams of the PMS blocks, orthogonally oriented in the directions X, Y, Z, respectively.

Figure 5 shows the electrical circuit of each PMS unit, which includes N geophones, which are connected to the adder through the corresponding N instrumentation amplifiers.

The figure 6 shows the electrical circuit of the reverse filter of each block PMS.

The figure 7 shows the electrical circuit of the high-pass filter of each block PMS.

The figure 8 shows the electrical circuit of the analog-to-digital converter driver of each PMS block.

The seismic receiver (Fig. 1) contains a housing 1, in which there are three PMS blocks 2, 3 and 4, orthogonally oriented in the X, Y, Z directions, respectively, the output signals of which are connected to the output connector 5 located on the front panel of the housing 1.

Seismic receiver block 2 (X-channel) includes N geophones 6 (6 ₁ , 6 ₂ ...6 _N ), which through the corresponding instrumental amplifiers 7 (7 ₁ , 7 ₂ ...7 _N ), adder 8, inverse filter 9, consisting of two series-connected bandpass integrators, configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ , and the high-frequency filter 10 are connected to the driver 11 of the analog-to-digital converter connected to the source 12 of the reference voltage and to the output socket 5.

The seismic receiver unit 3 (Y-channel) includes N geophones 13 (13 ₁ , 13 ₂ ...13 _N ), which, through the corresponding instrumental amplifiers 14 (14 ₁ , 14 ₂ ... 14 _N ), adder 15, inverse filter 16, consisting of two series-connected bandpass integrators, configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ , and the high-frequency filter 17 are connected to the analog-to-digital converter driver 18 connected to the reference voltage source 19 and to the output socket 5.

The seismic receiver block 4 (Z-channel) includes N geophones 20 (20 ₁ , 20 ₂ ...20 _N ), which, through the corresponding instrumental amplifiers 21 (21 ₁ , 21 ₂ ... 21 _N ), adder 22, inverse filter 23, consisting of two band-pass integrators connected in series, configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ , and the high-frequency filter 24 are connected to the driver 25 of the analog-to-digital converter connected to the reference voltage source 26 and to the output socket 5.

Thus, microseismic signals recorded by geophones (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ) from each orthogonal direction, X, Y , Z, respectively, are converted into analog electrical signals.

An example of a specific implementation and operation of a seismic receiver.

The developed seismic receiver is a mobile broadband device based on GS-ONE LF geophones with a natural frequency of 4.5 Hz (URL: https://geospace-ufa.ru/products/geofonybez-korpusov/gs-one-1f/:[website] ) and is a three-coordinate geophone in a single housing.

The seismic receiver contains, in each PMS block 2, 3, 4, boards from the corresponding instrumental amplifiers (7 ₁ , 7 ₂ ... 7 _N ), (14 ₁ , 14 ₂ ... 14 _N ), (21 ₁ , 21 ₂ ... 21 _N ), the corresponding adders 8, 15, 22 and the corresponding circuits for correcting the amplitude-frequency characteristic of each geophone (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,), (20 ₁ , 20 ₂ … _20N ).

Since the sensitivity of one GS-ONE LF geophone (89.4 V/m/s) is insufficient in seismic data acquisition systems, N geophones are installed for each orthogonal direction (X, Y, Z): (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,), (20 ₁ , 20 ₂ …20 _N ), signals from which, passing through the corresponding instrumental amplifiers (7 ₁ , 7 ₂ …7 _N ), (14 ₁ , 14 ₂ …14 _N ), (21 ₁ , 21 ₂ …21 _N ), are summed with the required gain using the corresponding adders 8, 15, 22, as a result of which the total sensitivity of the seismic receiver reaches a value of the order of 2000 V/m/s, which is comparable to broadband digital seismometers used in seismological observation networks.

Each geophone (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ) has a damping coefficient equal to one, using a geophone connected in parallel , shunt resistor R _d , the resistance value of which is determined from the ratio

where h _m - mechanical damping, R _c - resistance of the geophone coil, m - mass of the moving part of the geophone, ω ₀ - natural frequency of the geophone, G - sensitivity of the geophone in open circuit (see Fig. 5).

Each geophone (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ) contains two pull-up resistors R _p having a resistance value of 100 kOhm , by means of which the output signals of each geophone are pulled up to ground potential (see Fig. 5).

Each instrumentation amplifier (7 ₁ , 7 ₂ ... 7 _N ), (14 ₁ , 14 ₂ ... 14 _N ), (21 ₁ , 21 ₂ ... 21 _N ) is a differential ultra-low noise amplifier with a gain of 0 dB (see Fig. Fig. 5).

The output differential signal of each geophone (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ) goes to the corresponding instrumental amplifier (7 ₁ , 7 ₂ …7 _N ), (14 ₁ , 14 ₂ …14 _N ), (21 ₁ , 21 ₂ …21 _N ), which converts a balanced signal into an unbalanced one.

The output signal of each instrumental amplifier (7 ₁ , 7 ₂ ... 7 _N ), (14 ₁ , _{14 2} ... 14 _N ), (21 ₁ , 21 ₂ ... 21 _N ) is fed to the corresponding adder 8, 15, 22, which performs summation all signals from N geophones (7 ₁ , 7 ₂ …7 _N ), (14 ₁ , 14 ₂ …14 _N ), (21 ₁ , 21 ₂ …21 _N ).

раз.This summation reduces the noise in the output signal and increases the signal-to-noise ratio in

once.

Each adder 8, 15, 22 is an analog adder on an operational amplifier, and the output signal V _sum at the output of each adder 8, 15, 22 is determined from the relationship:

where V ₁ , V ₂ ,…V _N are the output voltages from each geophone, and the ratio of resistor values R _ƒ and R _a sets the required gain of the total signal (see Fig. 5).

The main limitation of the hardware correction of the geophone frequency response is the presence of hardware noise, primarily the noise of operational amplifiers.

As operational amplifiers included in adders 8, 15, 22, inverse filters 9, 16, 23, low-noise precision operational amplifiers OPA2211 from Texas Instruments with a noise power spectral density of 1.1 nV/Hz were selected.

These amplifiers have ultra-low temperature drift and low power consumption, which is an advantage when used in stand-alone seismological monitoring systems.

To restore the amplitude-frequency characteristic of each geophone (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ) in the frequency range from ω ₁ to ω ₀ , where ω ₀ is the natural frequency of the geophone, and ω ₁ is the lower frequency of correction of the amplitude-frequency characteristic of the geophone, a correction scheme based on an inverse filter is used.

The output signal from each adder 8, 15, 22 is fed to the corresponding inverse filter 9, 16, 23, each of which is two series-connected integrators with a frequency response slope of 12 dB/octave (the frequency response slope of each integrator is 6 dB/octave) in frequency band ω ₀ - ω ₁ .

The implementation of each inverse filter 9, 16, 23 based on two serially connected integrators is shown in Fig. 6.

The transfer characteristic of the first bandpass integrator is determined from the relationship:

where V _int1 is the output signal of the first bandpass integrator; V _sum - output signal from the adder.

Given the values of C ₁ , R ₂ , R ₃ , you can determine the resistance values R ₁ and R ₄ using the following equations:

The transfer characteristic of the second bandpass integrator is determined from the relationship:

where V _int2 is the output signal from the second bandpass integrator, _Vint1 is the output signal from the first bandpass integrator.

According to the given values of C ₂ , R ₆ , R ₇ , you can determine the resistance values R ₅ and R _Q using the following equations:

Accordingly, two series-connected integrators form a transfer characteristic:

To expand the frequency range of the GS-ONE LF geophone in the region of 0.5-4.5 Hz, a correction scheme based on an inverse filter was used. Inverse filters 9, 16, 23 have a gain of 12 dB per octave in the frequency band of 0.5-4.5 Hz.

In order to ensure a stable mode of operation of the correction circuit and suppression of low-frequency noise, which is amplified when passing the reverse filter in the frequency band below the correction frequency ω ₁ (in the frequency range below 0.5 Hz), filters 10, 17, 24 were used as filters high-pass, two series-connected 2nd order Butterworth high-pass filters that suppress all frequencies below 0.5 Hz.

The implementation of each high pass filter 10, 17, 24 based on two 2nd order Butterworth high pass filters connected in series is shown in FIG. 7.

The transfer characteristic of the first 2nd order Butterworth high-pass filter is determined from the relationship:

where V _int2 is the output signal from the second bandpass integrator; V _hrƒ1 - the output signal of the first Butterworth high-pass filter of the 2nd order.

The transfer characteristic of the second high-pass Butterworth 2nd order filter is determined from the relationship:

where V _hrƒ2 - the output signal of the second high-pass filter Butterworth 2nd order; V _hrƒ1 - the output signal of the first Butterworth high-pass filter of the 2nd order.

To transmit an analog signal to the path of analog-to-digital converters, the output signal from each high-pass filter 10, 17, 24 is connected to the corresponding driver 11, 18, 25 of the analog-to-digital converter, which are precision LMP8350 drivers with ultra-low distortion, which convert unbalanced the signal is symmetrical.

The implementation of each A/D converter driver 11, 18, 25 is shown in FIG. 8.

Thus, the boards from the corresponding instrumental amplifiers (7 ₁ , 7 ₂ ... 7 _N ), (14 ₁ , 14 ₂ ... 14 _N ), (21 ₁ , 21 ₂ ... 21 _N ), the corresponding adders 8, 15, 22 and the corresponding circuits for correcting the amplitude-frequency characteristic of each geophone GS-ONE LF (6 ₁ , 6 ₂ …6 _N ,), (13 ₁ , 13 ₂ …13 _N ,) and (20 ₁ , 20 ₂ …20 _N ), allow to expand the operating frequency range of GS-ONE LF geophones towards low frequencies from the initial 4.5 Hz to 0.5 Hz.

The measurement accuracy of an analog-to-digital converter, as well as its temperature stability, depends to a large extent on the accuracy and stability of the reference voltage source. The conversion accuracy for absolute measurements is determined by the accuracy of the reference signal. However, in the tasks of seismological monitoring, the main indicator is not absolute accuracy, but the stability and repeatability of measurement results with a low level of introduced hardware noise. Therefore, the ADR02 microcircuit was chosen as sources 12, 19, 26 of the reference voltage, which has an output voltage of 5 V, a noise value of 10 μV in a frequency band of 0.1-10 Hz, and a temperature stability of 3 ppm/C.

Thus, the implementation of the seismic receiver in accordance with the proposed technical solution allows you to register weak seismic signals in a large dynamic range by improving the signal-to-noise ratio and attenuating low-frequency noise in the frequency range below the lower cutoff frequency ω ₁ , improves the accuracy and reliability of the recorded microseismic signals through the use of grouping geophones, increase the noise immunity of the output signal through the use of a symmetrical output signal.

Claims (12)

1. A seismic receiver, characterized in that it contains a housing in which three blocks of microseismic signal receivers (PMS) are located, orthogonally oriented in the X, Y, Z directions, while each PMS unit includes N geophones, which, through the corresponding N instrumental amplifiers are connected to an adder connected through an inverse filter, consisting of two series-connected bandpass integrators, configured to operate in the frequency band from the lower cutoff frequency ω ₁ to the natural frequency of the geophone ω ₀ , and a high-pass filter with an analog-to-digital converter driver connected to the reference voltage source and to the output connector located on the front panel of the housing. 2. The seismic receiver according to claim 1, characterized in that each geophone has a damping factor equal to one, using a shunt resistor R _d connected in parallel to the geophone, the resistance value of which is calculated from the relation

where h _m - mechanical damping, R _c - resistance of the geophone coil, m - mass of the moving part of the geophone, ω ₀ - natural frequency of the geophone, G - sensitivity of the geophone in open circuit. 3. Seismic receiver according to claim 1, characterized in that each geophone contains two pull-up resistors R _p having a resistance value of 100 kOhm, through which the output signals of each geophone are pulled up to ground potential. 4. Seismic receiver according to claim 1, characterized in that each instrumentation amplifier is a differential ultra-low noise amplifier with a gain of 0 dB. 5. The seismic receiver according to claim 1, characterized in that the adder is an analog adder on an operational amplifier, and the output signal V _sum at the output of the adder is determined from the relationship:

where V ₁ ,V ₂ ,…V _N are the output voltages from each geophone, and the ratio of resistor values R _ƒ and R _a sets the required gain of the total signal. 6. Seismic receiver according to claim 1, characterized in that the transfer characteristic of the first bandpass integrator is determined from the relation

where V _int1 is the output signal of the first bandpass integrator, _Vsum is the output signal from the adder, and the transfer characteristic of the second bandpass integrator is determined from the relation

where V _int2 is the output signal from the second bandpass integrator, V _int1 is the output signal from the first bandpass integrator. 7. The seismic receiver according to claim 1, characterized in that the high-pass filter consists of two series-connected Butterworth high-pass filters of the 2nd order, while the transfer characteristic of the first Butterworth high-pass filter of the 2nd order is determined from the relation

where V _int2 is the output signal from the second bandpass integrator; V _hpƒ1 is the output signal of the first 2nd order Butterworth high-pass filter, and the transfer characteristic of the second 2nd order Butterworth high-pass filter is determined from the relation

where V _hpƒ2 - output signal of the second high-pass filter Butterworth 2nd order, V _hpƒ1 - output signal of the first high-pass filter Butterworth 2nd order. 8. The seismic receiver of claim. 1, characterized in that the A/D converter driver is a precision ultra-low distortion driver that converts a single-ended signal to a balanced one.

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