阅读说明：本技术 基于分布式光纤传感的时频电磁压裂监测系统及监测方法 (Time-frequency electromagnetic fracturing monitoring system and monitoring method based on distributed optical fiber sensing ) 是由 王熙明 余刚 梁兴 安树杰 王志刚 刘雪军 杨战军 夏淑君 于 2020-12-04 设计创作，主要内容包括：本发明提供一种基于分布式光纤传感的时频电磁压裂监测系统及监测方法,利用在水平井中进行压裂井段上方地面上布设的三维三分量光纤时频电磁数据采集站,压裂井附近观测井中或压裂井套管外布设的井下时频电磁数据采集铠装光缆或电缆,在压裂水平井段两侧平行于压裂井段布设的大功率偶极电流源,在压裂开始前、压裂过程中和压裂结束后持续同步采集地面或地-井三维三分量时频电磁数据。实时计算压裂过程中和压裂后采集的三维三分量时频电磁数据与压裂开始前采集的三维三分量时频电磁数据之间的差异,同时根据实测的地面或地-井三维三分量时频电磁数据反演不同压裂阶段的地下电阻率的分布,用不同压裂阶段地下电阻率的分布来实时评价压裂效果。(The invention provides a time-frequency electromagnetic fracturing monitoring system and a monitoring method based on distributed optical fiber sensing, which utilize a three-dimensional three-component optical fiber time-frequency electromagnetic data acquisition station arranged on the ground above a fracturing well section in a horizontal well, underground time-frequency electromagnetic data acquisition armored optical cables or electric cables arranged in an observation well near the fracturing well or outside a fracturing well casing pipe, high-power dipole current sources arranged on two sides of the fracturing horizontal well section in parallel with the fracturing well section, and continuously and synchronously acquiring the ground or ground-well three-dimensional three-component time-frequency electromagnetic data before fracturing starts, during fracturing and after fracturing finishes. And calculating the difference between the three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and the three-dimensional three-component time-frequency electromagnetic data acquired before fracturing, inverting the distribution of the underground resistivity of different fracturing stages according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data, and evaluating the fracturing effect in real time by using the distribution of the underground resistivity of different fracturing stages.)

1. Time frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing, which is characterized by comprising: the system comprises a ground time-frequency electromagnetic data acquisition station (1), an acquisition armored cable (2), a ground controllable high-power current source (3), a ground armored optical cable (4) and a distributed optical fiber sensing modulation and demodulation instrument (5);

the ground time-frequency electromagnetic data acquisition station (1) is arranged on the ground above a fracturing well section of the horizontal well and is arranged in a three-dimensional manner;

the acquisition armored cable (2) is arranged in an observation well near the fracturing well or outside a sleeve of the fracturing well and is used for acquiring underground time-frequency electromagnetic data;

the ground controllable high-power current source (3) is arranged on the two sides of the projection line of the fracturing horizontal well section on the ground and is parallel to the extending direction of the fracturing well section;

the ground time-frequency electromagnetic data acquisition station (1) is connected with a distributed optical fiber sensing modulation and demodulation instrument (5) in a work area or near a wellhead through a ground armored optical cable (4); the tail end of the ground armored optical cable (4) is provided with a deluster (7);

the acquisition armored cable (2) is connected with a distributed optical fiber sensing modulation and demodulation instrument (5); the tail end of the acquisition armored cable (2) is provided with a delustering device (7).

2. The distributed fiber sensing-based time-frequency electromagnetic fracturing monitoring system of claim 1, wherein the surface-controllable high-power current source (3) is a high-power dipole current source.

3. The time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing of claim 1, wherein the ground time-frequency electromagnetic data acquisition station (1) comprises a wired or wireless node type electromagnetic data acquisition unit, a three-component magnetic field sensor and an electric field sensor which are arranged according to pre-designed measuring lines and measuring points.

4. The distributed fiber sensing-based time-frequency electromagnetic fracturing monitoring system of claim 1,

the acquisition armored cable (2) comprises a plurality of wired time-frequency electromagnetic data acquisition short circuits (6), and the wired time-frequency electromagnetic data acquisition short circuits (6) are distributed in an array manner in a well;

the wired time-frequency electromagnetic data acquisition short circuit (6) comprises wired time-frequency electromagnetic data acquisition units, three-component magnetic field sensors and electric field sensors which are arranged at equal intervals;

the wired time-frequency electromagnetic data acquisition short circuit (6) is connected with the distributed optical fiber sensing modulation and demodulation instrument (5) through the acquisition armored cable (2).

5. The time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing of claim 3 or 4, wherein the three-component magnetic field sensor is one of an induction coil type magnetic field sensor, a fluxgate type magnetic field sensor, a MEMS magnetic field sensor, a superconducting magnetic field sensor and an optical fiber magnetic field sensor; the electric field sensor is one of copper sulfate, silver chloride, nano materials, tantalum capacitance non-polarized electrode pairs and an optical fiber electric field sensor.

6. The time-frequency electromagnetic fracturing monitoring method based on distributed optical fiber sensing is characterized in that the time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing, which is adopted by any one of claims 1 to 5, comprises the following steps:

(a) the method comprises the following steps that a ground time-frequency electromagnetic data acquisition station (1) is arranged on the ground according to a pre-design, and the ground time-frequency electromagnetic data acquisition station (1) is connected with a distributed optical fiber sensing modulation and demodulation instrument (5) in a work area or near a wellhead through a ground armored optical cable (4);

(b) an acquisition armored cable (2) is arranged in an observation or monitoring well near the fracturing well or outside a sleeve of the fracturing well, and an optical fiber at the head end of the acquisition armored cable (2) is connected with a distributed optical fiber sensing modulation and demodulation instrument (5);

(c) arranging transmitting antennas of a ground controllable high-power electromagnetic source (3) on two sides of a projection line of the fracturing horizontal well section on the ground in parallel to the extension direction of the fracturing well section, embedding two ends of each transmitting antenna into the underground deep part, and well performing treatment of reducing the grounding resistance of a grounding end of a power supply electrode; a ground controllable high-power current source (3) is arranged in the middle of each transmitting antenna;

(d) before the fracturing operation is started, in the fracturing process and after the fracturing is finished, repeatedly exciting a ground controllable high-power current source (3), and synchronously acquiring three-dimensional time-frequency electromagnetic or transient electromagnetic data of the ground or the ground and a well in real time;

(e) preprocessing three-dimensional original time-frequency electromagnetic or transient electromagnetic data acquired in real time on the ground or in the ground and a well, demodulating the phase and amplitude of an optical signal reflected by a received ground armored optical cable (4) and an acquired armored cable (2) by using a distributed optical fiber sensing modulation and demodulation instrument (5), acquiring three-dimensional three-component time-frequency or transient electric field and magnetic field data of each ground measuring point and each well measuring point, eliminating random noise, filtering, and normalizing or performing consistency processing on the three-dimensional three-component time-frequency or transient electric field and magnetic field data acquired in the ground and the well by using an excitation current value of a ground controllable emission source recorded in real time;

(f) calculating the difference between three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and three-dimensional three-component time-frequency electromagnetic data acquired before fracturing is started in real time for the preprocessed three-dimensional three-component time-frequency or transient electric field and magnetic field data, and simultaneously inverting the underground resistivity values of different fracturing stages and the distribution of the underground resistivity values around the fracturing well section according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data;

(g) displaying underground resistivity values of different fracturing stages and the change characteristics of the distribution of the underground resistivity values around a fracturing well section along with time, which are inverted according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data before the start of hydraulic fracturing, in the whole fracturing process and after the fracturing is finished, in a dynamic video mode;

(h) the range and time-varying trend of the low-resistivity region displayed on the three-dimensional geological model along the hydraulic fracturing horizontal well section is a structure that the low-resistivity fracturing fluid penetrates into the depth of the rock along a crack (8) after the rock around the horizontal well section is cracked by high-pressure hydraulic fracturing; and (3) obtaining the volume or envelope (9) of the underground low resistivity body by inversion of the ground or ground-well three-dimensional three-component time-frequency electromagnetic data measured after the underground pressure relief is finished after the fracturing is finished, wherein the volume or envelope can be regarded as the effective modified volume ESRV.

Technical Field

The invention belongs to the technical field of geophysical exploration, and particularly relates to a time-frequency electromagnetic fracturing monitoring system and a time-frequency electromagnetic fracturing monitoring method based on distributed optical fiber sensing.

Background

The electromagnetic prospecting method is an electric prospecting method which takes the electromagnetic difference of a medium as a material basis and achieves certain prospecting purposes by observing and researching the change rule of an artificial or natural alternating electromagnetic field along with the space distribution rule or along with time.

The mineral exploration principle of electromagnetic exploration is based on the change of electrical properties among different rocks and minerals, and the corresponding change of the spatial distribution state of an electromagnetic field (artificial and natural) is caused. Therefore, people can utilize instruments with different performances to survey mineral resources or find out the existing state of a geological target in the crust through observation and research on the spatial and temporal distribution state of a field, thereby realizing the geological target of electrical prospecting.

Induction electromagnetic prospecting methods are generally classified into two categories: one type is an electromagnetic method for directly searching oil gas, and at present, an induced polarization method, a magnetoelectric method, an electric field difference method and the like are mainly used. The other is a method for searching oil-gas-containing structures, and at present, the methods mainly comprise an earth electromagnetic Method (MT), an electromagnetic array profile method (EMAP), a field building and depth measurement method and the like.

The difference between the electromagnetic survey data acquisition and the data acquisition of other geophysical prospecting methods lies in the diversity of the electromagnetic survey data acquisition, which is indistinguishable from the diversity of the electromagnetic survey methods. The electromagnetic prospecting method is many, and the working method diverse, the device is different, and the characteristics in field are different, and the sensor is different for it is various to gather the form. It has both natural and artificial source methods. The electric field can be measured by adopting a grounding electrode, and the magnetic field can also be measured by adopting a non-grounding coil; both relative and absolute quantities can be measured; either scalar or vector measurements can be made; the amplitude and the phase can be measured, and real and imaginary components can be measured; both the total field and the pure anomalous field can be measured.

A time-frequency electromagnetic or transient electromagnetic method (TFEM) is a new method appearing in the field of petroleum exploration, adopts a working mode similar to large-offset seismic exploration, supplies strong current to the ground to excite an oil-gas exploration target, and measures a secondary electromagnetic field and an electromagnetic field frequency spectrum formed by discharge of a pore medium of an oil-gas reservoir; the technology simultaneously obtains time domain signals and frequency domain signals, and accurately reconstructs an underground physical property model through the combined processing of the time domain signals and the frequency domain signals to obtain the resistivity and polarizability abnormity of the oil-gas exploration target.

The time-frequency electromagnetic or transient electromagnetic technology combines frequency domain sounding and time domain sounding in one system, can select excitation waveforms with different frequencies and different types according to the depth of an exploration target, can provide resistivity information and excitation polarization information, and can detect the oil-gas content of the exploration target while researching the electrical property structure. The time domain depth measurement processing adopts quasi-two-dimensional resistivity inversion to obtain resistivity information, and the frequency domain depth measurement processing introduces a Cole-Cole model to extract induced polarization information. Time-frequency electromagnetic or transient electromagnetic methods (TFEM) utilize large devices to perform depth sounding of different depth targets by changing waveform length and frequency.

The field construction of the time-frequency electromagnetic or transient electromagnetic method adopts an equatorial dipole device and comprises a transmitting part and a receiving part. The transmitting field source is a wire source with limited length and two grounded ends formed by a plurality of parallel copper wires, a high-power transmitter is adopted to send a series of square wave currents with different periods to the underground according to different frequencies, and a receiving end measures an electric component E through a grounded dipole MN_XAnd a high-sensitivity magnetic bar for measuring vertical magnetic induction component (dB)_Z/dt)。

At present, the widely applied controllable source time-frequency electromagnetic or transient electromagnetic exploration method and the long offset distance transient electromagnetic exploration method only arrange one excitation field source, only receive electromagnetic field signals in a certain range near the field source, and when the excitation energy of one field source cannot meet the signal-to-noise ratio requirement of the received signals at a remote receiving point, select a proper position to re-arrange the field source. The signal of a single excitation field source presents a series of problems: firstly, due to the complexity of underground construction, excitation fields at different positions or orientations can generate obvious differences at receiving points due to different transmission processes of electromagnetic fields; secondly, the distance from the field source is different, and the signal components and energy of the field source reaching the receiving point through the ground, the air and the underground are greatly different, so that the field source characteristics of the receiving point are different. For example, near zones, mainly the underground through-going wavefield, and far zones, mainly plane waves propagating from the ground or in the air, so that the received signals are severely affected by non-exploration targets, and a transition zone exists between the near and far zones, the electromagnetic field characteristics of which are more complex. Therefore, the traditional electromagnetic method exploration with controllable source often has great reduction in application effect because the field source effect cannot be eliminated well, and even error results are generated.

Well-to-ground or earth-to-well electromagnetic technology has evolved and developed over the last two decades and has formed a relatively mature approach. The method of electromagnetic field excitation can be roughly divided into frequency domain excitation and time domain excitation. A limitation of frequency domain (continuous wave) excitation is the strong coupling between the transmitter and the receiver, such that the magnetic field signal transmitted from the transmitter to the receiver may be stronger than the signal received from the formation, making it difficult to accurately measure the signal received from the formation. Although the use of multi-objective processing techniques and the use of multiple sets of measurements in combination provide a great deal of information about the selected formation of interest, the net signal obtained is still small compared to the total measured signal and little useful information is available. The method of using time domain excitation generates transient signals by cutting off the excitation current and detects the transient signals by the receiver, and because there is no transmitter signal when detecting the transient signals, the received signals can be filtered to remove any residual influence of the direct coupling mode signals. Transient measurements also exclude direct mode signals that do not contain formation resistivity/conductivity information. Therefore, having the ability to separate the responses of different spatial regions of the formation in time in the detection signal is an important feature of transient electromagnetic methods.

At present, the real-time monitoring of hydraulic fracturing generally takes underground, ground and shallow well micro-seismic monitoring technology as a main technology. When the horizontal well is deep (more than 2500 meters), the ground or shallow micro-seismic monitoring technology can only receive micro-seismic events with large magnitude or energy due to the fact that the distance between a detector of the ground or shallow well and a fracturing well section is too far, the micro-seismic events which can be monitored are much less than underground micro-seismic monitoring of an adjacent well of the fracturing well, and the actual extension range of rock fracture caused by hydraulic fracturing cannot be well monitored in real time. In addition, the microseism events generated by hydraulic fracturing are not necessarily microseism events caused by further breaking of rocks in the fracture extending process, so the size of the modified volume (SRV) defined by the enveloping range of distribution of the microseism events is often inconsistent with the capacity of a horizontal well after fracturing, and the situation that a plurality of microseism occurring positions are not actually communicated with a fracture network is shown, so the effective modified volume (ESRV) is defined according to the actual volume of the effectively communicated fracture network, and the correlation of the ESRV and the capacity of a fractured horizontal well section is found to be better.

Disclosure of Invention

The invention provides a time-frequency electromagnetic fracturing monitoring system and a monitoring method based on distributed optical fiber sensing, aiming at solving the problems of a hydraulic fracturing microseism monitoring technology in the aspects of evaluating the fracturing effect in real time and calculating the effective reconstructed volume (ESRV). The method comprises the steps of calculating the difference between three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and three-dimensional three-component time-frequency electromagnetic data acquired before fracturing, inverting the distribution of underground resistivity in different fracturing stages according to the actually measured ground or ground-well three-component time-frequency electromagnetic data, evaluating the fracturing effect in real time by using the distribution change characteristics of the underground resistivity in different fracturing stages, and calculating the effective reconstructed volume (ESRV) by using the envelope of the distribution of the underground resistivity inversely represented by the actually measured ground or ground-well three-component time-frequency electromagnetic data after fracturing.

The specific technical scheme is as follows:

time frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing includes: the system comprises a ground time-frequency electromagnetic data acquisition station, an acquisition armored cable, a ground controllable high-power current source, a ground armored optical cable and a distributed optical fiber sensing modulation and demodulation instrument;

the ground time-frequency electromagnetic data acquisition station is arranged on the ground above a fracturing well section of the horizontal well and is distributed in a three-dimensional manner;

the acquisition armored cable is arranged in an observation well near the fracturing well or outside a sleeve of the fracturing well and is used for acquiring underground time-frequency electromagnetic data;

the ground controllable high-power current sources are distributed on two sides of a projection line of the fracturing horizontal well section on the ground and are parallel to the extending direction of the fracturing well section;

the ground time-frequency electromagnetic data acquisition station is connected with a distributed optical fiber sensing modulation and demodulation instrument in a work area or near a wellhead through an armored optical cable; the tail ends of the armored optical cables are provided with the delusters;

the acquisition armored cable is connected with a distributed optical fiber sensing modulation and demodulation instrument; the tail end of the acquisition armored cable is provided with a deluster;

further, the ground-controllable high-power current source is a high-power dipole current source.

The ground time-frequency electromagnetic data acquisition station comprises wired or wireless node type electromagnetic data acquisition units, three-component magnetic field sensors and electric field sensors, wherein the wired or wireless node type electromagnetic data acquisition units, the three-component magnetic field sensors and the electric field sensors are distributed according to pre-designed measuring lines and measuring points.

The acquisition armored cable comprises a plurality of wired time-frequency electromagnetic data acquisition short circuits, and the wired time-frequency electromagnetic data acquisition short circuits are distributed in an array mode in a well;

the wired time-frequency electromagnetic data acquisition short circuit comprises wired time-frequency electromagnetic data acquisition units, three-component magnetic field sensors and electric field sensors which are arranged at equal intervals;

the wired time-frequency electromagnetic data acquisition short circuit is connected with the distributed optical fiber sensing modulation and demodulation instrument through an acquisition armored cable.

Furthermore, the three-component magnetic field sensor is one of an induction coil type magnetic field sensor, a fluxgate type magnetic field sensor, an MEMS magnetic field sensor, a superconducting magnetic field sensor and an optical fiber magnetic field sensor; the electric field sensor is one of copper sulfate, silver chloride, nano materials, tantalum capacitance non-polarized electrode pairs and an optical fiber electric field sensor.

The invention also provides a time-frequency electromagnetic fracturing monitoring method based on distributed optical fiber sensing, which adopts the time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing and comprises the following steps:

(a) laying a ground time-frequency electromagnetic data acquisition station on the ground according to a pre-design, wherein the ground time-frequency electromagnetic data acquisition station is connected with a distributed optical fiber sensing modulation and demodulation instrument in a work area or near a wellhead through an armored optical cable;

(b) arranging an acquisition armored cable in an observation or monitoring well near the fracturing well or outside a sleeve of the fracturing well, wherein an optical fiber at the head end of the acquisition armored cable is connected with a distributed optical fiber sensing modulation and demodulation instrument;

(c) arranging transmitting antennas of a ground controllable high-power current source on two sides of a projection line of the fracturing horizontal well section on the ground in parallel to the extension direction of the fracturing well section, embedding two ends of each transmitting antenna into the underground depth, and well performing treatment of reducing the grounding resistance of a grounding end of a power supply electrode; a ground controllable high-power current source is arranged in the middle of each transmitting antenna;

(d) before the fracturing operation is started, in the fracturing process and after the fracturing is finished, repeatedly exciting a ground controllable high-power current source, and synchronously acquiring three-dimensional time-frequency electromagnetic data of the ground or the ground and a well in real time;

(e) preprocessing three-dimensional ground or three-dimensional original time-frequency electromagnetic data in the ground and a well, which are acquired in real time, wherein the preprocessing comprises demodulating the phase and amplitude of an optical signal reflected by a received armored cable and an acquired armored cable by a distributed optical fiber sensing modulation-demodulation instrument to obtain three-dimensional three-component time-frequency or transient electric field and magnetic field data of each ground measuring point and each well measuring point, eliminating random noise, filtering, and normalizing or performing consistency processing on the three-dimensional three-component time-frequency or transient electric field and magnetic field data acquired in the ground and the well by using an excitation current value of a ground controllable emission source recorded in real time;

(f) calculating the difference between three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and three-dimensional three-component time-frequency electromagnetic data acquired before fracturing is started in real time for the preprocessed three-dimensional three-component time-frequency or transient electric field and magnetic field data, and simultaneously inverting the underground resistivity values of different fracturing stages and the distribution of the underground resistivity values around the fracturing well section according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data;

(g) displaying underground resistivity values of different fracturing stages and the change characteristics of the distribution of the underground resistivity values around a fracturing well section along with time, which are inverted according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data before the start of hydraulic fracturing, in the whole fracturing process and after the fracturing is finished, in a dynamic video mode;

(h) the range and time-varying trend of the low-resistivity zone displayed on the three-dimensional geological model along the hydraulic fracturing horizontal well section is a structure in which the low-resistivity fracturing fluid penetrates into the depth of the rock along the fracture after the rock around the horizontal well section is fractured by high hydraulic pressure; and after fracturing is finished and underground pressure relief is carried out, the volume or envelope of the underground low resistivity body obtained by inversion of the ground or ground-well three-dimensional three-component time-frequency electromagnetic data obtained by actual measurement can be regarded as the effective reconstructed volume ESRV.

The time-frequency electromagnetic fracturing monitoring system and the monitoring method based on distributed optical fiber sensing can be used for monitoring hydraulic fracturing operation in real time, optimizing fracturing parameters in real time and evaluating the final fracturing effect.

The invention has the beneficial effects that: the invention provides a time-frequency electromagnetic fracturing monitoring system and a monitoring method based on distributed optical fiber sensing. The method comprises the steps of calculating the difference between three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and three-dimensional three-component time-frequency electromagnetic data acquired before fracturing, inverting the distribution of underground resistivity in different fracturing stages according to the actually measured ground or ground-well three-component time-frequency electromagnetic data, evaluating the fracturing effect in real time by using the distribution change characteristics of the underground resistivity in different fracturing stages, and calculating the effective reconstructed volume (ESRV) by using the envelope of the distribution of the underground resistivity inversely represented by the actually measured ground or ground-well three-component time-frequency electromagnetic data after fracturing.

Drawings

FIG. 1 is a schematic view of a monitoring system of the present invention.

Detailed Description

In order to facilitate the understanding of the technical contents of the present invention by those skilled in the art, the present invention will be further explained with reference to the accompanying drawings.

As shown in fig. 1, the time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing includes: the system comprises a ground time-frequency electromagnetic data acquisition station 1, an acquisition armored cable 2, a ground controllable high-power electromagnetic source 3 and a distributed optical fiber sensing modulation and demodulation instrument 5;

the ground time-frequency electromagnetic data acquisition station 1 is arranged on the ground above a fracturing well section of the horizontal well and is arranged in a three-dimensional manner;

the acquisition armored cable 2 is arranged in an observation well near the fracturing well or outside a sleeve of the fracturing well and is used for acquiring underground time-frequency electromagnetic data;

the ground controllable high-power current source 3 is arranged on two sides of a projection line of the fracturing horizontal well section on the ground and is parallel to the extending direction of the fracturing well section; the ground controllable high-power current source 3 is a high-power dipole current source.

The ground time-frequency electromagnetic data acquisition station 1 is connected with a distributed optical fiber sensing modulation and demodulation instrument 5 in a work area or near a wellhead through a ground armored optical cable 4; the tail ends of the armored optical cables 4 are provided with the delusters 7;

the acquisition armored cable 2 is connected with a distributed optical fiber sensing modulation and demodulation instrument 5; the tail end of the acquisition armored cable 2 is provided with a deluster 7;

the ground time-frequency electromagnetic data acquisition station 1 comprises wired or wireless node type electromagnetic data acquisition units, three-component magnetic field sensors and electric field sensors, wherein the wired or wireless node type electromagnetic data acquisition units, the three-component magnetic field sensors and the electric field sensors are distributed according to pre-designed measuring lines and measuring points. The three-component magnetic field sensor is one of an induction coil type magnetic field sensor, a fluxgate type magnetic field sensor, an MEMS (micro-electromechanical systems) magnetic field sensor, a superconducting magnetic field sensor and an optical fiber magnetic field sensor; the electric field sensor is one of copper sulfate, silver chloride, nano materials, tantalum capacitance non-polarized electrode pairs and an optical fiber electric field sensor.

The acquisition armored cable 2 comprises a plurality of wired time-frequency electromagnetic data acquisition short circuits 6, and the wired time-frequency electromagnetic data acquisition short circuits 6 are distributed in an array mode in a well; the wired time-frequency electromagnetic data acquisition short circuit 6 comprises wired time-frequency electromagnetic data acquisition units, three-component magnetic field sensors and electric field sensors which are arranged at equal intervals; the three-component magnetic field sensor is one of an induction coil type magnetic field sensor, a fluxgate type magnetic field sensor, an MEMS (micro-electromechanical systems) magnetic field sensor, a superconducting magnetic field sensor and an optical fiber magnetic field sensor; the electric field sensor is one of copper sulfate, silver chloride, nano materials, tantalum capacitance non-polarized electrode pairs and an optical fiber electric field sensor. The wired time-frequency electromagnetic data acquisition short circuit 6 is connected with the distributed optical fiber sensing modulation and demodulation instrument 5 through the acquisition armored cable 2.

The time-frequency electromagnetic fracturing monitoring method based on distributed optical fiber sensing adopts the time-frequency electromagnetic fracturing monitoring system based on distributed optical fiber sensing, and comprises the following steps:

(a) the method comprises the following steps that a ground time-frequency electromagnetic data acquisition station 1 is distributed on the ground according to a pre-design, and the ground time-frequency electromagnetic data acquisition station 1 is connected with a distributed optical fiber sensing modulation and demodulation instrument 5 in a work area or near a wellhead through an armored optical cable 4;

(b) an acquisition armored cable 2 is arranged in an observation or monitoring well near the fracturing well or outside a sleeve of the fracturing well, and an optical fiber at the head end of the acquisition armored cable 2 is connected with a distributed optical fiber sensing modulation and demodulation instrument 5;

(c) arranging transmitting antennas of a ground controllable high-power current source 3 on two sides of a projection line of the fracturing horizontal well section on the ground in parallel to the extension direction of the fracturing well section, embedding two ends of each transmitting antenna into the underground depth, and well performing treatment of reducing the grounding resistance of a grounding end of a power supply electrode; a ground controllable high-power current source 3 is arranged in the middle of each transmitting antenna;

(d) before the fracturing operation is started, in the fracturing process and after the fracturing is finished, repeatedly exciting a ground controllable high-power current source 3, and synchronously acquiring three-dimensional ground or three-dimensional time-frequency electromagnetic data in the ground and a well in real time;

(e) preprocessing three-dimensional ground or three-dimensional original time-frequency electromagnetic data in the ground and a well, which are acquired in real time, wherein a distributed optical fiber sensing modulation and demodulation instrument 5 demodulates the phase and amplitude of an optical signal reflected by a received armored optical cable 4 and an acquired armored cable 2 to obtain three-dimensional three-component time-frequency or transient electric field and magnetic field data of each ground measuring point and well measuring point, eliminates random noise, filters, and normalizes or coherently processes the three-dimensional three-component time-frequency or transient electric field and magnetic field data acquired in the ground and the well by using an excitation current value of a ground controllable emission source recorded in real time;

(f) calculating the difference between three-dimensional three-component time-frequency electromagnetic data acquired in the fracturing process and after fracturing and three-dimensional three-component time-frequency electromagnetic data acquired before fracturing is started in real time for the preprocessed three-dimensional three-component time-frequency or transient electric field and magnetic field data, and simultaneously inverting the underground resistivity values of different fracturing stages and the distribution of the underground resistivity values around the fracturing well section according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data;

(g) displaying underground resistivity values of different fracturing stages and the change characteristics of the distribution of the underground resistivity values around a fracturing well section along with time, which are inverted according to the actually measured ground or ground-well three-dimensional three-component time-frequency electromagnetic data before the start of hydraulic fracturing, in the whole fracturing process and after the fracturing is finished, in a dynamic video mode;

(h) the range and time-dependent trend of the low-resistivity zone displayed on the three-dimensional geological model along the hydraulic fracturing horizontal well section is the structure that the low-resistivity fracturing fluid penetrates into the depth of the rock along the crack 8 after the rock around the horizontal well section is cracked by high hydraulic pressure; and (3) obtaining the volume or envelope (9) of the underground low resistivity body by inversion of the ground or ground-well three-dimensional three-component time-frequency electromagnetic data measured after the underground pressure relief is finished after the fracturing is finished, wherein the volume or envelope can be regarded as the effective modified volume ESRV.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.