CN116449434A - Method and system for detecting geothermal energy by electromagnetic frequency sounding in electromagnetic interference area - Google Patents
Method and system for detecting geothermal energy by electromagnetic frequency sounding in electromagnetic interference area Download PDFInfo
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Abstract
The invention discloses a method and a system for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area, comprising the following steps: collecting data of an electromagnetic interference area to predict key characteristics of a target geologic body, and further determining the position and embedding mode of a field source AB electrode, the receiving and transmitting distance between a detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode; performing field test according to the position and embedding mode of the AB electrode of the field source, the receiving and transmitting distance and the direction and distance of the MN electrode of the detection area, and determining the parameter value of each key parameter according to the field test result; carrying out formal field production according to parameter values of key parameters, and acquiring complete data of an electromagnetic interference area; and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results. The invention achieves the purpose of improving the applicability of electromagnetic frequency sounding in geothermal energy exploration and the quality of achievements.
Description
Technical Field
The invention relates to the technical field of geological exploration, in particular to a method and a system for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area.
Background
The China is the biggest developing country, the high-speed development of over 40 years causes the excessive exploitation of the conventional energy in China, and clean energy resources such as geothermal energy, solar energy and the like are listed in a new energy development plan in China according to the national energy policy, so that the method is not only the requirement of a 'two-carbon' target, but also a solid foundation can be laid for relieving the situation of energy shortage in China.
The development and utilization of geothermal energy are mainly industrial and agricultural production, resident life and ecological tourism services, and development areas are mostly located in and around the urban developed areas. Town has brought dense population, dense buildings, more ground and underground projects, developed traffic, and corresponding optical fibers, high-voltage electricity, power electricity, mechanical equipment operation and the like to generate strong electromagnetic interference. These conditions make it difficult to survey geothermal energy, and many geophysical methods such as gravitational, magnetic, seismic, and magnetotelluric methods have not been effective.
Although the artificial source electromagnetic frequency sounding can obtain relatively good exploration results, on one hand, the intensive humanoid buildings on the ground limit the construction of the electromagnetic frequency sounding when the geothermal energy exploration is carried out, and influence the exploration efficiency and the quality of the acquired exploration data, and on the other hand, the strong electromagnetic interference seriously influences the electromagnetic frequency sounding data and influences the geothermal energy exploration results.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method and a system for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area, which are used for solving the technical problems that the prior art is limited by a human building and is interfered by electromagnetic waves when the geothermal energy is detected, and the exploration efficiency and the quality of acquired exploration data are affected, so that the purposes of improving the applicability of the electromagnetic frequency sounding in the geothermal energy exploration and improving the quality of achievements are achieved.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a method for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area comprises the following steps:
collecting data of an electromagnetic interference area, and predicting key characteristics of a target geologic body according to the data of the electromagnetic interference area;
determining the position and embedding mode of a field source AB electrode, the receiving-transmitting distance between a detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the data of the electromagnetic interference area and the prediction result of the key characteristics;
performing field test according to the position and embedding mode of the field source AB electrode, the receiving-transmitting distance and the direction and distance of the detection area MN electrode, and determining parameter values of all key parameters according to field test results;
carrying out formal field production according to the parameter values of the key parameters, and collecting the complete data of the electromagnetic interference area;
and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
In a preferred embodiment of the present invention, predicting key features of the target geologic volume according to the data of the electromagnetic interference area includes:
and collecting and analyzing the data of the topography, geology, hydrogeology, geothermal energy and geophysical prospecting of the electromagnetic interference area, and predicting and detecting the maximum depth, apparent resistivity and minimum frequency of the target geological body.
In a preferred embodiment of the present invention, when the lowest frequency of the target geologic volume is predicted to be detected, the method includes:
predicting the lowest frequency of the detected target geologic body through a detection depth calculation formula, particularly as a formula
Formula 1:
wherein D is the effective detection depth m, ρ is the formation resistivity Ω·m, and f is the frequency Hz.
In a preferred embodiment of the present invention, the method for determining the position and embedding scheme of the field source AB electrode includes:
acquiring the position of an interference source in the field source AB electrode layout area and the position of a local electrical non-uniform body between the field source AB electrode and the electromagnetic interference area;
the position of the interference source and the position of the local electrical non-uniform body are avoided, and the field source AB electrode is arranged;
the actual grounding point of the AB electrode of the field source is arranged at the wet position of soil, the distance between the electrode A and the electrode B is 1-3 km, the electrodes are connected in parallel by adopting multiple points, and the distance between the adjacent electrode points is not less than 3m.
In a preferred embodiment of the present invention, when determining a transmission/reception distance between a detection area MN electrode and a field source AB electrode, the method includes:
and judging whether the site conditions are limited, if so, setting the receiving and transmitting distance according to the detection depth which is more than 3 times, and if not, setting the receiving and transmitting distance according to the detection depth which is more than 2 times.
As a preferred embodiment of the present invention, in determining the direction and distance of the detection area MN electrode, it includes:
the direction of the field source AB electrode is obtained, and the direction of the MN electrode in the detection region is matched according to the direction of the field source AB electrode;
and acquiring the positions of an interference source and an obstacle in the detection area MN electrode layout area, avoiding the positions of the interference source and the obstacle, and layout the detection area MN electrode.
In a preferred embodiment of the present invention, when determining the parameter values of the respective key parameters according to the field test results, the method comprises:
presetting a test interval aiming at different key parameters, selecting different working frequencies, distances of field source AB electrodes, emission currents, emission-receiving distances and electrode pole pitch sizes of detection areas MN in the test interval, obtaining a plurality of field test results, and selecting proper parameter values aiming at different key parameters according to the plurality of field test results;
the key parameters comprise working frequency, distance of a field source AB electrode, emission current, emission-receiving distance and electrode pole distance of a detection area MN.
In a preferred embodiment of the present invention, the method for performing the field production comprises:
acquiring the frequency of the deepest target geologic body, and setting data acquisition frequency according to the frequency of the deepest target geologic body;
detecting the electromagnetic interference area according to the data acquisition frequency and the parameter values of the key parameters, and in the detection process, timely adjusting the position and the direction of an MN electrode of the detection area according to the positions of an interference source and an obstacle, acquiring electromagnetic interference area data, acquiring the root mean square error of the electromagnetic interference area data and establishing an original electric field-frequency curve;
and judging whether the quality of the electromagnetic interference area data is qualified or not according to the root mean square error and the original electric field-frequency curve, and if so, completing the acquisition of the electromagnetic interference area complete data.
As a preferred embodiment of the present invention, in the final explanation of the electromagnetic interference region, it includes:
performing electromagnetic interference suppression processing and filtering processing on the complete data of the electromagnetic interference area to obtain denoising data;
utilizing electric field data in the denoising data, obtaining full-period apparent resistivity at the position of an MN electrode of the detection region according to the position of an AB electrode of the field source, drawing a multi-frequency curve and an apparent resistivity-frequency simulated section diagram according to the full-period apparent resistivity, extracting double-frequency excitation amplitude frequency parameters, and performing preliminary explanation of a fracture structure and a substrate;
selecting proper parameters according to the multi-frequency curve and the apparent resistivity-frequency pseudo-section to perform static displacement correction, drawing the multi-frequency curve and the apparent resistivity pseudo-section after static displacement correction, and further performing preliminary explanation on the fracture structure and the substrate to obtain preliminary explanation results of the fracture structure and the substrate;
and extracting electromagnetic frequency sounding pseudo-earthquake display parameters, performing preliminary interpretation and inversion treatment on an aquifer interface, and performing final interpretation on the electromagnetic interference region by combining the fracture structure and the preliminary interpretation result of the substrate.
A system for electromagnetic frequency sounding of an electromagnetic interference region for detecting geothermal energy, comprising:
prediction unit: the method is used for collecting data of an electromagnetic interference area and predicting key characteristics of a target geologic body according to the data of the electromagnetic interference area;
electrode setting unit: the method is used for determining the position and embedding mode of the field source AB electrode, the receiving-transmitting distance between the detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the information of the electromagnetic interference area and the prediction result of the key characteristics;
parameter determination unit: the field test is carried out according to the position and the embedding mode of the field source AB electrode, the receiving-transmitting distance and the direction and the distance of the detection area MN electrode, and parameter values of all key parameters are determined according to field test results;
interpretation unit: the method is used for carrying out formal field production according to the parameter values of the key parameters and collecting the complete data of the electromagnetic interference area; and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention forms a technical flow of electromagnetic frequency sounding detection of geothermal energy in an electromagnetic interference area, can effectively solve the technical problems that the prior art is limited by human buildings and interfered by electromagnetic waves when detecting the geothermal energy, and improves the applicability and the achievement quality of the electromagnetic frequency sounding in the geothermal energy exploration;
(2) The invention provides basic guarantee for the development and utilization of geothermal energy, and plays a role of geophysical prospecting technology in realizing national 'double carbon' targets.
The invention is described in further detail below with reference to the drawings and the detailed description.
Drawings
FIG. 1 is a block diagram of basin construction elements in a research area gateway according to an embodiment of the present invention;
FIG. 2-is a schematic representation of a fracture of a study area according to an embodiment of the present invention;
FIG. 3 is a physical diagram of a wide area electromagnetic instrument signal transmitter apparatus according to an embodiment of the invention;
FIG. 4 is a schematic diagram of the location of the electromagnetic frequency sounding site in the investigation region according to an embodiment of the present invention;
FIG. 5 is a graph showing the multi-frequency potential difference between the receiving electrodes MN of line 1 according to the embodiment of the present invention;
FIG. 6 is a schematic cross-sectional view of apparent resistivity versus frequency for line 1 of an embodiment of the invention;
FIG. 7 is a schematic cross-sectional view of apparent resistivity versus frequency after static displacement correction for line 1 in accordance with an embodiment of the present invention;
FIG. 8-is a plot of inverted resistivity profiles for line 1 of an embodiment of the invention;
FIG. 9-is a line 1 simulated seismic cross-section of an embodiment of the invention;
FIG. 10 is a schematic representation of a 1-wire transient electromagnetic resistivity profile in accordance with an embodiment of the invention;
FIG. 11 is a graph of the amplitude frequency of a line 1 employing two frequency extractions in accordance with an embodiment of the present invention;
FIG. 12-is a 2-line simulated seismic cross-section of an embodiment of the invention;
fig. 13 is a step diagram of a method for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference region according to an embodiment of the present invention.
Detailed Description
The method for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area provided by the invention, as shown in fig. 13, comprises the following steps:
step S1: collecting data of an electromagnetic interference area, and predicting key characteristics of a target geologic body according to the data of the electromagnetic interference area;
step S2: determining the position and embedding mode of the field source AB electrode, the receiving and transmitting distance between the detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the data of the electromagnetic interference area and the prediction result of the key characteristics;
step S3: performing field test according to the position and embedding mode of the AB electrode of the field source, the receiving and transmitting distance and the direction and distance of the MN electrode of the detection area, and determining the parameter value of each key parameter according to the field test result;
step S4: carrying out formal field production according to parameter values of key parameters, and acquiring complete data of an electromagnetic interference area;
step S5: and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
In the step S1, when predicting the key feature of the target geologic volume according to the data of the electromagnetic interference area, the method includes:
and collecting and analyzing the data of the topography, geology, hydrogeology, geothermal energy and geophysical prospecting of the electromagnetic interference area, and predicting the maximum depth, apparent resistivity and minimum frequency of the detected target geological body.
Further, when the lowest frequency of the target geologic volume is predicted to be detected, the method comprises:
the lowest frequency of the detected target geologic body is predicted by a detection depth calculation formula, and the lowest frequency is specifically shown as a formula 1:
wherein D is the effective detection depth m, ρ is the formation resistivity Ω·m, and f is the frequency Hz.
In the step S2, when determining the position and the embedding manner of the field source AB electrode, the method includes:
acquiring the position of an interference source in a field source AB electrode layout area and the position of a local electrical non-uniform body between the field source AB electrode and an electromagnetic interference area;
avoiding the position of an interference source and the position of a local electrical non-uniform body, and arranging a field source AB electrode;
the actual grounding point of the AB electrode of the field source is arranged at the wet position of the soil, the distance between the electrode A and the electrode B is 1-3 km, the electrodes are connected in parallel by adopting multiple points, and the distance between the adjacent electrode points is not less than 3m.
Further, the electrode material can be selected from a plurality of metal rods or a plurality of metal plates, nets, foils and the like, and is buried by hammering into the ground or digging a plurality of electrode pits. The arrangement of the field source AB electrode needs to avoid high-voltage lines, above mines (holes), buried pipelines, stream water areas, parallel fracture structures and the like as much as possible so as to reduce electromagnetic interference. The layout of the field source AB electrode also considers that the partial electric non-uniformities such as known mines, lakes, karst cave and the like are avoided as much as possible between the AB electrode and the detection area (data acquisition area).
In the step S2, when determining the transmission/reception distance between the detection area MN electrode and the field source AB electrode, the method includes:
and judging whether the site conditions are limited, if so, setting the receiving and transmitting distance according to the detection depth which is more than 3 times, and if not, setting the receiving and transmitting distance according to the detection depth which is more than 2 times.
Further, under the condition that the receiving and transmitting distance meets the conditions, the receiving and transmitting distance is reduced as much as possible, so that the signal to noise ratio of the acquired data is improved.
In the above step S2, when determining the direction and distance of the detection area MN electrode, it includes:
the direction of a field source AB electrode is obtained, and the direction of a detection area MN electrode is matched according to the direction of the field source AB electrode;
and acquiring the positions of the interference source and the obstacle in the MN electrode layout area of the detection area, avoiding the positions of the interference source and the obstacle, and layout the MN electrode of the detection area.
Further, electromagnetic interference such as high-voltage wires, power wires, optical fibers and the like which are known in the detection area is vertical to the greatest extent while avoiding interference sources and obstacles.
In the step S3, when determining the parameter values of the key parameters according to the field test result, the method includes:
presetting a test interval aiming at different key parameters, selecting different working frequencies, distances of field source AB electrodes, emission currents, emission-receiving distances and electrode distance of detection area MN in the test interval, obtaining a plurality of field test results, and selecting proper parameter values aiming at different key parameters according to the plurality of field test results;
the key parameters include working frequency, distance of the field source AB electrode, emission current, emission-receiving distance and electrode pole distance of the detection area MN.
Further, field trials are developed according to design and engineering arrangements, and the objective of the field trials is to select appropriate parameter values for completing the objective task of detection.
In the step S4, when the official field production is performed, the method includes:
acquiring the frequency of the deepest target geologic body, and setting data acquisition frequency according to the frequency of the deepest target geologic body;
detecting an electromagnetic interference area according to the data acquisition frequency and the parameter values of each key parameter, and in the detection process, timely adjusting the position and the direction of an MN electrode of the detection area according to the positions of an interference source and an obstacle, acquiring the data of the electromagnetic interference area, acquiring the root mean square error of the data of the electromagnetic interference area and establishing an original electric field-frequency curve;
and judging whether the quality of the electromagnetic interference area data is qualified or not according to the root mean square error and the original electric field-frequency curve, and if so, completing the acquisition of the complete electromagnetic interference area data.
Further, in order to extract the frequency parameters of the dual-frequency excitation amplitude, two frequencies of the data acquisition frequency are smaller than the frequency satisfying the detection of the deepest target geologic body.
Specifically, data quality monitoring work and MN electrode direction adjustment work are required to be performed in formal field production, electric field data of each frequency are required to be monitored, root mean square error of field multiple superimposed data meets design requirements, field data of the same day draws a full-period apparent resistivity curve according to measuring points, and original electric field-frequency curves are spot checked to evaluate data quality. According to a field electromagnetic interference source and an obstacle, the position and the direction of an MN electrode are adjusted in time, electromagnetic interference such as voltage lines, power electricity and optical fibers is restrained, complete data of an electromagnetic interference area are acquired, and the coordinate of each M, N electrode is required to be actually measured for subsequent data processing.
In the step S5, when the electromagnetic interference area is finally explained, the method includes:
performing electromagnetic interference suppression processing and filtering processing on the complete data of the electromagnetic interference area to obtain denoising data;
utilizing electric field data in the denoising data, obtaining full-period apparent resistivity according to the position of an AB electrode of a field source and the position of an MN electrode of a detection area, drawing a multi-frequency curve and an apparent resistivity-frequency pseudo-section diagram according to the full-period apparent resistivity, extracting double-frequency excitation amplitude frequency parameters, and performing preliminary explanation of a fracture structure and a substrate;
selecting proper parameters to perform static displacement correction according to the multi-frequency curve and the apparent resistivity-frequency pseudo-section diagram, drawing the multi-frequency curve and the apparent resistivity pseudo-section diagram after static displacement correction, and further performing preliminary explanation on the fracture structure and the substrate to obtain preliminary explanation results of the fracture structure and the substrate;
and extracting electromagnetic frequency sounding simulated earthquake display parameters, performing preliminary interpretation and inversion treatment on an aquifer interface, and performing final interpretation on an electromagnetic interference region by combining a fracture structure and a preliminary interpretation result of a substrate.
Further, the final interpretation includes: construction, aquifer interface and water-rich zone anomalies.
The invention provides a system for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area, which comprises: a prediction unit, an electrode setting unit, a parameter determination unit, and an interpretation unit.
The prediction unit is used for collecting the data of the electromagnetic interference area and predicting the key characteristics of the target geologic body according to the data of the electromagnetic interference area.
The electrode setting unit is used for determining the position and embedding mode of the field source AB electrode, the receiving-transmitting distance between the detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the data of the electromagnetic interference area and the prediction result of the key characteristics.
The parameter determining unit is used for performing field test according to the position and embedding mode of the field source AB electrode, the receiving and transmitting distance, and the direction and distance of the detection area MN electrode, and determining the parameter value of each key parameter according to the field test result.
The interpretation unit is used for carrying out formal field production according to the parameter values of the key parameters and collecting complete data of the electromagnetic interference area; and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
The following examples are further illustrative of the present invention, but the scope of the present invention is not limited thereto. Example (application of electromagnetic frequency sounding in Hancheng geothermal energy detection of Shaanxi)
1. Geothermal energy geological conditions
1. Stratum layer
The geothermal energy of Shaanxi Korean is stored in the ancient Ore limestone, the upper part is covered with ancient stone carbon system and dyadic system, the middle-aged tri-system, the new system and the fourth system stratum, and the thickness of the cover layer is about 2500m. The old to new formation is briefly described as follows:
(1) Ancient world Olympic series (O)
The substrate of the region is north-deep, south-shallow, north-thick, south-thin. The upper part is mainly a thin plate-shaped or page-shaped limestone, and is used for clamping tuff and breccia limestone; the middle lower part is mainly limestone and dolomite, and the part is used for clamping the marl, the calcareous shale and the siliceous dolomite.
(2) Ancient world stone charcoal system (C)
The substrate of the region is north-deep, south-shallow, north-thick, south-thin. The upper part is light gray sandy mudstone claystone, wherein a coal bed exists, and the bottom of the sandy mudstone contains Shanxi pyrite tuberculosis; the lower part is a light gray clay rock coal line, a gray black block-shaped mudstone and a gray sandy mudstone.
(3) Ancient world two-fold system (P)
Buried under the tri-stack system, the north is deep, the south is shallow, and the north is thick, and the south is thin. The upper part is mainly made of dark red mudstone, gray green fine sandstone, gray black mudstone, siltstone and medium coarse sandstone; the lower part is variegated mudstone, dark grey, and black gray medium and fine sandstone, silty sandstone and sandy mudstone.
(4) Zhongsheng world triad (T)
Buried under the recent stratum, the north is deep, the south is shallow, and the north is thick, and the south is thin. The upper part is mainly made of purple red, brownish red, grayish green siltstone, mudstone, yellow green, grayish gray lamellar sandstone; the lower part is mainly made of sandstone which is formed by gray green thick-huge thick staggered layer, and brownish red mudstone is clamped.
(5) New world recent series (N)
Buried under the fourth line, the north is deep, the south is shallow, and the north is thick, the south is thin. Lithology is mainly made of mauve clay, and is clamped and cemented, semi-cemented, fine sand and gravel layers, and contains a large amount of calcium tuberculosis.
(6) New world fourth series (Q)
The new stratum is mainly updated and completely new stratum is covered on the new stratum, the lithology is mainly light yellow, gray yellow silty clay and silty clay, and fine sand and pebble layers are sandwiched.
2. Constructional features
The study area is in the border zone between the southwest edge and the Fenwei cutting of the Eldos plot on the ground structure, and is subdivided into the Pucheng protrusion of the Wei river subsidence basin, and the southern part is adjacent to the solid city depression with the Kongzhen-Guangshan fracture as a boundary, as shown in figure 1.
According to regional geological data, the developed fracture in the region has a large Korean fracture F1, as shown in FIG. 2. The large Korean fracture F1 is the maximum fracture of the standard mould in the area, the fracture is a large mountain front fracture, a Yu gate is started in the north east, a Xin Zhuang line from the south west to the Longtin origin extends for 26 km in the whole area, the fracture surface mainly shows positive faults, the fracture surface is in a gentle wave shape along the trend and tends to be in a trend NE20-50 degrees, the inclination angle is larger than 60 degrees, and the fracture distance is larger than 500m. The fracture is a boundary between the mountain region of the north mountain and the Guanzhong plain, the south east region of the fault is continuously fallen, a huge thick fourth-system loose sediment of hundreds of meters is deposited, the topography is gentle, the northeast part of Wei river cutting is constructed, and good heat storage conditions of a cover layer are provided; the North western terrains of faults are high in severity, the fault block terrains are composed of huge thick rock stratum and overlying fourth-series loose sediments, and the faults are mainly formed by the Otto limestone and the triathlon sand shale of the exposed stratum.
2. Implementation of electromagnetic frequency sounding
1. Outdoor construction
The electromagnetic frequency sounding exploration is constructed for three times in a year, adopts a wide area electromagnetic instrument system which is developed by combining Hunan secondary high-tech limited company and Zhongnan university, and mainly comprises the following equipment: wide area electromagnetic transmitter, wide area electromagnetic receiver, high power generator, etc.
1.1, emission field Source
The wide area electromagnetic instrument transmitter is composed of three parts: a high power diesel alternator, a rectifier inverter and a pseudorandom signaling controller. The transmitter system generates a large-energy pseudo-random signal through the rectifier cabinet under the action of the pseudo-random signal generator and supplies power to the underground, as shown in fig. 3.
The signal source of the wide area electromagnetic transmitter is 2 n The sequence pseudo-random signal can select different signal frequencies according to exploration needs, and 7 frequencies can be transmitted simultaneously at present, so that the requirement of simultaneous measurement of a plurality of frequencies is realized, and the exploration efficiency is greatly improved. The main technical indexes are as follows:
1) Voltage range: less than 1000V;
2) Current range: < 200A;
3) Frequency range: 0.0117-8192 HZ.
Three surveys used 4 different field sources, each transmitting electrode A, B being approximately 1km apart. A. The electrode B adopts 18 aluminum foil plates (about 1m multiplied by 1 m), 18 electrode pits are dug and buried, the pit depth is not less than 0.6m, the adjacent pit distance is not less than 3m, conductive liquid (sodium chloride solution) is poured on the aluminum foil plates, the grounding resistance of an AB field source is reduced, and finally the emission current is about 120A.
1.2 data acquisition
The wide-area electromagnetic exploration receiving system mainly comprises a wide-area electromagnetic instrument receiver, a receiving electrode and a computer workstation. The specific indexes of the wide-area electromagnetic instrument receiver are as follows:
1) Analog-to-digital converter resolution: 24 bits;
2) Analog-to-digital converter rate: greater than 600KSPS;
3) Signal input range: -37.5mv to +37.5mv;
4) Signal frequency range: 0.0117 Hz-10 KHz;
5) Detection sensitivity: more than or equal to 0.05mV;
6) Potential difference measurement accuracy: + -0.5%;
7) Input impedance: 3mΩ;
8) Fixed gain: 100 times.
The depth of the Otto limestone in a research area is about 2900m, and the geothermal energy detection depth is required to be 4000m, so that 11, 9, 7, 5, 3 and 1 frequency groups of 7 frequency waves of a wide area electromagnetic instrument are selected to supply power and collect data, the highest frequency is 8192Hz, the lowest frequency is 0.0117Hz, and the total number of frequency points is 40.
2. Engineering arrangement
Fig. 4 is a schematic diagram of the position of the electromagnetic frequency sounding point in the research area, and as can be seen from fig. 4, three constructions are at a certain distance from each other. The first construction site is located at the urban and rural junction of northeast of Hancheng, 1 line (named as 1 line), the length is 3km, the point distance and the MN electrode distance are 100m, and the frequency sounding points are 31. The system comprises 1 emission field source, about 12km receiving distance, and Korean urban area between the field source and receiving point. Meanwhile, transient electromagnetic exploration is carried out, the point distance is 25m, and the number of measuring points is 121.
The second construction site is located at about 1.2km in southwest of the first construction site, and has entered into a city area, 2 lines (named as 2 lines and 3 lines) are arranged along the street in the city area, and the lines are broken lines. The point distance is 50-100m different from the MN electrode distance, and 64 frequency sounding points are completed. 1 emitting field source is not far from the first time field source position, the receiving and transmitting distance is about 11km, and a Korean urban area is arranged between the field source and the receiving point.
The third construction site was located in the south of the first and second times, about 2.4km from the second construction site. The method is positioned between a city area and a yellow river, 3 construction test lines (named as 4, 5 and 6 lines) are arranged, the point distance and the MN electrode distance are about 100m, and 51 frequency sounding points are completed. The third survey uses 2 field sources and a number of modes of exploration studies were performed.
3. Geothermal energy detection result
Fig. 5 is a graph of the difference in potential between the receiving electrodes MN of 1 line (normalized by the transmitting current) for multiple frequencies, 3 bands from top to bottom. The 2750 point has high voltage line, and the voltage of the high frequency range is obviously higher than 2000-2500 sections. In the low frequency band, the multi-frequency curve shows that the voltage of the small-size point is higher than that of the large-size point, and the curve fluctuation form reflects the form of the high-resistance substrate of the Otto limestone, so that the northwest buried depth is small and the southeast buried depth is large.
Fig. 6 is a schematic view of apparent resistivity versus frequency along line 1, and the static displacements at points 800, 1200, 1700, 2400, 2600 are apparent from fig. 6. FIG. 7 is a schematic view of a corrected apparent resistivity versus frequency for a static displacement of line 1, with the corrected apparent resistivity contours substantially reflecting formation fluctuations and showing more visual effects on the northwest shallow and southeast deep of the Ortsea limestone high resistance substrate.
FIG. 8 is a 1-line inversion resistivity profile, and FIG. 8 shows the resistivity of different locations in the subsurface space, as explained by electrical stratification based on resistivity profile, with lower formation resistivity above elevation-1700-1400 m, as explained by the new-world (late-system) formation floor. The elevation of the Ore limestone is between-2750 and-2250 m, and the Otto limestone has an obvious low-resistance abnormality at 1500 points, which is interpreted as a fault.
Fig. 9 is a simulated seismic cross-section taken along line 1, with the reference plane selected in fig. 9 being 450m. By means of the simulated seismic section display, the structures of the electric stratum dividing line, faults and the like can be more accurately interpreted. Faults 3 were interpreted near the Otto limestone interface, with 1 large fault and 2 small faults. Fig. 10 is a 1-line transient electromagnetic resistivity profile, and fig. 10 can generally resolve the location of the top boundary of the oldham's ash and explain 4 water-rich anomaly regions in the oldham's ash.
FIG. 11 is a graph of the amplitude frequency of line 1 using two frequency extractions, with 800 points being maximum at a small amplitude frequency, greater than 0.46 average; the amplitude frequency around 2000 times, with 3 measurement point values greater than 0.46, are relatively strong rich zones.
By combining an inversion resistivity section chart, a quasi-seismic display section, a double-frequency amplitude frequency curve and transient electromagnetic exploration results, a geothermal energy well position No. 2000 is suggested to an owner. According to the proposal, the owner drills a hole in construction No. DRJ 2000, the depth of an Olympic Games roof interface is 2904m, and the water yield of a wellhead is 60m 3 And/h, the temperature is 82 ℃, the water yield and the temperature are higher than expected, and the water yield and the temperature are used as geothermal energy heating. The wellhead outlet temperature of DRJ 1400 meters away from the DRJ well was only 56 ℃.
Fig. 12 is a simulated seismic cross-section of line 2, and fig. 12 shows that the burial depth of the otto limestone is about 2800m, which is shallower than line 1. The relief forms of the top interface of the Ort gray rock and the bottom interface of the new world are similar to 1 line, and are generally expressed as North west high and south east low.
The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.
Claims (10)
1. The method for detecting the geothermal energy by electromagnetic frequency sounding in the electromagnetic interference area is characterized by comprising the following steps:
collecting data of an electromagnetic interference area, and predicting key characteristics of a target geologic body according to the data of the electromagnetic interference area;
determining the position and embedding mode of a field source AB electrode, the receiving-transmitting distance between a detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the data of the electromagnetic interference area and the prediction result of the key characteristics;
performing field test according to the position and embedding mode of the field source AB electrode, the receiving-transmitting distance and the direction and distance of the detection area MN electrode, and determining parameter values of all key parameters according to field test results;
carrying out formal field production according to the parameter values of the key parameters, and collecting the complete data of the electromagnetic interference area;
and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
2. The method for depth sounding geothermal energy of electromagnetic interference area according to claim 1, wherein when predicting key features of a target geologic volume according to data of the electromagnetic interference area, comprising:
and collecting and analyzing the data of the topography, geology, hydrogeology, geothermal energy and geophysical prospecting of the electromagnetic interference area, and predicting and detecting the maximum depth, apparent resistivity and minimum frequency of the target geological body.
3. The method for electromagnetic frequency sounding of a region of electromagnetic interference to detect geothermal energy of claim 2, wherein upon predicting a lowest frequency of the target geologic volume to be detected, comprising:
the lowest frequency of the target geologic body is predicted and detected through a detection depth calculation formula, and the method is specifically shown as a formula 1:
wherein D is the effective detection depth m, ρ is the formation resistivity Ω·m, and f is the frequency Hz.
4. The method for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area according to claim 1, wherein when determining the position and embedding mode of the AB electrode of the field source, comprising:
acquiring the position of an interference source in the field source AB electrode layout area and the position of a local electrical non-uniform body between the field source AB electrode and the electromagnetic interference area;
the position of the interference source and the position of the local electrical non-uniform body are avoided, and the field source AB electrode is arranged;
the actual grounding point of the AB electrode of the field source is arranged at the wet position of soil, the distance between the electrode A and the electrode B is 1-3 km, the electrodes are connected in parallel by adopting multiple points, and the distance between the adjacent electrode points is not less than 3m.
5. The method for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area according to claim 1, wherein when determining a transmission/reception distance between an electrode of the detection area MN and an electrode of the field source AB, comprising:
and judging whether the site conditions are limited, if so, setting the receiving and transmitting distance according to the detection depth which is more than 3 times, and if not, setting the receiving and transmitting distance according to the detection depth which is more than 2 times.
6. The method for electromagnetic frequency sounding of a detection area MN of claim 1, wherein determining the direction and distance of the detection area MN electrode comprises:
the direction of the field source AB electrode is obtained, and the direction of the MN electrode in the detection region is matched according to the direction of the field source AB electrode;
and acquiring the positions of an interference source and an obstacle in the detection area MN electrode layout area, avoiding the positions of the interference source and the obstacle, and layout the detection area MN electrode.
7. The method for measuring the depth of field of view by electromagnetic frequency in an electromagnetic interference area according to claim 1, wherein when determining the parameter values of each key parameter according to the field test result, the method comprises:
presetting a test interval aiming at different key parameters, selecting different working frequencies, distances of field source AB electrodes, emission currents, emission-receiving distances and electrode pole pitch sizes of detection areas MN in the test interval, obtaining a plurality of field test results, and selecting proper parameter values aiming at different key parameters according to the plurality of field test results;
the key parameters comprise working frequency, distance of a field source AB electrode, emission current, emission-receiving distance and electrode pole distance of a detection area MN.
8. The method for electromagnetic frequency sounding of a region of electromagnetic interference for detecting geothermal energy according to claim 1, wherein the method comprises, when performing official field production:
acquiring the frequency of the deepest target geologic body, and setting data acquisition frequency according to the frequency of the deepest target geologic body;
detecting the electromagnetic interference area according to the data acquisition frequency and the parameter values of the key parameters, and in the detection process, timely adjusting the position and the direction of an MN electrode of the detection area according to the positions of an interference source and an obstacle, acquiring electromagnetic interference area data, acquiring the root mean square error of the electromagnetic interference area data and establishing an original electric field-frequency curve;
and judging whether the quality of the electromagnetic interference area data is qualified or not according to the root mean square error and the original electric field-frequency curve, and if so, completing the acquisition of the electromagnetic interference area complete data.
9. The method for electromagnetic frequency sounding of an electromagnetic interference area for detecting geothermal energy according to claim 1, wherein the final interpretation of the electromagnetic interference area comprises:
performing electromagnetic interference suppression processing and filtering processing on the complete data of the electromagnetic interference area to obtain denoising data;
utilizing electric field data in the denoising data, obtaining full-period apparent resistivity at the position of an MN electrode of the detection region according to the position of an AB electrode of the field source, drawing a multi-frequency curve and an apparent resistivity-frequency simulated section diagram according to the full-period apparent resistivity, extracting double-frequency excitation amplitude frequency parameters, and performing preliminary explanation of a fracture structure and a substrate;
selecting proper parameters according to the multi-frequency curve and the apparent resistivity-frequency pseudo-section to perform static displacement correction, drawing the multi-frequency curve and the apparent resistivity pseudo-section after static displacement correction, and further performing preliminary explanation on the fracture structure and the substrate to obtain preliminary explanation results of the fracture structure and the substrate;
and extracting electromagnetic frequency sounding pseudo-earthquake display parameters, performing preliminary interpretation and inversion treatment on an aquifer interface, and performing final interpretation on the electromagnetic interference region by combining the fracture structure and the preliminary interpretation result of the substrate.
10. A system for depth sounding of geothermal energy by electromagnetic frequency in an electromagnetic interference region, comprising:
prediction unit: the method is used for collecting data of an electromagnetic interference area and predicting key characteristics of a target geologic body according to the data of the electromagnetic interference area;
electrode setting unit: the method is used for determining the position and embedding mode of the field source AB electrode, the receiving-transmitting distance between the detection area MN electrode and the field source AB electrode and the direction and distance of the detection area MN electrode according to the information of the electromagnetic interference area and the prediction result of the key characteristics;
parameter determination unit: the field test is carried out according to the position and the embedding mode of the field source AB electrode, the receiving-transmitting distance and the direction and the distance of the detection area MN electrode, and parameter values of all key parameters are determined according to field test results;
interpretation unit: the method is used for carrying out formal field production according to the parameter values of the key parameters and collecting the complete data of the electromagnetic interference area; and processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area by combining the plurality of preliminary interpretation results.
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