Method and system for detecting deep geothermal resources of the earth by means of controllable source electromagnetic surveying

Abstract

The application provides a method and system for detecting deep geothermal resources in the earth by controllable source electromagnetic method, according to geological data, the rock deposition type and the occurrence range of granite are determined; receiving signals generated by transmitting electromagnetic pulse signals to a set depth underground are obtained, three-component electric field signals at multiple transversely and longitudinally staggered receiving lines, the signal-to-noise ratio is improved through the transversely and longitudinally staggered receiving lines; the geoelectric response of the underground medium is recovered through deconvolution of the receiving signals and the transmitting current; the receiving signals are directly converted into Chebyshev waves by introducing detection parameters including receiving intervals and offset distances; the results obtained by the two methods are compared, the distribution range of the granite and the surrounding fissures is interpreted; three-dimensional imaging is performed, and the distribution range of the geothermal region and the potential fissure water-conducting channel are determined. The application can accurately locate the hot granite and natural water-conducting fissures in the deep underground, thereby providing accurate positioning for subsequent geothermal resource drilling development.

Description

Technical Field

[0001] This invention belongs to the field of geophysical exploration technology, specifically relating to a method and system for controlled-source electromagnetic detection of deep geothermal resources. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The massive emissions of carbon dioxide have exacerbated the greenhouse effect, leading to global warming. There is an urgent need to find sustainable energy alternatives to fossil fuels. The asthenosphere, deep underground, provides renewable thermal energy generated by thermal convection within the Earth, offering a new avenue for human development.

[0004] The inventors discovered that current geophysical exploration methods cannot accurately identify geological bodies deeper than 4,000 meters underground. Drilling to find geothermal resources requires substantial financial resources and is not cost-effective. Furthermore, energy extraction is limited to a narrow perspective. Electromagnetic exploration, on the other hand, primarily measures and receives signals to obtain geological information through inversion. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method and system for controlled-source electromagnetic detection of deep geothermal resources. This invention can accurately locate hot granite and natural water-conducting fissures deep underground, thereby providing accurate positioning for subsequent geothermal resource drilling and development.

[0006] According to some embodiments, the present invention adopts the following technical solution:

[0007] A method for controlled-source electromagnetic detection of deep geothermal resources of the Earth includes the following steps:

[0008] Based on geological data, determine the rock sedimentary type and the occurrence range of granite;

[0009] The system acquires the received signal generated by transmitting an electromagnetic pulse signal to a set depth underground, and the three-component electric field signal at multiple crisscrossing receiving lines. The signal-to-noise ratio is improved by using the crisscrossing receiving lines. The geoelectric response of the underground medium is recovered by deconvolution of the received signal and the transmitted current.

[0010] By introducing detection parameters including receiver spacing and offset, the received signal is directly converted into a Chebyshev wave;

[0011] By comparing the results obtained from the two methods, the distribution range of fractures in and around the granite can be interpreted.

[0012] Three-dimensional imaging was performed to determine the distribution range of geothermal areas and potential fissure water conduction channels.

[0013] As an alternative implementation method, the specific process of determining the rock sedimentary type and the occurrence range of granite based on geological data includes determining the geological history, tectonic features and rock type of the target area through geological data, combining the actual stratigraphic distribution, surface landforms and rock outcrops, making a preliminary assessment of the exploitability and usability of geothermal resources, inferring the rock sedimentary type and age, and estimating whether granite is present, its depth and approximate range.

[0014] As an alternative implementation, when transmitting electromagnetic pulse signals, the transmission frequency is a signal with a frequency lower than a set value and a period longer than a predetermined value, and the transmitting source adopts a single electric dipole source to transmit pseudo-random binary signals.

[0015] As an alternative implementation, when receiving transmitted electromagnetic pulse signals, the receiving end adopts receiving electrodes arranged in a cross pattern with alternating horizontal and vertical distribution, and records the signals simultaneously.

[0016] As an alternative implementation, the electric dipole source records the transmitting current and the spacing between the transmitting electric dipole sources, while simultaneously recording the voltage value of the receiving source and the spacing between the electric dipole sources in real time. The voltage is calculated as V = XS × XR × I * Gt, where XS is the distance between the transmitting sources, XR is the distance between the receiving sources, I is the current, V is the voltage, and GT is the ground response. The ground response is calculated using deconvolution.

[0017] As an alternative implementation, the specific process of directly converting the received signal into a Chebyshev wave includes iterating the diffusion process of the two-dimensional partial differential equation using Chebyshev polynomials. The final electric field is the integral of the Chebyshev polynomial and the Bessel equation. Before showing the final electric field, the Chebyshev polynomial iteration part is shown, with the vertical axis representing the Chebyshev iteration and the horizontal axis representing the electric field value at each step.

[0018] By recording time and sampling, experimental resistivity is obtained, and the depth can be calculated from the propagation speed in different media.

[0019] As an alternative implementation method, the specific process of comparing the results obtained by the two methods includes: obtaining the depth and range from the waveform diagram, determining the resistivity of the geoelectric body using the deconvolution method, and realizing tomographic imaging; comparing the distribution range determined by the two methods to verify each other.

[0020] As an alternative implementation method, during three-dimensional imaging, the three-dimensional distribution of geothermal resources is reflected in real time based on the acquired X, Y, Z coordinate information and time t, according to the changes in different detection times.

[0021] A system for controlled-source electromagnetic detection of deep geothermal resources of the Earth, comprising:

[0022] The signal acquisition module is configured to acquire the received signal generated by transmitting an electromagnetic pulse signal to a set depth underground, the three-component electric field signal at multiple crisscrossing receiving lines, improve the signal-to-noise ratio through the crisscrossing receiving lines, and recover the geoelectric response of the underground medium by deconvolution of the received signal and the transmitted current.

[0023] The conversion module is configured to directly convert the received signal into a Chebyshev wave by introducing detection parameters including the receiver spacing and offset.

[0024] The verification module is configured to compare the results obtained by the two methods and interpret the distribution range of fractures in and around the granite.

[0025] The three-dimensional imaging module is configured to perform three-dimensional imaging to determine the distribution range of geothermal areas and potential fissure water conduction channels.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a controllable source electromagnetic system that can simultaneously receive transmitted current and received signals, thereby achieving direct recovery of the geoelectric response through deconvolution. By utilizing the received signal and solving the Bessel function through input measurement parameters (offset distance, distance between transmitting and receiving points) to directly recover the Chebyshev polynomial wave, a "seismic" interpretation method is achieved. A single measurement yields two effective results that complement each other, providing conditions for the exploitation of geothermal resources caused by deep underground thermal convection.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a flowchart illustrating a method for detecting deep geothermal resources using a controllable source based on integrated transmission and reception, as provided in this embodiment.

[0031] Figure 2 This is a schematic diagram of the field-controlled source geomagnetic exploration provided in this embodiment. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] Example 1

[0036] like Figure 1 As shown, a method for controlled-source electromagnetic detection of deep geothermal resources based on integrated transmission and reception includes:

[0037] (1): Based on geological data, determine the rock sedimentary type and the occurrence range of granite;

[0038] The Earth's core has a temperature close to that of the sun. Due to radioactive isotope heat convection, the heat from the core overflows into the lower mantle, causing the rocks to fracture at high temperatures. This creates fissures, which are then injected into the rock through boreholes 4,000 meters underground into the granite (formed by the cooling of intrusive, non-erupting hot magma). The cool water flows through the bedrock fissures and is heated into extremely hot water. This hot water is then pumped to provide a continuous supply of hot water for human use, or it can be converted into high-energy steam to drive turbines and generate electricity, achieving combined heat and power (CHP).

[0039] Geological data can provide information on the region's geological history, structural features, and rock types. Subsequently, field investigations are conducted to observe and record the stratigraphic distribution, surface landforms, and rock outcrops, thereby assessing the exploitability and usability of geothermal resources.

[0040] Based on the above information, professionals can infer the type and age of rock sedimentation, thereby estimating whether granite exists, its depth, and approximate extent.

[0041] On-site sampling records and verification results.

[0042] (2): Using orthogonal frequency division multiplexing multicarrier as the transmitting electric dipole source to transmit electromagnetic pulse signals to a depth of 4,000 meters underground.

[0043] Orthogonal Frequency Division Multiplexing (OFDM): OFDM is a multi-carrier modulation technique that divides a signal into multiple orthogonal subcarriers for transmission. Each subcarrier has a narrow bandwidth, which reduces the impact of multipath interference and frequency-selective fading, improving signal transmission quality and anti-interference capability. Due to the relatively high construction cost of granite geothermal systems—requiring significant investment in drilling equipment, geothermal circuit installation and maintenance, heat pumps, and transmission systems—OFDM multi-carrier signals offer good strength and strong anti-interference capability, making them the preferred signal for detecting granite fractures at depths of up to 4,000 meters.

[0044] In this embodiment, a low-frequency, long-period signal is used for transmission to ensure detection depth. The transmitter is a single electric dipole source emitting a PRBS (pseudo-random binary signal).

[0045] (3): Acquire electric field signals from multiple intersecting receiving points using GPS synchronization time.

[0046] Unlike conventional transmitters and receivers that are arrayed on the same horizontal line, this embodiment uses a cross-shaped receiving end with horizontally and vertically staggered receiving electrodes to synchronously record signals with GPS signals. This method can effectively improve the signal-to-noise ratio and suppress environmental noise.

[0047] (4): The geoelectric response of the underground medium is recovered by deconvolution of the received signal.

[0048] Conventional electromagnetic exploration typically involves directly acquiring the received signals and then interpreting and analyzing the data. This embodiment synchronously records the transmitted current and received signals using GPS signals, and employs deconvolution to recover the geoelectric response. Because of the time-based recording, this acquisition method is four-dimensional (three-dimensional coordinates plus time), reflecting real-time changes in the underground medium and laying a theoretical foundation for future geothermal circulation development.

[0049] The GPS-enabled electric dipole source records the transmitting current and the spacing between the transmitting electric dipole sources in real time, while simultaneously recording the voltage value of the receiving source and the spacing between the electric dipole sources.

[0050] Final voltage:

[0051] V = XS × XR × I * Gt;

[0052] XS is the distance between the emission sources;

[0053] XR is the receiver spacing;

[0054] I is the electric current;

[0055] V is voltage;

[0056] Deconvolution is used to calculate the ground electrical response (GT).

[0057] (5): Since the acquisition method is fixed, the received signal is converted into Chebyshev waves by inputting detection parameters to achieve "earthquake" interpretation.

[0058] Another major technical advantage of this embodiment is that it not only explains the state of the medium surrounding the geothermal granite by restoring the conductivity of the underground medium through deconvolution, but also, since the conventional electromagnetic control equation is a two-dimensional partial differential equation, the electromagnetic signal can actually obtain the final electric field result through Chebyshev polynomial iteration. This embodiment directly converts the obtained signal into a Chebyshev polynomial by using known electrode device type, offset distance, sampling interval and other device information. The Chebyshev polynomial is actually a kind of "seismic" waveform. Through time inversion, the depth and spatial range of the underground medium can be accurately derived.

[0059] The diffusion process of the two-dimensional partial differential equation is iterated using Chebyshev polynomials, and the final electric field is the integral of the Chebyshev polynomials and the Bessel equations. Before showing the final electric field, the Chebyshev polynomial iteration part is shown, with the vertical axis representing the Chebyshev iteration and the horizontal axis representing the electric field value at each step. This part has been confirmed to be a seismic-like wavelength.

[0060] By recording time and sampling, experimental resistivity is obtained, and the depth can be calculated from the propagation speed in different media.

[0061] (6): Comparison of the results obtained by the two methods to interpret the distribution range of granite and surrounding fractures

[0062] The results obtained by the two methods can obtain effective information from the existing waveform results of resistivity results, thus realizing two data interpretation methods with one collection, making full use of existing scientific research information, saving a lot of financial investment, and improving the utilization rate of the collected signals.

[0063] Waveform images are used to obtain depth and range, and the deconvolution method can determine the resistivity of geoelectric bodies, thus enabling tomographic imaging.

[0064] Both can be compared to determine the distribution range and can be mutually verified.

[0065] (7): Three-dimensional imaging provides accurate location guidance for subsequent drilling energy.

[0066] Because this embodiment uses four-dimensional detection methods, it can achieve final three-dimensional imaging, providing effective prior information for the subsequent development of geothermal resources and improving energy extraction efficiency.

[0067] This embodiment records both the time t and the numerical value of the XYZ coordinates.

[0068] It can reflect the three-dimensional distribution of geothermal resources in real time based on changes over different detection times.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art without creative effort within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlled-source electromagnetic detection of deep geothermal resources, characterized in that, Includes the following steps: Based on geological data, determine the rock sedimentary type and the occurrence range of granite; The system acquires the received signal generated by transmitting an electromagnetic pulse signal to a set depth underground, and the three-component electric field signal at multiple crisscrossing receiving lines. The signal-to-noise ratio is improved by using the crisscrossing receiving lines. The geoelectric response of the underground medium is recovered by deconvolution of the received signal and the transmitted current. By introducing detection parameters including receiver spacing and offset, the received signal is directly converted into a Chebyshev wave; By comparing the results obtained from the two methods, the distribution range of fractures in and around the granite can be interpreted. Three-dimensional imaging was performed to determine the distribution range of geothermal areas and potential fracture water-conducting channels. When receiving transmitted electromagnetic pulse signals, the receiving end uses cross-shaped, crisscrossed receiving electrodes and records the signals simultaneously. The specific process of directly converting the received signal into a Chebyshev wave includes iterating the diffusion process of the two-dimensional partial differential equation using Chebyshev polynomials. The final electric field is the integral of the Chebyshev polynomial and the Bessel equation. Before showing the final electric field, the Chebyshev polynomial iteration part is shown. The vertical axis is the Chebyshev iteration formula, and the horizontal axis is the electric field value at each step. The experimental resistivity is obtained by recording time and sampling, and the depth is calculated by back-calculating the propagation speed of different media. The Chebyshev polynomial is a waveform diagram. The specific process of comparing the results obtained by the two methods includes: obtaining depth and range from waveform diagrams, determining the resistivity of the geoelectric body using the deconvolution method, and realizing tomographic imaging. The distribution ranges determined by comparing the two are used for mutual verification.

2. The method for controlled-source electromagnetic detection of deep geothermal resources as described in claim 1, characterized in that, The specific process of determining the rock sedimentary type and the occurrence range of granite based on geological data includes determining the geological history, tectonic features and rock types of the target area through geological data, combining the actual stratigraphic distribution, surface landforms and rock outcrops, making a preliminary assessment of the exploitability and usability of geothermal resources, inferring the rock sedimentary type and age, and estimating whether granite is present, its depth and approximate range.

3. The method for controlled-source electromagnetic detection of deep geothermal resources as described in claim 1, characterized in that, When transmitting electromagnetic pulse signals, the transmission frequency is lower than the set value and the period is longer than the predetermined value.

4. A method for controlled-source electromagnetic detection of deep geothermal resources as described in claim 1 or 3, characterized in that, The transmitter uses a single electric dipole source to emit pseudo-random binary signals.

5. The method for controlled-source electromagnetic detection of deep geothermal resources as described in claim 1, characterized in that, The specific process of recovering the geoelectric response of the underground medium by deconvolution of the received signal and the transmitted current includes recording the transmitted current by electric dipole sources, the spacing between the transmitting electric dipole sources, and simultaneously recording the voltage value of the receiving source and the spacing between the electric dipole sources in real time. The voltage is calculated as V=XS×XR×I*Gt, where XS is the spacing between the transmitting sources, XR is the receiving spacing, I is the current, V is the voltage, and Gt is the geoelectric response. The geoelectric response is then calculated by deconvolution.

6. The method for controlled-source electromagnetic detection of deep geothermal resources as described in claim 1, characterized in that, During 3D imaging, the three-dimensional distribution of geothermal resources is reflected in real time based on the acquired X, Y, Z coordinate information and time t, according to the changes in different detection times.

7. A system for controlled-source electromagnetic detection of deep geothermal resources, employing the method described in claim 1, characterized in that... include: The signal acquisition module is configured to acquire the received signal generated by transmitting an electromagnetic pulse signal to a set depth underground, the three-component electric field signal at multiple crisscrossing receiving lines, improve the signal-to-noise ratio through the crisscrossing receiving lines, and recover the geoelectric response of the underground medium by deconvolution of the received signal and the transmitted current. The conversion module is configured to directly convert the received signal into a Chebyshev wave by introducing detection parameters including the receiver spacing and offset. The verification module is configured to compare the results obtained by the two methods and interpret the distribution range of fractures in and around the granite. The three-dimensional imaging module is configured to perform three-dimensional imaging to determine the distribution range of geothermal areas and potential fissure water conduction channels.

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