Method and device for identifying porous media based on natural electromagnetic field source

Abstract

The present disclosure provides a method and device for identifying porous media based on natural electromagnetic field sources, which belongs to the technical field of exploration geophysics. It includes collecting initial signals; the initial signals include natural electric fields and / or magnetic fields incident underground, and when reflected and refracted back to the ground through the underground electrical impedance interface, they meet the natural electric fields and / or magnetic fields incident underground at the sensor at the time, and the two are superimposed to obtain the initial time series of synthetic electric field and / or magnetic field intensity; and Fourier transform is performed to obtain the initial spectrum; the dominant frequency components are screened and the correspondence between the top or bottom surface of the underground porous medium and the frequency in the dominant frequency components is obtained, so as to obtain the burial depth of the top / bottom surface of the underground porous medium or the liquid content of the underground porous medium. The device is used to execute the above method. The present disclosure can be widely used in geological and engineering fields such as oil and gas exploration, engineering survey, hydrogeological survey, and geological disaster early warning / monitoring.

Description

Technical Field

[0001] The present application relates to the technical field of geophysical exploration, and in particular to a method and device for identifying porous media based on a natural electromagnetic field source. Background Art

[0002] Conventional electromagnetic survey method is a kind of geophysical exploration method that uses the skin effect of electromagnetic induction to study geological structures, structures and other geological problems, and conduct engineering surveys. It is a volume exploration method. The electromagnetic survey method obtains the electrical distribution characteristics of underground rocks and ores through the measurement and analysis of electromagnetic field data on the ground, and combines the electromagnetic (resistivity, polarizability, magnetic susceptibility, etc.) property data of rocks and ores, geological and other geophysical data, and solves problems related to geological exploration and engineering surveys through comprehensive interpretation of various data.

[0003] The history of using natural electromagnetic fields as excitation sources for geological and engineering surveys can be traced back to the magnetotelluric method (MT) around 1950. Subsequent electromagnetic survey methods are the result of optimization and improvement based on the principle of MT, and their survey accuracy has not been substantially improved.

[0004] At present, geological exploration and engineering survey activities using natural electromagnetic fields as excitation sources are mostly devoted to the study of underground electrical properties (resistivity, polarizability) distribution (structure), with the main research objectives being to solve the stratum distribution and geological structure. However, due to the limited resolution of the skin effect volume exploration, only rough information on the underground electrical structure can be obtained, and the underground porous media cannot be identified.

[0005] Therefore, there is an urgent need for an electromagnetic survey method based on natural field sources for the identification of underground porous media. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present application provides a method and device for identifying porous media based on a natural electromagnetic field source.

[0007] A first aspect of the embodiments of the present disclosure provides a method for identifying porous media based on a natural electromagnetic field source, the method comprising:

[0008] Collecting initial signals; the initial signals include the initial time series of the synthetic electric field and / or magnetic field strength obtained by superimposing the natural electric field and / or magnetic field incident underground and the natural electric field and / or magnetic field incident underground at the moment of reflection and refraction back to the ground through the underground electrical impedance interface;

[0009] Perform Fourier transform on the initial time series to obtain the initial spectrum of the initial time series;

[0010] Screening the dominant frequency components in the initial spectrum; the dominant frequency components are related to the burial depth of the top / bottom surface of the underground porous medium;

[0011] Based on the synchronous and equal-ratio changes of the phase derivative and the amplitude derivative of the dominant frequency component, the corresponding relationship between the top surface or the bottom surface of the underground porous medium and the frequency in the dominant frequency component is obtained.

[0012] Optionally, the above method further includes:

[0013] Based on the frequency-depth conversion of the dominant frequency components, the burial depth of the top / bottom surface of the underground porous medium is obtained.

[0014] Optionally, the above method further includes:

[0015] The liquid content information of the underground porous medium is obtained based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

[0016] Optionally, obtaining the liquid-containing information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium includes:

[0017] When the variation characteristics of the phase delay amount respond to the following relationship, it is identified that the liquid contained in the underground porous medium is water:

[0018] When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

[0019] Optionally, obtaining the liquid-containing information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium includes:

[0020] When the variation characteristics of the phase delay amount respond to the following relationship, the liquid contained in the underground porous medium is identified as crude oil and / or natural gas:

[0021] When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

[0022] Optionally, the phase delay at least satisfies:

[0023]

[0024] in, is the phase delay of the electromagnetic wave when it enters / exits the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

[0025] Optionally, the amplitude derivative of the dominant frequency component satisfies at least one of the following relations:

[0026]

[0027]

[0028] Among them, a is the exponential function of σ and μ, a is the linear function of z; b is the exponential function of f. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave.

[0029] Optionally, the phase derivative of the dominant frequency component satisfies at least any of the following relations:

[0030]

[0031]

[0032] Among them, a is an exponential function of σ and μ, and a is a linear function of z. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium.

[0033] Optionally, the initial spectrum includes the frequency, real part, imaginary part, amplitude, and phase of the electric field and / or magnetic field.

[0034] Optionally, the time length of the Fourier transform is positively correlated with the burial depth of the underground porous medium to be identified.

[0035] A second aspect of the embodiments of the present disclosure provides a porous medium identification device based on a natural electromagnetic field source, which can execute the porous medium identification method as described in the first aspect when the device is running, including:

[0036] The acquisition module is configured to acquire initial signals; the initial signals include an initial time series of synthetic electric and / or magnetic field strengths obtained by superimposing the natural electric and / or magnetic fields incident underground and meeting the natural electric and / or magnetic fields incident underground at the sensor at the moment when the natural electric and / or magnetic fields are reflected and refracted back to the ground through the underground electrical impedance interface;

[0037] A synthesis module, configured to perform Fourier transform on the initial time series to obtain an initial spectrum of the initial time series;

[0038] A screening module is capable of screening the dominant frequency components in the initial spectrum; the dominant frequency components are related to the burial depth of the top / bottom surface of the underground porous medium;

[0039] The identification module can obtain the corresponding relationship between the top surface or bottom surface of the underground porous medium and the frequency in the dominant frequency component based on the synchronous and equal-multiplication changes of the phase derivative and amplitude derivative of the dominant frequency component.

[0040] Optionally, the identification module can identify the burial depth of the top / bottom surface of the underground porous medium based on the frequency-depth conversion of the dominant frequency components.

[0041] Optionally, the identification module can identify the liquid-containing information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

[0042] Optionally, the identification module can identify that the liquid contained in the underground porous medium is water when the change characteristic of the phase delay amount responds to the following relationship:

[0043] When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

[0044] Optionally, the identification module can identify that the liquid contained in the underground porous medium is crude oil and / or natural gas when the variation characteristics of the phase delay amount respond to the following relationship:

[0045] When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

[0046] Optionally, the phase delay at least satisfies:

[0047]

[0048] in, is the phase delay of the electromagnetic wave when it enters / exits the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

[0049] Optionally, the amplitude derivative of the dominant frequency component screened by the screening module satisfies at least any of the following relations:

[0050]

[0051]

[0052] Among them, a is the exponential function of σ and μ, a is the linear function of z; b is the exponential function of f. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave.

[0053] Optionally, the phase derivative of the dominant frequency component screened by the screening module satisfies at least any of the following relations:

[0054]

[0055]

[0056] Among them, a is an exponential function of σ and μ, and a is a linear function of z. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium.

[0057] Optionally, the synthesis module can obtain an initial spectrum including the frequency, real part, imaginary part, amplitude, and phase of the electric field and / or magnetic field.

[0058] Optionally, the synthesis module can perform Fourier transformation on the initial time series with a time length that is positively correlated with the burial depth of the underground porous medium to be identified.

[0059] Optionally, the acquisition module is provided with at least two acquisition channels.

[0060] A third aspect of an embodiment of the present disclosure provides an electronic device, comprising a bus, an amplifier, an acquisition card (A / D conversion), a comb filter / bandpass filter, a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the amplifier, the acquisition card (A / D conversion), the comb filter / bandpass filter, the memory, and the processor are respectively connected via a bus, and when the computer program is executed by the processor, the steps in the method for identifying porous media described in the first aspect are implemented.

[0061] The fourth aspect of the embodiments of the present disclosure further provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps in the method for identifying porous media described in the first aspect are implemented.

[0062] The technical solution provided by the present application collects the natural electromagnetic field incident on the underground half-space, which is reflected and refracted back to the ground through the top / bottom surface of the underground porous medium, and meets the natural electric field and / or magnetic field incident on the ground again at the sensor set on the ground at the time. The synthetic electric field intensity and / or magnetic field intensity time series obtained by superposition of the two, the amplitude and phase response relationship generated by the dispersion when the electromagnetic wave enters or leaves the "assembly" of the liquid-containing porous medium, and further, according to the characteristics of synchronous and equal-multiplied changes of the phase derivative value-electromagnetic wave amplitude derivative value, the porous medium can be effectively identified; the difference in the phase delay amount of the "assembly" containing water and crude oil in the porous medium can be used to effectively predict the liquid content of the porous medium. It can be widely used in geological and engineering fields such as oil and gas exploration, engineering survey, and hydrogeological survey. When only collecting and analyzing magnetic field data, it is not limited by the collection and analysis of water surface and air data, and can be conveniently applied to water surface and air working environments, with a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the background technology, the drawings required for use in the embodiments of the present application or the background technology will be described below.

[0064] Figure 1 A flowchart of a porous medium and liquid property identification method based on natural field sources provided in an embodiment;

[0065] Figure 2 is a schematic diagram of an exemplary porous medium and a method for identifying liquid content;

[0066] Figure 3 Schematic diagram of the time series of the initial signal magnetic field strength collected in the embodiment;

[0067] Figure 4 It is an initial spectrum diagram of magnetic field intensity amplitude obtained by Fourier transforming the initial signal magnetic field intensity time series collected in the embodiment;

[0068] Figure 5 The initial frequency spectrum diagram of the electric field intensity amplitude obtained by Fourier transforming the initial signal electric field intensity time series collected in the embodiment;

[0069] Figure 6 This is a schematic diagram (partial) of the results of high-resolution electromagnetic exploration of porous media and identification of liquid content near the D8 well in the Yihe fault depression in the Erlian Basin, Inner Mongolia (Part I) in the embodiment;

[0070] Figure 7 This is a schematic diagram (partial) of the results of high-resolution electromagnetic exploration of porous media and identification of liquid content near the D8 well in the Yihe fault depression in the Erlian Basin of Inner Mongolia in the embodiment (Part II);

[0071] Figure 8 The electromagnetic prediction results and seismic structure comparison diagram of the WEQ block in the WEX sag of the Hailar Basin in Northeast China in the embodiment;

[0072] Fig. 9 An optional structural diagram of an electronic device provided in an embodiment;

[0073] Fig.10 The following is an exemplary flow chart of a well logging project performed using the porous medium identification method in the embodiment. DETAILED DESCRIPTION

[0074] In the description of the embodiments of the present application, it should be understood by those skilled in the art that the embodiments of the present application can be implemented as methods, devices, electronic devices, and computer-readable storage media. Therefore, the embodiments of the present application can be specifically implemented in the following forms: complete hardware, complete software (including firmware, resident software, microcode, etc.), a combination of hardware and software. In addition, in some embodiments, the embodiments of the present application can also be implemented in the form of a computer program product in one or more computer-readable storage media, and the computer-readable storage medium contains computer program code.

[0075] The above-mentioned computer-readable storage medium may adopt any combination of one or more computer-readable storage media. Computer-readable storage media include: electrical, magnetic, optical, electromagnetic, infrared or semiconductor systems, devices or devices, or any combination of the above. More specific examples of computer-readable storage media include: portable computer disks, hard disks, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM), flash memories (Flash Memory), optical fibers, compact disk read-only memories (CD-ROM), optical storage devices, magnetic storage devices or any combination of the above. In an embodiment of the present application, a computer-readable storage medium may be any tangible medium containing or storing a program, which may be used by or in combination with an instruction execution system, device, or device.

[0076] The computer program code contained in the above-mentioned computer-readable storage medium can be transmitted using any appropriate medium, including: wireless, wire, optical cable, radio frequency (RF) or any suitable combination thereof.

[0077] The computer program code for executing the operation of the embodiment of the present application can be written in assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, integrated circuit configuration data, or in one or more programming languages ​​or a combination thereof, wherein the programming language includes an object-oriented programming language, such as Java, Smalltalk, C++, and also includes a conventional procedural programming language, such as C language or a similar programming language. The computer program code can be executed completely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer, partially on the remote computer, and completely on the remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer or to an external computer through any type of network, including a local area network (LAN) or a wide area network (WAN).

[0078] The embodiments of the present application describe the provided methods, devices, and electronic devices through flowcharts and / or block diagrams.

[0079] It should be understood that each box in the flowchart and / or block diagram and the combination of boxes in the flowchart and / or block diagram can be implemented by computer-readable program instructions. These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer or other programmable data processing device to produce a machine, and these computer-readable program instructions are executed by a computer or other programmable data processing device to produce a device that implements the functions / operations specified by the boxes in the flowchart and / or block diagram.

[0080] These computer-readable program instructions may also be stored in a computer-readable storage medium that enables a computer or other programmable data processing device to work in a specific manner. In this way, the instructions stored in the computer-readable storage medium produce an instruction device product including functions / operations specified by the blocks in the flowchart and / or block diagram.

[0081] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device, so that a series of operational steps are performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby enabling the instructions executed on the computer or other programmable data processing apparatus to provide a process for implementing the functions / operations specified in the blocks in the flowchart and / or block diagram.

[0082] From space exploration and universe exploration to engineering surveys, basic geological surveys, natural disaster warning and monitoring, underground resources and energy exploration and many other fields, detection technology based on electromagnetic principles has always been the main body of the detection technology system.

[0083] Ground remote sensing detection technology, ground penetrating radar technology, and various electromagnetic detection technologies are the most widely used methods and technologies for engineering surveys, basic geological surveys, natural disaster warning and monitoring, and underground resource and energy exploration. The objects of their research are all the interaction between electromagnetic fields (waves) and detection targets. The differences between the technologies are only reflected in two aspects: one is the difference in electromagnetic field excitation sources, which are divided into artificially excited electromagnetic field source survey technology and natural field electromagnetic field source survey technology; the other difference is the frequency band and wavelength (frequency) of the electromagnetic field (wave) used. Generally speaking, the high frequency band and short wavelength electromagnetic waves of the electromagnetic field are used to detect shallow underground targets (objects), while the low frequency band and long wavelength electromagnetic waves of the electromagnetic field are required to detect deep targets (objects). In general, as the burial depth of the detection target increases, the signal-to-noise ratio of the collected data decreases, the detection accuracy decreases, and the cost of collecting data increases.

[0084] In view of this, the present disclosure proposes a detection method technology based on natural electromagnetic field, high resolution and large detection depth. Further, the porous medium and liquid property identification method based on natural electromagnetic field source based on the same concept is emphasized.

[0085] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0086] In order to ensure the understanding of the technical solutions contained in this application and the reference of subsequent algorithm derivation, it is necessary to describe the prior art in detail here.

[0087] Among the existing electromagnetic survey technologies, the physics basis of magnetotelluric (MT) (CEMP) technology is the most rigorous and is also the basis for the development of other technologies.

[0088] MT technology was proposed by Soviet scholar Tikhonov and French scholar Garnier in 1950. Its basic assumptions were only three at the beginning:

[0089] ① The structure of the natural magnetotelluric field is complex, but the field source can be approximately regarded as a plane electromagnetic wave vertically incident on the earth;

[0090] ②Introducing wave impedance concept.

[0091] Here E is the electric field strength and H is the magnetic field strength. Wave impedance Z can be used to characterize the response of underground electrical distribution to the magnetotelluric field;

[0092] ③It is possible to study the underground electrical distribution using single-point magnetotelluric field observation data.

[0093] The basic relationship between the electrical distribution of the underground half-space and the electromagnetic field observed on the ground can be easily derived from the basic relationship between the electromagnetic field:

[0094]

[0095] Here ρ is the apparent resistivity, T is the period of the electromagnetic wave, and f is the frequency of the electromagnetic wave: f = 1 / T. This formula gives the relationship between the apparent resistivity and the electric and magnetic field amplitudes and electromagnetic field frequencies observed on the ground under the condition of underground uniform medium. This formula is generally called the Garnier (sub) formula.

[0096] The Tikhonov-Garnier magnetotelluric survey technology has been widely used due to its theoretical rigor and effectiveness in practical application.

[0097] Compare the Garnier resistivity formula with the electromagnetic field expression:

[0098] E=E0e -βz e jωt e -jαz

[0099]

[0100] Here E0 is the amplitude of the electric field intensity at the time of incidence, H0 is the amplitude of the magnetic field intensity at the time of incidence, z is the incidence depth, μ is the relative magnetic permeability of the medium, σ is the electrical conductivity of the medium, ω is the angular frequency of the monochromatic wave ω=2πf, f is the frequency of the monochromatic wave, α is the phase coefficient, β is the attenuation coefficient, and ε is the relative dielectric constant of the medium.

[0101] While the Garnier formula is concise, the "comparison" operation process between the electric field and the magnetic field implicitly cancels out the "dynamic" fluctuation term shared by both, and also implicitly cancels out the external incident electromagnetic field (primary field) component, leaving only the basic relationship between the electromagnetic field attenuation and frequency (secondary field effect) that characterizes the skin effect phenomenon, thus making the magnetotelluric MT technology have the characteristics of volume exploration - the electromagnetic field signal observed at the ground measuring point is a comprehensive response to the electrical inhomogeneity (difference) in a certain area below the observation point. Considering that the current magnetotelluric technology can only obtain apparent resistivity data of a small number of frequency points (generally only 40-80), the ability to solve geological exploration and engineering exploration problems is greatly reduced. Therefore, to this day, traditional magnetotelluric technology, including the later developed CEMP technology and CSAMT technology, still remains at a stage where it can only reflect the distribution of several large electrical layers underground and cannot depict the detailed structure of the electrical distribution.

[0102] The inventors discovered that by utilizing the strong frequency selectivity of the underground electrical impedance interface in enhancing and weakening electromagnetic wave components, and analyzing and studying these electromagnetic wave components that are enhanced after continuous and multiple superpositions, the purpose of studying and characterizing the underground electrical structure can be achieved.

[0103] After research, the inventor found that the electromagnetic wave frequency band used in the field of geological exploration and engineering exploration using natural electromagnetic fields is The conditions are strictly met, and the expressions of the electromagnetic wave phase coefficient α, attenuation coefficient β and phase velocity v are:

[0104]

[0105] The expression of electromagnetic wave phase velocity tells us that when electromagnetic waves propagate in the underground half-space medium, the phase velocity is related to the frequency of the electromagnetic waves. The higher the frequency, the faster the propagation speed. This is the dispersion phenomenon, which can serve as the physical basis for using natural electromagnetic field high-resolution electromagnetic technology to judge porous media and the liquid contained in porous media.

[0106] Porous media consists of two parts: a skeleton and pore fillings. Under natural conditions, the pores in porous media buried deep underground are often filled with solid or liquid substances. When the porous medium is filled with (primary) formation water, the (primary) formation water generally contains a variety of minerals, and the minerals exist in the formation water in the form of various ions, molecules, and compounds. Especially in the field of oil and gas exploration, because formation water has been in contact with rocks and crude oil in the formation for a long time, it usually contains a considerable amount of metal salts, such as potassium salts, sodium salts, calcium salts, magnesium salts, etc., especially potassium salts and sodium salts, so it is commonly called salt water. The salt content in formation water is its biggest feature that distinguishes it from surface water. Pure formation water is an insulator and is not conductive, but due to the presence of metal salts, formation water often exhibits good conductive properties.

[0107] Table 1 is a table of resistivity values ​​of formation (mineralized) water and crude oil. It can be seen from this table that there is a huge "contrast" in the resistivity values ​​of the two. When the porous medium contains (mineralized) water or crude oil, the porous medium-the liquid "assembly" contained in it will have significantly different conductivity - the conductivity becomes better when it contains (mineralized) water, and the conductivity becomes worse when it contains crude oil.

[0108] The different liquid contents and electrical properties of porous media are crucial to the development of high-precision and deep-depth electromagnetic geophysical detection technology.

[0109] Table 1 Resistivity values ​​of formation (mineralized) water and crude oil

[0110] liquid Resistivity ρ (Ohm-meter) Dielectric constant ε Formation (mineralized) water <<1 81 crude ∞ <10

[0111] Starting from the universal Maxwell equations, the inventors have rigorously derived the basic relationship satisfied by the electromagnetic field strengths Ex and Hy. The following four important expressions are rigorously derived by derivation of the basic relationship:

[0112] Electric field strength amplitude: |E| = -E0e -a (1-1)

[0113] Magnetic field strength amplitude: |H|=-H0e -a (1-2)

[0114] Electric field phase:

[0115] Magnetic field phase:

[0116] Electric field intensity amplitude derivative:

[0117] Derivative of magnetic field intensity amplitude:

[0118] Electric field phase derivative:

[0119] Magnetic field phase derivative:

[0120] In the above formulas, a is an exponential function of σ and μ, a is a linear function of z, and b is an exponential function of f. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom of the underground porous medium; σ is the conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; and f is the frequency of the electromagnetic wave.

[0121] Expressions (1)-(2)-(3)-(4) are the expressions of the electromagnetic field amplitude-phase-amplitude derivative-phase derivative when a single harmonic plane electromagnetic wave is vertically incident on the ground and propagates in the underground half-space medium.

[0122] According to expressions (3) and (4), except for the phase shift term 2πt and the amplitude attenuation term e -(e+b) , the amplitude derivative and the phase derivative both contain the same factor of variation:

[0123] Through numerical calculation, we know that the e in the amplitude derivative expression (3) is -b In the frequency range of several thousand Hertz, when the frequency changes, the effect of this term on the amplitude value is less than The term affects the amplitude value by more than one order of magnitude. Obviously, when electromagnetic waves propagate in a uniform medium with consistent conductivity (σ), the phase derivative value and the electromagnetic wave amplitude derivative value have the characteristic of changing with frequency in a "synchronous-equal-ratio" relationship. Combined with the basic characteristic that the electrical interface has frequency selectivity for electromagnetic wave components, the section with large electromagnetic field amplitude intensity and the phase derivative value and the electromagnetic wave amplitude derivative value changing with frequency in a "synchronous-equal-ratio" relationship is the reflection of the uniform electrical layer. Specifically for porous media, the "synchronous-equal-ratio" relationship between the phase derivative value and the electromagnetic wave amplitude derivative value reflects the position of the top and bottom surfaces of the porous medium.

[0124] After research, the inventors came to the following important conclusion: the porous medium can be effectively identified by utilizing the "synchronous-equal-rate" change characteristics of the phase derivative value - the electromagnetic wave amplitude derivative value when the electromagnetic wave enters or leaves the "assembly" of liquid-containing porous media.

[0125] After careful consideration of expression (2), the inventors learned that factor a reflects the magnitude of the phase shift. The magnitude of the phase shift when the electromagnetic wave propagates in the medium is different due to the different conductivity of the medium. When the electromagnetic wave enters the porous medium and propagates, when the porous medium contains water, the conductivity becomes better, the phase coefficient α value becomes larger, and the phase delay becomes larger; when the electromagnetic wave leaves the porous medium, the conductivity becomes worse, the phase coefficient α value becomes smaller, and the phase delay becomes smaller. When the electromagnetic wave enters the porous medium and propagates, when the porous medium contains crude oil (natural gas), the conductivity becomes worse, the phase coefficient α value becomes smaller, and the phase delay becomes smaller; when the electromagnetic wave leaves the porous medium, the conductivity becomes better, the phase coefficient α value becomes larger, and the phase delay becomes larger.

[0126] After further research, the inventors came to the following important conclusion: the difference in phase delay between the "assembly" of water and crude oil (natural gas) in the porous medium can be used to effectively predict the liquid content of the porous medium.

[0127] For example, reference may be made to Figure 2 Schematic diagram of porous media and liquid content identification method shown in FIG. Figure 2 The ordinate in the figure is depth, the group of curves on the left side of the figure are harmonic index curves, and the group of curves on the right side of the figure are phase delay curves.

[0128] The harmonic index curve is based on the phase derivative and amplitude derivative of the dominant frequency component, which change synchronously and at equal rates, to obtain the corresponding relationship between any frequency in the dominant frequency component and the top or bottom surface of the underground porous medium. The two parameters construct the first harmonic index that reflects the harmonic characteristics, and also include: constructing another harmonic variable with the cross-correlation results of the phase derivative and the amplitude derivative. They all reflect the characteristics of the "synchronous-equal rate" change of the phase derivative and the amplitude derivative when the electromagnetic wave enters or leaves the "assembly" of the liquid-containing porous medium.

[0129] The phase delay is based on the dispersion phenomenon. The dispersion phenomenon studies the relationship between the phase shift, attenuation, propagation speed and other parameters of electromagnetic waves and the frequency of electromagnetic waves and the resistivity of the liquid contained. As long as the harmonic index and high-order harmonic index corresponding to the porous medium reach the level that can be identified, we can identify the porous medium. Obviously, the resolution ability of judging (oil-gas-water) in the reservoir based on the dispersion principle is not limited by the 1 / 4 wavelength limit of the electromagnetic wave. Due to the different liquids contained in the porous medium, there is a characteristic phase delay difference response relationship between the amplitude derivative and the phase derivative of the electromagnetic wave when entering and leaving the porous medium. The difference in phase delay between the "assembly" of porous media containing water and crude oil (natural gas) can effectively predict the liquid contained in the porous medium. In practice, the frequency resolution during data acquisition and analysis can be used as a standard to measure the resolution ability of the technology of this application.

[0130] In view of this, the first embodiment of the present application provides a porous medium and liquid property identification method based on a natural electromagnetic field source. Figure 1 Schematic diagram of the above method is shown. Figure 1 As shown, the method comprises at least the following steps:

[0131] Collecting initial signals; the initial signals include the initial time series of the synthetic electric field and / or magnetic field strength obtained by superimposing the natural electric field and / or magnetic field incident underground and the natural electric field and / or magnetic field incident underground at the moment of reflection and refraction back to the ground through the underground electrical impedance interface;

[0132] The dominant frequency component is screened in the initial spectrum; the dominant frequency component is related to the burial depth of the top / bottom surface of the underground porous medium; based on the synchronous and equal-multiplied changes of the phase derivative and amplitude derivative of the dominant frequency component, the corresponding relationship between the top or bottom surface of the underground porous medium and the frequency in the dominant frequency component is obtained.

[0133] According to the step "collecting initial signals", this application takes the data collected beside an oil exploration well in the Puxi Depression in the Songliao Basin in Northeast China in December 2020 as an example. Figure 3 As shown, Figure 3 This is a time series diagram of the initial signal magnetic field strength collected at the observation point. Figure 3 The horizontal axis is time in seconds, and the vertical axis is magnetic field strength in nanometers. The vertical axis can also be an uncalibrated scale value, a voltage value, or other physical quantity that is directly proportional to the magnetic field strength. Figure 3 The upper figure is a time series of 0.4 seconds in length, and the lower figure is a time series of 0.025 seconds in length. The number of acquisition channels when acquiring the initial signal in this embodiment is 1, the sampling rate is 24000 times / second, the total acquisition time length is 30 seconds, and the acquisition data frequency band range is 0 to 12000 Hz.

[0134] According to the step of "selecting the dominant frequency components in the initial spectrum", the initial spectrum of the magnetic field intensity amplitude and the initial spectrum of the electric field intensity amplitude collected at a measurement point in Malan Town, Xunyi County, Shaanxi Province in June 2022 are used as an embodiment. Figure 4 and Figure 5 As shown, Figure 4 The initial spectrum of the magnetic field intensity amplitude obtained by Fourier transforming the initial signal magnetic field intensity time series collected at the observation point, Figure 5 It is the initial spectrum of the electric field intensity amplitude obtained by Fourier transform of the initial signal electric field intensity time series collected at the observation point. Figure 4 The horizontal axis is the frequency, and the vertical axis is the initial spectrum of the magnetic field intensity amplitude; Figure 5 The horizontal axis is the frequency, and the vertical axis is the initial spectrum of the electric field intensity amplitude. The sampling rate of this embodiment is 2000 times / second, the acquisition time is 600 seconds, and the displayed frequency range is 0-1000 Hz.

[0135] On the basis of the above steps, the method in the embodiment further includes:

[0136] Based on the frequency-depth conversion of the dominant frequency component, the burial depth of the top / bottom surface of the underground porous medium is obtained.

[0137] as well as

[0138] The liquid-containing property information of the underground porous medium is obtained based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

[0139] According to the disclosed embodiment, when judging the above liquid information, the liquid information is identified based on the change characteristics of the phase delay. The specific principles to be followed are:

[0140] When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

[0141] or

[0142] When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

[0143] In addition, for the above phase delay amount, it at least satisfies:

[0144]

[0145] in, is the phase delay of the electromagnetic wave when entering / exiting the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

[0146] According to an embodiment of the present disclosure, the amplitude derivative of the dominant frequency component satisfies at least one of the above expressions (1) and (2), that is:

[0147]

[0148]

[0149] Wherein, a is an exponential function of σ and μ, a is a linear function of z; b is an exponential function of f. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; and f is the frequency of the electromagnetic wave.

[0150] According to an embodiment of the present disclosure, the phase derivative of the dominant frequency component satisfies at least one of the expressions (4-1) and (4-2) described above, that is:

[0151]

[0152]

[0153] Wherein, a is an exponential function of σ and μ, and a is a linear function of z. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; and t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium.

[0154] According to an embodiment of the present disclosure, the initial spectrum includes the frequency, real part, imaginary part, amplitude, and phase of the electric field and / or magnetic field.

[0155] According to an embodiment of the present disclosure, the time length of the Fourier transform is positively correlated with the burial depth of the underground porous medium to be identified.

[0156] For example, Figure 2As shown, the number "4775" in the figure is the depth value, in meters. The light-colored surface map on the left part of the figure is the HAPC color-filled curve generated by processing the characteristics of the phase value of the "assembly" of the liquid-containing porous medium-the electromagnetic wave amplitude value "synchronous-equal ratio". The part with high amplitude corresponds to the position of the porous medium; the right part of the figure is the HAP color-filled curve generated by processing the difference in the phase delay between the porous medium containing water and the "assembly" containing crude oil. The right half of the gray surface map is the amplitude derivative value, and the left half is the phase derivative value. When the center of gravity of the left half is biased toward the deep part, it reflects that the phase delay becomes larger and the conductivity becomes better, indicating that the porous medium contains water (middle curve). When the center of gravity of the left half is biased toward the shallow part, it reflects that the phase delay becomes smaller and the conductivity becomes worse, indicating that the porous medium contains crude oil (natural gas) (upper curve). In practice, the "degree" of the deviation of the center of gravity is not always so clear (lower curve), and a comprehensive analysis is required to obtain a reasonable result.

[0157] In a preferred embodiment, the original time series data of the initial signal collected by each acquisition channel is converted into an initial spectrum of the initial signal by Fourier analysis;

[0158] The vector synthesis rule is used to synthesize the initial spectra corresponding to all acquisition channels into the total spectrum.

[0159] In a preferred embodiment, the time length of the Fourier analysis is positively correlated with the depth of the porous medium to be identified. For example, the time length selection principle for the analysis is: when the burial depth of the porous medium to be studied is less than 2000 meters, the time series length is between 50 and 200 seconds; when the burial depth of the porous medium to be studied is less than 5000 meters, the time series length is between 200 and 500 seconds.

[0160] In addition, in the above analysis steps, the number of data is preferably selected as a power of 2, so as to utilize a fast FFT transformation algorithm;

[0161] In a preferred embodiment, the three values ​​of the highest frequency, the lowest frequency, and the frequency range of the analysis data are determined according to the task requirements, and a frequency-real part-imaginary part-amplitude-phase data volume is formed.

[0162] In a preferred embodiment, the velocity value of the electromagnetic wave when propagating underground is determined, the frequency domain data is converted into depth domain data, and a depth-real part-imaginary part-amplitude-phase data volume is generated.

[0163] In a preferred embodiment, the original time series data includes time, magnetic field intensity and / or electric field intensity.

[0164] In a preferred embodiment, the total spectrum includes frequency, real part, imaginary part, amplitude and phase.

[0165] In a preferred embodiment, the initial signal is collected through four channels to obtain four time series data of magnetic field intensity and / or electric field intensity.

[0166] In a preferred embodiment, an industrial mapping step is also included. For example, an amplitude difference / phase difference weighted superposition HAPC curve is formed in the figure, and the curve is used for interpreting porous media; or, an amplitude-phase combination curve is formed, and the curve is used for interpreting the liquid content of porous media.

[0167] According to the implementation mode of the present application, the collected initial signal may include the moment of reflection and refraction back to the ground through the underground electrical impedance interface, and the natural electric field and / or magnetic field incident underground at the moment meets at the sensor, and the synthetic electric field intensity obtained by superposition of the two may also be the synthetic magnetic field intensity, or the intensity of the electric field and magnetic field at the same time. In the specific implementation process, the type of initial signal can be freely selected according to the needs of the survey task. Hereinafter, the magnetic field is used as an example for explanation. It should be noted that when the intensity of the magnetic field and the electric field is jointly collected, the minimum frequency collected is the frequency lower limit that the magnetic sensor can receive as the collection lower limit, so as to calculate the Garnier resistivity, so as to have a larger survey depth when inverting the underground geoelectric structure. When the intensity of the magnetic field or electric field is collected alone, the minimum frequency collected can optionally take any value in 1-10 Hz for calculation. In an optional embodiment, the frequency of the initial signal is greater than 0.1 Hz and less than or equal to 10000 Hz.

[0168] In an embodiment of the present application, the method further includes preparing a collection plan and determining collection parameters according to the survey task requirements before collecting the initial signal, wherein the collection parameters at least include the sampling rate, the maximum frequency to be collected, and the collection duration.

[0169] According to an embodiment of the present application, the sampling rate is negatively correlated with the depth to be surveyed. For example, for a survey depth of 2000 to 5000 meters, the sampling rate is greater than or equal to 2000 times / second. Preferably, for a survey target within 2000 meters, the sampling rate is taken from 5000 to 10000 times / second.

[0170] According to the implementation of the present application, the acquisition time is positively correlated with the burial depth of the survey target. For example, for a survey depth of 2000 meters, the acquisition time is preferably 600 seconds. For a survey depth of 5000 meters, the acquisition time is preferably 1200 seconds.

[0171] Furthermore, the electromagnetic survey method based on natural field sources provided in the embodiment of the present application also includes: performing a first comb filter processing and / or low-pass filtering before collecting the initial signal according to the highest frequency to be collected. Among them, the first comb filter processing is to suppress the power frequency and the multiples of the power frequency; the low-pass filter is to filter the frequency components higher than the highest frequency to be collected. The power frequency refers to the rated frequency used by the equipment, industrial electrical equipment and civil electrical equipment of the power system. Exemplarily, the power frequency is 50 Hz. In some optional cases, regardless of the burial depth of the detection object and the sampling rate during data collection, it is necessary to pre-suppress the intensity of the power frequency and its multiples. In some optional cases, it is necessary to perform a low-pass filter according to the highest frequency to be collected, and suppress the frequency components higher than the highest frequency to be collected. In most cases, the collection location of the initial signal can be in the field, and the collection location provided in the embodiment of the present application can also be at sea.

[0172] In view of the above, the above embodiments of the present application can be widely used in geological and engineering fields such as oil and gas exploration, engineering survey, and hydrogeological survey. Fig.10 The process shown is designed to achieve the following goals:

[0173] (1) Effectively predict the section with concentrated porous media development—reservoir groups in oil and gas exploration;

[0174] (2) Predict the main oil- (water-) bearing porous media with obvious characteristics - reservoir (single) individual;

[0175] (3) Based on the identification of various reservoir types, combined with other geological, drilling and geophysical data, research on geological issues such as stratum lithology and distribution, and structural interpretation is carried out;

[0176] As for prediction accuracy, ideally, it should reach ±5 meters when the reservoir burial depth is less than 2000 meters, and ±10 meters when the reservoir burial depth is less than 5000 meters.

[0177] The embodiments of the present application also involve a porous medium and liquid property identification device based on a natural field source, which is used to perform the porous medium and liquid property identification method described in the above embodiments, including:

[0178] An acquisition module is configured to acquire an initial signal; the initial signal includes an initial time series of synthetic electric field and / or magnetic field strength obtained by superimposing the natural electric field and / or magnetic field incident underground at the moment when the natural electric field and / or magnetic field incident underground at the moment meets the natural electric field and / or magnetic field incident underground at the sensor and the two are reflected and refracted back to the ground;

[0179] A synthesis module, configured to perform Fourier transform on the initial time series to obtain an initial spectrum of the initial time series;

[0180] A screening module capable of screening the dominant frequency components in the initial spectrum; the dominant frequency components are related to the burial depth of the top / bottom surface of the underground porous medium;

[0181] The identification module can obtain the corresponding relationship between the top surface or bottom surface of the underground porous medium and the frequency in the dominant frequency component based on the synchronous and equal-multiplication changes of the phase derivative and the amplitude derivative of the dominant frequency component.

[0182] According to an embodiment of the present disclosure, the identification module can identify the burial depth of the top / bottom surface of the underground porous medium based on the frequency-depth conversion of the dominant frequency component.

[0183] Furthermore, the identification module can identify the liquid-containing information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

[0184] According to an embodiment of the present disclosure, the identification module can identify that the liquid contained in the underground porous medium is water when the change characteristic of the phase delay amount responds to the following relationship:

[0185] When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

[0186] According to an embodiment of the present disclosure, the identification module can identify that the liquid contained in the underground porous medium is crude oil and / or natural gas when the change characteristics of the phase delay amount respond to the following relationship:

[0187] When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

[0188] According to an embodiment of the present disclosure, the phase delay at least satisfies:

[0189]

[0190] in, is the phase delay of the electromagnetic wave when entering / exiting the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

[0191] The amplitude derivative of the dominant frequency component screened by the screening module at least satisfies any of the following relationships:

[0192]

[0193]

[0194] Among them, a is an exponential function of σ and μ, a is a linear function of z; b is an exponential function of f. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave.

[0195] The phase derivative of the dominant frequency component screened by the screening module satisfies at least one of the following relations:

[0196]

[0197]

[0198] Wherein, a is an exponential function of σ and μ, and a is a linear function of z. z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; and t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium.

[0199] According to an embodiment of the present disclosure, the synthesis module can obtain an initial spectrum including the frequency, real part, imaginary part, amplitude, and phase of the electric field and / or magnetic field. Further, the synthesis module can perform Fourier transform on the initial time series with a time length positively correlated with the burial depth of the underground porous medium to be identified.

[0200] According to an embodiment of the present disclosure, the acquisition module is provided with at least two acquisition channels.

[0201] The embodiment of the present application also relates to an electronic device, referring to Fig. 9 , including a bus, an amplifier, an acquisition card (A / D conversion), a comb filter / bandpass filter, a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the amplifier, the acquisition card (A / D conversion), the comb filter / bandpass filter, the memory, and the processor are respectively connected via a bus, and when the computer program is executed by the processor, the steps in the method for identifying porous media described in the above embodiment are implemented.

[0202] The embodiments of the present application also relate to a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps in the method for identifying porous media and liquid properties contained therein as described in the aforementioned embodiments are implemented.

[0203] Examples

[0204] Example 1

[0205] like Figure 6 This is a schematic diagram (partial) of the results of high-resolution electromagnetic exploration of porous media and identification of liquid content near the D8 well in Jiadi, EL Basin. The EL Basin is a group of 58 Mesozoic Lower Cretaceous rifts, with an area of ​​hundreds to 2,000 square kilometers. The pre-Mesozoic basement is generally buried at a depth of about 2,500 to 4,000 meters. The source rocks are the first section of the TGE Formation and the A4 and A2 sections of the AES Formation in the Lower Cretaceous. The main reservoir is the A4 section, followed by the lower part of the TGE section. The D8 well in Jiadi is a key evaluation well with a drilling depth of 1,350.0 meters. After it was put into production, it produced 25 cubic meters of crude oil per day in the early stage. The oil-bearing stratum of the D8 well is the A4 section of the Lower Cretaceous of the Mesozoic. The reservoir lithology is muddy fine sandstone. The logging interpretation shows that the mud content of the reservoir is generally about 10%, and can reach up to 30%. The depth of the reservoir development section is 1205.6~1299.0 meters, which is composed of twelve sand layers with a thickness of 0.8~7.2 meters. The comprehensive interpretation of logging and well logging data shows that the deep detection resistivity of the oil layer section is 4.5~15.3Ω·m, the sonic time difference is 272.5~300.0μs / m, the calculated effective porosity is 16.5%~22.4%, and the calculated oil saturation is 38.7%~60.5%. Oil spots and oil traces are shown in logging and coring of the well wall. Comprehensive interpretation shows that except for layer 30, all other layers are oil layers.

[0206] Except for the No. 30 layer, the microelectrode curve of the well logging interpretation is a low-amplitude slightly positive difference, the natural potential curve has a large negative anomaly, the measured resistivity is 10.7Ω·m, the acoustic time difference is 278.6μs / m, the calculated effective porosity is 18.2%, and the calculated oil saturation is 33.9%. The well logging shows oil traces, and the well wall coring shows oil spots, which are comprehensively interpreted as oil and water in the same layer.

[0207] like Figure 6 As shown, after the well was completed, in the subsequent oil testing operations, the 29 and 30 reservoirs with a total thickness of 5 meters were opened first, and 9.6 cubic meters of crude oil were produced per day, and no bottom water was found as interpreted by the well logging.

[0208] Figure 6 The results of well logging, mud logging and high-resolution electromagnetic method for the identification of porous media and liquid content near the wells for the two reservoirs 29 and 30 with a total thickness of 5 meters. The group of curves and symbols on the right side of the figure show the comprehensive interpretation conclusions, the middle part is the well logging deep detection resistivity curve, and the left side is the high-resolution electromagnetic method exploration harmonic index curve and phase delay curve. It can be seen that the high-resolution electromagnetic method exploration porous media and liquid content identification results are basically consistent with the logging and mud logging results. The identification results of other water-bearing reservoirs are also basically consistent.

[0209] like Figure 7 This is the result of high-resolution electromagnetic survey of porous media and liquid content identification in ELD8 well (partial). Figure 7The figure shows the comparison of the results of well logging, mud logging and high-resolution electromagnetic exploration of porous media and liquid content identification in the upper reservoir section of the well. The dotted box in the figure is a partial picture of the results of high-resolution electromagnetic exploration of porous media and liquid content identification, and the outside of the dotted box is the results of well logging and mud logging. It can be seen that the results of high-resolution electromagnetic exploration of porous media and liquid content identification are in good agreement with the results of well logging and mud logging.

[0210] Example 2

[0211] like Figure 8 Shown is a comparison of electromagnetic prediction results and seismic structures in the WEQ block of the WEX Sag in the HLE Basin.

[0212] Similar to the EL Basin, the HLE Basin is also a group of sags composed of Mesozoic Lower Cretaceous rifts. The main reservoirs are the Lower Cretaceous TBM oil group and NT oil group, and the reservoir burial depth is generally 2000-3000 meters. In 2008, the WEX sag submitted a proven reserve of 40.1291 million tons in the WEQ block, of which 39.4631 million tons were submitted to the NT group I section and 666,000 tons were submitted to the TBM group. In 2018, 10 years after the WEX block was put into development, after a reserve review, the actual proven reserves of the block were only 8.1946 million tons, a decrease of 70%. Figure 8 The above figure is a cross-section diagram of reservoir liquid content in high-resolution electromagnetic exploration. The ordinate is the horizontal distance in meters, and the ordinate is the depth in meters. It can be seen that in the section where the survey line passes, only the 20561300-20562500 section has oil and gas indications, and the oil and gas indication depth is 1700-2700 meters. There are two oil groups, the NT oil group and the TBM oil group. There is no sign of oil and gas indication in other sections of the survey line. The figure below is a plane diagram of the effective thickness of the II oil group in the 2nd section of the NT group. Comparing the two, it can be seen that the boundaries of the oil and gas indication sections predicted by the high-resolution electromagnetic method are strictly restricted by the fault boundary faults. The NT oil group is distributed on both sides of the northeast fault No. 1, while the TBM oil group is only distributed on the blocks supported by the northeast fault No. 1 and the nearly north-south fault No. 2.

[0213] Compared with the reserve review conclusion in 2018, the prediction results of the liquid content of porous media by high-resolution electromagnetic method show that oil and gas shows are only found in a local section of about 1,000 meters on the entire 10,000-meter-long survey line, and there are no signs of oil and gas shows in other sections; the 1,000-meter-high showing section is strictly limited by the fault controlling the reservoir. Obviously, the results of this example are more consistent with the actual situation.

[0214] It should be understood by those skilled in the art that the computer-readable storage media described above include: permanent and non-permanent, removable and non-removable media, which are tangible devices that can retain and store instructions for use by instruction execution devices. Computer-readable storage media include: electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, and any suitable combination of the above. Computer-readable storage media include: phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassette storage, tape disk storage or other magnetic storage devices, memory sticks, mechanical encoding devices (such as punched cards or raised structures in grooves with instructions recorded thereon) or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined in the embodiments of the present application, computer-readable storage media do not include temporary signals themselves, such as radio waves or other freely propagating electromagnetic fields, electromagnetic fields propagating through waveguides or other transmission media (such as light pulses passing through fiber optic cables), or electrical signals transmitted through wires.

[0215] In the several embodiments provided in the present application, it should be understood that the disclosed devices, electronic devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, or it can be an electrical, mechanical or other form of connection.

[0216] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, and may be located in one location or distributed over multiple network units. Some or all of the units may be selected according to actual needs to solve the problem to be solved by the embodiments of the present application.

[0217] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0218] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiment of the present application is essentially or part of the prior art that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium, including several instructions for a computer device (including: a personal computer, a server, a data center or other network equipment) to perform all or part of the steps of the method described in each embodiment of the present application. The above-mentioned storage medium includes various media that can store program codes as listed above.

[0219] The above is only a specific implementation of the embodiment of the present application, but the protection scope of the embodiment of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the embodiment of the present application, which should be included in the protection scope of the embodiment of the present application. Therefore, the protection scope of the embodiment of the present application shall be based on the protection scope of the claims.

Claims

1. A method for identifying porous media based on a natural electromagnetic field source, characterized in that: The method comprises: Collecting initial signals; the initial signals include the initial time series of synthetic electric field and / or magnetic field strength obtained by superimposing the natural electromagnetic field incident underground and the natural electromagnetic field incident underground at the moment of reflection and refraction back to the ground at the underground electrical impedance interface; Performing Fourier transform on the initial time series to obtain an initial frequency spectrum of the initial time series; Screening dominant frequency components in the initial frequency spectrum; the dominant frequency components are related to the burial depth of the top / bottom surface of the underground porous medium; Based on the synchronous and equal-rate changes of the phase derivative and the amplitude derivative of the dominant frequency component, the corresponding relationship between the top surface or the bottom surface of the underground porous medium and the frequency in the dominant frequency component is obtained.

2. The method for identifying porous media according to claim 1, characterized in that: The method further comprises: Based on the frequency-depth conversion of the dominant frequency component, the burial depth of the top / bottom surface of the underground porous medium is obtained.

3. The method for identifying porous media according to claim 1, characterized in that: The method further comprises: The liquid-containing property information of the underground porous medium is obtained based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

4. The method for identifying porous media according to claim 3, characterized in that: The method of obtaining the liquid-containing property information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium comprises: When the variation characteristics of the phase delay amount respond to the following relationship, it is identified that the liquid contained in the underground porous medium is water: When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

5. The method for identifying porous media according to claim 3, characterized in that: The method of obtaining the liquid-containing property information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium comprises: When the variation characteristics of the phase delay amount respond to the following relationship, it is identified that the liquid contained in the underground porous medium is crude oil and / or natural gas: When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

6. The method for identifying a porous medium according to any one of claims 3 to 5, characterized in that: The phase delay at least satisfies: in, is the phase delay of the electromagnetic wave when entering / exiting the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

7. The method for identifying porous media according to claim 1, characterized in that: The amplitude derivative of the dominant frequency component satisfies at least one of the following relations: Among them, a is an exponential function of σ and μ, a is a linear function of z; b is an exponential function of f; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; E is the electric field intensity; H is the magnetic field intensity; E0 is the electric field intensity amplitude at the time of incidence; H0 is the magnetic field intensity amplitude at the time of incidence.

8. The method for identifying porous media according to claim 1, characterized in that: The phase derivative of the dominant frequency component satisfies at least one of the following relations: Wherein, a is an exponential function of σ and μ, and a is a linear function of z; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; is the phase of electromagnetic wave.

9. The method for identifying porous media according to claim 1, characterized in that: The initial spectrum includes the frequency, real part, imaginary part, amplitude, and phase of the electric field and / or magnetic field.

10. The method for identifying porous media according to claim 1, characterized in that ,The time length of the Fourier transform is positively correlated with the burial depth of the underground porous medium to be identified.

11. A porous medium identification device based on a natural electromagnetic field source, characterized in that: When the device is in operation, it is capable of executing the porous medium identification method according to any one of claims 1 to 10, comprising: The acquisition module is configured to acquire an initial signal; the initial signal includes an initial time series of synthetic electric field and / or magnetic field strength obtained by superimposing the natural electromagnetic field incident underground at the moment when the natural electromagnetic field incident underground at the moment meets the natural electromagnetic field incident underground at the sensor; A synthesis module, configured to perform Fourier transform on the initial time series to obtain an initial spectrum of the initial time series; A screening module capable of screening the dominant frequency components in the initial spectrum; the dominant frequency components are related to the burial depth of the top / bottom surface of the underground porous medium; The identification module can obtain the corresponding relationship between the top surface or bottom surface of the underground porous medium and the frequency in the dominant frequency component based on the synchronous and equal-multiplication changes of the phase derivative and the amplitude derivative of the dominant frequency component.

12. The porous medium identification device according to claim 11, characterized in that: The identification module can identify the burial depth of the top / bottom surface of the underground porous medium based on the frequency-depth conversion of the dominant frequency component.

13. The porous medium identification device according to claim 11, characterized in that: The identification module can identify the liquid-containing information of the underground porous medium based on the phase delay of the electric field and / or magnetic field when the electromagnetic wave enters and exits the underground porous medium.

14. The porous medium identification device according to claim 13, characterized in that: The identification module can identify that the liquid contained in the underground porous medium is water when the change characteristic of the phase delay amount responds to the following relationship: When the electromagnetic wave enters the porous medium, the phase delay increases, and when the electromagnetic wave leaves the porous medium, the phase delay decreases.

15. The porous medium identification device according to claim 13, characterized in that: The identification module can identify that the liquid contained in the underground porous medium is crude oil and / or natural gas when the change characteristic of the phase delay amount responds to the following relationship: When the electromagnetic wave enters the porous medium, the phase delay decreases, and when the electromagnetic wave leaves the porous medium, the phase delay increases.

16. The porous medium identification device according to any one of claims 13 to 15, characterized in that: The phase delay at least satisfies: in, is the phase delay of the electromagnetic wave when entering / exiting the underground porous medium; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; ω is the angular frequency of the electromagnetic wave: ω=2πf, f is the frequency of the electromagnetic wave.

17. The porous medium identification device according to claim 11, characterized in that: The amplitude derivative of the dominant frequency component screened by the screening module at least satisfies any of the following relations: Among them, a is an exponential function of σ and μ, a is a linear function of z; b is an exponential function of f; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; E is the electric field intensity; H is the magnetic field intensity; E0 is the electric field intensity amplitude at the time of incidence; H0 is the magnetic field intensity amplitude at the time of incidence.

18. The porous medium identification device according to claim 11, characterized in that: The phase derivative of the dominant frequency component screened by the screening module at least satisfies any of the following relations: Wherein, a is an exponential function of σ and μ, and a is a linear function of z; z is the propagation distance of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; σ is the electrical conductivity of the underground porous medium; μ is the relative magnetic permeability of the underground porous medium; f is the frequency of the electromagnetic wave; t is the propagation time of the electromagnetic wave from the ground to the top or bottom surface of the underground porous medium; is the phase of electromagnetic wave.

19. The porous medium identification device according to claim 11, characterized in that: The synthesis module can obtain an initial spectrum including the frequency, real part, imaginary part, amplitude and phase of the electric field and / or magnetic field.

20. The porous medium identification device according to claim 11, characterized in that: The synthesis module can perform Fourier transformation on the initial time series with a time length that is positively correlated with the burial depth of the underground porous medium to be identified.

21. The porous medium identification device according to claim 11, characterized in that: The acquisition module is provided with at least two acquisition channels.

22. An electronic device, comprising a bus, an amplifier, an acquisition card, a comb filter / bandpass filter, a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the amplifier, the acquisition card, the comb filter / bandpass filter, the memory, and the processor are respectively connected via a bus, and when the computer program is executed by the processor, the steps in the method for identifying porous media according to any one of claims 1 to 10 are implemented.

23. A computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the method for identifying a porous medium according to any one of claims 1 to 10 are implemented.

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