A method for calculating parameters of controllable source electromagnetic acquisition

Abstract

The present application belongs to the technical field of controllable source electromagnetic exploration, and specifically discloses a controllable source electromagnetic acquisition parameter calculation method, wherein a 1D background resistivity model is obtained through a total longitudinal conductance fitting method, then the lowest transmitting frequency is calculated according to a detection depth, and acquisition parameters such as transmitting-receiving distance are obtained through full-area apparent resistivity. The present application changes the previous acquisition parameter acquisition mode through amplitude and phase curve analysis, so that the calculation of acquisition parameters is more accurate and quantitative, and provides a new technology and means for the design of controllable source electromagnetic acquisition parameters, and also provides technical support and guarantee for the controllable source electromagnetic method in deep and residual hidden oil and gas exploration.

Description

Technical Field

[0001] This invention belongs to the field of controlled-source electromagnetic exploration technology, and relates to a calculation method, specifically a method for calculating controlled-source electromagnetic acquisition parameters. Background Technology

[0002] Electromagnetic exploration is an important method in geophysical exploration. It has achieved good geological results and played an important role in the fields of finding deep concealed metal ore bodies, oil and gas structure exploration, geothermal and hydrological engineering.

[0003] Controlled-source electromagnetic exploration (CSAMT) is an important branch of electromagnetic exploration methods and one of the most promising methods for detecting deep oil and gas targets. Currently, commonly used CSAMT, WFEM, and TFEM exploration techniques are all based on the principles of controlled-source electromagnetic methods. These methods all employ a bipolar source, i.e., a horizontal long-conductor source, as the transmission source. The bipolar source field can only be approximated as a plane wave in the far region, where the skin depth or effective penetration depth can be used as the detection depth. However, in the transition and near-field regions, the skin depth cannot be used as the actual exploration depth, and the influence of the transmitter-receiver distance must also be considered.

[0004] He Jishan proposed the wide-area electromagnetic sounding method based on the CSAMT method, while He Zhanxiang invented the time-frequency electromagnetic method based on the CSAMT method and the time-domain transient electromagnetic method (LOTEM). Although these two methods expanded the observation range of the original CSAMT method beyond the wave region and enabled electromagnetic sounding in the transition and far-field regions, the relationship between the transmitter-receiver distance and the detection depth they provided was a broad range without specific calculation formulas and methods.

[0005] Chen Mingsheng, Zhong Yousheng, and others analyzed the relationship between the detection depth and electric distance, frequency, transmit / receive distance, and field region of the controlled-source electromagnetic method, but did not provide a method for directly calculating the transmit / receive distance and minimum transmission frequency from the detection depth in the transition region and far region.

[0006] Developing a specific calculation method for controllable source electromagnetic acquisition parameters is one of the urgent technical problems that need to be solved. Breakthroughs in this area will provide a solid foundation for improving the ability of controllable source electromagnetic detection to detect ultra-deep and complex oil and gas targets. Summary of the Invention

[0007] The purpose of this invention is to provide a method for calculating controlled-source electromagnetic (CME) acquisition parameters. This method obtains a 1D background geoelectric model through total longitudinal conductivity fitting, then calculates the minimum transmission frequency based on the detection depth, and obtains acquisition parameters such as the transmitter-receiver distance using the apparent resistivity of the entire area. This invention changes the previous method of obtaining acquisition parameters by analyzing amplitude and phase curves, making the calculation of acquisition parameters more accurate and quantifiable. It provides a new technology and means for designing CME acquisition parameters, and also provides technical support and assurance for the application of CME in deep and remaining hidden oil and gas exploration.

[0008] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0009] A method for calculating electromagnetic acquisition parameters of a controllable source includes the following steps:

[0010] S1. Select the type of observation device based on the geological exploration tasks, minimum and maximum detection depths in the construction design;

[0011] The observation device is a horizontal long conductor source excitation device. The measuring points on the measuring line of the observation device collect the electric field component Ex parallel to the horizontal long conductor source and the vertical magnetic field component Bz.

[0012] S2. Based on the resistivity logging data in the construction design, design a 1D background resistivity model;

[0013] The 1D background resistivity model is a 1D homogeneous isotropic medium;

[0014] S3. Based on the geological exploration tasks and minimum exploration depth D in the construction design. min and maximum detection depth D max Based on the 1D background resistivity model obtained in step S2, the lowest frequency f of the excitation signal is calculated. low and the highest frequency f of the excitation signal high ;

[0015] S4. Based on the 1D background resistivity model established in step S2, calculate the electric field component Ex intensity and the vertical magnetic field component Bz intensity of the horizontal long conductor source at different transmit and receive distances.

[0016] The transmit / receive distance refers to the distance between the survey line and the horizontal long conductor source. Different transmit / receive distances refer to transmit / receive distances ranging from D... max ~D max +10000 meters change, the increment between transmit and receive distances is 1000 meters;

[0017] The electric field component Ex intensity and the vertical magnetic field component Bz intensity are calculated using analytical formulas for a horizontal long wire source at any point in a layered medium.

[0018] S5. Calculate the corresponding apparent resistivity of the entire region based on the electric field component Ex obtained in step S4.

[0019] S6. Based on the apparent resistivity of the whole area at different transmit / receive distances obtained in step S5, draw a comparison curve of apparent resistivity of the whole area and calculate its slope.

[0020] S7, according to f low Determine the maximum transmit / receive distance R by analyzing the slope of the apparent resistivity curves for different transmit / receive distances across the entire region. offset ;

[0021] S8. Based on steps S2, S3, and S7, use a horizontal long-wire source to excite the ground in a 1D background resistivity model, and calculate the maximum transmit / receive distance R. offset The electric field component Ex intensity and the perpendicular magnetic field component Bz intensity at the location.

[0022] The horizontal long conductor source is 1000 meters long and emits a current of 1A; the unit of the electric field component Ex intensity is V / (mA), and the unit of the magnetic field component Bz intensity is A / m;

[0023] S9, based on the maximum transmit / receive distance R offset The electric field component Ex and the vertical magnetic field component Bz at a given location determine the minimum emission current I of the horizontally long conductor source AB. ab ;

[0024] The horizontal long conductor source AB refers to a horizontal long conductor source that supplies power to the ground using two grounding points A and B, and the minimum emission current I of AB is... ab This refers to the current flowing into the ground from a horizontally long conductor source through grounding points A and B, with a maximum transmit / receive distance R. offset The electrode distance at position E is r. MN ;

[0025] S10, based on the energy E of the horizontal long conductor source bipole It is the current I ab and the length r of the horizontal long conductor source AB It's a multiplicative relationship, determining the length r of the horizontal long conductor source. AB ;

[0026] The length r of the horizontal long conductor source AB This refers to the distance between grounding points A and B;

[0027] S11. Based on the acquisition parameters determined in steps S2 to S10, conduct controlled source electromagnetic acquisition to obtain the controlled source electromagnetic observation electric field component Ex and vertical magnetic field component Bz data. Then, perform inversion processing on the actual data to obtain the resistivity distribution information below the survey line.

[0028] As a limitation, in step S2, the method for designing the 1D background resistivity model is to calculate the total longitudinal conductivity of the resistivity logging data, repeatedly change the thickness and resistivity of the 1D background resistivity model, and then calculate its total longitudinal conductivity so that the total longitudinal conductivity curve of the resistivity logging data and the 1D background resistivity model fits, and the relative fitting error is less than 2%.

[0029] The total longitudinal conductance is calculated using the following formula:

[0030]

[0031] In the formula, S m It is the total longitudinal conductivity from layer 1 to layer n, h i ρ is the thickness of the i-th layer. i It is the resistivity of the i-th layer.

[0032] As a second limitation, in step S3, f low and f high This refers to the frequency of the non-zero-crossing square wave signal in the controllable source electromagnetic method, f. low and f high Calculated using the following formula

[0033] f low =1 / (k0*k1*D) max *S ma， )0, ②

[0034] f high =1 / (k0*k1*D) min *S min ) O , ③

[0035] Where k0 is a coefficient, 0.1≤k0≤10, k1=2π*10- 6 ,S max The maximum detection depth D max The corresponding total longitudinal conductance, S min It is the minimum detection depth D min The corresponding total longitudinal conductance.

[0036] As a further restriction, k0 = 1.

[0037] As a third limitation, in step S5, the apparent resistivity of the entire region is solved by the recursive bisection method.

[0038] The electric field component Ex of a horizontal long conductor source is calculated using the following formula:

[0039]

[0040] In the formula, ρ is the resistivity of a uniform half-space, and l is half the distance AB between the long conductor source. ζ is the coordinate of the integration point, x and y are the coordinates of the measurement point, ω is the angular frequency, and μ = 4π * 10⁻⁶. -7 ,

[0041] As a fourth limitation, in step S6, the x-axis of the full-area apparent resistivity comparison curve is frequency, the y-axis is resistivity, and the curve is a double logarithmic coordinate. The apparent resistivity of the same transmit / receive distance is connected by a line.

[0042] The slope refers to the slope of the apparent resistivity over the entire region under the same transmit / receive distance. The formula for calculating the slope is as follows:

[0043]

[0044] In the formula, ρ i It is the i-th frequency f i The corresponding apparent resistivity over the entire region, ρ i+1 It is the (i+1)th frequency f i+1 The corresponding apparent resistivity of the entire region.

[0045] As a fifth limitation, in step S7, the maximum transmit / receive distance R is determined. offset The method is to sequentially determine the transmit / receive distance as D. max To D max The slope of the apparent resistivity curve for the entire region corresponding to the frequency of the lowest excitation signal at +1000 meters, with the absolute value of the slope.

[0046] In the above process, it is assumed that the maximum detection depth D max The current depth is at layer j, then the following steps are performed.

[0047] S71. When the resistivity of the j-th layer is higher than that of the (j-1)-th layer above it, select the transmit / receive distance with the lowest frequency of the excitation signal corresponding to the smallest apparent resistivity of the whole area that is greater than the resistivity of the (j-1)-th layer and the smallest slope of the apparent resistivity of the whole area as the maximum transmit / receive distance; otherwise, proceed to step S72.

[0048] S72. When the resistivity of the j-th layer is lower than that of the (j-1)-th layer above, the maximum transmit / receive distance is selected when the apparent resistivity of the entire region corresponding to the lowest frequency of the excitation signal is less than that of the (j-1)-th layer and the slope of the apparent resistivity of the entire region is the smallest.

[0049] As a sixth limitation, in step S9, I is determined. ab Includes the following steps,

[0050] S911, search for f low and f high The electric field signal with the lowest intensity between the electrodes is multiplied by the intensity of that signal by the electrode distance r. MNThen divide by the instrument's minimum effective signal value, and round the resulting ratio to the nearest integer.

[0051] S912. Take the reciprocal of the obtained integer to obtain the minimum emission current I. ab .

[0052] As a seventh limitation, in step S9, I is determined. ab Includes the following steps,

[0053] S921, Search for f low and f high The magnetic field signal with the lowest intensity is found by multiplying its intensity by the equivalent area of ​​the magnetic field sensor, then dividing by the instrument's minimum effective signal value. The resulting ratio is rounded to the nearest integer.

[0054] S922. Take the reciprocal of the obtained integer to obtain the minimum emission current I. ab .

[0055] The present invention, by adopting the above-described technical solution, achieves the following technical advancements compared to existing technologies:

[0056] (1) This invention combines the controllable source electromagnetic acquisition parameters with the maximum detection depth in the construction design through mathematical formulas, changing the previous method of roughly judging the transition zone and far zone by the controllable source electromagnetic method through the transmit / receive distance, frequency and resistivity parameters, and realizing the accurate acquisition of parameters such as the minimum transmission frequency, the maximum transmit / receive distance and the minimum transmission current from the maximum detection depth.

[0057] (2) This invention realizes the transformation of the design of controllable source electromagnetic acquisition parameters from a rough qualitative approach to a precise quantitative approach, making the design of controllable source electromagnetic acquisition parameters more reasonable and scientific.

[0058] (3) The present invention can ensure that when the controllable source electromagnetic energy meets the maximum detection depth in the construction design, the minimum transmit and receive distance can be used to collect data with high signal-to-noise ratio.

[0059] (4) Through this invention, it can also be demonstrated whether the controllable source electromagnetic can meet the maximum detection depth in the construction design. Under the condition of ensuring the signal-to-noise ratio, if the maximum detection depth requirement in the construction design cannot be met by adjusting the minimum transmission frequency or the transmit-receive distance, it is necessary to increase the acquisition of natural field source (MT), and then use the controllable source electromagnetic and MT joint inversion processing technology to process the acquired data, which ensures both the detection depth and the detection accuracy.

[0060] (5) The present invention can ensure that high-quality controllable source electromagnetic data can be collected in field construction, laying a solid foundation for obtaining high-precision resistivity inversion results, providing technical support for improving the detection accuracy and detection effect of controllable source electromagnetics, and also having great significance for improving the construction efficiency and prediction accuracy of controllable source electromagnetics in complex ground and underground oil and gas targets.

[0061] This invention belongs to the field of controlled-source electromagnetic exploration technology. It changes the previous method of obtaining acquisition parameters by analyzing amplitude and phase curves, making the calculation of acquisition parameters more accurate and quantitative. It provides a brand-new technology and means for the design of acquisition parameters for controlled-source electromagnetic exploration, and also provides technical support and guarantee for the application of controlled-source electromagnetic methods in deep and remaining hidden oil and gas exploration. Attached Figure Description

[0062] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0063] In the attached diagram:

[0064] Figure 1 This is a schematic diagram of the controllable source electromagnetic method observation device according to an embodiment of the present invention;

[0065] Figure 2 a is a diagram of the logging curve and 1D background resistivity model in an embodiment of the present invention;

[0066] Figure 2 b is the total longitudinal conductivity fitting curve of well logging data and 1D background resistivity model in the embodiment of the present invention;

[0067] Figure 3 This is a 1D background resistivity model diagram of an embodiment of the present invention;

[0068] Figure 4 The diagram shows the apparent resistivity curves of the entire area at different transmit and receive distances according to the embodiments of the invention. Detailed Implementation

[0069] The preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0070] Example: A method for calculating electromagnetic acquisition parameters of a controllable source

[0071] Controlled-source electromagnetic exploration was conducted in the western uplift of well Po1 in a basin in Junggar, Xinjiang. The construction parameters for controlled-source electromagnetic exploration were designed and demonstrated using the technology described in this embodiment, and were carried out in the following steps:

[0072] S1. Select the type of observation device based on the geological exploration tasks, minimum and maximum detection depths in the construction design;

[0073] The minimum detection depth in the construction design is 500m, and the maximum detection depth is 5000m.

[0074] The selected observation device type is the controlled-source electromagnetic method, using a horizontal long conductor source for excitation. Measurement points on the observation device's measuring line collect the electric field component Ex parallel to the horizontal long conductor source and the vertical magnetic field component Bz. The electric field component Ex and the magnetic field component Bz are observed simultaneously. Figure 1 The diagram shown is a schematic of a controllable source electromagnetic observation device.

[0075] S2. Based on the resistivity logging data in the construction design, design a 1D background resistivity model;

[0076] The 1D background resistivity model is a 1D homogeneous isotropic medium;

[0077] like Figure 2 As shown, the method for designing a 1D background resistivity model is to calculate the total longitudinal conductivity of resistivity logging data, such as... Figure 2 As shown in Figure a, the resistance logging curve of well SX1 in the work area is selected. The total longitudinal conductance of the resistivity logging data of well SX1 is calculated. The thickness and resistivity of the 1D background resistivity model are repeatedly changed, and then its total longitudinal conductance is calculated to fit the total longitudinal conductance curve of the resistivity logging data and the 1D background resistivity model. Figure 2 As shown in b, the relative fitting error is less than 1.5%, and a 1D background resistivity model has been established, as follows. Figure 3 As shown;

[0078] The total longitudinal conductance is calculated using the following formula:

[0079]

[0080] In the formula, S m It is the total longitudinal conductivity from layer 1 to layer n, h i ρ is the thickness of the i-th layer. i It is the resistivity of the i-th layer;

[0081] S3. Based on the geological exploration tasks and minimum exploration depth D in the construction design. min and maximum detection depth D max Based on the 1D background resistivity model obtained in step S2, the lowest frequency f of the excitation signal is calculated. low and the highest frequency f of the excitation signal high ;

[0082] f low and f high This refers to the frequency of the non-zero-crossing square wave signal in the controllable source electromagnetic method, f.low and f high f is calculated using the following formula. low =1 / (k0*k1*D) max *S max )0, ②

[0083] f high =1 / (k0*k1*D) min *S min ) o , ③

[0084] Where k0 is a coefficient, 0.1≤k0≤10, and in this embodiment, k0=1; k1=2π*10- 6 ,S max The maximum detection depth D max The corresponding total longitudinal conductance, S min It is the minimum detection depth D min The corresponding total longitudinal conductance;

[0085] In this embodiment, based on the minimum detection depth of 500m and the maximum detection depth of 5000m in the construction design, and combined with the 1D background resistivity model obtained in step S2, the lowest frequency of the excitation signal is calculated to be 0.028Hz and the highest frequency is 12.69Hz.

[0086] S4. Based on the 1D background resistivity model established in step S2, calculate the electric field component Ex intensity and the vertical magnetic field component Bz intensity of the horizontal long conductor source at different transmit and receive distances.

[0087] The horizontal long conductor source is composed of dipole sources. The length of the dipole source is 1m. The length of the horizontal long conductor source is determined by the length of the theoretical dipole source, that is, the length of the horizontal long conductor source is 1m.

[0088] The transmit / receive distance refers to the distance between the survey line and the horizontal long conductor source. Different transmit / receive distances refer to transmit / receive distances ranging from D... max ~D max +10000 meters change, the increment between transmit and receive distances is 1000 meters;

[0089] In this embodiment, D max = 5000 meters;

[0090] The electric field component Ex intensity and the vertical magnetic field component Bz intensity are calculated using analytical formulas for a horizontal long wire source at any point in a layered medium.

[0091] S5. Calculate the corresponding apparent resistivity of the entire region based on the electric field component Ex obtained in step S4.

[0092] The apparent resistivity of the entire region is solved using the recursive bisection method.

[0093] The electric field component Ex of a horizontal long conductor source is calculated using the following formula:

[0094]

[0095] In the formula, ρ is the resistivity of a uniform half-space, and l is half the distance AB between the long conductor source. ζ is the coordinate of the integration point, x and y are the coordinates of the measurement point, ω is the angular frequency, and μ = 4π * 10⁻⁶. -7 ,

[0096] S6. Based on the apparent resistivity of the whole area at different transmit / receive distances obtained in step S5, draw a comparison curve of apparent resistivity of the whole area and calculate its slope.

[0097] like Figure 4 The figure shows the apparent resistivity curves for the entire region at different transmit / receive distances. In the figure, the x-axis is the frequency and the y-axis is the resistivity. It is a double logarithmic coordinate system. The apparent resistivity at the same transmit / receive distance is connected by a line.

[0098] The slope refers to the slope of the apparent resistivity over the entire region under the same transmit / receive distance. The formula for calculating the slope is as follows:

[0099]

[0100] In the formula, ρ i It is the i-th frequency f i The corresponding apparent resistivity over the entire region, ρ i+1 It is the (i+1)th frequency f i+1 The corresponding apparent resistivity over the entire area;

[0101] S7, according to f low Determine the maximum transmit / receive distance R by analyzing the slope of the apparent resistivity curves for different transmit / receive distances across the entire region. offset ;

[0102] Determine the maximum transmit / receive distance R offset The method is to sequentially determine the transmit / receive distance as D. max To D max The slope of the apparent resistivity curve for the entire region corresponding to the frequency of the lowest excitation signal at +1000 meters, with the absolute value of the slope.

[0103] In the above process, it is assumed that the maximum detection depth D max The current depth is at layer j, then the following steps are performed.

[0104] S71. When the resistivity of the j-th layer is higher than that of the (j-1)-th layer above it, select the transmit / receive distance with the lowest frequency of the excitation signal corresponding to the smallest apparent resistivity of the whole area that is greater than the resistivity of the (j-1)-th layer and the smallest slope of the apparent resistivity of the whole area as the maximum transmit / receive distance; otherwise, proceed to step S72.

[0105] S72. When the resistivity of the j-th layer is lower than that of the (j-1)-th layer above, the maximum transmit / receive distance is selected when the apparent resistivity of the entire region corresponding to the lowest frequency of the excitation signal is less than that of the (j-1)-th layer and the slope of the apparent resistivity of the entire region is the smallest.

[0106] In this embodiment, based on the lowest frequency of 0.028Hz and a transmit / receive distance of 7000m, the apparent resistivity of the entire region is greater than 5.1 ohm-meters, which is greater than the resistivity of the 9th layer (5 ohm-meters). Furthermore, the slope at a transmit / receive distance of 7000m is smaller than that at transmit / receive distances of 8000m to 15000m. Therefore, the maximum transmit / receive distance R is determined. offset It is 7000m;

[0107] S8. Based on steps S2, S3, and S7, use a horizontal long-wire source to excite the ground in a 1D background resistivity model, and calculate the maximum transmit / receive distance R. offset The electric field component Ex intensity and the perpendicular magnetic field component Bz intensity at the location.

[0108] The horizontal long conductor source is 1000 meters long and emits a current of 1A; the unit of the electric field component Ex intensity is V / (mA), and the unit of the magnetic field component Bz intensity is A / m;

[0109] S9, based on the maximum transmit / receive distance R offset The electric field component Ex and the vertical magnetic field component Bz at a given location determine the minimum emission current I of the horizontally long conductor source AB. ab ;

[0110] A horizontal long conductor source AB refers to a horizontal long conductor source that supplies power to the ground through two grounding points A and B. The minimum emission current I of AB is... ab This refers to the current flowing into the ground from a horizontally long conductor source through grounding points A and B, with a maximum transmit / receive distance R. offset The electrode distance at position E is r. MN In this embodiment, r MN =100m.

[0111] Specifically, determine I ab Includes the following steps,

[0112] S911, search for f low and f high The electric field signal with the lowest intensity between the electrodes is multiplied by the intensity of that signal by the electrode distance r. MN Then divide by the instrument's minimum effective signal value, and round the resulting ratio to the nearest integer.

[0113] S912. Take the reciprocal of the obtained integer to obtain the minimum emission current I. ab ;

[0114] The search revealed that the signal strength of the electric field Ex was minimum at a frequency of 0.028 Hz. Based on the minimum effective signal of the receiving instrument and the electrode distance r... MN Finally, the minimum emission current I was determined. ab It is 15A;

[0115] S10, based on the energy E of the horizontal long conductor source bipole It is the current I ab and the length r of the horizontal long conductor source AB It's a multiplicative relationship, determining the length r of the horizontal long conductor source. AB ;

[0116] The length r of the horizontal long conductor source AB This refers to the distance between grounding points A and B;

[0117] Based on the energy E of the bipolar source bipole Current I ab and the length r of the bipolar source AB Positive correlation. Considering the requirement that the signal-to-noise ratio Q value be greater than 5 in the construction design, the transmission current is doubled to 30A and the transmission source length is 3km.

[0118] S11. Based on the acquisition parameters determined in steps S2 to S10, conduct controlled source electromagnetic acquisition to obtain the controlled source electromagnetic observation electric field component Ex and vertical magnetic field component Bz data. Then, perform inversion processing on the actual data to obtain the resistivity distribution information below the survey line.

[0119] In step S9 of this embodiment, I is determined. ab Alternatively, you can follow these steps:

[0120] S921, Search for f low and f high The magnetic field signal with the lowest intensity is found by multiplying its intensity by the equivalent area of ​​the magnetic field sensor, then dividing by the instrument's minimum effective signal value. The resulting ratio is rounded to the nearest integer.

[0121] S922. Take the reciprocal of the obtained integer to obtain the minimum emission current I. ab .

Claims

1. A method for calculating electromagnetic acquisition parameters of a controllable source, comprising the following steps: S1. Select the type of observation device based on the geological exploration tasks, minimum and maximum detection depths in the construction design; The observation device is a horizontal long conductor source excitation device. The measuring points on the measuring line of the observation device collect the electric field component Ex parallel to the horizontal long conductor source and the vertical magnetic field component Bz. The method for calculating controllable source electromagnetic acquisition parameters is characterized by the following steps: S2. Based on the resistivity logging data in the construction design, design a 1D background resistivity model; The 1D background resistivity model is a 1D homogeneous isotropic medium; S3. Based on the geological exploration tasks and minimum exploration depth in the construction design. and maximum detection depth Based on the 1D background resistivity model obtained in step S2, the lowest frequency of the excitation signal is calculated. and the highest frequency of the excitation signal ; S4. Based on the 1D background resistivity model established in step S2, calculate the electric field component Ex intensity and the vertical magnetic field component Bz intensity of the horizontal long conductor source at different transmit and receive distances. The transmit / receive distance refers to the distance between the survey line and the horizontal long conductor source; different transmit / receive distances refer to transmit / receive distances ranging from... ~ +10000 meters change, the increment between transmit and receive distances is 1000 meters; The electric field component Ex intensity and the vertical magnetic field component Bz intensity are calculated using analytical formulas for a horizontal long wire source at any point in a layered medium. S5. Calculate the corresponding apparent resistivity of the entire region based on the electric field component Ex obtained in step S4. S6. Based on the apparent resistivity of the whole area at different transmit / receive distances obtained in step S5, draw a comparison curve of apparent resistivity of the whole area and calculate its slope. S7, according to The slope of the apparent resistivity curves for different transmit / receive distances across the entire region is used to determine the maximum transmit / receive distance. ; S8. Based on steps S2, S3, and S7, use a horizontal long-wire source to excite the ground in a 1D background resistivity model, and calculate the maximum transmit / receive distance. The intensity of the electric field component Ex and the intensity of the perpendicular magnetic field component Bz at the location; The horizontal long conductor source is 1000 meters long and emits a current of 1A; the unit of the electric field component Ex intensity is V / (mA), and the unit of the magnetic field component Bz intensity is A / m; S9. Based on the maximum transmit / receive distance The electric field component Ex and the vertical magnetic field component Bz at a given location determine the minimum emission current of the horizontally long conductor source AB. ; The horizontal long conductor source AB refers to a horizontal long conductor source that supplies power to the ground using two grounding points A and B, and the minimum emission current of AB is... This refers to the current flowing into the ground from a horizontally long conductor source through grounding points A and B, with a maximum transmission / reception distance. The electrode distance at position Ex is ; S10, Based on the energy of the horizontal long conductor source It is electric current and the length of the horizontal long conductor source The multiplication relationship determines the length of the horizontal long conductor source. ; The length of the horizontal long conductor source This refers to the distance between grounding points A and B; S11. Based on the acquisition parameters determined in steps S2 to S10, conduct controlled source electromagnetic acquisition to obtain the controlled source electromagnetic observation electric field component Ex and vertical magnetic field component Bz data. Then, perform inversion processing on the actual data to obtain the resistivity distribution information below the survey line.

2. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S2, the method for designing the 1D background resistivity model is to calculate the total longitudinal conductivity of the resistivity logging data, repeatedly change the thickness and resistivity of the 1D background resistivity model, and then calculate its total longitudinal conductivity so that the total longitudinal conductivity curve of the resistivity logging data and the 1D background resistivity model fits each other with a relative fitting error of less than 2%. The total longitudinal conductance is calculated using the following formula: ， ① In the formula, It is 1 to Total longitudinal conductivity of the layer It is the first The thickness of the layer, It is the first The resistivity of the layer.

3. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S3 and This refers to the frequency of a non-zero-crossing square wave signal obtained by the controllable source electromagnetic method. and Calculated using the following formula ， ② ， ③ in, It is a coefficient, 0.1≤ ≤10, , Maximum detection depth The corresponding total longitudinal conductance, Minimum detection depth The corresponding total longitudinal conductance.

4. The method for calculating controllable source electromagnetic acquisition parameters according to claim 3, characterized in that, =1。 5. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S5, the apparent resistivity of the entire region is solved by the recursive bisection method. The electric field component Ex of a horizontal long conductor source is calculated using the following formula: ， ④ In the formula, It is the resistivity of a uniform half-space. It is half the distance AB of the long conductor source. , , , These are the coordinates of the integration point. and These are the coordinates of the measuring point. , It is angular frequency. .

6. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S6, the x-axis of the full-area apparent resistivity comparison curve is frequency, and the y-axis is resistivity. It is a double logarithmic coordinate system, and the apparent resistivity of the same transmit / receive distance is connected by a line. The slope refers to the slope of the apparent resistivity over the entire region under the same transmit / receive distance. The formula for calculating the slope is as follows: , ⑤ In the formula, It is the first frequency The corresponding apparent resistivity over the entire area, It is the first frequency The corresponding apparent resistivity of the entire region.

7. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S7, the maximum transmit / receive distance is determined. The method is to sequentially determine the transmit / receive distance as... arrive The slope of the apparent resistivity curve for the entire region corresponding to the frequency of the lowest excitation signal at +1000 meters, with the absolute value of the slope. In the above process, the maximum detection depth is assumed. The depth at which it is located is Layer, then perform the following steps, S71, when the The resistivity of the first layer is higher than that of the layer above it. When determining the resistivity of the layer, the apparent resistivity of the entire region corresponding to the lowest frequency of the excitation signal is greater than that of the first layer. The maximum transmit / receive distance is defined as the transmit / receive distance with the minimum slope of the layer's resistivity and the apparent resistivity of the entire region. Otherwise, proceed to step S72; S72, Dangdi The resistivity of the first layer is lower than that of the layer above it. When determining the resistivity of the layer, the apparent resistivity of the entire region corresponding to the lowest frequency of the excitation signal is less than that of the first layer. The maximum transmit / receive distance is defined as the transmit / receive distance with the minimum slope of the layer's resistivity and the apparent resistivity of the entire region.

8. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S9, determine Includes the following steps, S911, Search Results and The electric field signal with the lowest intensity between the electrodes is multiplied by the intensity of that signal. Then divide by the instrument's minimum effective signal value, and round the resulting ratio to the nearest integer. S912. Take the reciprocal of the obtained integer to obtain the minimum emission current. .

9. The method for calculating controllable source electromagnetic acquisition parameters according to claim 1, characterized in that, In step S9, determine Includes the following steps, S921, Search Results and The magnetic field signal with the lowest intensity is found by multiplying its intensity by the equivalent area of ​​the magnetic field sensor, then dividing by the instrument's minimum effective signal value. The resulting ratio is rounded to the nearest integer. S922. Take the reciprocal of the obtained integer to obtain the minimum emission current. .

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