Controllable source audio frequency magnetotelluric sounding transmitting end electrode arrangement system and method

Abstract

A controllable source audio frequency magnetotelluric sounding transmitting end electrode arrangement system and method belong to the technical field of electromagnetic prospecting, and particularly relate to the technical field of electromagnetic sounding electrode arrangement. The system and method solve the technical problem that the current CSAMT transmitting end electrode arrangement technology cannot simultaneously achieve the core target of "greatly reducing resistance and increasing current + zero field source distortion + high construction feasibility". The system and method comprise a main dipole unit and A-side and B-side distributed auxiliary electrode arrays. The main dipole unit is composed of A0 and B0 main transmitting electrodes. The A-side auxiliary electrode array is arranged in a direction away from the B0 along a dipole axis, the B-side auxiliary electrode array is arranged in a direction away from the A0 along the dipole axis, and the double-side arrays are completely symmetrical along the dipole center. All same-side electrodes are connected in parallel at an equal potential to a transmitter, and the transmitting current is in-phase and equal potential. The system and method only need short electrodes and artificial shallow pits for arrangement, the grounding resistance is greatly reduced, the transmitting current is steadily increased, and the ideal horizontal electric dipole field source characteristics are strictly guaranteed without field source distortion.

Description

Technical Field

[0001] This invention belongs to the field of geophysical electromagnetic surveying technology, specifically relating to the field of geophysical electromagnetic sounding pole distribution technology. Background Technology

[0002] Controlled-source audio-frequency magnetotelluric sounding (CSAMT) is an artificial-source frequency-domain electromagnetic exploration method. It uses a grounded horizontal electric dipole to emit alternating electromagnetic fields of different frequencies, measuring the orthogonal electric and magnetic field components in the distant region to calculate the apparent resistivity and phase of the subsurface medium, thus achieving vertical depth sounding of the subsurface strata. This method has advantages such as large exploration depth, high resolution, and strong anti-interference capability, and is widely used in fields such as metal mineral exploration, oil and gas resource exploration, hydrogeological surveys, engineering geological exploration, and geothermal resource exploration.

[0003] One of the core performance indicators of CSAMT exploration is the magnitude of the transmission current at the transmitter. The transmission current directly determines the field strength of the far-field electromagnetic field, the data signal-to-noise ratio, the effective exploration depth, and the formation resolution. At the same transmission frequency, the larger the transmission current, the higher the far-field field strength, the stronger the anti-interference capability, and the greater the achievable exploration depth.

[0004] The existing CSAMT transmitter electrode arrangement technology has the following core defects that prevent it from simultaneously achieving the desired field construction and exploration results, which are long-standing technical pain points that the industry has been unable to resolve: 1. Traditional single-dipole electrode arrangement has extremely poor resistance reduction capability: Traditional electrode arrangement uses two independent grounding electrodes A and B to form a single dipole. The total grounding resistance of the transmitting circuit is R = R_A + R_B + R_line, where R_A and R_B are the grounding resistances of the single electrodes, and R_line is the cable resistance. In high-resistivity areas (such as deserts, Gobi, exposed carbonate rock areas, and volcanic rock-covered areas), the surface resistivity is high, which severely limits the transmitting current I = U / R. Even if the transmitter output voltage is increased, it is still limited by the transmitter power limit, equipment insulation performance, and on-site safety requirements. Moreover, most of the transmitting power is dissipated in the grounding resistance, resulting in extremely low electromagnetic radiation efficiency and weak far-field signals, which cannot meet the needs of deep exploration.

[0005] 2. Concentrated parallel electrode arrangement suffers from severe shielding effect, resulting in extremely low resistance reduction efficiency: Existing improved technologies mostly adopt the method of concentrated parallel connection of multiple electrodes at poles A and B to reduce resistance. However, this method has a fatal flaw: when multiple electrodes are concentrated and the spacing is too small, the current fields between the electrodes superimpose, producing a severe current shielding effect, equivalent to a single large-size electrode. The grounding resistance reduction does not reach the theoretical limit of 1 / n (where n is the number of parallel electrodes), and the actual resistance reduction efficiency is less than 30% of the theoretical value, resulting in extremely poor resistance reduction effect. At the same time, concentrated parallel connection leads to excessive current density at the electrodes, severe grounding polarization effect, large heat loss, and even problems such as electrode ablation and rapid deterioration of grounding performance, which cannot meet the requirements of high power and long-term continuous transmission.

[0006] 3. Off-axis electrode arrangement leads to field source distortion and is incompatible with existing interpretation systems: Existing multi-electrode arrangements mostly adopt an arrangement perpendicular to the dipole axis, which will lead to a significant increase in the equivalent width of the dipole, causing the field source to deviate from the ideal horizontal electric dipole model, resulting in severe field source distortion, causing errors in apparent resistivity calculation, requiring complex field source correction processing, and is incompatible with existing mature CSAMT data processing and interpretation methods, resulting in extremely poor field applicability.

[0007] 4. Other combinations of pole arrangements completely change the characteristics of the field source, making them extremely difficult to promote: Improvements such as multi-dipole combinations and ring pole arrangements completely change the electromagnetic field distribution characteristics of the field source, making it impossible to interpret the data using traditional CSAMT theory. It is necessary to rebuild the interpretation model, and it cannot be applied on a large scale in the existing exploration system.

[0008] 5. Existing technologies do not standardize electrode selection, cable parameters, and burial depth control measures, resulting in poor feasibility of the solutions. The same electrode arrangement method has vastly different application effects in different work areas, making it impossible to stably achieve the goal of reducing resistance and increasing current.

[0009] Based on the above introduction, there is currently no publicly available CSAMT transmitter electrode arrangement technology that can simultaneously achieve the core objectives of "significantly reduced resistance and increased current + zero field source distortion + high construction feasibility". Summary of the Invention

[0010] To address the technical challenge of simultaneously achieving the core objectives of "significantly reduced resistance and increased current + zero field source distortion + high construction feasibility" in CSAMT transmitter electrode arrangement technology, which currently lacks any publicly available technology.

[0011] This invention provides a controllable source audio magnetotelluric sounding transmitter pole arrangement system, comprising a main dipole unit, an A-side distributed auxiliary pole array, and a B-side distributed auxiliary pole array; The main dipole unit includes a first main emitting electrode A0 and a second main emitting electrode B0, and the distance between the first main emitting electrode A0 and the second main emitting electrode B0 is a preset dipole distance L; The distributed auxiliary electrode array on side A includes n first auxiliary emitter electrodes A1, A2, ..., An. The n first auxiliary emitter electrodes are arranged sequentially in the opposite direction from A0 to B0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout the entire process. The B-side distributed auxiliary electrode array includes n second auxiliary emitter electrodes B1, B2, ..., Bn. The n second auxiliary emitter electrodes are arranged sequentially in the opposite direction from B0 to A0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout the entire process. The first main emitter electrode A0 is connected in parallel with all the first auxiliary emitter electrodes of the distributed auxiliary electrode array on side A through a low-resistance parallel cable at the same potential and is connected to the first output terminal of the transmitter; the second main emitter electrode B0 is connected in parallel with all the second auxiliary emitter electrodes of the distributed auxiliary electrode array on side B through a low-resistance parallel cable at the same potential and is connected to the second output terminal of the transmitter; the emitter currents of all emitter electrodes are in phase and at the same potential.

[0012] Furthermore, the first main emitting electrode A0 and the second main emitting electrode B0 are buried at the same depth, which is 0.3~0.4m.

[0013] Furthermore, in the distributed auxiliary electrode array on side A, the spacing D between adjacent first auxiliary emitter electrodes is ≥ 5 times the maximum electrode burial depth in the array, and the minimum spacing is not less than 5m; in the distributed auxiliary electrode array on side B, the spacing D between adjacent second auxiliary emitter electrodes is ≥ 5 times the maximum electrode burial depth in the array, and the minimum spacing is not less than 5m.

[0014] Furthermore, in the distributed auxiliary electrode array on side A, the burial depth of the n first auxiliary emitter electrodes increases sequentially in the direction away from the first main emitter electrode A0; in the distributed auxiliary electrode array on side B, the burial depth of the n second auxiliary emitter electrodes increases sequentially in the direction away from the second main emitter electrode B0.

[0015] Furthermore, in the distributed auxiliary electrode array on side A, the burial depth of the first auxiliary emitter electrode increases by 0.1~0.3m; in the distributed auxiliary electrode array on side B, the burial depth of the second auxiliary emitter electrode increases by 0.1~0.3m.

[0016] Furthermore, the number of the first auxiliary emitter electrodes of the distributed auxiliary pole array on side A is equal to the number of the second auxiliary emitter electrodes of the distributed auxiliary pole array on side B, and the spacing and burial depth are completely symmetrically distributed along the center of the main dipole unit.

[0017] Furthermore, the value of n ranges from 3 to 7, and is adjusted according to the resistivity of the formation in the exploration area and the preset emission current.

[0018] Furthermore, in the electrode arrangement system, both the main emitting electrode and the auxiliary emitting electrode are solid rod-shaped electrodes made of oxygen-free copper; the main emitting electrode is 0.5m long and 18~25mm in diameter; the auxiliary emitting electrode is 0.5~1.1m long and 12~18mm in diameter; and the outer wall of all electrodes is wrapped with a resistivity ≤5Ω. The drag-reducing agent layer is m.

[0019] Furthermore, the low-resistance parallel cable adopts oxygen-free copper multi-core cross-linked polyethylene insulated power cable. Under 20℃ environment, the DC resistance of a single insulated core wire per kilometer is ≤0.8Ω, and the rated withstand voltage is ≥2 times the maximum output voltage of the transmitter. Each transmitting electrode is connected to an independent insulated core wire, and all insulated core wires on the same side are connected together at the transmitter output end.

[0020] The present invention also provides a method for arranging electrodes suitable for the above-mentioned electrode arrangement system, specifically as follows: S1. Parameter preset: Based on the exploration target depth and the strata conditions at the transmitter, preset the dipole distance L and the target emission current; the number of auxiliary emission electrodes n is determined through field tests to ensure that the emission current reaches the ideal value. S2. Main Dipole Layout: At the emission points of the preset survey line, the first main emission electrode A0 and the second main emission electrode B0 are laid out. The distance between A0 and B0 is the dipole moment L, and the line connecting the two points is the axis of the main dipole. The main emission electrodes are laid out by manually excavating shallow pits and hammering the electrodes vertically to the ground. The holes are backfilled with drag-reducing agent and fine soil. Salt water is poured into the pits to ensure that the electrodes are in full contact with the strata. The burial depths of A0 and B0 are completely consistent. S3, A-side auxiliary electrode array layout: Along the opposite direction of the dipole axis A0 to B0, n first auxiliary emitting electrodes A1~An are sequentially arranged. The distance between adjacent first auxiliary emitting electrodes D is ≥ 5 times the maximum electrode burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the first auxiliary emitting electrodes increases progressively in the direction away from A0, with the increase in burial depth between adjacent first auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all first auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. Salt water is poured at the grounding point of each first auxiliary emitting electrode. S4, B-side auxiliary electrode array layout: Along the opposite direction of the dipole axis B0 to A0, n second auxiliary emitting electrodes B1~Bn are sequentially arranged. The distance between adjacent second auxiliary emitting electrodes D is ≥ 5 times the maximum electrode burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the second auxiliary emitting electrodes increases progressively in the direction away from B0, with the increment of the burial depth between adjacent second auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all second auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. Salt water is poured at the grounding point of each second auxiliary emitting electrode. The number of the first auxiliary emitter electrodes of the distributed auxiliary pole array on side A is equal to that of the second auxiliary emitter electrodes of the distributed auxiliary pole array on side B, and the spacing and burial depth are completely symmetrically distributed along the center of the main dipole unit. S5. Equipotential Parallel Connection and Quality Control: Connect A0 and A1~An to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the first output terminal of the transmitter after the current bus connection; connect B0 and B1~Bn to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the second output terminal of the transmitter after the current bus connection; complete the electrode arrangement.

[0021] The beneficial effects of the electrode distribution system described in this invention are as follows: Fully adaptable to actual field conditions, with extremely low construction difficulty: This invention adopts a design with short electrodes of 0.5~1.1m, electrodes exposed on the ground surface, maximum burial depth ≤1m, and adjacent spacing ≥5m. The entire deployment can be completed by manually excavating shallow pits, without the need for drilling rigs or large construction equipment. It is perfectly adapted to field exploration scenarios and has extremely strong engineering versatility.

[0022] Significantly reduced resistance and increased current: This invention, through a distributed parallel design along the dipole axis and a parameter design where the horizontal spacing D between adjacent auxiliary emitter electrodes is ≥ 5 times the maximum depth of the array, significantly reduces the overlap of the underground current diffusion field between parallel electrodes of the same polarity, thereby weakening the current shielding effect from the root and thus keeping the shielding coefficient (K) stably controlled within 2. Based on this, through the coordinated design of parallel equipotential connection of electrodes on the same side and progressively increasing burial depth, the resistance reduction efficiency of the existing centralized parallel electrode arrangement has been improved, making the resistance reduction efficiency more than twice that of the centralized parallel electrode arrangement at the same point. Finally, according to Ohm's law, the transmission current is inversely proportional to the total grounding resistance of the circuit. Under the premise of fixed transmitter rated output voltage, the significant decrease in the total grounding resistance of the circuit enables the transmission current under the same transmission voltage to be increased several times, with an efficiency increase of 3 to 5 times. The far-field field strength is also increased synchronously, and the data signal-to-noise ratio is significantly improved.

[0023] Strictly guaranteeing field source characteristics, zero distortion, and full compatibility: This invention adopts a double-sided array arranged symmetrically outward along the dipole axis, with all electrodes on the same side connected in parallel at the same potential and in phase. The center of the equivalent dipole completely coincides with the main dipole, and the electromagnetic field distribution matches the theoretical value of the ideal horizontal electric dipole by more than 99%. There is no field source distortion, and it is fully compatible with all existing CSAMT data processing and interpretation methods without any additional correction, making it extremely suitable for field applications.

[0024] Graded shallow burial penetration of high-resistivity layers, suitable for most work areas: This invention adopts a burial depth increasing design of 0.1~0.3m. Based on the preliminary survey of construction, it can basically penetrate the shallow high-resistivity covering layer in most work areas, so that the electrode can contact the underlying low-resistivity stratum, completely solving the current blockage problem of shallow high-resistivity layer, and achieving extreme resistance reduction without deep hole construction.

[0025] Convenient construction, controllable cost, and easy to promote: This invention does not require additional special equipment and can be achieved using only conventional CSAMT transmitting electrodes and low-resistance cables. The electrode arrangement method is simple and standardized, and on-site construction is convenient. Compared with traditional electrode arrangement, it only increases the cost of electrodes and cables by a small amount, but can achieve a significant improvement in exploration performance. It has a very high cost performance and is easy to promote and apply on a large scale in the industry. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the planar structure of the pole distribution system described in an embodiment of the present invention; Figure 2 This is a schematic diagram of the burial depth of the distributed auxiliary pole array on side A in an embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0028] Example 1 This embodiment provides a controllable source audio magnetotelluric sounding transmitter pole arrangement system.

[0029] It includes a main dipole unit, an A-side distributed auxiliary pole array, and a B-side distributed auxiliary pole array.

[0030] like Figure 1As shown, the main dipole unit includes a first main emitting electrode A0 and a second main emitting electrode B0. The distance between the first main emitting electrode A0 and the second main emitting electrode B0 is a preset dipole moment L, which conforms to the requirements of the controlled-source audio-frequency magnetotelluric sounding exploration specification. The main emitting electrode is the reference anchor point of the entire emission field source, defining the dipole moment, dipole axis, and equivalent dipole center, which is the core foundation for ensuring the distortion-free field source.

[0031] The axis of the main dipole is the line connecting A0 and B0, and the center of the main dipole is the midpoint of the line connecting A0 and B0. Since the main and auxiliary poles on both sides of A and B are completely symmetrically distributed and the auxiliary poles are arranged outward along A0 and B0 without entering between A0 and B0, the center of the equivalent dipole is the midpoint of the line connecting A0 and B0.

[0032] The distributed auxiliary electrode array on side A includes n first auxiliary emitter electrodes A1, A2, ..., An. These n first auxiliary emitter electrodes are arranged sequentially in the opposite direction from A0 to B0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout their arrangement. The distributed auxiliary electrode array on side B includes n second auxiliary emitter electrodes B1, B2, ..., Bn. These n second auxiliary emitter electrodes are arranged sequentially in the opposite direction from B0 to A0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout their arrangement. The auxiliary emitter electrodes are functional supplementary units for parallel current shunt and resistance reduction, and are arranged only along the axis outside the main electrodes, without changing the core dipole moment and the field source reference.

[0033] The first main emitting electrode A0 and the second main emitting electrode B0 are buried at the same depth, which is 0.3~0.4m.

[0034] like Figure 1 As shown, the first main emitting electrode A0 is connected in parallel with all the first auxiliary emitting electrodes of the distributed auxiliary electrode array on side A through a low-resistance parallel cable, and is connected to the first output terminal of the transmitter; the second emitting electrode B0 is connected in parallel with all the second auxiliary emitting electrodes of the distributed auxiliary electrode array on side B through a low-resistance parallel cable, and is connected to the second output terminal of the transmitter; the emitting currents of all emitting electrodes are in phase and at the same potential, with no phase difference, ensuring that the equivalent dipole field source is completely consistent with the ideal horizontal electric dipole.

[0035] The first and second output terminals of the transmitter are the positive and negative terminals, respectively.

[0036] In the distributed auxiliary electrode array on side A, the spacing D between adjacent first auxiliary emitter electrodes is greater than or equal to 5 times the maximum electrode burial depth in the array, and the minimum spacing is not less than 5m. In the distributed auxiliary electrode array on side B, the spacing between adjacent second auxiliary emitter electrodes follows the same rule as the array on side A, thereby completely avoiding the strong shielding effect of existing centralized parallel connection and improving the resistance reduction efficiency.

[0037] In the distributed auxiliary electrode array on side A, the buried depth of the first auxiliary emission electrode gradually increases along the direction away from the first main emission electrode A0, that is, h_A1 < h_A2 < … < h_An; h_A1, h_A2, …, h_An respectively correspond to the buried depths of A1, A2, …, An; in the distributed auxiliary electrode array on side B, the buried depth of the second auxiliary emission electrode gradually increases along the direction away from the second main emission electrode B0, that is, h_B1 < h_B2 < … < h_Bn, h_B2, …, h_Bn respectively correspond to the buried depths of B1, B2, …, Bn; by increasing the buried depth in stages, the shallow high-resistance covering layer is penetrated step by step, further significantly reducing the grounding resistance and solving the current blocking problem of the shallow high-resistance layer. As Figure 2 The figure shows a schematic diagram of the buried depth profile of the distributed auxiliary electrode array on side A.

[0038] The buried depth refers to the effective length of the electrode vertically buried underground, and the upper ends of all electrodes are exposed on the ground surface for layout.

[0039] In the distributed auxiliary electrode array on side A and the distributed auxiliary electrode array on side B, the increasing amplitude of the buried depth of adjacent auxiliary emission electrodes is 0.1 - 0.3 m; the maximum buried depth of the auxiliary emission electrode at the end of the array does not exceed 1 m. This increasing amplitude is fully adapted to manual shallow pit excavation without a drill. At the same time, when selecting the CSAMT emission position, technicians will conduct a site survey in advance and select areas with a relatively thin high-resistance covering layer or a low-resistance covering layer on the surface. This design can achieve extreme resistance reduction.

[0040] The number of auxiliary emission electrodes n in the distributed auxiliary electrode array on side A is equal to that on side B. The arrangement spacing and buried depth gradient are completely symmetric along the center of the main dipole unit, ensuring that the center of the equivalent dipole coincides completely with the center of the main dipole unit, strictly maintaining the field source characteristics of an ideal horizontal electric dipole, without any field source distortion, and being fully compatible with the existing CSAMT data processing and interpretation methods.

[0041] Both the main emission electrode and the auxiliary emission electrode are solid rod-shaped electrodes made of oxygen-free copper. Oxygen-free copper has excellent electrical conductivity and strong corrosion resistance, which can effectively reduce the grounding contact resistance and the electrochemical polarization effect; the length of the main emission electrode is 0.5 m, and the diameter is 15 - 18 mm; the length of the auxiliary emission electrode is 0.5 - 1.1 m, and the diameter is 18 - 20 mm, which is fully adapted to the electrode specifications for actual field use; the outer walls of all electrodes are wrapped with a resistance-reducing agent layer with a resistivity ≤ 5Ω m to further reduce the contact resistance between the electrode and the formation.

[0042] The low-resistance parallel cable uses oxygen-free copper multi-core cross-linked polyethylene insulated power cable. At 20℃, the DC resistance of a single insulated core wire per kilometer is ≤0.8Ω, and the rated withstand voltage of the core wire is ≥2 times the maximum output voltage of the transmitter. Each transmitting electrode is connected to an independent insulated core wire, and all insulated core wires on the same side are connected at the transmitter output terminal to ensure a low potential difference between the farthest electrode on the same side and the main transmitting electrode, achieving strict equipotential and in-phase transmission and avoiding field source distortion.

[0043] The core difference between the main emitter electrode and the auxiliary emitter electrode: All parameter differences between the main and auxiliary emitting electrodes in this invention are based on the differences in their core functional positioning, as detailed below: Functional positioning differences: The main emitting electrode is the field source reference anchor point, which defines the core dipole moment and the field source center, and undertakes the function of total current collection; the auxiliary emitting electrode is a current shunt and resistance reduction supplementary unit, which is only used to reduce the grounding resistance and increase the emitting current, and absolutely does not change the field source reference.

[0044] The arrangement rules are different: the main emitting electrodes A0 and B0 form the core dipole moment with a distance of kilometers; the auxiliary emitting electrodes can only be arranged along the dipole axis outside the main emitting electrodes with a distance of tens of meters between adjacent electrodes, and they do not enter the core dipole moment range at all, and must be arranged symmetrically on both sides.

[0045] Differences in burial depth design: The main emitting electrode adopts a fixed and uniform burial depth, with A0 and B0 having completely identical burial depths, requiring only penetration of the surface loose soil; the auxiliary emitting electrode adopts a burial depth design that gradually increases along the direction away from the main electrode, with the goal of penetrating the high-resistivity cover layer.

[0046] Example 2 The embodiments further define Embodiment 1, providing a specific application example of the system described in Embodiment 1 in a real-world environment.

[0047] During water exploration in a mountain foothill area in Nankou, Changping District, Beijing, although the field source was located seven kilometers east of the receiving area, far from the foothills, the transmitting electrode was situated in a demolished village. Initially, a circular array of 10 electrodes was used at the A and B ends, all buried at a depth of 0.7 meters. The transmitter used 450V, with a transmission current of only 6.5A, and the data acquisition and post-processing results were unsatisfactory. Later, the transmitting device of this invention was adopted, increasing the transmission voltage to 450V and the transmission current to 15A. Furthermore, the data acquired using this device, after conventional processing, showed a significant improvement in exploration results.

[0048] Example 3 This embodiment provides a method for setting up the poles of the controllable source audio magnetotelluric sounding transmitter system described in Embodiment 1, specifically as follows: S1. Parameter preset: Based on the exploration target depth and the strata conditions at the transmitting end, preset the dipole distance L of the main dipole (L is usually 1~3km according to the specification) and the target transmission current. The number of auxiliary poles n can be determined through field tests under the premise of meeting the preset requirements in Example 1, to ensure that the transmission current reaches the ideal value.

[0049] Existing electrode placement methods generally use a uniform burial depth, lacking a method with progressively varying burial depths, and the electrode spacing and position are unclear. A uniform burial depth increases workload and can cause shielding effects. In most CSAMT transmitter sites, the thickness of the surface high-resistivity overburden layer (dry soil, gravel, weathered rock) is not a completely uniform plane, but rather undulating and gradually changing. The progressively varying burial depth distributed electrode placement method of this invention has the following characteristics: (1) Significantly reduces the difficulty of field construction; (2) Significantly reduces the overlap of the current field, and the resistance reduction efficiency is infinitely close to the theoretical limit: For two adjacent electrodes with increasing burial depths, the first electrode is shallow and has a small current diffusion radius, while the second electrode is deep and has a large current diffusion radius. The overlap of the two underground current hemispheres is reduced compared to electrodes of equal depth. For example, for two electrodes with a spacing of 5m and the same burial depth of 1.0m, the shielding coefficient K=1.9; while for the incremental design of burial depth of 0.7m+1.0m, the shielding coefficient K=1.3, and the resistance reduction efficiency is significantly improved, which is closer to the theoretical limit of 1 / n. (3) The array of increasing burial depths forms a gradient current distribution along the axis outward: from near to far, the electrode burial depth increases, the grounding resistance decreases, and the shunt current increases step by step. The equivalent current center is always locked at the position of the main electrode A0 / B0 and will not shift.

[0050] S2. Main Dipole Layout: At the emission points of the preset survey line, the first main emission electrode A0 and the second main emission electrode B0 are laid out. The distance between A0 and B0 is the dipole distance L, and the line connecting the two points is the dipole axis. The main emission electrodes are laid by manually excavating shallow pits and hammering the electrodes vertically to the ground. The upper end of the electrode protrudes 10-20cm above the ground surface to facilitate wiring. The hole is backfilled with resistance-reducing agent and fine soil. An appropriate amount of salt water is poured into the pit to ensure that the electrode is in full contact with the stratum. The burial depth of A0 and B0 is completely consistent.

[0051] S3, A-side auxiliary electrode array layout: Along the opposite direction of the dipole axis A0 to B0, n first auxiliary emitting electrodes A1~An are sequentially arranged. The distance between adjacent first auxiliary emitting electrodes D is ≥ 5 times the maximum burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the first auxiliary emitting electrodes increases progressively in the direction away from A0, with the increase in burial depth between adjacent first auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all first auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. An appropriate amount of salt water is poured at the grounding point of each electrode.

[0052] S4. Layout of the auxiliary electrode array on side B: Along the opposite direction of the dipole axis from B0 to A0, n second auxiliary emitting electrodes B1~Bn are sequentially laid out. The distance between adjacent second auxiliary emitting electrodes D is ≥ 5 times the maximum electrode burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the second auxiliary emitting electrodes increases progressively in the direction away from B0, with the increment of the burial depth between adjacent second auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all second auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. Salt water is poured at the grounding point of each second auxiliary emitting electrode.

[0053] The number of the first auxiliary emitter electrodes of the distributed auxiliary pole array on side A is equal to that of the second auxiliary emitter electrodes of the distributed auxiliary pole array on side B. The spacing and burial depth are symmetrically distributed along the center of the main dipole, ensuring that the center of the equivalent dipole coincides 100% with the center of the main dipole. S5. Equipotential Parallel Connection and Quality Control: Connect A0 and A1~An to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the first output terminal of the transmitter after they are combined; connect B0 and B1~Bn to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the second output terminal of the transmitter after they are combined; after completing the electrode arrangement, CSAMT transmission operation can be carried out.

Claims

1. A controllable source audio magnetotelluric sounding transmitter pole arrangement system, characterized in that, The system includes a main dipole unit, an A-side distributed auxiliary pole array, and a B-side distributed auxiliary pole array; The main dipole unit includes a first main emitting electrode A0 and a second main emitting electrode B0, and the distance between the first main emitting electrode A0 and the second main emitting electrode B0 is a preset dipole distance L. The distributed auxiliary electrode array on side A includes n first auxiliary emitter electrodes A1, A2, ..., An. The n first auxiliary emitter electrodes are arranged sequentially in the opposite direction from A0 to B0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout the entire process. The B-side distributed auxiliary electrode array includes n second auxiliary emitter electrodes B1, B2, ..., Bn. The n second auxiliary emitter electrodes are arranged sequentially in the opposite direction from B0 to A0 along the axis of the main dipole, and do not enter the dipole moment interval between A0 and B0 throughout the entire process. The first main emitter electrode A0 and all the first auxiliary emitter electrodes of the distributed auxiliary electrode array on side A are connected in parallel at the same potential through a low-resistance parallel cable and connected to the first output terminal of the transmitter. The second main emitter electrode B0 is connected in parallel with all the second auxiliary emitter electrodes of the distributed auxiliary electrode array on the B side through a low-impedance parallel cable at the same potential, and is connected to the second output terminal of the transmitter; the emitter currents of all emitter electrodes are in phase and at the same potential.

2. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 1, characterized in that, The first main emitting electrode A0 and the second main emitting electrode B0 are buried at the same depth, which is 0.3~0.4m.

3. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 2, characterized in that, In the distributed auxiliary electrode array on side A, the distance D between adjacent first auxiliary emitter electrodes is greater than or equal to 5 times the maximum electrode burial depth in the array, and the minimum distance is not less than 5m; in the distributed auxiliary electrode array on side B, the distance D between adjacent second auxiliary emitter electrodes is greater than or equal to 5 times the maximum electrode burial depth in the array, and the minimum distance is not less than 5m.

4. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 3, characterized in that, In the distributed auxiliary electrode array on side A, the burial depth of the n first auxiliary emitter electrodes increases sequentially in the direction away from the first main emitter electrode A0; in the distributed auxiliary electrode array on side B, the burial depth of the n second auxiliary emitter electrodes increases sequentially in the direction away from the second main emitter electrode B0.

5. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 4, characterized in that, In the distributed auxiliary electrode array on side A, the burial depth of the first auxiliary emitter electrode increases by 0.1~0.3m; in the distributed auxiliary electrode array on side B, the burial depth of the second auxiliary emitter electrode increases by 0.1~0.3m.

6. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 5, characterized in that, The number of the first auxiliary emitter electrodes of the distributed auxiliary pole array on side A is equal to the number of the second auxiliary emitter electrodes of the distributed auxiliary pole array on side B, and the spacing and burial depth are completely symmetrically distributed along the center of the main dipole unit.

7. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 6, characterized in that, The value of n ranges from 3 to 7, and is adjusted according to the resistivity of the formation in the exploration area and the preset emission current.

8. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 7, characterized in that, In the electrode arrangement system, both the main emitting electrode and the auxiliary emitting electrode are solid rod-shaped electrodes made of oxygen-free copper; the main emitting electrode is 0.5m long and 18~25mm in diameter; the auxiliary emitting electrode is 0.5~1.1m long and 12~18mm in diameter; the outer wall of all electrodes is wrapped with a resistivity ≤5Ω. The drag-reducing agent layer is m.

9. The controllable source audio magnetotelluric sounding transmitter pole arrangement system according to claim 8, characterized in that, The low-resistance parallel cable uses oxygen-free copper multi-core cross-linked polyethylene insulated power cable. At 20℃, the DC resistance of a single insulated core wire per kilometer is ≤0.8Ω, and the rated withstand voltage is ≥2 times the maximum output voltage of the transmitter. Each transmitting electrode is connected to an independent insulated core wire, and all insulated core wires on the same side are connected together at the transmitter output end.

10. A method for setting up the poles of a controllable source audio magnetotelluric sounding transmitter system according to any one of claims 1-9, characterized in that, The method is specifically as follows: S1. Parameter preset: The dipole distance L and target emission current are preset according to the exploration target depth and the strata conditions of the transmitter end; the number of auxiliary emission electrodes n is determined through field tests. S2. Main Dipole Layout: At the emission points of the preset survey line, the first main emission electrode A0 and the second main emission electrode B0 are laid out. The distance between A0 and B0 is the dipole moment L, and the line connecting the two points is the axis of the main dipole. The main emission electrodes are laid out by manually excavating shallow pits and hammering the electrodes vertically to the ground. The holes are backfilled with drag-reducing agent and fine soil. Salt water is poured into the pits to ensure that the electrodes are in full contact with the strata. The burial depths of A0 and B0 are completely consistent. S3, A-side auxiliary electrode array layout: Along the opposite direction of the dipole axis A0 to B0, n first auxiliary emitting electrodes A1~An are sequentially arranged. The distance between adjacent first auxiliary emitting electrodes D is ≥ 5 times the maximum electrode burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the first auxiliary emitting electrodes increases progressively in the direction away from A0, with the increase in burial depth between adjacent first auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all first auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. Salt water is poured at the grounding point of each first auxiliary emitting electrode. S4, B-side auxiliary electrode array layout: Along the opposite direction of the dipole axis B0 to A0, n second auxiliary emitting electrodes B1~Bn are sequentially arranged. The distance between adjacent second auxiliary emitting electrodes D is ≥ 5 times the maximum electrode burial depth of the array, and the minimum distance is not less than 5m. The burial depth of the second auxiliary emitting electrodes increases progressively in the direction away from B0, with the increment of the burial depth between adjacent second auxiliary emitting electrodes being 0.1~0.3m. The upper ends of all second auxiliary emitting electrodes are exposed above the ground surface. The holes are backfilled with drag-reducing agent and fine soil and compacted. Salt water is poured at the grounding point of each second auxiliary emitting electrode. The number of the first auxiliary emitter electrodes of the distributed auxiliary pole array on side A is equal to that of the second auxiliary emitter electrodes of the distributed auxiliary pole array on side B, and the spacing and burial depth are completely symmetrically distributed along the center of the main dipole. S5. Equipotential Parallel Connection and Quality Control: Connect A0 and A1~An to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the first output terminal of the transmitter after the current is connected; connect B0 and B1~Bn to the independent insulated core wires in the low-resistance parallel cable respectively, and connect them to the second output terminal of the transmitter after the current is connected; complete the electrode arrangement.

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