CN104020496A

CN104020496A - Ground controlled source magnetotelluric method based on axial collinear manner

Info

Publication number: CN104020496A
Application number: CN201410304975.3A
Authority: CN
Inventors: 刘长胜; 曾新森; 胡瑞华; 周逢道; 刘立超; 史志辉; 康利利
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2014-06-27
Filing date: 2014-06-27
Publication date: 2014-09-03
Anticipated expiration: 2034-06-27
Also published as: CN104020496B

Abstract

The invention relates to a ground controllable source electromagnetic prospecting method based on an axial co-linear method. By changing the distribution mode of the receiving system, the receiving system is distributed along the axial direction of the transmitting system, and by measuring the horizontal electric field strength of each receiving point distributed in the axial direction. Ex, the calculated apparent resistivity. Compared with the existing technology, the transmission system and the receiving system are arranged in the same axial direction, which is sensitive to the information of underground high-resistance bodies, has a stronger ability to distinguish underground resistivity, and can more clearly reflect the details of the spatial distribution of geological bodies. It is sensitive to deep electrical changes and has strong resolution ability; it only needs to measure the electric field component Ex in the horizontal direction, reducing the measurement of the magnetic field component Hy in the vertical direction, making the measurement process more convenient and reducing the introduction of noise, which is conducive to improving the signal quality. noise ratio. In the process of data processing, the influence factor of air wave is calculated, and it is removed from the received signal to improve the signal-to-noise ratio and the credibility of the measurement results.

Description

A kind of ground controllable source electromagnetic exploration method of axial collinear mode

Technical field:

The present invention relates to a kind of ground controllable source electromagnetic exploration method, especially a kind of ground controllable source electromagnetic exploration method based on axial collinear mode.

Technical background:

Controllable source audiomagnetotelluric sounding method (Controlled Source Andio-frequency Magnetotelluric, be abbreviated as CSAMT) be a kind of artificial source frequency domain electromagnetic sounding method growing up on the basis of magnetotelluric method (MT), along with popularization and the development of geophysical survey, its look for ore deposit, water detection, engineering construction, many fields such as calamity control have important influence power.The method by feeding tone currents in having limit for length's earth lead or earth-free coil, to produce the electromagnetic field of corresponding frequencies, on the survey line apart from tens kilometers of emissive sources, receive mutually orthogonal electromagnetic field response component, by inversion interpretation to obtain subsurface geology information.At present, the geophysical survey application under shallow-layer, simple geologic structure has all obtained very large breakthrough, and by perfect gradually.Conventional CSAMT detection method receives and is positioned at transmitting side 4-10Km, has that depth of exploration is large, data acquisition amount is large, resolution is high, be subject to the influence of topography little, to features such as low resistivity zone sensitivities, in deep resource is reconnoitred, is widely used, and develops very swift and violent.But response is insensitive when measuring high resistant objective body, when needs show as the stratum resource detection of high resistant, conventional method can not meet detection demand.

CN102707323A discloses a kind of < < for the controllable source audio frequency magnetic field bathymetry > > of geologic prospecting: adopt the emissive source distribution mode parallel with receiving system side, measuring system is arranged as shown in Figure 2.This measuring system be take has limit for length's earthing electrical double pole as field source, in the far field of emissive source (transmitting-receiving is apart from r >=3-5 δ), locate to observe electricity, magnetic field parameter simultaneously, system is surveyed horizontal component of electric field intensity Ex and the vertical magnetic field intensity Hy of each acceptance point in district by measurement, thereby associating calculates the apparent resistivity of subsurface geologic structures, and then is finally inversed by underground medium structural information.But this metering system is only responsive to low-resistance region, insensitive to the reflection of high resistant target, and insensitive to the reaction of geologic body space distribution details.

In marine electromagnetic is measured, have the measuring method that pulls based on axial collinear direction, but in marine electromagnetic measuring process, frequency used is single, can not descend corresponsively on a large scale geological condition.

Summary of the invention:

Object of the present invention is exactly the deficiency for above-mentioned technology, and a kind of ground controllable source electromagnetic surveying method of axial collinear mode is provided.By changing receiving system distribution mode, make receiving system along emission coefficient axial distribution, by measuring the horizontal component of electric field intensity Ex of each acceptance point of axial distribution, and then obtain electromagnetic response with transmission frequency change curve.By the information in source, the electromagnetic response receiving and axial magnetic response whole district formula, calculate underground medium apparent resistivity with the relation of frequency, finally by inverting, obtain underground medium structural information.

A kind of ground controllable source electromagnetic exploration method of axial collinear mode is in the following manner:

A, according to measuring task setting transmitting-receiving distance, concrete transmitting-receiving is apart from according to surveying district's landform and geologic condition by skin depth formula r>=2 δ _maxcalculate, arrange emission coefficient position, δ _maxfor maximum skin depth;

B, along the axial collinear orientation determination survey line of emissive source and arrange emission coefficient and receiving system, the information that simultaneously records emission coefficient comprises: geographical position coordinates, transmitter current size, transmitting-receiving pole span;

Above-mentioned survey line, arranges and can survey sector angle along the axial collinear direction of emissive source and should not surpass 60 degree;

C, according to search coverage and investigation depth, determine look-in frequency, definite frequency range is listed as into a frequency meter, field source is set and by frequency meter, launches successively the electromagnetic wave of different frequency, until each the frequency battery has fired in frequency meter;

Said frequencies table, frequency range be 0.1Hz to 10kHz, concrete frequency values determined by required investigation depth and longitudinal frame, skin depth corresponding to transmission frequency fn is arbitrarily wherein ρ is ground resistivity.

D, receiving system are synchronizeed with transmitting, receive and record x direction electric field strength E x, and the data of record are stored by time series;

E, the following air wave of basis affect the factor of influence that formula calculates air wave:

E_{0, x}^{air} = Pi {ωμ}_{0} {&Integral;}_{0}^{\infty} D_{0} e^{- u_{0} z} J_{0} (λρ) dλ + \frac{{Pμ}_{0}}{k_{0}^{2}} {&Integral;}_{0}^{\infty} (D_{0} - u_{0} F_{0}) e^{- u_{0} z} \frac{{&PartialD;}^{2}}{{&PartialD; x}^{2}} J_{0} (λρ) dλ - - - (1)

Wherein: μ ₀for space permeability, ω is that angular frequency value is 2 π f, and f is artificial source frequency, i is emissive source electric current, and dl is Electric Dipole length, σ ₀for space conductivity, D ₀, F ₀for its value of coefficient asks method as follows:

D_{0} = \frac{λ (U_{- 1} - U_{0}) [(R_{x 1} - \frac{U_{1}}{U_{0}}) e^{- U_{0} h} + (R_{x 1} + \frac{U_{1}}{U_{0}}) e^{U_{0} h}]}{(U_{- 1} - U_{0}) (U_{1} - U_{0} R_{x 1}) - (U_{- 1} + U_{0}) (U_{1} + U_{0} R_{x 1}) e^{2 U_{0} H_{0}}} - - - (2)

F_{0} = \frac{\begin{matrix} \frac{1}{λ} (σ_{0} U_{- 1} - σ_{- 1} U_{0}) (- 2 {U_{0}}^{2} σ_{1} R_{v 1} R_{x 1} + 2 {U_{1}}^{2} σ_{0}) [(U_{0} - U_{- 1}) e^{- U_{0} h} + (U_{0} - U_{- 1}) e^{U_{0} (g - 2 H_{0})}] + \\ 2 λ (U_{1} σ_{0} + σ_{1} U_{0} R_{v 1}) (σ_{- 1} - σ_{0}) [(U_{1} - U_{0} R_{x 1}) e^{- U_{0} h} - (U_{1} + U_{0} R_{x 1}) e^{U_{0} h}] \end{matrix}}{\begin{matrix} [(U_{0} R_{x 1} + U_{1}) (U_{- 1} + U_{0}) e^{U_{0} H_{0}} + (U_{0} R_{x 1} - U_{1}) (U_{- 1} - U_{0}) e^{- U_{0} H_{0}}] \cdot \\ [(U_{1} σ_{0} + σ_{1} U_{0} R_{v 1}) (σ_{0} U_{- 1} + U_{0}) e^{U_{0} H_{0}} - (U_{- 1} σ_{0} - σ_{- 1} U_{0}) (σ_{0} U_{1} - σ_{1} U_{0} R_{x 1}) e^{- U_{0} H_{0}}] \end{matrix}} - - - (3)

R_{x 1} = \coth [u_{1} D_{1} + \coth^{- 1} \frac{u_{1}}{u_{2}} R_{x 2}] - - - (4)

\begin{matrix} R_{xn} = \coth [u_{n} D_{n} + \coth^{- 1} \frac{u_{1}}{u_{n + 1}} R_{x, n + 1}] (2 \leq n \leq N - 1) & R_{xN} = 1 \end{matrix} - - - (5)

R_{v 1} = \coth [u_{1} D_{1} + \coth^{- 1} \frac{u_{1} σ_{2}}{u_{2} σ_{2}} R_{v 2}] - - - (6)

\begin{matrix} R_{vn} = \coth [u_{n} D_{n} + \coth^{- 1} \frac{u_{1} σ_{n + 1}}{u_{n + 1} σ_{n}} R_{v, n + 1}] (2 \leq n \leq N - 1) & R_{vN} = 1 \end{matrix} - - - (7)

F, according to formula (1), calculate air wave factor of influence, it is deducted from data measured to the measurement data that obtains removing air wave impact, then utilize field source information and remove air wave the measurement data combined axis affecting to whole district's electromagnetic response formula, to calculate the apparent resistivity of each frequency that each measuring point is corresponding.

G, the same transmission frequency of the apparent resistivity obtaining in step f, acceptance point positional information input Mtsoft2D Inversion Software is obtained to subsurface resistivity distribution figure.

Beneficial effect: compared with prior art, (1) the present invention is by adopting the axial collinear arrangement of emission coefficient and receiving system, measure in this way details sensitive to underground high resistant body message reflection, more by force can clearer reflection geologic body space distribution to subsurface resistivity resolution characteristic, and Deep Electrical is changed to reflection is sensitive, resolution characteristic is strong.(2) while adopting this measurement arrangement to measure, we only need to measure the electric field component Ex of horizontal direction, reduced the measurement to vertical direction magnetic-field component Hy, made the introducing that the easier while of measuring process has also reduced noise be conducive to improve signal to noise ratio (S/N ratio).(3) the present invention falls into a trap and has calculated the factor of influence of air wave in the process of data processing, and it is rejected from receive signal, improves the confidence level of signal to noise ratio (S/N ratio) and measurement result.

Accompanying drawing explanation:

Fig. 1 is the ground controllable source electromagnetic survey field work figure of axial collinear mode

Fig. 2 is the ground controllable source electromagnetic survey field work figure of traditional approach

Fig. 3 is axial collinear mode field detection Geological deduction and drilling well material comparison diagram

Fig. 3 (a) is to be field survey inversion chart; Fig. 3 (b) is boring material figure

Fig. 4 is axial collinear mode field detection arrangenent diagram

Fig. 5 is axial collinear mode and the abnormal amplitude Contrast on effect of traditional approach curve map

Fig. 6 is transmission frequency table.

1 transmitter, 2 receivers, AB emitting electrode, MN receiving electrode.

Embodiment:

Below in conjunction with drawings and Examples, the present invention is described in further detail:

Fig. 1 is axial collinear mode field survey arrangenent diagram, comprises emission coefficient and receiving system, surveys district and arranges in the following manner:

Plane right-angle coordinate as shown in fig. 1, artificial emissive source is all laid in the x-direction with survey line, survey zone position range transmission source x direction r>=2 δ _maxin addition, y direction be take emissive source center as the upper and lower radiation scope of starting point is in 30 °.

It is the equidistantly discontented whole survey of starting point district that survey line be take No. 0 line, and interval of survey line, according to detection accuracy and demand setting, is generally a certain particular value of 50-500m.

On every survey line, measuring point be take No. 0 point and is equidistantly arranged as starting point from x direction near-end to far-end, and measuring point spacing is generally a certain particular value between 50-200m by detection accuracy and demand setting.

Take the controllable source electromagnetic survey of Fuyu County, Jilin Province as example detailed description:

A, according to measuring mission area, guaranteeing that the nearest acceptance point of emission coefficient positional distance is apart from r>=2 δ _maxarrange emission coefficient position, specifically apart from You Ce district landform and geologic condition, determine;

As shown in Figure 4, in figure, the nearest point position of emissive source centre distance is 820m in field test emission coefficient position, and field test design investigation depth is that 400m (is δ _max=400m).

Field test survey line position as shown in Figure 4 Line1, Line2 is two axial arranged surveys line, interval of survey line is 400m, on survey line, respectively there are 13 measuring points, measuring point spacing is 50m, measuring point position is receiving electrode position, receiving electrode is connected on receiver by cable, and receiver is called receiving system together with receiving electrode.In Fig. 4, A, B position are emitting electrode position, and transmitter is positioned at AB line mid point.Transmitter is called emission coefficient together with emitting electrode.There is the automatic record of GPS module in geographic position, and transmitter current is 20A, and transmitting-receiving is apart from 820+50*n, and n be the measuring point number away from emission coefficient, in measuring process transmitting-receiving distance by receiving system from line item;

The scope of emitting electromagnetic wave frequency is from 0.1Hz to 10000Hz, and the skin depth that optional frequency fn is corresponding is wherein ρ is ground resistivity, and concrete frequency values is determined by required investigation depth and longitudinal frame.

Ground observation transmission frequency is as follows from high to low: 9600Hz, 7680Hz, 6400Hz, 5120Hz, 3840Hz, 3200Hz, 2560Hz, 1920Hz, 1600Hz, 1280Hz, 1024Hz, 853.3333Hz, 640Hz, 512Hz, 426.666667Hz, 341.333333Hz, 256Hz, 213.333333Hz, 170.666666Hz, 128Hz, 106.666667Hz, 85.3333332Hz, 64Hz, 53.3333333Hz, 42.6666666Hz, 32Hz, 26.6666667Hz, 21.3333333Hz, 16Hz, 13.3333333Hz, 10.6666667Hz, 8Hz, 6.66666667Hz, 5.33333333Hz, 4Hz, 3.33333333Hz, 2.66666666Hz, 2Hz, 1.66666667Hz, 1.33333333Hz, 1Hz

E_{0, x}^{air} = Pi {ωμ}_{0} {&Integral;}_{0}^{\infty} D_{0} e^{- u_{0} z} J_{0} (λρ) dλ + \frac{{Pμ}_{0}}{k_{0}^{2}} {&Integral;}_{0}^{\infty} (D_{0} - u_{0} F_{0}) e^{- u_{0} z} \frac{{&PartialD;}^{2}}{{&PartialD; x}^{2}} J_{0} (λρ) dλ

Fig. 3 is field survey Geological deduction borehole data comparison diagram corresponding to survey line, and Fig. 3 (a) is inversion chart, and y direction is the degree of depth, and x direction is horizontal level, and different colours represents the resistivity of different sizes.Fig. 3 (b) is boring material figure, and this boring is ZK1 in Fig. 4, and y direction is the degree of depth, and x direction is that resistivity is big or small.From figure a, can find out that underground degree of depth 0-20m shows as high resistant and coincide intact with figure b, in the degree of depth, to be 250m-350m interval can find out from figure b can clearly reflect the variation of resistivity resistivity range of variation is less than 50 figure a, when geologic body resistivity changes among a small circle, this metering system also can clearly react it.

Fig. 5, for just drilling simulation calculation figure, is respectively high resistant objective body model and low-resistance objective body model to be carried out to the relative abnormal amplitude Contrast on effect curve that traditional approach is measured with axial collinear mode shown in figure.In figure, curve can be found out, when being resistive formation, objective body adopt the relatively abnormal amplitude of axial collinear metering system gained to be obviously greater than traditional approach, objective body is that low resistivity zone is there is no obvious beneficial effect, can reach a conclusion: adopt axial collinear metering system sensitiveer to the measurement reaction of high resistant objective body, measurement effect is better.

Claims

1. A ground controllable source electromagnetic prospecting method of an axial co-linear mode, characterized in that receiving electrode MN and transmitting electrode AB are laid on the same axis, comprising the following steps:

a. Determine the survey line according to the requirements of the exploration task, and arrange the artificial source transmitting system and receiving system on the survey line in an axial and co-linear manner;

The artificial source transmitting system includes a transmitter and a transmitting electrode AB, and the receiving system includes a receiver and a receiving electrode MN;

b. Arrange the transmitting electrodes AB on the measuring line according to the transmitting and receiving distance of r≥2δ _max , the distance between the transmitting electrodes is 1-3Km, and the distance between the electrodes of the receiving electrodes MN is 25-200 meters, check the coupling and connection; δ _max is the maximum skin depth ;

Turn on the transmitter and receiver at the same time, record the geographic coordinates of the artificial source, the position coordinates of the receiving system, the transmitting current, and the transmitting and receiving distance;

c. Determine the detection frequency according to the detection area and detection depth, list the determined frequency range into a frequency table, and launch electromagnetic waves of different frequencies in sequence according to the frequency table until each frequency point in the frequency table is launched;

The frequency range of the frequency table is 0.1Hz to 10kHz, and the specific frequency value is determined by the detection depth and longitudinal resolution through the skin depth formula Calculated;

Where fn is the transmission frequency, ρ is the earth resistivity;

d. The receiving system receives and records the electric field strength Ex in the x direction synchronously with the transmission, and stores the recorded data in time series;

e. Calculate the air wave influence factor according to the following air wave influence formula:

{E E.}_{00,, x x}^{air the air} = = Pi Pi {ωμ ωμ}_{00} {&Integral; &Integral;}_{00}^{\infty \infty} {D D.}_{00} {e e}^{- - {u u}_{00} z z} {J J}_{00} ((λρ λρ)) dλ dλ + + \frac{{Pμ Pμ}_{00}}{{k k}_{00}^{22}} {&Integral; &Integral;}_{00}^{\infty \infty} (({D D.}_{00} - - {u u}_{00} {F f}_{00})) {e e}^{- - {u u}_{00} z z} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; x x}^{22}} {J J}_{00} ((λρ λρ)) dλ dλ - - - - - - ((11))

Among them: μ ₀ is the space magnetic permeability, ω is the angular frequency value 2πf, f is the artificial source frequency, I is the emission source current, dl is the length of the galvanic source, σ ₀ is the space conductivity, D ₀ and F ₀ are the coefficients, and their values are calculated as follows:

{D D.}_{00} = = \frac{λ λ (({U u}_{- - 11} - - {U u}_{00})) [[(({R R}_{x x 11} - - \frac{{U u}_{11}}{{U u}_{00}})) {e e}^{- - {U u}_{00} h h} + + (({R R}_{x x 11} + + \frac{{U u}_{11}}{{U u}_{00}})) {e e}^{{U u}_{00} h h}]]}{(({U u}_{- - 11} - - {U u}_{00})) (({U u}_{11} - - {U u}_{00} {R R}_{x x 11})) - - (({U u}_{- - 11} + + {U u}_{00})) (({U u}_{11} + + {U u}_{00} {R R}_{x x 11})) {e e}^{22 {U u}_{00} {H h}_{00}}} - - - - - - ((22))

{F f}_{00} = = \frac{\begin{matrix} \frac{11}{λ λ} (({σ σ}_{00} {U u}_{- - 11} - - {σ σ}_{- - 11} {U u}_{00})) ((- - 22 {U u}_{00}^{22} {σ σ}_{11} {R R}_{v v 11} {R R}_{x x 11} + + 22 {U u}_{11}^{22} {σ σ}_{00})) [[(({U u}_{00} - - {U u}_{- - 11})) {e e}^{- - {U u}_{00} h h} + + (({U u}_{00} - - {U u}_{- - 11})) {e e}^{{U u}_{00} ((g g - - 22 {H h}_{00}))}]] + + \\ 22 λ λ (({U u}_{11} {σ σ}_{00} + + {σ σ}_{11} {U u}_{00} {R R}_{v v 11})) (({σ σ}_{- - 11} - - {σ σ}_{00})) [[(({U u}_{11} - - {U u}_{00} {R R}_{x x 11})) {e e}^{- - {U u}_{00} h h} - - (({U u}_{11} + + {U u}_{00} {R R}_{x x 11})) {e e}^{{U u}_{00} h h}]] \end{matrix}}{\begin{matrix} [[(({U u}_{00} {R R}_{x x 11} + + {U u}_{11})) (({U u}_{- - 11} + + {U u}_{00})) {e e}^{{U u}_{00} {H h}_{00}} + + (({U u}_{00} {R R}_{x x 11} - - {U u}_{11})) (({U u}_{- - 11} - - {U u}_{00})) {e e}^{- - {U u}_{00} {H h}_{00}}]] \cdot \cdot \\ [[(({U u}_{11} {σ σ}_{00} + + {σ σ}_{11} {U u}_{00} {R R}_{v v 11})) (({σ σ}_{00} {U u}_{- - 11} + + {U u}_{00})) {e e}^{{U u}_{00} {H h}_{00}} - - (({U u}_{- - 11} {σ σ}_{00} - - {σ σ}_{- - 11} {U u}_{00})) (({σ σ}_{00} {U u}_{11} - - {σ σ}_{11} {U u}_{00} {R R}_{x x 11})) {e e}^{- - {U u}_{00} {H h}_{00}}]] \end{matrix}} - - - - - - ((33))

{R R}_{x x 11} = = coth coth [[{u u}_{11} {D D.}_{11} + + {coth coth}^{- - 11} \frac{{u u}_{11}}{{u u}_{22}} {R R}_{x x 22}]] - - - - - - ((44))

\begin{matrix} {R R}_{xn xn} = = coth coth [[{u u}_{n no} {D D.}_{n no} + + {coth coth}^{- - 11} \frac{{u u}_{11}}{{u u}_{n no + + 11}} {R R}_{x x,, n no + + 11}]] ((22 \leq \leq n no \leq \leq N N - - 11)) & {R R}_{xN xN} = = 11 \end{matrix} - - - - - - ((55))

{R R}_{v v 11} = = coth coth [[{u u}_{11} {D D.}_{11} + + {coth coth}^{- - 11} \frac{{u u}_{11} {σ σ}_{22}}{{u u}_{22} {σ σ}_{22}} {R R}_{v v 22}]] - - - - - - ((66))

\begin{matrix} {R R}_{vn vn} = = coth coth [[{u u}_{n no} {D D.}_{n no} + + {coth coth}^{- - 11} \frac{{u u}_{11} {σ σ}_{n no + + 11}}{{u u}_{n no + + 11} {σ σ}_{n no}} {R R}_{v v,, n no + + 11}]] ((22 \leq \leq n no \leq \leq N N - - 11)) & {R R}_{vN vN} = = 11 \end{matrix} - - - - - - ((77))

f. Calculate the air wave influence factor according to the formula (1), subtract it from the measured data to get the measured data without the influence of the air wave, and then use the field source information and the measured data without the influence of the air wave to combine the axial whole area The electromagnetic response formula calculates the apparent resistivity of each frequency point corresponding to each measuring point; c

g. Input the apparent resistivity obtained in step f into the Mtsoft2D inversion software together with the transmitting frequency and receiving point location information to obtain the underground resistivity distribution map.

2. According to the ground controllable source electromagnetic prospecting method of the axial co-linear mode according to claim 1, it is characterized in that, the artificial source emission system and the receiving system are laid out in the axial co-linear mode described in step a, and can measure The sector angle does not exceed 60 degrees.