WO2016011627A1 - Amplitude-preserved static correction method for magnetic data - Google Patents

Abstract

An amplitude-preserved static correction method for magnetic data, comprising the following steps: 1) determining an electrical layer with stable depth and resistivity based on magnetotelluric (MT) data collected in a work zone, obtaining a corresponding frequency band on a magnetic data curve, and averaging two apparent resistivity curves of all test points on a magnetic data test curve in the frequency band to obtain an average apparent resistivity data Ρi^α; 2) obtaining an initial correction factor of the two curves of the test points; 3) performing initial correction and obtaining data Ρsi^XY and Ρsi^YX of the two corrected apparent resistivity curves; 4) reselecting a frequency band and, according to steps 1) to 3), respectively calculating arithmetic or geometric apparent resistivity averages Ρsi^{α XY}, Psi^{α YX} and Ρfsi^αXY, Ρfsi^αYX of the two curves of the test points within the reselected frequency band before and after filtering; 5) obtaining amplitude-preserved static correction factors of the two curves of the test points; and 6) calculating to obtain final apparent resistivity data Ρpsi^XY and Ρpsi^YX of the two corrected curves to complete static correction.

Description

 Method for preserving static correction of electromagnetic data

TECHNICAL FIELD The present invention relates to geophysical exploration methods, and is an electromagnetic survey data including data processing techniques of magnetotelluric (MT), audio earth magneto (AMT), and continuous profile magnetotelluric (CEMP). BACKGROUND OF THE INVENTION The static effect in electromagnetic exploration refers to the distortion of an electric field caused by the accumulation of polarized charges at a resistivity interface due to the presence of a local electrical inhomogeneity in the vicinity, thereby generating an additional electric field proportional to the external electric field. , and has nothing to do with frequency. For magnetotelluric data (MT), on a single point curve, the logarithmic domain resistivity curve translates along the vertical axis, and the phase curve is essentially unaffected. It is manifested in the apparent resistivity cross-section, that is, the resistivity value shows an upright abrupt zone, commonly known as the "hanging noodle" phenomenon, and there is no such phenomenon on the corresponding phase pseudo-section. On the apparent resistivity plan of a single frequency point, there are many "distortion points" phenomena. The intensity of static effects can be up to two or three orders of magnitude, causing large errors in inferring depth and complicating structural interpretation, so static correction is required before inversion interpretation. At present, there are many methods for static correction. In order to suppress static effects and continuously improve the application effect of MT, many experts at home and abroad have published related papers, and proposed filtering methods, theoretical calculation methods, transient electromagnetic correction methods, surface resistivity correction methods, The high frequency electromagnetic function is extended upwards and the like. Most of these methods are based on two-dimensional MT static correction. The principles of various calibration methods and the requirements for data are different, and they are subject to a certain degree of limitation in practical applications. Because the filtering method is easy to implement and the processing speed is fast, it is the most widely used in the static correction processing of MT/CEMP data. However, after the filtering method, the apparent resistivity curve shape of many measuring points will be changed, especially in the piedmont belt and the surface lithologic mutation zone. In practice, the static correction effect is not good. SUMMARY OF THE INVENTION The present invention is directed to the defect that the effect of electromagnetic data static correction is not good after using the conventional filtering method, and provides a static correction of electromagnetic data for the purpose of overcoming the defect that the apparent resistivity curve shape can be changed and achieving the amplitude retention. method. The invention is implemented by the following steps:

1) According to the magnetotelluric data collected in the work area, determine a stable electrical layer with depth and resistivity, obtain the corresponding frequency band on the electromagnetic data curve, and do two apparent resistivity curves for all the measuring points on the electromagnetic data line on the frequency band. Average, calculate flat The resistivity data is uniform; the electromagnetic data includes magnetotelluric data (MT), audio magnetotelluric data (AMT), and continuous section method magnetotelluric data (CEMP). The average includes the arithmetic mean and the geometric mean. The calculated flat resistivity data is:

Where, , are the measured apparent resistivity values of the XY and YX modes of the first frequency of the i-th measuring point, respectively, and " ^m is the selected frequency point number.

其中， 和 分别为第 个测点 XY和 YX模式数据的初步校正因子， 为由 (4)式获 得的计算平均值， 其它参数的含义与 (4)式相同。 2) Use the following formula to obtain the initial correction factor for the two curves of each measurement point;

Wherein, and the preliminary correction factor for the first measurement point XY and YX mode data respectively, is the calculated average value obtained by the equation (4), and the meanings of the other parameters are the same as the equation (4).

3) Perform a preliminary correction according to the following formula to obtain the corrected two apparent resistivity curve data ^^ and p = 10 * *(lo _g pf ^Y + kf ^Y ), = 10 * *(lo _g p + k ) _{( 6)} Filter Af and P separately, and obtain the filtered apparent resistivity curve data and other parameters with the same meanings as (4) and (5). The filtering includes two-dimensional median filtering, two-dimensional spatial filtering, three-dimensional median filtering, and three-dimensional spatial filtering.

4) Reselect a frequency segment and calculate the arithmetic or geometric mean ^xy , ^p , and the apparent resistivity of the two curves of each of the measured points before and after filtering according to steps 1) to 3). Nf l

 Σ ) ∑ ( ,)

其中， 和" /²分别为选定的频点号， ^{p f} 、 ^^( ）分别为第 个测点第 ·/个频率 的 XY和 YX模式实测视电阻率值， A^、 ^^分别为计算的滤波前 XY和 YX模式的视 电阻率算术或者几何平均值， 和 分别为计算的滤波后 XY和 YX模式的视电阻率算 术或者几何平均值。

Wherein, and " / ² are the selected frequency point numbers respectively, ^pf and ^^( ) are the measured apparent resistivity values of the XY and YX modes of the first measuring frequency of the first measuring point, respectively, A^, ^^ are Calculate the apparent resistivity arithmetic or geometric mean of the pre-filtered XY and YX modes, and the apparent resistivity arithmetic or geometric mean of the calculated filtered XY and YX modes, respectively.

 Calculate the amplitude correction factor of the two curves of each measuring point according to the following formula: fsi ^ = log ^ -log

(9) where ^K and the amplitude-preserving correction factor of the XY and YX curves of the first measuring point are respectively calculated according to the following formula to obtain the two curves of the apparent resistivity data "' and ^ after the final amplitude-correction correction, and the static correction is completed.

PZ = 10 * *dog + ), PZ = ¹⁰ * *( ^lo g + ^k ) (10)

Ppsi and Π P are the amplitude-corrected back-resistivity data of the final XY and YX curves. Compared with the background art, the present invention can overcome the drawback that the shape of the back-resistivity curve can be changed by applying the conventional filtering method, especially In the mountain front belt, the surface lithology mutation zone, etc., the effect is improved obviously, and the purpose of maintaining the amplitude is achieved. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic flow chart of an electromagnetic data amplitude correction static correction method. detailed description

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts, All fall within the scope of protection of the present invention. The invention will be described in detail below with reference to the accompanying drawings and experimental examples. Figure 1 is a flow chart showing the implementation of the amplitude-preserving static correction method. The specific method is:

其中， P fj 、 ^ ( ）分别为第 个测点第 ·个频率 的 χγ和 γχ模式实测视电阻 率值， "和 ^m为选定的频点号， 在本例子中分别为 5和 9。 2) 利用以下公式求取各个测点两支曲线的初步校正因子； 1) According to the magnetotelluric data collected in the work area, determine a stable electrical layer with depth and resistivity, and obtain the corresponding frequency band on the electromagnetic data curve. For example, if the frequency band No. 5 to No. 9 are selected, then in formula (4) =5, ^ = 9. Average the apparent resistivity curves of all the measuring points on the electromagnetic data line on the frequency band, and calculate the average apparent resistivity data; the electromagnetic data includes magnetotelluric data (MT), audio ground Electromagnetic data (AMT), continuous section method magnetotelluric data (CEMP). The average includes arithmetic mean and geometric mean. The calculated flat resistivity data is:

Where P fj and ^ ( ) are the measured values of the measured values of the χγ and γχ modes of the first frequency of the first measuring point, respectively, and “ ^m is the selected frequency point number, which is 5 and 9 respectively in this example. 2) Use the following formula to obtain the initial correction factor for the two curves of each measurement point;

Kf = log _P - log^ -, k = log _P - log

 m - n + lm - n + l (5) where , and the initial correction factor for the first measurement point XY and YX mode data, respectively, is the calculated average value obtained by equation (4), and the meanings of other parameters are (4) The same formula.

3) Perform preliminary correction according to the following formula to obtain the corrected two apparent resistivity curve data ^^ and ^^ : p = 10 * *(log pf ^Y + k ), = 10 * *(log p + k ) _{( 6)} Then, P is separately filtered, as in this example, using two-dimensional median filtering, the median filtering window is selected as (5,3), obtain the filtered apparent resistivity curve data and; the meanings of other parameters are the same as (4) and (5). The filtering includes two-dimensional median filtering, two-dimensional spatial filtering, three-dimensional median filtering, and three-dimensional spatial filtering. 4) Reselect a frequency segment, such as the frequency from the 7th to the 13th frequency, ie ^^ ¹ ?, ^nf2 =n in the formula (7) and the formula (8), and calculate according to steps 1) to 3) respectively. The arithmetic or geometric mean of the apparent resistivity of the two curves of each measurement point before and after filtering, ^xy , ^p , ^ and ^ : nfl nfl

 Nfl nfl aXY _ j:nfl aYX _ j:nfl

^P " 分别为第 个测点第 个频率 的 χγ和 γχ模式实测视电阻率值， ^ρ 、 ^分别为计算 的滤波前 χγ和 γχ模式的视电阻率算术或者几何平均值， 和 分别为计算的滤波后f ^Sl ~ nfl- nf l + l' ^Ρ ' ~ nf2-nf\ + \ ₍₈₎ where, and " / ² are the selected frequency points respectively, in this example, 7 and 13, respectively.

^P " is the measured apparent resistivity value of the χγ and γχ modes of the first frequency of the first measuring point, respectively, ^ρ and ^ are the calculated apparent resistivity arithmetic or geometric mean values of the pre-filtering χγ and γχ modes, respectively, and calculated separately. After filtering

The apparent resistivity arithmetic or geometric mean of the ΧΥ and ΥΧ modes.

其中， 和 分别为第 个测点的 XY和 YX曲线的保幅校正因子 5) Calculate the amplitude correction factor of the two curves of each measuring point according to formula (9):

Where, and the amplitude correction factor of the XY and YX curves of the first measurement point respectively

6) Calculate the apparent resistivity data " ' and ^ V of the two curves after the final amplitude correction according to formula (10), and complete the amplitude correction.

P = 10 * *dog + ), PZ =10* *(lo _{g A} + k )

 (10)

Ppsi and Π P are the amplitude-corrected back-view resistivity data of the final XY and YX curves. The specific embodiments described above further explain the objectives, technical solutions and beneficial effects of the present invention. It should be understood that The above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Claim  1. A method for amplitude-preserving static correction of electromagnetic data, which is characterized by the following steps: 1) According to the magnetotelluric data collected in the work area, determine a stable electrical layer with depth and resistivity, obtain the corresponding frequency band on the electromagnetic data curve, and do two apparent resistivity curves for all the measuring points on the electromagnetic data line on the frequency band. On average, the average apparent resistivity data is calculated; the calculated flat resistivity data is:

Where Pi " and ( ) are the measured values of the measured values of the χγ and γχ modes of the first frequency of the first measuring point, respectively, and " ^w is the selected frequency point number; 2) Use the following formula to obtain the initial correction factor for the two curves of each measurement point;

Wherein, and the preliminary correction factor for the first measurement point XY and YX mode data respectively, is the calculated average value obtained by the equation (4), and the meanings of the other parameters are the same as the equation (4). 3) Perform preliminary calibration according to the following formula to obtain corrected two apparent resistivity curve data ^^ and ^ A = 10 * *do _g pf ^Y + k ), = 10 * *(log p + k ) ₍₆₎ Filter Af and P separately to obtain the meaning of filtered apparent resistivity curve data and other parameters. (4), (5) are the same. 4) Reselect a frequency segment and calculate the arithmetic or geometric mean ^xy , ^p , and the apparent resistivity of the two curves of each measurement point before and after filtering according to steps 1) to 3). (7)  Nf2 nf2 aXY _ j nf\ ^aYX _ j nf\ ^Pfsi ~ nfl-nfl + l' ^Pfsi ~ nf2-nf\ + \ Where, and " ² are the selected frequency point numbers respectively, ^pf j, and are the measured values of the measured values of the χ γ and γ χ modes of the first frequency of the first measuring point, respectively, and the calculated pre-filtering and ΥΧ modes. The apparent resistivity arithmetic or geometric mean, and the apparent resistivity arithmetic or geometric mean of the calculated filtered XY and YX modes, respectively. 5) Calculate the amplitude correction factor of the two curves of each measuring point according to the following formula:

Where, and are the amplitude correction factors of the XY and YX curves of the first measurement point, respectively. 6) Calculate the apparent resistivity data P and complete static correction of the two curves after the final amplitude correction is obtained according to the following formula; PZ = 10«(log PZ = 10"(log _{A (10)} where ^^ and ^^' are the amplitude-corrected back-view resistivity data for the final XY and YX curves.  2. A method of amplitude-preserving static correction for electromagnetic data according to claim 1, wherein the electromagnetic data of step 1) comprises magnetotelluric data (MT), audio magnetotelluric data (AMT), and continuous profile method. Magnetotelluric Data (CEMP).  3. A method of amplitude-preserving static correction for electromagnetic data according to claim 1, wherein the average of said step 1) comprises an arithmetic mean and a geometric mean. 4. The amplitude-preserving static correction method for electromagnetic data according to claim 1, wherein the filtering according to step 3) comprises two-dimensional median filtering, two-dimensional spatial filtering, three-dimensional median filtering, and three-dimensional spatial filtering. ,

Where: is the Poisson's ratio of the soil medium.