CN-116953800-B - Improved method for surveying underground water in high-resistance surrounding rock area by transient electromagnetic

CN116953800BCN 116953800 BCN116953800 BCN 116953800BCN-116953800-B

Abstract

The invention belongs to the technical field of surveying, and provides an improved method for surveying groundwater in a high-resistance surrounding rock area by transient electromagnetic, which comprises the steps of acquiring high-resistance surrounding rock area, collecting transient electromagnetic data in the high-resistance surrounding rock area, checking whether negative response exists in a later stage, introducing a Cole-Cole model to conduct forward modeling when negative response exists, extracting three induced polarization parameters of zero frequency resistivity, charging rate, time constant and frequency correlation coefficient, adopting quasi-two-dimensional regularized Newton inversion to solve the zero frequency resistivity and the three induced polarization parameters simultaneously, and adopting joint interpretation of the zero frequency resistivity and the three induced polarization parameters to circle a subterranean water-containing stratum. The invention aims at negative response in late stages caused by the induced polarization effect of underground water in high-resistance surrounding rock areas by transient electromagnetic, can utilize the negative response to extract three parameters of zero frequency resistivity and other three induced polarization, and adopts quasi-two-dimensional regularized Newton inversion interpretation to survey underground water.

Inventors

HU QINGLONG
YAO DEWU
YU NIAN
LU JUNTAO
LI QIANGQIANG
CAO MENG
SHOU QI
TANG WEI

Assignees

四川中水成勘院工程物探检测有限公司

Dates

Publication Date: 20260512
Application Date: 20230721

Claims (5)

1. An improved method for surveying groundwater in a high-resistance surrounding rock area by transient electromagnetic, which is characterized by comprising the following steps: acquiring a high-resistance surrounding rock area, and acquiring transient electromagnetic data in the high-resistance surrounding rock area; checking whether negative response exists in the later stage, if so, introducing a Cole-Cole model to replace a resistivity model for forward modeling; Extracting zero-frequency resistivity, and simultaneously extracting three induced polarization parameters including charging rate, time constant and frequency correlation coefficient; adopting quasi-two-dimensional regularized Newton inversion to simultaneously solve zero frequency resistivity and three induced polarization parameters; The zero frequency resistivity of the water-bearing stratum is a relatively low value, the three induced polarization parameters of the charging rate, the time constant and the frequency correlation coefficient are relatively high values, and the investigation of the underground water-bearing stratum is completed through joint interpretation of the zero frequency resistivity and the three induced polarization parameters: the quasi-two-dimensional regularized Newton inversion is adopted to simultaneously solve zero frequency resistivity and three induced polarization parameters, and the method specifically comprises the following steps: The quasi-two-dimensional inversion is a method for inverting the whole two-dimensional survey line data based on a one-dimensional model, and comprises the following steps of The measuring lines of the measuring points are used for arranging the data of all the measuring points along the column direction to form a one-dimensional column inversion data set: Wherein T represents the transpose of the matrix; The model parameters of each measuring point in inversion setting comprise zero frequency resistivity and three induced polarization parameters, and when the inversion model is an N-layer model, the model parameters of the ith measuring point are as follows: In the pseudo-two-dimensional inversion algorithm, a model parameter set is formed by arranging model parameters of all measuring points along a column direction: fitting data to model constraint terms Merging regularized problem equations that constitute the inversion: in the formula, the regularization factor is given as a formula, Fitting a term for the least squares data, the expression being: Wherein F is a forward calculation process, The data is a weighted matrix of data, For model constraint terms, the expression is: In the middle of Constraining the weighting matrix for the model, wherein R is a transverse constraint operator; Solving an inverted regularization problem equation by adopting a Newton method to obtain a model update equation expression at the (k+1) th iteration as follows: In the middle of , For the jacobian matrix, resolving by adopting an analytic method; the fitting difference calculation formula is as follows: Stopping iteration when the fitting difference is less than 5% or the relative fitting difference change is less than 1% in the inversion process; in the inversion process, an improvement measure is applied to carry out inversion, wherein the improvement measure is specifically as follows: step one, converting inversion model parameters into a logarithmic domain and restraining the logarithmic domain in a certain variation range: In the middle of For the parameters of the logarithmic domain conversion model, And The upper and lower limit values of the model parameters are respectively represented as follows: because the model parameters are subjected to logarithmic domain conversion, the expression of the jacobian matrix in the inversion process is changed, and the expression is as follows: Intercepting early responses of all measuring points without negative values before multi-parameter inversion, performing conventional resistivity inversion on the intercepted responses, taking inversion results as initial zero-frequency resistivity models in quasi-two-dimensional regularized Newton four-parameter inversion, selecting uniform half-space models for all initial models of three induced polarization parameters, wherein the charging rate value range is 0.1-0.3, so that negative responses of forward responses of the initial models can not occur, and the time constant and the frequency correlation coefficient are respectively selected at a median value And ; And thirdly, fixing the time constant and the frequency correlation coefficient in the early stage of inversion iteration, only inverting the zero-frequency resistivity and the charging rate, substituting the time constant and the frequency correlation coefficient into a model in the subsequent inversion process to update and invert, so that inversion and update are concentrated on the zero-frequency resistivity and the charging rate with larger sensitivity, and meanwhile, obtaining abnormal distribution of the time constant and the frequency correlation coefficient.
2. An improved method of surveying groundwater in a high resistivity surrounding area for transient electromagnetic waves in accordance with claim 1, wherein said acquiring a high resistivity surrounding area comprises the steps of: selecting a region to be tested; analyzing the on-site hydrogeologic features, basic geologic materials and on-site electrical tests in the region to be tested, and evaluating whether the region to be tested accords with the high-resistance surrounding rock features; and selecting an area which accords with the characteristics of the high-resistance surrounding rock in the area to be detected as a high-resistance surrounding rock area.
3. The improved method for surveying groundwater in a high resistivity surrounding rock area with transient electromagnetic data according to claim 1, wherein the transient electromagnetic data is acquired by using a receiving coil along a survey line at a certain point distance.
4. An improved method of surveying groundwater in a high resistivity surrounding area with transient electromagnetic data according to claim 1, wherein after the transient electromagnetic data acquisition is completed, the data display is performed using multiple tracks, and during the data display, it is checked whether a negative response occurs in the late track.
5. The improved method for surveying groundwater in a high resistivity surrounding rock area by transient electromagnetic according to claim 1, wherein said introducing Cole-Cole model is used for forward modeling instead of resistivity model, specifically: when the induced polarization effect exists in the underground water containing the electronic conductor, the Cole-Cole complex resistivity model is adopted to quantitatively describe the induced polarization characteristic instead of the common resistivity model, and the expression is as follows: In the formula, To account for the complex resistivity when inducing polarization effects, In order to be of an angular frequency, Is the zero-frequency resistivity of the material, In order for the charge rate to be high, As a function of the time constant, Is a frequency correlation coefficient.

Description

Improved method for surveying underground water in high-resistance surrounding rock area by transient electromagnetic Technical Field The invention relates to the technical field of surveying, in particular to an improved method for surveying groundwater in a high-resistance surrounding rock area by transient electromagnetic. Background In the conventional case, transient electromagnetic finding of the distribution of groundwater is based on a survey of characteristics of lower resistivity of the aqueous rock formation relative to the surrounding rock, so that inversion interpretation is typically performed using only one parameter, resistivity, in conventional inversion imaging. In recent years, along with the gradual improvement of the signal-to-noise ratio of a geophysical survey instrument, the quality of the acquired data late passage is generally improved, and abnormal negative response of the transient electromagnetic late passage can be frequently observed when transient electromagnetic method underground water exploration is carried out in some high-resistance surrounding rock areas. It is found that this is because in high-resistance surrounding rock areas, the total response of transient electromagnetic is caused by induced polarization effect generated by groundwater containing electronic conductors, and can be understood to be composed of induced response and polarization response, in late stage, the induced polarization current direction is opposite to the induced current direction, and when the polarization current intensity in the opposite direction is larger than the induced current, that is, the polarization response in the opposite direction is larger than the induced response in the positive direction, negative response occurs in late stage, especially in high-resistance surrounding rock areas, transient electromagnetic induction response is attenuated rapidly, and the earlier the time that the polarization response in the opposite direction takes the dominant place, negative abnormality is more obvious. When data processing is carried out, the negative responses cannot be fitted by using a conventional resistivity inversion method, and the previous solutions adopt inversion after eliminating the negative responses, so that the inversion accuracy and the depth of investigation are greatly reduced. Disclosure of Invention The invention aims to provide an improved method for surveying groundwater in a high-resistance surrounding rock area by transient electromagnetic, and aims to realize negative response in a later stage caused by the induced polarization effect of groundwater in the high-resistance surrounding rock area by the transient electromagnetic. The invention solves the technical problems and adopts the following technical scheme: an improved method for surveying underground water in a high-resistance surrounding rock area by transient electromagnetic, which comprises the following steps: acquiring a high-resistance surrounding rock area, and acquiring transient electromagnetic data in the high-resistance surrounding rock area; checking whether negative response exists in the later stage, if so, introducing a Cole-Cole model to replace a resistivity model for forward modeling; Extracting zero-frequency resistivity, and simultaneously extracting three induced polarization parameters including charging rate, time constant and frequency correlation coefficient; adopting quasi-two-dimensional regularized Newton inversion to simultaneously solve zero frequency resistivity and three induced polarization parameters; the zero-frequency resistivity of the water-bearing stratum is a relatively low value, the three induced polarization parameters of the charging rate, the time constant and the frequency correlation coefficient are relatively high values, and the investigation of the underground water-bearing stratum is completed through joint interpretation of the zero-frequency resistivity and the three induced polarization parameters. As a further optimization, the obtaining of the high-resistance surrounding rock area comprises the following steps: selecting a region to be tested; analyzing the on-site hydrogeologic features, basic geologic materials and on-site electrical tests in the region to be tested, and evaluating whether the region to be tested accords with the high-resistance surrounding rock features; and selecting an area which accords with the characteristics of the high-resistance surrounding rock in the area to be detected as a high-resistance surrounding rock area. As further optimization, when transient electromagnetic data is acquired in a high-resistance surrounding rock area, a receiving coil is used for acquiring the transient electromagnetic data according to a certain point distance along a measuring line. As further optimization, after the transient electromagnetic data acquisition is completed, the data display is performed by using multiple measuring channels, an