A method for extracting time-lapse resistivity anomalies

Abstract

The present invention discloses a method for extracting time-lapse resistivity anomalies. Through the analysis of the measured resistivity data in the front and back time periods, by quickly calculating the difference between the theoretical resistivity data in a certain time period and the measured resistivity data in the corresponding time period for comparative analysis, the resistivity mutation amount can be quickly obtained. Since the resistivity data simultaneously carries spatial position information, the corresponding mutation position can be obtained while obtaining the resistivity mutation amount, providing a reference basis for time-lapse resistivity early warning work. This calculation method is simple and fast, the results are accurate and reliable, easy to identify, and easy to promote.

Description

Technical Field

[0001] The present invention belongs to the field of geophysical exploration, and specifically relates to a method for extracting time-lapse resistivity anomalies. Specifically, it uses a special method to quickly calculate the theoretical resistivity value for a certain time period, and then compares and analyzes the theoretical value with the actual observed value, so as to quickly and accurately obtain the resistivity mutation position and mutation amount. Background Art

[0002] The time-lapse resistivity method is currently widely used in the monitoring of dam leakage. Many domestic units have carried out a large number of research works on time-lapse electrical method monitoring technology for dams. Zhang Qingming et al. from the Yellow River Institute of Hydraulic Research of the Yellow River Water Conservancy Commission have carried out work on detecting the contact leakage of dam culverts based on time-lapse 3D high-density electrical method. Li Wenzhong, Sun Weimin et al. from the Yangtze River Engineering Corporation for Survey, Design and Research have carried out research on time-lapse detection of levees. Xu Tao et al. have also carried out time-lapse electrical method detection of expansive soil in levees. At present, most of the time-lapse resistivity data processing methods use the method of multiple inversions to calculate the resistivity model results of multiple time segments, and then extract the resistivity change rate of the model. There are also proposals to discretize the data set and model parameters in the spatio-temporal domain, and use the time parameter as one of the variables to perform full four-dimensional inversion; or to simultaneously invert and iterate the data sets and model parameters at multiple different time points. At present, most of these time-lapse electrical method data inversion processing methods are in the research stage, and the calculation efficiency is relatively low, and they have not been able to be popularized and applied in the processing of time-lapse electrical method monitoring data for dams.

[0003] The forward and inverse modeling of time-lapse resistivity data is also based on the conventional 2D / 3D resistivity forward and inverse algorithms. The core is to compare and analyze the difference changes in the observed data at different times, and forward model the difference in the electrical parameters of the corresponding underground electrical structure model, and display the real changes in the underground medium over time through the calculated model. Since the forward and inverse modeling of time-lapse resistivity takes a long time and consumes a lot of computing power, and the electrical anomalies inside the dam cannot be analyzed in time, it cannot support the flood season command work in time. Therefore, a fast calculation method for extracting time-lapse resistivity anomalies is proposed. Summary of the Invention

[0004] In order to solve the problem of quickly locating the prominent changes in resistivity during the flood season for monitoring the leakage of river embankments, the present invention provides a method for extracting time-lapse resistivity anomalies. This method mainly calculates the theoretical resistivity value based on the relative stability coefficient of the resistivity change rate between adjacent time segments, and timely displays the resistivity anomalies of a certain time segment through the calculated change amount, and at the same time provides a background model for future fast time-series forward and inverse modeling. The principle of this method is simple and reliable, the calculation results are easy to identify, and it is easy to promote.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for extracting time-lapse resistivity anomalies, which is used to quickly extract the resistivity mutation amount and mutation position in resistivity monitoring work. The method is characterized in that the method includes the following steps:

[0007] Step 1): Obtain the observed resistivity data of multiple time periods;

[0008] Step 2): Calculate the theoretical resistivity values of different time periods according to the observed resistivity data;

[0009] Step 3): Calculate the resistivity change amount according to the theoretical resistivity value and the observed resistivity data, define the resistivity mutation amount according to the threshold designed by experience, and at the same time locate the spatial position of the resistivity mutation.

[0010] Further, in step 2), calculate the theoretical resistivity value according to formulas (1)-(3); wherein, the formulas (1)-(3) are expressed as follows:

[0011]

[0012]

[0013]

[0014] Wherein, is the observed resistivity data of the T time period, k is a constant coefficient, is the theoretical resistivity value of the T time period, x, y, z are spatial position parameters corresponding to the resistivity, and T-1, T or T+1 are time period information.

[0015] Further, in step 3), calculate the resistivity change amount according to formula (4); wherein, the formula (4) is expressed as follows:

[0016]

[0017] Wherein, is the anomaly resistivity deviation degree of the T time period.

[0018] The present invention can achieve the following beneficial effects:

[0019] By analyzing the measured resistivity data of the front and back time periods, and comparing and analyzing the difference between the theoretical resistivity data of a certain time period and the measured resistivity data of the corresponding time period calculated quickly, the present invention can quickly obtain the resistivity mutation value. Since the resistivity data synchronously carries spatial position information, the corresponding mutation position can be obtained while obtaining the resistivity mutation value, providing a reference basis for time-lapse resistivity early warning work. The calculation method is simple and fast, the results are accurate and reliable, easy to identify, and easy to promote. Description of the Drawings

[0020] Figure 1 It is the layout diagram of the time-lapse resistivity observation system for the dam.

[0021] Figure 2 It is the distribution diagram of the calculated resistivity mutation value and position. Among them, the area where the calculated change amount is more than 5% is selected as the resistivity mutation area. Specific implementation manner

[0022] The following further explains the specific implementation manner of the present invention with reference to the accompanying drawings. Note that the following description is not a limitation of the present invention, but an elaboration of the spirit of the present invention and an explanation of the principle.

[0023] The present invention relates to a method for extracting time-lapse resistivity anomalies, which is used to quickly extract the resistivity mutation amount and mutation position in time-lapse resistivity monitoring work, and includes the following steps:

[0024] Step 1): Obtain the observed resistivity data of multiple time periods; the resistivity information of multiple different time periods is shown in Table 1;

[0025] Table 1

[0026]

[0027] Step 2): Calculate the theoretical resistivity values of different later time periods according to the observed resistivity data; the calculated theoretical resistivity values of different later time periods are shown in Table 2;

[0028] Table 2

[0029]

[0030] Step 3): Calculate the resistivity change amount according to the theoretical resistivity value and the actual resistance value to quickly obtain the magnitude of the change amount and the corresponding resistivity mutation spatial position.

[0031] Further, in step 2), the theoretical resistivity value is calculated according to formulas (1)-(3); among them, the formulas (1)-(3) are expressed as follows:

[0032]

[0033]

[0034]

[0035] Among them, is the observed resistivity data of the T time period, k is a constant coefficient, is the theoretical resistivity value of the T time period, x, y, z are the corresponding resistivity spatial position parameters, and T-1, T, T+1 are the time period information.

[0036] Further, in step 3), calculate the resistivity change amount according to formula (4), as shown in Table 3; wherein, the formula (4) is expressed as follows:

[0037]

[0038] wherein, is the deviation degree of the abnormal resistivity in the T time period.

[0039] Table 3

[0040]

[0041] Further, in step 3), it also includes marking out the values with larger resistivity change amounts and their spatial positions, as shown in Table 4, which is convenient for on-site personnel to locate and check.

[0042] Table 4

[0043]

[0044] Example 1:

[0045] When carrying out the time-lapse resistivity observation work on the dam of a certain reservoir, attach Figure 1 is the layout schematic diagram of the observation system. As Figure 1 shown, arrange an electrical monitoring line on the back slope of a certain dam section, which can monitor the resistivity change situation under the back slope in real time, so as to judge the seepage law of the dam through the resistivity change situation and carry out the time-lapse resistivity monitoring work;

[0046] In this embodiment, the time-lapse resistivity anomaly extraction method includes the following steps:

[0047] (1) Obtain the resistivity information measured on site at different time periods. The resistivity information at different time periods is shown in Table 5;

[0048] Table 5

[0049]

[0050] (2) Calculate the resistivity data for the corresponding time periods according to the resistivity information at different time periods. The specific data are shown in Table 6 below;

[0051] Table 6

[0052]

[0053] (3) Calculate and compare the difference between the resistivity in the theoretical calculation time period and the measured resistivity using Formula 4, and mark the values with relatively large resistivity changes and their spatial positions. The specific data are shown in Table 7 below. Here, a resistivity change of 5% is used as the resistivity mutation threshold, and the resistivity values with resistivity changes exceeding 5% are regarded as values with relatively large changes;

[0054] Table 7

[0055]

[0056] As Figure 2 shown, the left graph is the monitored time-lapse resistivity data, and the right graph is the extracted resistivity change data. According to on-site experience, a change of 5% is designed as the threshold. Then, a resistivity change above 5% is a resistivity mutation amount, and a resistivity change below 5% is a normal resistivity value. By comparison, it is found that the resistivity change range is within 5%, indicating that the resistivity inside the dam in this area is stable, the dam body is stable, there are no abnormal changes, and there are no leakage hazards.

[0057] The parts not elaborated in detail in the present invention belong to the well-known technologies in the art. The above-described embodiments are only descriptions of the preferred embodiments of the present invention. The preferred embodiments do not elaborate all the details, nor do they limit the invention to the specific embodiments described. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for extracting time-lapse resistivity anomalies, which is used to quickly extract the resistivity mutation amount and mutation position in resistivity monitoring work, Characterized in that, The method comprises the following steps: Step 1): Obtain the observed resistivity data of multiple time periods; Step 2): Calculate the theoretical resistivity values of different time periods according to the observed resistivity data; Step 3): Calculate the resistivity change amount according to the theoretical resistivity value and the observed resistivity data, delimit the resistivity mutation amount according to the threshold designed by experience, and at the same time locate the spatial position of the resistivity mutation; In step 2), calculate the theoretical resistivity value according to formulas (1)-(3); wherein, the formulas (1)-(3) are expressed as follows: （1） （2） （3） Among them, is the observed resistivity data in the T time period, k is a constant coefficient, is the theoretical resistivity value in the T time period, x, y, and z are spatial position parameters corresponding to the resistivity, and T - 1, T, or T + 1 are time period information.

2. A method for extracting time-lapse resistivity anomalies according to claim 1, Characterized in that, In step 3), calculate the resistivity change amount according to formula (4); wherein, the formula (4) is expressed as follows: （4） Among them, is the abnormal resistivity deviation degree in the T time period.

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