Method for determining basement undulation characteristics

Abstract

This application provides a method for determining the basement undulation characteristics, relating to the field of geological exploration technology. The method includes: acquiring time series of electrical characteristic values ​​corresponding to multiple measuring points at various locations within a geographic area to be measured using sensors deployed at these points; processing the time series of electrical characteristic values ​​at these points to obtain a geoelectric profile of the geographic area to be measured; reading resistivity data from multiple pre-selected locations within the strata of the geographic area to be measured from the geoelectric profile, using these as multiple data to be processed; and clustering these multiple data using a pre-defined clustering algorithm to obtain a stratigraphic classification result characterizing the basement undulation characteristics of the geographic area to be measured. This method can accurately determine the basement undulation characteristics of sedimentary basins, providing valuable reference for delineating favorable mineralization areas of sandstone-type uranium deposits.

Description

Technical Field

[0001] This application relates to the field of geological exploration technology, specifically to a method for determining the characteristics of basement undulations. Background Technology

[0002] In sandstone-type uranium exploration, the exposed basement provides the uranium source for mineralization, while the undulating morphology of the deep basement influences the sedimentary formation of the overlying strata and the direction of groundwater flow, thus affecting the accumulation and occurrence location of uranium. Therefore, accurately detecting the basement undulation characteristics of sedimentary basins can provide important evidence for delineating favorable mineralization areas in sandstone-type uranium deposits.

[0003] Currently, in existing exploration methods for sandstone-type uranium deposits, the determination of stratigraphic structure characteristics is mostly based on rough estimation methods, which fail to accurately determine the basement undulation characteristics of sedimentary basins. Furthermore, due to limitations in exploration conditions, it is difficult to simultaneously explore geological information from both deeper and shallower geological areas. Summary of the Invention

[0004] In view of the above problems, embodiments of this application provide a method for determining the basement undulation features, so as to at least partially solve the above technical problems.

[0005] The method for determining the base undulation features according to embodiments of this application includes:

[0006] By using sensors deployed at multiple measurement points in the geographical area to be measured, time series of electrical characteristic values ​​corresponding to the multiple measurement points are collected.

[0007] The time series of electrical characteristic values ​​corresponding to multiple measuring points are processed to obtain the geoelectric profile of the geographic area to be measured. The geoelectric profile is used to characterize the resistivity distribution with depth at different profile locations in the strata of the geographic area to be measured.

[0008] Resistivity data from multiple pre-selected locations in the strata of the geographic area to be tested are read from the geoelectric cross-section map and used as multiple data to be processed.

[0009] Multiple datasets are clustered using a pre-defined clustering algorithm to obtain stratigraphic classification results that characterize the basal undulation features of the geographic region under test.

[0010] According to the embodiments of this application, in the above-mentioned method for determining the basement undulation characteristics, by using a preset clustering algorithm to perform clustering on the resistivity of multiple points in the strata of the geographic area to be measured, the stratigraphic classification results of the geographic area to be measured based on resistivity characteristics can be obtained, which are used to characterize the basement undulation characteristics of the geographic area to be measured. Compared with the method in the prior art that determines the stratigraphic structure characteristics by rough estimation, the method of this application embodiment is based on measured data for data analysis, and the results obtained are more objective and can more accurately determine the basement undulation characteristics of sedimentary basins, providing valuable reference for delineating the favorable mineralization areas of sandstone-type uranium deposits. Attached Figure Description

[0011] Figure 1 This is a flowchart of a method for determining the basement undulation features according to an embodiment of this application. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only one embodiment of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0013] It should be noted that, unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by a person with ordinary skill in the art to which this application pertains. Where the terms "first," "second," etc., are used throughout the text, they are used only to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the number of technical features indicated. It should be understood that the data in the descriptions of "first," "second," etc., can be interchanged where appropriate. Where "and / or" appears throughout the text, it means that it includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution that simultaneously satisfies A and B.

[0014] Currently, in exploration methods for sandstone-type uranium deposits, the determination of stratigraphic structure characteristics is mostly based on rough estimations, failing to accurately determine the basement undulations of sedimentary basins. Furthermore, limitations in exploration conditions make it difficult to simultaneously probe geological information from both deeper and shallower geological areas. For example, commonly used exploration methods for sandstone-type uranium deposits include audio-frequency magnetotelluric (AMT), controlled-source audio-frequency magnetotelluric (CSAMT), and magnetotelluric (MT). Among these, AMT and CSAMT utilize frequencies in the n×10n range. -1 ~n×10 3Between Hz, with a detection depth of less than 1000m, it is mainly used for detecting relatively shallow geological bodies. MT uses a frequency range of n×10 -4 ~n×10 2 While the detection depth is relatively deep (Hz), there is a certain detection blind zone in the shallow part. Therefore, it is necessary to design a detection method based on a wider frequency range and process the detection results to accurately determine the basement undulation characteristics of sedimentary basins, providing a basis for delineating favorable mineralization areas of sandstone-type uranium deposits.

[0015] Figure 1 Here is a flowchart of a method for determining basement undulation features according to an embodiment of this application, as shown below. Figure 1 As shown, the method for determining the base undulation features according to an embodiment of this application includes operations S201 to S204.

[0016] In operation S201, time series of electrical characteristic values ​​corresponding to multiple measuring points are collected by sensors deployed at multiple measuring points in the geographic area to be measured. The geographic area to be measured can be a specific geographical location of a sedimentary basin type to be explored. The method of this embodiment aims to probe the geographic area to be measured in order to determine the basement undulation characteristics of its sedimentary basin.

[0017] This application employs magnetotelluric sounding, specifically using electromagnetic waves with a wide frequency range to probe the geographic area under test, facilitating the simultaneous detection of geological information from both deeper and shallower geological regions. Before the probe is conducted, sensors are first deployed at multiple predetermined measuring points. For example, electric and magnetic sensors can be deployed at multiple measuring points using a cross-pole arrangement to collect time series of electromagnetic characteristic values, expressed as voltage (mV) and magnetic field strength (nT), at the corresponding measuring points.

[0018] In operation S202, the time series of electrical characteristic values ​​corresponding to multiple measurement points are processed to obtain the geoelectric profile of the geographic area to be measured. The geoelectric profile is used to characterize the resistivity distribution with depth at different profile locations in the strata of the geographic area to be measured.

[0019] Specifically, processing the time series of electrical characteristic values ​​corresponding to multiple measurement points to obtain a geoelectric profile of the geographic area to be measured may include:

[0020] First, the time series of electrical characteristic values ​​corresponding to multiple measurement points are transformed to obtain the apparent resistivity and impedance phase curves for each measurement point. For example, Fourier transform and ROBUST operation can be performed on the time series of the acquired electrical characteristic values ​​to remove "flying points" and obtain the apparent resistivity and impedance phase curves for the corresponding measurement points.

[0021] Then, the apparent resistivity and impedance phase curves corresponding to multiple measurement points are inverted to obtain a geoelectric profile of the geographic area to be measured. Since the multiple measurement points are distributed along the electromagnetic wave probe lines, the apparent resistivity and impedance phase of each probe line can be inverted to obtain a geoelectric profile with the section distance as the abscissa and depth as the ordinate. This geoelectric profile can represent the distribution of resistivity with depth at different section locations within the strata of the geographic area to be measured.

[0022] In operation S203, resistivity data from multiple pre-selected locations in the strata of the geographic area to be tested are read from the geoelectric cross-section map and used as multiple data to be processed.

[0023] In operation S204, a preset clustering algorithm is used to cluster multiple datasets to obtain stratigraphic classification results that characterize the basal undulation features of the geographic region under test. The preset clustering algorithm can be, for example, the K-means clustering algorithm. During this clustering process, the number of clusters is predetermined, and the resistivity of multiple pre-selected locations within the stratigraphy of the geographic region under test is used as the basic data for clustering. Each cluster is associated with a set of pre-selected locations within the stratigraphy of the geographic region under test. Thus, stratigraphic classification results based on resistivity characteristics of the geographic region under test can be obtained, with each cluster representing a stratigraphy, and resistivity within the same stratigraphy being relatively similar.

[0024] According to the embodiments of this application, the above method uses a preset clustering algorithm to perform clustering based on the resistivity of multiple points in the strata of the geographic area to be tested, thereby obtaining the stratigraphic classification results of the geographic area to be tested based on resistivity characteristics. This is used to characterize the basement undulation features of the geographic area to be tested. Compared with the method in the prior art that determines the stratigraphic structure characteristics by rough estimation, the method of this application embodiment is based on measured data for data analysis, and the results obtained are more objective. It can more accurately determine the basement undulation features of sedimentary basins and provide valuable reference for delineating the favorable mineralization areas of sandstone-type uranium deposits.

[0025] According to the embodiments of this application, before using magnetotelluric sounding to explore the geographic area to be measured, various geological reference information of the geographic area to be measured can be collected first, such as geological and physical property data of the sedimentary basin inside and around the geographic area to be measured, including but not limited to basic geological information, core logging data and core resistivity data, etc.

[0026] Furthermore, before the above-mentioned operation S201 is carried out, the locations of multiple measuring points within the geographical area to be measured can be determined based on the basic geological information of the geographical area to be measured and in combination with the predetermined measurement standards (measurement requirements in the geophysical and geochemical exploration measurement specifications), so that sensors can be deployed at the measuring point locations.

[0027] Specifically, determining the locations of multiple measuring points within the geographic area to be measured, based on predetermined measurement standards and basic geological information of the geographic area to be measured, includes the following operations:

[0028] Operation 1: Based on the stratigraphic trend in the basic geological information of the geographic area to be measured, determine the direction of the electromagnetic wave probe line, wherein the direction of the electromagnetic wave probe line is set to be perpendicular to the stratigraphic trend.

[0029] Step 2: Determine the distance between adjacent measuring points and the distance between adjacent electromagnetic wave measuring lines according to the predetermined measurement standards. For example, the distance between adjacent measuring points and the distance between adjacent electromagnetic wave measuring lines can be determined according to the scale requirements in the geophysical and geochemical exploration specifications.

[0030] Step 3: Determine the locations of multiple measuring points based on the direction of the electromagnetic wave detection line, the distance between adjacent measuring points, and the line spacing between adjacent electromagnetic wave detection lines. Specifically, multiple measuring points can be set up on each electromagnetic wave detection line. The distance between adjacent measuring points should conform to the scale requirements in the geophysical and geochemical exploration specifications, and the line spacing between adjacent electromagnetic wave detection lines should also conform to the scale requirements in the geophysical and geochemical exploration specifications.

[0031] According to an embodiment of this application, an electromagnetic wave with a relatively wide frequency range is used to probe the geographic area to be measured, which facilitates the simultaneous detection of geological information in both deeper and shallower geological areas. To accurately detect the depth of the sedimentary basin basement, further, before the above-mentioned operation S201, it is necessary to determine the frequency range of the probe electromagnetic wave. Specifically, this can be determined based on the core logging data and core resistivity data of the geographic area to be measured.

[0032] Specifically, before the above-mentioned operation S201 is performed, based on the core logging data and core resistivity data of the geographic area to be measured, the frequency range of the detection electromagnetic waves used to detect the geographic area to be measured is determined, including the following operations:

[0033] Step 1: Based on the core logging data and core resistivity data of the geographic area to be measured, determine the lower limit of the frequency of the electromagnetic waves to be detected. Specifically, the following method can be used to determine the lower limit of the frequency of the electromagnetic waves to be detected:

[0034] First, the average burial depth of the basement of the geographic area to be measured is determined based on the burial depth of each stratum in the core logging data of the geographic area to be measured, which was collected in advance.

[0035] Then, the electromagnetic detection depth is determined based on the average burial depth of the basement of the geographic area to be measured; for example, a depth within a reasonable range (e.g., 200 meters) can be added to the average burial depth of the sedimentary basin basement as the electromagnetic detection depth.

[0036] Then, based on the core resistivity data of the geographic area to be tested, the average resistivity of the working interval of the strata in the geographic area to be tested is calculated.

[0037] Finally, based on the electromagnetic detection depth and the average resistivity of the working range, the lower limit of the frequency of the detected electromagnetic wave is calculated.

[0038] Specifically, the depth estimation formula for frequency domain electromagnetic sounding exploration described in formula (1) can be used for calculation:

[0039]

[0040] In formula (1) above:

[0041] d represents the detection depth, in meters (m). is the average resistivity of the working area, in Ω·m; f is the minimum frequency required to reach the target body, which is the lower limit of the frequency of the electromagnetic wave to be detected, in Hz; based on the above formula (1), the minimum frequency required to reach the electromagnetic detection depth d can be calculated according to the predetermined electromagnetic detection depth and the average resistivity of the working area.

[0042] Step 2: After calculating the lower limit of the frequency of the electromagnetic wave to be detected using the above method, determine the frequency range of the electromagnetic wave to be detected based on the lower limit of the frequency of the electromagnetic wave to be detected and the upper limit of the frequency of the electromagnetic detection equipment. For example, select all frequency groups within the range from the lowest required frequency to the highest frequency range that the equipment can transmit to as the frequency range of the electromagnetic wave to be detected.

[0043] According to an embodiment of this application, in the above operation S204, the K-means clustering algorithm is used to cluster multiple data to be processed, that is, the K-means clustering algorithm is used to perform geological interpretation of the geoelectric cross section to outline the undulating features of the sedimentary basin basement.

[0044] Specifically, the clustering process using the K-means clustering algorithm may include the following operations:

[0045] Step 1: Determine the total number of stratigraphic categories in the geographic area to be measured, i.e., first determine the number of clusters. For example, based on basic geological information, core logging data, and geoelectric profiles, the strata and basement of the geographic area to be measured can be divided into 4 to 5 major categories. The number of major categories is the number of clusters. Each cluster contains a cluster center, which is the center of each cluster and represents the characteristics of each cluster. The distance from each object in each cluster to the cluster center is represented by the cluster distance. In the scenario of this application embodiment, the cluster center represents the resistivity data of a certain location in the strata of the geographic area to be measured, and the cluster distance represents the resistivity difference between the data to be processed and the cluster center.

[0046] Operation 2: Use a preset clustering algorithm to determine the target distance discrimination threshold and multiple target cluster centers (i.e., the cluster distance discrimination threshold and cluster centers are finally determined through multiple iterations). The number of multiple target cluster centers is equal to the total number of strata categories. Multiple target cluster centers represent resistivity data of multiple target locations in the strata of the geographic area to be measured. The target distance discrimination threshold is used to discriminate the resistivity difference between the data to be processed and the target cluster centers.

[0047] Step 3: Cluster the multiple data sets to be processed into multiple target datasets based on multiple target cluster centers and target distance thresholds. For example, based on each target cluster center, calculate the resistivity difference between the processed data and each target cluster center, and assign the processed data whose resistivity difference is less than the target distance threshold to the dataset belonging to the corresponding target cluster center. In the clustering results, the processed data in each target dataset is associated with a set of pre-selected location points in the strata of the geographic area to be measured.

[0048] Operation 4: Based on multiple sets of pre-selected location points associated with multiple target datasets, obtain the stratigraphic classification results for the geographic area to be tested.

[0049] According to the embodiments of this application, the clustering process performed using the K-means clustering algorithm is an iterative calculation process. When the preset termination condition is reached through multiple iterations, the final target distance discrimination threshold and multiple target cluster centers can be determined. Based on the final determined target cluster centers and target distance discrimination threshold, clustering is performed using the resistivity of multiple different pre-selected location points in the strata of the geographic area to be tested as the basic data. Each cluster is associated with a set of pre-selected location points in the strata of the geographic area to be tested. In this way, the stratigraphic classification result of the geographic area to be tested based on resistivity characteristics can be obtained. Each class represents a type of stratum, and the resistivity in the same stratum is relatively similar.

[0050] According to an embodiment of this application, further, determining the target distance discrimination threshold and multiple target cluster centers through multiple iterations using a preset clustering algorithm specifically includes the following operations.

[0051] Specifically: A preset clustering algorithm is used to determine the current distance discrimination threshold and multiple current cluster centers, where the number of current cluster centers equals the total number of stratigraphic categories. After completing the current clustering of multiple data points based on the current distance discrimination threshold and multiple current cluster centers, the operation of determining the next distance discrimination threshold and multiple next cluster centers based on the current clustering results is iteratively executed until a preset termination condition is met, resulting in the final determined target distance discrimination threshold and multiple target cluster centers.

[0052] During the initial iteration calculation, it is necessary to initialize the distance discrimination threshold (cluster distance) and cluster centers, that is, to determine the initial distance discrimination threshold and multiple initial sub-cluster centers. The initialization of each cluster center and cluster distance threshold can be based on the core resistivity data and the number of clusters.

[0053] According to an embodiment of this application, in the above iterative calculation process, the method for determining the next distance discrimination threshold and multiple next cluster centers based on the current clustering result can be performed as follows.

[0054] Specifically, based on the current clustering result, the mean of the data to be processed in each current dataset can be calculated and used as multiple clustering centers for the next time.

[0055] Specifically, based on the current clustering results, the resistivity difference between the data to be processed in each current dataset and the current cluster center can be calculated respectively. Then, based on the resistivity difference between the data to be processed in each current dataset and the current cluster center, the next distance discrimination threshold can be calculated. For example, the mean of the resistivity difference can be used as the next distance discrimination threshold.

[0056] According to the embodiments of this application, the clustering algorithm described above can be used to perform multiple iterations of calculations to obtain accurate cluster centers and cluster distances. Stratigraphic division based on the clustering results can make the division of each stratum accurate and reasonable, and ultimately determine the basement undulation characteristics of the sedimentary basin more accurately.

[0057] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. All contents not described in detail in the present invention can be derived from existing technologies.

Claims

1. A method of determining a substrate relief feature, the method comprising: The method comprises the following steps: Collecting time series of electrical characteristic values corresponding to a plurality of measuring point positions by arranging sensors at the plurality of measuring point positions in a to-be-measured geographic area; Processing the time series of electrical characteristic values corresponding to the plurality of measuring point positions to obtain a geoelectric section map of the to-be-measured geographic area, wherein the geoelectric section map is used to represent the distribution of resistivity with depth at different profile positions in the stratum of the to-be-measured geographic area; Reading resistivity data of a plurality of different preselected position points in the stratum of the to-be-measured geographic area from the geoelectric section map as a plurality of to-be-processed data; Using a preset clustering algorithm to perform clustering processing on the plurality of to-be-processed data to obtain a stratum classification result used to represent a basement relief feature of the to-be-measured geographic area; The method further comprises the following steps: Determining a total number of stratum categories of the to-be-measured geographic area; Using the preset clustering algorithm to determine a target distance discrimination threshold and a plurality of target cluster centers, wherein the number of the plurality of target cluster centers is equal to the total number of stratum categories, the plurality of target cluster centers represent resistivity data of a plurality of target position points in the stratum of the to-be-measured geographic area, and the target distance discrimination threshold is used to discriminate a resistivity difference between to-be-processed data and a target cluster center; Clustering the plurality of to-be-processed data into a plurality of target data sets according to the plurality of target cluster centers and the target distance discrimination threshold, wherein to-be-processed data in each target data set is associated with a set of preselected position points in the stratum of the to-be-measured geographic area; Obtaining the stratum classification result of the to-be-measured geographic area according to a plurality of sets of preselected position points associated with the plurality of target data sets; The method further comprises the following steps: Converting the time series of electrical characteristic values corresponding to the plurality of measuring point positions to obtain apparent resistivity and impedance phase curves corresponding to the plurality of measuring point positions; Inverting the apparent resistivity and impedance phase curves corresponding to the plurality of measuring point positions to obtain the geoelectric section map of the to-be-measured geographic area; The method further comprises the following steps: Determining a frequency range of a detection electromagnetic wave used to detect the to-be-measured geographic area according to stratum distribution and core resistivity data of core logging data of the to-be-measured geographic area; The method further comprises the following steps: Determining a lower limit value of the frequency of the detection electromagnetic wave according to the stratum distribution and core resistivity data of the core logging data of the to-be-measured geographic area; Determining the frequency range of the detection electromagnetic wave based on the lower limit value of the frequency of the detection electromagnetic wave and an upper limit value of the frequency of an electromagnetic detection device.

2. The method of claim 1, wherein, The method further comprises the following steps: Determining a current distance discrimination threshold and a plurality of current cluster centers using the preset clustering algorithm, wherein the number of the plurality of current cluster centers is equal to the total number of stratum categories. In a case of completing the current clustering based on the current distance discrimination threshold and the plurality of current clustering centers for the plurality of to-be-processed data, the operation of determining the next distance discrimination threshold and the plurality of next clustering centers based on the current clustering result is iteratively performed until a preset termination condition is met, and finally the target distance discrimination threshold and the plurality of target clustering centers are determined.

3. The method of claim 2, wherein, The operation of determining the next distance discrimination threshold and the plurality of next clustering centers based on the current clustering result comprises: Based on the current clustering result, the mean value of the to-be-processed data in each current data set is calculated as the plurality of next clustering centers; Based on the current clustering result, the resistivity difference between the to-be-processed data in each current data set and each current clustering center is calculated; According to the resistivity difference between the to-be-processed data in each current data set and each current clustering center, the next distance discrimination threshold is calculated.

4. The method of claim 1, wherein, Further comprising: According to the predetermined measurement standard and the basic geological information of the to-be-measured geographic area, a plurality of measuring point positions within the range of the to-be-measured geographic area are determined.

5. The method of claim 4, wherein, According to the predetermined measurement standard and the basic geological information of the to-be-measured geographic area, a plurality of measuring point positions within the range of the to-be-measured geographic area are determined, comprising: According to the stratum structure trend in the basic geological information of the to-be-measured geographic area, the direction of the detection electromagnetic wave measuring line is determined; According to the predetermined measurement standard, the point distance between adjacent measuring points and the line distance between adjacent detection electromagnetic wave measuring lines are determined; According to the direction of the detection electromagnetic wave measuring line, the point distance between adjacent measuring points, and the line distance between adjacent detection electromagnetic wave measuring lines, a plurality of measuring point positions distributed along the detection electromagnetic wave measuring line are determined.

6. The method of claim 5, wherein: The direction of the detection electromagnetic wave measuring line is perpendicular to the stratum structure trend.

7. The method of claim 1, wherein, According to the core logging data and the core resistivity data of the to-be-measured geographic area, the lower limit value of the frequency of the detection electromagnetic wave is determined, comprising: According to the core logging data of the to-be-measured geographic area, the average burial depth of the base of the to-be-measured geographic area is determined; According to the average burial depth of the base of the to-be-measured geographic area, the electromagnetic detection depth is determined; According to the core resistivity data of the to-be-measured geographic area, the average resistivity of the working interval is calculated; According to the electromagnetic detection depth and the average resistivity of the working interval, the lower limit value of the frequency of the detection electromagnetic wave is calculated.

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