A method for designing a depth of a shooting well in a three-dimensional seismic exploration of a coal mining area in a loess plateau region

Abstract

The application relates to the field of three-dimensional seismic exploration field data acquisition technology in loess plateau areas, in particular to a three-dimensional seismic exploration shooting well depth design method for a coal mining area in a loess plateau area. The method comprises the following steps: in a determined exploration area, shallow geological survey work is carried out to track a favorable shooting layer, gully outcrop area data and shallow drilling survey result data are obtained; a favorable layer position is tracked by adopting a geological comparison method, and a shallow stratum model is constructed; a conventional three-dimensional seismic single factor test is carried out, and the best shooting well depth of each point is selected; the most favorable layer position is comprehensively analyzed and determined; and the best well depth of all designed shooting points is calculated. The application realizes the rationality and accuracy of the advanced design of the observation system shooting well depth by carrying out investigation and well depth design around the ideal layer position in the area as the core target, and lays a foundation for improving the efficiency and quality of field data acquisition.

Description

Technical Field

[0001] This application relates to the field of 3D seismic exploration field data acquisition technology in the Loess Plateau region, and in particular to a method for designing the excitation well depth in 3D seismic exploration of coal mining areas in the Loess Plateau region. Background Technology

[0002] Seismic exploration utilizes the differences in elasticity and density of underground media. Seismic waves are artificially generated at the surface. As these waves propagate underground, they encounter interfaces between rock strata with different properties, resulting in reflection and refraction. Detectors at the surface or in the well receive, process, and interpret these reflected or refracted waves to infer the properties and morphology of the underground rock layers. Seismic exploration is a crucial method for geological prospecting for oil, natural gas, and solid resources before drilling, and it is also widely used in coalfield and engineering geological exploration, regional geological studies, and crustal research.

[0003] 3D seismic field data acquisition is a crucial foundational step in 3D seismic exploration. The quality of the acquired data directly impacts the quality of subsequent data processing and, consequently, the overall exploration results. The excitation well depth is one of the most critical operational parameters for 3D seismic field data acquisition. Determining the optimal excitation well depth is crucial for improving the signal-to-noise ratio and resolution of the seismic record.

[0004] Through years of construction experience, we have found that in areas with surface conditions such as the Loess Plateau in Shanxi, Shaanxi, Inner Mongolia, and Gansu, for 3D seismic surveys of coal mining areas, firstly, the exploration range is relatively small (mostly a few square kilometers to a dozen square kilometers). Within this small area, there are generally one or two layers (clay layers or similar layers) that are suitable for seismic explosive activation. Secondly, these Cenozoic strata exhibit a relatively gentle undulating curved surface in space, which is mathematically a continuous and differentiable surface, and can be continuously traced using geological methods. Thirdly, due to surface erosion, a certain layer or all of these layers may be exposed in the area of ​​the chicken claw-shaped gully, but relative to the whole area, this phenomenon is localized.

[0005] In the past, well depth design for coal mine 3D seismic exploration in the Loess Plateau region mainly relied on single-factor tests conducted at various test sites. These tests, combined with research on the relationship between low-velocity zones and water table (or high-velocity layers) using micrologging and shallow refraction wave surveys, were used to summarize the optimal excitation method for missing sections of the exploration area, inferring the excitation well depth for different blocks and thus determining the actual excitation construction plan. However, limited by the number of test sites, the density and accuracy of micrologging and shallow survey points, the excitation well depth for unknown points was determined through simple linear interpolation. This design approach cannot eliminate the influence of complex surface undulations, resulting in inherent and difficult-to-overcome irrational elements in the excitation well depth design.

[0006] In view of the problems and shortcomings of the currently used related technologies mentioned above, the inventors believe that optimizing the tracking and investigation of the excitation layer and improving the accuracy of the optimal excitation well depth are areas that need to be studied in the design of excitation well depth in seismic exploration. Summary of the Invention

[0007] The purpose of this application is primarily to address 3D seismic exploration in coal mining areas of the Loess Plateau. To accurately design the excitation well depth, this method focuses on investigating and designing the optimal stratigraphic level within the tracking area. It eliminates the shortcomings of relying solely on a few test points and conventional shallow refraction point selection for well depth selection. It overcomes the drawbacks of previous methods that blindly tracked excitation stratigraphic levels in complex surface undulations, which negatively impacted well depth selection. This achieves the goal of advanced and accurate design of the excitation well depth for the observation system, laying the foundation for improving the efficiency and quality of field data acquisition. This application provides a method for designing the excitation well depth in 3D seismic exploration of coal mining areas in the Loess Plateau.

[0008] This application provides a method for designing the excitation well depth in three-dimensional seismic exploration of coal mining areas in the Loess Plateau region. The following technical solution is adopted: A method for designing well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region includes the following steps: Acquire shallow geological survey data: Conduct shallow geological surveys in the exploration area with the aim of tracking and selecting the required strata, and acquire data on gully outcrops and shallow drilling survey results in non-gully outcrops. Constructing a favorable stratigraphic model: Using geological correlation methods, we completed the comparison of shallow drilling survey data and gully outcrop data, preliminarily inferred that the target suitable for the initiation layer in the area is the favorable stratigraphic layer, and established the occurrence model of the favorable stratigraphic layer, and compiled the contour map and isopyroline map of the bottom interface of the favorable stratigraphic layer. Conduct single-factor tests at each test site: Based on the quality of the test records at each test site, conduct a comprehensive comparison and analysis to determine the optimal activation well depth (stratum) for each test site; Determine the optimal favorable layer: By comprehensively analyzing the relationship between the optimal activation well depth selected at each test point and the occurrence model of each favorable layer obtained from the above shallow geological survey, the most favorable layer is determined as the optimal activation layer; Calculate the well depth of all designed excitation points in the 3D seismic observation system: Based on the bottom interface contour map and the surface topographic contour map of the most favorable excitation layer, calculate the optimal excitation well depth for each excitation point. These calculation results can be directly used for 3D seismic field data acquisition.

[0009] By adopting the above technical solution, this application conducts investigations and well depth designs centered on the ideal strata within the tracking area. Considering the realities of the Loess Plateau region, it first conducts route surveys and shallow drilling surveys in both gully and non-gully exposed areas, tracing and forming survey results for each favorable stratum. Favorable strata are initially determined. Then, through single-factor tests at each test point, the most favorable stratum, i.e., the most ideal stratum, is determined as the activation stratum. Finally, based on the surface elevation and the bottom interface elevation of the selected optimal activation stratum, the optimal activation well depth is calculated, resulting in the actual activation construction plan. This application achieves precise design of activation well depths point-by-point throughout the entire exploration area by determining the optimal activation well depth for each designed activation point. Even in cases where undesirable activation strata exist locally, the investigation work of this invention provides a contingency plan. This application overcomes the shortcomings and drawbacks of previous blind attempts to track excitation layers under complex surface undulations, which affected well depth selection. It achieves the goal of rational and accurate advance design of excitation well depth for all designed well locations in the 3D seismic observation system, realizing precise design of excitation well depth at each point, and laying the foundation for improving the efficiency and quality of field data acquisition.

[0010] Optionally, the steps for obtaining shallow geological survey data include: Investigation and analysis of gully outcrop areas: A detailed reconnaissance of the exploration area was conducted, the route survey design for the gully outcrop areas was completed, and the survey was carried out. Through the investigation of the strata in the gully outcrop areas, a preliminary understanding of the occurrence of shallow strata was obtained.

[0011] By adopting the above-mentioned survey plan, geological route surveys were conducted at certain intervals in the gully outcrop area to collect data.

[0012] Optionally, in the investigation and analysis steps of the outcrop area of ​​the gully, the investigation content includes the investigation point number, the coordinates of the investigation point, the elevation of the bottom interface of the target stratum, the lithology, thickness, name of each exposed stratum, and stratum photographs.

[0013] By adopting the above technical solution, the survey content involved in the investigation of the outcrop area of ​​the gully has been disclosed. Of course, the actual record may also include other content, such as stratigraphic photographs and lithological descriptions.

[0014] Optionally, the step of obtaining shallow geological survey data may also include... Shallow drilling survey and analysis; shallow drilling survey design is carried out in non-gully outcrop areas of the exploration area according to a certain grid, and the shallow drilling survey project is completed according to the design to obtain the results data of shallow strata.

[0015] By adopting the above technical solution, shallow drilling surveys are used in non-gully outcrop areas to obtain survey data on the occurrence and distribution of shallow strata.

[0016] Optionally, in the shallow drilling investigation and analysis step, shallow strata exploration wells are carried out at a certain density in non-gully outcrop areas. Lightweight drilling equipment is used to drill and core at the designed points. The cores are cataloged, and the coordinates of the well locations, the elevation of the wellhead, the lithology of different layers and the depth of the interface are recorded. All cores are photographed in a timely manner.

[0017] By adopting the above technical solution, the survey content of the investigation in the non-gully exposed area (loess-covered area) was disclosed.

[0018] Optionally, the compilation and analysis of shallow geological survey data results includes using geological comparison methods to compare the data from shallow drilling surveys with the data from gully outcrop areas, preliminarily inferring the target layers suitable as induction layers in the area as favorable layers, establishing the occurrence models of these favorable layers, and compiling the contour maps and isopyrograph maps of the bottom interfaces of each favorable layer.

[0019] By adopting the above technical solution, the process of compiling and analyzing the results of shallow geological surveys has been made public.

[0020] Optionally, in conducting single-factor experiments and analysis at each experimental site, including Determine the test sites and develop a test work plan; Single-factor tests and low-speed-deceleration zone surveys were conducted at each test site. By comparing and comprehensively analyzing the test record quality of different parameters at each test site, the optimal excitation depth and optimal parameters for each site were determined.

[0021] By adopting the above technical solution, the process of single-factor experiments at each test site was disclosed.

[0022] Optionally, the analysis of the relationship between the single-factor test results of each test site and the model established by the shallow geological survey includes analyzing the relationship between the optimal activation well depth selected for each test site and the favorable strata in the shallow geological survey results, and determining the most favorable strata as the activation strata.

[0023] By adopting the above technical solution, a method for determining the most favorable stratum is disclosed.

[0024] Optionally, in the step of calculating the well depth of all designed excitation points in the 3D seismic observation system, the formula for calculating the optimal excitation well depth of the excitation points in the 3D seismic engineering design is as follows: D i =H i -h i In the formula, D i For the ideal excitation well depth at a certain location, H ih is the surface elevation value at this point. i This represents the optimal elevation of the bottom interface of the excitation layer at that point.

[0025] By adopting the above technical solution, a method for calculating the optimal excitation well depth is disclosed.

[0026] Optionally, in the well depth step of all designed excitation points in the 3D seismic observation system, the surface elevation and the elevation of the bottom interface of the optimal excitation layer at each point are automatically picked up by the graphics software to form a table file, and the excitation well depth of all designed shot points is calculated by the calculation formula.

[0027] By adopting the above technical solution, the optimal method for directly obtaining the well depth is achieved.

[0028] Optionally, when encountering ground obstacles that affect the layout of the excitation point, the location of the excitation point can be changed according to the actual ground conditions. The changed excitation well depth is calculated by the surface elevation at the coordinates of the changed location and the elevation of the bottom interface of the optimal excitation layer according to the calculation formula of the optimal excitation well depth of the excitation point.

[0029] By adopting the above technical solution, a well depth optimization method for encountering ground features is disclosed.

[0030] For exploration areas where the stimulating layer near the gully is shallow or the velocity is significantly lower, or in local areas where there is no ideal stimulating layer in the gully outcrop area, the stimulating well depth shall be constructed using the parameters selected from the test work at each test point.

[0031] By adopting the above technical solution, a method for optimizing well depth in locations that induce poor well depth, such as outcrop areas of scour channels, is disclosed.

[0032] This application includes at least one of the following beneficial technical effects: 1. This application conducts investigations and well depth designs centered on the core objective of identifying ideal strata within the region. Considering the realities of the Loess Plateau region, it first investigates both gully-exposed and non-gully-exposed areas to preliminarily determine favorable strata. Then, through single-factor tests at various test points, it identifies the most favorable, or ideal, stratum as the activation stratum, and subsequently obtains the well depth for this activation stratum. The well depth is then optimized to obtain the actual activation construction scheme.

[0033] 2. This application distinguishes between gully outcrop areas and non-gully outcrop areas, and optimizes local locations to obtain the optimal activation well depth for each designed activation point. This achieves precise deep design of activation well depth for each point in the entire exploration area. Even if there are unfavorable activation strata in some areas, there will be contingency plans due to prior investigation.

[0034] 3. This application overcomes the shortcomings of previous methods that failed to track the excitation layer under complex surface undulations, thus affecting well depth selection. It achieves the goal of optimizing the rationality and accuracy of the advanced design of excitation well locations and depths in the observation system, and realizes the precise design of point-by-point excitation well depths in the exploration area. This lays the foundation for improving the efficiency and quality of field data acquisition. Attached Figure Description

[0035] Figure 1 This is a flowchart of the three-dimensional seismic exploration method for designing well depths in coal mining areas of the Loess Plateau region, as described in this application.

[0036] Figure 2 This is a schematic diagram of the engineering layout for the gully stratigraphy survey and shallow drilling stratigraphy survey in this application.

[0037] Figure 3 This is a schematic diagram of sampling the exposed clay layer in the gully of this application.

[0038] Figure 4 This is a schematic diagram showing the comparison between the core sampling results and the stratigraphic position during the shallow drilling survey in this application.

[0039] Figure 5 This is a schematic diagram showing the correlation of sounding layers in the shallow stratigraphic survey of this application.

[0040] Figure 6 This is a contour map of the interface and thickness of layer A in the shallow stratigraphic survey of this application.

[0041] Figure 7 This is a contour map of the B-layer interface and thickness contour map from the shallow stratigraphic survey of this application.

[0042] Figure 8 This is a composite map of the B-layer interface and surface contour lines from the shallow stratigraphic survey in this application.

[0043] Figure 9 This is a schematic diagram illustrating the calculation of the well depth for this application. Detailed Implementation

[0044] The present application will be further described in detail below with reference to the accompanying drawings.

[0045] This application discloses a method for designing the excitation well depth in 3D seismic exploration of coal mining areas in the Loess Plateau region. This method is suitable for 3D seismic exploration field data acquisition operations in coal mining areas of the Loess Plateau region with relatively small exploration areas. It allows for the precise design of the excitation well depth before conducting experimental work, with the optimal stratum ultimately determined from several candidate strata through experimental work. This method is based on the premise that the ideal excitation stratum within the area does not change drastically. Specifically, it assumes that the area of ​​the 3D exploration zone is comparable to one or more mining areas of the coal mine, and that most sections within the zone possess an ideal excitation stratum with minimal lateral variation. This method also has good adaptability if a relatively stable ideal excitation stratum exists over a large area.

[0046] The technical approach of this application for the design method of 3D seismic exploration excitation well depth in coal mining areas of the Loess Plateau region is as follows: First, conduct a line survey of clay layers in the gully outcrop area, requiring the recording of layer names, layer thicknesses, coordinates and elevations of bottom interface survey points, layer photographs, and lithological descriptions; Second, design preliminary survey wells with a certain grid density in non-scour outcrop areas, conduct shallow lithological core sampling, and carry out layer comparison studies; Third, complete the comparison work of different clay layers in the entire area; Fourth, input the data of the one or two most important clay layers that are expected to be suitable as excitation layers into contour line calculation software to complete the compilation of bottom interface contour maps and isopyroline maps; Fifth, conduct excitation tests on different excitation layers for comparison and select the optimal excitation layer; Sixth, for the selected optimal excitation layer, calculate the precise well depth of each designed well location by combining the bottom interface elevation plan map and surface contour map of that layer; Seventh, for local sections in the gully outcrop area where there is no corresponding excitation layer, select the excitation method and parameters through other experimental means.

[0047] The proposed method for designing well depths for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region involves investigation within a designated exploration area, and includes the following steps.

[0048] Obtain survey data. Conduct a detailed survey of the exploration area to obtain geological data from boreholes in non-gully outcrop areas and data on gully outcrop areas.

[0049] Data on gully outcrops were obtained through investigation and analysis of these areas. In the Loess Plateau region, gully outcrops are often formed within the exploration area due to surface erosion, exposing one or all of these strata. A detailed reconnaissance of the exploration area was conducted to identify these gully outcrops. These outcrops were then investigated, including a line survey of clay layers. During the survey, it was important to distinguish the different geological characteristics and interfaces of the exposed surfaces. For some important clay layers, the bottom interface should be probed. For some interfaces that are partially not exposed, micro-trenches can be excavated for detection. Appropriate records were kept during the investigation, including the survey point number, coordinates, lithology, thickness, and bottom interface elevation of the target stratum, descriptions of the lithology and thickness of other exposed strata, and photographs of the survey points.

[0050] The borehole geological data was obtained through shallow drilling surveys and analysis. Preliminary survey wells with a certain grid density were designed and completed in non-scour areas. Detailed reconnaissance was conducted in non-scour outcrop areas, and preliminary survey wells with a certain grid density were designed in these areas for shallow lithological coring and stratigraphic correlation studies. In loess-covered areas, shallow stratigraphic surveys were conducted at a certain density, drilling was carried out, and core samples were taken at the designed locations using drilling equipment. Core logging was performed, recording the well station number, borehole coordinates, borehole elevation, lithology of different strata, and interface depths. Photographs and logging were also performed. For shallow drilling and coring, a Luoyang shovel can be used; for deeper drilling, a lightweight truck-mounted drilling rig can be used. Core logging mainly focuses on the location, stratification, state description, lithology of different strata, and interface depths of the core samples. Well logging is the process of observing, collecting, recording, and analyzing information from solid, liquid, and gaseous materials returned from the wellbore during drilling. This information is used to establish a well logging geological profile, discover formation displays, evaluate strata, and provide drilling information services. Well logging interprets and locates lithology based on comprehensive field geological data, field logging data, and comprehensive analytical test data to determine formation conditions. Users can freely choose drawing projects and formats to create different types of well logging diagrams. On-screen editing and modification work includes correcting drill string errors, processing broken core samples, and adjusting strata boundaries. Core samples and drilling data are also photographed and archived.

[0051] Based on the above survey data, a shallow lithology and stratigraphic correlation study was conducted. Using geological borehole correlation methods, the stratigraphic correspondence between each outcrop survey point and shallow borehole survey point was determined. The distribution of the target stratigraphic layers (different clay layers) within the area was traced, and the survey results table was compiled. The table includes information such as the name of the target stratigraphic layer, the coordinates of the survey points, the elevation of the bottom interface of the stratigraphic layer, and the thickness of the stratigraphic layer, laying the foundation for compiling the planar results of the target stratigraphic layers.

[0052] The survey results table is edited (or converted) into a format file that can be read by automatic drawing software. There are various software programs that can complete the calculation and automatic mapping of bottom interface contour maps and thickness prediction plan maps. The unreasonable parts of the map generated by the software are then manually optimized to obtain the survey results map.

[0053] For data processing, records can be created to form data tables with certain rules. Using dedicated data processing software such as seismic acquisition systems, common maps and tables can be calculated and generated. Specific data processing, calculation procedures, and software usage methods are not described in detail here. For example, in this application, a surface survey interpretation result table includes columns such as the survey point's line number, station number, low-velocity layer thickness, low-velocity layer velocity, decreasing-velocity layer thickness, decreasing-velocity layer velocity, high-velocity layer velocity, survey method, acceptor, and remarks. Data from a certain firing point includes columns such as line number, station number, east coordinate, north coordinate, and elevation. The software can also automatically process and generate data such as elevation, thickness, total thickness velocity, velocity difference, similarity coefficient, as well as control points, receiving points, firing points, benchmark maps, reference maps, thickness profile maps, well depth design maps, and well depth design tables.

[0054] Favorable stratigraphic horizon investigation. By comparing borehole geological data and gully outcrop data, relevant data are compiled to preliminarily infer suitable targets for initiation in the area, identifying them as favorable stratigraphic horizons, and obtaining occurrence models of these favorable horizons. Through comprehensive investigation, a basic model of shallow surface strata is established; through stratigraphic correlation, contour maps of the bottom interface and thickness contour maps of several horizons of interest are compiled.

[0055] Based on the acquired data and years of experience, it can be determined which layers cannot be activated and which can. Favorable layers refer to those that can be activated; generally, there is more than one, or while not the best layer, the best layer does not exist, so the study of these layers should not be underestimated. The storage model includes information such as undulation morphology, lateral thickness variations, changes in burial depth, depth, extent, velocity, etc. Combined with surface contour maps, the burial depth of the bottom interface of several layers can be obtained.

[0056] In the investigation of favorable stratigraphic positions, a basic model of shallow surface strata was established; contour maps of the bottom interface and thickness of several stratigraphic positions of interest were compiled. Subsequently, single-factor tests and analyses were conducted at each test site. Following standard procedures, tests with different activation depths and other parameters were carried out at the selected test sites, along with routine field tests and low-velocity zone surveys, yielding quality analysis results for each test site. Through the single-factor test data at each test site, the correspondence between the optimal activation depth and stratigraphic position was determined, as well as the optimal activation rate or the allowable range of the optimal activation rate. The relationship between record quality and the investigated stratigraphic position was analyzed, and the correspondence between the optimal test effect and the activation rate was clarified. By testing the well depth parameters at each test site, the goal of selecting the optimal activation stratigraphic position and activation rate was achieved. By synthesizing the test results from multiple test sites, the most ideal activation stratigraphic position and activation rate were identified, thereby establishing the selection principles for activation stratigraphic position and depth. Through the experimental work, the correspondence between activation stratigraphic position and record quality was clarified, thus establishing the selection principles for activation stratigraphic depth. When selecting the depth of the induction well, the influence of factors such as the amount of propellant and the length of the propellant string should also be considered.

[0057] Determine the most favorable layer; based on the comprehensive quality analysis results of each test site, analyze the favorable layers and compare them to determine the most favorable layer as the activation layer.

[0058] Obtain the well depth of the trigger point; compile the bottom interface contour map, surface topographic contour map, and thickness contour map of the trigger layer, and obtain the optimal trigger well depth data for each trigger point through calculation or picking.

[0059] For the selected optimal triggering layer, the precise triggering well depth for each design well location is calculated by combining the elevation plan of the bottom interface of that layer and the surface contour map. Finally, the triggering well depth calculation for all design shot points is completed. The method for obtaining the optimal triggering well depth data for each triggering point through calculation is as follows: In the well depth calculation step for the triggering point, the formula for calculating the optimal triggering well depth for the triggering point in 3D seismic engineering design is: D i =H i -h i In the formula, D i For the ideal excitation well depth at a certain location, H i h is the surface elevation value at this point. i The ideal bottom interface elevation value at this point is defined. The surface elevation value and the bottom interface elevation value can be automatically extracted from the vector surface contour map and the optimal bottom interface contour map using professional software, and generated into spreadsheets and other formatted files required for calculation. The calculated well depth data can also be generated into spreadsheets for use during field data collection and construction.

[0060] The method for obtaining the optimal firing depth data for each firing point by picking is as follows: Relevant data for each point is automatically picked up using graphics software, organized into a table, and the firing depth of all designed shot points is obtained. Based on the design location coordinates of the firing points throughout the area, surface elevation and bottom-of-strata interface elevation data are extracted from the surface contour map and the bottom-of-strata interface contour map, respectively, to determine the optimal firing depth data for each firing point location. In the software, any vector map can be read from coordinates and a table can be generated.

[0061] For areas near gully outcrops where the stimulating strata are shallow or have significantly lower velocities, and for local areas where ideal stimulating strata are not available in the gully outcrop development zone, the stimulating well depth is optimized based on the conclusions drawn from single-factor test data at each test point.

[0062] For sections where no suitable activation layers exist, optimization should be performed based on the conclusions drawn from single-factor test data at each test point. Factors such as well depth, combination of wells, and single-well charge should also be considered. For example, in gully outcrop areas, where there may be no corresponding activation layer or the activation layer may be too shallow to facilitate activation, the activation method and parameters for such sections should be rationally selected based on relevant experimental findings. This includes determining the number and combination of activation wells, single-well depth, and single-well charge, serving as an effective supplement to this method.

[0063] For areas affected by terrain features, when partially altering the exploration location, the optimal well depth for each repositioned shot point can be determined by repeating the previous steps after changing the coordinates of the repositioned shot point. This allows for rapid, precise, and point-by-point well depth design. For example, if the design excitation point must be adjusted due to buildings, underground pipelines, high-voltage lines, etc., the well depth can be recalculated based on the new surface elevation and the bottom interface elevation of the optimal excitation layer.

[0064] For the depth of the activation well, factors such as the amount of propellant, the length of the propellant string, and the combination of activation methods should also be considered.

[0065] A practical excitation construction plan was developed, and a design table for the excitation well depth was created using construction harnesses as units to guide the construction of excitation boreholes.

[0066] The selection and design of the activation well depth in this application are based on a relatively intensive survey of shallow subsurface strata combined with conventional seismic testing. When designing the well depth, the selection principle for the optimal activation velocity can also be established using the microseismic logging (or shallow refraction) results obtained during the testing process. By determining the optimal activation well depth for each designed activation point, precise deep design of the activation well depth at each point throughout the entire exploration area can be achieved. Even in cases where unfavorable activation strata exist locally, contingency plans can be quickly developed due to prior investigation.

[0067] Based on our experience in multiple 3D seismic exploration areas, we know that the surface undulations in the Loess Plateau region are significant, making it impossible to achieve high point densities for small refraction and micrologging. Relying solely on shallow survey data and experimental data from a few points is insufficient to accurately design the well depth for each trigger point. This is not a linear interpolation problem; using linear interpolation introduces significant irrationality. This conventional method cannot accurately track and understand the occurrence of relatively ideal strata in the exploration area, nor can it effectively address the impact of surface elevation variations on well depth design. This application overcomes the shortcomings of previous methods that blindly tracked trigger strata in complex surface undulations, thus preventing well depth selection. It achieves the goal of optimizing the rationality and accuracy of the advanced design of trigger well locations and depths in the observation system, enabling precise design of trigger well depths point-by-point throughout the exploration area. This lays the foundation for improving the efficiency and quality of field data acquisition.

[0068] Example 1 This embodiment introduces a method for designing the excitation well depth in three-dimensional seismic exploration of coal mining areas in the Loess Plateau region.

[0069] The exploration area shall be determined based on the actual situation of the exploration.

[0070] Through reconnaissance of the exploration area, the lithological stratification of the shallow strata in the gully outcrop area was initially understood, and several important strata of interest among the outcrop strata were preliminarily identified.

[0071] Conduct a stratigraphic survey of the exposed strata in the gullies. Surveys should be carried out in each gully exposure area, with survey points spaced 300–500 meters apart. Survey points should be numbered according to the gully exposure area, and the stratigraphic information should be tabulated (as shown in Table 1), including the survey point number, coordinates, and elevation of the bottom interface of the target stratigraphic layer. The coordinates of the most relevant stratum (the thicker clay layer) at each survey point should be measured in person. For other strata, thickness measurements should be performed using distance measuring equipment (such as a mobile phone's distance measurement function). For each stratum at the survey point, a description of its lithology, dip, and other stratigraphic occurrence morphology should be provided. Photographs should be taken at each survey point.

[0072] Table 1: Record of Stratum Survey of Outcropped Sections in Gully Section Survey Site Number: YZG-01 (Yangzhuangou Site No. 1) Table 1 lists the layers of interest in smaller tables, providing measured and calculated information such as the elevation, thickness, and planar coordinates of the bottom (or top) interface. This information is used for drawing plan views. The lower tables in the table summarize the key layers from the upper tables, forming the overall analysis results.

[0073] Table 2 illustrates the field record table for shallow stratigraphic exploration well surveys. Generally, the density of exploration wells for shallow stratigraphic surveys in loess-covered areas should not exceed 500m x 500m. Initially, wells can be drilled in shallow stratigraphic areas without pebble layers, using suitable drilling rigs such as Luoyang shovels or truck-mounted drills. Drilling at each survey point requires full-well coring and logging, with timely photographing of the core samples. Record information such as wellbore coordinates, wellhead elevation, lithology of different stratigraphic layers, and interface depths to form the survey record table (Table 2).

[0074] Table 2: Shallow strata exploration well stratigraphic survey field record form Well Number: T01-1 Date: Year Month Day Orifice coordinates: X = , Y = ; Orifice elevation: (meters) Reference Appendix Figure 2 This is a schematic diagram of the engineering layout for gully stratigraphy survey and shallow drilling stratigraphy survey. The survey points, drilling points and their corresponding line numbers in the gully outcrop area are marked in the diagram. The base map for the survey work is a surface contour map.

[0075] Reference Appendix Figure 3 This is a schematic diagram of sampling the exposed clay layer in a gully, which reflects the actual on-site conditions of a gully exposure area.

[0076] Reference Appendix Figure 4 This is a schematic diagram comparing the core samples obtained from shallow drilling surveys with the stratigraphic sequence. The diagram reflects the actual conditions of core samples obtained from two different shallow drilling surveys, and the obtained core samples are classified and segmented according to lithology.

[0077] Based on the survey data of the gully outcrop area, shallow lithological correlation was carried out using exploratory wells. Figure 4 , Figure 5 ), organize relevant data, preliminarily infer suitable targets within the area as induction layers, identify favorable strata in the stratigraphy, complete the regional distribution tracking of the target strata (favorable strata), and compile bottom interface contour maps and thickness prediction plan maps. Figure 6 , Figure 7 ).

[0078] Reference Appendix Figure 4 To conduct shallow lithological comparison of core samples from two different shallow drilling investigations.

[0079] Reference Appendix Figure 5 This diagram illustrates the comparison of sounding layers in shallow geological surveys. The diagram compares and analyzes the lithology and thickness of core samples from multiple consecutive shallow drilling surveys, forming continuous layered curves and tracing the distribution within favorable layer areas. The diagram shows two layers that can be used as favorable layers for induction: the upper red clay layer (layer A) and the lower brownish-red clay layer (layer B).

[0080] Reference Appendix Figure 6 This is a contour map of the bottom interface and thickness of layer A in the shallow strata survey. The map shows the isopyres and contour curves of the red clay layer (layer A) within the exploration area.

[0081] Reference Appendix Figure 7 The map shows the contour lines and thickness contour lines of the bottom interface of the B layer in the shallow strata survey. The map shows the isopyres and contour curves of the brownish-red clay layer (B layer) in the exploration area.

[0082] Single-factor tests were also conducted at various test sites, along with routine field testing and surveys of low-velocity zones. (See attached reference.) Figure 2 , 6 Figures 7 and 8 show the locations of each test site. Following standard practice, tests for various construction factors and investigations of low-velocity zones were conducted at three sites throughout the region. The quality of the test records at each site indicates that the reddish-brown clay layer (layer B) is the most favorable activation layer.

[0083] By analyzing the quality analysis results of each test site, and by testing the well depth parameters of each test site, the correspondence between the optimal excitation well depth and the formation was selected. It is also possible to grasp the relationship between the best effect and the excitation layer velocity, so as to achieve the purpose of selecting the optimal excitation layer and excitation velocity. At the same time, the principle of designing or selecting the excitation well depth when the excitation layer and velocity change is clarified.

[0084] Based on the comprehensive quality analysis results of each test site, the favorable strata were compared and the brownish-red clay layer (layer B) was determined to be the most favorable stratum and was used as the activation stratum.

[0085] Based on the surface topographic contour map and the bottom interface contour map of the target layer, the optimal excitation well depth for the excitation point in the three-dimensional seismic engineering design of the reddish-brown clay layer (layer B) was determined. Figure 8 , Figure 9 ).

[0086] Reference Appendix Figure 8 This is a comprehensive map of the B-layer interface and surface contour lines from a shallow stratigraphic survey. Based on this map, relevant data can be exported using software, and then the optimal activation well depth can be calculated using formulas, or the optimal activation well depth for each activation point can be obtained through a picking method. Different software programs may have slightly different operational variations.

[0087] The formula for calculating the optimal well depth is: D i =H i -h i D i For the ideal excitation well depth at a certain location, H i h is the surface elevation value at this point. i This represents the ideal bottom interface elevation at that point. The surface elevation and bottom interface elevation are derived from the software.

[0088] Reference Appendix Figure 9 This is a schematic diagram for calculating well depth.

[0089] Using professional drawing software, the elevation values ​​of the surface contour map and the bottom interface of layer B can be automatically read from the vectorized surface contour map and exported in the form of tables, etc., and then the optimal excitation well depth for each point can be calculated. The calculated optimal excitation well depth data is then used to form an excitation well depth table in line bundles to guide construction.

[0090] Of course, appropriate optimizations are needed for certain localized areas, and the optimization results will be incorporated into the actual activation and construction plan.

[0091] Through practice, combined excitation was found to be very effective in areas of exploration where the strata near the gully outcrop are shallowly buried or where the velocity is significantly lower. Excitation was also effective in strata with good water content within the gully outcrop or in bedrock at a depth of 5 meters or more.

[0092] The method for designing the excitation well depth in 3D seismic exploration of coal mining areas presented in this application has achieved good results through practical application, realizing the accurate design of the excitation well depth for each shot point. This improves the integrity of the overall observation system design, enhances the success rate of drilling during field operations, and improves the recording quality of field acquisitions, providing a fundamental guarantee for the quality of field acquisitions in 3D seismic exploration of coal mining areas. In this application, the reconnaissance and survey design before the investigation are crucial; a reasonable design of the survey route and the density of survey points is a key prerequisite for obtaining accurate results. Comparative analysis through geological drilling is an important means of tracing favorable excitation layers, and the resulting contour lines and isopylines of the bottom interfaces of each layer are the key technical aspects of this invention. Combining this with conventional experimental work to determine the optimal excitation layer, and then calculating the optimal excitation well depth for each excitation point, is the essential feature that distinguishes this invention from previous methods.

[0093] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape, process and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for designing the excitation well depth in three-dimensional seismic exploration of coal mining areas in the Loess Plateau region, characterized in that, Including the following steps: Obtain shallow geological survey data: Conduct shallow geological surveys in the exploration area with the aim of selecting the required strata, and obtain data on gully outcrop areas and shallow drilling survey results in non-gully outcrop areas; Constructing a favorable stratigraphic model: Using geological correlation methods, we completed the comparison of shallow drilling survey data and gully outcrop data to preliminarily infer suitable targets for induction in the area as favorable stratigraphic layers, and established a model of the occurrence of favorable stratigraphic layers. The model includes undulation morphology, lateral thickness variation, burial depth variation, depth, range, and velocity information. We also compiled contour maps and isopyrograph maps of the bottom interface of favorable stratigraphic layers. Conduct single-factor tests at each test site: comprehensively compare and analyze the quality of the test records at each test site to determine the optimal activation well depth for each test site; Determining the optimal induction layer: This involves comprehensively analyzing the relationship between the optimal induction well depth selected for each test site and the favorable layer occurrence models obtained from the shallow geological survey. The analysis steps include comparing the results of single-factor tests at each test site with the models established by the shallow geological survey. This includes analyzing the relationship between the optimal induction well depth selected for each test site and the favorable layers in the shallow geological survey results. By comprehensively analyzing the quality analysis results of each test site, comparing the favorable layers, and determining the most favorable layer as the optimal induction layer. Calculate the well depth of all designed excitation points in the 3D seismic observation system: Based on the bottom interface contour map and surface topographic contour map of the most favorable excitation layer, calculate the optimal excitation well depth for each excitation point. The calculation results can be directly used for 3D seismic field data acquisition.

2. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 1, characterized in that, The steps involved in obtaining shallow geological survey data include: Investigation and analysis of gully outcrop areas: A detailed reconnaissance of the exploration area was conducted, the route survey design for the gully outcrop areas was completed, and the survey was carried out. Through the investigation of the strata in the gully outcrop areas, a preliminary understanding of the occurrence of shallow strata was obtained.

3. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 2, characterized in that, In the investigation and analysis steps of the outcropping gully area, the investigation content includes the investigation point number, the coordinates of the investigation point, the elevation of the bottom interface of the target stratum, the lithology, thickness, name of each exposed stratum, and stratum photographs.

4. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 3, characterized in that, The steps for obtaining shallow geological survey data also include... Shallow drilling survey and analysis; shallow drilling survey design is carried out in non-gully outcrop areas of the exploration area according to a certain grid, and the shallow drilling survey project is completed according to the design to obtain the results data of shallow strata.

5. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 4, characterized in that, In the shallow drilling investigation and analysis process, shallow strata exploration wells are investigated at a certain density in non-gully outcrop areas. Drilling equipment is used to drill and core samples are taken at the designed points. The core samples are cataloged, and the coordinates of the well locations, the elevation of the wellheads, the lithology of different strata and the depth of the interfaces are recorded. All core samples are photographed in a timely manner.

6. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 5, characterized in that, The compilation and analysis of shallow geological survey data includes... The geological correlation method was used to compare the data from shallow drilling surveys with the data from gully outcrop surveys. The target layers suitable for activation were preliminarily identified as favorable layers, and the occurrence models of these favorable layers were established. The contour maps and isopyrograph maps of the bottom interfaces of each favorable layer were compiled.

7. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 1, characterized in that, In conducting single-factor experiments and analysis at each experimental site, including Determine the test sites and develop a test work plan; Single-factor tests and low-speed-deceleration zone surveys were conducted at each test site. By comparing and comprehensively analyzing the test record quality of different parameters at each test site, the optimal parameters for the optimal excitation depth at each site were determined.

8. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 1, characterized in that, In the step of calculating the well depth of all designed excitation points in a 3D seismic observation system, the formula for calculating the optimal excitation well depth of the excitation points in the 3D seismic engineering design is as follows: D i = H i -hi In the formula, Di is the ideal well depth at a certain location, Hi is the surface elevation at that point, and hi is the optimal bottom interface elevation of the induction layer at that point.

9. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 8, characterized in that, In the well depth step of all designed excitation points in the 3D seismic observation system, the surface elevation and the elevation of the bottom interface of the optimal excitation layer at each point are automatically picked up by the graphics software and a table file is formed. The excitation well depth of all designed shot points is then calculated by the calculation formula.

10. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 9, characterized in that, When ground obstacles affect the placement of the excitation point, the location of the excitation point is changed according to the actual ground conditions. The changed excitation well depth is calculated by the surface elevation at the coordinates of the changed location and the elevation of the bottom interface of the optimal excitation layer according to the calculation formula of the optimal excitation well depth of the excitation point.

11. The method for designing the excitation well depth for three-dimensional seismic exploration in coal mining areas of the Loess Plateau region according to claim 9, characterized in that, For exploration areas where the stimulating layer near the gully is shallow or the velocity is significantly lower, or in local areas where there is no ideal stimulating layer in the gully outcrop area, the stimulating well depth shall be constructed using the parameters selected from the test work at each test point.

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