Method for determining favorable seismic wave excitation part of seismic exploration by using electrical exploration

Abstract

The invention discloses a method for determining a favorable seismic wave excitation part of seismic exploration by using electrical exploration, which belongs to the technical field of seismic exploration, and comprises the following steps of: 1, deploying an electrical exploration survey line; step 2, field data acquisition of electrical method data; 3, electrical method data processing and inversion imaging are carried out; 4, determining a resistivity threshold value of favorable-more favorable earthquake excitation; 5, circling a candidate favorable-more favorable seismic wave excitation section on a resistivity profile or plane distribution result; and step 6, optimizing shot point deployment in the candidate favorable-more favorable seismic excitation section. The method can solve the problem of selection of a favorable seismic wave excitation part in a complex surface lithology exposure area, and greatly improves the seismic exploration imaging quality and exploration precision. Meanwhile, due to the fact that shot point distribution is required to have certain uniformity, large notches on a seismic section are prevented.

Description

Technical Field

[0001] This invention belongs to the field of seismic exploration technology, specifically relating to a method for determining favorable seismic wave excitation locations using electrical exploration. Background Technology

[0002] The quality of seismic wave excitation conditions determines the conversion rate of explosive source energy into seismic wave energy, and thus the quality of seismic data. Therefore, the selection of seismic wave excitation points is particularly important in seismic exploration data acquisition.

[0003] The effectiveness of seismic wave excitation is closely related to the physical properties of the excitation rocks. In complex areas such as piedmont zones, the surface distribution includes rigid, dense, low-quality excitation rocks represented by limestone, dolomite, igneous rocks, and calcareous cemented rocks; plastic, low-quality excitation rocks represented by Quaternary undercompacted loose sandstone and loose sedimentary layers; and elastic, high-quality excitation rocks represented by clastic rocks. Surface excitation conditions vary greatly, and low-quality excitation rocks are widely distributed. Therefore, selecting optimal and favorable excitation sites is crucial for obtaining high-quality seismic data. Conventional near-surface structure survey methods such as micrologging are difficult to effectively observe near-surface structure and excitation condition variations due to low sampling density and the underdeveloped three-layer structure in complex near-surface areas. In recent years, the method of inverting apparent shear wave velocity profiles using micro-motion detection technology has been tested and applied in surface structure surveys and excitation point selection. The principle is to obtain the S-wave velocity structure through inversion using Rayleigh surface wave dispersion curves. This method has shown some effectiveness in surveying the surface structure of undercompacted loose Quaternary layers. However, the development of surface waves is subject to strict geological conditions; therefore, micro-motion technology has limited application conditions. In complex areas where dense, rigid rocks such as carbonate rocks are exposed, surface waves are often underdeveloped, making it difficult to effectively characterize the surface velocity structure. More importantly, its correlation and sensitivity with excitation effects are low, making it difficult to guide the selection of favorable excitation points.

[0004] The resistivity of rocks is strongly correlated with the quality of seismic wave excitation; resistivity effectively indicates and distinguishes seismic wave excitation quality, forming the technical basis of this invention. The key advantage of using electrical resistivity methods to identify and pinpoint favorable seismic wave excitation sites is that it eliminates the need for extensive near-surface surveys such as micro-logging, as well as large-scale surface lithology investigations and excitation lithology tests. The high-density resistivity method offers advantages such as convenient fieldwork, low cost, high efficiency, high exploration accuracy, large depth, multi-parameter detection, rich information, and easy interpretation. By using electrical resistivity methods to determine and optimize the deployment of seismic wave excitation points, avoiding unfavorable excitation sites, the signal-to-noise ratio and imaging quality of seismic data in complex areas can be significantly improved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining favorable seismic wave excitation sites in seismic exploration using electrical exploration, aiming to solve the problem of selecting favorable seismic wave excitation sites in complex surface lithology outcrops.

[0006] To achieve the goal of using electrical resistivity tomography to determine favorable seismic wave excitation locations in seismic exploration, this invention adopts the following technical solution: A method for determining favorable seismic wave excitation locations in seismic exploration using electrical exploration includes the following steps: Step 1, Deployment of Electrical Resonance Detection Lines: Before 2D and 3D seismic field acquisition, deploy electrical resonance detection lines along the theoretical shot line of the seismic exploration area to be carried out. The electrical resonance detection lines coincide with the theoretical shot line of the seismic exploration area to be carried out. Step 2, Field data acquisition of electrical resistivity data: Using electrical resistivity exploration technology, obtain shallow resistivity or electrical properties-related data of the area to be seismically explored; Step 3, Electrical data processing and inversion imaging: Using the obtained data, obtain resistivity profiles or planar distribution results of the area to be explored for seismic exploration, which reflect the characteristics of the underground electrical structure. Step 4, Determination of the resistivity threshold for favorable to relatively favorable earthquake excitation: Based on resistivity profile or planar distribution results, determine the resistivity threshold for favorable to relatively favorable earthquake excitation. Step 5: Delineate candidate favorable to relatively favorable seismic wave excitation zones on the resistivity profile or planar distribution results: Delineate the area within the resistivity threshold range on the resistivity profile or planar distribution results as candidate favorable to relatively favorable seismic wave excitation zones. Step 6, optimize shot point deployment in candidate favorable to relatively favorable seismic excitation zones: taking into account the uniformity of shot point distribution, design and optimize shot point deployment in candidate favorable to relatively favorable seismic excitation zones using densification and variation methods.

[0007] In step 1, electrical exploration refers to a near-surface detection method where the survey results are resistivity or electrical profiles and planar distribution results.

[0008] Step 4 specifically involves: The distribution of shallow resistivity on resistivity profiles or plane distribution results should be considered in a balanced way. Seismic exploration requires both good excitation effect and a certain degree of uniformity in shot point deployment. The area to be explored should be divided into high-value shallow resistivity zone, medium-value shallow resistivity zone, and low-value shallow resistivity zone along the shot line resistivity profiles or plane distribution results. Thresholds were selected for the high resistivity region, the medium resistivity region, and the low resistivity region in the shallow layer. The threshold of the shallow resistivity median zone is determined as the resistivity threshold for favorable to relatively favorable seismic wave excitation.

[0009] The shallow high resistivity zone, shallow medium resistivity zone, and shallow low resistivity zone correspond to the following three types of rock distribution areas: I, II, and III. The specific classification criteria are as follows: Class I consists of dense, rigid rock outcrops composed of unweathered carbonate rocks, igneous rocks, and gypsum-salt rocks, as well as rigid rocks composed of unweathered chemical rocks, igneous rocks, and dense sandstone cemented by calcareous materials. These rocks are characterized by their density, lack of pores and fissures, and high strata velocity, and are classified as shallow areas with high resistivity. Class II consists of clastic rock overburden areas with well-consolidated rock-forming mineral grains and developed pores, and semi-weathered to weathered sections in rigid carbonate strata that have been modified by faults and fracture fluids, as well as local clastic rock interlayers in rigid and dense rock strata. Its lithology includes: first, clastic rocks with a certain porosity due to the consolidation of rock-forming mineral grains after a certain degree of compaction; second, local sections in areas where large areas of rigid strata such as carbonate rocks have been modified by fracture water seepage, and local clastic rock interlayers in rigid strata, which are classified as shallow median resistivity zones. Class III consists of under-compacted Quaternary Holocene colluvial and alluvial deposits, loose sandstone-covered areas, and collapse deposits. Its characteristic is that the newly deposited rock layers have not undergone effective compaction and are classified as shallow low resistivity areas.

[0010] The resistivity of the shallow high resistivity region is greater than 1000 Ω·m; the resistivity of the shallow medium resistivity region is greater than or equal to 10 Ω·m and less than or equal to 1000 Ω·m; the resistivity of the shallow low resistivity region is greater than or equal to 0 Ω·m and less than 10 Ω·m.

[0011] In step 4, the resistivity threshold for favorable to relatively favorable seismic wave excitation is greater than or equal to 10 Ω·m and less than or equal to 1000 Ω·m.

[0012] The resistivity threshold for favorable to relatively favorable earthquake excitation can be selected as greater than or equal to 20 Ω·m and less than or equal to 900 Ω·m.

[0013] In step 6, the principle for optimizing the deployment of firing points is to ensure both good firing point activation effect and to maintain a certain degree of uniformity in the distribution of firing points along the firing line.

[0014] The term "good excitation effect" refers to the acquisition of seismic data with strong reflection energy and high signal-to-noise ratio; the term "uniformity of shot point distribution along the shot line" refers to avoiding large-scale gaps in shot point deployment on the ground, ensuring that the number of coverages caused by empty shot points is not less than three-quarters of the designed number of coverages, so as to ensure that the shot-receiver distance distribution within the surface gather is uniform and that the number of coverages of common center points or common reflection points is uniform.

[0015] The present invention has the following beneficial technical effects: Based on this invention, in complex areas such as the piedmont zone, seismic triggering points were selected and optimized, resulting in the best optimized deployment scheme for shot points and high-quality seismic acquisition data. This overcomes the problems of low signal-to-noise ratio, weak energy, and poor imaging quality in seismic data from complex areas like the piedmont zone, significantly improving the quality of seismic data in complex areas and thus greatly enhancing the imaging quality and accuracy of seismic exploration. Simultaneously, the requirement for a certain degree of uniformity in shot point distribution prevents large gaps from appearing on the seismic profile. Attached Figure Description

[0016] Figure 1 It is a typical shot cluster in the outcropping area of ​​the piedmont thrust carbonate rock and the outcropping area of ​​the foreland clastic rock. Figure 1 (a) is a typical shot collection in an area where rigid strata such as limestone are exposed over a large area; Figure 1 (b) is a typical shot collection in an area where large areas of sandstone, mudstone and other clastic rocks are exposed; Figure 2 This is a flowchart illustrating the method of using electrical exploration to determine favorable seismic wave excitation locations in seismic exploration. Figure 3 It is a schematic diagram showing the distribution and identification of high, medium and low resistivity regions on the resistivity profile. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] See Figure 2 The method of determining favorable seismic wave excitation locations for seismic exploration using electrical exploration according to the present invention includes steps 1 to 6.

[0019] Step 1, Deployment of Electrical Resistivity Survey Lines: Before 2D and 3D seismic field acquisition, deploy electrical resistivity survey lines along the theoretical shot points of the area to be explored. These lines coincide with the theoretical shot points of the area. The purpose is to obtain the resistivity or electrical profile of the area to be explored along the theoretical shot points using electrical methods. Electrical methods are highly sensitive to physical properties such as lithology, porosity, water content, and weathering intensity. Electrical methods can be classified into DC methods (steady field), transition field methods (time field), and AC methods (alternating field). Among them, high-density resistivity methods and audio-frequency magnetotelluric sounding, among other electrical sounding methods, obtain the electrical structure of the subsurface medium by injecting current underground and measuring the subsurface electric field. High-density resistivity (HDR) and audio-frequency magnetotelluric (AFM) sounding are widely used in mineral exploration due to their advantages of convenient construction, stable results, and high resolution. When using HDR, the electrical resistivity data collected is HDR data. Compared with traditional resistivity methods, HDR offers advantages such as convenient field construction, low cost, high efficiency, high exploration accuracy, large depth, multi-parameter detection, rich information, and easy interpretation.

[0020] Step 2, Field Data Acquisition of Electrical Resistivity: Electrical resistivity exploration techniques are used to obtain shallow resistivity or electrical properties data for the area to be explored during seismic exploration. Different electrical resistivity exploration methods employ different field data acquisition and observation methods. High-density resistivity methods, an array exploration method, only require placing all electrodes (dozens to hundreds) at the measuring points during field measurements. Data can then be rapidly and automatically acquired using a programmable electrode switch and a computer-controlled engineering electrical measuring instrument.

[0021] Step 3, Electrical data processing and inversion imaging: Using the results data, obtain resistivity profiles or planar distribution results of the area to be explored for seismic exploration, which reflect the characteristics of the underground electrical structure.

[0022] High-density resistivity method data processing includes initial data noise suppression, subsequent forward and inverse parameter adjustment, and output and mapping of results. After the electrical resistivity measurement results are fed into a microcomputer, the data is processed to generate various geoelectric sections or profiles reflecting the underground electrical structure. With the development of computer technology and forward and inverse methods, the high-density resistivity method data processing and imaging methods have been continuously improved and perfected, resulting in processing results that more closely approximate the characteristics of the underground electrical structure.

[0023] Since the apparent resistivity difference between rigid strata (such as limestone and igneous rocks) and clastic rock outcrops can be several orders of magnitude, in order to highlight the difference in resistivity variation on the electrical profile and facilitate the identification and differentiation of resistivity changes, the rigid strata (such as carbonate rocks and igneous rocks) outcrops and the elastic strata (such as sandstone, mudstone and other clastic rocks) outcrops can be segmented and the electrical profile can be displayed segment by segment.

[0024] Step 4, Determination of the resistivity threshold for favorable to relatively favorable seismic excitation: See [link to relevant documentation] Figure 3 Based on resistivity profiles or planar distribution results, the resistivity threshold for favorable to relatively favorable seismic induction is determined. Specifically, considering the shallow resistivity distribution on the resistivity profiles or planar distribution results, and balancing the need for good induction effects with the requirement for a certain degree of uniformity in shot point deployment, the seismic exploration area to be explored is divided into shallow resistivity high-value areas, shallow resistivity medium-value areas, and shallow resistivity low-value areas along the shot line resistivity profiles or planar distribution results. Thresholds for the shallow resistivity high-value areas, shallow resistivity medium-value areas, and shallow resistivity low-value areas are selected; the threshold for the shallow resistivity medium-value area is determined as the resistivity threshold for favorable to relatively favorable seismic induction.

[0025] The shallow resistivity high value area, shallow resistivity medium value area, and shallow resistivity low value area correspond to the following three types of rock distribution areas: I, II, and III. The specific classification criteria are as follows: Class I consists of dense, rigid rock outcrops composed of unweathered carbonate rocks, igneous rocks, and gypsum-salt rocks, as well as rigid rocks composed of unweathered chemical rocks, igneous rocks, and dense sandstone cemented by calcareous materials. These rocks are characterized by their density, lack of pores and fissures, and high strata velocity, and are classified as shallow areas with high resistivity. Class II consists of clastic rock overburden areas with well-consolidated rock-forming mineral grains and developed pores, and semi-weathered to weathered sections in rigid carbonate strata that have been modified by faults and fracture fluids, as well as local clastic rock interlayers in rigid and dense rock strata. Its lithology includes: first, clastic rocks with a certain porosity due to the consolidation of rock-forming mineral grains after a certain degree of compaction; second, local sections in areas where large areas of rigid strata such as carbonate rocks have been modified by fracture water seepage, and local clastic rock interlayers in rigid strata, which are classified as shallow median resistivity zones. Class III consists of undercompacted Quaternary Holocene colluvial and alluvial deposits, loose sandstone-covered areas, and caving deposits. Its characteristic is that the newly deposited rock layers have not undergone effective compaction. For example, it is a section composed of unconsolidated or poorly consolidated loose sandstone, clay, soft soil, rheological soil, and gravel layers. The rocks are prone to rheology and undergo plastic deformation under the impact of external forces, failing to undergo effective elastic strain. This is classified as a shallow low resistivity zone.

[0026] Seismic triggering wells are generally shallow, less than 30m deep. Based on the resistivity distribution in the shallow layer on the resistivity profile, and considering the need for both good triggering effects and a certain degree of uniformity in the deployment of trigger points, thresholds are rationally selected to delineate high-resistivity, mid-resistivity, and low-resistivity zones in the shallow layer. The mid-resistivity zone in the shallow layer on the resistivity profile represents a favorable to relatively favorable seismic triggering area. Based on previous seismic acquisition experiments in the western Sichuan piedmont region, the resistivity ρ value in the favorable to relatively favorable seismic triggering area is in the range of 10–1000 Ω·m, i.e., 10 Ω·m ≤ ρ ≤ 1000 Ω·m, indicating good seismic triggering effects. However, due to differences in geological targets, surface lithology exposure, and variations, the thresholds for delineating resistivity zones can fluctuate slightly in different regions or even among different lithological outcrops within the same region.

[0027] In step 4, the threshold for dividing resistivity intervals can fluctuate to some extent, depending on the different needs of the geological targets of seismic exploration and the actual distribution of exposed surface rocks. For example, in the seismic exploration area where the distribution area of ​​shallow high resistivity and extremely low resistivity is small, the well location can be selected with higher standards, and the resistivity threshold for favorable to relatively favorable seismic excitation can be set to greater than or equal to 20 Ω·m and less than or equal to 900 Ω·m.

[0028] In step 4, since the depth of the seismic blasting well is generally less than 30m, the determination of the threshold values ​​for the shallow resistivity high value zone, the shallow resistivity medium value zone, and the shallow resistivity low value zone mainly considers the distribution of shallow resistivity values ​​along the survey line.

[0029] In step 4, the determination of the threshold values ​​for the high-value shallow resistivity zone, the medium-value shallow resistivity zone, and the low-value shallow resistivity zone needs to balance the principle that seismic exploration requires both a good excitation effect and that the deployment of shot points needs to maintain basic uniformity.

[0030] In step 4, when the seismic shot line is located in a complex area such as the piedmont zone, for example, when it simultaneously crosses a large area of ​​rigid carbonate rock strata and a large area of ​​elastic clastic rock strata, the threshold values ​​for the high-value shallow resistivity zone, the medium-value shallow resistivity zone, and the low-value shallow resistivity zone can be selected in segments.

[0031] The determination of the resistivity threshold for favorable to relatively favorable seismic excitation is to identify favorable to relatively favorable seismic wave excitation sites in rigid, high-resistivity carbonate and igneous rock strata, which are formed by mudstone interlayers or by weathering of cracks; to identify local high-resistivity unfavorable seismic wave excitation sites in elastic clastic rock strata such as sandstone and mudstone (e.g., sandstone with calcareous filling and cementation, and dense quartz sandstone); and to identify local low-resistivity unfavorable seismic wave excitation sites in undercompacted loose sandstone, Quaternary Holocene alluvial and diluvial deposits.

[0032] (1) The shallow resistivity high value area (resistivity greater than 1000 Ω·m) corresponds to the outcrop area of ​​dense rigid rocks such as unweathered carbonate rocks, igneous rocks, and gypsum-salt rocks, and the seismic wave excitation effect is poor. Unweathered chemical rocks (such as carbonate rocks), igneous rocks (such as granite and basalt), dense sandstone cemented by calcareous cement, and other rigid rocks are characterized by undeveloped or zero porosity. The conversion ratio of explosive shock waves to elastic waves is small, the seismic excitation effect is the worst, and the high-frequency interference is strong. On the electrical profile, it is a shallow resistivity high value area, which is an unfavorable location for seismic wave excitation.

[0033] (2) The shallow median resistivity zone (resistivity greater than or equal to 10 Ω·m and less than or equal to 1000 Ω·m) generally corresponds to the clastic rock cover area with well-consolidated rock-forming mineral particles and developed pores, as well as the semi-weathered to weathered parts and clastic rock interlayers in rigid strata that have been locally modified by faults and fracture fluids, and the seismic wave excitation effect is good. Clastic rocks such as sandstone and mudstone with good mineral particle consolidation and medium porosity after compaction, as well as the parts of rigid rock outcrops that have been locally modified by fracture water and pore water and the clastic rock interlayers, have a high energy conversion rate of explosive shock waves to elastic waves, and the best seismic excitation effect. On the electrical profile, it is shown as a median resistivity zone, which is a favorable location for seismic wave excitation.

[0034] (3) Shallow low resistivity zone (resistivity greater than or equal to 0 Ω·m and less than 10 Ω·m), generally corresponds to undercompacted Quaternary Holocene colluvial and alluvial deposits and loose sandstone cover. It is composed of unconsolidated or poorly consolidated, high-porosity loose sandstone, clay, soft soil, rheological soil and gravel layers. Under the impact of external forces, the rock undergoes inelastic strain or plastic deformation. The energy conversion rate of explosive shock wave to elastic wave is low, the seismic excitation energy is low, and the low and medium frequency linear interference is heavy. On the electrical profile, it is a shallow low resistivity zone, which is an unfavorable location for seismic wave excitation.

[0035] The resistivity of the excitation sites for favorable to relatively favorable earthquakes can be predefined as 10 Ω·m ≤ ρ ≤ 1000 Ω·m. Different regions have different geological requirements for seismic exploration, and the exposure of rigid surface rocks varies, so the resistivity threshold for classifying favorable to relatively favorable earthquake excitation can have some fluctuation. While ensuring the uniformity of excitation point distribution, a higher standard can be adopted, with the resistivity threshold for favorable to relatively favorable earthquake excitation being greater than or equal to 20 Ω·m and less than or equal to 900 Ω·m, in order to obtain higher quality seismic data.

[0036] Step 5: Delineate candidate favorable to relatively favorable seismic wave excitation zones on the resistivity profile or planar distribution results: On the resistivity profile or planar distribution results, delineate the area within the resistivity threshold range as candidate favorable to relatively favorable seismic wave excitation zones. On the resistivity profile or planar distribution results, after excluding areas with high and low resistivity values, delineate the area within the resistivity threshold range that belongs to favorable to relatively favorable seismic excitation as candidate favorable to relatively favorable seismic wave excitation areas.

[0037] Step 6: Optimize shot point deployment in candidate favorable to relatively favorable seismic excitation zones: While ensuring the uniformity of shot point distribution, design and optimize shot point deployment using densification and variation methods in candidate favorable to relatively favorable seismic excitation zones. Obtain the optimal shot point deployment scheme and high-quality seismic acquisition data. This method yields seismic profiles that ensure relatively uniform coverage without large-scale gaps in the profile, while also providing high-quality seismic profile imaging results.

[0038] The principle for optimizing shot point deployment is to ensure both good shot point excitation effect and a certain degree of uniformity in shot point distribution along the shot line. Good excitation effect refers to the acquisition of seismic data with strong reflection energy and a high signal-to-noise ratio. A certain degree of uniformity in shot point distribution along the shot line means avoiding large-scale gaps in shot point deployment on the ground, ensuring that the number of coverages caused by empty shot points is no less than three-quarters of the designed coverage, ensuring uniformity in the distribution of shot-receiver offsets within the gather and uniformity in the distribution of coverages at common midpoints or common reflection points, and reducing gaps in the seismic profile that could affect the geological interpretation of the target layer.

[0039] Technical principle of the invention: The resistivity of rocks is highly correlated with the quality of seismic wave excitation, and the resistivity can well indicate the quality of seismic wave excitation, which is the technical basis of this invention.

[0040] Except for some special lithofacies (such as undercompacted Quaternary rocks, loose sandstone, and dense rigid rocks), rocks generally exhibit elastic properties. Typically, mechanical vibrations generated in rocks can be considered as elastic vibrations in an elastic medium. Seismic waves, which are mechanical waves propagating in an elastic medium, can also be considered as elastic waves propagating in rock strata. The study of the relationship between seismic wave characteristics and source characteristics is called the seismic wave excitation problem. The seismic wave excitation effect of an explosive source, i.e., the energy spectrum characteristics of seismic waves generated by rock blasting, is determined by the physical properties of the rock, namely, rock type, composition, hardness, density, porosity, and water content, and is particularly affected by the degree of consolidation, density, porosity, and water content of the rock-forming minerals. Except for extreme cases where the resistivity is extremely low due to the abundance of highly conductive minerals such as iron, copper, graphite, and cassiterite, the elastic wave excitation effect of rocks by explosive sources has a good correlation with their electrical characteristics. Therefore, electrical profiles can be used to determine favorable seismic wave excitation sites.

[0041] The resistivity of common rocks is shown in the table below.

[0042]

[0043] Before commencing seismic exploration field acquisition projects, electrical resistivity survey lines are deployed along the theoretical seismic shot lines to obtain electrical profiles. Electrical profiles effectively reflect rock type and physical property variations. The seismic excitation effect is most significantly influenced by the degree of consolidation, density, porosity, and water content of the rock-forming minerals, which correspond well to resistivity characteristics. High-density resistivity methods, in particular, offer advantages such as convenient field construction, low cost, high efficiency, high exploration accuracy, large depth, multi-parameter detection, rich information, and convenient interpretation. In practice, in seismic exploration projects in the southern piedmont zone, comparative analysis with single-shot quality showed that shot gathers excited in the median resistivity region exhibited excellent quality, while shot gathers excited in high-resistivity and extremely low-resistivity regions often showed weak energy and low signal-to-noise ratio. This confirms the feasibility and effectiveness of using electrical profiles to determine and optimize favorable seismic wave excitation locations.

[0044] The surface of the thrust plate in the piedmont zone exposes Permian and Triassic limestone, dolomite, and other carbonate rocks, as well as a small amount of igneous rocks. The lithology is dense, representing typical rigid strata, resulting in generally poor seismic wave excitation and difficulty in obtaining high-quality seismic data. However, comparative analysis of shot gather data reveals that one-quarter to one-third of the area still yields relatively good seismic data. These areas with higher-quality seismic wave excitation are often associated with rigid, dense faults, well-developed fractures, long-term seepage and weathering of groundwater along fractures, and the transformation of rigid strata into viscoelastic media. These areas also coincide well with locally relatively low resistivity sections on the electrical resistivity profile. These locally relatively low resistivity sections on the electrical resistivity profile represent favorable local seismic wave excitation sites within the rigid strata outcrop area of ​​the thrust plate.

[0045] The conditions for seismic excitation directly determine the conversion rate of explosive source energy into seismic elastic waves, and thus directly determine the quality of seismic data. Electrical resistivity profiling in complex areas such as piedmont zones shows a strong correlation between shallow resistivity values ​​obtained from electrical exploration and the seismic wave excitation effect. Unweathered carbonate rocks and other dense, rigid rock strata have poor coupling with explosive seismic sources, resulting in a low conversion rate of explosive source energy to seismic elastic waves and poor data quality, corresponding to areas with high shallow resistivity. Undercompacted, unconsolidated rock strata, represented by Quaternary colluvial-alluvial deposits and loose sandstone, exhibit plastic characteristics and fail to undergo elastic strain and generate elastic waves under external forces, making them unfavorable locations for seismic wave excitation, corresponding to areas with low shallow resistivity. Regions represented by Mesozoic-Cenozoic clastic rocks within basins, as well as areas where rigid carbonate strata have been weathered by long-term groundwater seepage and clastic interlayers within rigid rock masses, exhibit rock physics characteristics of elastic media. The conversion rate of explosive source energy to seismic elastic waves is generally excellent, resulting in good seismic excitation effects, corresponding to areas with medium resistivity.

[0046] In the foreland clastic rock outcrops within the basin, high-resistivity sections with localized carbonate rock interlayers and extremely low-resistivity sections with localized Quaternary and loose sandstone interlayers are unfavorable locations for seismic wave excitation and should be avoided in the deployment of seismic excitation points.

[0047] This invention utilizes electrical resistivity tomography (EDT) profiles to effectively and intuitively identify localized low-resistivity seismic wave excitation sites within large areas of rigid rock in thrust zones. It also identifies high-resistivity localized dense, rigid limestone or calcareous interlayers in outcrops of foreland clastic rocks, as well as undercompacted, low-resistivity sites such as loose sandstone, colluvial deposits, and alluvial deposits, which are unfavorable for seismic wave excitation. Based on this, optimal shot locations are selected for deployment in medium- to low-resistivity areas, effectively improving seismic excitation energy, profile quality, and imaging effects.

[0048] When collecting seismic data in complex areas such as the piedmont zone, seismic survey lines cross areas of rigid strata exposed by thrust sheets and areas of clastic rock exposed by basin margins. Seismic data quality is generally poor in areas of rigid strata exposed, but good seismic excitation and data quality can still be obtained in local clastic interlayers and weathered areas modified by fracture water, accounting for about 1 / 4 to 1 / 3 of the rigid strata exposed area. In areas of elastic strata exposed by basin margins such as clastic rocks, seismic data quality is generally good, but in 1 / 4 to 1 / 3 of the area, due to undercompacted rock layers exhibiting plastic rock characteristics such as collapsed deposits, loose sandstone, and Quaternary colluvial deposits, as well as local sections of rigid rock layers covered by calcareous interlayers and dense sandstone, the seismic wave excitation effect is very poor. The purpose of this invention is to utilize electrical exploration results to identify a small number of locally favorable seismic excitation sites in large-scale rigid strata exposed areas for full utilization, and to identify and avoid locally unfavorable seismic excitation sites in large-scale clastic rock elastic rock development areas. By optimizing the design and deployment of shot points, the signal-to-noise ratio and imaging quality of seismic data can be improved as a whole while ensuring a relatively uniform distribution of shot points.

[0049] Taking the seismic exploration of the southern piedmont zone as an example, see Figure 1The seismic exploration area spans the thrust belt and the piedmont basin margin, with drastic changes in near-surface structure and lithology. The near-surface characteristics are as follows: (1) On the thrust body, the seismic exploration excitation effect is generally poor in areas where large areas of dense and rigid strata such as carbonate rocks and calcareous clastic rocks are exposed. The resistivity is generally high in the electrical resistivity profile, but there are low-resistivity areas in the carbonate rocks inside that have been modified and weathered by fissure water seepage, as well as local argillaceous clastic rock interlayers. These are local areas that are conducive to seismic wave excitation. The low-resistivity anomaly areas can be well identified by the electrical resistivity profile. (2) The foreland basin margin area appears to be a large area of ​​Mesozoic and Cenozoic clastic rocks exposed, but the following two unfavorable excitation sections are developed: (a) The clastic rock area has a large number of limestone interlayers, or dense limestone sandstone and conglomerate layers cemented by limestone, which show high resistivity on the electrical profile, and is a high-resistivity section that is unfavorable for local earthquake excitation in the favorable area; (b) The clastic rock distribution area has a large number of Quaternary undercompacted colluvial and alluvial layers and loose sandstone, which show extremely low resistivity on the electrical profile. The rocks are loose and easily broken, and are plastic media, which are also extremely low resistivity parts that are unfavorable for earthquake wave excitation. Figure 1 (a) is a typical shot gathering in a large area of ​​rigid strata such as limestone. The seismic data generally have the characteristics of weak energy, strong interference wave energy, very low signal-to-noise ratio, and basically no reflected wave. However, in these areas, 1 / 4 to 1 / 3 of the local areas can still obtain high-quality seismic data. These areas can be identified through electrical resistivity tomography results and shot points can be deployed in a priority manner to improve the signal-to-noise ratio of the data. Figure 1 (b) is a typical shot gathering area with large areas of exposed sandstone, mudstone and other clastic rocks. The seismic data generally have the characteristics of strong energy in the shot gathering, weak or undeveloped interference wave energy, high signal-to-noise ratio and strong reflected wave energy. However, in these areas, the seismic data obtained in 1 / 4 to 1 / 3 of the local areas is of very low quality. This can be identified through electrical resistivity tomography results, and the shot point deployment can be optimized to reduce the amount of low-quality shot gathering data. Through the above methods, the signal-to-noise ratio of seismic acquisition data in complex areas such as the piedmont zone can be improved as a whole.

[0050] Advantages of this invention: (1) This invention is a new discovery based on the analysis and research of seismic acquisition data in the southern piedmont zone, and on the quantitative analysis of seismic data obtained from different lithologies such as thrust bodies in the piedmont zone. Its outstanding features are: it does not require extensive near-surface surveys such as micro-logging, extensive surface lithology surveys and lithology testing, or cumbersome core sampling and analysis. It can determine favorable seismic wave excitation locations using only electrical properties. Moreover, the high-density resistivity method has the advantages of high sampling rate and strong planar continuity along the shot line, which can more accurately reflect changes in near-surface physical structure and make the selection of excitation points more accurate. It is not only highly accurate, but also efficient, accurate and applicable. It provides a new method for selecting and deploying shot points to improve the seismic excitation effect and obtain high-quality data and imaging quality in complex areas in the future. (2) The present invention requires that the distribution of shot points has a certain degree of uniformity, thus preventing large gaps from appearing on the seismic profile; (3) The present invention uses electrical exploration to determine favorable excitation sites, which has the advantages of convenient field construction, low cost, high work efficiency, high exploration accuracy, rich information, intuitive and effective, and easy interpretation; (4) The present invention can better implement the near-surface electrical structure along the seismic survey line. Its resistivity value can well indicate the favorable and unfavorable seismic wave excitation locations along the seismic exploration shot line, thereby effectively guiding the optimized deployment of seismic excitation shot points, improving the quality of seismic data and imaging effect, especially in complex lithological outcrop areas such as the piedmont zone.

Claims

1. A method for determining favorable seismic wave excitation locations in seismic exploration using electrical exploration, characterized in that, Includes the following steps: Step 1, Deployment of Electrical Resonance Detection Lines: Before 2D and 3D seismic field acquisition, deploy electrical resonance detection lines along the theoretical shot line of the seismic exploration area to be carried out. The electrical resonance detection lines coincide with the theoretical shot line of the seismic exploration area to be carried out. Step 2, Field data acquisition of electrical resistivity data: Using electrical resistivity exploration technology, obtain shallow resistivity or electrical properties-related data of the area to be seismically explored; Step 3, Electrical data processing and inversion imaging: Using the obtained data, obtain resistivity profiles or planar distribution results of the area to be explored for seismic exploration, which reflect the characteristics of the underground electrical structure. Step 4, Determination of the resistivity threshold for favorable to relatively favorable earthquake excitation: Based on resistivity profile or planar distribution results, determine the resistivity threshold for favorable to relatively favorable earthquake excitation. Step 5: Delineate candidate favorable to relatively favorable seismic wave excitation zones on the resistivity profile or planar distribution results: Delineate the area within the resistivity threshold range on the resistivity profile or planar distribution results as candidate favorable to relatively favorable seismic wave excitation zones. Step 6, optimize shot point deployment in candidate favorable to relatively favorable seismic excitation zones: taking into account the uniformity of shot point distribution, design and optimize shot point deployment in candidate favorable to relatively favorable seismic excitation zones using densification and variation methods.

2. The method for determining favorable seismic wave excitation locations using electrical exploration according to claim 1, characterized in that, In step 1, electrical exploration refers to a near-surface detection method where the survey results are resistivity or electrical profiles and planar distribution results.

3. The method for determining favorable seismic wave excitation locations using electrical exploration according to claim 1, characterized in that, Step 4 specifically involves: The distribution of shallow resistivity on resistivity profiles or plane distribution results should be considered in a balanced way. Seismic exploration requires both good excitation effect and a certain degree of uniformity in shot point deployment. The area to be explored should be divided into high-value shallow resistivity zone, medium-value shallow resistivity zone, and low-value shallow resistivity zone along the shot line resistivity profiles or plane distribution results. Thresholds were selected for the high resistivity region, the medium resistivity region, and the low resistivity region in the shallow layer. The threshold of the shallow resistivity median zone is determined as the resistivity threshold for favorable to relatively favorable seismic wave excitation.

4. The method for determining favorable seismic wave excitation locations using electrical resistivity tomography according to claim 3, characterized in that, The shallow high resistivity zone, shallow medium resistivity zone, and shallow low resistivity zone correspond to the following three types of rock distribution areas: I, II, and III. The specific classification criteria are as follows: Class I consists of dense, rigid rock outcrops composed of unweathered carbonate rocks, igneous rocks, and gypsum-salt rocks, as well as rigid rocks composed of unweathered chemical rocks, igneous rocks, and dense sandstone cemented by calcareous materials. These rocks are characterized by their density, lack of pores and fissures, and high strata velocity, and are classified as shallow areas with high resistivity. Class II consists of clastic rock overburden areas with well-consolidated rock-forming mineral grains and developed pores, and semi-weathered to weathered sections in rigid carbonate strata that have been modified by faults and fracture fluids, as well as local clastic rock interlayers in rigid and dense rock strata. Its lithology includes: first, clastic rocks with a certain porosity due to the consolidation of rock-forming mineral grains after a certain degree of compaction; second, local sections in areas where large areas of rigid strata such as carbonate rocks have been modified by fracture water seepage, and local clastic rock interlayers in rigid strata, which are classified as shallow median resistivity zones. Class III consists of under-compacted Quaternary Holocene colluvial and alluvial deposits, loose sandstone-covered areas, and collapse deposits. Its characteristic is that the newly deposited rock layers have not undergone effective compaction and are classified as shallow low resistivity areas.

5. The method for determining favorable seismic wave excitation locations using electrical resistivity tomography according to claim 3, characterized in that, The resistivity of the shallow high resistivity region is greater than 1000 Ω·m; the resistivity of the shallow medium resistivity region is greater than or equal to 10 Ω·m and less than or equal to 1000 Ω·m; the resistivity of the shallow low resistivity region is greater than or equal to 0 Ω·m and less than 10 Ω·m.

6. The method for determining favorable seismic wave excitation locations using electrical exploration according to claim 1, characterized in that, In step 4, the resistivity threshold for favorable to relatively favorable seismic wave excitation is greater than or equal to 10 Ω·m and less than or equal to 1000 Ω·m.

7. The method for determining favorable seismic wave excitation locations using electrical exploration according to claim 6, characterized in that, The resistivity threshold for favorable to relatively favorable seismic excitation is greater than or equal to 20 Ω·m and less than or equal to 900 Ω·m.

8. The method for determining favorable seismic wave excitation locations for seismic exploration using electrical exploration according to claim 1, characterized in that, In step 6, the principle for optimizing the deployment of firing points is to ensure both good firing point activation effect and to maintain a certain degree of uniformity in the distribution of firing points along the firing line.

9. The method for determining favorable seismic wave excitation locations for seismic exploration using electrical exploration according to claim 8, characterized in that, The term "good excitation effect" refers to the acquisition of seismic data with strong reflection energy and high signal-to-noise ratio; the term "uniformity of shot point distribution along the shot line" refers to avoiding large-scale gaps in shot point deployment on the ground, ensuring that the number of coverages caused by empty shot points is not less than three-quarters of the designed number of coverages, so as to ensure that the shot-receiver distance distribution within the surface gather is uniform and that the number of coverages of common center points or common reflection points is uniform.

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