Igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling

Abstract

The present invention provides a method for igneous rock wave impedance inversion based on combined magnetic and seismic low-frequency modeling. This method comprises the following steps: 1. using multi-scale analysis to strip deep magnetic anomalies and quantitatively obtain residual magnetic anomalies in igneous rocks; 2. analyzing seismic reflection characteristics to characterize the three-dimensional boundary geometry of igneous rocks; 3. performing deep-domain three-dimensional combined magnetic and seismic modeling; 4. constructing a combined magnetic and seismic low-frequency wave impedance model; and 5. performing combined magnetic and seismic wave impedance inversion. This method effectively integrates the respective advantages of magnetic and seismic methods to construct low-frequency and high-resolution wave impedance models of igneous rock development zones, providing a more comprehensive reference for the subsequent detailed description of favorable volcanic reservoirs and the deployment of exploration targets.

Description

Technical Field

[0001] The present invention relates to the field of exploration geophysical technology, and in particular to an igneous rock wave impedance inversion method based on magnetic-seismic combined low-frequency modeling. Background Art

[0002] Igneous rocks are one of the important areas of mineral exploration. However, unlike sedimentary strata, the lithology and lithofacies of igneous rocks change rapidly in space. How to obtain high-precision prediction results has always been a key issue in this exploration field.

[0003] Seismic data is one of the most important techniques in igneous rock exploration. Seismic data typically depicts the geometric morphology of igneous rock lithology and lithofacies, but the same reflection characteristics appear between different igneous rocks, making it difficult to accurately depict lithology and lithofacies. Seismic inversion technology is an important interpretation method for identifying lithofacies, lithology, and reservoirs, and the accuracy of low-frequency model construction is a key factor affecting the reliability of the results. However, in the study area, where volcanic eruption intervals are short and tectonic activity is intense, the spatial distribution of igneous rock wave impedance is often highly heterogeneous, and even wells that are very close to each other in the same formation can experience significant changes. When the number of wells is small, it is difficult to use the layer-by-layer interpolation method used in sedimentary formations to achieve reliable low-frequency model construction.

[0004] Magnetic exploration technology also plays a vital role in igneous rock exploration. Compared to other rocks, igneous rocks not only exhibit high wave impedance but also distinct high magnetic properties. This allows magnetic technology to overcome the difficulty of seismic analysis in distinguishing igneous rock facies and lithology. Furthermore, magnetism is not shielded by strong reflecting interfaces, making it useful for assisting seismic analysis of igneous rock developmental characteristics. However, the challenge is that magnetic data is a superposition of subsurface geological structures, resulting in low vertical resolution.

[0005] In order to integrate the respective advantages of magnetic and seismic technologies, research on joint exploration technology has received widespread attention.

[0006] Chinese patent application CN201510420518.5 discloses a method for comprehensively identifying igneous rocks using gravity, magnetic, electromagnetic, and seismic data. The method includes the following steps: establishing templates for different igneous rocks and formation properties; conducting forward modeling of igneous rocks using gravity, magnetic, electrical, and seismic data to identify response characteristics and patterns; extracting planar gravity and magnetic anomalies from igneous rocks and enhancing weak anomalies to interpret and delineate the planar distribution zones and ranges of igneous rocks; processing and interpreting igneous rock targets using electrical and seismic profile data to identify the vertical distribution patterns of igneous rocks; performing joint profile inversion of gravity, magnetic, electromagnetic, and seismic data to establish a vertical distribution framework for igneous rocks; using the results of the joint profile inversion and drilling data as constraints, and combining the planar distribution of igneous rocks with gravity and magnetic anomalies, three-dimensional inversion of igneous rock properties is performed; and based on the three-dimensional distribution of physical properties and the combined characteristics of different igneous rock properties, the spatial distribution of igneous rocks and the distribution patterns of lithology and lithofacies are comprehensively identified. This method achieves the identification of igneous rocks using multiple data, which is more reliable than igneous rock identification using single data.

[0007] Chinese patent application CN201710865447.9 discloses an igneous reservoir prediction method based on magnetic, seismic and drilling joint simulation inversion. The method comprises the following steps: step 1, performing depth-domain source separation on two-dimensional measured magnetic anomalies to obtain a three-dimensional magnetic data volume, and preliminarily clarifying the distribution trend of igneous rocks at different depths; step 2, performing constrained sparse pulse inversion using seismic data and well logging data to obtain a relatively reliable wave impedance volume that retains the three-dimensional seismic framework; step 3, statistically analyzing the relationship between the magnetic characteristics and wave impedance of different igneous rock lithologies; step 4, performing geostatistical co-simulation inversion based on the sequential Gaussian algorithm, using the magnetic data as the first variable and the wave impedance volume as the second variable, to obtain an initial magnetic inversion result constrained by the three-dimensional seismic framework; step 5, measuring the magnetic susceptibility of the igneous rock core, and fitting the correlation equation between the magnetic susceptibility of the coring section and other well logging curves, thereby constructing a magnetic susceptibility curve for the entire well section using the well logging curves; step 6, performing geostatistical co-simulation using the drilling magnetic susceptibility curve as the first variable and the initial magnetic inversion result obtained in step 4 as the second variable, to obtain a final magnetic inversion result with higher resolution and better fit to the well, and to carry out igneous reservoir prediction.

[0008] Chinese patent application CN201510420518.5 utilizes four types of geophysical data: gravity, magnetic, electric, and seismic. It primarily uses a joint inversion of gravity, magnetic, and electric seismic profiles to establish a vertical distribution framework for igneous rocks, and then uses gravity and magnetic three-dimensional inversion to determine the distribution of volcanic rocks. This patent application, on the other hand, utilizes magnetic technology to establish the low-frequency model required for seismic inversion, obtaining wave impedance information and effectively improving resolution. Chinese patent application CN201710865447.9 utilizes magnetic anomaly separation results, seismic wave impedance inversion results, and well logging data to obtain high-resolution magnetic inversion results using geostatistical methods. However, geostatistical inversion requires a large amount of well logging data and is only applicable to mature exploration areas with abundant well data.

[0009] The above existing technologies are significantly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling. Summary of the Invention

[0010] The purpose of the present invention is to provide an igneous rock wave impedance inversion method based on magnetic-seismic combined low-frequency modeling, which can effectively integrate the respective advantages of magnetism and seismicity to jointly construct a low-frequency model of the igneous rock development area and a high-resolution wave impedance model.

[0011] The object of the present invention can be achieved by the following technical measures: an igneous rock wave impedance inversion method based on magnetic-seismic combined low-frequency modeling, the igneous rock wave impedance inversion method based on magnetic-seismic combined low-frequency modeling comprising:

[0012] Step 1: Use multi-scale analysis to strip away deep magnetic anomalies and quantitatively obtain igneous rock residual magnetic anomalies;

[0013] Step 2: Analyze seismic reflection characteristics and characterize the three-dimensional boundary geometry of igneous rocks;

[0014] Step 3: Conduct deep-domain magnetic-seismic three-dimensional joint modeling;

[0015] Step 4: construct a combined magnetic-seismic low-frequency wave impedance model;

[0016] Step 5: Perform magnetic-seismic combined wave impedance inversion.

[0017] The purpose of the present invention can also be achieved by the following technical measures:

[0018] In step 1, the magnetic anomaly is first separated into multiple scales using continuous wavelet transform, and then the two-dimensional correlation between adjacent scale magnetic anomalies is analyzed to calculate the correlation coefficient curve;

[0019] Secondly, calculate the local extreme points of the correlation coefficient curve;

[0020] Thirdly, the anomalies of multiple scales are separated according to the local extreme points, and the anomalies of different scales between the extreme points are superimposed to obtain multiple separated magnetic anomalies. Among them, the frequency of the separation results of the larger-scale magnetic anomalies is low, reflecting the deep-buried magnetic bodies.

[0021] Finally, according to research needs, the deep magnetic anomaly is stripped to obtain the magnetic anomaly corresponding to the target layer.

[0022] In step 2, first, analyze the reflection characteristics of the seismic phase in the work area. Igneous rocks usually show chaotic, oblique, and blank reflection characteristics, while sedimentary strata usually show more continuous reflection characteristics.

[0023] Secondly, the seismic facies are further subdivided in combination with the drilled well data, and the three-dimensional boundary morphology of the igneous rock boundary is characterized based on the seismic facies characteristics in the three-dimensional work area.

[0024] In step 3, under the constraints of the volcanic rock geometry obtained in step 2, the statistical results of the magnetic susceptibility of igneous rocks in the core and outcrop rocks in the work area are used to provide a reference basis for subsequent joint interpretation; a joint magnetic and seismic interpretation is performed to obtain a detailed three-dimensional spatial distribution of magnetic parameters.

[0025] In step 3, first, the magnetic susceptibility of igneous rocks is measured based on the core and outcrop samples collected near the work area, and the magnetic susceptibility values of different strata and lithologies are statistically calculated;

[0026] Secondly, using the 3D boundary morphology of the igneous rock as a constraint, a 3D magnetic interactive interpretation is carried out to fill the internal igneous rock boundary morphology with magnetic susceptibility values. A 3D magnetic forward modeling is then performed on the 3D grid. The magnetic susceptibility value filling results and the igneous rock boundary geometry are adjusted based on the fitting residuals with the magnetic anomaly separation results of the target layer.

[0027] Again, the process of magnetic susceptibility model modification, forward modeling, and fitting residual calculation is repeated to obtain a refined three-dimensional spatial distribution of magnetic susceptibility.

[0028] In step 4, the correlation between the magnetic susceptibility and wave impedance parameters of the work area is statistically analyzed, and the magnetic susceptibility model in step 3 is converted into a low-frequency wave impedance model.

[0029] In step 4, first, the correlation between the physical properties of magnetic susceptibility and wave impedance parameters of different strata and lithologies in the work area is statistically analyzed;

[0030] Secondly, the three-dimensional magnetic susceptibility model is converted into a depth-domain seismic wave impedance model using the statistical results of physical property correlation.

[0031] In step 5, the depth-domain low-frequency wave impedance waveform obtained in step 4 is converted into time-depth using well-seismic calibration and velocity spectrum data. The depth-domain low-frequency wave impedance model of igneous rock is converted to the time domain, and time-domain seismic inversion is performed to obtain a high-resolution wave impedance model, providing a basis for the detailed characterization of igneous rock lithology.

[0032] In step 5, first, the low-frequency seismic wave impedance waveform in the depth domain is converted into a seismic wave impedance model in the time domain by combining the time-depth data and the three-dimensional velocity spectrum data at the well point;

[0033] Secondly, the converted time-domain seismic impedance model is used as the initial model to carry out seismic impedance inversion under logging constraints to obtain a high-resolution impedance model, thereby providing a basis for the detailed characterization of igneous rock lithology.

[0034] The igneous rock wave impedance inversion method based on combined magnetic and seismic low-frequency modeling in the present invention first obtains a fine three-dimensional magnetic susceptibility inversion result under the constraint of the seismic phase igneous rock geometric morphology prediction results, and then uses it as a low-frequency model to carry out joint inversion of seismic wave impedance. Even without the participation of too much well data, ideal application effects can be obtained, and it has strong applicability for both mature exploration areas and new exploration areas. The present invention can effectively integrate the respective advantages of magnetism and seismicity to jointly construct a technical process of low-frequency model and high-resolution wave impedance model of igneous rock development areas, thereby providing a more sufficient reference basis for the subsequent detailed description of favorable volcanic reservoirs and the deployment of exploration targets. The present invention discloses an igneous rock wave impedance inversion method based on combined magnetic and seismic low-frequency modeling when in new areas with low exploration levels, there is less well data and it is difficult to meet the exploration targets of igneous rocks with strong heterogeneity. Compared with the existing technology, the innovation of the present invention mainly lies in:

[0035] (1) Three-dimensional modeling of magnetic susceptibility based on magnetic-seismic combination. Traditional magnetic susceptibility models are mainly obtained through magnetic anomalies alone. Although the reliability of magnetic susceptibility results can be improved through logging, magnetic susceptibility value boundaries, model focusing, model smoothing and other constraint information in the traditional process, the resulting magnetic susceptibility model has low resolution, and it is difficult to obtain a reliable magnetic susceptibility geological model in areas with many volcanic eruptions and strong late tectonic movements, making it difficult to use for designated oil and gas exploration deployments. The present invention combines the advantages of strong seismic boundary morphology characterization capabilities with the advantages of sensitive magnetic igneous rock lithology responses, and obtains a more refined magnetic susceptibility model through three-dimensional joint interpretation.

[0036] (2) Construction of a low-frequency seismic impedance model based on magnetic and seismic combination. Traditional seismic inversion technology mostly uses a layer-controlled geometric grid combined with well point impedance interpolation to establish a low-frequency model. However, the low-frequency model obtained in this way is not suitable for research targets such as volcanic rocks with rapid vertical and horizontal changes in wave impedance. The obtained inversion results cannot accurately describe the impedance distribution characteristics of volcanic rocks. The present invention fully incorporates magnetic anomaly information, better reflects the lateral lithologic changes of igneous rocks, and can construct a more reliable low-frequency wave impedance model of igneous rocks. Using this as an initial model can greatly improve the reliability of igneous rock seismic inversion and provide a more effective reference basis for subsequent lithologic identification, reservoir prediction and exploration deployment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flowchart of a specific embodiment of the igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling of the present invention;

[0038] Figure 2 A plan view of residual magnetic anomaly of an igneous rock research target in a specific embodiment of the present invention;

[0039] Figure 3 This is a cross-sectional diagram of the results of the combined interpretation of magnetic susceptibility under the constraints of seismic geometry in a specific embodiment of the present invention;

[0040] Figure 4 This is the combined magnetic-seismic seismic wave impedance inversion result and the seismic superposition profile diagram described in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0043] like Figure 1 As shown, Figure 1 This is a flow chart of the igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling of the present invention. It mainly includes the following steps:

[0044] (1) Separation of magnetic anomalies of igneous rock exploration targets. Multi-scale analysis methods are used to separate deep magnetic anomalies and quantitatively obtain the residual magnetic anomalies of igneous rocks.

[0045] (2) Geometric classification of igneous rock seismic facies. Analyze seismic reflection characteristics and characterize the three-dimensional boundary geometry of igneous rocks;

[0046] (3) Deep-domain magnetic and seismic three-dimensional joint modeling. Under the constraints of the volcanic rock geometry obtained in step 2, the magnetic susceptibility statistics of igneous rocks in the work area cores, outcrops, etc. are used to provide a reference for subsequent joint interpretation; magnetic and seismic joint interpretation is performed to obtain a detailed three-dimensional spatial distribution of magnetic parameters;

[0047] (4) Construction of a combined magnetic-seismic low-frequency wave impedance model. Statistically analyze the correlation between the magnetic susceptibility and wave impedance parameters of the work area, and convert the magnetic susceptibility model in step 3 into a low-frequency wave impedance model.

[0048] (5) Combined magnetic and seismic impedance inversion. Using well-seismic calibration and velocity spectrum data, the depth-domain low-frequency impedance waveform obtained in step 4 is converted to time-depth. The depth-domain low-frequency impedance model of igneous rocks is converted to the time domain, and time-domain seismic inversion is performed to obtain a high-resolution impedance model, providing a basis for the detailed characterization of igneous rock properties.

[0049] Example 1:

[0050] In a specific embodiment 1 of the present invention, a method for igneous rock wave impedance inversion based on combined magnetic-seismic low-frequency modeling includes the following steps:

[0051] Step 1: Isolation of magnetic anomalies of igneous rock exploration targets. Multi-scale analysis is used to separate deep magnetic anomalies and quantitatively obtain the residual magnetic anomalies of igneous rocks.

[0052] Firstly, the continuous wavelet transform is used to separate the magnetic anomalies into multiple scales. Then the two-dimensional correlation between the magnetic anomalies at adjacent scales is analyzed and the correlation coefficient curve is calculated.

[0053] Secondly, calculate the local extreme points of the correlation coefficient curve;

[0054] Next, we separate anomalies of multiple scales based on local extreme points, and superimpose the anomalies of different scales between the extreme points to obtain multiple separated magnetic anomalies. Among them, the frequency of separation results of larger-scale magnetic anomalies is low, reflecting the deep-buried magnetic bodies.

[0055] Finally, according to the research needs, the deep magnetic anomaly is stripped to obtain the magnetic anomaly corresponding to the target layer;

[0056] Step 2: Geometric morphology of igneous rock seismic facies: Analyze seismic reflection characteristics and characterize the three-dimensional boundary geometry of igneous rocks.

[0057] First, the reflection characteristics of the seismic phase in the work area are analyzed. Igneous rocks usually show chaotic, oblique, and blank reflection characteristics, while sedimentary strata usually show more continuous reflection characteristics.

[0058] Secondly, the seismic facies are further subdivided based on the drilling data, and the 3D boundary morphology of the igneous rock boundary is characterized based on the seismic facies characteristics within the 3D work area;

[0059] Step 3: Deep-domain 3D joint magnetic and seismic modeling. Constrained by the volcanic rock geometry obtained in Step 2, and based on the magnetic susceptibility statistics of igneous rocks in cores, outcrops, and other locations within the work area, this provides a reference for subsequent joint interpretation. Joint magnetic and seismic interpretation is performed to obtain a detailed 3D spatial distribution of magnetic parameters.

[0060] First, the magnetic susceptibility of igneous rocks was measured based on core and outcrop samples collected near the work area, and the magnetic susceptibility values of different strata and lithologies were statistically calculated;

[0061] Secondly, using the 3D boundary morphology of the igneous rock as a constraint, a 3D magnetic interactive interpretation is carried out to fill the internal igneous rock boundary morphology with magnetic susceptibility values. A 3D magnetic forward modeling is then performed on the 3D grid. The magnetic susceptibility value filling results and the igneous rock boundary geometry are adjusted based on the fitting residuals with the magnetic anomaly separation results of the target layer.

[0062] Thirdly, the process of magnetic susceptibility model modification, forward modeling, and fitting residual calculation is repeated to obtain a precise three-dimensional spatial distribution of magnetic susceptibility.

[0063] Step 4: Construct a combined magnetic-seismic low-frequency wave impedance model. Statistically analyze the correlation between the magnetic susceptibility and wave impedance parameters of the work area, and convert the magnetic susceptibility model from step 3 into a low-frequency wave impedance model.

[0064] First, the correlation between the magnetic susceptibility and wave impedance parameters of different strata and lithologies in the work area was statistically analyzed;

[0065] Secondly, the obtained three-dimensional magnetic susceptibility model is converted into a depth-domain seismic impedance model using the statistical results of physical property correlation.

[0066] Step 5: Combined magnetic and seismic impedance inversion. Using well-seismic calibration and velocity spectrum data, the depth-domain low-frequency impedance waveform obtained in Step 4 is converted to time and depth. The depth-domain low-frequency impedance model of the igneous rock is then converted to the time domain. Time-domain seismic inversion is then performed to obtain a high-resolution impedance model, providing a basis for detailed characterization of the igneous rock lithology.

[0067] First, the low-frequency seismic impedance waveform in the depth domain is converted into a seismic impedance model in the time domain by combining the time-depth data and the three-dimensional velocity spectrum data at the well point.

[0068] Secondly, the converted time-domain seismic impedance model is used as the initial model to perform seismic impedance inversion under well logging constraints to obtain a high-resolution impedance model, thereby providing a basis for the detailed characterization of igneous rock lithology.

[0069] Example 2:

[0070] In the second specific embodiment of the present invention, the specific steps of the igneous rock wave impedance inversion method based on magnetic-seismic combined low-frequency modeling are as follows:

[0071] (1) Separation of magnetic anomalies for igneous rock exploration targets. The measured data were subjected to polarization processing to eliminate the influence of the geomagnetic field. Then, the influence of shallow magnetic bodies was eliminated by three-dimensional forward modeling. Multi-scale analysis was performed, and the deep magnetic anomalies were quantitatively determined using the calculation results of correlation coefficients at different scales and logarithmic power spectrum. The shallow and deep magnetic anomalies were subtracted from the polarized magnetic anomaly to obtain the classification results of magnetic anomaly separation for igneous rock exploration targets.

[0072] (2) Geometry of igneous rock seismic facies. Using the experience of adjacent work areas and existing wells to analyze the seismic response characteristics of different volcanic rocks, a seismic facies analysis was then conducted throughout the work area to characterize the three-dimensional boundary geometry of the igneous rocks.

[0073] (3) Deep domain magnetic and seismic three-dimensional joint modeling. Under the constraints of the geometric morphology of the igneous rock seismic phase, combined with the statistical results of the magnetic susceptibility of igneous rocks in the cores, outcrops, etc. in the work area, a three-dimensional joint interpretation of magnetic and seismic data is performed to ensure that the fitting residual of the magnetic anomaly results of the interpretation model forward model and the magnetic anomaly separation results of the igneous rock exploration target are minimized, thereby determining the three-dimensional spatial distribution of magnetic parameters;

[0074] (4) Construction of a combined magnetic-seismic low-frequency wave impedance model. Based on the fitting formula of the physical property correlation between the magnetic susceptibility and wave impedance parameters of the study area, the magnetic susceptibility model obtained by the deep-domain magnetic-seismic three-dimensional combined modeling is converted into a low-frequency wave impedance model;

[0075] (5) Combined magnetic and seismic impedance inversion. Combining well-seismic calibration and velocity spectrum data, the waveform of the low-frequency impedance model in the depth domain is converted into a low-frequency impedance model in the time domain. The sparse pulse seismic inversion method is then used to perform seismic impedance inversion in the time domain to obtain a high-resolution impedance model for detailed characterization of igneous rock properties.

[0076] Example 3

[0077] The present invention will be further described below with reference to specific embodiments.

[0078] Figure 2 This is a plan view of the residual magnetic anomaly of the igneous rock study target. Multi-scale quantitative separation of the original magnetic anomaly in the study area yielded the igneous rock magnetic anomaly. The separation results reveal a northwest-trending banded distribution of magnetic anomalies, with alternating high and low anomaly zones. This suggests that the igneous rocks were controlled by northwest-trending faults, resulting in fissure-like, banded eruptions.

[0079] Figure 3 This is a cross-section of the combined interpretation of magnetic susceptibility under seismic geometry constraints. Vertically, the igneous rocks are deeply buried and contain a variety of volcanic lithofacies, including explosive, effusive, and volcanic sedimentary facies. Seismic reflections primarily exhibit chaotic and oblique reflections. Based on the seismic reflection signatures, the volcanic boundaries are delineated. Then, based on geometric constraints, the magnetic susceptibility values of the subsurface subdivisions are adjusted. The residual magnetic anomalies of the igneous rock research targets are continuously fitted. After repeated corrections, a deep-domain magnetic susceptibility model is derived.

[0080] Figure 4 This is a combined magnetic-seismic seismic impedance inversion result and a seismic superimposed profile. The correlation between the magnetic susceptibility and impedance parameters in the work area was statistically analyzed to convert the deep-domain magnetic susceptibility model into a low-frequency impedance model. Next, using well-seismic calibration and velocity spectrum data, a time-depth conversion was performed on the obtained deep-domain low-frequency impedance waveform, converting the deep-domain igneous rock low-frequency impedance model to the time domain. Finally, a time-domain seismic inversion was performed to obtain a high-resolution impedance model. The inversion results clearly distinguish the spatial distribution of volcanic rocks in different phases and the internal impedance variations. The lithologic identification results based on this are highly consistent with known drilling results, providing a more comprehensive geophysical basis for exploration deployment.

[0081] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0082] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling is characterized by: The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling includes: Step 1: Use multi-scale analysis to strip away deep magnetic anomalies and quantitatively obtain igneous rock residual magnetic anomalies; Step 2: Analyze seismic reflection characteristics and characterize the three-dimensional boundary geometry of igneous rocks; Step 3: Conduct deep-domain magnetic-seismic three-dimensional joint modeling; Step 4: construct a combined magnetic-seismic low-frequency wave impedance model; Step 5: Perform magnetic-seismic combined wave impedance inversion; In step 3, under the constraints of the volcanic rock geometry obtained in step 2, a combined magnetic and seismic interpretation is performed based on the magnetic susceptibility statistics of the core and outcrop rocks in the work area to obtain a detailed three-dimensional spatial distribution of the magnetic susceptibility. In step 3, first, the magnetic susceptibility of igneous rocks is measured based on the core and outcrop samples collected near the work area, and the magnetic susceptibility values of different strata and lithologies are statistically calculated; Secondly, using the 3D boundary morphology of the igneous rock as a constraint, a 3D magnetic interactive interpretation is carried out to fill the internal igneous rock boundary morphology with magnetic susceptibility values. A 3D magnetic forward modeling is then performed on the 3D grid. The magnetic susceptibility value filling results and the igneous rock boundary geometry are adjusted based on the fitting residuals with the magnetic anomaly separation results of the target layer. Thirdly, the process of magnetic susceptibility model modification, forward modeling, and fitting residual calculation is repeated to obtain a precise three-dimensional spatial distribution of magnetic susceptibility. In step 4, first, the correlation between the physical properties of magnetic susceptibility and wave impedance parameters of different strata and lithologies in the work area is statistically analyzed; Secondly, the three-dimensional magnetic susceptibility model is converted into a depth-domain seismic wave impedance model using the statistical results of physical property correlation.

2. The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling according to claim 1 is characterized in that: In step 1, the magnetic anomaly is first separated into multiple scales using continuous wavelet transform, and then the two-dimensional correlation between adjacent scale magnetic anomalies is analyzed to calculate the correlation coefficient curve; Secondly, calculate the local extreme points of the correlation coefficient curve; Thirdly, the anomalies of multiple scales are separated according to the local extreme points, and the anomalies of different scales between the extreme points are superimposed to obtain multiple separated magnetic anomalies. Among them, the frequency of the separation results of the larger-scale magnetic anomalies is low, reflecting the deep-buried magnetic bodies. Finally, according to research needs, the deep magnetic anomaly is stripped to obtain the magnetic anomaly corresponding to the target layer.

3. The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling according to claim 1 is characterized in that: In step 2, first, analyze the reflection characteristics of the seismic phase in the work area. Igneous rocks usually show chaotic, oblique, and blank reflection characteristics, while sedimentary strata usually show more continuous reflection characteristics. Secondly, the seismic facies are further subdivided in combination with the drilled well data, and the three-dimensional boundary morphology of the igneous rock boundary is characterized based on the seismic facies characteristics in the three-dimensional work area.

4. The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling according to claim 1 is characterized in that: In step 5, the depth-domain low-frequency wave impedance waveform obtained in step 4 is converted into time-depth using well-seismic calibration and velocity spectrum data. The depth-domain low-frequency wave impedance model of igneous rock is converted to the time domain, and time-domain seismic inversion is performed to obtain a high-resolution wave impedance model, providing a basis for the detailed characterization of igneous rock lithology.

5. The igneous rock wave impedance inversion method based on combined magnetic-seismic low-frequency modeling according to claim 4 is characterized in that: In step 5, first, the low-frequency seismic wave impedance waveform in the depth domain is converted into a seismic wave impedance model in the time domain by combining the time-depth data and the three-dimensional velocity spectrum data at the well point; Secondly, the converted time-domain seismic impedance model is used as the initial model to carry out seismic impedance inversion under logging constraints to obtain a high-resolution impedance model, thereby providing a basis for the detailed characterization of igneous rock lithology.

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