A method for restoring the erosion amount of facies zones in buried volcanic structures

Abstract

This invention discloses a method for recovering the erosion volume of facies zones within buried volcanic structures, belonging to the technical field of erosion volume recovery in sedimentary basins. The method comprises six steps: establishing a basic database for erosion volume recovery; identifying buried volcanic structures and dividing their internal facies zones; determining erosion recovery methods for different facies zones; determining regional erosion baselines; and recovering erosion volumes for near-source, intermediate-source, and distal-source facies zones. Based on the morphological characteristics and weathering erosion differences of different facies zones within buried volcanic structures, this invention determines erosion volume recovery methods for near-source, intermediate-source, and distal-source facies zones separately, avoiding the errors caused by uniformly assigning regional erosion volumes to the entire volcanic structure. This invention achieves differentiated recovery of erosion volumes for different facies zones within buried volcanic structures, improving the rationality and quantification of erosion volume recovery for buried volcanic structures, thus possessing significant application value for deep-to-ultra-deep oil and gas exploration.

Description

Technical Field

[0001] This invention belongs to the field of sedimentary basin erosion recovery technology, specifically relating to a method for recovering the erosion of facies zones of buried volcanic structures. Background Technology

[0002] With the increasing exploration of deep and ultra-deep oil and gas reservoirs, volcanic reservoirs have become one of the important targets for oil and gas exploration. The original morphology and degree of erosion and alteration of buried volcanic structures have a significant impact on the spatial distribution, trap formation, reservoir effectiveness evaluation, and prediction of favorable targets in volcanic reservoirs. Therefore, accurately reconstructing the erosion amount of different facies zones of buried volcanic structures is an important foundation for carrying out original morphology restoration, lithological prediction, and reservoir evaluation of volcanic structures.

[0003] Existing methods for reconstructing erosion volume primarily employ tectonic trend analysis, residual thickness analysis, equilibrium profile analysis, and thermochronology. While these methods can reconstruct stratigraphic erosion volume at a regional scale, their direct application to the reconstruction of erosion volume in buried volcanic structures remains limited. Buried volcanic structures exhibit distinct internal facies differentiation, with near-source, intermediate-source, and far-source facies zones showing significant differences in original morphology, lithological assemblage, and subsequent weathering alteration. Existing methods typically treat the volcanic structure as a homogeneous geological body and use uniform regional erosion volumes for reconstruction, making it difficult to accurately reflect the differential erosion characteristics between different facies zones.

[0004] Specifically, near-source and intermediate-source facies zones typically retain some of the original volcanic structure's morphology, and can be reconstructed using a combination of Move equilibrium profile restoration under regional erosion constraints and volcanic morphology constraints. However, distant-source facies zones usually exhibit parallel or sub-parallel reflection structures in seismic reflections, lacking obvious cut-off points and traceable trend extrapolation boundaries, making it difficult to reconstruct their erosion amount through reflection trend extrapolation. Furthermore, distant-source facies zones are subject to intense weathering and erosion; setting their erosion amount to zero solely based on the lack of obvious cut-off features in seismic profiles easily underestimates their actual degree of erosion and alteration.

[0005] Therefore, it is necessary to establish a method for restoring the erosion amount of facies zones of buried volcanic structures that can comprehensively consider the regional erosion background, the morphology of buried volcanic structures, and the geochemical weathering and modification characteristics, so as to improve the rationality and quantification of the restoration of the erosion amount of buried volcanic structures. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for recovering the erosion amount of facies zones within buried volcanic structures. This method is based on volcanic morphology constraints and geochemical mass balance to recover the erosion amount of facies zones within buried volcanic structures. First, the buried volcanic structure is identified and divided into near-source, intermediate-source, and distal-source facies zones. Then, based on the seismic reflection characteristics, morphological preservation levels, and weathering differences of different facies zones, applicable erosion amount recovery methods are determined for each. For the near-source and intermediate-source facies zones, a method combining Move equilibrium profile recovery under regional erosion benchmark constraints with volcanic morphology constraints is used to recover the erosion amount. For the distal-source facies zone, the geochemical mass balance method is used to calculate the chemically equivalent erosion amount, thereby achieving differentiated quantitative recovery of the erosion amount of different facies zones within the buried volcanic structure.

[0007] The technical solution of the present invention is as follows: This invention provides a method for recovering the erosion amount of phasic zones in buried volcanic structures, comprising the following steps: (1) Establish a basic database for erosion recovery Collect seismic data, well logging data, core data, geochronological data, and geochemical test data of the study area to establish a basic database for the reconstruction of the erosion volume of buried volcanic structures; (2) Identification of buried volcanic structures and division of internal facies zones Based on the seismic phase reflection characteristics of buried volcanic structures, the buried volcanic structures are identified and their spatial distribution range is delineated; on this basis, the near-source facies zone, intermediate-source facies zone, and far-source facies zone are further identified based on the seismic reflection parameters inside the volcanic structures. (3) Differentiating erosion recovery methods for different phase zones Based on the seismic reflection characteristics, spatial distribution characteristics, and weathering and erosion characteristics of the near-source facies zone, intermediate-source facies zone, and distal-source facies zone, the appropriate erosion recovery methods for each facies zone are determined. (4) Determine the baseline amount of regional erosion. The tectonic trend method and the tectonic-thermal chronology method were used to calculate the regional erosion amount in the study area, and the regional erosion baseline amount was determined by combining the two methods. (5) Recovery of erosion in near-source and intermediate-source facies zones Time-depth conversion, Move equilibrium profile establishment, fault displacement elimination, and tectonic restoration were performed on the near-source and intermediate-source facies zones to obtain the residual morphology of the volcanic structure after tectonic correction. Using the regional erosion baseline as the vertical constraint for the restoration of the original top boundary, extrapolation was performed based on the seismic reflection axis distribution trend of the residual volcanic structure to restore the original volcanic structure boundary before erosion, and the erosion amount of the near-source and intermediate-source facies zones was calculated. Then, the average erosion amount of the near-source and intermediate-source facies zones was calculated using the area-weighted average method. (6) Recovery of erosion in the distant source facies zone For the distant source facies zone, the parent rock end-member and non-migrating reference elements are selected. The volumetric strain coefficient is calculated based on the content of non-migrating elements in the parent rock and weathered samples and the rock density. The comprehensive chemical depletion index is further determined, and the chemical equivalent erosion amount is calculated in combination with the current residual thickness of the distant source facies zone.

[0008] In the above technical solution, in step (1), the seismic data includes three-dimensional seismic data volume, stratigraphic interpretation results, fault interpretation results, and seismic attribute data; the logging data includes relevant well column data, lithological interpretation, logging data, and logging curves for the study area; the core data includes core observation, lithological description, volcanic rock structure, alteration and weathering characteristics, and sampling stratigraphic information; the geochronological data includes zircon U-Pb age, apatite fission track age, zircon fission track age, regional paleothermal gradient, and burial history data; and the geochemical testing data includes volcanic rock density and major element test data.

[0009] In the above technical solution, in step (2), the seismic phase reflection characteristics of the buried volcanic structure include external geometry, reflection difference at the top and bottom interfaces, internal reflection structure, contact relationship with the surrounding rock or overlying strata, and lateral pinch-out characteristics.

[0010] In the above technical solution, in step (2), the seismic reflection parameters include the reflecting structure, amplitude, frequency and continuity.

[0011] In the above technical solution, in step (3), the near-source facies zone and the intermediate source facies zone are restored by combining the Move equilibrium profile restoration under the constraint of regional erosion benchmark quantity with the volcanic morphology constraint, and the distant source facies zone is restored by the geochemical mass balance method.

[0012] In the above technical solution, in step (4), the regional erosion reference amount is used as a vertical constraint for the restoration of the original boundary of the near-source facies zone and the intermediate source facies zone, and is not directly used as a unified erosion amount for all facies zones.

[0013] In the above technical solution, in step (4), the formula for calculating the regional erosion amount using the tectonic trend method is as follows:

[0014] In the formula, E t H represents the area erosion amount calculated using the tectonic trend method. e H represents the theoretical deposition thickness. o This represents the current thickness of the remaining strata. The formula for calculating the amount of regional erosion using the tectonic-thermal chronology method is as follows:

[0015] In the formula, Eh For the amount of regional erosion calculated using tectonic-thermal chronology; T c -T0 is the cooling temperature; G is the regional paleothermal gradient; By combining the results of the tectonic trend method and the tectonic-thermal chronology method, the baseline amount of regional erosion was determined:

[0016] In the formula, E r w is the baseline for regional erosion. t and w h The weights are respectively the weights for the tectonic trend method and the tectonic-thermal chronology method, and satisfy the following: .

[0017] In the above technical solution, the specific operation steps for restoring the erosion amount of the near-source phase zone and the intermediate source phase zone in step (5) are as follows: The seismic time-domain profile of the area where the target volcanic structure is located is converted into a depth-domain profile, and the interpreted data is imported into Move software to establish a two-dimensional equilibrium profile model. Fault displacement elimination and structural restoration are carried out on the faults that cut through the volcanic structure and its overlying strata, so that the top and bottom boundaries of the structure, the marker layer and the interface of the overlying strata that were dislocated by the faults are restored to a relatively continuous geometric state. Using the regional erosion baseline as the vertical constraint for the restoration of the original top boundary of the near-source facies zone and the intermediate-source facies zone, and extrapolating the trend based on the seismic reflection axis distribution trend of the residual volcanic structure after tectonic restoration, the original volcanic structure boundary before erosion is restored. By comparing the original volcanic structure boundary obtained by trend extrapolation with the current residual volcanic structure boundary after tectonic reconstruction, the erosion amount of the near-source and intermediate-source facies zones is calculated using the following formula:

[0018] In the formula, E i H represents the erosion amount at the i-th calculation point. p,i H is the original height before erosion obtained by trend extrapolation recovery. r,i This is the current remaining height; Then, the average erosion amount of the near-source facies zone and the intermediate source facies zone is calculated using the area-weighted average method; where the point erosion amount is used to characterize the local erosion difference, and the area-weighted average erosion amount is used to characterize the overall erosion degree of the facies zone.

[0019] In the above technical solution, the specific operation method for calculating the average erosion amount of the near-source facies zone and the intermediate source facies zone using the area-weighted average method is as follows: Several calculation points are selected along the phasor distribution direction, and the erosion area of ​​the profile is calculated using the trapezoidal method based on the erosion amount and horizontal distance between adjacent calculation points:

[0020] In the formula, A E E represents the cross-sectional erosion area bounded between the original boundary before erosion and the current residual boundary; i and E i+1 These represent the erosion amounts at two adjacent calculation points; ∆x i Let n be the horizontal distance between the i-th calculation point and the (i+1)-th calculation point; n is the number of calculation points. The lateral width of the phase band is calculated using the following formula:

[0021] In the formula, L is the lateral width of the phase band; x1 and x n These are the horizontal positions of the first and last calculation points within the phase band, respectively. Furthermore, the ratio of the eroded area of ​​the profile to the lateral width of the facies zone is used as the area-weighted average erosion amount of that facies zone:

[0022] In the formula, This represents the area-weighted average erosion amount of the facies zone. From this, the point erosion and area-weighted average erosion amounts for the near-source and intermediate-source facies zones can be obtained separately. The point erosion amount is used to characterize local erosion differences, while the area-weighted average erosion amount is used to characterize the overall erosion degree of the facies zone.

[0023] In the above technical solution, the specific operation steps for restoring the erosion amount of the distant source phase zone in step (6) are as follows: Unweathered or weakly weathered volcanic rock samples from the study area were selected as parent rock end-members to represent the original chemical composition of the volcanic rocks before weathering. When unweathered or weakly weathered volcanic rock samples were lacking in the study area, unweathered volcanic rock samples from the same stratigraphic position, lithology, and genetic background were selected as substitute parent rock end-members. Volcanic rock samples affected by weathering in the distal facies zone were selected as weathered samples to characterize the geochemical composition and density change characteristics of the distal facies zone after weathering. Elements that are geochemically stable and not easily migrated during chemical weathering were selected as reference elements; Based on the content of non-migrating reference elements in the parent rock endmember and weathered sample, and the rock density, the volumetric strain coefficient of the weathered sample is calculated using the following formula:

[0024] In the formula, ε i,w ρ is the volumetric strain coefficient of the rock in the weathered sample. ρ ρ is the density of the parent rock sample. w Density of weathered sample; C i,p The content of non-migrating element i in the parent rock; Ci,w The content of element i, which is not easily migrated, in the weathered sample; A comprehensive chemical deficit index is established based on the volumetric strain coefficient to reflect the volumetric change characteristics of the weathered sample relative to the parent rock during the chemical weathering process. The calculation formula is as follows:

[0025]

[0026] In the formula, L i，j D represents the volume deficit ratio of element i. c The comprehensive chemical depletion index is used to characterize the degree of overall chemical quality loss of volcanic rocks relative to their parent rocks. The current residual thickness H of the distant source phase zone p As a reference thickness, the chemically equivalent erosion amount of the distal phase zone is calculated using the following formula:

[0027] In the formula: E c H is the chemically equivalent erosion amount. p For the current thickness, D c This is a comprehensive chemical loss index.

[0028] In the above technical solution, in step (6), the reference element is Ti; it has extremely low migration during weathering and can stably reflect the relative mass change in the rock system.

[0029] This invention provides the application of the above-mentioned method for recovering the erosion amount of the facies zone of buried volcanic structures in volcanic rock lithology prediction, reservoir evaluation, trap effectiveness analysis, and exploration target selection.

[0030] The beneficial effects of this invention are as follows: This invention utilizes regional erosion baselines to constrain the boundary restoration of near-source and intermediate-source facies zones, and combines Move equilibrium profile restoration with volcanic morphology calculations to improve the geometric rationality of erosion restoration in these zones. Addressing the issue of distant-source facies zones lacking clear truncation characteristics and being difficult to directly restore erosion through seismic trends, this invention introduces the geochemical mass balance method to calculate their chemically equivalent erosion, achieving quantitative restoration of erosion in distant-source facies zones.

[0031] Based on the morphological characteristics and weathering and erosion differences of different facies zones of buried volcanic structures, this invention determines the erosion recovery methods for near-source, intermediate-source, and far-source facies zones, respectively. This avoids the error caused by uniformly attributing regional erosion to the entire volcanic structure, which is of great significance in the field of sedimentary basin erosion recovery technology and has good application value for deep-ultra-deep oil and gas exploration.

[0032] This invention achieves differentiated recovery of erosion amounts in different facies zones of buried volcanic structures, improving the rationality and quantification of erosion amount recovery. Specifically, based on the differentiation characteristics of facies zones within the volcanic structure, this invention divides it into near-source, intermediate-source, and far-source facies zones, and selects appropriate erosion amount recovery methods for each facies zone, thereby avoiding errors caused by uniformly assigning erosion amounts to a region. For the near-source and intermediate-source facies zones, time-depth conversion, Move equilibrium profile modeling, fault displacement elimination, and structural recovery are performed to obtain the structurally corrected residual morphology of the volcanic structure. The maximum recovery height of the original top boundary is constrained by the regional erosion baseline, and the original boundary before erosion is extrapolated based on the seismic reflection axis distribution trend of the residual volcanic structure, thereby calculating the erosion amounts of the near-source and intermediate-source facies zones. For the far-source facies zone, a geochemical mass balance relationship is established using parent rock endmembers, weathered samples, non-migrating reference elements, and rock density, converting volumetric strain into chemically equivalent erosion amounts. Therefore, this invention achieves synergistic constraints on erosion amount from three levels: regional erosion background, volcanic morphology restoration, and chemical mass depletion, making the restoration results more geologically reasonable, quantitative, and verifiable. Attached Figure Description

[0033] Figure 1 The seismic facies characteristics and planar distribution of the No. 1 volcanic structure in a basin of Bohai Bay are shown in the following diagrams: (a) shows the seismic facies characteristics of the A-A' section of the No. 1 volcanic structure; (b) shows the seismic facies characteristics of the B-B' section of the No. 1 volcanic structure; and (c) shows the planar distribution and facies zone division of the No. 1 volcanic structure.

[0034] Figure 2 The diagram shows the calculation of regional erosion using the tectonic trend method; (a) shows the original seismic profile and tectonic trend characteristics of the study area; (b) shows the geological interpretation profile and erosion calculation based on the tectonic trend method.

[0035] Figure 3 This is a map showing the tectonic cooling history of a basin in the Bohai Bay.

[0036] Figure 4 This is a schematic diagram of the fault displacement recovery process of Volcanic Mechanism No. 1 in a basin of the Bohai Bay.

[0037] Figure 5 A schematic diagram of the erosion recovery of volcanic structure No. 1 in a basin of Bohai Bay based on volcanic morphology constraints.

[0038] Figure 6 A reconstruction of the original morphology of Volcanic Structure No. 1 in a basin of the Bohai Bay. Detailed Implementation

[0039] This invention provides a method for restoring the erosion amount of facies zones of buried volcanic structures based on volcanic morphology constraints and geochemical mass balance. The specific steps are as follows: 1. Data Preparation Collect seismic data, well logging data, core data, geochronological data, and geochemical test data of the study area to establish a basic database for the reconstruction of erosion volume of buried volcanic structures.

[0040] Seismic data includes 3D seismic data volumes, stratigraphic interpretation results, fault interpretation results, and seismic attribute data; well logging data includes relevant well column data, lithological interpretation, logging data, and logging curves for the study area; core data includes core observations, lithological descriptions, volcanic rock structure and texture, alteration and weathering characteristics, and sampling stratigraphic information; geochronological data includes zircon U-Pb ages, apatite fission track ages, zircon fission track ages, regional paleothermal gradients, and burial history data; geochemical testing data includes volcanic rock density and major element test data.

[0041] 2. Identification of buried volcanic structures and division of internal facies zones (1) Identification of buried volcanic structures Based on the external geometry of earthquake reflections, the difference in reflections at the top and bottom interfaces, the internal reflection structure, the contact relationship with the surrounding rock or overlying strata, and the lateral pinch-out characteristics, buried volcanic structures can be identified and their spatial distribution range can be delineated.

[0042] Buried volcanic structures typically appear as cone-shaped, mound-shaped, sheet-shaped, basin-shaped, funnel-shaped, or lenticular shapes on seismic profiles. The top and bottom interfaces often exhibit medium to strong amplitude reflections, with the two flanks covered by overlying sedimentary rocks. The internal reflections of the structure are controlled by differences in lithology and structure, and can exhibit characteristics such as strong amplitude continuous reflections, weak amplitude chaotic reflections, or layered continuous reflections. Some structures also exhibit low amplitude reflections that tilt to both sides along the apex of the volcanic dome.

[0043] (2) Division of phagocytic structures within the volcanic structure Based on the identification of buried volcanic structures, the near-source phalanx, intermediate-source phalanx, and far-source phalanx of buried volcanic structures are identified according to the amplitude strength, frequency, reflection continuity, and reflection structure differences within the volcanic structure.

[0044] The near-source facies zone is characterized by medium to strong amplitude seismic reflections, poor continuity, and medium to low frequencies, exhibiting an overall chaotic reflection pattern, reflecting the complex lithology and heterogeneous structure near the volcanic eruption center. The intermediate-source facies zone is characterized by medium amplitude, moderate continuity, and medium to low frequencies, generally exhibiting a near-parallel reflection structure, with localized chaotic or weakly continuous reflections, reflecting the outward transition and deposition of volcanic material. The distal-source facies zone is characterized by medium to weak amplitude, good continuity, and medium to high frequencies, exhibiting an overall parallel or near-parallel reflection structure, reflecting the long-distance transport and redeposition of volcanic sediments.

[0045] 3. Selection of restoration methods for erosion in different phasing zones After identifying the buried volcanic structures and dividing the internal facies zones, the appropriate erosion recovery methods for each facies zone are determined based on their seismic reflection characteristics, spatial distribution, and weathering and erosion characteristics.

[0046] (1) Selection of methods for reconstructing near-source and intermediate-source phasing zones The near-source and intermediate-source facies zones are typically located in the main body of volcanic structures, exhibiting relatively distinct original morphological undulations. Their top, flank, and facies zone distribution boundaries can be identified on seismic profiles. Even in areas lacking clear cut-off points or extrapolated tectonic boundaries, geometric constraints can still be applied to reconstruct the erosion amounts of the near-source and intermediate-source facies zones based on the residual morphology of the volcanic structure, the spatial distribution of facies zones, and regional erosion baselines. Therefore, this invention employs a method combining Move equilibrium profile reconstruction with volcanic morphological constraints to recover the erosion amounts of the near-source and intermediate-source facies zones.

[0047] (2) Selection of methods for distant phase zone restoration Distant-source facies zones are typically located on the periphery of volcanic structures, with their upper boundaries often nearly parallel to the overlying sedimentary strata. They lack traceable trend extrapolation boundaries, making it difficult to reconstruct their erosion amount through volcanic morphology constraints. Furthermore, these zones have undergone intense weathering and erosion, making it unsuitable to set their erosion amount to zero. This invention employs a geochemical mass balance method to reconstruct their erosion amount.

[0048] 4. Determination of regional erosion baseline (1) Calculation of regional erosion using the tectonic trend method Unconformities, cut-off points, and stratigraphic truncation relationships are identified in seismic profiles to determine the areas where tectonic erosion occurs. Based on the residual stratigraphic thickness in uneroded or weakly eroded areas, an original sedimentary thickness trend model is established. This model is extrapolated to the eroded area to obtain the theoretical sedimentary thickness. The theoretical sedimentary thickness is compared with the current residual stratigraphic thickness, and the regional erosion amount is calculated using the following formula:

[0049] In the formula, E t H represents the area erosion amount calculated using the tectonic trend method. e H represents the theoretical deposition thickness. o This represents the current thickness of the remaining strata.

[0050] (2) Calculation of regional erosion using tectonic-thermal chronology method Based on the chronological data and paleothermal gradient of the study area, a cooling history map was drawn, and the regional erosion amount for the corresponding period was calculated using the following formula:

[0051] In the formula, E h For the amount of regional erosion calculated using tectonic-thermal chronology; T c-T0 is the cooling temperature; G is the regional paleothermal gradient.

[0052] (3) Calculation of regional erosion baseline By combining the results of the tectonic trend method and the tectonic-thermal chronology method, a weighted average method was used to determine the regional erosion baseline.

[0053] In the formula, E r w is the baseline for regional erosion. t and w h The weights are respectively the weights for the tectonic trend method and the tectonic-thermal chronology method, and satisfy the following:

[0054] 5. Recovery of erosion in near-source and intermediate-source facies zones Considering that near-source and intermediate-source facies zones still retain certain original volcanic structural features on seismic profiles, this invention employs a method combining Move equilibrium profile restoration and volcanic morphology constraints to recover the erosion amount of near-source and intermediate-source facies zones. The specific steps are as follows: (1) Time-depth conversion Convert the time-domain profile of the area where the target volcanic structure is located into a depth-domain profile.

[0055] (2) Establishment of Move equilibrium profile Based on the detailed depiction of the volcanic structure, the interpreted data is imported into Move software to establish a two-dimensional equilibrium profile model. The specific operation method is as follows: (a) Create a new work area: Open the Move software, select File → new section → set the actual length and width of the section in Section Extend; (b) Insert a bitmap file: Model Building → Image → Create image → Basic. Adjust the image size until it matches the actual length and width of the initial profile. (c) Structural interpretation and digitization: Based on the seismic facies characteristics, the strata, faults, volcanic structures, etc. in the images are interpreted and digitized.

[0056] (3) Elimination of discontinuity In Move software, fault displacement recovery is performed on faults that cut through volcanic structures and strata, restoring the original state of the faulted top and bottom boundaries of volcanic structures, marker beds, and overlying strata interfaces. Fault displacement recovery is performed using a simple shear method, following the principle of recovery from newest to oldest and from top to bottom. For faults with multiple active phases, recovery should be carried out in stages according to the fault's activity phases. After each fault displacement recovery is completed, the alignment of the hanging wall and footwall strata, the top and bottom boundaries of volcanic rocks, and the structure boundaries is checked. If overlapping or gaps exist, the fault geometry or recovery parameters are adjusted. The specific operation steps are as follows: (a) Select Modules → 2D Move-on-Fault → Method (simple shear).

[0057] (b) Active Fault: Select the fault line to be restored.

[0058] (c) Objects to be moved: Select the stratigraphic lines on the hanging wall of the fault that are affected.

[0059] (d) Movement: Select the hanging wall and footwall of the strata to be restored, and then select apply to complete the restoration of the corresponding fault displacement.

[0060] (4) Extrapolation of the original boundary of the mechanism and recovery of erosion amount under the constraint of regional erosion amount After completing time-depth conversion, establishing the Move equilibrium profile, and eliminating fault displacement, the morphology of residual volcanic structures in the near-source and intermediate-source facies zones after tectonic restoration was obtained. This was combined with the regional erosion baseline E. r The boundaries of the volcanic structures before the near-source facies zone and intermediate-source erosion are reconstructed, and the corresponding erosion amounts are calculated. The specific steps are as follows: (a) Based on regional erosion baseline E r As a vertical constraint for the restoration of the original top boundary of the near-source and intermediate-source facies zones, it limits the maximum restoration height of the top boundary before erosion.

[0061] (b) Based on the distribution characteristics of the seismic reflection axes of the residual volcanic structure after tectonic restoration, the extension directions of continuous or semi-continuous seismic reflection axes within the near-source facies zone and the intermediate-source facies zone are extracted, and seismic reflection trend lines are drawn.

[0062] (c) Extrapolate the boundary of the residual volcanic structure along the earthquake reflection trend line to restore the original morphology of the near-source facies zone and the intermediate-source facies zone before stripping.

[0063] (d) Compare the volcanic structure morphology obtained by trend extrapolation with the morphology of the currently buried volcanic structure, and calculate the erosion amount of the near-source and intermediate-source facies zones:

[0064] In the formula, E i H represents the erosion amount at the i-th calculation point. p,i H is the original height before erosion obtained by trend extrapolation recovery. r,i This is the current remaining height.

[0065] (5) Average erosion amount in near-source and intermediate-source facies zones The average erosion amount in the near-source and intermediate-source facies zones was calculated using the area-weighted average method. Specifically, several calculation points were selected along the facies zone distribution direction, and the erosion area of ​​the profile was calculated using the trapezoidal method based on the erosion amount and horizontal distance between adjacent calculation points.

[0066] In the formula, A E E represents the cross-sectional erosion area bounded between the original boundary before erosion and the current residual boundary; i and E i+1 These represent the erosion amounts at two adjacent calculation points; ∆x i is the horizontal distance between the i-th calculation point and the (i+1)-th calculation point; n is the number of calculation points.

[0067] The lateral width of the phase band is calculated using the following formula:

[0068] In the formula, L is the lateral width of the phase band; x1 and x n These are the horizontal positions of the first and last calculation points within this phase band, respectively.

[0069] Furthermore, the ratio of the eroded area of ​​the profile to the lateral width of the facies zone is used as the area-weighted average erosion amount of that facies zone:

[0070] In the formula, This represents the area-weighted average erosion amount of the facies zone. From this, the point erosion and area-weighted average erosion amounts for the near-source and intermediate-source facies zones can be obtained separately. The point erosion amount is used to characterize local erosion differences, while the area-weighted average erosion amount is used to characterize the overall erosion degree of the facies zone.

[0071] 6. Recovery of erosion in the distant source facies zone (1) Selection of weathered samples from the parent rock end-member and distal facies zone Unweathered or weakly weathered volcanic rock samples from the study area were selected as parent rock end-members to represent the original chemical composition of the volcanic rocks before weathering. Parent rock end-members were preferentially selected from samples with low degrees of oxidative weathering, dense rock structure, and weak alteration in near-source facies zones. When samples from near-source facies zones were unavailable, unweathered volcanic rock samples from the same stratigraphic position, lithology, and genetic background were selected as substitutes.

[0072] Volcanic rock samples affected by weathering in the distal facies zone were selected as weathering samples to characterize the geochemical composition and density changes after weathering in the distal facies zone. To ensure comparability between the parent rock endmembers and the weathered samples, the selected samples should have similar or identical lithological types, stratigraphic assignments, and genetic backgrounds as much as possible.

[0073] (2) Selection of reference elements that are not easily transferable Elements that are geochemically stable and do not readily migrate during chemical weathering are selected as reference elements. This invention selects Ti as the reference element because it exhibits extremely low migration during weathering and can stably reflect relative mass changes in the rock system, thus serving as a benchmark for volumetric strain calculations.

[0074] (3) Calculation of volumetric strain coefficient Based on the principle of mass conservation, and combined with parameters such as the content of non-migrating elements and rock density in the parent rock and weathered samples, the volumetric strain coefficient of volcanic rocks during the weathering process is calculated:

[0075] In the formula, ε i,w ρ is the volumetric strain coefficient of the rock in the weathered sample. ρ ρ is the density of the parent rock sample. w Density of weathered sample; C i,p The content of non-migrating element i in the parent rock; C i,w ε represents the content of element i, which is not easily migrated, in the weathered sample. i,w When ε < 0, it indicates that volume compression has occurred; when ε i,w When ε = 0, it indicates an approximate volume change; when ε i,w When the value is greater than 0, it indicates that the volume has expanded.

[0076] (4) Calculation of the comprehensive chemical loss index A comprehensive chemical deficit index is established based on the volumetric strain coefficient to reflect the volumetric change characteristics of the weathered sample relative to the parent rock during the chemical weathering process. The calculation formula is as follows:

[0077]

[0078] In the formula, L i，j D represents the volume deficit ratio of element i. c The comprehensive chemical depletion index is used to characterize the degree of overall chemical quality loss of volcanic rocks relative to their parent rock. (D) c The higher the value, the higher the degree of chemical erosion.

[0079] (5) Calculation of chemical erosion amount in the distant source facies zone Based on the seismic profile after time-depth transformation, the locations of the top and bottom boundaries of the distal source facies zone are extracted, and the current residual thickness H of the distal source facies zone is calculated. p When the transverse thickness of the distal facies zone changes significantly in the profile, multiple measuring points can be selected along the distribution direction of the distal facies zone, the thickness of each measuring point can be calculated, and the average value can be taken as the current average residual thickness of the distal facies zone.

[0080] Due to the comprehensive chemical loss index D c The thickness revealed by the seismic profile represents the current residual thickness after erosion, while the thickness shown is the loss ratio relative to the original thickness or original volume. Therefore, the chemically equivalent erosion amount needs to be calculated based on the mass conservation principle. The current residual thickness H of the distal facies zone revealed by the seismic profile is used as an example. p As a reference thickness, the chemically equivalent erosion amount is calculated using the following formula:

[0081] In the formula: E c H is the chemically equivalent erosion amount. p For the current thickness, D c This is a comprehensive chemical loss index.

[0082] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0083] Example 1

[0084] Taking the No. 1 buried volcanic structure in a basin of the Bohai Bay as an example, the erosion volume of different facies zones in the Cretaceous is reconstructed. The specific operation is as follows: 1. Data Preparation We collected seismic data, well logging data, core data, geochronological data, and geochemical test data from the study area to establish a basic database for the reconstruction of erosion volume of tectonic-buried volcanic structures in a basin in the Bohai Bay.

[0085] Seismic data includes 3D seismic data volumes, stratigraphic interpretation results, fault interpretation results, and seismic attribute data. Well logging data includes relevant well column data, lithological interpretation, logging data, and well logging curves for the study area; core data includes core observations, lithological descriptions, volcanic rock structure and texture, alteration and weathering characteristics, and sampling stratigraphic information; geochronological data includes zircon U-Pb ages, apatite fission track ages, zircon fission track ages, regional paleotemperature gradients, and burial history data. Geochemical testing data includes volcanic rock density and major elemental analysis data.

[0086] 2. Identification of buried volcanic structures and division of internal facies zones (1) Identification of buried volcanic structures Based on the external geometry of earthquake reflections, the difference in reflections at the top and bottom interfaces, the internal reflection structure, the contact relationship with the surrounding rock or overlying strata, and the lateral pinch-out characteristics, the No. 1 buried volcanic structure in a basin of the Bohai Bay was identified, and its external morphology and distribution range were depicted.

[0087] The volcanic structure exhibits an irregular basin-funnel-shaped composite morphology on the seismic profile, with significant differences in reflection between the top and bottom interfaces and the surrounding rock. The top of the volcanic structure is covered by well-continuous overlying sedimentary reflections, with local top boundary morphology showing some degree of morphological adjustment due to later sedimentary burial and tectonic modification. The internal reflection structure of the volcanic structure is complex, mainly characterized by poor continuity, locally disordered reflections, and the development of weakly continuous reflections. Overall, the volcanic structure has a relatively clear lateral distribution on the profile, gradually thinning towards both sides, displaying the external morphology and internal reflection structure characteristics of a typical buried volcanic structure.

[0088] (2) Division of phagocytic structures within the volcanic structure Based on the seismic reflection structure, amplitude, frequency, and continuity characteristics of volcanic structures in the Bohai Bay Basin, a classification standard for near-source, intermediate-source, and distal-source facies zones of volcanic structures in the study area was established (Table 1). Furthermore, the facies zones of the No. 1 buried volcanic structure in a certain tectonic structure of the Bohai Bay Basin were divided, as shown in Table 1. Figure 1 As shown.

[0089] The near-source facies zone is characterized by medium to strong amplitude, poor reflection continuity, and medium to low frequency features, with a relatively chaotic internal reflection structure and locally visible upward-extending channel-like reflections. The intermediate-source facies zone is characterized by medium amplitude, moderate reflection continuity, and medium to low frequency features, with locally developed near-parallel or weakly continuous reflections. The distal-source facies zone is characterized by medium to weak amplitude, good reflection continuity, and medium to high frequency features, with internal reflections mostly exhibiting parallel or near-parallel distribution. Overall, this volcanic structure demonstrates a seismic facies zoning characteristic that gradually transitions from chaotic near-source reflections to weakly continuous intermediate-source reflections, and then to continuous parallel reflections at the distal source.

[0090] Table 1. Seismic facies characteristics of different tectonic facies zones in a basin in the Bohai Bay.

[0091] 3. Differentiation of erosion recovery methods for different phase zones Based on the facies distribution characteristics of the No. 1 buried volcanic structure in a basin of the Bohai Bay, a differentiated erosion recovery method was adopted for different facies zones. The near-source and intermediate-source facies zones are located in the main part of the volcanic structure and still retain certain remnants of the volcanic structure's appearance, internal reflection structures, and reflection axis distribution trends on seismic profiles. Their erosion amounts can be recovered using a combination of Move equilibrium profile recovery under regional erosion baseline constraints and volcanic morphology constraints. The distal-source facies zone is located on the periphery of the volcanic structure, with its top boundary nearly parallel to the overlying sedimentary strata. Lacking clear cut-off points and traceable trend extrapolation boundaries, it is difficult to directly recover erosion amounts from volcanic morphology. Therefore, the geochemical mass balance method was used to calculate the erosion amount of the distal-source facies zone.

[0092] 4. Determination of regional erosion baseline (1) Calculation of regional erosion using the tectonic trend method Unconformities, cut-off points, and stratigraphic truncation relationships are identified in seismic profiles to determine the areas where tectonic erosion occurs. Based on the residual stratigraphic thickness in uneroded or weakly eroded areas, an original sedimentary thickness trend model is established and extrapolated to the eroded areas to obtain the theoretical sedimentary thickness. The theoretical sedimentary thickness is compared with the current residual thickness, and the regional erosion amount is calculated using the following formula:

[0093] In the formula, E t H represents the area erosion amount calculated using the tectonic trend method. e H represents the theoretical deposition thickness. o This represents the current thickness of the remaining strata.

[0094] like Figure 2 As shown, by identifying obvious tectonic erosion areas in the study area and combining the above calculation process, the Cretaceous erosion amount in the study area, Et = 1334.45m, was obtained.

[0095] (2) Calculation of regional erosion using tectonic-thermal chronology method Based on the chronological data and paleothermal gradient of the study area, a cooling history map was drawn, such as... Figure 3 As shown, the regional erosion amount of the Cretaceous system is calculated using the following formula:

[0096] In the formula, E h For the amount of regional erosion calculated using tectonic-thermal chronology; T c -T0 represents the cooling temperature; G represents the regional paleothermal gradient. The Cretaceous erosion amount E in the study area was calculated using the tectonic-thermal chronology method. h = 1999.87m.

[0097] (3) Calculation of regional erosion baseline By combining the results of the tectonic trend method and the tectonic-thermal chronology method, a weighted average method was used to determine the regional erosion baseline.

[0098] In the formula, E r w is the baseline for regional erosion. t and w h The weights are respectively the weights for the tectonic trend method and the tectonic-thermal chronology method, and satisfy the following:

[0099] In this embodiment, an equal-weighted average is used for calculation: E r = (1334.45 + 1999.87) / 2 = 1667.16 m. The reference erosion amount E for the region. r It is used to constrain the vertical extent of the restoration of the original boundaries of the near-source and intermediate-source facies zones of the No. 1 volcanic structure in a basin of the Bohai Bay, and is not directly used as the uniform erosion amount of all facies zones.

[0100] 5. Recovery of erosion in near-source and intermediate-source facies zones (1) Time-depth conversion A time-depth transformation was performed on the seismic profile containing Volcano No. 1, converting the time-domain profile to a depth-domain profile. Based on the drilling calibration results and velocity data of the study area, a depth-time relationship was established: D=0.001t 2 +1.3366t +45.822; In the formula, D is the stratum depth; t is the one-way reflection time.

[0101] (2) Establishment of Move equilibrium profile Based on a detailed characterization of the No. 1 volcanic structure in a basin in the Bohai Bay, the time-depth converted seismic profile, stratigraphic interpretation lines, fault interpretation lines, and volcanic structure boundaries were imported into Move software to establish a two-dimensional equilibrium profile model. The top and bottom boundaries of the volcanic rocks, the overlying strata interfaces, major faults, and the external boundaries of the volcanic structure were digitized in the model, forming a basic profile for structural reconstruction and boundary extrapolation.

[0102] (3) Elimination of discontinuity For the faults cutting through volcanic structure No. 1 and its overlying strata in a basin of the Bohai Bay, the simple shear recovery method in Move software was used for fault displacement elimination. During the recovery process, based on the fault cutting relationship and stratigraphic faulting characteristics, the fault displacement was restored in order from newest to oldest and from top to bottom, restoring the top and bottom boundaries, marker beds, and overlying strata interfaces of the faulted volcanic structure to a relatively continuous geometric state. After fault displacement elimination, the morphologies of the remnant volcanic structures in the near-source and intermediate-source facies zones, after structural correction, were obtained, such as... Figure 4As shown.

[0103] (4) Extrapolation of the original boundary of the mechanism and recovery of erosion amount under the constraint of regional erosion amount In the depth domain profile after structural restoration, the regional erosion reference quantity E is used. r = 1667.16m serves as the vertical constraint for restoring the original top boundary of the near-source and intermediate-source facies zones. Based on the extension direction of continuous or semi-continuous seismic reflection axes within the residual volcanic structure, seismic reflection trend lines for the near-source and intermediate-source facies zones are drawn, and the original boundaries of the pre-erosion volcanic structure are reconstructed by extrapolating along these trend lines. Figure 5 As shown. The original boundary before erosion, obtained by trend extrapolation reconstruction, is compared with the current residual boundary after tectonic reconstruction. The erosion amount of the near-source and intermediate-source facies zones is calculated using the following formula:

[0104] In the formula, E i H represents the erosion amount at the i-th calculation point. p,i H is the original height before erosion obtained by trend extrapolation recovery. r,i This is the current remaining height.

[0105] (5) Average erosion amount in near-source and intermediate-source facies zones The average erosion amount of the near-source and intermediate-source facies zones of volcanic structure No. 1 in a basin of the Bohai Bay was calculated using the area-weighted average method. Specifically, 10 calculation points were selected along the distribution direction of the near-source facies zone, and 5 calculation points were selected for the intermediate-source facies zone. Based on the erosion amount and horizontal distance between adjacent calculation points, the erosion area was calculated using the trapezoidal method.

[0106] In the formula, A E E represents the cross-sectional erosion area bounded between the original boundary before erosion and the current residual boundary; i and E i+1 These represent the erosion amounts at two adjacent calculation points; ∆x i Let be the horizontal distance between the i-th calculation point and the (i+1)-th calculation point; n is the number of calculation points. The relevant calculation results are shown in Table 2.

[0107] Table 2. Calculation table of relevant data on segmented erosion area in the intermediate source facies zone.

[0108] The lateral width of the phase band is calculated using the following formula:

[0109] In the formula, L is the lateral width of the phase band; x1 and x n These are the horizontal positions of the first and last calculation points within this phase band, respectively.

[0110] Furthermore, the ratio of the eroded area of ​​the profile to the lateral width of the facies zone is used as the area-weighted average erosion amount of that facies zone:

[0111] In the formula, The area-weighted average erosion amount is denoted as . Therefore, the point erosion and area-weighted average erosion amounts for the near-source and intermediate-source facies zones can be obtained separately. The point erosion amount is used to characterize local erosion differences, while the area-weighted average erosion amount is used to characterize the overall erosion degree of the facies zone. The final calculation results are shown in Table 3.

[0112] Table 3. Calculation data related to the weighted average erosion amount in the near-source and intermediate-source facies zones.

[0113] Based on the erosion amount and horizontal distance between adjacent calculation points, the trapezoidal integral method was used to calculate the erosion area of ​​the profile, and the area-weighted average erosion amount was obtained by dividing the erosion area of ​​the profile by the lateral width of the facies zone. The calculation results show that the maximum erosion amount in the intermediate source facies zone is 1.21 km, and the weighted average erosion amount is 0.75 km; the maximum erosion amount in the near-source facies zone is 1.67 km, and the weighted average erosion amount is 1.45 km.

[0114] 6. Recovery of erosion in the distant source facies zone (1) Selection of weathered samples from the parent rock end-member and distal facies zone Unweathered or weakly weathered volcanic rock samples from the Bohai Bay Basin were selected as parent rock end-members to represent the original chemical composition of the volcanic rocks before weathering. Volcanic rock samples from the distal facies zone that have been affected by weathering were selected as weathered samples to characterize the geochemical composition of the distal facies zone after weathering. The major element contents, loss on ignition, and rock density of the parent rock end-member samples and the distal facies zone weathered samples were compiled as the data basis for subsequent volumetric strain coefficient calculations, as shown in Table 4.

[0115] Table 4. Major element content and density data of weathered samples from parent rock endmembers and distal facies zones.

[0116] (2) Selection of reference elements that are not easily transferable Based on the major element data listed in Table 4, Ti, which has stable geochemical properties and is not easily migrated during chemical weathering, was selected as the reference element.

[0117] (3) Calculation of volumetric strain coefficient Based on the principle of mass conservation, and combined with the contents of non-migrating reference elements and rock density of weathered samples from the parent rock endmember and distal facies zone in Table 4, the volumetric strain coefficient of the weathered samples relative to the parent rock endmember is calculated:

[0118] In the formula, ε i,w ρ is the volumetric strain coefficient of the rock in the weathered sample. ρ ρ is the density of the parent rock sample. w Density of weathered sample; C i,p The content of Ti element in the parent rock; C i,w This represents the Ti element content in the weathered sample.

[0119] When ε i,w When ε < 0, it indicates that volume compression has occurred; when ε i,w When ε = 0, it indicates an approximate volume change; when ε i,w A value greater than 0 indicates that the volume has expanded. The calculation results are shown in Table 5.

[0120] (4) Calculation of the comprehensive chemical loss index Based on the volumetric strain coefficient of weathered samples from distant source facies zones, the comprehensive chemical depletion index is calculated using the following formula:

[0121]

[0122] In the formula, L i，j D represents the volume defect ratio of Ti. c The comprehensive chemical depletion index of the distant-source facies zone is used. In this embodiment, the calculated Dc is averaged to obtain the average comprehensive chemical depletion index D of the distant-source facies zone. c = 0.60, and the specific calculation results are shown in Table 5.

[0123] Table 5. Calculation table of relevant data on tectonic chemical erosion in a basin of Bohai Bay.

[0124] (5) Calculation of chemical erosion amount in the distant source facies zone Based on the seismic profile after time-depth conversion, the locations of the top and bottom boundaries of the distal source facies zone are extracted, and the current average residual thickness of the distal source facies zone is calculated as: H p = 277.70m.

[0125] Due to the comprehensive chemical loss index D c The thickness identified by the seismic profile is the current residual thickness after erosion, which is the loss ratio relative to the original thickness or original volume. Therefore, the chemically equivalent erosion amount needs to be calculated based on the mass conservation principle.

[0126] In the formula, E c H is the chemically equivalent erosion amount.p For the current thickness, D c The average comprehensive chemical loss index.

[0127] H p = 277.70m, D c Substituting 0.60 into the above formula, we can obtain the erosion amount E of the distal facies zone of tectonic structure No. 1 in a basin of the Bohai Bay. c = 416.54m.

[0128] I. Practical Application of Calculation Results of Erosion Amount in Different Phase Zones The erosion amounts of the near-source, intermediate-source, and distal-source facies zones calculated in this invention can be further used to restore the original morphology of buried volcanic structures before erosion and to reconstruct the original distribution of internal facies zones. Specifically, the erosion amounts of the near-source and intermediate-source facies zones are used to constrain the restoration of the original top boundary and flank morphology of the main body of the volcanic structure, while the chemically equivalent erosion amount of the distal-source facies zone is used to compensate for weathering quality defects that are difficult to identify using conventional seismic geometry methods. By backfilling the erosion amounts of different facies zones into the existing residual volcanic structure, the pre-erosion morphology of the volcanic structure can be reconstructed, such as... Figure 6 As shown, this provides a basis for volcanic rock lithology prediction, reservoir evaluation, trap effectiveness analysis, and exploration target selection.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for recovering the erosion amount of phasic zones in buried volcanic structures, characterized in that, Includes the following steps: (1) Establish a basic database for erosion recovery Collect seismic data, well logging data, core data, geochronological data, and geochemical test data of the study area to establish a basic database for the reconstruction of the erosion volume of buried volcanic structures; (2) Identification of buried volcanic structures and division of internal facies zones Based on the seismic phase reflection characteristics of buried volcanic structures, the buried volcanic structures are identified and their spatial distribution range is delineated; on this basis, the near-source facies zone, intermediate-source facies zone, and far-source facies zone are further identified based on the seismic reflection parameters inside the volcanic structures. (3) Differentiating erosion recovery methods for different phase zones Based on the seismic reflection characteristics, spatial distribution characteristics, and weathering and erosion characteristics of the near-source facies zone, intermediate-source facies zone, and distal-source facies zone, the appropriate erosion recovery methods for each facies zone are determined. (4) Determine the baseline amount of regional erosion. The tectonic trend method and the tectonic-thermal chronology method were used to calculate the regional erosion amount in the study area, and the regional erosion baseline amount was determined by combining the two methods. (5) Recovery of erosion in near-source and intermediate-source facies zones Time-depth conversion, Move equilibrium profile establishment, fault displacement elimination, and tectonic restoration were performed on the near-source and intermediate-source facies zones to obtain the residual morphology of the volcanic structure after tectonic correction. Using the regional erosion baseline as the vertical constraint for the restoration of the original top boundary, extrapolation was performed based on the seismic reflection axis distribution trend of the residual volcanic structure to restore the original volcanic structure boundary before erosion, and the erosion amount of the near-source and intermediate-source facies zones was calculated. Then, the average erosion amount of the near-source and intermediate-source facies zones was calculated using the area-weighted average method. (6) Recovery of erosion in the distant source facies zone For the distant source facies zone, the parent rock end-member and non-migrating reference elements are selected. The volumetric strain coefficient is calculated based on the content of non-migrating elements and rock density in the parent rock and weathered samples. The comprehensive chemical depletion index is further determined, and the chemical equivalent erosion amount is calculated in combination with the current residual thickness of the distant source facies zone. In step (3), the near-source facies zone and the intermediate-source facies zone are restored by combining the Move equilibrium profile restoration under the constraint of regional erosion benchmark quantity with the volcanic morphology constraint, and the distant-source facies zone is restored by the geochemical mass balance method. In step (5), the specific operational steps for restoring the erosion amount of the near-source facies zone and the intermediate-source facies zone are as follows: The seismic time-domain profile of the area where the target volcanic structure is located is converted into a depth-domain profile, and the interpreted data is imported into Move software to establish a two-dimensional equilibrium profile model. Fault displacement elimination and structural restoration are carried out on the faults that cut through the volcanic structure and its overlying strata, so that the top and bottom boundaries of the structure, the marker layer and the interface of the overlying strata that were dislocated by the faults are restored to a relatively continuous geometric state. Using the regional erosion baseline as the vertical constraint for the restoration of the original top boundary of the near-source facies zone and the intermediate-source facies zone, and extrapolating the trend based on the seismic reflection axis distribution trend of the residual volcanic structure after tectonic restoration, the original volcanic structure boundary before erosion is restored. By comparing the original volcanic structure boundary obtained by trend extrapolation with the current residual volcanic structure boundary after tectonic reconstruction, the erosion amount of the near-source and intermediate-source facies zones is calculated using the following formula: In the formula, E i For the first i The erosion amount at each calculation point H p,i The original height before erosion is obtained by trend extrapolation and reconstruction. H r,i This is the current remaining height; Then, the average erosion amount of the near-source facies zone and the intermediate source facies zone was calculated using the area-weighted average method; where the point erosion amount was used to characterize the local erosion difference, and the area-weighted average erosion amount was used to characterize the overall erosion degree of the facies zone. In step (6), the specific steps for restoring the erosion amount of the distant source phase zone are as follows: Unweathered or weakly weathered volcanic rock samples from the study area were selected as parent rock end-members to represent the original chemical composition of the volcanic rocks before weathering. When unweathered or weakly weathered volcanic rock samples were lacking in the study area, unweathered volcanic rock samples from the same stratigraphic position, lithology, and genetic background were selected as substitute parent rock end-members. Volcanic rock samples affected by weathering in the distal facies zone were selected as weathered samples to characterize the geochemical composition and density change characteristics of the distal facies zone after weathering. Elements that are geochemically stable and not easily migrated during chemical weathering were selected as reference elements; Based on the content of non-migrating reference elements in the parent rock endmember and weathered sample, and the rock density, the volumetric strain coefficient of the weathered sample is calculated using the following formula: In the formula, ε i,w denoted as the volumetric strain coefficient of the rock in the weathered sample; ρ ρ Density of the parent rock sample; ρ w Density of the weathered sample; C i,p Elements that are not easily migrated in the parent rock i The content; C i,w Elements that do not easily migrate in weathered samples i The content; A comprehensive chemical deficit index is established based on the volumetric strain coefficient to reflect the volumetric change characteristics of the weathered sample relative to the parent rock during the chemical weathering process. The calculation formula is as follows: In the formula, L i，j For elements i The volume loss ratio, D c The comprehensive chemical depletion index is used to characterize the degree of overall chemical quality loss of volcanic rocks relative to their parent rocks. The remaining thickness of the distant-source phalanx H p As a reference thickness, the chemically equivalent erosion amount of the distal phase zone is calculated using the following formula: In the formula: E c This is the chemically equivalent erosion amount. H p For the current thickness, D c This is a comprehensive chemical loss index.

2. The method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to claim 1, characterized in that, In step (1), the seismic data includes three-dimensional seismic data volume, stratigraphic interpretation results, fault interpretation results, and seismic attribute data; the logging data includes relevant well column data, lithological interpretation, logging data, and logging curves for the study area; the core data includes core observation, lithological description, volcanic rock structure, alteration and weathering characteristics, and sampling stratigraphic information; the geochronological data includes zircon U-Pb age, apatite fission track age, zircon fission track age, regional paleothermal gradient, and burial history data; and the geochemical testing data includes volcanic rock density and major element test data.

3. The method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to claim 1, characterized in that, In step (2), the seismic phase reflection characteristics of the buried volcanic structure include external geometry, reflection differences at the top and bottom interfaces, internal reflection structure, contact relationship with the surrounding rock or overlying strata, and lateral pinch-out characteristics.

4. The method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to claim 1, characterized in that, In step (2), the seismic reflection parameters include the reflecting structure, amplitude, frequency, and continuity.

5. The method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to claim 1, characterized in that, In step (4), the formula for calculating the amount of regional erosion using the tectonic trend method is as follows: In the formula, E t The amount of regional erosion calculated using the tectonic trend method; H e The theoretical deposition thickness; H o This represents the current thickness of the remaining strata. The formula for calculating the amount of regional erosion using the tectonic-thermal chronology method is as follows: In the formula, E h For the amount of regional erosion calculated by tectonic-thermal chronology; T c - T 0 This refers to the cooling temperature. G The regional paleothermal gradient; By combining the results of the tectonic trend method and the tectonic-thermal chronology method, the baseline amount of regional erosion was determined: In the formula, Er As a baseline for regional erosion, w t and w h The weights are respectively the weights for the tectonic trend method and the tectonic-thermal chronology method, and satisfy the following: .

6. The method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to claim 1, characterized in that, The specific operation method for calculating the average erosion amount of the near-source and intermediate-source facies zones using the area-weighted average method is as follows: Several calculation points are selected along the phasor distribution direction, and the erosion area of ​​the profile is calculated using the trapezoidal method based on the erosion amount and horizontal distance between adjacent calculation points: In the formula, A E The cross-sectional erosion area enclosed between the original boundary before erosion and the current residual boundary; E i and E i+1 These represent the erosion amounts at two adjacent calculation points; ∆x i For the first i The calculation point and the first i+1 The horizontal distance between the calculation points; n To calculate the number of points; The lateral width of the phase band is calculated using the following formula: In the formula, L This refers to the lateral width of the phase band. x 1 and x n These are the horizontal positions of the first and last calculation points within the phase band, respectively. Furthermore, the ratio of the eroded area of ​​the profile to the lateral width of the facies zone is used as the area-weighted average erosion amount of that facies zone: In the formula, The area-weighted average erosion amount of the facies zone is used to represent the local erosion difference, while the area-weighted average erosion amount represents the overall erosion degree of the facies zone.

7. The application of the method for restoring the erosion amount of the phasic zone of a buried volcanic structure according to any one of claims 1 to 6, characterized in that, Used for volcanic rock lithology prediction, reservoir evaluation, trap effectiveness analysis, and exploration target selection.

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