System and method for analyzing influence of stratum elements on reservoir forming-decomposition process of natural gas hydrate in sea area

Abstract

The invention belongs to but is not limited to the technical field of sea area natural gas hydrate research, and discloses a system and a method for analyzing the influence of stratum elements on the reservoir forming-decomposition process of sea area natural gas hydrates. The control effect of formation elements such as lithology, granularity, formation thickness, dip angle and structural form such as wrinkles on distribution characteristics (including BSR, an overlying hydrate layer and an underlying free gas layer) of a static hydrate system and processes such as migration, aggregation or leakage of methane in the migration process of the dynamic hydrate system is researched. Specifically, the control effects of stratum elements on BSR types, high-low amplitude interaction characteristics of the BSR on a section and a plane, heterogeneity distribution of a hydrate layer and a free gas layer in a static hydrate system, methane migration-aggregation-leakage after BSR migration of a dynamic hydrate system and other processes are analyzed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of marine natural gas hydrate research, and particularly relates to a system and method for analyzing the influence of formation elements on the accumulation and decomposition process of marine natural gas hydrate. BACKGROUND

[0002] Natural gas hydrate is widely distributed in the global range and is considered to be a clean alternative energy source in the future, more than 90% of which exists in the marine environment. Ruppel and Kessler (2017) predicted that the carbon storage in hydrate was predicted to be 1800 Gt C. Based on the resource type and occurrence state of natural gas hydrate, combined with the geological conditions, the China Mineral Resources Report 2018 preliminarily predicted that the amount of natural gas hydrate resources in the marine environment of China was about 80 billion tons of oil equivalent, close to the amount of conventional oil resources in China, and about twice the amount of conventional natural gas resources. In addition to providing a large amount of clean energy, natural gas hydrate is also considered to play an important role in marine geological disasters and ecological threats (such as submarine landslides, ocean acidification, etc.) and global climate warming due to its shallow burial depth, poor stability, and the fact that the methane contained therein has a stronger greenhouse effect than carbon dioxide. In particular, the hydrate is close to the land boundary, which is most sensitive to temperature change events on the seabed, and the hydrate is easy to decompose, and the free gas released by the decomposition of deep hydrate can also occur lateral long-distance migration along the hydrate bottom boundary. Therefore, there may be a large methane release flux at the boundary, and the released methane and other gases may enter the water body and even the atmosphere, causing carbon circulation between the lithosphere, hydrosphere and atmosphere, and causing certain environmental and climate impacts.

[0003] In recent years, the research on gas hydrate in the South China Sea has made significant progress in gas source identification, migration pathway delineation, reservoir characterization, and accumulation mechanism, and formed a systematic understanding. A large number of geochemical data show that the gas source types of hydrate in many marine areas in the world are diverse, mainly mixed, containing biogenic gas and thermogenic gas. Through the statistics of hundreds of seismic profiles, Yang et al. (2025) sorted out the spatial relationship between different fluid migration pathways and hydrate systems, and believed that faults and gas chimneys were the main fluid migration pathways, accounting for 47% and 33% of hydrate-related fluid migration pathways, respectively. Other migration pathways mainly included diapiric structures, mud volcanoes, unconformities, and inclined permeable sandstone layers. In terms of reservoirs, Zhou et al. (2024) characterized the spatial distribution of sandstone reservoir hydrate and shallow gas in the Qiongdongnan Basin through seismic spectral decomposition-amplitude attribute fusion. Liang et al. (2024) and Jia et al. (2024) summarized the reservoir characteristics and distribution of high-saturation hydrate through well logging, seismic, and core sample testing data, and discussed the comprehensive logging-seismic response discrimination method of hydrate layer, free gas layer, and coexisting layer. In terms of accumulation, different experts and scholars used 3D seismic, multi-beam, and seafloor sampling data to comprehensively analyze the distribution characteristics and accumulation mechanism of hydrate in the South China Sea, and established the hydrate accumulation model and seafloor fluid leakage model in different work areas.

[0004] Although some understanding has been achieved in gas source, migration pathway, reservoir characterization, and accumulation, the research on the control of stratigraphic elements on hydrate systems is still not deep. In terms of stratigraphic elements, although it is recognized that reservoir quality will affect the saturation of hydrate and free gas, the detailed description of the influence of stratigraphic elements on static and dynamic hydrate systems is still not deep.

[0005] Static gas hydrate system refers to a gas hydrate system that has migrated from a past location to a location controlled by present temperature and pressure conditions and is in equilibrium state, and is temporarily in a migration state without being affected by other events. For a static gas hydrate system, formation elements affect the type (divided into two types) and profile and plane characteristics of a BSR (Bottom simulating reflection, a seismic reflection interface of the bottom boundary of a hydrate stability zone in a sea area), and the heterogeneity distribution of a hydrate layer above the BSR and a free gas layer underlying the BSR. Type 1 BSR is not easy to accumulate free gas below the BSR, and type 2 BSR is easy to accumulate free gas below the BSR. Dynamic gas hydrate system refers to the upward or downward migration of the bottom boundary of a hydrate stability zone (seismically represented as a BSR) controlled by temperature and pressure condition changes caused by events such as sea level changes, global warming, deposition, erosion, and heat flow anomalies. The process is accompanied by frequent hydrate formation and decomposition, and the hydrate system at this time is referred to as a dynamic gas hydrate system. For a dynamic hydrate system, although Wang Xiujun et al. (2024) analyzed four main control factors of BSR adjustment for the dynamic adjustment problem of multiple phase states coexisting in a hydrate system, the methane fate problem after BSR migration (especially upward migration) was not analyzed. At present, the study of methane in the hydrate decomposition zone mainly focuses on the characteristics of a large amount of seafloor fluid leakage along the boundary, and the understanding of the methane fate in the entire hydrate decomposition zone after the dynamic migration of the hydrate stability zone and the role of formation elements in the process is still unclear.

[0006] For example, CN114542022B discloses a "deep-sea gas hydrate filling mining method", which discloses a technical solution of horizontal well and vertical well combined arrangement, grouting filling, pressure reduction or hot injection mining. The focus is to improve the mining efficiency of seafloor hydrate reservoirs and control the problem of formation deformation.

[0007] Although this scheme provides specific well type arrangement and construction measures for mining operations, it does not fully address the control of formation elements (such as dip angle, thickness, and fault connectivity) on the hydrate system accumulation-decomposition process based on seismic-logging joint interpretation, BSR migration, and paleo-BSR identification. Therefore, there are still deficiencies in the evolution mechanism of the hydrate system, the control model of the formation elements, the identification and inversion analysis capability of the decomposition zone. SUMMARY

[0008] In view of the problems existing in the prior art, the present application provides a system and method for analyzing the influence of formation elements on the accumulation-decomposition process of gas hydrate in a sea area.

[0009] The present application is realized in a kind of stratum element influence analysis method of marine gas hydrate accumulation-decomposition process, which comprises:

[0010] S101, a certain marine gas hydrate development area is selected as research work area, and well logging, seismic data, and report and published literature and other information are collected;

[0011] Seismic interpretation is carried out on present seabed to master seabed distribution characteristics;

[0012] Seismic interpretation is carried out on present BSR to determine the inclination and dip angle parameters of BSR;

[0013] Seismic interpretation and attribute extraction are carried out on present BSR, profile amplitude characteristics of BSR are analyzed, and plane attribute maps such as RMS amplitude, frequency, coherence and the like of BSR are made;

[0014] Seismic interpretation and attribute extraction are carried out on paleo-BSR existing near (upper or lower) present BSR to master distribution characteristics of paleo-BSR;

[0015] If seismic characteristics of paleo-BSR are not obvious, numerical simulation means can be used to predict paleo-BSR at a certain period in geological history;

[0016] Present gas hydrate system, i.e. the region between seabed and present BSR, is determined;

[0017] Based on seismic interpretation and numerical simulation prediction results of present BSR and paleo-BSR, migration process of gas hydrate stable domain since a certain period in geological history is determined, and there are two migration conditions of BSR upward migration and BSR downward migration;

[0018] S102, stratum element parameters of development position of gas hydrate system (especially near BSR and hydrate decomposition zone) are determined through well-seismic data analysis;

[0019] S103, control action analysis of stratum element on static hydrate system is carried out;

[0020] S104, distribution characteristics of hydrate layer above present BSR are depicted based on well-seismic data analysis and inversion results;

[0021] S105, control action analysis of stratum element on hydrate layer is carried out in combination with stratum element characteristics;

[0022] S106, distribution characteristics of free gas layer below present BSR are depicted based on well-seismic data analysis and inversion results;

[0023] S107, control action analysis of stratum element on free gas layer is carried out in combination with stratum element characteristics;

[0024] S108, analyze and summarize the control of the stratigraphic elements on the static gas hydrate system;

[0025] S109, analyze the control of the stratigraphic elements on the dynamic hydrate system; first determine the migration direction of the BSR in the study area;

[0026] S110, if the BSR moves upward, the hydrate dissociation zone (HDZ) is between the ancient and modern BSRs, and the reflection layer in the hydrate dissociation zone needs to be interpreted and analyzed, the related reflection anomalies are identified, the fluid migration path in the hydrate dissociation zone is revealed, and the free gas is accumulated;

[0027] S111, analyze the control of the stratigraphic elements on the process of methane migration, accumulation or leakage in the dissociation zone;

[0028] S112, if the BSR moves downward, the free gas under the ancient BSR can form gas hydrate as a gas source, which is beneficial to the preservation of methane in the hydrate system;

[0029] S113, analyze and summarize the control of the stratigraphic elements on the dynamic gas hydrate system;

[0030] S114, based on the above analysis of the control of the stratigraphic elements on the modern static hydrate system and the dynamic hydrate system in the geological history period, establish the stratigraphic element control model of the hydrate system in the study area.

[0031] Further, the stratigraphic element parameters of the natural gas hydrate system development position (especially near the BSR and the hydrate dissociation zone) are determined through well-seismic data analysis:

[0032] Including lithology, particle size, physical property, stratigraphic thickness, dip angle, structural form such as fold, etc.; the specific methods and technical means include well logging and sediment sample interpretation and analysis, seismic interpretation and attribute analysis, and reservoir inversion prediction based on well-seismic combination.

[0033] Further, the control of the stratigraphic elements on the static hydrate system is analyzed:

[0034] First, analyze the control of the stratigraphic elements on the BSR, describe the amplitude characteristics of the modern BSR on the seismic profile and plan view, and then analyze the genetic relationship between the two, i.e. whether the stratigraphic elements control the planar and profile characteristics of the BSR.

[0035] Further, the control of the stratigraphic elements on the hydrate layer is analyzed in combination with the characteristics of the stratigraphic elements:

[0036] The upper hydrate layer of BSR has great difference in different areas, and the distribution of hydrate layer in different positions of the same area is also different, which may be controlled by the difference of stratum dip angle in two positions, and the position with larger stratum dip angle is more favorable for the transportation of gas source and thus forms the hydrate layer with higher saturation.

[0037] Further, the analysis and summary of the control effect of the stratum element on the static natural gas hydrate system are as follows:

[0038] It is considered that the stratum element influences and controls the plane and profile features and distribution of BSR, upper hydrate layer and underlying free gas layer; another typical case is that the static hydrate system of the anticline belt is controlled by the stratum element (especially the structural form).

[0039] Further, the analysis and summary of the control effect of the stratum element on the dynamic natural gas hydrate system are as follows:

[0040] The main hydrate stability zone and the landward distribution boundary of hydrate stability zone often have different BSR types and dip angle features, and the main hydrate stability zone and the landward distribution boundary of hydrate stability zone can be researched respectively, and thus the control effect of the stratum element on the entire hydrate system accumulation-decomposition is mastered.

[0041] Another purpose of the present application is to provide a stratum element influence analysis system for the accumulation-decomposition process of marine natural gas hydrate, which comprises:

[0042] The parameter acquisition module is used for selecting a certain marine natural gas hydrate development area as a research work area, collecting logging, seismic and other data, and report and published literature and other materials; performing seismic interpretation on the present sea bottom to master the sea bottom distribution features; performing seismic interpretation on the present BSR to determine the dip direction and dip angle parameters of the BSR; performing seismic interpretation and attribute extraction on the present BSR to analyze the profile amplitude features of the BSR, and making plane attribute maps of the BSR such as RMS amplitude, frequency, coherence and the like; performing seismic interpretation and attribute extraction on the paleo-BSR existing near (upper or lower) the present BSR to master the distribution features of the paleo-BSR; if the seismic features of the paleo-BSR are not obvious, the numerical simulation means can be used to predict the paleo-BSR in a certain period of geological history; determining the present natural gas hydrate system; that is, the region between the sea bottom and the present BSR; based on the seismic interpretation and numerical simulation prediction results of the paleo-BSR and the present BSR, determining the migration process of the natural gas hydrate stability zone since a certain period of geological history, and there are two cases of BSR upward migration and BSR downward migration; determining the stratum element parameters of the development position (especially the position near the BSR and the hydrate decomposition zone) of the natural gas hydrate system through well-seismic data analysis;

[0043] The analysis module is used for analyzing the control effect of the formation elements on the static hydrate system; based on the well seismic data analysis and inversion results, the distribution characteristics of the hydrate layer above the present BSR are depicted; in combination with the formation element characteristics, the control effect of the formation elements on the hydrate layer is analyzed; based on the well seismic data analysis and inversion results, the distribution characteristics of the free gas layer below the present BSR are depicted; in combination with the formation element characteristics, the control effect of the formation elements on the free gas layer is analyzed; the control effect of the formation elements on the static natural gas hydrate system is analyzed and summarized; the control effect of the formation elements on the dynamic hydrate system is analyzed; the BSR migration direction of the research area is determined firstly;

[0044] The identification module is used for, if the BSR moves upwards, the hydrate decomposition zone HDZ between the ancient and present BSRs, the reflection layer of the hydrate decomposition zone needs to be interpreted and analyzed by using the seismic data, the related reflection abnormal characteristics are identified, the distribution of the fluid migration path of the hydrate decomposition zone and the aggregation of the free gas are revealed, and the control effect of the formation elements on the migration, aggregation or leakage process of the released methane in the decomposition zone is analyzed; if the BSR moves downwards, the underlying free gas of the ancient BSR can form the natural gas hydrate and is beneficial to the preservation of the methane in the hydrate system; the control effect of the formation elements on the dynamic natural gas hydrate system is analyzed and summarized.

[0045] The reservoir controlling mode establishing module is used for establishing the formation element reservoir controlling mode of the hydrate system in the research area based on the above analysis on the control effect of the formation elements on the present static hydrate system and the dynamic hydrate system in the geological history period.

[0046] Another object of the present application is to provide a computer device comprising a memory and a processor, wherein the memory stores a computer program, and the computer program is executed by the processor to enable the processor to execute the steps of the method for analyzing the influence of formation elements on the natural gas hydrate formation-decomposition process in a sea area.

[0047] Another object of the present application is to provide a computer readable storage medium storing a computer program, and the computer program is executed by a processor to enable the processor to execute the steps of the method for analyzing the influence of formation elements on the natural gas hydrate formation-decomposition process in a sea area.

[0048] Another object of the present application is to provide an information data processing terminal for realizing the system for analyzing the influence of formation elements on the natural gas hydrate formation-decomposition process in a sea area.

[0049] In combination with the above technical solutions and the technical problems solved, the technical solution to be protected by the present application has the following advantages and positive effects:

[0050] The application provides a system and method for analyzing the influence of stratum elements on the formation and decomposition process of marine gas hydrate, and belongs to the front field. From the perspective of stratum elements, the control effect of lithology, particle size, stratum thickness, dip angle, tectonic shape such as fold and other stratum elements on the distribution characteristics of static hydrate system (including BSR, overlying hydrate layer and underlying free gas layer) and the migration, accumulation or leakage process of methane in the dynamic hydrate system migration process is studied. Specifically, the control effect of stratum elements on the type of BSR, the high-low amplitude interaction characteristics of BSR in the profile and plane, the heterogeneous distribution of hydrate layer and free gas layer in the static hydrate system, and the methane migration-accumulation-leakage process after BSR migration in the dynamic hydrate system is analyzed.

[0051] (1) The technical scheme of the application fills the technical blank in the industry at home and abroad:

[0052] In recent years, the research on natural gas hydrate, especially the research on hydrate in the South China Sea, has made significant progress and formed a systematic understanding in gas source identification, migration pathway depiction, reservoir characterization and accumulation mechanism. However, the control effect of stratum elements on the hydrate system has not been deeply studied. In terms of stratum elements, although it is realized that the reservoir quality (sandy reservoir is better than argillaceous reservoir) will affect the saturation of hydrate and free gas, the detailed depiction of the control effect of stratum elements on static and dynamic hydrate systems is not deep. For example, the stratum lithology and dip angle, and the spatial relationship with BSR jointly control the amplitude characteristics of BSR in the plane and profile of the static hydrate system, and the heterogeneous distribution of the hydrate layer and the underlying free gas layer. In addition to the pathway, the stratum elements also control the end type of methane migration-accumulation-leakage of the dynamic hydrate system. Therefore, a comprehensive understanding and evaluation of the control effect of stratum elements on static and dynamic hydrate systems is indispensable for understanding the hydrate formation and decomposition process and mechanism, and is a powerful supplement to the current hydrate accumulation research which focuses on gas source and fluid migration.

[0053] (2) Does the technical scheme of the application solve the technical problems that people have been eager to solve but have failed to succeed:

[0054] The technical scheme of the application is aimed at a reservoir-controlling element that is ignored in the current hydrate research, and is helpful for comprehensively understanding the hydrate formation and decomposition process and mechanism.

[0055] (3) Does the technical scheme of the application overcome the technical prejudice:

[0056] The present hydrate reservoir research focuses on the prediction of hydrate saturation, and the research on the details of static and dynamic hydrate system and the control effect of formation elements is not deep enough. In fact, the formation elements not only affect the hydrate saturation from the perspective of reservoir quality, but also have certain control effect on the details such as the transportation of gas source, the type of BSR, the amplitude and strip features of BSR / hydrate layer / free gas layer, and the methane migration and dispersion process accompanied by the dynamic hydrate system. The present application provides a set of research methods and processes for the control of hydrate accumulation-decomposition process by formation elements, which is helpful for comprehensively evaluating the control effect and influence of formation elements on the hydrate accumulation-decomposition process in the sea area, and is a powerful supplement to the present hydrate accumulation research. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 It is the influence analysis method and process diagram of the formation elements on the hydrate accumulation-decomposition process in the sea area provided by the embodiment of the present application.

[0058] Figure 2 It is the structural block diagram of the influence analysis system of the formation elements on the hydrate accumulation-decomposition process in the sea area provided by the embodiment of the present application.

[0059] Figure 3 It is the intersection position of the (a) natural gas hydrate phase equilibrium curve (red line) and the geothermal gradient curve (blue line) provided by the embodiment of the present application, which is the BSR development position. Global warming and sedimentation change the temperature and pressure conditions, so that the BSR moves upward. (c) Schematic diagram of dynamic natural gas hydrate system. The hydrate decomposition zone is between the ancient and modern BSRs.

[0060] Figure 4 It is the control effect schematic diagram of the formation elements (lithology sand-shale interbedding, BSR / formation dip angle) on the BSR amplitude attribute provided by the embodiment of the present application. (a) When the BSR is consistent with the formation tendency and the BSR dip angle is steep, it is BSR type 1, and at this time, the underlying free gas is easy to migrate laterally, so that the lower free gas is not easy to accumulate. (b) When the BSR is consistent with the formation tendency and the BSR dip angle is gentle, it is BSR type 2, and at this time, the underlying free gas is capped by the upper hydrate, and is easy to accumulate in the lower free gas.

[0061] Figure 5 It is the research scheme and technical flowchart provided by the embodiment of the present application.

[0062] Figure 6is the feature of BSR on RMS amplitude attribute plane map and typical seismic profile provided by the embodiment of the present application (a) RMS amplitude attribute plane map of BSR shows that BSR presents high and low amplitude band interbedding on the plane, and the approximately symmetrical distribution ring on both sides is inclined to the opposite direction respectively; (b) the seismic profile shows that when BSR is consistent with the stratum tendency and the BSR dip angle is steep, it is BSR type 1, the amplitude band on the plane is inclined to the land uplift, and the underlying free gas of this type of BSR is easy to migrate laterally along the stratum, so that the free gas is not easy to accumulate in the lower part; (c) the seismic profile shows that when BSR is consistent with the stratum tendency and the BSR dip angle is gentle, it is BSR type 2, the amplitude band on the plane is inclined to the sea uplift, and at this time, the underlying free gas is capped by the upper hydrate, and is easy to accumulate in the lower part; (d) the seismic profile shows that when BSR is opposite to the stratum tendency, the free gas is accumulated in the lower part of BSR.

[0063] Figure 7 is the seismic profile (a) and the inversion profile (b-c) provided by the embodiment of the present application, which shows the distribution of hydrate layer above BSR and the distribution of underlying free gas layer.

[0064] Figure 8 is the RMS amplitude attribute map of BSR to the lower 50ms time window range provided by the embodiment of the present application, which shows the stratified distribution of free gas.

[0065] Figure 9 is the distribution characteristic diagram of BSR, upper hydrate and underlying free gas in anticline stratum provided by the embodiment of the present application.

[0066] Figure 10 is the stratum element control reservoir diagram in the marine gas hydrate system provided by the embodiment of the present application. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0068] In the actual industrial scene of gas hydrate investigation and development in the sea area, a long-standing key technical bottleneck is that the stable state, decomposition degree and migration trajectory of the hydrate system in geological history cannot be accurately determined, resulting in uncertainty in resource assessment, production risk control and stratum safety research. The traditional interpretation process relies on single seismic amplitude reflection, simple BSR depiction or local well data comparison, and the understanding of stratum factors in the hydrate accumulation process is limited, especially in areas with strong sedimentary structure changes, ambiguous paleo-BSR records and significant fault channels, making it difficult to establish a complete evolution framework. This method attempts to systematically analyze the control of stratum elements on the hydrate layer, free gas layer and BSR between the hydrate / free gas interface, in order to solve the cognitive blind spot commonly faced by the industry in the resource evaluation and engineering deployment stages.

[0069] At the operational level, the research process first restores the continuity of the seismic data in the sea area and corrects the energy structure, so that the BSR and the interface morphology of the overlying sediment can be stably identified under high signal-to-noise ratio conditions. This paper focuses on the combined performance of envelope energy, instantaneous phase and coherence volume, which correspond to reflection intensity, phase change and phase destruction, respectively. In areas where hydrate decomposition or fluid intrusion is significant, these attributes often show coordinated anomalies. Through this joint attribute constraint, the present BSR and potential paleo-BSR residual interface can still be reliably located in weak reflection, slope terrain or high-frequency attenuation background.

[0070] Secondly, with the aid of joint inversion framework of logging and seismic, the spatial variation of acoustic velocity, density, porosity and saturation is converted into interpretable stratum physical property distribution. The inversion module uses the error iteration between the reflection coefficient sequence and the acoustic impedance model to make the bright and weak bands of the seismic section consistent with the real parameters of the sediment phase. After inversion, key horizons directly related to hydrate formation and decomposition can be identified, such as stable intervals with low porosity and high impedance, and sensitive bands with significantly enhanced amplitude due to free gas intrusion. Such physical indicators provide reliable basis for evaluating the sealing capacity of the sediment and the gas accumulation effect.

[0071] In the geological history analysis section, by comparing the vertical migration of present BSR and paleo-BSR in depth domain, the migration direction of the upper or lower limit of the stable domain in geological period can be inferred. When there is an upward trend, it means that the study area has experienced hydrate decomposition process due to temperature rise, pressure drop or fluid intrusion. The decomposition zone is often accompanied by reflection energy enhancement, main frequency drop and coherence destruction, which indicates that the fluid is migrating upward through interlayer seepage, tectonic fractures or fault channels. Conversely, if the downward trend is obvious, the ancient free gas may participate in accumulation again under new stable conditions, providing support for explaining the methane preservation mechanism.

[0072] Further, the analysis system is integrated with the stratigraphic dip, the sedimentary layer thickness variation and the fault conductivity, so as to construct a geometric framework for controlling fluid migration. A large stratigraphic dip can change the local distribution of the heat flow density, thereby affecting the thickness of the hydrate stability zone; the permeability gradient caused by the thickness difference between layers can guide the gas to migrate along the high-permeability layer preferentially; and the sealing or opening of the fault directly affects whether the deep free gas can penetrate the stable zone to the shallow part. The responses of these elements in the seismic attribute volume are not isolated, but together with the reflection frequency, the coherence and the phase stability, constitute the key evidence for judging the control mechanism.

[0073] Finally, by integrating the above stratigraphic parameters, the inverted physical properties, the seismic attributes and the BSR migration characteristics, a control model can be constructed, which not only contains the static accumulation pattern, but also reflects the decomposition and re-accumulation path in the geological history. The model not only describes the spatial relationship between the hydrate layer and the free gas layer, but also reveals the role of the sedimentary structure, the tectonic framework and the thermodynamic condition in the accumulation evolution, thereby providing an applicable interpretation system for the industry in the aspects of resource development, safety evaluation, stratigraphic stability analysis and submarine engineering planning.

[0074] As shown in Figure 1 The method provided by the embodiment of the present application for analyzing the influence of the stratigraphic elements on the accumulation-decomposition process of the marine natural gas hydrate includes the following steps:

[0075] S101, a marine natural gas hydrate development area is selected as a research work area, and well logging, seismic data, and reported and published literature materials are collected;

[0076] The present-day seafloor is interpreted by using the seismic data, so as to master the distribution characteristics of the seafloor; and the present-day BSR is interpreted by using the seismic data, so as to determine the inclination and the dip angle parameters of the BSR;

[0077] The present-day BSR is interpreted by using the seismic data and the attribute extraction is performed, the profile amplitude characteristics of the BSR are analyzed, and the planar attribute map of the BSR such as the RMS amplitude, the frequency, the coherence and the like is made; and the paleo-BSR existing in the vicinity (the upper part or the lower part) of the present-day BSR is interpreted by using the seismic data and the attribute extraction is performed, so as to master the distribution characteristics of the paleo-BSR;

[0078] If the seismic characteristics of the paleo-BSR are not obvious, the numerical simulation means can be used to predict the paleo-BSR in a geological history period;

[0079] The present-day natural gas hydrate system, i.e., the region between the seafloor and the present-day BSR, is determined;

[0080] Based on the seismic interpretation of the paleo-BSR and the prediction result of the numerical simulation, the migration process of the natural gas hydrate stable zone since a geological history period is determined, and there are two cases of the BSR upward migration and the BSR downward migration;

[0081] S102, by well-seismic data analysis, determine the stratigraphic element parameters of the gas hydrate system development position (especially near the BSR and the hydrate dissociation zone);

[0082] Including lithology, grain size, physical property, formation thickness, dip, structural form such as fold, etc. The specific methods and technical means include well logging and sediment sample interpretation and analysis (which can determine lithology, grain size, physical property, etc.), seismic interpretation and attribute analysis (which can determine formation thickness, dip, structural form such as anticline, etc.), and reservoir inversion prediction based on well-seismic combination (which can predict the distribution characteristics of each stratigraphic element related to the hydrate system);

[0083] S103, analyze the control effect of stratigraphic elements on static hydrate system;

[0084] First, analyze the control effect of stratigraphic elements on BSR, depict the amplitude characteristics of present BSR on seismic profile and plan view, and then analyze the genetic relationship between the two, that is, whether the stratigraphic elements control the planar and profile characteristics of BSR;

[0085] The seismic reflection signal, velocity curve and rock physical parameters of the study area are obtained through multi-component seismic data and logging data. After field acquisition, the seismic signal is first denoised, including random noise suppression, surface multiple wave suppression and instrument response correction. Then, according to the geometric configuration of the observation system, de-static correction, synthetic trace analysis and normalization processing are carried out to make the seismic signal have consistent dynamic range and time resolution. The logging signals (acoustic wave, density, resistivity, etc.) are simultaneously sampled and filtered to ensure the consistency of the frequency spectrum of the well-seismic signals, providing a basis for well-seismic correction.

[0086] In the pre-processed pre-stack or post-stack seismic data, the sea bottom reflection interface and the pseudo-sea bottom reflection layer (BSR) are identified by automatic picking and manual checking. The BSR identification features include high amplitude, negative polarity opposite to the sea bottom reflection, and usually cutting the isochronous strata controlled by temperature and pressure conditions. Envelope energy method, instantaneous phase method and frequency spectrum analysis method are used to extract the attribute signals of BSR, such as RMS amplitude, main frequency and instantaneous coherence coefficient. Through time-depth conversion and attribute stacking analysis, the distribution continuity of BSR on profile and plane is obtained, which lays a signal foundation for subsequent BSR migration analysis.

[0087] The acoustic impedance model is built by using well logging curves, and the wavelet is extracted by the reflection coefficient sequence and the measured seismic record. The synthetic seismic profile is generated by using the well-to-seismic synthesis technology, the similarity of the seismic reflection signal and the synthetic signal is compared, and the time-depth calibration is completed. Further, the distribution of the parameters such as the acoustic impedance, the porosity and the gas saturation is inverted by using the technology based on the constrained inversion (such as the pulse inversion, the model-driven inversion or the multi-attribute inversion). The signal processing in this stage emphasizes the spectral decomposition and the wavelet inversion, so as to improve the thin layer identification ability and reveal the physical property difference of the strata above and below the BSR.

[0088] On the basis of the inversion result, the signal attribute volume analysis method is used to perform the three-dimensional visualization on the RMS amplitude volume, the coherent volume, the main frequency volume and the instantaneous energy volume. The abnormal reflection zone above and below the BSR is identified by using the threshold grading and the correlation analysis. The frequency-amplitude discrimination is performed on the high-amplitude low-frequency reflection (representing the free gas layer) and the high-frequency low-amplitude reflection (representing the hydrate layer). The spectral decomposition and the volume coherence algorithm are used to reveal the discontinuity characteristics of the reflection signal, and the spatial distribution of the fluid migration channel and the interlayer fault is inferred.

[0089] According to the depth difference and the reflection intensity change of the BSRs in the past and present, the time migration model is built. The seismic time domain signal is converted into the depth domain data in the thermodynamic stable domain by using the sound velocity-pressure-temperature correction model, and then the BSR upward or downward trend is inferred. If the seismic characteristics of the ancient BSR are not obvious, the forward calculation of the ancient BSR position in different geological periods is performed by restoring the ancient environmental parameters, and the prediction profile of the ancient BSR is generated. The phase change and the accumulation-decomposition dynamic process of the methane gas in the reflection layer are identified by using the reflection amplitude variation with offset (AVO) analysis and the reverse time migration (RTM) technology.

[0090] The identification, the explanation, the forward and inversion results in the foregoing stages are integrated, and the corresponding relationship between the stratum elements and the hydrate system seismic response is built. The key stratum parameters (such as the lithological interface, the dip angle, the fault conductivity and the like) controlling the amplitude and the spectrum change of the BSR are identified by using the multi-attribute cross plot and the principal component analysis. Finally, the stratum element controlled reservoir mode is built by combining the spatial distribution of the seismic reflection characteristics, the well-to-seismic inversion parameters and the simulation results, and the comprehensive explanation and prediction of the hydrate accumulation and the decomposition process in the sea area are realized.

[0091] As shown in FIG. 1, Figure 6 The RMS amplitude attribute plane of the BSR in a certain sea area in West Africa shows that the BSR presents the characteristics of the high-low amplitude band interbedding in the plane, the two sides are approximately symmetrically distributed in the ring shape, and the uplift axes are respectively inclined to the opposite directions (FIG. 2). Figure 6a), the width of the amplitude strip on the plane is closely related to the thickness of the sandy and muddy sedimentary strata. Seismic profile shows that when the BSR is consistent with the strata tendency and the BSR dip angle is steep, it is BSR type 1, the amplitude strip on the plane uplifts towards the land, and the free gas under the BSR is easy to migrate laterally along the strata, so the free gas is not easy to accumulate in the lower part ( Figure 6 b); when the BSR is consistent with the strata tendency and the BSR dip angle is gentle, it is BSR type 2, the amplitude strip on the plane uplifts towards the sea, at this time, the underlying free gas is capped by the upper hydrate, and is easy to accumulate in the lower part ( Figure 6 c). In addition, in the Pitu area in the northwest of Greenland, the developed BSR is opposite to the strata tendency, at this time, the BSR is easy to accumulate free gas in the lower part under the sealing of the upper inclined hydrate ( Figure 6 d).

[0092] S104, based on the well seismic data analysis and inversion results, the distribution characteristics of the hydrate layer above the present BSR are depicted ( Figure 7 );

[0093] S105, combined with the characteristics of the strata elements, the control action of the strata elements on the hydrate layer is analyzed;

[0094] The hydrate layer above the BSR has great difference in different areas, and the distribution of the hydrate layer is different at different positions in the same area ( Figure 7 bc), which may be controlled by the difference of the strata dip angle at two positions, the dip angle of profile c is larger, which may be more conducive to the drainage of the gas source and thus form a hydrate layer with higher saturation;

[0095] S106, based on the well seismic data analysis and inversion results, the distribution characteristics of the free gas layer under the present BSR are depicted ( Figure 7 );

[0096] S107, combined with the characteristics of the strata elements, the control action of the strata elements on the free gas layer is analyzed;

[0097] As shown in Figures 6-7 , the lithology and the dip angle jointly affect the existence of the free gas under the BSR. When the BSR is type 2, or the BSR is opposite to the strata tendency, the upper inclined direction of the strata is sealed by the hydrate, and the free gas is easy to accumulate in the lower part of the BSR; in addition, the distribution of the free gas is also stratified, which is affected by the distribution of the strata elements (the strata lithology, thickness and tectonic shape) ( Figure 8 );

[0098] S108, the control action of the strata elements on the static natural gas hydrate system is analyzed and summarized;

[0099] It is believed that the control of stratigraphic elements affects the planar and profile features and distribution of BSR, upper hydrate layer and underlying free gas layer. Another typical case is that the static hydrate system in the anticline belt is controlled by stratigraphic elements (especially structural configuration) Figure 9 ).

[0100] S109, analyze the control of stratigraphic elements on dynamic hydrate system; first determine the migration direction of BSR in the study area.

[0101] S110, if BSR moves upward, the hydrate dissociation zone (HDZ) between the ancient and modern BSRs needs to be interpreted and analyzed, and the related reflection anomalies are identified to reveal the distribution of fluid migration path in the hydrate dissociation zone and the accumulation of free gas;

[0102] S111, analyze the control of stratigraphic elements on the migration, accumulation or leakage process of methane released in the dissociation zone;

[0103] In the West African marine area, for example, dissociated methane can migrate laterally along the inclined high-permeability strata, accumulate in the strata or structural traps in the updip direction, or even migrate a long distance (> 40 km) along the progradational layers on the continental shelf to the hydrate boundary (Davies et al., 2024); while in the anticline area (such as Figure 9 ), dissociated methane can migrate along the anticline strata to the shallow new hydrate system to form new hydrate or free gas after the upward migration of BSR. The lateral migration distance of methane released in the hydrate dissociation zone depends on the control of stratigraphic elements, but vertical migration along the pre-existing faults in the dissociation zone cannot be ruled out.

[0104] S112, if BSR moves downward, the underlying free gas in the ancient BSR can form gas hydrate as a gas source, which is beneficial to the preservation of methane in the hydrate system;

[0105] S113, analyze and summarize the control of stratigraphic elements on dynamic gas hydrate system;

[0106] As shown in Figure 3 c, the main part of the hydrate stability zone and the landward distribution boundary of the hydrate stability zone often have different BSR types and dip angle characteristics. The main part of the stability zone and the landward distribution boundary of the hydrate stability zone in the study area can be studied respectively, and then the control of stratigraphic elements on the entire hydrate system accumulation-dissociation can be understood;

[0107] S114, based on the above analysis of the control of stratigraphic elements on the present static hydrate system and the dynamic hydrate system in the geological history period, establish the stratigraphic element-controlled reservoir model of the hydrate system in the study area Figure 10 ).

[0108] As Figure 2 shown, the system for analyzing the influence of formation elements on the formation and decomposition process of marine gas hydrate in the embodiment of the present application comprises:

[0109] The parameter acquisition module is configured to select a certain marine gas hydrate development area as a research area, collect logging, seismic and other data, and report and published literature and other materials; perform seismic interpretation on the present seabed to master the distribution characteristics of the seabed; perform seismic interpretation on the present BSR to determine the inclination and dip angle parameters of the BSR; perform seismic interpretation and attribute extraction on the present BSR to analyze the profile amplitude characteristics of the BSR, and make a plane attribute map of the BSR such as RMS amplitude, frequency, coherence and the like; perform seismic interpretation and attribute extraction on the paleo-BSR existing near (upper or lower) the present BSR to master the distribution characteristics of the paleo-BSR; if the seismic characteristics of the paleo-BSR are not obvious, the paleo-BSR at a certain period of geological history can be predicted through numerical simulation; determine the present gas hydrate system, i.e. the area between the seabed and the present BSR; based on the seismic interpretation and numerical simulation prediction results of the paleo-BSR and the present BSR, determine the migration process of the hydrate stability zone since a certain period of geological history, which includes two cases of BSR upward migration and BSR downward migration; determine the formation element parameters of the development position of the gas hydrate system (especially the formation element parameters of the hydrate decomposition zone near the BSR) through well-seismic data analysis;

[0110] The analysis module is configured to analyze the control effect of the formation elements on the static hydrate system; depict the distribution characteristics of the hydrate layer above the present BSR based on the well-seismic data analysis and inversion results; analyze the control effect of the formation elements on the hydrate layer in combination with the characteristics of the formation elements; depict the distribution characteristics of the free gas layer below the present BSR based on the well-seismic data analysis and inversion results; analyze the control effect of the formation elements on the free gas layer in combination with the characteristics of the formation elements; analyze and summarize the control effect of the formation elements on the static gas hydrate system; analyze the control effect of the formation elements on the dynamic hydrate system; first determine the migration direction of the BSR in the research area;

[0111] The identification module is configured to, if the BSR upward migration case occurs, the hydrate decomposition zone HDZ is between the paleo-BSR and the present BSR, and the reflection layer in the hydrate decomposition zone needs to be interpreted and analyzed to identify the related reflection abnormal characteristics, reveal the distribution of the fluid migration path in the hydrate decomposition zone, and analyze the accumulation of the free gas; analyze the control effect of the formation elements on the migration, accumulation or leakage process of the released methane in the decomposition zone in combination with the characteristics of the formation elements; if the BSR downward migration case occurs, the free gas underlying the paleo-BSR can form gas hydrate as a gas source, which is beneficial to the preservation of methane in the hydrate system; analyze and summarize the control effect of the formation elements on the dynamic gas hydrate system.

[0112] The control mode establishing module is used for establishing a formation element control mode of the hydrate system in the study area based on the analysis of the control effect of the formation elements on the present static hydrate system and the dynamic hydrate system in the geological history period.

[0113] Another object of the present application is to provide a computer device comprising a memory and a processor, wherein the memory stores a computer program, and the computer program is executed by the processor to enable the processor to perform the steps of the method for analyzing the influence of formation elements on the hydrate accumulation and decomposition process in a sea area.

[0114] Another object of the present application is to provide a computer readable storage medium storing a computer program, and the computer program is executed by a processor to enable the processor to perform the steps of the method for analyzing the influence of formation elements on the hydrate accumulation and decomposition process in a sea area.

[0115] Another object of the present application is to provide an information data processing terminal for implementing the system for analyzing the influence of formation elements on the hydrate accumulation and decomposition process in a sea area.

[0116] Figure 4 The control effect of formation elements (lithologic sand-shale interbedding, BSR / formation dip) on BSR amplitude attribute is shown in the schematic view (a) BSR type 1 when BSR is consistent with the formation tendency and the BSR dip angle is steep, at this time, the underlying free gas is easy to migrate laterally, so the lower free gas is not easy to accumulate; (b) BSR type 2 when BSR is consistent with the formation tendency and the BSR dip angle is gentle, at this time, the underlying free gas is capped by the upper hydrate, and is easy to accumulate in the lower part.

[0117] Gas hydrate: is a kind of ice-like crystalline substance formed by hydrocarbon gas such as methane and water under high pressure and low temperature conditions, and its stability is poor, and when the temperature and pressure conditions change, it is easy to decompose and release a large amount of methane gas and water.BSR: is the seismic reflection interface of the bottom boundary of the gas hydrate stability zone, with high amplitude, negative polarity opposite to the seafloor reflection, and is usually oblique to the isochronal strata.GHSZ (Gas hydrate stability zone): controlled by hydrate stability, the area between the seafloor and the BSR is the GHSZ, which is wedge-shaped on the profile and thickens towards the sea.Dynamic gas hydrate system: in deep sea environment, the formation, stability and decomposition of gas hydrate are mainly controlled by temperature and pressure conditions, and events such as sea level change, global warming, sedimentation, denudation and heat flow anomaly will cause the temperature and pressure conditions in the sedimentary strata to change, resulting in the upward or downward migration of the bottom boundary of the gas hydrate stability zone (seismic reflection as BSR), and the landward and landward migration of the hydrate land boundary, and the process is accompanied by frequent hydrate formation and decomposition, so the hydrate system is also called dynamic gas hydrate system.When the BSR migrates downward to adjust the bottom boundary of the hydrate stability zone, the underlying free gas can form gas hydrate as a gas source, so the downward migration of the BSR is beneficial to the preservation of natural gas in the hydrate system. Figure 3 Global warming and sedimentation can cause the BSR to move upwards, forming a hydrate dissociation zone (HDZ) between the ancient and modern BSRs. The methane released by the hydrate dissociation zone after the BSR moves upwards is an important problem in hydrate research. Methane migration, re-aggregation or leakage is an important part of carbon cycle in shallow sediments of the seafloor. Static gas hydrate system: refers to the gas hydrate system that has migrated from the past to the present temperature and pressure conditions controlled position, and is in equilibrium state, and is temporarily not affected by other events and is in migration state. Strata elements: mainly include lithology (sand, mud), particle size, physical properties, geometric characteristics and distribution (thickness, dip angle, structural form such as fold) and other characteristics.

[0118] The present application provides a strata element influence analysis system and method for marine gas hydrate accumulation-decomposition process, based on the interpretation, numerical simulation, reservoir inversion and other methods of seismic and logging data, combined with the hydrate research cases in various marine areas around the world, a research method and process for analyzing the influence of strata elements on the accumulation-decomposition process of marine gas hydrate is established (the method and process are shown in the following table) Figure 5 , which helps to fully understand the accumulation-decomposition process and mechanism of hydrate.

[0119] The related evidence of the technical effects obtained by the embodiments of the present application.

[0120] The high-low amplitude alternation of BSRs in plan and profile, and the tilt direction of the planar ridge axis are controlled by the stratigraphic elements, specifically, the coarse and fine grain sedimentary interbedding and the relationship between BSR and stratigraphic dip angle Figure 6 The distribution of free gas underlying BSRs is also stratified, which indicates that the accumulation of free gas is affected by the distribution of the underlying coarse sedimentary strata Figure 8 Figure 7 bc).

[0121] In addition, anticlines, or special anticline / dome structures closely related to mud diapirs and fluid activity, are tectonic elements, but they can cause changes in stratigraphic dip angle. The tilted high-permeability strata will migrate free gas to the top of the BSR (high structural position), and the top of the anticline will be fractured by strong tensile stress, resulting in a series of fractures (reservoir reconstruction), thus, high-saturation hydrates can be formed in the reservoir at the top of the anticline extending to the BSR, and free gas can be sealed below it Figure 9

[0122] It should be noted that the embodiments of the present application can be realized by hardware, software, or a combination of software and hardware. The hardware part can be realized by special logic; the software part can be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or a specially designed hardware. Those skilled in the art can understand that the above-mentioned devices and methods can be realized by computer executable instructions and / or included in processor control code, such as provided on a carrier medium, such as a magnetic disk, CD or DVD-ROM, a programmable memory, such as a read-only memory (firmware), or a data carrier, such as an optical or electronic signal carrier. The devices of the present application and their modules can be realized by hardware circuits, such as very large scale integrated circuits or gate arrays, semiconductors, such as logic chips, transistors, or programmable hardware devices, such as field programmable gate arrays, programmable logic devices, etc. They can also be realized by software executed by various types of processors, or by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0123] The above description is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement made by those skilled in the art within the technical range disclosed by the present application, as long as it is within the spirit and principle of the present application, should be covered within the protection scope of the present application.​​

Claims

1. A method for analyzing the influence of stratigraphic elements on the formation and decomposition processes of marine natural gas hydrates, characterized in that, include: Acquire seismic and well logging data for the study area; Noise suppression, static correction, and normalization are performed on seismic data to obtain seismic reflection signals; Identify the seafloor reflector and the seabed reflector (BSR), and determine the dip angle and amplitude characteristics of the BSR; A well-seismic consistency signal is established based on well logging data, and acoustic impedance and porosity parameters are obtained through inversion. By combining the spatial changes of the present-day BSR and the ancient BSR, the migration direction of the BSR can be determined; Based on the migration direction of BSR, determine the hydrate accumulation or decomposition region, and analyze the controlling role of stratigraphic elements in the evolution of the hydrate system.

2. The method according to claim 1, characterized in that, Seismic reflector identification involves using envelope energy extraction, instantaneous phase analysis, and coherence volume analysis to identify seismic reflectors (BSRs), and determining the spatial location of BSRs through time-depth conversion.

3. The method according to claim 1, characterized in that, The upward or downward shift is determined based on the depth difference between the current BSR and the ancient BSR: when the depth decreases, it is an upward shift, and the hydrate decomposition reflection layer with high amplitude, low dominant frequency and weak coherence characteristics is identified in the upward shift interval; when the depth increases, it is a downward shift, and the reflection enhancement zone of the underlying free gas layer is identified.

4. The method according to claim 1, characterized in that, By using a stability constraint model based on sound speed, temperature, and pressure, the time-domain reflection signal is converted into a stability domain boundary that varies with depth, thereby obtaining the spatial evolution process of the hydrate stability region.

5. The method according to claim 1, wherein the migration path of the released gas is analyzed based on the dip angle, thickness and fault conductivity of the formation, and the control relationship of formation elements on hydrate decomposition and gas accumulation is determined.

6. A method for analyzing the formation control of marine natural gas hydrate systems based on well-seismic joint inversion, characterized in that, include: Establish an acoustic impedance model using well logging curves; Extract the reflection coefficient sequence and generate a synthetic seismic profile; Calculate the correlation between synthetic earthquakes and measured earthquakes; Porosity, gas saturation, and fluid type distribution were obtained through model-constrained inversion. Based on the inversion results, the control effect of stratigraphic elements such as lithology, grain size, thickness and tectonic morphology on hydrate layers and free gas layers is analyzed.

7. The method according to claim 6, characterized in that, The inversion process employs a multi-attribute fusion algorithm to coordinate and constrain amplitude, frequency, and coherence attributes to form a set of joint control parameters for acoustic impedance and reflection characteristics.

8. The method according to claim 6, characterized in that, The reflection anomaly surface is extracted by the root mean square amplitude, dominant frequency and coherence coefficient, and the hydrate decomposition region is identified based on the characteristics of high amplitude, low frequency and weak coherence.

9. The method according to claim 6, characterized in that, By analyzing the characteristic that the reflection amplitude increases with the increase of the offset distance, the fluid type in the reflective layer is determined to be free gas.

10. The method according to claim 6, characterized in that, Based on the stratigraphic element database obtained by inversion, the correlation coefficient between reflection intensity and stratigraphic elements is calculated, and the response function between stratigraphic elements and hydrate accumulation is established to construct the accumulation control models of static and dynamic hydrate systems.

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