Comprehensive Method, System, Storage Medium, Device and Terminal for Extracting Microcrack Information

Abstract

The present invention belongs to the technical field of fracture information extraction, and discloses a comprehensive method, system, storage medium, device and terminal for micro-fracture information extraction, including: production of high-quality coherence volume; browsing of special geological bodies; hollowing and fracture display; selection of fracture attribute value range; comparison of special geological markers and correction of voxel filtering. Based on seismic coherence data volume filtering and 3D visualization functions, the present invention can initially meet the requirements. In the 3D visualization window, the discontinuity of seismic trace data is highlighted in the coherence volume through filtering, and useless information is suppressed, so as to achieve the purpose of observing fractures. The applicability of this technology in the deep-water survey of the Qiongdongbei Basin in the northwestern South China Sea is verified through cases, providing a detailed description of the methods for characterizing fractures and the aspects that should be noted. For the first time, the extraction of 3D seismic spatial fracture information is realized through computer software, which has a wide range of applications in the evaluation of the formation of hydrate and oil and gas systems in deep-water basins.

Description

Technical Field

[0001] The present invention belongs to the technical field of fracture information extraction, and particularly relates to a comprehensive method, system, storage medium, device and terminal for micro-fracture information extraction. Background Art

[0002] At present, fractures, also known as joints, are small fracture structures without displacement, which are generated in the tectonic stress field, near the main fault, the upper part of the diapir structure, and the overpressure fluid activities in deep-water basins. Fracture research has wide applications in the fields of hydrate migration and accumulation, oil and gas reservoir formation, geological engineering evaluation, hydrogeology, seepage mechanics, etc. It mainly explores the distribution, scale, genetic mechanism and continuous activity of fractures. For example, Cook et al. believed that in the study of hydrate mineralization in the northern Gulf of Mexico, during the hydrate mineralization process, large fracture systems, diapirs and original channels such as channel sands mostly disappeared in the ultra-shallow layer, and natural gas was enriched and accumulated in the reservoir mainly through the micro-fracture system. Therefore, geological fractures can only be directly observed locally in a few high-resolution seismic profiles, but their development degree and distribution law cannot be studied in three-dimensional space. Thus, exploring the spatial structure, development intervals, scale and distribution characteristics of geological fractures is helpful for the study of the hydrate accumulation system.

[0003] Fractures are often observed in field geological outcrops, drilling cores and logging images, but it is almost impossible to achieve in the shallow layer of deep-water sedimentary basins. The reasons are as follows: 1) The Quaternary in deep-water basins shows continuous subsidence, and there are few outcrops; 2) Due to the restriction of water depth (some ≥ 1500m), researchers cannot go to the site in person; 3) Since its scale may be smaller than that of polygonal faults, and the distribution is uneven, and even on seismic coherence cube slices, only a very small number of fractures may be presented, so it is easy to be ignored; 4) Seismic profiles and coherence cube slices only reflect the planar attributes of fractures and cannot reveal their spatial distribution scale, density and extension, etc.

[0004] Through the above analysis, the problems and defects existing in the prior art are that geological fractures can only be directly observed locally in a few high-resolution seismic profiles, but their development degree and distribution law cannot be studied in three-dimensional space.

[0005] The difficulties in solving the above problems and defects are as follows: There are two major difficulties not mentioned above. 1) How to adopt a method to present fractures in three-dimensional space, which involves the selection, extraction of seismic data attributes, and three-dimensional carving technology. 2) The semi-quantification of fracture extraction, that is, through special methods, relatively accurately depict fractures, including information such as true scale and density, and suppress background interference information.

[0006] The significance of solving the above problems and defects is as follows: to retain the real and objective fracture images, enabling researchers to accurately evaluate the scale and spatial distribution structure of the fracture-type fluid conduction system, and further to judge the hydrocarbon filling conditions and conduction capacity of underground traps in the absence of conduction systems such as faults and unconformities. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a comprehensive method, system, storage medium, device and terminal for extracting microfracture information, and particularly relates to a comprehensive method, system, storage medium, device and terminal for extracting microfracture information based on seismic data coherence fusion and three-dimensional visualization.

[0008] The present invention is implemented as follows. A comprehensive method for extracting microfracture information suppresses continuous signals based on the discontinuity of adjacent seismic traces in the coherence volume to highlight fracture attribute signals. The spatial structure of fractures is characterized by three-dimensional visualization technology, and real fractures are retained through comparison with special geological markers, volume element filtering correction. The comprehensive method for extracting microfracture information includes the following steps:

[0009] Step 1, production of a high-quality coherence volume;

[0010] Step 2, browsing of special geological bodies;

[0011] Step 3, hollowing out and fracture display;

[0012] Step 4, selection of fracture attribute value range;

[0013] Step 5, comparison with special geological markers and volume element filtering correction.

[0014] Furthermore, the production of the high-quality coherence volume in Step 1 includes: before fracture characterization, the step size is selected as 3×3, 5×5, 7×7, preferably 3×3 is used for extraction, and a high-quality three-dimensional seismic coherence volume is calculated by using the fracture characterization method; wherein, the fracture characterization method includes the dip angle method, azimuth angle method, ant volume method and tensor method.

[0015] Furthermore, the browsing of special geological bodies in Step 2 includes: during the browsing process, check whether there are special geological bodies and memorize the main parts where special geological bodies are distributed, including the development parts and degrees of fractures, for verifying whether the special geological bodies are effectively displayed in the subsequent three-dimensional display.

[0016] The browsing of special geological bodies adopts a two-step method. The first step is to quickly and automatically browse the data along the Inline, Crossline or Z direction to generally understand the types and main distribution positions of special geological bodies; the second step is a man-machine interaction method, by gradually clicking on Line, CDP and Z to determine the main parts and distribution conditions of special geological bodies, especially the developed fractures.

[0017] Furthermore, the hollowing and fissure display in Step 3 includes: determining the internal structure by adjusting the transparency parameter to "penetrate" through the outer layer to the target body, or observing only the remaining voxels by hiding the voxels within a specific range of values.

[0018] The coherent body hollowing and fissure display is based on the volume perspective function and the color value range assigned to the fissures, which is the most important process for the three-dimensional visualization of fissures; the visualization parameters - color value range and transparency are controlled through the filter curve to filter out or retain certain voxels and adjust the transparency of the retained voxels.

[0019] Furthermore, the selection of the fissure attribute value range in Step 4 includes: in the voxels, the coherent attribute of the fissure is assigned, and there is a certain range of coherence degrees, which is called the value range. Fissures with different coherence degrees correspond to different color values. The larger the scale of the fissure, the stronger the coherence degree, corresponding to a certain color. On the contrary, the weaker the coherence degree, the corresponding to another color. The fissures with the coherence degree to be displayed are determined by adjusting the color, and the color value range of the fissures is selected according to the research purpose.

[0020] Furthermore, the comparison of special geological markers and voxel filtering correction in Step 5 includes: in the three-dimensional visualization window, the voxel transparency is the most important visualization parameter, indicating the degree of transparency (opacity) of the data volume, which is called the filtering value. The filtering value ranges from 0 to 1. 0 means opaque, and the data is obscured, that is, the data cannot be seen; 0.5 means semi-transparent, and the data looks hazy, while 1 means the background data is completely transparent. The background is adjusted to be transparent, while the main geological targets are adjusted to be opaque to clarify the seismic characteristics or attribute characteristics of the geological targets. In this step, it is necessary to compare the markers of the fissures with special geological bodies and control the filtering parameters so that the degree of fissure development reflects the real underground conditions. For example, in the area where the seismic event axis is continuous, it represents a stable sedimentary layer, and there are no fissures or few and small-scale fissures in this area; in the area where the seismic reflection event axis is discontinuous, obvious faults or the discontinuous points of the event axis should show fissures.

[0021] Another object of the present invention is to provide a comprehensive microfracture information extraction system for implementing the above-mentioned comprehensive microfracture information extraction method, and the comprehensive microfracture information extraction system includes:

[0022] A coherent body production module, used for selecting a step size of 3×3, 5×5, 7×7 before fissure characterization, preferably using 3×3 for extraction, and calculating a high-quality three-dimensional seismic coherent body by using the fracture characterization method;

[0023] A special geological body browsing module, used for checking whether there are special geological bodies and memorizing the main parts where the special geological bodies are distributed, including the development parts and degrees of fissures, through the browsing process;

[0024] A hollowing and fracture display module, which is used to "penetrate" the outer layer to reach the target object by adjusting the transparency parameter and determine the internal structure, or to only observe the remaining voxels by hiding the voxels within a specific range of values;

[0025] A fracture color value range selection module, which is used to determine the fractures with the coherence degree to be displayed by adjusting the color, and select the color value range of the fractures according to the research purpose;

[0026] A voxel transparency adjustment module, which is used to select the color value range of the fractures according to the research purpose.

[0027] Another object of the present invention is to provide a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor performs the following steps:

[0028] Fabrication of high-quality coherent bodies. Before fracture characterization, the step sizes of 3×3, 5×5, and 7×7 are selected, and preferably 3×3 is used for extraction. A high-quality three-dimensional seismic coherent body is calculated by using the fracture characterization method; browsing of special geological bodies. Through the browsing process, check whether there are special geological bodies and remember the main parts where the special geological bodies are distributed, including the development parts and degrees of fractures, which are used to check whether the special geological bodies are effectively displayed in the subsequent three-dimensional display;

[0029] Hollowing and fracture display. "Penetrate" the outer layer to reach the target object by adjusting the transparency parameter and determine the internal structure, or only observe the remaining voxels by hiding the voxels within a specific range of values; fracture color value range selection. Determine the fractures with the coherence degree to be displayed by adjusting the color, and select the color value range of the fractures according to the research purpose; voxel transparency adjustment. Select the color value range of the fractures according to the research purpose.

[0030] Another object of the present invention is to provide a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the processor performs the following steps:

[0031] Fabrication of high-quality coherent bodies. Before fracture characterization, the step sizes of 3×3, 5×5, and 7×7 are selected, and preferably 3×3 is used for extraction. A high-quality three-dimensional seismic coherent body is calculated by using the fracture characterization method; browsing of special geological bodies. Through the browsing process, check whether there are special geological bodies and remember the main parts where the special geological bodies are distributed, including the development parts and degrees of fractures, which are used to check whether the special geological bodies are effectively displayed in the subsequent three-dimensional display;

[0032] Hollow and fracture display, which reaches the target body through the outer layer by adjusting the transparency parameter and determines the internal structure, or only observes the remaining voxels by hiding the voxels within a specific range of values; fracture color value range selection, which determines the coherent fractures to be displayed by adjusting the color and selects the color value range of the fractures according to the research purpose; voxel transparency adjustment, which selects the color value range of the fractures according to the research purpose.

[0033] Another object of the present invention is to provide an information data processing terminal for implementing the above-mentioned comprehensive microfracture information extraction system.

[0034] Combining all the above technical solutions, the advantages and positive effects of the present invention are as follows: The comprehensive method for extracting microfracture information provided by the present invention mainly includes the following working processes: 1) Production of high-quality coherent bodies; 2) Browsing of special geological bodies; 3) Hollowing and fracture display of the body; 4) Selection of fracture attribute value ranges; 5) Comparison of special geological markers and voxel filtering correction. In the case demonstration of fracture extraction in the deep water area of the South China Sea, the process of unifying fractures and geological conditions and the coordination between color and voxel transparency are introduced to prove how to refine the inspection of the rationality of fracture characterization according to the above working processes. Compared with the two-dimensional attributes of seismic profiles and coherent body slices, this method reflects the spatial distribution scale, density, and extension of fractures, etc., and is more conducive to mastering the intersection scale between the fracture conduction system and traps (hydrate reservoirs), especially the indication of discontinuous signals in shallow sedimentary layers is more accurate.

[0035] The present invention combines seismic coherent data volume and three-dimensional visualization technology to provide an effective method for extracting geological microfracture information, especially in the evaluation of the formation of hydrate oil and gas systems in deep water basins. The advantages and positive effects are as follows: 1) It solves the problem that the end of the traditional oil and gas conduction system is invisible to the naked eye on two-dimensional and three-dimensional seismic profiles and coherent body slices, and provides technology for studying the conduction systems in fracture-deficient areas and stable sedimentary layers; 2) It is an effective method for semi-quantitatively evaluating the development scale and spatial distribution law of fractures, realizing the vertical scale, density of fracture groups, and the configuration relationship between three-dimensional fracture distribution and traps, and thus is an effective research means for evaluating the accumulation and filling conditions of oil and gas and hydrates. 3) Based on this method, it has been successfully applied to the study of the oil and gas conduction system in the fault area of the diapir wing structure in the Yinggehai Basin in the northern South China Sea, discovering China's first superpressure gas field with a scale of over 100 billion cubic meters (Dongfang 13 Gas Field), and it has also been extended and applied to the Lingshui 17 Gas Field and Lingshui 25 Gas Field in the deep water area of the Qiongdongnan Basin.

[0036] The present invention discusses a method for extracting fracture information (FIEfracture information extraction) based on seismic coherent data volume and three-dimensional visualization. The method can preliminarily meet the above requirements based on the filtering of seismic coherent data volume and three-dimensional visualization function. It mainly highlights the discontinuity of seismic trace data in the coherent volume through filtering in the three-dimensional visualization window, suppresses useless information, and thus achieves the purpose of fracture observation. This situation provides a detailed description of the method of characterizing fractures and the aspects that should be paid attention to, and realizes the extraction of three-dimensional seismic spatial fracture information for the first time through computer software.

[0037] The integration of seismic coherent data and three-dimensional visualization technology provides an effective method for extracting geological microcrack information, especially in the evaluation of hydrate oil and gas system accumulation in deepwater basins. The conclusions of this invention are as follows:

[0038] 1) The problem that the end of the traditional oil and gas transmission system is invisible to the naked eye on two-dimensional and three-dimensional seismic profiles and coherence volume slices has been preliminarily solved, providing a new observation perspective for the present invention to understand the development type, scale and spatial distribution law of fractures.

[0039] 2) The advantage of the present invention is that it can present to people the sparse, small-scale, and difficult-to-observe fracture structure of the underground space, study the density of the fracture group, and the configuration relationship between the three-dimensional fracture distribution and the closure, and then effectively evaluate the accumulation and filling conditions of hydrates.

[0040] 3) Since the spatial distribution of cracks is directly affected by the extraction of coherent bodies, the crack research of this method is equivalent to providing the spatial distribution form of discontinuous waves and inhomogeneous bodies in the coherent body, including information such as microcracks, fluids, and rock heterogeneity. Therefore, this method is suitable for the study of the overall distribution law of special attribute bodies in the coherent body. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 It is a basic principle diagram of the three-dimensional visualization technology provided by an embodiment of the present invention.

[0043] Figure 2The cross-BSR profile in the deepwater area of the northwest South China Sea provided by the embodiment of the present invention reveals the faults during the Paleogene rifting period, the polygonal and inherited faults during the Miocene, and the faults and cracks near the BSR in the shallow stable sedimentary zone are not obvious.

[0044] FIG. 3 is a schematic diagram of a crack information extraction process provided by an embodiment of the present invention.

[0045] FIG. 3( a ) is a schematic diagram of manufacturing a high-quality coherent body provided by an embodiment of the present invention.

[0046] FIG3( b ) is a schematic diagram of browsing special geological bodies provided by an embodiment of the present invention, such as diapirs and fissures.

[0047] FIG3( c ) is a schematic diagram of body hollowing and crack display provided by an embodiment of the present invention.

[0048] FIG3( d ) is a schematic diagram of adjusting the transparency of a voxel provided by an embodiment of the present invention.

[0049] FIG. 3( e ) is a schematic diagram of adjusting the transparency of a voxel provided in an embodiment of the present invention.

[0050] Figure 4 It is a spatial crack under the condition of continuous marking of seismic phase axis provided by an embodiment of the present invention, which is used to illustrate that there is no crack in the marked continuous seismic reflection position, and the result is consistent with the actual situation.

[0051] FIG. 5 is a schematic diagram of crack display of different color value ranges under full perspective conditions provided by an embodiment of the present invention.

[0052] FIG. 5( a ) is a schematic diagram of a lower color value provided by an embodiment of the present invention.

[0053] FIG5( b ) is a schematic diagram of crack display corresponding to a lower color value provided by an embodiment of the present invention. There is a lot of interference information, which indicates that the result is unreasonable.

[0054] FIG5( c ) is a schematic diagram of a higher color value provided by an embodiment of the present invention.

[0055] FIG5( d ) is a schematic diagram of crack display corresponding to a higher color value provided by an embodiment of the present invention, which has less interference information and is more reasonable.

[0056] FIG. 6 is a schematic diagram of a transparent display under a fixed color range condition provided by an embodiment of the present invention.

[0057] FIG. 6( a ) is a filtering curve diagram of a coherent volume with a transparency of 20% provided by an embodiment of the present invention.

[0058] FIG6( b ) is a schematic diagram of a crack structure with a coherent body transparency of 20% provided in an embodiment of the present invention.

[0059] Figure 6(c) is a schematic diagram of the filtering curve with 50% coherence transparency provided by an embodiment of the present invention.

[0060] Figure 6(d) is a schematic diagram of the fracture structure with 50% coherence transparency provided by an embodiment of the present invention.

[0061] Figure 6(e) is a schematic diagram of the filtering curve with 100% coherence transparency provided by an embodiment of the present invention.

[0062] Figure 6(f) is a schematic diagram of the fracture structure with 100% coherence transparency provided by an embodiment of the present invention.

[0063] Figure 7 is a diagram showing the fracture characterization results of different methods in the plane and three-dimensional space provided by an embodiment of the present invention.

[0064] Figure 7(a) is a schematic diagram of the seismic amplitude slice of the target layer provided by an embodiment of the present invention, revealing the existence of fractures that are not easily observable.

[0065] Figure 7(b) is a schematic diagram of the coherence slice of the target layer provided by an embodiment of the present invention, revealing the existence of fractures that are not easily observable.

[0066] Figure 7(c) is a schematic diagram of the three-dimensional fracture display in the space of the target layer provided by an embodiment of the present invention.

[0067] Figure 8 It is a schematic diagram of the configuration relationship between the fracture leakage system in the deep-water basin, the gas layer, and the BSR provided by an embodiment of the present invention.

[0068] Figure 9 is a schematic diagram of the application of attribute hollowing in sand body carving provided by an embodiment of the present invention.

[0069] Figure 9(a) is a three-dimensional seismic profile of the sand body provided by an embodiment of the present invention, revealing the profile characteristics of the sand body.

[0070] Figure 9(b) is a schematic diagram of the planar amplitude attribute of the sand body provided by an embodiment of the present invention, as well as its configuration relationship with the bottom diapir fracture.

[0071] Figure 9(c) is a schematic diagram of stripping single sand bodies using the pseudo-isochronous slice technique provided by an embodiment of the present invention, which can only be displayed within the seismic isochronous surface.

[0072] Figure 9(d) is a three-dimensional display schematic diagram of seismic data volume hollowing provided by an embodiment of the present invention, which can reveal the spatial relationship of sand bodies or seismic bright spots within the unequal isochronous surface in the seismic volume space.

[0073] Figure 10 It is a schematic diagram of the cross-section passing through the BSR in the deep-water area of the Qiongdongnan Basin provided by an embodiment of the present invention.

[0074] Figure 11 is a schematic diagram of the spatial distribution of fractures in the BSR area provided by an embodiment of the present invention.

[0075] Figure 11(a) is a schematic diagram of the BSR upper space fracture filtering structure provided by an embodiment of the present invention.

[0076] Figure 11(b) is a schematic diagram of the BSR lower space fracture filtering structure provided by an embodiment of the present invention.

[0077] Figure 12 is a schematic diagram of the deep - water area seabed BSR and fracture structure provided by an embodiment of the present invention.

[0078] Figure 13 is a schematic diagram of the fracture seismic characteristics of the flank of the Dongfang 1 - 1 diapir structure in the Yinggehai Basin provided by an embodiment of the present invention.

[0079] Figure 14 is a schematic diagram of the characteristics of Paleogene inherited fractures and Neogene newly - formed fractures in the 3D area of the Changchang Sag provided by an embodiment of the present invention.

[0080] Figure 14(a) is a schematic diagram of the fracture system of two sets of strata in two segments of the same structure provided by an embodiment of the present invention, which are the coherence attributes of Paleogene inherited fractures and Neogene newly - formed fractures respectively.

[0081] Figure 14(b) is a schematic diagram of the seismic characteristics of Paleogene inherited fractures provided by an embodiment of the present invention.

[0082] Figure 14(c) is a schematic diagram of the seismic characteristics of Neogene newly - formed fractures provided by an embodiment of the present invention.

[0083] Figure 15 is a schematic diagram of overpressure fractures and fluid diapir structures in the deep - water canyon area provided by an embodiment of the present invention.

[0084] Figure 16 is a schematic diagram of the Tertiary pressure structure in the shallow - water to deep - water area in the southwestern part of the Qiongdongnan Basin provided by an embodiment of the present invention.

[0085] Figure 16(a) is a schematic diagram of the single - well pressure regression provided by an embodiment of the present invention.

[0086] Figure 16(b) is a cross - sectional view of the pressure structure provided by an embodiment of the present invention.

[0087] Figure 17 is a flow chart of the comprehensive method for extracting micro - fracture information provided by an embodiment of the present invention. Detailed implementation manners

[0088] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0089] In view of the problems existing in the prior art, the present invention provides a comprehensive method, system, storage medium, device and terminal for extracting micro - fracture information. The following describes the present invention in detail with reference to the accompanying drawings.

[0090] As Figure 17 shown, the comprehensive method for extracting micro - fracture information provided by the embodiments of the present invention includes the following steps:

[0091] S101, production of high - quality coherence volume;

[0092] S102, browsing of special geological bodies;

[0093] S103, hollowing and fracture display;

[0094] S104, selection of fracture attribute value range;

[0095] S105, comparison of special geological markers and correction of voxel filtering.

[0096] The comprehensive system for extracting micro - fracture information provided by the embodiments of the present invention includes:

[0097] Coherence volume production module 1, which is used to select step sizes of 3×3, 5×5, 7×7 before fracture characterization, preferably using 3×3 for extraction, and calculating to obtain a high - quality three - dimensional seismic coherence volume by using the fracture characterization method;

[0098] Special geological body browsing module 2, which is used to check whether there are special geological bodies during the browsing process and remember the main parts where the special geological bodies are distributed, including the development parts and degrees of fractures;

[0099] Hollowing and fracture display module 3, which is used to "penetrate" the outer layer to reach the target body by adjusting the transparency parameter and determine the internal structure, or only observe the remaining voxels by hiding the voxels within a specific range of values;

[0100] Fracture color value range selection module 4, which is used to determine the fractures with the coherence degree to be displayed by adjusting the color and select the color value range of the fractures according to the research purpose;

[0101] Voxel transparency adjustment module 5, which is used to select the color value range of the fractures according to the research purpose.

[0102] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0103] Embodiment 1: Method for extracting non - structural fracture information based on seismic coherence data volume and 3D visualization

[0104] 1. In the post-rift stage of a rift basin, since faults basically stop moving and conduits such as diapirs and gas chimneys are not well developed, deep-water basin geological microfractures are a potential way to reveal the vertical transport of methane gas and form hydrates. However, due to the influence of water depth, fracture scale, and seismic resolution, existing 3D seismic and slicing techniques cannot achieve this. The present invention provides a method for extracting microfracture information based on seismic coherence volume and 3D visualization. The main workflow is divided into: 1) production of high-quality coherence volume; 2) browsing of special geological bodies; 3) volume hollowing and fracture display; 4) selection of fracture color value range; 5) adjustment of voxel transparency. In the case demonstration of fracture extraction in the deep-water area of the South China Sea, the process of aligning fractures with geological conditions and the coordination between color and voxel transparency is introduced to prove how to refine and verify the rationality of fracture characterization according to the above workflow. Compared with the 2D attributes of seismic profiles and coherence slices, this method reflects the spatial distribution scale, density, and extension of fractures, etc., and it is easier to grasp the intersection scale between the fracture conduit system and traps (hydrate reservoirs), especially the indication of discontinuous signals in shallow sedimentary layers is more accurate.

[0105] The present invention explores a method for extracting fracture information (FIE - fracture information extraction) based on seismic coherence volume and 3D visualization. This method can initially meet the above requirements based on the filtering of seismic coherence volume and 3D visualization functions. It mainly enables the discontinuity of seismic trace data to stand out in the coherence volume and suppresses useless information through filtering in the 3D visualization window, thereby achieving the purpose of observing fractures. This situation provides a detailed description of the method for characterizing fractures and aspects that should be noted, and for the first time, the extraction of 3D seismic spatial fracture information is realized through computer software.

[0106] 2. Technical introduction and regional research

[0107] 2.1 Technical introduction

[0108] Since the early application of 3D visualization technology in the early 1990s, computer graphics and image processing technologies have been used to convert 3D volume data into 2D images or graphic models, and then based on the optical principle, calculate the luminance and color of the object projected onto the observer. This provides great convenience for presenting the 3D subsurface geological structure of seismic data and its derived volume data. VoxelGeo allows the study of the internal structure of geological bodies. Researchers can "penetrate" the outer layer to reach the target body and study its internal structure by adjusting the parameter of opacity, or they can hide the voxels within a specific range value and only observe the remaining voxels (data) (see Figure 1 ). This will achieve hiding weak coherence values and retaining strong coherence geological structures within a specific space and presenting them with established color values.

[0109] The seismic coherence cube technology was proposed by M. Bahorich and S. Farmer at the 65th SEG Annual Meeting in 1995. Subsequently, Gersztenkorn and Marfurt further improved the calculation accuracy. Currently, this technology has been widely applied in the field of oil and gas exploration. It has the advantages of being fast and accurate in identifying small faults, fractures, special lithologic bodies, etc., which are incomparable to conventional 3D seismic interpretation.

[0110] The reason why the current horizontal coherence cube slices cannot well reflect fractures is that the intersections of a small number of fractures with the slices are dot-like after cutting through the strata. According to Bahorich's matrix formula, the T and T’ values between points are constant, so the R values are equal. This makes it impossible to present linear or banded discontinuity attributes like fractures on the slices when the computer calculates the discontinuity of seismic trace data (such as dip angles), so it is difficult to form an image with characteristic signs. However, in three-dimensional space, fracture aggregates such as fracture tubes and fracture bundles show linear or banded characteristics in the formation surrounding rock, so there will be changes in T and T’ values laterally, and the R values of the surrounding rock and fractures are also not equal. Furthermore, continuous or scattered fractures can produce discontinuities with the surrounding rock longitudinally.

[0111]

[0112] In the formula, t is time; φ is the dip angle; φ max is the maximum dip angle; L is the coherence time window; T and T' are seismic data pairs; R is the coherence coefficient.

[0113] 2.2 Regional study

[0114] The study area is located in the deep water area in the northern part of the South China Sea system (see Figure 2 ), with a water depth of 1400 - 1800 m. It can be seen from the profile that the Paleogene faults in the basin extend to near the T40 seismic reflection interface (the top boundary of the Meishan Formation, 10.5 Ma), and large-scale fault systems are generated by the Neogene neotectonic movement. However, the fractures in the hydrate accumulation zone near T20 are almost invisible (see Figure 3). Cook et al. believed in the study of hydrate mineralization in the northern Gulf of Mexico that large fault systems, diapirs, and original channels such as channel sands mostly disappear in the ultra-shallow layer during the hydrate mineralization process. However, it is speculated that they actually mostly exist as micro-fracture systems that enable natural gas to accumulate in the reservoir. These fractures are difficult to observe under the current technical presentation methods.

[0115] 3. Data preparation

[0116] 3.1 Seismic data

[0117] High-precision three-dimensional seismic data is the basis for three-dimensional visualization of coherent bodies. On the one hand, it is to obtain all-round information about fractures in the geological space, including the scale, density, combination form, etc. of fractures; on the other hand, it is to improve the prediction accuracy and reduce noise interference information. Therefore, seismic data is preferably obtained through a calibrated seismic source, a calibrated digital geophone, high-density acquisition, and a controllable cable to obtain higher positioning accuracy, which is more conducive to noise suppression and high-precision three-dimensional seismic. In complex geological areas such as rough seabeds and conglomerate collapse layers, try to eliminate the influence of uncertain data caused by many factors. Currently, most of the high-resolution three-dimensional seismic data collected has a seismic source and cable sinking depth of 5-10m, a seismic sampling interval of 1ms, and a acquisition bin of 12.5m×12.5m or 12.5m×25m, meeting the needs of three-dimensional visualization coherence attribute research.

[0118] 4. Workflow

[0119] 4.1 Production of high-quality coherent bodies

[0120] As shown in Figure 3(a), before fracture characterization, it is very necessary to obtain a high-quality three-dimensional seismic coherent body (SGF - spatial geology fractures). This requires controlling the step size of coherent attribute extraction. The most crucial thing is that in order to reveal the morphology of small-scale fractures as much as possible, the smaller the calculation step size, the better the coherent body reveals the similarity of local seismic waveforms and the discontinuity of reflected wave waveforms, and the better the spatial presentation effect of fractures will be. For example, the step size can be selected as 3×3, 5×5, 7×7, and it is best to extract using 3×3. The smaller the step size, the more time-consuming the calculation. It should be noted that fractures are not sensitive to traditional fracture characterization methods such as dip angle method, azimuth method, ant body method, tensor, etc., so which method is used for calculation is not important.

[0121] 4.2 Browsing of special geological bodies

[0122] Browsing of special geological bodies is not a necessary but very necessary process, because this process is mainly to check whether there are special geological bodies and remember the main parts where special geological bodies are distributed, including the development parts and degrees of fractures, etc., so as to check whether special geological bodies are effectively displayed in the subsequent three-dimensional display.

[0123] It should be noted that browsing special geological bodies requires a two-step method. The first step is to quickly and automatically browse the data along the Inline, Crossline or Z (Time / Depth) direction. This is mainly to generally understand the types of special geological bodies and their main distribution positions. The second step is a human-computer interaction method. By gradually clicking on Line, CDP, Z, the present invention can further determine the main parts where special geological bodies, especially fractures, develop and their distribution conditions.

[0124] 4.3 Hollowing and fracture display

[0125] Since each voxel contains the geophysical properties defined by the user to control the voxel, it is possible to "penetrate" the outer layer to reach the target volume and study its internal structure by adjusting the transparency parameter. You can also hide the voxels with a specific range of values and only observe the remaining voxels.

[0126] The hollowing and fracture display of the coherent body is based on the volume perspective function and the color value range assigned to the fractures, which is the most important process for the 3D visualization of fractures. The visualization parameters - color value range and transparency - are controlled by the filter curve to filter out or retain certain voxels and adjust the transparency of the retained voxels.

[0127] 4.4 Selection of fracture attribute value range

[0128] In the voxel, the coherence attribute of the fracture is assigned a value, and there is a certain range of coherence, which is called the value range. At the same time, fractures with different degrees of coherence correspond to different color values. The larger the fracture, the stronger the coherence, corresponding to a certain color. On the contrary, the weaker the coherence, the corresponding to another color. Therefore, the adjustment of color actually determines which fractures with what degree of coherence to display. For example, the abscissa in Figure 3 represents the value range of the fractures and corresponds to a color scale. If the coherence value of the fractures in a geological body is 63.0 - 127.0, then near 127 are the larger-scale fractures with large fracture scale and the most obvious coherence attribute, while the fracture scale will relatively decrease and the coherence will weaken towards 63.0. Therefore, usually, the color value range of the fractures needs to be selected according to the research purpose. For example, in the study of fractures in the hydrate accumulation model, most fractures basically need to be presented because the combination form between short fractures and the combination of short fractures and long fractures determines the methane gas conduction ability of hydrate accumulation.

[0129] 4.5 Comparison of special geological markers and voxel filtering correction.

[0130] The voxel opacity is a major visualization parameter, which represents the degree of transparency of the data volume. The transparency value ranges from 0 to 1. 0 means opaque, the data is obscured, that is, the data cannot be seen. 0.5 means semi-transparent, and the data looks hazy, while 1 means that the background data is completely transparent.

[0131] Generally, the background is adjusted to be transparent and the main geological targets are adjusted to be opaque, so as to highlight geological targets such as channels, fans, bright spot reservoirs, sand bodies, fractures, etc. When specifically adjusting this parameter, first, it is necessary to clarify the seismic characteristics or attribute characteristics of the geological target you want to study. For example, whether the color representing the fracture is strongly coherent or weakly coherent. If it is strongly coherent, the shape of the transparency curve is asFigure 4 As shown, weak to medium coherence is suppressed, indicating that medium to high coherence is semi-transparent while strong coherence is opaque. This form of the transparency curve highlights strong coherence. Similarly, if the color representing fractures is weak coherence, then medium to strong coherence is suppressed, indicating that weak to medium coherence is semi-transparent and weak coherence is opaque.

[0132] However, in the fully transparent state, within the limited fracture value range, some fractures may also be filtered out by the transparency effect, which will affect the quantitative study of fracture scale in the present invention. Therefore, how to select opacity is very important.

[0133] 5. Case study

[0134] Using the above work process, only most of the geological fractures in the 3D data volume can be qualitatively identified. At the same time, a large amount of interference information is also shown, such as chaotic bedrock reflections, unfiltered data volume background, fluid characteristics, etc. Therefore, how to quantitatively and semi-quantitatively determine the spatial distribution of fractures is crucial. The present invention finds that to control the authenticity of fractures, that is, the display scale within the window, it is necessary to use real geological conditions as the standard for inspection.

[0135] 5.1 Unification of fractures and geological conditions

[0136] 1) Seismic event continuity area marker

[0137] Generally, areas with continuous seismic reflection events and good seismic facies homogeneity indicate that there are no or few fractures and small fracture scales in these areas. Continuous seismic reflection events and good seismic facies homogeneity represent stable stratigraphic deposition, no strong tectonic movement damage resulting in formation fragmentation, and maintaining the sedimentary structure and texture of the original formation. Therefore, generally fractures do not develop. Or the degree of modification is low during subsequent weak tectonic movements and fractures do not develop. As Figure 4 shown, relatively dense fractures develop in the deep part of the formation, and there is also a certain degree of development in the shallow part, but there are few fractures in the middle part of the formation. The formation shows high-frequency, continuous, and weak reflection characteristics. Therefore, Figure 4 the parameter setting has a certain degree of rationality.

[0138] 2) Fracture development area marker

[0139] In contrast, unlike the continuous area of seismic phase axis, there must be cracks displayed at the place where the seismic reflection has obvious faults or phase axis dislocation. Seismic wave is an elastic wave propagating in the rock layer, and its propagation speed is mainly related to the properties of the rock layer. The inhomogeneity and anisotropy of the medium are the characteristics of the elastic medium that change with the position coordinates. The distribution density, development direction and scale of the cracks may change the inhomogeneity or anisotropy of the original stratum medium, and also change the acoustic properties of the stratum and cause abnormal seismic wave velocity. Fault-associated cracks, or cracks caused by new tectonic movements, overpressure fluids, etc. can all destroy the continuity of the original strata. Figure 5 is a dense area of Paleogene tectonic movement in the basin, where a large number of faults and cracks are developed. Therefore, the present invention needs to check whether the cracks in these key parts are displayed.

[0140] 5.2 Coordination of crack filter color value VS volume transparency

[0141] The crack filter color value VS volume perspective controls the coordination of the crack display scale level and the data volume background. Therefore, the appropriate ratio will help to more accurately express the spatial structure effect of the crack. In order to discuss the semi-quantitative type of color and perspective, the present invention assumes two situations: crack display with different color value ranges under full transparency conditions, and variable transparent display under fixed color value range conditions.

[0142] 1) Fracture display in different color value ranges under full transparency conditions. As shown in Figure 5(a) and Figure 5(c), the coherent background of the seismic data body is 100% transparent, and only the coherent color value range is changed. In the case of the wider color value range of Figure 5(a), Figure 5(b) shows part of the main fractures while showing a large amount of interference information, making the transparency of the coherent body poor. The color value range of Figure 5(c) is narrower, and Figure 5(d) shows that it is basically all main fractures. The above results show that the color value range must be controlled within the effective range.

[0143] In most geological spaces, the number of fractures that are effective for fluid seepage is limited, so the coherence color range of fractures must be narrow. The wide coherence range expresses the nature of the coherence from small to large in the seismic data body, so the color range information with relatively small coherence (grayish white) contains part of the microcracks, fluid information, lithology heterogeneity and other causes, so the part different from the main fracture (yellow-red) color range should be ignored.

[0144] 2) Transparent display under fixed color value range (attribute) conditions

[0145] Within a specific color gamut range, the present invention needs to adjust the opacity to ensure that the main fractures within the color gamut range are displayed. However, as can be seen from Figure 5, not all fractures within the coherent body need to be displayed, which needs to match the geological conditions at that time. For this purpose, the present invention compares the fracture structures under the conditions of the volume transparency being 20%, 50%, and 100% respectively. Figures 6(a) and 6(b) show that when the coherence body is transparent near 20%, the display degree of fractures is somewhat suppressed. At the parts where fractures are obvious in the seismic profile, fractures are not displayed in the three-dimensional coherent body; in contrast, Figures 6(c) to 6(f) in this case, fractures are better reflected. The difference is that Figures 6(e) and 6(f) represent the situation when the dry body is transparent near 100%, and the display of fractures is the most real, and the scale of the spatial fractures can better match the scale of the fractures in the seismic profile.

[0146] According to the above-determined parameters, Figure 7 reveals the three-dimensional spatial fracture characterization results of the whole body. The results show that in Figures 7(a) and 7(b), obvious fracture characteristics cannot be observed in the seismic profile and the coherent body slice. Moreover, even if there are fracture signs, they only reflect the plane attributes of the fractures and cannot reveal their spatial distribution scale, density, extension, etc. Figure 7(c) reflects that the vertical upward distribution scale of fractures in the upper and lower spaces of the isochronous slice gradually decreases, indicating the characteristics that the methane gas supply is greater than the dispersion during the formation process of hydrates, thereby promoting the accumulation of methane gas in the reservoir.

[0147] 5.3 Application scope

[0148] Since the spatial distribution of fractures is directly affected by the extraction of the coherent body, the fracture research of this method is equivalent to providing the spatial distribution patterns of discontinuous waves and inhomogeneous bodies within the coherent body, including information such as microfractures, fluid information, and lithological inhomogeneity. Therefore, this method is applicable to the research on the overall distribution law of special properties within the coherent body. However, in the shallow layer of sedimentary basins, due to the lack of special structures such as volcanic rocks and basement fault blocks, this signal basically indicates the existence of geological fractures.

[0149] The research on fractures in deep-water basins mainly provides the spatial distribution law of a single type of leakage system (see Figure 8 ). In actual research, the spatial configuration mode of fractures and traditional conduction systems such as diapir, fault, sand body and hydrate reservoir helps the present invention to judge the potential dominant conduction pathways for methane gas accumulation.

[0150] In addition to carving the distribution of fractures in 3D data volume, this method is also applicable to geological targets such as river channels, fans, bright spot reservoirs, and sand body carving. When specifically adjusting this parameter, first clarify the seismic or attribute characteristics of the geological target you want to study. For example, carve sand bodies with strong amplitude seismic attribute types. Figure 9 shows that submarine fan lobe sand bodies are characterized by low frequency, continuity, and strong amplitude seismically (see Figure 9(a)), and their distribution on the plane is shown in Figure 9(b). The present invention can combine the spatial configuration of sand bodies and fractures to explore the locations of hydrocarbon charging. In addition, in the study of sand body attributes, most previous methods of the present invention extracted the planar characteristics of sand bodies (see Figure 9(c)). This method can obviously reflect the planar structural relationship of the target body within the same equipotential surface. However, it cannot reflect the spatial relationship of sand bodies in different periods, and the 3D data volume hollowing solves this problem well (see Figure 9(d)), which is beneficial for the present invention to conduct joint research on multiple attributes and multiple target bodies.

[0151] 6. Results

[0152] The integration of seismic coherence data volume and 3D visualization technology provides an effective method for extracting geological microfracture information, especially in the evaluation of the formation of hydrate hydrocarbon systems in deep-water basins. The conclusions of the present invention are as follows:

[0153] 1) It has preliminarily solved the problem that the end of the traditional hydrocarbon migration and accumulation system is not visible to the naked eye on 2D and 3D seismic profiles and coherence volume slices, providing a new observation perspective for the present invention to understand the development types, scales, and spatial distribution laws of fractures.

[0154] 2) The advantage of the present invention is that it can present to people the sparse, small-scale, and difficult-to-observe fracture structures in the underground space, study the density of fracture groups, and the configuration relationship between the 3D fracture distribution and traps, thereby effectively evaluating the aggregation and charging conditions of hydrates.

[0155] 3) Since the spatial distribution of fractures is directly affected by the extraction of coherence volume, the fracture research of this method is equivalent to providing the spatial distribution patterns of discontinuous waves and heterogeneous bodies in the coherence volume, including information such as microfractures, fluids, and lithological heterogeneities. Therefore, this method is applicable to the study of the overall distribution laws of special attribute bodies in the coherence volume.

[0156] Example 2: Spatial Distribution Characteristics of the Fracture System in the BSR Zone in the Deep Water Area of the Qiongdongnan Basin

[0157] 1. To solve the problem of the spatial distribution law of the fracture system at the end of the methane leakage system, based on the high-resolution three-dimensional seismic data in the deep water area of the northern South China Sea, visualization and coherence body techniques are used to describe the spatial structure and distribution characteristics of fractures in the area of the bottom-simulating reflector, elaborate the geological genetic types of fractures, and discuss the relationship between fractures and other types of transport systems for methane gas accumulation. The geological structure with far fewer fractures in the upper space than in the lower space above the bottom-simulating reflector interface makes the supply of methane gas greater than the dissipation during the gas hydrate accumulation process, which has a general guiding effect on the study of gas hydrate accumulation and the detection of methane gas leakage. According to the development scale of fractures, four types of fractures, namely short fractures, long fractures, fracture bundles, and fracture groups (sets), can be roughly identified in the study area, and their fluid leakage capabilities increase in turn. These fractures often coexist in multiple types in the strata or jointly form a leakage system with other geological structures. These results and understandings have broad significance for improving the gas hydrate accumulation model and accumulation mechanism of the methane gas leakage system in deep water basins.

[0158] 2. Regional Geological Overview

[0159] The study area is located in the middle of the deep water area of the Qiongdongnan Basin. The Qiongdongnan Basin is located on the continental margin of the northern South China Sea, generally trending in the NE-SW direction, about 500 km long from east to west, about 150 - 200 km wide from north to south, and with a total area of about 7×10 4 km 2 .

[0160] Three sets of source rocks, namely Eocene lacustrine facies, Oligocene marine-continental transitional facies, and Miocene bathyal-abyssal facies, are mainly developed in this basin; the reservoirs are mainly sandstones in fluvial and fan-delta facies during the rifting period from the Eocene to the lower Oligocene, sandstones in (fan) delta-shallow marine facies during the fault-depression transition period of the upper Oligocene, sandstones in coastal facies of the middle Miocene in the post-fault depression, platform carbonate rocks, and deep-water turbidite sandstones.

[0161] The Qiongdongnan Basin has a typical double-layer structure of faulting in the lower part and depression in the upper part, with typical continental shelf, continental slope, and deep water basin developed, and the maximum water depth reaching 3000 m. After the Miocene, the basin entered the post-rift thermal subsidence stage, and strong overpressure occurred in the western part of the basin. Mud diapirs, fluid diapirs, gas chimneys and other structures are commonly developed in Ledong Sag, Lingshui Sag, and Songnan Sag, resulting in a complex hydrocarbon migration and accumulation environment in the basin. Since the Pliocene (T30), due to the basic cessation of activity of the basin-controlling faults, the continental slope has gradually changed from a tectonic activity type to a flexural type, and multi-phase and multi-type submarine landslides have also occurred during the continuous advancement of the Hainan provenance sedimentary system. At present, the proven natural gas reserves in the Huangliu Formation reservoir of the deep water canyon are nearly 200 billion m 3 , and it is considered that the diapirs and fractures in the depression formed by deep abnormal high pressure are efficient vertical source supply channels (see Figure 10 ).

[0162] 3. Data and Methods

[0163] In the Z2 block of the Yinggehai Basin, 3D seismic data collected and processed by the operator in 2004 was used. The source depth was 3 m, the cable depth was 4 m, the sampling frequency was 1 ms, and the acquisition bin was 12.5 m × 18.75 m. The Z1 block in the deep water area of the basin is the main research area, with high-resolution 3D seismic data collected by British Gas (BG) in 2013. The source depth was 6 m, the cable depth was 7 m, the seismic sampling interval was also 1 ms, and the acquisition bin was 12.5 m × 25 m. The 3D seismic data of the Z3 block in the east deep water area was collected by Chevron in 2011. The power source depth was 6 m, the cable depth was 8 m, the sampling frequency was 2 ms, and the acquisition bin was 12.5 m × 25 m.

[0164] The BG 3D seismic exploration area in the Qiongdongnan Basin is the main research object, where a large number of BSRs exist. Through 3D seismic volume coherence and visualization fusion techniques, imaging research on the conduction fractures was carried out to describe the spatial distribution types and characteristics. On this basis, according to the tectonic geological conditions of the Yingqiong Basin, the geological genetic types, characteristics of the fractures and the fracture combination patterns conducive to the accumulation and formation of hydrates were discussed.

[0165] 4. Spatial characteristics of the fracture system

[0166] 4.1 BSR-related leakage system

[0167] As Figure 10 can be seen, the BSR is above the T20 seismic interface, in the depth range of 2.0 - 2.5 s of the two-way seismic reflection time and 50 - 230 m below the seabed, with the characteristics of strong seismic reflection amplitude and wide distribution. BSR-related leakage system diapirs such as Paleogene faults, central canyon channels, Miocene fracture systems, ultra-shallow fractures, fluid diapirs / gas chimneys, and multi-phase mud gullies are widely developed.

[0168] (1) Paleogene faults, during the first episode of Paleogene rifting, the faults stopped moving before T70 (the top boundary of the Yacheng Formation, 30.0 Ma BP), and some faults had inherited activities after the second episode of rifting, breaking up to above T40 (the top boundary of the Meishan Formation, 10.5 Ma BP). Although the fault throw was small, it had a certain effect on the late methane gas leakage. Such fractures are not widely developed in the basin, and the conduction effect of the fractures themselves is difficult to have a large-scale impact (see Figure 10 ).

[0169] (2) The central canyon channel is a channel of the Huangliu Formation - Meishan Formation, with obvious erosion walls, showing a multi-phase sand body filling structure inside, and also showing obvious strong amplitude reflection characteristics on the seismic profile. This canyon is considered to be formed by the gravity flow erosion during the large-scale marine regression period in the Miocene. Wu Shiguo et al. believe that the sand bodies in the deep water canyon channel are one of the important leakage systems for shallow hydrate accumulation.

[0170] (3) At the existing seismic resolution, the fractures in the northern part of the profile are difficult to directly identify, while large-scale fractures occur in the range of 20 - 30 km in the southern area of the profile. Vertically, they are mainly distributed in the Miocene (T60 - T30) strata, and are locally connected to fractures with small fault offsets. The influence of the fractures makes the strata vertically fragmented and discontinuous along the fractures. It is called the vertical discontinuous zone.

[0171] (4) Small fluid diapirs / gas chimneys. Gas chimneys are abnormal reflectors with relatively steep shapes in seismic profiles and have poor sealing ability during the vertical migration of natural gas / fluids. These low-velocity anomalies, due to relatively high gas concentrations, show obvious weak signals, discontinuities, and blurred seismic reflections on seismic data.

[0172] (5) Multiple mud gullies can also be seen in the thick muddy sedimentary layer shown in the T30 - T20 sequence. Most of them are weak-amplitude continuous seismic reflection structures, and a large area of BSR distribution appears above T20, indicating that natural gas still migrates through certain fractures to form reservoirs above the T20 interface.

[0173] 4.2 Spatial distribution of fractures in the deep-water BSR area

[0174] There are many fractures several meters to more than ten meters and dozens of meters long in the ultra-shallow BSR layer. The length of a single fracture is far lower than the seismic resolution and is difficult to directly observe on seismic profiles. However, the secondary effects related to leakage fractures will lead to enhanced formation heterogeneity and seismic coherence anomalies where the wave impedance and acoustic velocity continuity are disrupted. This makes it feasible to generate new coherent data volumes by quantifying and processing the coherence attributes of seismic data volumes to highlight and emphasize the incoherence of seismic data. Combining with the hollowing-out technology of 3D visualization, the morphology of the fracture aggregate and the spatial distribution characteristics of the internal fractures can be roughly analyzed.

[0175] Based on the above principle, the fracture characteristics in the BSR distribution area in the basin can be seen from Figure 11. Figure 11(a) is the fracture filtering structure in the upper space of the strong-amplitude anomaly body, and Figure 11(b) is the fracture filtering structure in the lower space of the strong-amplitude anomaly body.

[0176] 4.2.1 Distribution law of fractures in the upper and lower spaces of BSR

[0177] As shown in Figure 11, generally, the longitudinal distribution of the fracture density shows a decreasing distribution characteristic in an upward layered manner. According to the fracture density, the upper and lower spaces of the BSR can be roughly divided into three layers: L, M, and U. Among them, the L and M layers are the lower space layers of the BSR interface, and U is the upper space layer of the BSR. The fractures in the upper space of the BSR interface are much fewer than those in the lower space, and they only develop in some parts with strong amplitude reflections. The fractures in the lower space of the BSR interface are generally developed, but the scale of the M layer is smaller than that of the L layer. Such a distribution law precisely reflects that the strata were strongly affected by the Paleogene tectonic movement during the fault depression period, and its active tectonics controlled the degree of fracture development. The influence of post-fracture thermal subsidence on this effect is significantly weakened.

[0178] 4.2.2 Distribution form

[0179] Only from the observation of the fracture distribution structure in the lower formation space of the BSR interface, the fractures are distributed in two forms: overall dispersion and local concentration. The dispersion form is that most fractures are horizontally dispersed, generally appearing in homogeneous geological bodies or primary formations affected uniformly by tectonic stress. The local concentration distribution form of fractures is tubular and tower-shaped, and their spatial forms are mainly affected by the forms of special geological bodies or controlled by the concentrated action of tectonic stress, such as mud diapirs, gas chimneys, early fracture concentration zones, and chaotic reflection basement blocks. The seismic reflection characteristics of tower-shaped geological bodies often have obvious anomalies compared with the geophysical properties of the surrounding rocks.

[0180] 4.2.3 Distribution scale

[0181] The scale of fractures includes two factors: size and quantity. Yang Shengxiong et al. confirmed the existence of fractures in the gas hydrate accumulation system through the study of borehole cores and logging data, but they could not quantitatively characterize the scale of formation fractures because the extension length of fractures far exceeded the range revealed by boreholes. High-resolution seismic data is different. Taking the seismic data with a resolution of 30 Hz in the deep-water area as an example, according to the calculation of its resolution as λ / 4, in shallow conditions, fractures with an extension length greater than 12 m can be identified vertically, and fractures with an extension length greater than 20 m can be identified in the strata below the Huangliu Formation. Therefore, according to the development scale of fractures, four types are generally identified: short fractures, long fractures, fracture bundles, and fracture swarms (groups). The present invention believes that on the geological scale, the length of short fractures ≤ 20 m, and this length is basically less than the thickness of mudstone that can be resolved by a single seismic event. Fractures with a length > 20 m are long fractures, which can be single fractures or composed of connected long and short fractures. At the same time, their ability to conduct fluids is greater than that of short fractures. Fracture bundles are formed by the head-to-tail connection of long and short fractures, or the scale becomes larger due to the bridging of thin sand layers between fractures longitudinally; and multiple fractures are concentrated and developed laterally, presenting an overall bundle-like structure. The single fractures in fracture bundles may be tubular. Because their scale is larger than that of long fractures, they are more conducive to the conduction of oil and gas. Fracture swarms are the densely developed areas of fracture bundles, long and short fractures, and are the channels with the least resistance to fluid migration, generally including fracture dense areas, large gas chimneys, and diapir zones, etc., which are mainly manifested as fuzzy zones, disorderliness, and discontinuous reflection characteristics on seismic profiles.

[0182] 5. Results

[0183] 5.1 Geological factors related to large-scale fractures

[0184] The development and scale of fractures are controlled by their related tectonic and sedimentary factors, and there are many influencing factors. In the Yingqiong Basin, they are mainly related to factors such as mud diapir tectonic activities, secondary faults and late fracture activities, fluid diapir piercing, overpressure hydraulic fracturing, and neotectonic movements.

[0185] 5.1.1 Shallow short fractures

[0186] Although in Figure 10At the seismic resolution of 1.5 s, the fractures in the northern area of the profile cannot be identified, but they are partially visible on the seismic profile displayed at a large scale (see Figure 12). Ultra-shallow fractures are formed by the connection of large and small fractures. Small fractures are commonly developed in local areas within the layer, with a length of only a few meters to tens of meters. They are fracture systems induced by hydraulic fracturing. Because the ultra-shallow strata are loose, hydraulic fracturing occurs when the pore pressure exceeds the sum of the minimum horizontal stress and tensile strength of the rock during pore compaction and drainage. Mandl, Harkness and Vernik calculated that the critical length of hydraulic fractures (i.e., the maximum fracture length) in hard rock is 35 to 73 meters, and only a few meters for very soft rock. Therefore, hydraulically fractured rocks must consist of a group of fractures that are only connected to each other for a short time when the pressure is highest and the fracture reaches its maximum length.

[0187] As can be seen from the above, the transport system is mainly distributed in the Miocene and lower strata. The key issue in reservoir evaluation is that the hydrate reservoir and the seepage system must be a complete system, that is, the oil and gas must reach the reservoir from the source layer through the seepage system and accumulate into a reservoir, so that the present invention can observe BSR on the seismic profile, thereby judging that hydrates or hydrocarbon gas may exist in the reservoir. However, shallow fault systems are not universally developed, and hydrate reservoirs and other transport systems are only separated by a large set of muddy sedimentary layers with weak seismic reflection phases or multi-stage muddy waterway filling phases (see Figure 10 ), which makes the hydrate reservoir lack a complete leakage system. Therefore, the spatial distribution structure of the leakage system is particularly important.

[0188] 5.1.2 Long fracture system

[0189] 1) Structural fractures on the diapir wing

[0190] The most typical example is the wing of the Dongfang 1-1 diapir structure in the Yinggehai Basin (see Figure 13). Since the Miocene, the Dongfang 1-1 diapir has experienced at least three phases of tectonic activity. Wang Zhenfeng and Pei Jianxiang found that the fissures are not only developed in the diapir structure, but also in large numbers on the western wing of the Dongfang 1-1 structure. The fissure structure is clear, and has broken into the source rock layers of the Meishan Formation-Sanya Formation downward, and has broken into the sand body of the first section of the Huangliu Formation upward and ended in the overlying large set of mudstone. These faults were formed in the early to middle Pliocene. The large number of faults and fissures generated by diapir activity provided the main channels for the upward migration of natural gas generated by the deep Meishan Formation-Sanya Formation source rocks. The abnormally high pressure at the bottom of the diapir provided the main driving force for the upward migration of natural gas. The overpressure gas layer drilled in the DF14 well of the Dongfang 13-1 structure confirmed that methane gas from the diapir structure (gas chimney) could not be injected into the trap from the core to the wing, because these sand bodies pinched out upward toward the high part of the diapir. Therefore, the fissure objectively existed as the only methane leakage system.

[0191] 2) Secondary fractures and fissures

[0192] The inherited strong activity of the basin-controlling faults in the fault-depression basin generates a large number of secondary faults in the sedimentary layer of its downthrown block. Some secondary faults still have a certain weak activity during the post-rift thermal subsidence stage. When the sedimentary layer has not been completely consolidated into rock, the weak activity causes the surrounding rock to be continuously fractured, forming associated fractures, thus becoming a channel for oil and gas migration and accumulation.

[0193] At the west-dipping end of the low-elevation structure in the Changchang Sag of the Qiongdongnan Basin, the Oligocene faults have large throw in the Paleogene (below T60), but the throw basically disappears in the Neogene, forming inherited fractures and generating some new fractures (see Figure 14).

[0194] 3) Fractures caused by neotectonic movement

[0195] Different from secondary structural fractures, fractures caused by neotectonic movement do not need to be related to the basement structure. Their genetic mechanisms include surface creep, compaction drainage of aquifers, dehydration shrinkage due to mineral chemical reactions, gravity collapse, and unstable fracture, etc.

[0196] Fractures caused by neotectonic movement are widely developed in the deep water area of the South China Sea, such as the polygonal faults in the Guanghua Sag, the Miocene fractures in the central and southern parts of the deep water depression (see Figure 10 ), and the high-density faults and fractures in the upper part of the low-elevation structure in the Changchang Sag (see Figure 14(c)). Yu Junfeng used the fine interpretation of high-precision 3D seismic data and the variance volume bedding slice technology to first discover high-density faults and fractures in the Miocene of the Changchang Sag in the Qiongdongnan Basin (see Figure 14(c)). These fractures are nearly N-S trending, with a throw of 6 - 28 m, a length of 0.5 - 4 km, and an inclination angle of about 60°. They are Miocene newborn faults and fractures, coexisting with a few early inherited faults. The research believes that these small faults are neither Oligocene inherited faults nor the polygonal faults currently hotly discussed, but microstructures formed by local tension under specific geological conditions in the Miocene, which are of great significance to the accumulation of shallow hydrates.

[0197] 4) Overpressure fractures

[0198] Overpressure fractures are fractures generated by the fluid front piercing and fracturing the overlying strata under overpressure conditions. The fluid occupies these fractures, forming a dynamic equilibrium system coexisting with fracture swarms and sand bodies. Hao Fang et al. pointed out that when the fluid pressure in the deep strata is more than 85% of the net water pressure of the overlying strata, a piercing effect will occur, causing the upper strata to fracture.

[0199] On seismic profiles, overpressure fractures are only partially visible (see Figure 15). They are characterized by single or several fractures connected closely and scattered. They can coexist with fluid diapirs, but do not necessarily appear simultaneously. Overpressure fractures also mostly show irregular curves, and their fundamental mechanism is hydraulic fracturing. Therefore, it is consistent with the shallow fracture structural characteristics revealed in Figure 12. Strong overpressure formations develop below the Meishan Formation in the Yingqiong Basin, with a pressure coefficient above 2.0 (see Figure 16(b)). Deepwater drilling reveals that the formation pressure regression line of the Huangliu Formation shows an inflection point between the depths of 3200 - 3500 m, and the deep pressure gradient increases significantly (see Figure 16(a)). This is sufficient to cause the overpressure fracturing of the Meishan Formation and Sanya Formation, forming an independent oil and gas conduction system.

[0200] 5.1.3 Fracture bundles (tubes)

[0201] Fracture bundles occur in the initial fracture zone above fluid diapirs and mud diapirs, especially obvious in the shallow layer. Its mechanism is fluid piercing fracture. Therefore, on the magnified seismic profile, the fracture bundles in the fluid diapir show the variant characteristics of fracture tubes. It is manifested that the area similar to a pipeline has very obvious distorted seismic reflection characteristics and is perpendicular or sub - perpendicular to the bedding plane of the original formation. This phenomenon has been observed on the Rhodes outcrop in Greece.

[0202] It can be seen from Figure 12 that fracture bundles occur at the front end of the fluid diapir, close to the BSR interface. On the seismic imaging profile, the most significant difference between the fluid diapir and the mud diapir and salt diapir is that the original formation is clearly distinguishable, while the local formation is transformed by fracture bundles and forms a seismic reflection discontinuity zone vertically (see Figure 12(a)). With the further development of the fluid diapir, the fracture bundles will expand in scale, and the fracture tubes may be filled with sandy, muddy, and fluid substances, etc.

[0203] 5.1.4 Fracture swarms (groups)

[0204] Fracture swarms (groups) are generally located in the deep part of the conduction system (see Figure 11), which is the part with the most intense tectonic activity and the most active fluid flow. It is the result of the high - stage evolution of mud - fluid diapirs and shows relatively steep abnormal reflection characteristics on seismic profiles. During the fluid migration process, due to relatively high gas concentrations, some low - velocity abnormal zones are formed, which are manifested as areas with poor wave - group continuity on seismic profiles.

[0205] The fluid diapir, gas chimney, fracture concentration zone, and basement fault block tectonic fragmentation can all be important causes for the generation of fracture swarms. Several important seismic reflection characteristics of fracture swarms are (see Figures 11 and 15): (1) The morphology is steep and the outer boundary is irregular; (2) In the fuzzy zone, the formation reflection interface can still be identified, but its lateral continuity is relatively poor compared to the surrounding rock; (3) Due to the action of low-velocity fluids, the seismic reflection wave groups sometimes show a certain degree of micro-curvature deformation; (4) Fractures are concentrated and developed (not dispersed) within the fracture swarm, and their scale is much larger than that of fracture bundles, damaging the original formation. Therefore, the seismic wave groups within them are extremely discontinuous compared to the surrounding rock.

[0206] 5.2 The accumulation effect of the spatial distribution of the fracture system on natural gas

[0207] 5.2.1 The tower-shaped distribution pattern is conducive to natural gas accumulation

[0208] The fracture combination form shown in Figure 11(b) is consistent with the "model of hydrocarbon migration where supply is greater than dissipation, which is conducive to trap accumulation" in petroleum geology theory. The fracture density and scale of this structure decrease successively from layer L to layers M and U, forming a tower-shaped distribution pattern. This is mainly because the tectonic activities and fluid migration in the strata below the BSR interface are greater than those in the strata above, resulting in more developed fractures in the lower strata. Therefore, this structure enables the supply of methane gas to be greater than its dissipation during the hydrate accumulation process, that is, it is conducive to the rapid accumulation of natural gas within the hydrate reservoir layer. This has general guiding significance for the study of hydrate accumulation and the detection of methane gas leakage in the reservoir in this invention.

[0209] Of course, overpressure fractures and tectonic fractures are more widely developed in deep-water basins, and they mostly exist in the form of long and short fractures and fracture bundles. Therefore, the corresponding contact relationship and scale between fractures and hydrate reservoirs will be crucial. The more long fractures and fracture bundles extending to the BSR interface, the more conducive it is to methane gas accumulation, and vice versa.

[0210] Similarly, there is also a situation where the fracture system in the upper space of the BSR interface is more developed than the underlying space, such as the surface seismic fracture zone and the loose sediment of the slope collapse body. This situation is also not conducive to the accumulation and preservation of methane gas.

[0211] 5.2.2 The configuration of fractures and traditional conduction systems

[0212] As can be seen from Figure 11, due to different scales, the fluid leakage capabilities of the four types of fractures, namely shallow short fractures, long fractures, fracture bundles, and fracture swarms (groups), increase in sequence. However, they do not exist independently in geological bodies, but several types of fractures coexist, or together with other geological structures, they form a leakage system. Generally, the fracture system is often configured with diapirs, large fractures, unconformities, etc. in deep structures, and forms a complete leakage system with hydrate reservoirs in shallow layers.

[0213] It should be noted that in practical applications, the scale of fractures cannot be simply characterized by length and width. The fluid conduction ability under specific geological conditions should also be considered. For example, in some special cases, short fractures also have a good cross-layer effect on thin mudstone, thus forming a good conduction system.

[0214] In the deep-water area of the Qiongdongnan Basin, a leakage system has developed in the strata underlying the BSR interface, including Paleogene faults, central canyon channels, Miocene fracture systems, etc., as well as ultra-shallow fractures, fluid diapirs / gas chimneys, multi-stage mud erosion gullies, etc. These structures are all methane gas leakage systems that are crucial for the accumulation of natural gas hydrates. By integrating 3D visualization and coherence body technology, the development characteristics of faults and fractures are finely revealed, and the development and distribution characteristics of fractures in the space underlying the BSR interface in this area are studied, and the following understandings are obtained: ① Generally, the number of fractures decreases layer by layer longitudinally upwards. The fractures in the upper space of the BSR are much fewer than those in the lower space, and they only develop in some strong amplitude parts; while the fractures in the lower space of the BSR are generally developed. This structure makes the supply of methane gas greater than the dissipation during the process of hydrate accumulation, and has a general guiding role for the study of hydrate accumulation and the detection of methane gas leakage in the present invention. ② The difference in the production scale of fractures in the formation space results in the increasing leakage ability of short fractures, long fractures, fracture bundles and fracture groups (sets) for fluids. In fact, several types of them coexist in the strata, and they often form a complete leakage system together with other geological structures. This will greatly promote the research on the methane gas accumulation mode and accumulation mechanism of hydrate reservoirs. ③ The difference in the scale of fractures / fracture combinations is related to different geological origins, such as diapiric tectonic activities, secondary basin fault activities, neotectonic movements, fluid activities, overpressure effects, etc. Therefore, these geological factors will become an important basis for the present invention to judge whether fractures develop in the hydrate accumulation system.

[0215] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented in whole or in part in the form of a computer program product, the computer program product includes one or more computer instructions. When the computer program instructions are loaded or executed on a computer, the processes or functions described in the embodiments of the present invention are generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by wire (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.). The computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or a data center that includes one or more integrated available media. The available medium may be a magnetic medium (such as a floppy disk, a hard disk, or a magnetic tape), an optical medium (such as a DVD), or a semiconductor medium (such as a solid state disk (SSD)).

[0216] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A comprehensive method for extracting microcrack information, characterized in that, The comprehensive method for extracting microfracture information is based on the discontinuity of adjacent seismic traces in the coherence cube, suppressing the continuous signals to highlight the fracture attribute signals; depicting the spatial structure of fractures through 3D visualization technology, and using special geological markers for comparison, volume element filtering correction to retain real fractures. The comprehensive method for extracting microfracture information includes the following steps: Step 1, production of high-quality coherence cube; Step 2, browsing of special geological bodies; Step 3, hollowing out and fracture display; Step 4, selection of fracture attribute value range; Step 5, comparison of special geological markers and volume element filtering correction; The production of the high-quality coherence cube in Step 1 includes: before fracture depiction, extracting with a step size of 3×3, and calculating a high-quality 3D seismic coherence cube using the fracture depiction method; among them, the fracture depiction method includes the dip angle method, azimuth method, ant volume method and tensor method.

2. The comprehensive method for extracting microcrack information according to claim 1, wherein The browsing of special geological bodies in Step 2 includes: during the browsing process, checking whether there are special geological bodies and memorizing the main parts where special geological bodies are distributed, including the development parts and degrees of fractures, for checking whether special geological bodies are effectively displayed in subsequent 3D displays; The browsing of special geological bodies adopts a two-step method. The first step is to quickly and automatically browse the data along Inline, Crossline or Z direction to generally understand the types and main distribution positions of special geological bodies; the second step is a man-machine interaction method, by gradually clicking on Line, CDP and Z to determine the main parts and distribution conditions where special geological bodies, especially fractures, are developed.

3. The comprehensive method for extracting microcrack information according to claim 1, wherein, The hollowing out and fracture display in Step 3 includes: reaching the target body through the outer layer by adjusting the transparency parameter to determine the internal structure, or observing only the remaining voxels by hiding the voxels within a specific range of values; The coherence cube hollowing out and fracture display is based on the volume perspective function and the color value range assigned to fractures, which is the most important process for 3D visualization of fractures; controlling the visualization parameters - color value range, transparency through the filter curve, filtering out or retaining which voxels, and adjusting the transparency of the retained voxels.

4. The comprehensive method for extracting microfracture information according to claim 1, characterized in that, The selection of fracture attribute value range in Step 4 includes: in the voxel, the coherence attribute of the fracture is assigned, and the coherence degree has a certain range, which is called the value range; fractures with different coherence degrees correspond to different color values. The larger the scale of the fracture, the stronger the coherence degree, corresponding to a certain color, and vice versa, the weaker the coherence degree, corresponding to another color; determining the fractures with the coherence degree to be displayed by adjusting the color, and selecting the color value range of the fractures according to the research purpose.

5. The comprehensive method for extracting microcrack information according to claim 1, characterized in that, The special geological feature comparison and voxel filtering correction in the fifth step include: In the 3D visualization window, the voxel transparency is the most important visualization parameter, representing the degree of transparency Opocity of the data volume, called the filtering value. The filtering value ranges from 0 to 1. 0 means opaque, the data is obscured, that is, the data cannot be seen; 0.5 means semi-transparent, the data looks hazy, and 1 means the background data is completely transparent; adjust the background to be transparent and the geological target to be opaque to clarify the seismic characteristics or attribute characteristics of the geological target; make the fractures contrast with the special geological bodies, control the filtering parameters, and make the fracture development degree reflect the real underground conditions.

6. A comprehensive microcrack information extraction system for implementing the comprehensive microcrack information extraction method according to any one of claims 1 to 5, characterized in that, The microfracture information extraction integrated system described above includes: A coherent body production module, which is used to extract with a step size of 3×3 before fracture characterization and calculate a high-quality 3D seismic coherent body using the fracture characterization method; A special geological body browsing module, which is used to check whether there are special geological bodies during the browsing process and remember the main parts where the special geological bodies are distributed, including the development parts and degrees of fractures; A hollowing and fracture display module, which is used to "penetrate" the outer layer to reach the target body by adjusting the transparency parameter and determine the internal structure, or only observe the remaining voxels by hiding the voxels within a specific range of values; A fracture color range selection module, which is used to determine the fractures with the coherence degree to be displayed by adjusting the color and select the color range of the fractures according to the research purpose; A voxel transparency adjustment module, which is used to select the color range of the fractures according to the research purpose.

7. A computer device, characterized in that, The computer device described above includes a memory and a processor. When the computer program stored in the memory is executed by the processor, the processor is caused to execute the steps of the microfracture information extraction integrated method as described in any one of claims 1 to 5: Production of high-quality coherent bodies. Before fracture characterization, extract with a step size of 3×3 and calculate a high-quality 3D seismic coherent body using the fracture characterization method; Browsing of special geological bodies. During the browsing process, check whether there are special geological bodies and remember the main parts where the special geological bodies are distributed, including the development parts and degrees of fractures, which is used to check whether the special geological bodies are effectively displayed in the subsequent 3D display; Hollowing and fracture display. "Penetrate" the outer layer to reach the target body by adjusting the transparency parameter and determine the internal structure, or only observe the remaining voxels by hiding the voxels within a specific range of values; Fracture color range selection. Determine the fractures with the coherence degree to be displayed by adjusting the color and select the color range of the fractures according to the research purpose; Voxel transparency adjustment. Select the color range of the fractures according to the research purpose.

8. A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor is caused to execute the steps of the microfracture information extraction integrated method as described in any one of claims 1 to 5: For the production of high-quality coherent bodies, before fracture characterization, a step size of 3×3 is selected for extraction, and a fracture characterization method is used to calculate and obtain high-quality three-dimensional seismic coherent bodies; for the browsing of special geological bodies, during the browsing process, check whether there are special geological bodies and memorize the main parts where special geological bodies are distributed, including the development parts and degrees of fractures, which are used to check whether the special geological bodies are effectively displayed in subsequent three-dimensional displays; Hollowing and fracture display, by adjusting the transparency parameter to "penetrate" the outer layer to reach the target body and determine the internal structure, or by hiding the voxels within a certain specific range value and only observing the remaining voxels; fracture color value range selection, by adjusting the color to determine the fractures with the coherence degree to be displayed and selecting the fracture color value range according to the research purpose; voxel transparency adjustment, selecting the fracture color value range according to the research purpose.

9. An information data processing terminal, characterized in that The information data processing terminal is used to implement the microfracture information extraction integrated system as described in claim 6.

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