A comprehensive characterization method for ancient karst fracture-cavity structures

Abstract

The present invention discloses a comprehensive characterization method for the ancient karst fracture-vug structure. Based on geophysical carving and taking comprehensive karst geological research as the technical method, the present invention comprehensively discriminates the background and conditions for the formation of various fracture-vug bodies, divides the control areas of karst fracture-vug types in the well area, determines the development laws and controlling factors of karst fracture-vugs. Different geophysical attributes are used to characterize each type of karst fracture-vug; on the basis of classification and identification, the final ancient karst fracture-vug structure is formed by combination, the distribution positions and controlling factors of the main hall caves in the well area are analyzed, the utilization status of reserves is analyzed in combination with production dynamics, and finally the distribution positions of remaining reserves are determined, laying a geological foundation for the efficient development of the oilfield. This method has the characteristics of multi-disciplinary integration, and for the first time proposes a method and process for describing ancient karst fracture-vugs, which has extremely important guiding significance for the development of this type of oil reservoir.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas reservoir exploration and development, and relates to technologies such as karst geological analysis, three-dimensional geological carving, fracture-vug description technology, and analysis of the connection and separation relationship of fractures and vugs. Specifically, it relates to a comprehensive characterization method for the ancient karst fracture-vug structure. Background Art

[0002] Scholars at home and abroad have carried out multi-angle research on ancient karst fracture-vug description in terms of geophysics, karst geology, geochemistry, karst dynamics, etc., and determined the main periods of karstification. The Ordovician in Tahe Oilfield has successively experienced the Middle Caledonian I, II, and III episodes and the Early Hercynian karstification, and finally formed the current fracture-vug structure after later burial. The Tahe area can be divided into the Middle-Upper Ordovician erosion area and the covered area. The karstification in the erosion area is mainly dominated by the Hercynian period, and the karstification in the covered area is mainly dominated by the Caledonian period. There is an overlap of two periods of karstification in the transition area where the Middle-Upper Ordovician is thinly covered; therefore, the fractures and vugs in the erosion area are mainly manifested as relatively complex fracture-vug combinations such as underground river-type pipelines, vertically controlled karst caves by faults, and small-scale fracture-vug bodies; the fractures and vugs in the covered area are mainly centered on faults and form fracture-vug combination bodies by dissolution and expansion along the faults, with a relatively single form; both exist in the transition area, but are mainly dominated by fracture-controlled dissolution fracture-vug bodies, and the fracture-vug types such as underground river type are reduced. Vertically, the underground rivers and pipelines in the erosion area are mainly horizontal runoff, with an obvious karst termination layer, and the bottom boundary of the fractures and vugs is relatively stable, and is strongly controlled by the structure; the fault-karst bodies in the covered area mainly expand longitudinally along the faults by dissolution, with local horizontal runoff development, and there is no unified karst bottom surface as a whole, and the structural control is weak.

[0003] At present, the research on karst fractures and vugs only stays at the macroscopic regular understanding, lacking the research on the influencing and controlling factors of specific fracture-vug bodies. The description of the internal structure of fractures and vugs and the correlation between fractures and vugs mainly relies on single geophysical property carving. For example, amplitude-based properties are mainly used to carve the spatial distribution characteristics of large-scale fracture-vug bodies in three-dimensional space; related properties such as wave impedance inversion are mainly used to locate the core depth of fracture-vug bodies longitudinally; GR inversion, porosity inversion, etc. are used to comprehensively identify the distribution characteristics and filling characteristics of shale content in the area; discontinuous properties such as coherence, tensor, ant tracking, AFE, etc. are mainly used to identify fractures of different levels and scales; discontinuous detection properties such as edge detection, maximum dissimilarity, chaos, etc. are used to identify small-scale fracture-vug bodies. The specific single geophysical carving technology is relatively complete.

[0004] As disclosed in Chinese Patent Application CN102681013A, a method and device for establishing a carbonate reservoir space model are provided. The method includes: obtaining seismic P-wave transmission signals; performing correction, amplitude preservation, and pre-stack time migration processing on the seismic P-wave transmission signals; determining seismic wave reflection anomaly zones in the target interval based on the processed seismic P-wave transmission signals; determining the approximate positions where reservoirs develop according to the seismic wave reflection anomaly zones in the target interval; determining the types and development characteristics of near-wellbore reservoirs in the target interval based on combined logging data and logging curve characteristics; determining the types and development characteristics of far-wellbore reservoirs in the target interval based on pressure build-up test data and the characteristics of the double logarithmic curves of pressure build-up test pressure and pressure reciprocal; and constructing a space model of the reservoir according to the approximate positions where reservoirs develop, the types and development characteristics of near-wellbore reservoirs in the target interval, and the types and development characteristics of far-wellbore reservoirs in the target interval. This method only uses a single geophysical property, seismic waves, with weak pertinence and low accuracy.

[0005] As disclosed in Chinese Patent Application CN102465699A, a method for predicting carbonate reservoirs is provided. This patent proposes a method for predicting carbonate reservoirs, which calculates the amplitude change rate by measuring the seismic reflection wave amplitude of fractures and cavities, and predicts the development scale of fracture-cavity bodies based on strength criteria and the magnitude of the amplitude change rate. It includes: obtaining the seismic reflection wave amplitude of the test object; calculating the amplitude change rate according to the reflection wave amplitude; and predicting the reservoir of the test object based on strength criteria and the magnitude of the amplitude change rate. In the main area of Tahe in the early stage and the current peripheral area, the amplitude change rate technology has always been a key technology for well placement. Statistics of drilling in the Tahe area show that the success rate of using the seismic amplitude change rate technology to predict carbonate karst fracture-cavity reservoirs reaches over 90%. However, this prediction method has a single means and poor applicability, and it is impossible to accurately describe different types of fractures and cavities using different methods.

[0006] Again, as disclosed in Chinese Patent Application CN109425889A, a method for depicting ancient karst underground rivers is provided. This method uses seismic waveform classification analysis technology to make a detailed classification of seismic waveforms within the distribution range of ancient karst underground rivers, and combines well point interpretation of reservoir body characteristics to achieve the characterization of the development characteristics of the reservoir body inside the underground river. In the actual interpretation of seismic data, the seismic waveform classification analysis method can run completely unsupervised or with wells involved. It is completely classified based on the waveform differences of adjacent seismic traces, and at the same time, it can calibrate the well point interpretation results to provide a geological interpretation basis for the classification results, further guiding the fine development of the oilfield. However, this method only uses a single geophysical property to depict fractures and cavities, and its applicability and accuracy need to be improved.

[0007] The following problems exist in the description of ancient karst fracture-cavity systems in the prior art:

[0008] 1) In terms of the description of fractures and caves in carbonate rock fractured-vuggy reservoirs, there is currently no effective research idea available for reference at home and abroad. Modern karst research mainly stays at the stage of surface hydrogeological research. The research on the internal structure of ancient karst caves and the correlation between fractures and caves is only limited to macroscopic qualitative aspects. There is an urgent need for a technical method for fine description of ancient karst fractures and caves to provide a basis for the fine development of oil reservoirs.

[0009] 2) The three-dimensional carving accuracy of a single geophysical attribute is low. Currently, the attributes are relatively complex, and each attribute has different pertinence, resulting in inconsistent analysis results. Moreover, the multi-solution of each geophysical attribute is relatively strong, which cannot accurately reflect the real and reliable fracture-cave bodies. And there is no formed systematic carving technology for multi-attribute fusion, which cannot directly carve effective fracture-cave bodies and judge the scale of fracture-cave bodies. Summary of the Invention

[0010] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a comprehensive description technology for ancient karst fractures and caves. This technology adopts different geophysical attribute carving methods according to the types of ancient karst fractures and caves, analyzes the formation mechanism of large-scale hall caves, determines their main distribution laws and distribution areas, and determines the internal filling characteristics of fracture-cave bodies by integrating geological analysis and geophysical inversion methods, and clarifies the connectivity and separation characteristics of fracture-cave bodies. This technology changes the phenomenon of the disconnection between karst geology and fracture-cave characterization before, makes the basic analysis of karst geology more refined, the geophysical characterization more accurate, and provides a more reliable basis for oilfield development.

[0011] To achieve the above object, the present invention provides a comprehensive characterization method for the structure of ancient karst fractures and caves, including the following steps:

[0012] (1) Distinguish the types of ancient karst fractures and caves based on the comprehensive research results of karst geology. The types of karst fractures and caves include underground river type, fault-controlled type and surface type;

[0013] (2) Use amplitude seismic attributes to identify the types of underground river karst fractures and caves, and analyze the formation mechanism of large-scale hall caves in this type of karst fractures and the internal filling, connectivity and separation characteristics of fracture-cave bodies;

[0014] (3) Use tensor seismic attributes to identify the types of fault-controlled karst fractures and caves, and analyze the formation mechanism of large-scale hall caves in this type of karst fractures and the internal filling, connectivity and separation characteristics of fracture-cave bodies;

[0015] (4) Use maximum likelihood attributes to identify the types of surface leaching fractures and caves, and analyze the internal filling, connectivity and separation characteristics of fracture-cave bodies;

[0016] (5) Stereoscopically superimpose the spatial structures of the three types of karst fractures and caves identified in steps (1)-(4) to obtain the overall structure of ancient karst fractures and caves.

[0017] Preferably, the karst fissure-cave of the underground river type in the above step (1) refers to a karst cave with horizontal runoff characteristics developed under the comprehensive control of the underground river and pipelines. It is mainly developed with horizontal fissure-caves, easy to be filled, and locally developed water inlet holes such as sinkholes, and large-scale fissure-caves are developed. The characteristics of the development area of the underground river type fissure-caves are that the amplitude change rate attribute is distributed in a continuous or discontinuous strip shape, and has a poor correlation with the coherence or tensor attribute. It has the characteristics of concentrated flow in the pipelines of the underground river on the plane and shows a continuous strong reflection characteristic in the section.

[0018] Preferably, the karst fissure-cave of the fault-controlled type in the above step (1) refers to a karst cave mainly developed vertically with the fault as the core. The surface is separated, and part of the deep part of the fault develops runoff characteristics, and relatively large-scale fissure-caves are developed. The characteristics of the development area of the fault-controlled fissure-caves are that the amplitude change rate layer attribute has a strong correlation with the coherence and tensor attributes. It shows a local dot-shaped and overall linear distribution characteristic on the plane and shows a vertical discontinuous strong reflection and chaotic reflection characteristic in the section.

[0019] Preferably, the karst fissure-cave of the surface type in the above step (1) refers to small-scale dissolution holes only developed on the surface, which are distributed within 0-20 ms of the whole area surface, and the whole area is the control area of the surface type.

[0020] Preferably, the karst fissure-cave structure of the underground river type in the above step (2) has obvious directionality. The combination of the karst cave + pipeline shows a curved slug-like characteristic on the plane. The ancient karst water is mainly concentrated flow in continuous underground pipelines, mainly developing horizontal runoff characteristics, and has a relatively unified karst datum plane. The main body of the karst fissure-cave of the underground river type is a horizontally developed karst cave, accompanied by multiple vertically developed sinkholes. The impedance of the development parts of the underground river and local sinkholes is lower than that of the surrounding rock, showing the characteristics of low impedance and strong amplitude. The main body of the underground river shows continuous low impedance and strong amplitude characteristics, showing a transverse bead-like strong reflection or chaotic strong reflection. The sinkholes are locally developed above the continuous strong amplitude underground river, from the top surface of the target layer to the underground river.

[0021] Preferably, the amplitude type attributes in the above step (2) can reflect the size of the wave impedance difference. The height of the main part of the fissure-cave is the largest, and the amplitude attribute reacts the strongest. Since the height becomes smaller on the flanks of the fissure-cave, the amplitude attribute reacts weaker. Therefore, the amplitude attribute can preferably reflect the distribution of karst caves such as underground rivers and sinkholes.

[0022] Preferably, the common amplitude type attributes in the above step (2) are root mean square, instantaneous energy, absolute amplitude, amplitude gradient, etc.

[0023] More preferably, the instantaneous energy attribute is generally used in the above step (2) in Tahe to identify the type of underground river fissure-caves, and the function formula is: where f is the original seismic trace sample and g is the Hilbert transform.

[0024] Karst water flows from the surface into the underground river through sinkholes. In the section of the underground river where sinkholes are concentrated, the karstification ability is strong, and large-scale hall caves are likely to develop. Based on this, the development location of hall caves can be determined by combining the development characteristics of sinkholes with the morphology of the underground river.

[0025] The filling characteristics of karst fissures and caves are predicted by using the shale content inversion technique. Specifically, different degrees of filling develop in the fissures and caves of the underground river type, resulting in lateral compartmentalization within the underground river. Based on the identification of the types of underground river fissures and caves, the shale content inversion technique is used to predict the filling property, and a non-linear mapping relationship between seismic frequency division attributes and well logging data is established to invert the shale content and predict the filling property. The function formula is: K(x,x j )=[(x·x j )+1] d , where K(x,x j ) is the kernel function, x·x j is the inner product operation, and d is the polynomial classifier.

[0026] Preferably, the fault-controlled karst fissure and cave type described in step (3) above is formed by the infiltration and corrosion of meteoric fresh water along the fault plane. With the strengthening of the corrosion effect, the initial corrosion fissures develop into larger karst caves, and corrosion fissures, corrosion pores, karst caves and pipelines can develop. The fault-controlled karst fissure and cave type mainly develops vertical karst caves, with no obvious horizontal runoff characteristics, and a local karst datum plane develops. The fissures and caves are mainly connected by faults, so the shallow connectivity between the fissures and caves is poor.

[0027] The fault-controlled karst fissure and cave type is overall linearly distributed, mainly non-continuously enhanced along a certain fixed direction, and the non-continuity gradually weakens in the direction transverse to the fissure and cave. The seismic tensor attribute is used to judge the strike of the seismic event axis, and the method of judging the potential energy change is used to judge the occurrence of the seismic event axis, so as to effectively identify the fissure and cave abnormal body within the fault control range; Therefore, the tensor attribute can better delineate the fault-controlled karst fissure and cave type, and the establishment of the tensor attribute is as follows:

[0028] The tensor calculation is not affected by the coordinate system and can usually be represented by a three-dimensional matrix. The gradient vector at each point is composed of 3 elements, representing the x, y, and t directions respectively. At the position point (x, y, t), the three-dimensional gradient vector describing the dip angle and azimuth angle of the seismic event axis can be expressed as: In the formula: μ represents the three-dimensional seismic data; is to calculate the gradient; the superscript "T" represents the transpose of the matrix. To reduce the influence of noise interference in the seismic data, the structure tensor method is used to smooth the gradient vector, and the seismic data structure tensor is expressed as the product relationship between the gradient vector and its transpose:

[0029]

[0030] The average gradient structure tensor S is a 3×3 positive semi - definite symmetric matrix, whose eigenvalues are greater than or equal to 0 and satisfy the following relationship:

[0031]

[0032] The eigenvectors and eigenvalues (λ 1 , λ 2 , λ 3 ) can be conveniently calculated by the eigenvalue decomposition method. The eigenvector corresponding to the largest eigenvalue is perpendicular to the reflection interface, indicating the normal direction of the seismic event axis.

[0033] aλ 3 + bλ 2 + cλ + d = 0 (ab ≠ 0)

[0034] For curved layered texture units, generally λ1≥λ2≥λ3 = 0 is satisfied. Sorting all the eigenvalues from largest to smallest, the eigenvalues can be used to construct different structural attributes or identify and distinguish the types of image texture units according to the relative size relationship of the above three eigenvalues.

[0035] Large - scale fracture - cavity bodies with long planar extension and large vertical depth develop in the strongly dissolution areas controlled by faults, while small - scale pore - cavity bodies with planar punctate distribution and small vertical depth develop in the weakly dissolution fractures. The dissolution is strong at the intersection of secondary fractures, the part where the main fracture cuts deeply, and the part of the secondary fracture with a large cutting depth, and large - scale hall - like caves are likely to develop. Based on this, the development position of hall - like caves can be judged by combining the structural characteristics of fractures with sculptured bodies.

[0036] The fracture - controlled karst fracture - cavity type mainly develops vertical karst caves, and the fracture - cavity bodies are mainly connected by fractures. Therefore, the direct connection within the fracture - cavity bodies is poor. As a result, the filling effect has a low connectivity transformation effect on the fracture - controlled karst fracture - cavity type, only affecting the local reservoir space.

[0037] Preferably, the surface - type karst fracture - cavity described in step (4) above develops between 0 - 20 ms below the top surface of the weathered crust and is the product of shallow - layer karst water - cycle dissolution. The planar distribution is significantly controlled by the paleo - karst micro - geomorphology and mostly develops in the tectonic high - land platform area and the low - angle gentle slope zone. The surface - type karst fracture - cavity is mainly composed of fracture - cavity aggregates below the meter scale. The outcrop in the field shows dissolution fractures, dissolution pores, and small karst caves; macroscopically, it is connected by a crack system in the longitudinal (vertical dissolution - expansion cracks) and transverse (tectonic fracture network) directions on the surface. Such fracture - cavities are mostly formed in the initial stage of exposure and erosion or the late stage of long - term weathering and erosion, with a high degree of filling by foreign substances and a low proportion of effective space per unit volume.

[0038] The seismic reflection characteristics of the surface leaching fracture-vug type are chaotic and weak reflections. Due to the influence of the strong reflection interface on the top surface of the target layer in some well areas, it is necessary to use the de-strong axis technology to obtain the maximum likelihood attribute and predict its planar distribution characteristics. The maximum likelihood attribute calculates the dissimilarity through the similarity coefficient, highlighting the impedance difference. The formula for the maximum likelihood attribute function is: likelihood(x,y,τ)=1-C(x,y,τ) n , where C(x,y,τ) is the similarity coefficient of the analysis point, and the exponent n enlarges the similarity coefficient. The larger the value, the greater the probability of the development of small-scale fracture-vugs.

[0039] Preferably, in the above step (5), the above three karst fracture-vug types are spatially and stereoscopically superimposed to form a complete paleokarst fracture-vug structure. Under different geomorphic and tectonic backgrounds, the paleokarst fracture-vug structure shows different vertical superposition and planar configuration relationships, resulting in different fracture-vug structure development characteristics:

[0040] ① The paleokarst highland residual mounds are manifested as a vertical superposition combination of the surface type + underground river type. The fracture-vug structure is small-scale fracture-vugs on the surface, with local development of sinkholes, and different-level horizontal karst caves developed in the middle and deep parts. Large-scale hall caves are easily developed in the higher parts of the structure, and are easily filled in the lower parts of the structure, resulting in poor connectivity between the residual mounds;

[0041] ② The paleokarst platform area is manifested as a superposition combination of the fault-controlled type + underground river type. The development degree of small surface fractures is relatively low. Horizontal karst caves are developed in the areas controlled by underground rivers, vertical karst caves are developed at sinkholes, and hall caves are developed in the concentrated areas of sinkholes. The local constricted parts of karst caves are easily filled, showing a slug-like feature; Vertical karst caves are developed in the fault-controlled areas, distributed in dot-like strips horizontally, and hall caves are developed at the intersections of faults. The filling degree in the fault-controlled areas is low, and the connectivity shows poor shallow connectivity and good deep connectivity;

[0042] ③ The paleokarst gentle slope area is manifested as a combination of the surface type + fault-controlled type + underground river type. Small-scale surface fracture-vug bodies are developed in the local high parts of the structure. The development of various types of fracture-vugs in the middle and deep parts is comprehensively controlled by faults and underground rivers. Therefore, the development law of middle and deep karst caves is similar to that of the platform area;

[0043] ④ The annular depression in the paleokarst basin area is manifested as a planar configuration combination of the underground river type + fault-controlled type. The development degree of surface fracture-vug dissolution types is relatively low, and they are often filled with sand and mud. The middle and deep karst cave structures are similar to those of the platform area, but are more easily filled, resulting in a low development degree of effective space.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The comprehensive description of paleokarst fracture-cave structure by combining karst geological theory and geophysical characterization has improved the accuracy of carbonate fracture-cave description, clarified the genetic mechanism and distribution characteristics of fracture-cave, established a comprehensive characterization technology method for different types of paleokarst fracture-cave structures, reduced the multi-solution of geophysical carving, enhanced the applicability of different attribute combinations, determined the spatial location and lateral separation characteristics of the main karst reservoirs, and guided the efficient development of fracture-cave oil reservoirs;

[0046] (2) The present invention is applied to the field of comprehensive description of ancient karst fractures and caves, and different geophysical attributes are used to carve different karst fracture and cave types to determine the distribution characteristics of effective fracture and cave bodies. The present invention changes the previous phenomenon of disconnection between karst geology and fracture and cave characterization, and pioneered a technical method for the fusion of multiple seismic attributes guided by karst geology. This method can be used for the identification and description of ancient karst fractures and caves, reserve calculation, well location deployment, well network planning and other reservoir management in the entire production cycle of oil fields, and has a broad application and promotion prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figures 1-3 This is the zoning map of the underground river karst fracture cave types in the TK440 well area: Figure 1 This is a sculpture of a dark river karst cave. Figure 2 Invert the mud content to predict the sand and mud filling map. Figure 3 This is a plan view of the underground river karst crack cave type;

[0048] Figures 4-6 This is the plan view of the underground river karst cave types in the TK440 well area: Figure 4 This is a sculpture of a dark river karst cave. Figure 5 Invert the mud content to predict the sand and mud filling map. Figure 6 This is a plan view of the underground river karst crack cave type;

[0049] Figures 7-9 This is the plan view of fault-controlled karst fracture-cave types in the TK440 well area: Figure 7 It is the tensor attribute carving body + tensor layer attribute map, Figure 8 It is the tensor attribute carving body + coherent layer attribute map, Figure 9 This is a plan view of the fault-controlled karst fracture-cave types;

[0050] Figures 10-11 This is the plan view of fault-controlled karst fracture-cave types in the TK440 well area: Figure 10 is the maximum likelihood attribute carving graph, Figure 11 It is the maximum likelihood attribute karst type + T74 top surface structure map;

[0051] Figure 12 This is the plan view of the karst fractures and caves in the TK440 well area;

[0052] Figure 13 It is the karst fissure and cave profile of Well TK440 area. Specific implementation manners

[0053] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further clarified below in conjunction with specific embodiments. However, the following embodiments are only the preferred embodiments of the present invention, not all. Based on the embodiments in the implementation manners, other embodiments obtained by those skilled in the art without creative efforts all fall within the protection scope of the present invention.

[0054] In the following embodiments, the experimental methods are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0055] Embodiment

[0056] In Well TK440 area of the fourth district of Tahe, the comprehensive water cut is as high as 85%, water channeling between wells is serious, the well control degree is relatively high, and no new wells have been deployed in the past decade. Later analysis shows that the remaining oil is mainly distributed in large-scale hall caves, the remaining reserves in small-scale fissure and cave bodies between wells are relatively low, and the hall caves mainly rely on filling and separation. Therefore, the work of describing the paleokarst fissures and caves in the well area has been carried out.

[0057] By comparing the carved fissure and cave bodies with coherence and tensor attributes, analyzing the matching relationship between the fissure and cave bodies and faults, according to the coincidence degree of the planar distribution pattern of the fissure and cave bodies and the faults, the energy bodies in the middle and north are distributed in strip shapes, and the characteristics of underground rivers are obvious. The energy bodies in the south are distributed in dot-like linear shapes along coherence and tensor. Thus, it can be judged that the main developed karst fissure and cave type in the middle and north is the underground river type, and the main developed karst fissure and cave type in the south is the fault-controlled type, as Figures 1-3 shown.

[0058] In the area where the underground river karst fissure and cave type is developed in the middle and north, the instantaneous energy attribute is used to depict the shape of the underground river fissures and caves. The underground river as a whole develops from west to east and then to southwest. Combining the development position of the sinkholes and the described width of the underground river to judge the development position of the hall caves. The sinkholes are mainly developed in the north and south sections, and the planar scale of the underground river is relatively wide and the filling degree is relatively low. The sinkholes in the east and west sections of the underground river are not developed, the planar scale of the underground river is relatively narrow and the filling degree is high. Thus, it can be judged that the probability of the development of hall caves in the north-south direction is relatively high, the scale of the reservoir body is relatively large, and the planar distribution of the fissure and cave types is as Figures 4-6 shown.

[0059] In the area where the fault-controlled karst fissure and cave type is developed, the basic shape of the fault is judged according to the tensor and coherence attributes. Well TK440 area is located at the northern end of the main fault in the northeast direction. The scale of the fissure and cave bodies along the main fault in the northeast direction is relatively large. Some smaller-scale secondary faults are mainly developed in the west. Large-scale hall caves are developed at the intersection of multiple secondary faults. The planar distribution of the fissure and cave types is as Figures 7-9 shown.

[0060] In the TK440 well area, the maximum likelihood attribute is used to carve the small-scale surface fracture-cavity bodies in the surface layer of 0 - 20 ms. The types of surface karst fracture-cavities are controlled by the structure and are mainly distributed in the high parts of the structure. They are distributed in patches at the tops of residual hills and in strips along the axes of structural ridges, as Figures 10-11 shown.

[0061] The reservoir spaces of different karst dynamic types are characterized by zoning, layering, and seismic attributes respectively. The surface layer is mainly of the surface karst fracture-cavity type, and the plane combination of the underground river karst fracture-cavity type and the fault-controlled karst fracture-cavity type is in the middle and deep parts, finally forming a complete ancient karst fracture-cavity structure, as Figure 12 shown.

[0062] The comprehensive analysis of the ancient karst fracture-cavity structure in the well area shows that large-scale hall caves are mainly concentrated in the underground river fracture-cavity type, and the reservoir bodies are relatively large. Through the analysis of the production status of the hall caves, a total of 3 new wells are deployed, all of which take into account the middle and deep underground river hall caves and the surface karst fracture-cavity type, maximizing the degree of reserve production, as Figure 13 shown.

[0063] Among them, Well TK495X has produced 31,000 tons of cumulative oil after 2 years of production, with a current daily production of 40 t and water-free production; Well TK4116X was put into production with a daily oil production of 35 t and water-free production; the other well is under drilling.

[0064] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A comprehensive characterization method for the ancient karst fracture-vug structure, characterized in that, it includes the following steps: (1) Distinguish the types of ancient karst fracture-vugs according to the comprehensive research results of karst geology, and the types of karst fracture-vugs include underground river type, fault-controlled type and surface type; (2) Use amplitude seismic attributes to identify the type of underground river karst fracture-vugs, analyze the formation mechanism of large-scale hall caves in this type of karst fracture-vugs, and the filling, connectivity and separation characteristics inside the fracture-vug body; (3) Use tensor seismic attributes to identify the type of fault-controlled karst fracture-vugs, analyze the formation mechanism of large-scale hall caves in this type of karst fracture-vugs, and the filling, connectivity and separation characteristics inside the fracture-vug body; (4) Use the maximum likelihood attribute to identify the type of surface leaching fracture-vugs, and analyze the filling, connectivity and separation characteristics inside the fracture-vug body; (5) Stereoscopically superimpose the three types of karst fracture-vugs identified in steps (1)-(4) in space to obtain the overall structure of the ancient karst fracture-vugs; the stereoscopic spatial superimposition is the superposition combination of the surface type + underground river type from top to bottom, and the corresponding overall structure of the ancient karst fracture-vugs is the ancient karst highland residual hill; the stereoscopic spatial superimposition is the superposition combination of the fault-controlled type + underground river type, and the corresponding overall structure of the ancient karst fracture-vugs is the ancient karst platform; the stereoscopic spatial superimposition is the combination of the surface type + fault-controlled type + underground river type, and the corresponding overall structure of the ancient karst fracture-vugs is the ancient karst gentle slope area; the stereoscopic spatial superimposition is the planar configuration combination of the underground river type + fault-controlled type, and the corresponding overall structure of the ancient karst fracture-vugs is the annular depression in the ancient karst basin area.

2. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, in step (2), the amplitude seismic attributes are selected from one or several of root mean square, instantaneous energy, absolute amplitude and amplitude gradient.

3. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, when analyzing the formation mechanism of large-scale hall caves in this type of karst fracture-vugs in step (2), the development position of the hall cave is judged by combining the development characteristics of the sinkhole with the underground river morphology.

4. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, when judging the filling, connectivity and separation characteristics inside the fracture-vug body in step (2), the shale content inversion technology is adopted to establish the non-linear mapping relationship between seismic frequency division attributes and logging data, invert the shale content, and predict the filling property.

5. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, when analyzing the formation mechanism of large-scale hall caves in this type of karst fracture-vugs in step (3), the development position of the hall cave is judged by combining the structural characteristics of the fault with the carved body.

6. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, when judging the filling, connectivity and separation characteristics inside the fracture-vug body in step (3), since the direct connectivity inside the fracture-vug body in the fault-controlled karst fracture-vug type is relatively poor, it can be judged that the filling effect has a relatively low connectivity transformation effect on the fault-controlled karst fracture-vug type, and only affects the local reservoir space.

7. The comprehensive characterization method for the ancient karst fracture-vug structure according to claim 1, characterized in that, When judging the internal filling, connectivity and separation characteristics of the fracture-vug body in step (4), the degree of foreign matter filling in the surface leaching fracture-vug type is high, and it can be judged that the proportion of effective space per unit volume is low.

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