Near-surface fault identification method

Abstract

The invention belongs to the technical field of seismic data interpretation in seismic exploration, and particularly relates to a near-surface fault identification method. The method comprises the following steps: determining the thickness of a repeated high-speed layer / low-speed layer encountered by drilling of each micro-logging well according to the formation speed corresponding to each micro-logging well in a target work area; according to the thickness of the repeated high-speed layer / low-speed layer, a micro-logging well point corresponding to the thickness 0 value of the repeated high-speed layer / low-speed layer is determined to serve as a 0 value point, and 0 value points with the proportion of the number of other 0 value points in a first set nearby area to the total number of micro-logging wells in the area smaller than a first set proportion threshold value are selected as breakpoints; fault positions are identified according to the breakpoints; therefore, by utilizing the characteristics that the inverse inference layer causing the breakpoint can cause a high-speed layer / low-speed layer repetition phenomenon of a stratum in a certain area range where the fault is located and the thickness of the high-speed layer / low-speed layer at the breakpoint is 0, the position of the breakpoint is determined so as to identify the fault, and the influence of seismic data with relatively poor shallow earth surface quality and relatively large notches is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic data interpretation in seismic exploration, and particularly relates to a method for identifying near-surface faults. Background Art

[0002] Faults are important controlling factors for the formation of oil and gas reservoirs. Reasonable fault interpretation technical means play a crucial role in the accuracy of the final interpretation result. Currently, the commonly used fault identification technologies are generally divided into three categories:

[0003] 1. Fault manual identification technology based on well trajectory breakpoints and seismic profiles;

[0004] 2. Fracture image recognition technology based on seismic attributes;

[0005] 3. Fracture image recognition technology based on automatic recognition technology.

[0006] Among them, the fault image recognition technology based on seismic attributes and fracture automatic recognition is more commonly used. It mainly includes technologies such as fault seismic response feature analysis, fault imaging technology enhancement, and ant body, eigenvalue coherence, AFE coherence enhancement, maximum likelihood body attribute, and correlation length attribute.

[0007] For fractures with relatively obvious in-phase axis offsets, the fault manual identification technology is mainly used. According to the profile identification marks of fractures in the seismic profile image, such as Figure 1 shown, manual profile interpretation is carried out; the main marks for identifying faults in the profile are:

[0008] (1) The in-phase axis of the reflected wave is offset, which is generally a reflection of medium and small faults;

[0009] (2) The number of in-phase axes of the reflected wave suddenly increases, decreases or disappears, and the wave group suddenly changes, which is generally a sign of regional large faults;

[0010] (3) The shape of the in-phase axis of the reflected wave suddenly changes, the reflection is chaotic or a blank zone appears;

[0011] (4) The in-phase axis of the reflected wave bifurcates, merges, twists, undergoes strong phase conversion, etc., which is generally a reflection of small faults;

[0012] (5) The appearance of the fault plane wave, which generally shows: large dip angle reflected wave, often intersecting with the general formation reflected wave to produce interference; large energy change, often appearing intermittently; the fault plane can be closed in the superposition profile of intersecting survey lines. Generally, faults with large throw and long extension often show fault plane waves, etc.

[0013] The fracture image recognition technology based on seismic attributes conducts spatial interpretation of fractures under the guidance of 3D visualization technology by analyzing fault-sensitive attributes and selecting the most effective fracture-sensitive attributes. Different techniques are used according to the different fault-sensitive attributes at different scales.

[0014] Large faults have obvious in-phase axis offsets. Based on the original stacked migration seismic data volume, most of them can be interpreted manually according to the profile recognition marks of fractures. For faults that are difficult to identify manually, fracture image recognition technologies based on seismic attributes can be used, such as eigenvalue coherence, AFE coherence enhancement, etc., as Figures 2a - 2d shown; while the seismic reflection characteristics of small faults are not as obvious as those of large faults. In the interpreted interval, they usually only show in-phase axis distortion, bifurcation, merging, or even no obvious in-phase axis change, making it difficult to identify and trace them only relying on conventional seismic profiles. For the identification of small faults, fracture image recognition technologies based on seismic attributes are usually used, such as using the maximum likelihood volume and ant volume technologies to assist in fault interpretation and identification, as Figure 3a 、 3b shown.

[0015] The fracture image recognition technology based on automatic recognition technology refers to Figures 4a - 4d , where Figure 4a 、 4c are the automatic recognition results of fractures on different survey lines; Figure 4b 、 4d correspond to Figure 4a 、 4c automatic recognition fault bars respectively.

[0016] Most of the above-mentioned fault recognition technologies extract seismic attributes based on seismic data and conduct fracture recognition on images. However, the surface lithology distribution changes greatly, the surface structure is unstable, the lateral variation is large, seismic acquisition is affected by well depth, excitation lithology, various interferences, etc. At the same time, the geomorphic features affect the distribution of shot points, which may lead to insufficient coverage. And because the main target layer of seismic exploration is the deep strata, there is a large gap in shallow surface seismic data or the shallow layer is directly cut off; thus, it is difficult to identify near-surface faults and there are multiple solutions. Summary of the Invention

[0017] The purpose of the present invention is to provide a method for identifying near-surface faults to solve the problems of difficult identification and multiple solutions in the identification of near-surface faults by the fault recognition technology for stratigraphic interpretation based on seismic data in the prior art.

[0018] To achieve the above object, the present invention provides a method for identifying near-surface faults, which is characterized in that, according to the formation velocities corresponding to each micro-log in the target work area, high-velocity layers / low-velocity layers drilled by each micro-log and their repetition situations are determined; according to the repetition situations of the high-velocity layers / low-velocity layers drilled by each micro-log, the thicknesses of the repeated high-velocity layers / low-velocity layers drilled by each micro-log are determined;

[0019] According to the thickness of the repeated high-velocity layer / low-velocity layer, the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity layer / low-velocity layer are determined as 0-value points, and the 0-value points that meet the breakpoint conditions are selected as breakpoints; the fault positions are identified according to the breakpoints;

[0020] The breakpoint conditions include: the proportion of the number of other 0-value points in the first set nearby area of the 0-value point to the total number of micro-logs in this area is less than the first set proportion threshold.

[0021] The above technical solution provides a brand-new method for identifying near-surface faults, and its beneficial effects are as follows: By utilizing the characteristic that the reverse-inferred fault causing the breakpoint will cause the high-velocity layer / low-velocity layer to repeat in a certain area where the fault is located, and the thickness of the repeated high-velocity layer / low-velocity layer at the breakpoint itself is 0, according to the situation of the high-velocity layer / low-velocity layer repeating in the micro-log, the position of the breakpoint is determined according to the 0-value point of the high-velocity layer / low-velocity layer thickness caused by the breakpoint. This fault identification method is based on micro-logs and assisted by seismic profiles, reducing the influence of poor-quality and large-gap seismic data in the shallow surface on the identification of near-surface faults, thereby avoiding the situation of difficult identification of near-surface faults and multiple solutions.

[0022] Further, the method for determining the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity layer / low-velocity layer as 0-value points according to the thickness of the repeated high-velocity layer / low-velocity layer is as follows:

[0023] Micro-logs without repeated high-velocity layers / low-velocity layers or with the thickness of the repeated high-velocity layer / low-velocity layer less than the set threshold are screened out, and the well points of the screened micro-logs are determined as the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity layer / low-velocity layer, and the micro-log well points are used as 0-value points.

[0024] The beneficial effects of the above technical solution are as follows: Micro-logs without repeated high-velocity layers / low-velocity layers or with the thickness of the repeated high-velocity layer / low-velocity layer less than the set threshold are all determined as the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity layer / low-velocity layer to be used as 0-value points, which is equivalent to regarding micro-logs with the thickness of the repeated high-velocity layer / low-velocity layer less than the set threshold as without repeated high-velocity layers / low-velocity layers. Thus, it can reduce the situation that due to the error in the thickness of the repeated high-velocity layer / low-velocity layer, the determined thickness value of the repeated high-velocity layer / low-velocity layer is too large, resulting in misjudging micro-logs with basically no repeated high-velocity layers / low-velocity layers as micro-logs with repeated high-velocity layers / low-velocity layers.

[0025] Further, the method for screening micro-logging without repeated high-velocity / low-velocity layers includes:

[0026] If a micro-logging encounters a high-velocity / low-velocity layer only once, or if the micro-logging repeatedly encounters a high-velocity / low-velocity layer but the number of other micro-logging that encounter the high-velocity / low-velocity layer only once in the second set adjacent area of this micro-logging accounts for a proportion greater than the second set proportion threshold of the total number of micro-logging in this area, then this micro-logging is regarded as a micro-logging without repeated high-velocity / low-velocity layers.

[0027] The beneficial effect of the above technical solution is that: even if a micro-logging is determined to repeatedly encounter a high-velocity / low-velocity layer, but the proportion of the number of other micro-logging that do not repeatedly encounter the high-velocity / low-velocity layer nearby is relatively large, this micro-logging is also regarded as a micro-logging without repeated high-velocity / low-velocity layers, that is, it can eliminate the interference of logging errors as much as possible, and further avoid the situation of misjudging a micro-logging that basically has no repeated high-velocity / low-velocity layers as having repeated high-velocity / low-velocity layers.

[0028] Further, the method for determining the high-velocity / low-velocity layers encountered by each micro-logging and their repetition situations according to the formation velocities corresponding to each micro-logging in the target work area includes:

[0029] In the target work area, if the formation velocity corresponding to a certain depth section of a micro-logging is greater than the set high-velocity threshold, it is determined that this micro-logging encounters a high-velocity layer, and this depth section is used as the encountered high-velocity layer; if the formation velocity corresponding to a certain depth section of a micro-logging is less than the set low-velocity threshold, it is determined that this micro-logging encounters a low-velocity layer, and this depth section is used as the encountered low-velocity layer;

[0030] If there are at least two depth sections corresponding to a micro-logging whose formation velocities are greater than the set high-velocity threshold and there are other depth sections with formation velocities less than or equal to the set low-velocity threshold between these depth sections, it is determined that this micro-logging repeatedly encounters a high-velocity layer, and these depth sections are used as the encountered high-velocity layers; if there are at least two depth sections corresponding to a micro-logging whose formation velocities are less than the set low-velocity threshold and there are other depth sections with formation velocities greater than the set high-velocity threshold between these depth sections, it is determined that this micro-logging repeatedly encounters a low-velocity layer, and these depth sections are used as the encountered low-velocity layers; the set low-velocity threshold is less than or equal to the set high-velocity threshold.

[0031] The beneficial effect of the above technical solution is that: it ensures that the judgment results of whether a micro-logging repeatedly encounters a high-velocity / low-velocity layer and which depth sections belong to the repeated high-velocity / low-velocity layers are more reliable, and avoids misidentifying several consecutive depth sections with formation velocities greater than the set high-velocity threshold as multiple high-velocity / low-velocity layers, resulting in misjudgment of repeated high-velocity / low-velocity layers.

[0032] Further, the method for determining the thickness of the repeated high-velocity layer / low-velocity layer encountered by each micro-logging includes:

[0033] Compare the depths of the high-velocity layers / low-velocity layers encountered by the micro-logging that repeatedly encounters the high-velocity layer / low-velocity layer, and take the thickness corresponding to the high-velocity layer / low-velocity layer with the second smallest depth as the thickness of the repeated high-velocity layer / low-velocity layer encountered by the micro-logging.

[0034] The beneficial effect of the above technical solution is that: the thickness corresponding to the high-velocity layer / low-velocity layer with the second smallest depth is selected as the thickness of the repeated high-velocity layer / low-velocity layer encountered by the micro-logging for subsequent identification steps, avoiding misusing the corresponding thickness data of the high-velocity layer / low-velocity layer generated by another deeper fault when there are multiple repeated high-velocity layers / low-velocity layers, and improving the identification accuracy.

[0035] Further, the method for identifying the fault position based on the breakpoints includes:

[0036] Based on the planar distribution positions of each micro-logging in the target work area and the thickness of the repeated high-velocity layers encountered by each micro-logging, obtain the thickness contour lines corresponding to the thickness of the repeated high-velocity layer / low-velocity layer encountered by each micro-logging in the target work area; mark the points with a thickness value of 0 and the breakpoints in the image corresponding to the thickness contour lines and connect the marked points to obtain the identified fault position.

[0037] The beneficial effect of the above technical solution is that: the points with a thickness value of 0 are more comprehensively marked through the thickness contour lines, and the fault position can be more accurately identified based on the marked points with a thickness value of 0. Brief Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the seismic profile used for artificial profile interpretation in the embodiment of the near-surface fault identification method of the present invention;

[0039] Figure 2a It is an example diagram after dip volume enhancement corresponding to the fracture image recognition technology based on seismic attributes in the embodiment of the near-surface fault identification method of the present invention;

[0040] Figure 2b It is an example diagram after AFE coherence enhancement corresponding to the fracture image recognition technology based on seismic attributes in the embodiment of the near-surface fault identification method of the present invention;

[0041] Figure 2c It is an example diagram after fracture enhancement corresponding to the fracture image recognition technology based on seismic attributes in the embodiment of the near-surface fault identification method of the present invention;

[0042] Figure 2dIt is an exemplary diagram after guided filtering enhancement corresponding to the fracture image recognition technology based on seismic attributes in the embodiment of the near-surface fault recognition method of the present invention;

[0043] Figure 3a It is an exemplary diagram for assisting fault interpretation and recognition through the maximum likelihood volume technology in the embodiment of the near-surface fault recognition method of the present invention;

[0044] Figure 3b It is an exemplary diagram for assisting fault interpretation and recognition through the ant volume technology in the embodiment of the near-surface fault recognition method of the present invention;

[0045] Figure 4a It is a schematic diagram of the automatic recognition result of the fracture on Line A in the embodiment of the near-surface fault recognition method of the present invention;

[0046] Figure 4b In the embodiment of the near-surface fault recognition method of the present invention corresponding to Figure 4a the schematic diagram of the fault stick of the automatic recognition result;

[0047] Figure 4c It is a schematic diagram of the automatic recognition result of the fracture on Line B in the embodiment of the near-surface fault recognition method of the present invention;

[0048] Figure 4d In the embodiment of the near-surface fault recognition method of the present invention corresponding to Figure 4c the schematic diagram of the fault stick of the automatic recognition result;

[0049] Figure 5 It is the main flow block diagram of the near-surface fault recognition method in the embodiment of the near-surface fault recognition method of the present invention;

[0050] Figure 6a It is a schematic diagram of the vertical time-distance curve principle of the transmission wave travel time and the micro-logging depth in the embodiment of the near-surface fault recognition method of the present invention;

[0051] Figure 6b It is a schematic diagram of the vertical time-distance curve of the transmission wave travel time and the micro-logging depth corresponding to the logging interpretation result of the test point S2 in the eastern flat area of a certain work area in the embodiment of the near-surface fault recognition method of the present invention;

[0052] Figure 7a It is a schematic diagram of the vertical time-distance curve of the transmission wave travel time and the micro-logging depth corresponding to the micro-logging without repeated drilling of high-velocity / low-velocity layers in the target work area in the embodiment of the near-surface fault recognition method of the present invention;

[0053] Figure 7b It is a schematic diagram of the vertical time-distance curve of the transmission wave travel time and the micro-logging depth corresponding to the micro-logging with repeated drilling of high-velocity layers in the target work area in the embodiment of the near-surface fault recognition method of the present invention;

[0054] Figure 8 Schematic diagram of the distribution positions of micro-logging wells that do not encounter high-velocity / low-velocity layers repeatedly and micro-logging wells that encounter high-velocity layers repeatedly in the target work area in the embodiment of the near-surface fault identification method of the present invention;

[0055] Figure 9 Elevation plane distribution map of micro-logging wells that do not encounter high-velocity / low-velocity layers repeatedly and micro-logging wells that encounter high-velocity / low-velocity layers repeatedly in the target work area in the embodiment of the near-surface fault identification method of the present invention;

[0056] Figure 10 Schematic diagram of the identified fault positions obtained by marking each break point in the image corresponding to the thickness isolines and connecting each break point in the embodiment of the near-surface fault identification method of the present invention;

[0057] Figure 11a Schematic diagram of the on-site profile interpretation of line 620 in the embodiment of the near-surface fault identification method of the present invention;

[0058] Figure 11b Schematic diagram of the on-site profile interpretation of line 560 in the embodiment of the near-surface fault identification method of the present invention;

[0059] Figure 11c Schematic diagram of the on-site profile interpretation of line 500 in the embodiment of the near-surface fault identification method of the present invention;

[0060] Figure 12 Schematic diagram of several possible formation repetition situations that the micro-logging wells may encounter in the embodiment of the near-surface fault identification method of the fault identification method of the present invention. Detailed implementation manners

[0061] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0062] Embodiment of the near-surface fault identification method

[0063] This embodiment provides a technical solution of a near-surface fault identification method. Referring to Figure 5 , it mainly includes the following steps:

[0064] 1) Determine the high-velocity / low-velocity layers encountered by each micro-logging well and their repetition situations according to the formation velocities corresponding to the micro-logging wells in the target work area; determine the thicknesses of the repeatedly encountered high-velocity / low-velocity layers by each micro-logging well according to the repetition situations of the high-velocity / low-velocity layers encountered by each micro-logging well. Specifically, in this embodiment, according to the formation velocities and thicknesses corresponding to the micro-logging wells in the target work area, and based on the velocity characteristics, the micro-logging wells are divided into two categories, normal micro-logging wells and high (low)-velocity repeated micro-logging wells, where the high (low)-velocity repeated micro-logging wells are the micro-logging wells where the high-velocity / low-velocity layers have repetition situations.

[0065] In this embodiment, the method for determining the high-velocity layer / low-velocity layer drilled by each micro-logging well in the target work area and its repetition situation according to the formation velocity corresponding to each micro-logging well includes:

[0066] In the target work area, if the formation velocity corresponding to a certain depth section of a certain micro-logging well is greater than the set high-velocity threshold, it is determined that the micro-logging well drills through a high-velocity layer, and this depth section is used as the drilled high-velocity layer; if the formation velocity corresponding to a certain depth section of a certain micro-logging well is less than the set low-velocity threshold, it is determined that the micro-logging well drills through a low-velocity layer, and this depth section is used as the drilled low-velocity layer;

[0067] If there are at least two depth sections corresponding to a certain micro-logging well whose formation velocities are greater than the set high-velocity threshold, and there are other depth sections with corresponding formation velocities less than or equal to the set low-velocity threshold between these depth sections, it is determined that the micro-logging well repeatedly drills through the high-velocity layer, and these depth sections are used as the drilled high-velocity layers; if there are at least two depth sections corresponding to a certain micro-logging well whose formation velocities are less than the set low-velocity threshold and there are other depth sections with corresponding formation velocities greater than the set high-velocity threshold between these depth sections, it is determined that the micro-logging well repeatedly drills through the low-velocity layer, and these depth sections are used as the drilled low-velocity layers; where the set low-velocity threshold is less than or equal to the set high-velocity threshold.

[0068] The formation velocities corresponding to each micro-logging well in the target work area can be obtained through micro-logging well interpretation. Specifically, the micro-logging well drills a well to achieve in-well reception and surface excitation or in-well excitation and surface reception, and uses the first arrival of the transmitted wave recorded to obtain the surface thickness model, which is used to characterize the corresponding relationship between the medium model and the transmitted wave travel time; the corresponding relationship between the medium model and the transmitted wave travel time is as Figure 6a shown by the vertical time-distance curve of the transmitted wave travel duration and the micro-logging well depth. Among them, different depth sections correspond to line segments with different slopes in the curve. Each depth section corresponding to a line segment can be regarded as a velocity layer, and the reciprocal of the line segment slope is the layer velocity of the velocity layer where it is located (which can also be called the formation velocity of the velocity layer where it is located); the media corresponding to different velocity layers are different, and the intersection point of the two line segments corresponds to the interface of the media. Then in this embodiment, the micro-logging well data and the corresponding lithology data in the work area can be obtained, and after correcting the elevation and vertical depth of these data according to the measured measurement results, a vertical time-distance curve can be made. According to the different slopes of the vertical time-distance curve, different velocity layers can be divided to complete the interpretation of the micro-logging well data. Taking the test point S2 in the eastern flat area of a certain work area as an example, the micro-logging well interpretation results are shown in Table 1:

[0069] Table 1

[0070]

[0071] In Table 1, V0 is the interval velocity of the shallowest velocity layer of the micro-logging, and H0 is the thickness of the shallowest velocity layer of the micro-logging; V1 is the interval velocity of the second shallowest velocity layer, and H1 is the thickness of the second shallowest velocity layer of the micro-logging; V2 is the interval velocity of the third shallowest velocity layer, and H2 is the thickness of the third shallowest velocity layer of the micro-logging. The vertical travel time curve of the transmitted wave corresponding to the logging interpretation result and the depth of the micro-logging is referred to Figure 6b .

[0072] The situation of the vertical travel time curve of the transmitted wave and the depth of the micro-logging in the target work area of this embodiment is referred to Figure 7a and Figure 7b . If the formation velocity corresponding to a certain depth section of a certain micro-logging is greater than the set high-speed threshold, it is determined that the micro-logging encounters a high-speed layer, and this depth section is used as the encountered high-speed layer. The determination of the low-speed layer is the same. If the formation velocity corresponding to a certain depth section of a certain micro-logging is less than the set low-speed threshold, it is determined that the micro-logging encounters a low-speed layer, and this depth section is used as the encountered low-speed layer. For example, if the set high-speed threshold is 1800 m / s, then Figure 7a the depth section corresponding to V2 (i.e., the formation velocity is 2723 m / s) in is the high-speed layer encountered by this micro-logging; Figure 7b the depth sections corresponding to V2 and V3 (i.e., the formation velocities are 2305 m / s and 1902 m / s) in are the high-speed layers encountered by this micro-logging; If there are at least two depth sections corresponding to the formation velocity greater than the set high-speed threshold in a certain micro-logging, and there are other depth sections with corresponding formation velocities less than or equal to the set low-speed threshold between these depth sections, it is determined that the micro-logging encounters a high-speed layer repeatedly, and these depth sections are used as the encountered high-speed layers. For example, in Figure 7b , there are other depth sections with corresponding formation velocities less than or equal to the set low-speed threshold (in this embodiment, the set low-speed threshold is equal to the set high-speed threshold of 1800 m / s. In other embodiments, the set low-speed threshold can also be less than the set high-speed threshold, which can be specifically set according to the accuracy requirements) between the depth sections corresponding to V2 and V3, that is, the depth section corresponding to V2 (formation velocity is 962 m / s), indicating that there are two high-speed layers encountered by this micro-logging, that is, it encounters a high-speed layer repeatedly, and the repeated high-speed layer is one; In other embodiments, there can also be three high-speed layers encountered, which also belong to the repeated encounter of the high-speed layer, and there are two repeated high-speed layers; It should be noted that if several depth sections corresponding to the formation velocity greater than the set high-speed threshold in a certain micro-logging are continuous and there are no other depth sections with corresponding formation velocities less than or equal to the set low-speed threshold in between, then these depth sections should actually be regarded as the same high-speed layer. If this micro-logging only has these depth sections corresponding to the formation velocity greater than the set high-speed threshold, then this micro-logging should be regarded as not encountering a high-speed layer repeatedly, and there is no repeated high-speed layer.

[0073] After determining the repetition of high-velocity layers / low-velocity layers encountered by each micro-logging, the method for determining the thickness of the repeated high-velocity layers / low-velocity layers encountered by each micro-logging according to the repetition of high-velocity layers / low-velocity layers encountered by each micro-logging includes:

[0074] Compare the depths of the high-velocity layers / low-velocity layers encountered by the micro-logging that repeatedly encounters high-velocity layers / low-velocity layers, and take the thickness corresponding to the high-velocity layer / low-velocity layer with the second smallest depth as the thickness of the repeated high-velocity layer / low-velocity layer encountered by this micro-logging. Since one fault of the reverse inference fault (i.e., the identification target type of the near-surface fault identification method in this embodiment) corresponding to the high-velocity layer / low-velocity layer of the normal formation generally only produces one repeated high-velocity layer / low-velocity layer, if there are multiple repeated high-velocity layers / low-velocity layers, the deeper repeated high-velocity layer / low-velocity layer is usually produced by another deeper fault. Only by uniformly using the repeated high-velocity layer / low-velocity layer closest to the normal high-velocity layer / low-velocity layer (i.e., the shallowest high-velocity layer / low-velocity layer, with the smallest depth), that is, the second shallowest high-velocity layer / low-velocity layer, with the second smallest depth, as the identification basis can the accuracy of the fault identification result be ensured. To avoid mistakenly using the corresponding thickness data of the high-velocity layer / low-velocity layer produced by another deeper fault when there are multiple repeated high-velocity layers / low-velocity layers, the near-surface fault identification method in this embodiment selects the thickness corresponding to the high-velocity layer / low-velocity layer with the second smallest depth as the thickness of the repeated high-velocity layer / low-velocity layer encountered by this micro-logging for subsequent identification steps to improve the identification accuracy.

[0075] 2) According to the thickness of the repeated high-velocity layer / low-velocity layer, determine the micro-logging well points corresponding to the thickness value of 0 of the repeated high-velocity layer / low-velocity layer as 0-value points, and select the 0-value points that meet the breakpoint conditions as breakpoints; identify the fault position according to the breakpoints;

[0076] In this embodiment, the breakpoint conditions include: the proportion of the number of other 0-value points in the first set nearby area of the 0-value point to the total number of micro-logging in this area is less than the first set proportion threshold.

[0077] After analysis, it was found that when a fault occurs, especially an inverse inference layer, there will be a phenomenon of partial strata duplication between the upper and lower plates of the fault within a certain range, and the thickness of the repeated strata at the breakpoint is 0 (it should be noted that the "thickness is 0" mentioned in this embodiment actually refers to the thickness value being less than the set thickness threshold), and the breakpoint position can be used to indicate the position of the fault section. Therefore, the repetition of high (low) velocity layers can be used as a criterion for determining whether there is an inverse inference layer in the nearby area. Therefore, if the high-speed layer / low-speed layer duplication phenomenon occurs in multiple micro-wells in a certain area, it means that there is a high possibility that an inverse inference layer exists in the area. In addition to the micro-wells corresponding to the breakpoints, micro-wells at a certain depth in the area will usually encounter inverse inference layers and repeated strata. The near-surface fault identification method of this embodiment utilizes the above characteristics, and utilizes the characteristics that the reverse inference layer that causes the breakpoint will cause the high-speed layer / low-speed layer to repeat in the strata within a certain area where the fault is located, and the thickness of the repeated high-speed layer / low-speed layer at the breakpoint of the fault is 0. The position of the breakpoint is determined according to the high-speed layer / low-speed layer repeat phenomenon in micro-logging and the high-speed layer / low-speed layer thickness 0 value point caused by the breakpoint. Specifically, according to the thickness of the repeated high-speed layer / low-speed layer, the micro-logging well point corresponding to the repeated high-speed layer / low-speed layer thickness 0 value is determined as the 0 value point in the following manner:

[0078] Screen the micro-logging points that do not have repeated high-speed layers / low-speed layers or whose thickness of repeated high-speed layers / low-speed layers is less than a set threshold, and determine the screened micro-logging points as micro-logging points corresponding to the repeated high-speed layer / low-speed layer thickness of 0, and use these micro-logging points as 0-value points. In order to avoid being affected by the accuracy of the determined thickness of the repeated high-speed layer / low-speed layer as much as possible, in this embodiment, in accordance with the above method, the micro-logging points that do not have repeated high-speed layers / low-speed layers or whose thickness of repeated high-speed layers / low-speed layers is less than a set threshold are all determined as micro-logging points corresponding to the repeated high-speed layer / low-speed layer thickness of 0 as 0-value points, which is equivalent to treating the micro-logging points whose thickness of repeated high-speed layers / low-speed layers is less than the set threshold as also not having repeated high-speed layers / low-speed layers, thereby reducing the situation where the thickness value of the determined repeated high-speed layers / low-speed layers is too large due to the error in the thickness of the repeated high-speed layers / low-speed layers, resulting in the misjudgment of the micro-logging points that basically do not have repeated high-speed layers / low-speed layers as micro-logging points that have repeated high-speed layers / low-speed layers.

[0079] Reference Figure 8 The area in the box is the target work area. The 0-value point can actually be regarded as the micro-logging of the high-speed layer / low-speed layer that is not repeatedly drilled, which is represented by a black dot; the micro-logging of the high-speed layer / low-speed layer that is repeatedly drilled is represented by a star icon. Figure 9 It is the elevation plane distribution diagram of each micro-logging well in the target work area. The zero-value point is represented by a black dot, and the micro-logging wells that repeatedly encounter high-speed layers / low-speed layers are represented by star icons. Figure 9 The value in is the elevation value.

[0080] The method for screening micro-logging without repeated high-velocity / low-velocity layers includes:

[0081] If the micro-logging encounters a high-velocity / low-velocity layer only once, or the micro-logging repeatedly encounters a high-velocity / low-velocity layer but the proportion of other micro-logging that only encounters a high-velocity / low-velocity layer once in the second set of nearby areas of the micro-logging accounts for more than the second set of proportional thresholds of the total number of micro-logging in the area, then the micro-logging is regarded as a micro-logging without repeated high-velocity / low-velocity layers. After analysis, since both the micro-logging that repeatedly encounters a high-velocity / low-velocity layer and the micro-logging that does not repeatedly encounter a high-velocity / low-velocity layer are caused by the corresponding formation conditions in a certain area, the micro-logging that repeatedly encounters a high-velocity / low-velocity layer and the micro-logging that does not repeatedly encounter a high-velocity / low-velocity layer usually appear in clusters. Among them, if there are a small number of micro-logging with the characteristics of not repeatedly encountering a high-velocity / low-velocity layer in the area where the micro-logging that repeatedly encounters a high-velocity / low-velocity layer clusters, then these micro-logging are caused by fault breaks, and if there are a small number of micro-logging with the characteristics of repeatedly encountering a high-velocity / low-velocity layer in the area where the micro-logging that does not repeatedly encounter a high-velocity / low-velocity layer clusters, then these micro-logging are usually caused by logging errors; to avoid the interference of logging errors, the near-surface fault identification method of this embodiment also regards the micro-logging that repeatedly encounters a high-velocity / low-velocity layer but has a large proportion of other micro-logging that do not repeatedly encounter a high-velocity / low-velocity layer nearby as a micro-logging without repeated high-velocity / low-velocity layers, that is, it can eliminate the interference of logging errors as much as possible and further avoid the situation of misjudging the micro-logging that basically does not have repeated high-velocity / low-velocity layers as having repeated high-velocity / low-velocity layers.

[0082] Referring to Figure 10 , the method for identifying the fault position according to the break points includes:

[0083] According to the planar distribution positions of each micro-logging in the target work area and the thickness of the repeated high-velocity / low-velocity layers drilled by each micro-logging, obtain the thickness contour lines corresponding to the thickness of the repeated high-velocity / low-velocity layers drilled by each micro-logging in the target work area; mark the points with a thickness value of 0 and each break point in the image corresponding to the thickness contour line and connect the marked points to obtain the identified fault position; specifically, the points with a thickness value of 0 can also be all marked as new break points, and then connect the previously determined break points and the marked new break points to obtain the identified fault position, as Figure 10 shown, the line after connecting each break point can be regarded as the identified fault, as Figure 10 the lines corresponding to the labels 1, 2, and 3 in are the positions of the three identified faults. In other embodiments, other methods for identifying faults through break points can also be used, which will not be elaborated here.

[0084] Specifically, in this embodiment, based on the interpretation results of each micro-log in the target work area, the velocities and thicknesses of each near-surface formation are determined. The micro-logs are classified into two categories according to whether velocity repetition occurs: normal micro-logs, with velocity characteristics of low, decreasing, and high; high-velocity layer repeated micro-logs, which show high and low velocity interlayers under the velocity characteristics of normal micro-logs, such as low, decreasing, low, high low-velocity interlayers, or low, decreasing, high, high high-velocity interlayers. Taking the zero-value point of the thickness of the high (low)-velocity layer as the fault breakpoint position, and combining regional tectonic analysis to orderly connect the breakpoint positions, the strike and dip of the reverse inferred fault are determined. This method is based on micro-logs and assisted by seismic profiles, reducing the influence of seismic data with poor shallow surface quality and large gaps on the identification of near-surface faults.

[0085] In this embodiment, after obtaining the identification result of the fault identified by the micro-log, the identification result can also be combined with the seismic profile to verify the reliability and accuracy of the fault identification method of this embodiment. Figures 11a - 11c That is the schematic diagram of the near-surface seismic profile. Faults No. 1, No. 2, and No. 3 all have profile identification marks of faulting such as in-phase axis distortion and offset on the seismic profile, which are basically consistent with the three faults identified by the fault identification method of this embodiment, thus proving that the fault identification method of this embodiment is relatively reliable.

[0086] The present invention is applicable to areas with relatively strong thrust nappe tectonic movements. The phenomenon of repetition of high-velocity / low-velocity layers in micro-logs is highly correlated with the formation repetition caused by reverse fault nappes. The new and old contact relationship of the formation is the essence of judging faults, and the high and low velocities are a manifestation of new and old formations. Usually, the velocity of old formations is high, and the velocity of new formations is relatively low. By analyzing the distribution of micro-logs in the plane, several possible situations that the micro-logs may encounter are shown, which can be used to predict the development of near-surface faults and the new and old formation contact relationship. Specifically refer to Figure 12 :

[0087] Situation 1: The micro-log encounters normal formations, with velocity characteristics of low, decreasing, and high, as shown by micro-log 1 in Figure 12 ;

[0088] Situation 2: After the micro-log passes through the reverse inferred fault and encounters normal formations, with velocity characteristics of low, decreasing, and high. The hanging wall is eroded, and there is no thickness in the upper part of the high-velocity layer, only the lower part has thickness, as shown by micro-log 2 in Figure 12 ;

[0089] Situation 3: The micro-log encounters the upper and lower walls of the reverse inferred fault, with velocity characteristics of low, decreasing, high, then low, decreasing, high. There is no thickness at the breakpoint, and both the upper and lower walls have the thickness of the high-velocity layer, as shown by micro-log 3 in Figure 12 ;

[0090] Case 4: Micro-logging drilling encounters the upper and lower plates of the inferred layer, and the velocity is low, decreasing, high speed, and then low, decreasing, and high speed. There is no thickness at the breakpoint, and both the upper and lower plates have high-speed layer thickness, such as Figure 12 The micro-logging 4 is shown;

[0091] Case 5: When micro-logging encounters the footwall of the inferred layer, the velocity is low, decreasing, and high. Figure 12 The micro-logging 5 is shown;

[0092] Case 6: The micro-logging drilling encounters the upper wall of the inferred layer, but the upper wall strata are eroded, and the drilling encounters an older stratum with a relatively high velocity, such as Figure 12 As shown in the micro-logging 6.

[0093] The present invention has the following characteristics:

[0094] 1) The reverse inference layer that causes the breakpoint will cause the high-speed layer / low-speed layer repetition phenomenon in the strata within a certain area where the fault is located. According to the high-speed layer / low-speed layer repetition phenomenon in micro-logging, the position of the breakpoint is determined according to the high-speed layer / low-speed layer thickness 0 value point caused by the breakpoint. This near-surface fault identification method is based on micro-logging and supplemented by seismic data, which reduces the impact of shallow surface seismic data with poor quality and large gaps on near-surface fault identification.

[0095] 2) Micro-logging points corresponding to the repeated high-speed layer / low-speed layer thickness of 0 are judged as 0-value points for micro-logging where there is no repeated high-speed layer / low-speed layer or the thickness of the repeated high-speed layer / low-speed layer is less than the set threshold, which is equivalent to considering the micro-logging points where the thickness of the repeated high-speed layer / low-speed layer is less than the set threshold as having no repeated high-speed layer / low-speed layer. This can reduce the situation where the micro-logging points where there is basically no repeated high-speed layer / low-speed layer are misjudged as micro-logging points where there is a repeated high-speed layer / low-speed layer due to errors in the thickness of the repeated high-speed layer / low-speed layer.

[0096] 3) Although it is judged that a high-speed layer / low-speed layer is repeatedly drilled, but the number of other micro-logging wells nearby that have not repeatedly encountered a high-speed layer / low-speed layer accounts for a relatively large proportion, the micro-logging well is also regarded as a micro-logging well without a repeated high-speed layer / low-speed layer. That is, the interference of logging errors can be eliminated as much as possible, and the situation where a micro-logging well with basically no repeated high-speed layer / low-speed layer is misjudged as a micro-logging well with a repeated high-speed layer / low-speed layer can be further avoided.

[0097] 4) The thickness corresponding to the high-velocity layer / low-velocity layer with the second smallest depth is selected as the thickness of the repeated high-velocity layer / low-velocity layer encountered by the micro-logging for subsequent identification steps, avoiding misusing the corresponding thickness data of the high-velocity layer / low-velocity layer generated by another deeper fault in the case of multiple repeated high-velocity layers / low-velocity layers, and improving the identification accuracy.

[0098] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation on the present invention.

Claims

1. A method for identifying near-surface faults, characterized in that, Based on the formation velocities corresponding to each micro-log in the target work area, determine the high-velocity / low-velocity layers encountered by each micro-log and their repetition situations; based on the repetition situations of the high-velocity / low-velocity layers encountered by each micro-log, determine the thicknesses of the repeated high-velocity / low-velocity layers encountered by each micro-log. Based on the thicknesses of the repeated high-velocity / low-velocity layers, determine the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity / low-velocity layers as 0-value points, and select the 0-value points that meet the breakpoint conditions as breakpoints. Identify the fault positions based on the breakpoints. The breakpoint conditions include: the proportion of the number of other 0-value points within the first set nearby area of the 0-value point to the total number of micro-logs in this area is less than the first set proportion threshold.

2. The near-surface fault identification method according to claim 1, wherein The method of determining the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity / low-velocity layers as 0-value points based on the thicknesses of the repeated high-velocity / low-velocity layers is as follows: Screen out the micro-logs without repeated high-velocity / low-velocity layers or with the thicknesses of the repeated high-velocity / low-velocity layers less than the set threshold, determine the micro-log well points of the screened micro-logs as the micro-log well points corresponding to the thickness value of 0 of the repeated high-velocity / low-velocity layers, and take the micro-log well points as 0-value points.

3. The near-surface fault identification method according to claim 2, wherein The methods of screening out the micro-logs without repeated high-velocity / low-velocity layers include: If a micro-log encounters a high-velocity / low-velocity layer only once, or if a micro-log repeatedly encounters a high-velocity / low-velocity layer but the proportion of the number of other micro-logs that encounter the high-velocity / low-velocity layer only once within the second set nearby area of this micro-log to the total number of micro-logs in this area is greater than the second set proportion threshold, then take this micro-log as a micro-log without repeated high-velocity / low-velocity layers.

4. The near-surface fault identification method according to claim 1 or 2, characterized in that, The methods of determining the high-velocity / low-velocity layers encountered by each micro-log and their repetition situations based on the formation velocities corresponding to each micro-log in the target work area include: In the target work area, if the formation velocity corresponding to a certain depth section of a micro-log is greater than the set high-velocity threshold, it is determined that the micro-log encounters a high-velocity layer, and this depth section is used as the encountered high-velocity layer; if the formation velocity corresponding to a certain depth section of a micro-log is less than the set low-velocity threshold, it is determined that the micro-log encounters a low-velocity layer, and this depth section is used as the encountered low-velocity layer; if there are at least two depth sections of a micro-log corresponding to formation velocities greater than the set high-velocity threshold and there are other depth sections with corresponding formation velocities less than or equal to the set low-velocity threshold between these depth sections, it is determined that the micro-log repeatedly encounters a high-velocity layer, and these depth sections are used as the encountered high-velocity layers; if there are at least two depth sections corresponding to formation velocities less than the set low-velocity threshold and there are other depth sections with corresponding formation velocities greater than the set high-velocity threshold between these depth sections, it is determined that the micro-log repeatedly encounters a low-velocity layer, and these depth sections are used as the encountered low-velocity layers; the set low-velocity threshold is less than or equal to the set high-velocity threshold.

5. The near-surface fault identification method according to claim 4, characterized in that The methods of determining the thicknesses of the repeated high-velocity / low-velocity layers encountered by each micro-log based on the repetition situations of the high-velocity / low-velocity layers encountered by each micro-log include: Compare the depth sizes of the high-velocity / low-velocity layers encountered by the micro-logs that repeatedly encounter the high-velocity / low-velocity layers, and take the thickness corresponding to the second smallest depth of the high-velocity / low-velocity layer as the thickness of the repeated high-velocity / low-velocity layer encountered by this micro-log.

6. The method for identifying near-surface faults according to claim 1 or 2, characterized in that, The methods of identifying the fault positions based on the breakpoints include: According to the planar distribution positions of each micro-log in the target work area and the thicknesses of the repeated high-velocity layers / low-velocity layers encountered by each micro-log, obtain the thickness contour lines corresponding to the thicknesses of the repeated high-velocity layers / low-velocity layers encountered by each micro-log in the target work area; mark the points with a thickness value of 0 and the break points in the image corresponding to the thickness contour lines and connect each marked point to obtain the identified fault positions.

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