Method for identifying cut-off layer of buried hill unconformity surface

Abstract

The present application provides a kind of buried hill unconformity on the recognition method of cutting type fault layer of intercept, the buried hill unconformity on the recognition method of cutting type fault layer of intercept includes: step 1, according to the well logging data of drilled well, carry out buried hill inside formation, fault interpretation;Step 2, carry out buried hill top unconformity seismic reflection characteristics forward modeling;Step 3, carry out the recognition of cutting type fault layer of intercept on the unconformity of pre-third system buried hill.The recognition method of cutting type fault layer of intercept on the buried hill unconformity effectively solves the recognition problem of cutting type fault layer of intercept on the buried hill unconformity, and has great significance for the oil and gas exploration work of pre-third system buried hill.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration technology, and in particular relates to a method for identifying cut-off ancient faults on buried hill unconformities. Background Technology

[0002] With the increasing demand for oil and gas energy, exploration of pre-Tertiary buried hill oil and gas has become a key focus. Based on the currently discovered types of pre-Tertiary buried hill reservoirs, the main reservoir types are structural and stratigraphic oil and gas reservoirs. Therefore, detailed structural interpretation is a crucial aspect of the work.

[0003] Pre-Tertiary strata generally underwent multiple tectonic movements. In the early stages of the Jiyang Depression, they were mostly compressional reverse faults, which later experienced extensional forces leading to tectonic inversion and the transformation of faults into normal faults. During this period, multiple strike-slip movements and repeated uplift and erosion of the strata resulted in highly complex pre-Tertiary faults. Furthermore, most pre-Tertiary faults extend to the unconformity surface, where there is essentially no fault displacement, but significant internal fault displacement below the unconformity surface. These types of faults play a controlling role in trap formation, reservoir improvement, oil and gas sealing, and the connection and conduction of oil and gas. Therefore, identifying these faults is both necessary and of great significance.

[0004] Currently, researchers both domestically and internationally lack a clear method for identifying ancient faults that have virtually no displacement on the unconformity surface of pre-Tertiary buried hills but still play a controlling role in the formation of hydrocarbon reservoirs in buried hills. This has brought many inconveniences to the exploration of oil and gas in pre-Tertiary buried hills.

[0005] Chinese patent application CN201410447961.7 discloses a method for processing fault polygons to correct transect anomalies in paleotopographic reconstruction. The method involves dividing irregular fault polygons at specified upper and lower strata, output by an interpretation system, into two or more convex polygons. By comparing area size, distance, and extension direction, the obtained convex polygons at the upper and lower strata are combined, assigning a unified identifier to polygons describing the same fault. Two convex polygons with the same identifier are merged to obtain a new convex polygon used to describe the range of transect data anomalies caused by the same fault. By applying this method, transect data processing can be performed based on a strictly defined distribution range of anomalies, thereby improving the accuracy of transect anomaly correction and ultimately enhancing the accuracy of paleotopographic reconstruction.

[0006] Chinese patent application CN202010308474.8 discloses a quantitative analysis method for the resolution of low-order faults in buried hills based on forward modeling. Based on the analysis of the geological characteristics of Paleozoic buried hills in the study area, corresponding geological models were established for low-order faults in buried hills with different displacements. Forward modeling was then used to systematically study the seismic response characteristics of these faults. Combining the established geological models, the different seismic response characteristics of low-order faults in Paleozoic buried hills under different dominant frequencies and noise conditions were analyzed in detail. Based on this, quantitative identification templates for the resolution of low-order faults in buried hills under noise-free conditions and under different noise conditions were established. This quantitatively studied the resolution capability of low-order faults in buried hills under different conditions, providing valuable guidance for subsequent research on low-order faults in buried hills.

[0007] Chinese patent application CN202010354227.1 discloses a method, apparatus, device, and storage medium for earthquake fault identification. The method includes: determining a dip volume based on the original seismic data volume of the earthquake fault to be identified; performing guided filtering of the earthquake fault to be identified under the constraint of the dip volume to determine an optimized seismic data volume; enhancing the optimized seismic data volume to obtain an enhanced seismic data volume; and performing fault identification processing on the enhanced seismic data volume to obtain a fault identification result for the earthquake fault to be identified, wherein the fault identification result includes at least the segmentation points and / or transition points of the earthquake fault to be identified. This embodiment of the invention performs guided filtering of the seismic data volume of the earthquake fault to be identified under the constraint of the dip volume to achieve smoothing processing of the phase axis parallel to the earthquake fault, improving the sharpness of the fault and thus increasing the accuracy of fault identification; and enhances the seismic data volume to improve the accuracy of fault identification.

[0008] The existing technologies described above are significantly different from the present invention and have failed to solve the technical problem we want to address. Therefore, we have invented a new method for identifying cut-type ancient faults on buried hill unconformities. Summary of the Invention

[0009] The purpose of this invention is to provide a method for identifying truncated paleofaults on buried hill unconformities by first applying forward modeling to guide the identification of such faults, and then further clarifying the fault location of truncated paleofaults on buried hill unconformities through a comprehensive seismic identification method.

[0010] The objective of this invention can be achieved through the following technical measures: a method for identifying cut-type paleofaults on buried hill unconformities, the method comprising:

[0011] Step 1: Based on the logging and well logging data of the drilled wells, interpret the strata and faults inside the buried hill;

[0012] Step 2: Perform forward modeling of the seismic reflection characteristics of the unconformity at the top of the buried hill;

[0013] Step 3: Identify the cut-type paleofaults on the pre-Tertiary buried hill unconformity surface.

[0014] The objective of this invention can also be achieved through the following technical measures:

[0015] The method for identifying cut-type ancient faults on the buried hill unconformity also includes, before step 1, obtaining the basic geological overview of the study area, collecting relevant data on tectonic evolution, and understanding the tectonic movements and stress directions experienced by the study area.

[0016] In step 1, based on the sonic transit time and density logging curves, a synthetic record is created to calibrate the formation and interpret the internal strata and faults of the buried hill.

[0017] In step 1, during the interpretation process, it is necessary to check whether the interpretation horizon and fault are closed.

[0018] In step 2, based on the reservoir and non-reservoir rock physical parameters obtained from actual drilling, a geological model is designed, and forward modeling is performed to analyze the seismic reflection characteristics of the unconformity. The forward modeling results are then applied to structural interpretation, effectively guiding the identification of cut-off paleofaults on the buried hill unconformity.

[0019] In step 2, two types of geological models are designed: one that ignores faults and one that does not.

[0020] In step 2, a forward modeling simulation of the seismic reflection characteristics of the pre-Tertiary buried hill cut-off unconformity surface, ignoring faults, is performed. Combined with actual seismic data, a geological model profile (ignoring faults) with longitudinal and transverse velocity gradient variations is established using sonic or density curves from wells passing through complex geological bodies. Multi-frequency wavelet forward modeling is then applied to analyze the seismic reflection characteristics of the pre-Tertiary buried hill unconformity surface, ignoring faults. The forward modeling results show that different sandstone and mudstone structures on the pre-Tertiary cut-off unconformity surface exhibit characteristics such as energy variations, torsion of the same phase axis, and slippage. Those without faults within the unconformity surface exhibiting the above-mentioned changes are not faults, but rather variations in lithology.

[0021] In step 2, a forward modeling simulation of the seismic reflection characteristics of the cut-off fault points on the unconformity surface of the pre-Tertiary buried hill is performed without neglecting the fault. Combining actual seismic data, a geological model profile with longitudinal and transverse velocity gradient changes (without neglecting the fault) is established using sonic or density curves from wells passing through complex geological bodies. A single-frequency wavelet is then used for forward modeling. The forward modeling results show that the seismic reflections of different exposed strata of the pre-Tertiary exhibit characteristics such as energy changes, elongation of the in-phase axis, and torsion. Among these, the fault reflections on the unconformity surface show characteristics of significantly elongated waveforms and reduced frequencies, and the fault displacement of the internal faults below the unconformity surface is obvious.

[0022] In step 2, the principle for determining the breakpoint location on the cut-off unconformity surface is as follows: First, the fault displacement of the internal fault below the unconformity surface is obvious; second, the fault is extrapolated to the unconformity surface according to the attitude trend of the internal fault, and the point on the unconformity surface where the waveform is obviously elongated and the frequency decreases is taken as the breakpoint location.

[0023] In step 3, the pre-tertiary system generally undergoes multiple tectonic movements, with most faults reaching the unconformity. Although there is basically no fault displacement on the unconformity, the internal fault displacement is obvious below the unconformity. Based on the regional tectonic evolution, it is believed that fault characteristics should be interpreted regardless of whether they exist on the unconformity. The location of the fault is determined according to the understanding obtained from forward modeling and in combination with the attitude trend of the internal faults.

[0024] The method for identifying cut-type paleofaults on buried hill unconformities in this invention effectively solves the problem of identifying cut-type paleofaults on buried hill unconformities, and is of great significance for oil and gas exploration work in pre-Tertiary buried hills. The advantages and positive effects of this invention are as follows:

[0025] The method for identifying cut-type paleofaults on unconformities of buried hills provided by this invention is currently unique among researchers both domestically and internationally. This invention creatively categorizes the reflection characteristics of the pre-Tertiary buried hill top into two cases: the first case involves reflections with weak to medium amplitude and intermittent phase axes; the second case involves reflections with relatively continuous strong amplitude phase axes. Cut-type paleofaults on unconformities of buried hills are identified under these two cases, representing a significant improvement over traditional paleofault identification methods. This invention applies a forward modeling method based on wave equations to simulate the seismic reflection characteristics of the unconformity at the top of the buried hill, serving as a basis for identifying cut-type paleofaults on pre-Tertiary buried hill unconformities. This method has high practical value and strong operability, and can provide a reference for oil and gas exploration in pre-Tertiary buried hills related to hydrocarbons in the Jiyang Depression and even the Bohai Bay Basin. Attached Figure Description

[0026] Figure 1A flowchart illustrating a specific embodiment of the method for identifying cut-off ancient faults on buried hill unconformities according to the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the internal strata and faults in a specific embodiment of the present invention;

[0028] Figure 3 This is a geological model diagram of the seismic reflection characteristics of the pre-Tertiary buried hill unconformity surface in a specific embodiment 1 of the present invention (ignoring faults);

[0029] Figure 4 The above are forward modeling cross-sections of wavelet at 20Hz, 25Hz, 30Hz, and 40Hz in a specific embodiment 1 of the present invention (ignoring faults);

[0030] Figure 5 This is a geological model diagram of the location of the cut-off fault on the pre-Tertiary buried hill unconformity surface in a specific embodiment 1 of the present invention (faults are not ignored);

[0031] Figure 6 This is a 30Hz wavelet forward modeling profile of the cut-off fault point on the pre-Tertiary buried hill unconformity surface in a specific embodiment 1 of the present invention (faults are not ignored);

[0032] Figure 7 This is a schematic diagram of the fault structure on the top surface of the Tertiary strata in a specific embodiment 1 of the present invention;

[0033] Figure 8 This is a schematic diagram illustrating the internal strata and faults in a specific embodiment 2 of the present invention;

[0034] Figure 9 The following are the forward model profile, original profile, wavelet frequency-division filtered profile, seismic profile along the trajectory of well Z213-X10 pile, and wavelet frequency-division filtered seismic profile along the trajectory of well Z213-X10 pile in specific embodiment 2 of the present invention;

[0035] Figure 10 The Tr structure diagram of the long dike area in specific embodiment 2 of the present invention. Detailed Implementation

[0036] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0038] The method for identifying cut-type ancient faults on buried hill unconformities of the present invention specifically includes the following steps:

[0039] Step 1: Based on the logging and well logging data of the drilled wells, interpret the strata and faults inside the buried hill;

[0040] Step 2: Combining actual seismic data, using the sonic or density curves of wells passing through complex geological bodies, design two types of geological models (ignoring faults and not ignoring faults), perform forward modeling respectively, analyze the seismic reflection characteristics of buried hill unconformities, and apply the forward modeling results to structural interpretation to effectively guide the identification of cut-off paleofaults on buried hill unconformities.

[0041] Step 3: The pre-Tertiary system generally underwent multiple tectonic movements, with most faults extending to the unconformity surface. There is essentially no fault displacement on the unconformity surface, but the internal faults below the unconformity surface exhibit significant fault displacement. Therefore, regardless of whether fault characteristics are present on the unconformity surface, they should be interpreted. The location of the fault point is determined by extrapolating from the understanding obtained through forward modeling and combining it with the attitude trends of the internal faults.

[0042] The following are several specific embodiments of the application of the present invention.

[0043] Example 1

[0044] In a specific embodiment 1 of the present invention, the method for identifying cut-off paleofaults on the buried hill unconformity surface includes the following steps:

[0045] Step 1: Obtain the basic geological overview of the study area, collect relevant data on tectonic evolution, and understand the tectonic movements and stress directions experienced by the study area.

[0046] Step 2: Based on the logging and well logging data of the drilled wells, interpret the strata and faults inside the buried hill;

[0047] Based on the logging curves such as sonic transit time and density, a synthetic record is made to calibrate the formation, and the internal formations and faults of the buried hill are interpreted. During the interpretation process, it is necessary to check whether the interpreted layers and faults are closed.

[0048] Step 3: Combining actual seismic data, using the sonic or density curves of wells passing through complex geological bodies, design two types of geological models (ignoring faults and not ignoring faults), perform forward modeling respectively, analyze the seismic reflection characteristics of the unconformity, and apply the forward modeling results to structural interpretation to effectively guide the identification of cut-off paleofaults on buried hill unconformities.

[0049] Based on actual seismic data, and using the sonic or density curves of wells passing through complex geological bodies, two types of geological models (ignoring faults and not ignoring faults) were designed, and forward modeling was performed to analyze the seismic reflection characteristics of unconformities.

[0050] Step 4: The pre-Tertiary strata generally underwent multiple tectonic movements, with most faults extending to the unconformity. Although there is essentially no fault displacement on the unconformity, the internal faults below the unconformity exhibit significant displacement. Considering regional tectonic evolution, it is argued that fault characteristics, regardless of whether they exist on the unconformity, should be interpreted. The fault locations are determined based on information obtained from forward modeling and the attitude trends of the internal faults.

[0051] Pre-Tertiary strata generally undergo multiple tectonic movements, with most faults extending to erosion-uplift unconformities. Although there is essentially no fault displacement on the unconformity surface, the internal fault displacement is significant below the unconformity surface. Therefore, regardless of whether fault characteristics exist on the unconformity surface, they should be interpreted, and the fault location should be determined by extrapolating from the understanding obtained through forward modeling and in conjunction with the attitude trends of internal faults.

[0052] Example 2

[0053] In a specific embodiment 2 of the present invention, the Gudao buried hill is located in the northeastern part of the Zhanhua Depression. It is connected to the Gunan and Gubei Depressions to the south and north by the Gunan and Gubei Faults, respectively, and separated from the Bonan Depression to the west by the Guxi Fault. To the east lies the Gudong Low Uplift. Due to the complex longitudinal and transverse lithology of the pre-Tertiary strata, forming a weak-amplitude, intermittent, and co-phase axis with the overlying Paleogene strata, it is difficult to identify the truncated paleofaults on the unconformity surface of the pre-Tertiary buried hill. Therefore, it is necessary to conduct in-depth research on the identification of truncated paleofaults on the unconformity surface of the pre-Tertiary buried hill.

[0054] like Figure 1 This is a flowchart illustrating the method for identifying cut-type ancient faults on buried hill unconformities according to the present invention.

[0055] In step 101, we learn about the basic geological conditions of the study area, collect relevant data on tectonic evolution, and become familiar with the tectonic movements and stress directions experienced by the study area. The main purpose of this step is to understand the basic geological framework of the study area, so as to ensure that the results of the next tectonic interpretation are consistent with the actual situation of the area and make the tectonic interpretation more reasonable. The process then proceeds to step 102.

[0056] In step 102, the internal strata and faults within the buried hill are interpreted. Based on the logging data from the drilled wells, the internal strata and faults are interpreted according to the conventional formation interpretation process. This step is fundamental to this invention. Figure 2 The Geoframe interpretation software was used to perform structural interpretation of the buried hill interior. The specific steps were: importing AC (acoustic transit time) and Den (density) curves into the seismic interpretation software—synthetic record calibration—stratigraphic and fault interpretation. During the interpretation process, the interpreted horizons and fault closures were checked. The process then proceeded to step 103.

[0057] In step 103, two types of geological models (ignoring faults and not ignoring faults) are designed and forward modeling is performed to analyze the seismic reflection characteristics of the buried hill unconformity. This step is the focus of this invention.

[0058] First, a forward modeling simulation of the seismic reflection characteristics of the pre-Tertiary buried hill cut-off unconformity was performed (ignoring faults). Velocity, density, and other parameters of reservoir (sandstone) and non-reservoir (mudstone, coal) data were statistically analyzed on the Gugu 13-Cecil side and Gugu 13-Cecil side. Based on this, a geological model was designed. Figure 3 Forward modeling was performed using wavelets at frequencies of 20Hz, 25Hz, 30Hz, and 40Hz, respectively. Figure 4 This study analyzes the seismic reflection characteristics of the pre-Tertiary buried hill unconformity (ignoring faults). Forward modeling results show that different sandstone and mudstone structures exhibit seismic reflection characteristics such as energy variations, torsion of the same phase axis, and fault displacement on the pre-Tertiary cut-off unconformity. The aforementioned changes observed on the unconformity surface, even without well-developed faults within the inner layer, are not due to faults but rather to variations in lithology (excluding later-developed faults).

[0059] Next, forward modeling of seismic reflection characteristics of truncated fault points on the pre-Tertiary buried hill unconformity surface is performed (without neglecting the fault). Figure 5 A geological model was designed based on the layer velocities of the Shahejie Formation (Section 1), Mesozoic, Upper Paleozoic, Lower Paleozoic, and Archean strata obtained from actual drilling statistics (faults are not ignored), and forward modeling was performed using a 30Hz wavelet. Figure 6 Forward modeling results show that seismic reflections from different exposed pre-Tertiary strata exhibit characteristics such as energy variations, elongation of the in-phase axis, and torsion. Specifically, fault reflections on the unconformity surface show significantly elongated waveforms and decreased frequencies, with a clear fault displacement of the internal faults below the unconformity surface. Therefore, the principle for determining the fault location on the cut-off unconformity surface is as follows: First, the fault displacement of the internal faults below the unconformity surface is clear. Second, the orientation trend of the internal faults is extrapolated to the unconformity surface, and the point on the unconformity surface where the waveform is significantly elongated and the frequency is decreased is taken as the fault location. The process proceeds to step 104.

[0060] In step 104, a method for identifying cut-type paleofaults on the pre-Tertiary buried hill unconformity surface is performed. This step is also a key aspect of this invention. The identification method is based on... Figure 2 For example, the isolated buried hill underwent uplift, erosion, and peneplaining during the late Indosinian and late Yanshanian orogenies, resulting in some ancient faults on the pre-Tertiary unconformity surface. These faults were continuously active during the Indosinian and Yanshanian periods, ceasing activity after the uplift and erosion of the late Yanshanian orogeny. Therefore, faults that were active throughout the Mesozoic era, regardless of whether they exhibit fault characteristics on the pre-Tertiary unconformity surface, should be interpreted, and their location should be determined based on the understanding obtained from the forward modeling in step 103. When interpreting faults on seismic profiles, first, attention should be paid to the inheritance of faults in adjacent strata above and below; second, the tectonic evolution history of the study area should be referenced to determine whether the fault is a normal or reverse fault, whether it conforms to the tectonic stress direction of that period, and whether the cutting relationship is correct. Figure 7 This is a structural outline of the top surface of the Tertiary strata in front of the buried hill on the isolated island. Classified by fault strike, there are three main groups of faults: northwest-trending faults, supplemented by northeast-northeast and east-west trending faults. Classified by fault development period, firstly, there are boundary faults: the Gubei and Gunan faults became active during the Yanshanian period and continued their activity into the Neogene; the Guxi fault became active during the Indosinian period and ceased activity during the deposition of the Shahejie Formation (Sha-3). Secondly, there are buried hill faults: most of these faults became active during the Indosinian and Yanshanian periods, developing continuously until they ceased activity after uplift and erosion in the late Yanshanian period.

[0061] Example 3

[0062] In a specific embodiment 3 of the present invention, the Changdi Oilfield is located in the northeastern part of the Jiyang Depression, adjacent to the Yellow River Estuary Depression. It possesses favorable oil source conditions, with the Mesozoic strata and the overlying Paleogene strata forming an angular unconformity, creating an unconformity trap. This trap is characterized by shallow burial depth and high natural production capacity, making it a realistic and profitable reserve area. The Mesozoic strata are extensively developed with large sets of tight, high-velocity sandstone. These high-velocity sandstones and the overlying Paleogene low-velocity mudstone form continuous, low-frequency, strong reflection Tr phase axes, making it difficult to identify truncated paleofaults on the unconformity surface of the pre-Tertiary buried hill. Therefore, it is necessary to conduct in-depth research on paleofault identification methods based on relatively continuous, strong-amplitude reflection phase axes on the pre-Tertiary buried hill top.

[0063] like Figure 1 This is a flowchart illustrating the method for identifying cut-type ancient faults on buried hill unconformities according to the present invention.

[0064] In step 101, we learn about the basic geological conditions of the study area, collect relevant data on tectonic evolution, and become familiar with the tectonic movements and stress directions experienced by the study area. The main purpose of this step is to understand the basic geological framework of the study area, so as to ensure that the results of the next tectonic interpretation are consistent with the actual situation of the area and make the tectonic interpretation more reasonable. The process then proceeds to step 102.

[0065] In step 102, the internal strata and faults within the buried hill are interpreted. Based on the logging data from the drilled wells, the internal strata and faults are interpreted according to the conventional formation interpretation process. This step is fundamental to this invention. Figure 8 The Geoframe interpretation software was used to perform structural interpretation of the buried hill interior. The specific steps were: importing AC (acoustic transit time) and Den (density) curves into the seismic interpretation software—synthetic record calibration—stratigraphic and fault interpretation. During the interpretation process, the interpreted horizons and fault closures were checked. The process then proceeded to step 103.

[0066] In step 103, a geological model is first designed for forward modeling to analyze the seismic reflection characteristics of the buried hill unconformity. Secondly, wavelet frequency division filtering is applied to separate the Tr phase axes and identify paleofaults on the pre-Tertiary buried hill unconformity. This step is the core of this invention.

[0067] First, a forward modeling simulation of the seismic reflection characteristics of the pre-Tertiary buried hill cut-off unconformity was conducted. A model was constructed based on actual drilling data of the Mesozoic strata in the Changdi area for forward modeling. The velocity characteristics of 38 wells in the work area were statistically analyzed. The Paleogene strata bottom, consisting of the Shahejie Formation 3 mudstone, had a velocity of 3300 m / s; the Mesozoic sandstone velocity was around 4500 m / s, and the mudstone velocity was 3800 m / s. Based on these velocity characteristics, a geological model of the reflection characteristics of the top surface of the Mesozoic strata in the Changdi area was established. The results of the forward modeling simulation show that the reflection phase axis of the top surface of the pre-Tertiary buried hill exhibits relatively continuous strong amplitude (…). Figure 9 a).

[0068] Secondly, wavelet frequency division filtering was applied to separate the Tr phase axes and identify paleofaults on the pre-Tertiary buried hill unconformity surface. Wavelet frequency division filtering uses the wavelet spectrum as a frequency domain filter to filter the seismic signal, equivalent to a bandpass filter. On the original seismic profile ( Figure 9 b) It exhibits continuous and stable low-frequency strong amplitude, and after wavelet frequency division filtering, it can be observed from the cross-section ( Figure 9 c) Observe that the Tr reflection phase axis becomes a medium-to-weak amplitude, intermittent, and the obvious change point shows the characteristic reflection features of a significantly elongated waveform and a decreased frequency. Based on the understanding of the forward model in Example 1, the principle for determining the location of the breakpoint on the truncated unconformity is as follows: First, the fault displacement of the internal fault is obvious below the unconformity. Second, extrapolate the attitude trend of the internal fault to the unconformity, and take the point on the unconformity where the waveform is significantly elongated and the frequency decreases as the breakpoint location. Figure 9 (d, e). The process proceeds to step 104.

[0069] In step 104, a method for identifying cut-type paleofaults on the pre-Tertiary buried hill unconformity surface is performed. This step is also the core of this invention. The identification method is based on... Figure 8 , Figure 10 For example, the buried hill of Changdi underwent uplift, erosion, and peneplaining during the late Indosinian and late Yanshanian orogenies, resulting in some ancient faults on the pre-Tertiary unconformity surface. These faults were continuously active during the Indosinian and Yanshanian periods, ceasing activity after the uplift and erosion during the late Yanshanian orogeny. Therefore, faults that were active in the Mesozoic era, regardless of whether they exhibit fault characteristics on the pre-Tertiary unconformity surface, should be interpreted, and their fault locations should be determined based on the understanding obtained from the forward modeling in step 103. The principle for determining the fault location on the truncated unconformity surface is as follows: First, the internal fault displacement is obvious below the unconformity surface. Second, extrapolate the attitude trend of the internal faults to the unconformity surface, and the point on the unconformity surface where the waveform is significantly elongated and the frequency decreases is taken as the fault location.

[0070] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A method for identifying cut-type paleofaults on buried hill unconformities, characterized in that, The methods for identifying cut-off paleofaults on the buried hill unconformity include: Step 1: Based on the logging and well logging data of the drilled wells, interpret the strata and faults inside the buried hill; Step 2: Perform forward modeling of the seismic reflection characteristics of the unconformity at the top of the buried hill; Step 3: Identify the cut-off paleofaults on the pre-Tertiary buried hill unconformity surface; In step 2, combined with actual seismic data, a geological model profile of longitudinal and transverse velocity gradient changes is established using the sonic or density curves of wells passing through complex geological bodies. Forward modeling is then performed to analyze the seismic reflection characteristics of the unconformity. The results of the forward modeling are then applied to structural interpretation, effectively guiding the identification of cut-off paleofaults on buried hill unconformities. In step 2, two types of geological models are designed: one that ignores faults and one that does not. In step 2, a forward modeling simulation of the seismic reflection characteristics of the pre-Tertiary buried hill cut-off unconformity surface, ignoring faults, is performed. Combined with actual seismic data, a geological model profile ignoring faults and longitudinal and transverse velocity gradient variations is established using sonic or density curves from wells passing through complex geological bodies. Multi-frequency wavelet forward modeling is then applied to analyze the seismic reflection characteristics of the pre-Tertiary buried hill unconformity surface. The forward modeling results show that different sandstone and mudstone structures on the pre-Tertiary cut-off unconformity surface exhibit characteristics such as energy variations, torsion of the same phase axis, and slippage. Those without faults within the inner layer and exhibiting the above-mentioned changes on the unconformity surface are not faults, but rather variations in lithology. In step 2, a forward modeling simulation of the seismic reflection characteristics of the cut-off fault points on the unconformity surface of the pre-Tertiary buried hill is performed without neglecting the fault. Combining actual seismic data, a geological model profile of the longitudinal and transverse velocity gradients without neglecting the fault is established using the sonic or density curves of wells passing through complex geological bodies. A single-frequency wavelet is then used for forward modeling. The forward modeling results show that the seismic reflections of different exposed strata of the pre-Tertiary exhibit characteristics such as energy changes, elongation of the in-phase axis, and torsion. Among them, the fault reflections on the unconformity surface show the characteristics of significant waveform elongation and frequency reduction, and the fault displacement of the internal fault below the unconformity surface is obvious.

2. The method for identifying cut-type paleofaults on buried hill unconformities according to claim 1, characterized in that, The method for identifying cut-type ancient faults on the buried hill unconformity also includes, before step 1, obtaining the basic geological overview of the study area, collecting relevant data on tectonic evolution, and understanding the tectonic movements and stress directions experienced by the study area.

3. The method for identifying cut-type paleofaults on buried hill unconformities according to claim 1, characterized in that, In step 1, based on the sonic transit time and density logging curves, a synthetic record is created to calibrate the formation and interpret the internal strata and faults of the buried hill.

4. The method for identifying cut-type paleofaults on buried hill unconformities according to claim 3, characterized in that, In step 1, during the interpretation process, it is necessary to check whether the interpretation horizon and fault are closed.

5. The method for identifying cut-type paleofaults on buried hill unconformities according to claim 1, characterized in that, In step 2, the principle for determining the breakpoint location on the cut-off unconformity surface is as follows: First, the fault displacement of the internal fault below the unconformity surface is obvious; second, the fault is extrapolated to the unconformity surface according to the attitude trend of the internal fault, and the point on the unconformity surface where the waveform is obviously elongated and the frequency decreases is taken as the breakpoint location.

6. The method for identifying cut-type paleofaults on buried hill unconformities according to claim 1, characterized in that, In step 3, the pre-tertiary system generally undergoes multiple tectonic movements, with most faults reaching the unconformity. Although there is basically no fault displacement on the unconformity, the internal fault displacement is obvious below the unconformity. Based on the regional tectonic evolution, it is believed that fault characteristics should be interpreted regardless of whether they exist on the unconformity. The location of the fault is determined according to the understanding obtained from forward modeling and in combination with the attitude trend of the internal faults.

Images