A method for identifying strike-slip faults through seismic profile heave curves

Abstract

This invention discloses a method for identifying strike-slip faults using seismic profile displacement curves, relating to the fields of structural geology and seismic interpretation. The method includes the following steps: obtaining fault profile interpretation based on seismic data and interpretation of the target block; selecting seismic profiles with significant fault characteristics based on the fault profile interpretation, measuring the vertical displacement, and calculating the displacement change rate based on the vertical displacement; drawing a displacement profile based on the vertical displacement, drawing a displacement change rate profile based on the displacement change rate, and identifying strike-slip faults based on the displacement profile and displacement change rate profile: if the displacement and displacement change rate show frequent wavy changes on the same profile, and / or, the downward displacement value decreases and the downward displacement change rate is negative, then the fault is identified as a strike-slip fault. This invention's method directly identifies strike-slip faults through seismic profiles and proposes an intuitive identification chart with qualitative-semi-quantitative characteristics, resulting in more reliable predictions.

Description

Technical Field

[0001] This invention relates to the field of structural geology and seismic interpretation technology, specifically a method for identifying strike-slip faults using seismic profile displacement curves. Background Technology

[0002] Strike-slip faults are widely distributed in nature and are an important part of structural geology research and related engineering applications. In sedimentary basins, strike-slip faults are usually identified using seismic data, and the identification of strike-slip faults is the foundation for fault interpretation and evaluation.

[0003] Because strike-slip faults are primarily characterized by horizontal movement, horizontal displacement cannot be determined from seismic profiles. Since strike-slip faults typically exhibit a certain vertical displacement on the profile, displaying characteristics of normal faults (downward displacement) or reverse faults (upward displacement), it is often difficult to distinguish strike-slip faults from normal / reverse faults on seismic profiles. On the profile, the fault assemblages of strike-slip fault zones exhibit a flower-like structure, with flower-like structures appearing in reverse fault assemblages or negative flower-like structures in normal fault assemblages. In the interpretation of seismic profiles in sedimentary basins, strike-slip faults are usually identified comprehensively based on their downward convergence characteristics and typical flower-like structures. However, the quality of deep seismic data in many basins is poor, and the vertical displacement of strike-slip faults is small, making typical strike-slip fault structures inconspicuous. This makes it difficult to distinguish strike-slip faults from normal / reverse faults on seismic profiles, leading to misjudgments in fault interpretation and affecting the accuracy of fault interpretation and structural analysis. Therefore, directly identifying strike-slip faults from seismic profiles plays a crucial role in the seismic interpretation and structural analysis of strike-slip faults.

[0004] Regarding patents, CN117434596A proposes a quantitative identification template for strike-slip fault resolution; CN114970295A discloses a method and device for identifying the active block of a strike-slip fault based on discrete element simulation; CN113589372A provides a quantitative identification method for extensional faults in continental rift basins; and CN115453625A provides a method for identifying the structural properties of faults of different series in compression-torsional fault zones. However, these methods do not involve seismic displacement analysis methods to distinguish between strike-slip faults and normal / reverse faults. CN116520406A provides a method for identifying apparent strike-slip faults by superimposing multi-stage tectonic stress fields, using the ratio of the fault extension component to the strike-slip component as the basis for identifying apparent strike-slip faults, where the known strike-slip component is not obtained from seismic profiles.

[0005] Therefore, previous studies have proposed to distinguish strike-slip faults from normal / reverse faults by integrating different strike-slip fault markers, but lack a method to identify strike-slip faults using quantitative fault displacement data templates on seismic profiles. Summary of the Invention

[0006] To address at least one of the aforementioned problems, this invention proposes a method for identifying strike-slip faults using seismic profile displacement curves. This method directly identifies strike-slip faults from seismic profiles and provides an intuitive identification chart with qualitative and semi-quantitative characteristics, resulting in more reliable predictions.

[0007] The technical solution of this invention is: a method for identifying strike-slip faults through seismic profile displacement curves, comprising the following steps:

[0008] S1. Based on the seismic data and seismic interpretation of the target block, obtain fault profile interpretation;

[0009] S2. Based on fault profile interpretation, select seismic profiles with significant fault characteristics, measure the vertical fault displacement, and calculate the fault displacement variation rate based on the vertical fault displacement: Hc=(H i -H0) / H i-1 In the formula, Hc is the rate of change of the dislocation, H i H0 is the vertical displacement of segment i, and H0 is the displacement of the reference plane.

[0010] S3. Draw a fault displacement profile based on the vertical fault displacement, draw a fault displacement change rate profile based on the fault displacement change rate, and determine the strike-slip fault based on the fault displacement profile and the fault displacement change rate profile: If the fault displacement and the fault displacement change rate show frequent wavy changes on the same profile, and / or the downward fault displacement value decreases and the downward fault displacement change rate is negative, then the fault is determined to be a strike-slip fault.

[0011] Beneficial effects:

[0012] (1) A fault displacement / fault displacement change rate curve model for identifying strike-slip faults was established, which enabled direct identification of strike-slip faults through seismic profiles. The method is simple and easy to implement.

[0013] (2) This invention overcomes the problem of lacking a unified standard to distinguish between strike-slip faults and normal / reverse faults, and proposes an intuitive identification chart with qualitative and semi-quantitative characteristics, making the prediction results more reliable.

[0014] (3) This invention is applicable to identifying strike-slip faults in sedimentary basins through seismic profiles, and can also be applied to identifying strike-slip faults in outcrop geological profiles. Attached Figure Description

[0015] Figure 1 Examples of fault displacement profiles and fault displacement rate profiles for different types of faults;

[0016] Figure 2 Examples of seismic profiles, displacement profiles, and displacement rate profiles traversing strike-slip faults. Detailed Implementation

[0017] The specific embodiments of the present invention will be clearly and completely described below with reference to examples. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments.

[0018] A method for identifying strike-slip faults using seismic profile displacement curves includes the following steps:

[0019] S1. Based on the seismic data and seismic interpretation of the target block, obtain fault profile interpretation;

[0020] In this step, seismic data can be interpreted using conventional seismic interpretation software to obtain fault profile interpretation. Seismic interpretation software includes Geoscan and Seismic Unix, both of which can be used in this embodiment. Before seismic interpretation, the corresponding seismic data (SEGY format, pixel density ≥25m×25m, frequency band between 10-80Hz) and drilling data (including well trajectory coordinates, VSP logging, and stratigraphic data) need to be input; these are conventional data in this field.

[0021] The main operations in this step are as follows:

[0022] Loading seismic data into the seismic interpretation software; this data includes the seismic data and drilling data mentioned above, which is standard practice in this field.

[0023] Stratigraphic calibration is carried out to determine the strata that need to be interpreted and to perform stratigraphic interpretation. In this step, seismic profiles with high seismic resolution and significant stratigraphic and fault response characteristics are selected for stratigraphic calibration, which is a routine operation in this field.

[0024] Based on stratigraphic interpretation, fault analysis and fault profile interpretation are conducted. First, seismic attributes reflecting faults are analyzed, and seismic attributes reflecting fault distribution (coherence attributes or likelihood attributes) are extracted to obtain the planar distribution of faults. Second, seismic profiles perpendicular to the main fault are selected, and fault profile characteristics are analyzed to carry out fault profile interpretation.

[0025] S2. Based on fault profile interpretation, select seismic profiles with significant fault characteristics, measure the vertical fault displacement, and calculate the fault displacement variation rate based on the vertical fault displacement: Hc=(H i -H0) / H i-1 In the formula, Hc is the rate of change of fault displacement, Hi is the vertical fault displacement of segment i, and H0 is the fault displacement of the reference plane.

[0026] In this step, the characteristic of a seismic profile with significant fault features is obvious faulting of the seismic phase axis. Since it is necessary to measure the vertical fault displacement in this embodiment, the selected fault is a vertical fault zone.

[0027] When measuring vertical fault displacement, it can be detected based on the fault obtained above. However, in actual production, the fault situation is more complex. Therefore, the measurement method of vertical fault displacement is also different. The measurement methods of vertical fault displacement under different conditions are given below.

[0028] In sections with small fault displacement and unclear fault surfaces, the vertical structural elevation difference is used as the vertical fault displacement. In depth-migrated seismic profiles, the vertical fault displacement is measured directly. In time-seismic profiles, when velocity data is available, it is converted into vertical fault displacement; when the velocity is uncertain, the vertical fault displacement is calculated using time-depth. Vertical fault displacement measurements are intensified in strata with significant variations in vertical fault displacement. "Significant variations" here refers to faults with a fault displacement variation rate greater than 5%. Of course, those skilled in the art can choose different indicators based on the actual situation. Simultaneously, for stratigraphic positions, the stratigraphic sequence is selected from top to bottom.

[0029] After obtaining the vertical displacement, it is also necessary to calculate the displacement change rate. In this step, the displacement change rate refers to the change in the vertical displacement of this layer relative to the vertical displacement of the previous layer: Hc = (H i -H0) / H i-1 When selecting a reference plane, a segment of the same fault with a relatively stable fault displacement on different cross sections is usually chosen as the reference plane for that vertical fault displacement. When there are multiple relatively stable segments, the uppermost segment is preferred as the reference plane. In actual calculations, segment i and segment i-1 are segments below the reference plane, and segment i-1 is located above segment i and the two are adjacent.

[0030] The fault displacement variation rate can reflect the variation characteristics of fault displacement on a seismic profile, avoiding comparison problems caused by large measurement errors of the absolute value of fault displacement on different profiles or large differences between different profiles and different layers. At the same time, if the fault displacement on the seismic profile is small, the fault is not significant, or the strata near the fault have large flexural deformation, resulting in low accuracy of absolute fault displacement measurement, the fault displacement variation rate can highlight the change in fault displacement and reduce comparison and identification errors.

[0031] S3. Draw a fault displacement profile based on the vertical fault displacement, draw a fault displacement change rate profile based on the fault displacement change rate, and determine the strike-slip fault based on the fault displacement profile and the fault displacement change rate profile: If the fault displacement and the fault displacement change rate show frequent wavy changes on the same profile, and / or the downward fault displacement value decreases and the downward fault displacement change rate is negative, then the fault is determined to be a strike-slip fault.

[0032] When drawing fault displacement profiles, the vertical fault displacement data for each profile are first collected. Then, fault displacement profiles of the same profile at different horizons and fault displacement profiles of different profiles at the same horizon are drawn. During the drawing process, horizons represented by axes with weaker seismic axes are deleted.

[0033] When drawing a profile of the rate of change of fault displacement, the main focus is on drawing curves of the rate of change of fault displacement at different strata for the same profile.

[0034] After obtaining the fault displacement profile and the fault displacement rate profile, strike-slip faults can be identified, as well as other types of faults, such as normal / reverse faults.

[0035] The final fault displacement profiles and fault displacement rate profiles obtained at different strata of the same section can be used as a reference. Figure 1 and Figure 2 .

[0036] The method for determining strike-slip faults is as follows:

[0037] On the one hand, since the horizontal and diagonal movements of strike-slip faults are often not uniform, in the part of a large torsional fault, the fault displacement and the rate of change of fault displacement on the same cross section show frequent wavy changes. This is a characteristic of strike-slip faults that are different from normal / reverse faults. Therefore, it can be determined that the fault is a strike-slip fault.

[0038] On the other hand, similar to the downward increasing displacement curves of normal and reverse faults, when strike-slip faults develop positive and negative flower-like structures upwards, their displacement may gradually decrease downwards, or even disappear into the main fault. Therefore, if the downward displacement value decreases and the downward displacement change rate is negative, then the fault is judged to be a strike-slip fault.

[0039] In practice, only one condition needs to be met to determine if it is a strike-slip fault, and the reliability is higher when both conditions are met.

[0040] As mentioned above, normal / reverse faults can be judged based on the above-mentioned fault displacement profile and fault displacement rate of change profile. The judgment criteria are as follows: Normal / reverse faults that are active in the late stage usually show the same fault displacement or fault displacement rate above and below, and appear as a straight line on the fault displacement and fault displacement rate of change profile.

[0041] Of course, in the actual production process, we also need to verify and check the above data to prevent data errors from causing errors in the judgment results. However, this is a routine operation in this field, so the specific process will not be described in detail.

[0042] After identifying the strike-slip fault, by referring to the fault displacement profiles at the same level in different sections, we can obtain the distribution of the strike-slip fault on the profile and its extension in the plane. Combined with the interpretation of seismic profiles, we can analyze the segmentation and structural style of the strike-slip fault corresponding to different profile patterns, thereby guiding the detailed interpretation and structural analysis of the strike-slip fault.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for identifying strike-slip faults using seismic profile displacement curves, characterized in that, Includes the following steps: S1. Based on the seismic data and seismic interpretation of the target block, obtain fault profile interpretation; S2. Based on fault profile interpretation, select seismic profiles with significant fault characteristics, measure the vertical fault displacement, and calculate the fault displacement variation rate based on the vertical fault displacement: Hc = (H i -H0) / H i-1 In the formula, Hc is the rate of change of the dislocation, H i Let H0 be the vertical fault displacement of segment i, and H0 be the fault displacement of the reference plane. The measurement method of the vertical fault displacement is as follows: In sections with small fault displacement and unclear cross-sections, the vertical structural elevation difference is used as the vertical fault displacement; in depth-shifted seismic profiles, the vertical fault displacement is directly measured; in time-seismic profiles, when velocity data is available, the velocity data is converted into vertical fault displacement, and when the velocity is uncertain, the vertical fault displacement is calculated using time-depth; vertical fault displacement measurement is densified in strata with large variations in vertical fault displacement. S3. Draw a fault displacement profile based on the vertical fault displacement, draw a fault displacement change rate profile based on the fault displacement change rate, and determine the strike-slip fault based on the fault displacement profile and the fault displacement change rate profile: If the fault displacement and the fault displacement change rate show frequent wavy changes on the same profile, and / or the downward fault displacement value decreases and the downward fault displacement change rate is negative, then the fault is determined to be a strike-slip fault.

2. The method according to claim 1, characterized in that, In S1, seismic interpretation of the target block is performed based on the seismic data and seismic interpretation software of the target block.

3. The method according to claim 1 or 2, characterized in that, The methods for obtaining stratigraphic interpretation and fault profile interpretation include the following steps: Load earthquake data into earthquake interpretation software; Conduct stratigraphic calibration to determine the stratigraphic levels that need to be interpreted and perform stratigraphic interpretation; Based on stratigraphic interpretation, fault analysis and fault profile interpretation are performed.

4. The method according to claim 1, characterized in that, In S3, the fault displacement profile includes fault displacement profiles between different layers of the same profile and fault displacement profiles of different profiles at the same layer.

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