An interpretation method based on low signal-to-noise ratio and high-density marine seismic data

Abstract

The invention discloses an interpretation method based on low signal-to-noise ratio high-density seismic data. The method collects as much high-density seismic data as possible and processes the data in a unified format. Then, the closure errors between survey lines are eliminated to achieve full-area seabed closure. The target layer is divided into a reliable segment, a pending segment and an unreliable segment. The reliable segment, the pending segment and the unreliable segment are divided according to the signal-to-noise ratio of the target layer and the reliability of the interpretation result. The target layer has a high signal-to-noise ratio and a high reliability of the interpretation result. Then, according to the reliability of the interpretation result and relying on the intersection closure principle, the three segments are interpreted in sequence, and the pending segment and the unreliable segment are upgraded to the reliable segment. The scheme combines high-density data for seismic interpretation, realizes the maximum utilization of seismic profiles with low signal-to-noise ratio, achieves the purpose of fully tapping the maximum potential of existing "abandoned data", gives full play to the value of seismic profile data, and provides new ideas for marine seismic interpretation.

Description

Technical Field

[0001] The invention belongs to the field of marine seismic data interpretation, and in particular relates to an interpretation method based on low signal-to-noise ratio and high-density marine seismic data. Background Art

[0002] Seismic interpretation generally refers to structural interpretation, which mainly determines the outline and structural characteristics of the geological body. Traditional marine seismic data interpretation requires seismic profiles with a high signal-to-noise ratio. If the overall signal-to-noise ratio of the seismic profile is low, according to quality control standards, it is often necessary to discard this part of the seismic profile during interpretation to avoid misleading the overall interpretation.

[0003] In fact, any seismic profile is obtained after seismic acquisition and seismic data processing. The initial investment is huge, and abandoning its use is a huge waste. In addition, although the abandoned seismic profiles have a low signal-to-noise ratio as a whole, there are some areas with relatively high signal-to-noise ratios. Therefore, how to effectively utilize the so-called abandoned seismic profiles is of great significance. Summary of the invention

[0004] In order to solve the defect of discarding seismic data with low signal-to-noise ratio in traditional marine seismic data interpretation, the present invention proposes an interpretation method based on low signal-to-noise ratio and high-density marine seismic data, aiming to fully explore the value of abandoned seismic profiles, ensure the seismic interpretation effect and make full and effective use of them, so as to achieve the purpose of seismic data interpretation.

[0005] The present invention is implemented by adopting the following technical solution: an interpretation method based on low signal-to-noise ratio high-density marine seismic data, comprising the following steps:

[0006] Step A, high-density seismic data input: collect high-density seismic data and process them in a unified format, including unification of seismic data appearance and coordinates;

[0007] Step B: Eliminate the closure difference between the survey lines and achieve closure of the seabed in the entire area;

[0008] Step C, the first round of interpretation of the target layer: the target layer is divided into reliable segments, pending segments and unreliable segments to achieve a preliminary division of the entire area, and the interpretation of the reliable segments and the preliminary interpretation of the pending segments are completed based on the intersection closure principle;

[0009] The reliable segment, pending segment and unreliable segment are divided according to the signal-to-noise ratio of the target layer and the reliability of the interpretation result. The layer segment with high signal-to-noise ratio and high reliability of the interpretation result is the reliable segment, and the signal-to-noise ratio and reliability of the pending segment and unreliable segment decrease in turn.

[0010] Step D, second round of interpretation of target layer: further interpret the undetermined segment based on the intersection closure principle and upgrade the undetermined segment to a reliable segment;

[0011] Step E, the third round of interpretation of the target layer: interpret the unreliable segment based on the intersection closure principle, connect the reliable segment control points on the unreliable segment survey line to complete the interpretation purpose. The reliable segment control point mentioned here is the intersection point of the unreliable segment survey line and the reliable segment.

[0012] Furthermore, the step D is specifically implemented in the following manner:

[0013] Step (1) first find the undetermined segment that intersects with multiple reliable segment survey lines. At this time, the undetermined segment has multiple reliable segment intersection points to determine the direction of the target layer, and then compare it with the interpretation result of the undetermined segment in the first round of interpretation, and comprehensively judge and upgrade the undetermined segment to a reliable segment;

[0014] Step (2) is to first interpret the undetermined segment with more reliable segment control points and then interpret the undetermined segment with fewer reliable segment control points, and process the undetermined segments at other locations according to the scheme of step (1); here, the reliable segment control point refers to the intersection of the reliable segment survey line and the undetermined segment;

[0015] Step (3) As more and more pending segments are upgraded to reliable segments, the number of control points in the reliable segments continues to increase, and the interpretation of the pending segments becomes more reliable, completing the second round of interpretation of the target layer.

[0016] Furthermore, in step B, the seabed time of all survey lines is first picked up, and the closure error is determined according to the difference in seabed time at the intersection of the survey lines; then, the goal of eliminating the closure error is achieved by adjusting the seabed time difference of all survey lines in the entire area, thereby achieving the purpose of seabed closure in the entire area.

[0017] Furthermore, in step A, the unification of seismic data appearance is achieved through automatic gain control, and the unification of seismic data coordinates is achieved through the unification of projection parameters.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are:

[0019] This plan creatively proposes to use low signal-to-noise ratio seismic data combined with high-density data for seismic interpretation. As long as there are some seismic profiles with high signal-to-noise ratio, they are worth using even if their proportion is low. This can maximize the use of low signal-to-noise ratio seismic profiles, fully tap the potential of existing "waste data", give full play to the value of seismic profile data, and provide new ideas for marine seismic interpretation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1Schematic diagram of comparison between traditional seismic interpretation and high-density seismic data interpretation according to an embodiment of the present invention, left: traditional seismic interpretation; middle: low-density seismic interpretation; right: high-density seismic interpretation;

[0021] Among them, the thick line represents the part with high signal-to-noise ratio, and the thin line represents the part with low signal-to-noise ratio;

[0022] Figure 2 A schematic diagram of a flow chart of a seismic interpretation method according to an embodiment of the present invention;

[0023] Figure 3 A schematic diagram of a typical seismic profile of the Bohai Sea Cross-Sea Channel Project according to an embodiment of the present invention;

[0024] Figure 4 This is a quality control chart of high-density data interpretation according to an embodiment of the present invention; left: after the first round of interpretation; middle: after the interpretation of the pending segment; right: after the interpretation of the unreliable segment;

[0025] Among them, the black line is a reliable segment, the gray line is a pending segment, and the thin line is an unreliable segment;

[0026] Figure 5 This is a schematic diagram of the interpretation results of extremely low signal-to-noise ratio survey lines after high-density interpretation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Introduction to basic principles:

[0029] Marine seismic data contains noise and is also affected by the seismic acquisition technology and processing process. It is difficult for seismic profiles to meet the interpretation requirements 100%, that is, the so-called event axes are very clear on the entire seismic profile and can be continuously tracked in the horizontal direction. Generally, there will be some areas with low signal-to-noise ratios. For example, the underground strata in shallow gas development areas will be relatively fuzzy, and the imaging quality in complex structural areas will also be poor. Based on the actual situation of the seismic data interpretation process, seismic profiles can be divided into areas with high signal-to-noise ratios and areas with low signal-to-noise ratios. Areas with high signal-to-noise ratios indicate that the event axes are clear and can be continuously tracked in the horizontal direction during the seismic interpretation of this section of the survey line, that is, the certainty of the interpretation is strong. Areas with low signal-to-noise ratios indicate that the event axes are unclear and difficult to track continuously in the horizontal direction, and are basically impossible to interpret.

[0030] In traditional seismic interpretation, the seismic profile has a large proportion of areas with high signal-to-noise ratio, such as Figure 1 As shown in the left figure, Figure 1Although the signal-to-noise ratio in the middle circle area is low, it can be interpolated through the interpretation results at both ends of the circle area. In this case, the interpolation result is generally accepted. However, when the proportion of areas with high signal-to-noise ratio is low, for example Figure 1 In the circled area in the middle figure, if the interpretation results at both ends are used to control the strata, the interpretation results will be difficult to be recognized. However, as the density of seismic sections increases, the proportion of areas with high signal-to-noise ratio also increases. Figure 1 In the circled area on the right, the area with high signal-to-noise ratio accounts for a high proportion, which meets the requirements of seismic interpretation. The result of seismic interpretation at this time is also relatively reliable. Although the area with high signal-to-noise ratio for a single survey line does not account for a high proportion, it can still meet the requirements of seismic interpretation through quantitative compensation. This is the basic principle of the low signal-to-noise ratio and high-density seismic data interpretation method described in the scheme of the present invention.

[0031] Specific as Figure 2 As shown, an interpretation method based on low signal-to-noise ratio high-density marine seismic data includes the following steps:

[0032] Step A, high-density seismic data input: collect high-density seismic data and process them in a unified format, including unification of seismic data appearance and coordinates;

[0033] Step B: Eliminate the closure difference between the survey lines and achieve seabed closure in the entire area:

[0034] First, the seabed time of all survey lines is picked up, and the closure error is determined based on the difference in seabed time at the intersection of the survey lines; then the goal of eliminating the closure error is achieved by adjusting the seabed time difference of all survey lines in the entire area, thereby achieving the purpose of seabed closure in the entire area.

[0035] Step C, the first round of interpretation of the target layer: the target layer is divided into reliable segments, pending segments and unreliable segments to achieve the preliminary division of the entire area, complete the interpretation of the reliable segments and the preliminary interpretation of the pending segments, and generate the first round of interpretation quality control map for the entire area:

[0036] The reliable section refers to a section where the target layer has a high signal-to-noise ratio and a reliable interpretation result;

[0037] The undetermined section refers to a section where the signal-to-noise ratio of the target layer is slightly low and the interpretation result is uncertain;

[0038] The unreliable section refers to a section where the signal-to-noise ratio of the target layer is extremely low and the interpretation result is completely uncertain;

[0039] Step D, second round of interpretation of target layer: further interpret the undetermined segment based on the intersection closure principle and upgrade the undetermined segment to a reliable segment;

[0040] Step E, the third round of interpretation of the target layer: interpret the unreliable segment based on the intersection closure principle, and complete the interpretation purpose by connecting the reliable segment control points on the unreliable segment survey line. The reliable segment control point mentioned here is the intersection point of the unreliable segment survey line and the reliable segment.

[0041] In step A, the collected high-density seismic data is input. The basis of the present invention is high-density seismic data, so the more seismic data, the better. Generally speaking, the collected seismic data may be based on different units, different acquisition equipment, and different acquisition times. Therefore, it is necessary to organize the different seismic data in a unified format, mainly including the unification of the seismic data appearance and the unification of coordinates:

[0042] (1) Unification of seismic data appearance: This is achieved through automatic gain control in data processing. Common gain factors are 100ms, 200ms, 400ms, etc. The specific gain factor is determined according to the characteristics of the seismic profile during data processing. However, for seismic data in the same work area, consistent parameters are required. Unification of seismic data appearance through automatic gain control is a relatively mature technical means, which will not be elaborated in detail here.

[0043] (2) Unification of seismic data coordinates: Coordinate unification mainly involves the unification of projection parameters. Commonly used projections include Mercator projection, UTM projection, TM projection, etc. If different seismic data use different projection systems, they need to be unified into the same projection system. There are relatively mature conversion modules for the transformation between different projections. The specific operation can select the corresponding conversion module according to actual needs. After projection, it mainly involves the setting of X coordinates and Y coordinates. Generally, the X coordinate is set at 77 bytes of SEGY data and the Y coordinate is set at 81 bytes of SEGY data.

[0044] In step B, when closing the seabed in the whole area, due to different equipment, different acquisition conditions, and seismic data from different ages, there must be large closure errors between the survey lines. If this closure error is not eliminated, it will cause major problems in the later interpretation. Therefore, for high-density seismic data, closure error elimination is extremely important. Based on the characteristics of marine seismic data, the seabed is generally continuous and well-imaged, so the closure error can generally be corrected through the seabed.

[0045] In step C, the entire area is initially divided into reliable segments, pending segments and unreliable segments.

[0046] The interpretation of the target layer is generally determined by technical indicators such as overlap, underlap, truncation, and overlap, which is consistent with the traditional seismic interpretation method. This solution uses the technology consistent with the traditional interpretation when performing seismic interpretation, which will not be described in detail here. The difference from the traditional interpretation method is mainly that the target layer is divided into a reliable segment, a pending segment, and an unreliable segment according to the concept of the present invention, and then the three segments are interpreted in turn according to the reliability of the interpretation results, realizing the processing idea of ​​upgrading the pending segment and the unreliable segment to the reliable segment. When interpreting, the reliable segment is a thick line, the pending segment is a thin line, and the unreliable segment is not interpreted.

[0047] The reliable section refers to a section with a high signal-to-noise ratio of the target layer and reliable interpretation results, that is, a section whose interpretation results will hardly be adjusted in the later stage, and is the focus of the first round of interpretation.

[0048] The pending section refers to the target layer with a slightly lower signal-to-noise ratio, and the interpretation result has a certain uncertainty. The interpretation result may be adjusted in the later interpretation.

[0049] The unreliable segment refers to a target layer with an extremely low signal-to-noise ratio, and the interpretation result is completely uncertain, and finally the interpretation of the unreliable segment is performed.

[0050] After the first round of interpretation, the first round of interpretation quality control map for the whole area is generated, which is also an important basis for the evaluation of the later seismic interpretation results. The definition of the reliable segment should be particularly cautious, because it is related to the interpretation of the subsequent pending segment and unreliable segment. If there is a problem with the interpretation of the reliable segment, it will have a huge impact on the later interpretation, and often requires the entire area to be revised. Therefore, this problem should be avoided as much as possible. In specific implementation, the reliable segment should be determined based on the actual situation.

[0051] In step D, the second round of interpretation of the target layer is mainly to determine the undetermined section, which is also the difficulty and focus of the interpretation. The main interpretation steps are as follows:

[0052] First, find the pending section that intersects with multiple reliable section survey lines. Since the pending section has multiple reliable section intersections at this time, its interpretation result is more reliable, which is equivalent to having more confirmed control points on the pending section. In this way, the direction of the target layer can generally be basically determined. Then, compared with the preliminary interpretation result of the pending section, the pending section can be upgraded to a reliable section through comprehensive judgment.

[0053] The method for determining the pending segments at other locations is similar to this, and its basic principle is: first interpret the pending segments with more reliable segment control points, and then interpret the pending segments with fewer reliable segment control points; first interpret the pending segments with relatively high signal-to-noise ratios, and then interpret the pending segments with relatively low signal-to-noise ratios. Here, the reliable segment control point refers to the intersection of the reliable segment survey line and the pending segment.

[0054] As more and more pending segments are upgraded to reliable segments, the number of control points of the reliable segments continues to increase, which will further strengthen the basis for interpretation of other unexplained pending segments, thus facilitating the interpretation of the remaining pending segments.

[0055] In step E, the third round of interpretation of the target layer is mainly to solve the unreliable segment. Since the signal-to-noise ratio of the unreliable segment is too poor and there is too little effective judgment information, it cannot participate in the early seismic interpretation. It is often completed by connecting the reliable segment control points on the unreliable segment line at the end. The unreliable segment is mainly judged comprehensively based on the large stratigraphic trend in the region. Due to the high density of seismic lines, this means that the stratigraphic trend of the unreliable segment is similar to that of the adjacent lines, which can basically ensure that there will be no principled problems in the interpretation.

[0056] In this embodiment, reliable segments, pending segments and unreliable segments are all relative concepts, and are only relatively high in probability, but it is difficult to reach 100%. This means that large local closure errors may occur during the interpretation process. This is often because the reliable segments are incorrectly defined. At this time, it is necessary to re-check and re-judge and correct the reliable segments based on local formation trends, survey line closure, etc., and correct local problems.

[0057] The following is a detailed description of the method of the present invention using the Bohai Sea Cross-Sea Channel Interpretation Project as an example:

[0058] The Bohai Cross-sea Channel Project is mainly to conduct preliminary feasibility analysis for the construction of an undersea tunnel across the Bohai Strait, and seismic exploration is the most important work in the early stage. The project was initiated in 1992. During the nearly 30 years of preliminary research, more than 10,000 kilometers of high-resolution seismic data have been accumulated, which provides a good data foundation for high-density seismic interpretation. However, due to factors such as instruments and acquisition methods, most seismic data have low signal-to-noise ratios. Figure 3 As shown in the figure, taking the basement of the region as an example, according to the traditional interpretation point of view, the overall signal-to-noise ratio of the seismic profile is too low, which is basically an unqualified profile and cannot be used in seismic interpretation. However, according to the definition of the present invention, the black arrow points to a reliable section, which has a high signal-to-noise ratio and a reliable interpretation result. The basement strata in the box are relatively fuzzy, but can still be vaguely distinguished, which is a pending section. The basement strata in the circle are basically invisible and are unreliable sections.

[0059] The first round of interpretation is conducted for all the seismic survey lines in the area. Unreliable sections do not need to be interpreted. After the interpretation of the entire area is completed, the first round of interpretation quality control chart is generated. Figure 4 As shown in the left figure, the black line is the reliable segment, corresponding to Figure 3 The arrow points to the part; the gray line is the undetermined segment, corresponding to Figure 3 The thin line in the box is an unreliable segment, corresponding to Figure 3 The inner part of the circle.

[0060] After the first round of interpretation, the reliable sections of the survey lines are relatively fragmented. If the density of the survey lines is too low, it will be difficult to complete the closed interpretation of the entire area. Thanks to the high-density seismic survey lines, even if the proportion of reliable sections of the survey lines is not high, the defects can be compensated by the advantage of quantity. The second round of interpretation is mainly to determine the undetermined sections. The reliability of the undetermined sections is relatively high, that is, the relevant phase axes can generally be roughly distinguished on the seismic profile. However, due to the low signal-to-noise ratio, the interpretation has a certain degree of multi-solution. The undetermined sections of the main survey line can determine the stratigraphic direction through the control points of multiple intersecting survey lines with the connecting survey lines, and then realize the upgrade from the undetermined sections to the reliable sections. Figure 4 As shown in the middle figure, it can be seen that the proportion of reliable sections in the work area has greatly increased after the second round of interpretation. The third round of interpretation is mainly to determine the unreliable sections. After the second round of interpretation, the proportion of reliable sections in the entire work area is already relatively high. Most unreliable sections can roughly outline the stratigraphic direction only by relying on the control points of the reliable sections. Therefore, after the third round of interpretation is completed, the reliable sections can almost cover the entire work area ( Figure 4 Right figure), only in some areas with low survey line density, especially at the edge of the map, the direction of the strata cannot be determined.

[0061] After the interpretation by the method of the present invention, almost all the survey lines can be closed well. Figure 5 This is one of the typical sections with the lowest signal-to-noise ratio in this work area, and the basement is only vaguely displayed in a few places ( Figure 5 After being interpreted by this method, the overall basement trend is consistent with the actual situation, achieving the goal of effectively utilizing abandoned seismic profiles.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An interpretation method based on low signal-to-noise ratio high-density marine seismic data, characterized in that: The following steps are involved: Step A, high-density seismic data input: collect high-density seismic data and process them in a unified format, including unification of seismic data appearance and coordinates; Step B: Eliminate the closure difference between the survey lines and achieve the closure of the seabed in the whole area; Step C, the first round of interpretation of the target layer: the target layer is divided into reliable segments, pending segments and unreliable segments to achieve a preliminary division of the entire area, and the interpretation of the reliable segments and the preliminary interpretation of the pending segments are completed based on the intersection closure principle; The reliable segment, pending segment and unreliable segment are divided according to the signal-to-noise ratio of the target layer and the reliability of the interpretation result. The layer segment with high signal-to-noise ratio and high reliability of the interpretation result is the reliable segment, and the signal-to-noise ratio and reliability of the pending segment and unreliable segment decrease in turn. Step D, second round of interpretation of target layer: further interpret the undetermined segment based on the intersection closure principle and upgrade the undetermined segment to a reliable segment; Step E, the third round of interpretation of the target layer: interpret the unreliable segment based on the intersection closure principle, connect the reliable segment control points on the unreliable segment survey line to complete the interpretation purpose.

2. The interpretation method based on low signal-to-noise ratio high-density marine seismic data according to claim 1, characterized in that: The step D is specifically implemented in the following manner: Step (1) first find the undetermined segment that intersects with multiple reliable segment survey lines. At this time, the undetermined segment has multiple reliable segment intersection points to determine the direction of the target layer, and then compare it with the preliminary interpretation result of the undetermined segment, and comprehensively judge and upgrade the undetermined segment to a reliable segment; Step (2) is to first interpret the undetermined segments with more reliable segment control points and then interpret the undetermined segments with fewer reliable segment control points, and process the undetermined segments at other locations according to the solution of step (1); Step (3) As more and more pending segments are upgraded to reliable segments, the number of control points in the reliable segments continues to increase, and the interpretation of the pending segments becomes more reliable, completing the second round of interpretation of the target layer.

3. The interpretation method based on low signal-to-noise ratio high-density marine seismic data according to claim 1, characterized in that: In step B, the seabed time of all survey lines is first picked up, and the closure error is determined according to the difference of the seabed time at the intersection of the survey lines; then, the seabed time difference of all survey lines in the whole area is adjusted to achieve the goal of eliminating the closure error, thereby achieving the purpose of closing the seabed in the whole area.

4. The interpretation method based on low signal-to-noise ratio high-density marine seismic data according to claim 1, characterized in that: In the step A, the unification of seismic data appearance is achieved through automatic gain control, and the unification of seismic data coordinates is achieved through the unification of projection parameters.

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