Method for determining reservoir top and base using seismic attributes

Abstract

The application provides a method for determining reservoir top and bottom surfaces by using seismic attributes, which comprises the following steps: step 1, selecting wave peaks and extracting selected wave peak and upper and lower wave valley attributes; step 2, meshing three attribute data; step 3, calculating the attribute difference between the upper wave valley and the wave peak, and calculating the standard deviation c1 of the attribute difference scatter point sample; step 4, calculating the attribute difference between the lower wave valley and the wave peak, and calculating the standard deviation c2 of the attribute difference scatter point sample; and step 5, comparing the results of the two standard deviations to determine the top surface and the bottom surface of the reservoir. The method for determining reservoir top and bottom surfaces by using seismic attributes can quickly identify the reservoir top and bottom surfaces on the seismic, can guide well-seismic calibration, can help the reservoir to quickly establish a relationship with the seismic, and can further guide reservoir description, development and the like.

Description

Technical Field

[0001] This invention relates to the field of seismic prediction technology for sandstone and mudstone fluvial reservoirs, and in particular to a method for determining the top and bottom surfaces of reservoirs using seismic properties. Background Technology

[0002] Sandstone and mudstone reservoirs in sedimentary rocks are the most abundant reservoirs for oil and gas discovery. Seismic data is the basic data for predicting and describing sandstone and mudstone reservoirs. Identifying the top and bottom of the reservoir in seismic data is the most important foundational work for conducting further research.

[0003] In seismic data, when the thickness of a sandstone reservoir is between one-quarter and one-half of the wavelength, and the upper and lower mudstone layers are relatively thick, the top and bottom surfaces of this sandstone reservoir correspond to adjacent wave crests (valleys) and wave troughs (peaks), respectively. In positive polarity seismic data, when the wave impedance of the sandstone reservoir is less than that of the mudstone, the top of the sandstone corresponds to a wave trough, and the bottom to a wave crest; when the wave impedance of the sandstone reservoir is greater than that of the mudstone, the top of the sandstone corresponds to a wave crest, and the bottom to a wave trough. In negative polarity seismic data, when the wave impedance of the sandstone reservoir is less than that of the mudstone, the top of the sandstone corresponds to a wave crest, and the bottom to a wave trough; when the wave impedance of the sandstone reservoir is greater than that of the mudstone, the top of the sandstone corresponds to a wave trough, and the bottom to a wave crest.

[0004] To conduct the above analysis and establish the correspondence between the reservoir top and bottom and the peaks and troughs of the seismic axis, the usual practice involves studying the burial depth of the target layer, statistically analyzing the wave impedance relationship between sandstone and mudstone reservoirs in the corresponding sections, and making predictions for the study area by referring to the reservoir-seismic correspondence of similar sections in nearby blocks. It also requires confirming the polarity of the seismic data with the providing unit, performing detailed synthetic seismic record calibration for each well, and so on. Only when all the conclusions are consistent can the final determination be made. This involves many concepts, is prone to errors, and any error can affect the entire analysis.

[0005] Studies of numerous fluvial reservoirs have revealed that when a set of sandstone reservoirs corresponds to a set of adjacent crests and troughs, regardless of whether the sandstone has high or low impedance relative to mudstone, whether the seismic data is of normal or reverse polarity, or whether the top of the sandstone or sandstone group corresponds to a trough or a crest, the crest (trough) amplitude of the seismic wave corresponding to the sandstone crest is strong, and the trough (crest) amplitude corresponding to the sandstone bottom is also strong; conversely, the crest (trough) amplitude of the seismic wave corresponding to the sandstone crest is weak, and the trough (crest) amplitude of the seismic wave corresponding to the sandstone bottom is also weak. Therefore, extracting the top and bottom amplitude attributes of a set of sandstone bodies from seismic data should yield similar results. However, if adjacent crests and troughs are not the top and bottom of a set of sandstone bodies, the results of their amplitude-type seismic attributes will differ.

[0006] Chinese patent application CN202110886389.4 discloses a method for identifying the bottom interface of weathered crust reservoirs based on mathematical statistics. The method includes the following steps: S1, constructing a rock physics model based on well data; S2, determining the relationship between granite weathered crust reservoirs of different thicknesses and seismic response; S3, determining the paleogeography of granite buried hills using the impression method, selecting different exposure time points on the paleogeographic map, statistically analyzing the relative time difference between the top and bottom interfaces of the weathered crust reservoirs at different exposure time points on the seismic profile, and performing multi-point fitting analysis based on forward modeling to obtain the corresponding quantitative relationship; S4, obtaining the calibration results of the bottom interface of weathered crust reservoirs across the entire region, as well as a quantitative result map of the time thickness of the weathered crust reservoirs, using the top interface of the weathered crust reservoirs in the entire region as input. This invention demonstrates excellent feasibility and reliability, providing a good approach and method for delineating the weathered crust of granite buried hills.

[0007] Chinese patent application CN201711459715.3 discloses a method and apparatus for reservoir determination. The method includes: acquiring seismic and well logging data of a target area; determining the stratigraphic position of a target layer based on the seismic and well logging data; performing waveform decomposition on the seismic data of the target layer to obtain multiple seismic component data; selecting seismic component data characterizing the reservoir from the multiple seismic component data based on reconstructed well logging curves; and determining the distribution characteristics of the reservoir in the target area based on the seismic component data characterizing the reservoir. This approach considers the waveform characteristics of reservoir reflections. By performing waveform decomposition on the seismic data to obtain multiple seismic component data, and selecting the seismic component data characterizing the reservoir from the multiple seismic component data based on the reservoir reflection characteristics using reconstructed well logging curves, the reservoir is then determined based on this seismic component data. Therefore, it solves the technical problems of inaccurate reservoir determination and large errors in existing methods.

[0008] Chinese patent application CN201910367837.2 discloses a method and system for classifying and determining fractured reservoirs in buried hill sections. By using well logging data and seismic data, seismic attribute data and top surface structural features related to the target reservoir characteristics are obtained. Combined with a classification neural network, the classification information of complex fractured reservoirs is accurately determined, thereby accurately knowing the classification of reservoirs in the entire area. This facilitates guidance for subsequent well location deployment and reservoir development, and has promotional significance.

[0009] The above-mentioned existing technologies are all quite different from the present invention and have failed to solve the technical problem we want to solve. Therefore, we have invented a new method for determining the top and bottom surfaces of reservoirs by applying seismic properties. Summary of the Invention

[0010] The purpose of this invention is to provide an application that can quickly identify the top and bottom surfaces of reservoirs in earthquakes, and a method for quickly determining the top and bottom surfaces of reservoirs through earthquake amplitude-type attributes.

[0011] The objective of this invention can be achieved through the following technical measures: a method for determining the top and bottom surfaces of a reservoir using seismic attributes, the method comprising:

[0012] Step 1: Select the peaks and extract the selected peaks and their upper and lower troughs, and extract their attributes respectively;

[0013] Step 2: Grid the three attribute data;

[0014] Step 3: Calculate the attribute difference between the trough and the peak, and calculate the standard deviation c1 of the attribute difference scatter sample.

[0015] Step 4: Calculate the attribute difference between the trough and the peak, and calculate the standard deviation c2 of the attribute difference scatter sample.

[0016] Step 5: Compare the results of the two standard deviations to determine the top and bottom surfaces of the reservoir.

[0017] The objective of this invention can also be achieved through the following technical measures:

[0018] The method for determining the top and bottom surfaces of a reservoir using seismic attributes also includes, before step 1, performing synthetic seismic record calibration, finding the time-depth range of the target layer on the seismic data, and selecting peaks within that range.

[0019] In step 1, a set of peak seismic axes is selected in the target seismic data segment, denoted as A, and its adjacent upper and lower valleys are denoted as B1 and B2, respectively.

[0020] In step 1, wave peaks are selected from the seismic profile passing through the well. Wave peaks with significant reflection amplitudes and similar to the locations of typical reservoirs above the well are selected for comparative analysis.

[0021] The method for determining the top and bottom surfaces of a reservoir using seismic attributes also includes, after step 1, performing axial tracing (structural interpretation) on the selected peaks and two troughs before extracting attributes. When opening a time window for extracting seismic attributes, it should be noted that if a time window is opened for a peak, the upper and lower time windows should not include the area above or below the highest amplitude value of the center of the adjacent upper and lower troughs, or any further range beyond that point. Similarly, when opening a time window for a trough, the time window range should not exceed the area below or below the highest amplitude value of the center of the adjacent peak.

[0022] In step 2, the root mean square amplitude attribute is extracted for the three axes A, B1, and B2 respectively, and the three attribute results are meshed with the same range and scatter distance.

[0023] In step 3, subtract the gridded upper trough from the gridded peak attributes to obtain the difference between the two attributes: C1 = B1 - A.

[0024] In step 3, take the C1 scatter values as a set of samples and calculate the standard deviation c1 of the samples.

[0025] In step 4, subtract the gridded lower trough from the gridded peak attributes to obtain the difference between the two attributes: C2 = B2 - A.

[0026] In step 4, take the C2 scatter values as a set of samples and calculate the standard deviation c2 of the samples.

[0027] In step 5, if c1 < c2, it means that the attribute results of the peak and the upper trough are more similar. For this set of data, the top of the sand body corresponds to the trough and the bottom of the sand corresponds to the peak.

[0028] In step 5, if c2 < c1, it means that the attributes of the peak and the lower trough are more similar. Then, for this set of data, the top of the sand corresponds to the peak and the bottom of the sand corresponds to the trough.

[0029] The method for determining the top and bottom surfaces of a reservoir using seismic attributes in the present invention has the advantage that it is fast and intuitive to identify the top and bottom surfaces of the reservoir in seismic data, and can quickly figure out whether the reservoir in the seismic data of a certain formation section in a certain area corresponds to a peak-trough pair or a trough-peak pair. In the development stage of an oil and gas field, especially during the design of horizontal wells, it is necessary to accurately determine the depth of the top surface of the reservoir. Therefore, higher requirements are put forward for accurately finding the top surface of the reservoir in seismic data. Quickly determining the top and bottom surfaces of the reservoir can guide well-seismic calibration, help quickly establish the relationship between the reservoir and the seismic data, and further guide reservoir description, development and other work.

[0030] While figuring out the top and bottom surfaces of the reservoir, it is also possible to combine velocity logging curves to determine the polarity of the seismic data. For example, sandstone corresponds to a low-velocity and high-acoustic wave curve. If it is determined by this method that the trough of the seismic data is the top of the sand and the peak is the bottom of the sand, it can be inferred that the seismic data has normal polarity, and vice versa for abnormal polarity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flowchart of a specific embodiment of the method for determining the top and bottom surfaces of a reservoir using seismic attributes of the present invention;

[0032] Figure 2 is an example diagram of the peak A and adjacent upper trough B1 and adjacent lower trough B2 selected in a specific embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the root mean square amplitude attribute result of the trough B1 in a specific embodiment of the present invention;

[0034] <00000This is a schematic diagram of the root mean square amplitude property result of trough B2 in a specific embodiment of the present invention.

[0035] Figure 5 This is a schematic diagram of the root mean square amplitude property of wave peak A in a specific embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram of the amplitude difference between trough B1 and peak A in a specific embodiment of the present invention.

[0037] Figure 7 This is a schematic diagram of the amplitude difference between trough B2 and peak A in a specific embodiment of the present invention.

[0038] Figure 8 This is a schematic diagram of the root mean square amplitude property result of the upper trough B1 in another specific embodiment of the present invention.

[0039] Figure 9 This is a schematic diagram of the root mean square amplitude property of wave peak A in another specific embodiment of the present invention;

[0040] Figure 10 This is a schematic diagram of the root mean square amplitude property of the lower trough B2 in another specific embodiment of the present invention;

[0041] Figure 11 This is a schematic diagram of the amplitude difference between the upper trough B1 and the peak A in another specific embodiment of the present invention;

[0042] Figure 12 This is a schematic diagram of the amplitude difference between the lower trough B2 and the peak A in another specific embodiment of the present invention. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] The method for determining the top and bottom surfaces of a reservoir using seismic attributes in the present invention introduces the concept of the standard deviation of attribute differences. When two amplitude attributes are similar, the absolute values of the amplitudes at the same position increase or decrease simultaneously in the two attributes. Subtracting these two attributes, the values at each point in the attribute difference are relatively small, that is, the values of all points are concentrated within a small range, and its standard deviation is small; conversely, when the two amplitude attributes differ greatly, the attribute differences are discrete and the standard deviation is large. Therefore, the similarity degree of the two attributes can be judged through the standard deviation of the attribute differences, and then the wave peak and wave trough pairs with more similar attributes can be found through the attribute combination with a smaller difference standard deviation, and the corresponding relationship between the sandstone top and bottom and the wave peak and wave trough can be directly deduced inversely.

[0046] As Figure 1 shown, Figure 1 is a flow chart of the method for determining the top and bottom surfaces of a reservoir using seismic attributes in the present invention. The method for determining the top and bottom surfaces of a reservoir using seismic attributes includes the following steps:

[0047] Step 1, select a set of wave peak seismic axes in the target layer segment of the seismic data, denoted as A, and denote the adjacent upper wave trough and the adjacent lower wave trough as B1 and B2 respectively;

[0048] Step 2, extract the root mean square amplitude attributes for the three axes of A, B1, and B2 respectively, and perform grid division with exactly the same range and scatter point distance for the three attribute results;

[0049] Step 3, subtract the gridded two wave trough attributes from the gridded wave peak attribute respectively to obtain the differences of the two attributes: C1 = B1 - A, C2 = B2 - A;

[0050] Step 4, take the two scatter point values of C1 and C2 as two groups of samples, and calculate the standard deviations c1 and c2 of the two groups of samples respectively;

[0051] Step 5, compare the results of the two standard deviations. If c1 < c2, it means that the attribute results of the wave peak and the upper wave trough are more similar. The top of the sand body in this set of data corresponds to the wave trough, and the bottom corresponds to the wave peak. If c2 < c1, it means that the attributes of the wave peak and the lower wave trough are more similar. Then the top of the sand in this set of data corresponds to the wave peak, and the bottom of the sand corresponds to the wave trough.

[0052] In one embodiment, before step 1, synthetic seismic record calibration is required to locate the time-depth range of the target layer in the seismic data, and peaks are selected within this range. In step 1, peaks can be selected "arbitrarily," but for better operational results, peaks are best selected from seismic profiles passing through the well, choosing peaks with significant reflection amplitudes and locations close to typical reservoirs on the well surface for comparative analysis. After step 1, the selected peaks and two troughs should be subjected to "axis tracing," i.e., structural interpretation, before attribute extraction. When opening time windows for seismic attribute extraction, it should be noted that if a time window is opened for a peak, the upper and lower time windows should not include the area above or below the highest amplitude value of the adjacent upper and lower troughs; similarly, when opening a time window for a trough, the time window range should not exceed the area below or below the highest amplitude value of the adjacent peak. This is to ensure that the attribute results reflect only one set of seismic axes, avoiding interference from other seismic axis information.

[0053] It should be noted that there are many types of seismic attributes, and the attributes mentioned in this invention refer to amplitude-type attributes. While the selection of a specific amplitude-type attribute is not limited, for certain attributes, the absolute value of the attribute should be used for calculation. Taking instantaneous amplitude as an example, when extracting instantaneous amplitude from wave crests, the range of wave crests that need to be highlighted should be concentrated in the high-positive-value region; when extracting instantaneous amplitude from wave troughs, the range of wave troughs that need to be highlighted should be concentrated in the low-negative-value region. Directly subtracting the attribute results of these wave crests and troughs will produce the opposite effect: the standard deviation of the attribute difference reflecting the same set of sandstone will be larger. However, selecting attributes such as root mean square amplitude and absolute amplitude value avoids this problem.

[0054] The following are several specific embodiments of the application of the present invention.

[0055] Example 1

[0056] In a specific embodiment 1 of the present invention, the present invention is applied. Figure 2 To select the peaks and adjacent upper and lower troughs of the target layer; Figure 3-5 The root mean square amplitude attributes of the upper trough, peak, and lower trough are respectively identified. These three attributes are then gridded within a unified range using a grid spacing of 50 meters × 50 meters. The attribute difference is obtained by subtracting the root mean square amplitude of the upper trough from that of the peak, and represented by a contour map, as shown below. Figure 6 The attribute difference is obtained by subtracting the root mean square amplitude of the lower trough and the peak after meshing, and represented by a contour map, such as... Figure 7 .

[0057] contrast Figure 6 and Figure 7 It can be seen that, Figure 6 The attribute differences shown are quite dispersed, while Figure 7The scatter plots of the attribute differences shown are relatively clustered. Calculating the standard deviation of the attribute difference for each of the two attribute difference scatter plots reveals that... Figure 6 The standard deviation is 1222. Figure 7 The standard deviation is 721. Figure 7 A smaller standard deviation indicates that the peaks and troughs in this example are more similar in properties.

[0058] Example 2

[0059] In a specific embodiment 2 of the present invention, the invention is applied. Figure 8 — Figure 10 The root mean square amplitude attributes were extracted from the upper trough, peak, and lower trough of the target layer, respectively. These three attributes were then gridded within a unified range using a 50m x 50m grid. The attribute difference was obtained by subtracting the root mean square amplitude of the upper trough from that of the peak, and represented by a contour map, as shown below. Figure 11 The attribute difference is obtained by subtracting the root mean square amplitude of the lower trough and the peak after meshing, and represented by a contour map, such as... Figure 12 .

[0060] contrast Figure 11 and Figure 12 It can be seen that, Figure 11 The attribute differences shown are relatively concentrated, while Figure 12 The scatter plots of the attribute differences shown are quite dispersed. Calculating the standard deviation of the attribute difference for each of the two attribute difference scatter plots reveals that... Figure 11 The standard deviation is 254. Figure 12 The standard deviation is 635. Figure 11 A smaller standard deviation indicates that the upper trough and peak properties are more similar in this example. Therefore, in this example, the trough corresponds to the top of the sandstone, and the peak corresponds to the bottom of the sandstone.

[0061] Example 3

[0062] In a specific embodiment 3 of the present invention, multiple fluvial reservoirs have developed in the upper section of the Shengli Chengdao Oilfield. Their thicknesses are mostly between one-quarter and one-half of the wavelength, meaning the top and bottom of the reservoirs correspond to adjacent wave crests and troughs. It was determined that the reservoirs in this area have sand tops corresponding to wave troughs and sand bottoms corresponding to wave crests. Based on this understanding, wellbore calibration, reservoir inversion, description, and well location design were carried out. From 2015 to 2022, over 10 million tons of geological oil reserves were predicted in the western new area of ​​the Shengli Chengdao Oilfield. Nearly 50 wells were drilled, with a drilling success rate greater than 95%, establishing a production capacity of 250,000 tons.

[0063] 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.

[0064] 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 determining the top and bottom surfaces of a reservoir using seismic attributes, characterized in that, The method for determining the top and bottom surfaces of a reservoir using seismic attributes includes the following: Step 1: Select a wave peak and extract the attributes of the selected wave peak and the upper and lower wave troughs, including: Select a set of wave peak seismic axes in the target layer section of the seismic data, denoted as A, and denote the adjacent upper wave trough and adjacent lower wave trough as B1 and B2 respectively; Step 2: Grid the three attribute data, including: Extract the root mean square amplitude attribute for each of the three axes A, B1, and B2, and grid the three attribute results with exactly the same range and scatter point distance; Step 3: Calculate the attribute difference between the upper wave trough and the wave peak, and calculate the standard deviation c1 of the scatter point samples of the attribute difference; Step 4: Calculate the attribute difference between the lower wave trough and the wave peak, and calculate the standard deviation c2 of the scatter point samples of the attribute difference; Step 5: Compare the results of the two standard deviations to determine the top and bottom surfaces of the reservoir, including: If c1 < c2, it means that the attribute results of the wave peak and the upper wave trough are more similar. For this set of data, the top of the sand body corresponds to the wave trough and the bottom of the sand corresponds to the wave peak; If c2 < c1, it means that the attributes of the wave peak and the lower wave trough are more similar. Then, for this set of data, the top of the sand corresponds to the wave peak and the bottom of the sand corresponds to the wave trough.

2. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 1, characterized in that, Before Step 1, perform synthetic seismogram calibration to find the time-depth range of the target layer on the seismic data, and select a wave peak within this range.

3. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 1, characterized in that, In Step 1, select a wave peak on the seismic profile passing through the well, and select a wave peak with obvious reflection amplitude and close to the typical reservoir position on the well for comparative analysis.

4. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 3, characterized in that, The method for determining the top and bottom surfaces of a reservoir using seismic attributes also includes that after Step 1, tracking the axes of the selected wave peak and the two wave troughs, that is, performing structural interpretation, to extract attributes; When opening a time window for extracting seismic attributes, it should be noted that if opening a time window for a certain wave peak, with this wave peak as the center, the upper and lower time windows should not include the highest amplitude value at the center of its adjacent upper and lower wave troughs and the further upper or lower ranges; When opening a time window for a certain wave trough, the time window range should also not exceed the highest amplitude value at the center of its adjacent wave peak and the further lower or lower ranges.

5. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 1, characterized in that, In Step 3, subtract the gridded upper wave trough attribute from the gridded wave peak attribute to obtain the difference between the two attributes: C1 = B1 - A.

6. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 5, characterized in that, In Step 3, use the scatter point values of C1 as a set of samples and calculate the standard deviation c1 of the samples.

7. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 6, characterized in that, In Step 4, subtract the gridded lower wave trough attribute from the gridded wave peak attribute to obtain the difference between the two attributes: C2 = B2 - A.

8. The method for determining the top and bottom surfaces of a reservoir using seismic attributes according to claim 7, characterized in that, In Step 4, use the scatter point values of C2 as a set of samples and calculate the standard deviation c2 of the samples.

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