Terrestrial clastic rock stratigraphic division method

Abstract

The invention provides a terrestrial clastic rock stratigraphic division method which comprises the following steps: analyzing geology and logging information, and selecting a logging curve Log sensitive to lithology and sedimentary cycle of terrestrial clastic rock; decomposing the logging curve into a plurality of frequency bands by adopting maximum overlapped wavelet transform, and establishing a decomposition coefficient matrix based on a depth domain and a frequency band domain; starting from a depth domain, calculating a maximum value and an information entropy curve as a basis, and carrying out geologic horizon division on a typical well in a work area; on the basis of the maximum value curve, an adjacent typical well is used as a reference template, and geologic horizon division is carried out on other wells in a work area in a mode of combining curve overall and local comparison. According to the method, the geology principle and the mathematical method are combined, and more effective information capable of reflecting the lithology and the sedimentary cycle performance is extracted; the requirement for personnel experience can be lowered, and the working efficiency of stratigraphic division is further improved by means of the similarity of logging curves in the same sedimentary environment.

Description

Technical Field

[0001] The invention relates to the field of oil and gas reservoir description and reservoir evaluation, and in particular to a method for dividing terrigenous clastic rock strata. Background Art

[0002] Stratigraphic division is a key technology in the detailed description of oil and gas reservoirs and is the basic work of geological research on oil and gas reservoirs. Using well logging curves to divide strata is the most practical way of stratigraphic division. The reason is that well logging curves, especially conventional well logging curves (natural gamma GR, natural potential SP, acoustic wave AC and resistivity R, etc.) are the most common data in the process of oil and gas exploration and development. Secondly, well logging curves comprehensively reflect the various physical properties of underground geological bodies and record various changes in the sedimentary environment during the sedimentation process, which is very representative.

[0003] At present, the stratigraphic division based on logging curves mainly utilizes the curve characteristics (waveform, extreme value, zero-crossing value, etc.) or mathematical statistics values ​​(mean, variance, etc.) of logging curves, which are divided into two categories: characteristic analysis method and mathematical statistics method. With mathematical methods as the entry point, it mainly relies on mathematical tools and personnel experience. For terrigenous clastic rocks, logging curves are affected by sedimentary cyclicity, and logging curves in the same sedimentary environment often have obvious similarities. Especially in the re-evaluation of oil and gas reservoirs in the middle and late stages of exploration and development, a large amount of data is usually involved, the number of wells drilled is huge, the data span is long, and the basic data are highly different. The workload of geological stratum division increases, the standard is difficult to unify, the difficulty of division increases, and the requirements for personnel experience increase.

[0004] Therefore, how to realize stratigraphic division efficiently and accurately has great practical significance. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a method for effectively realizing stratigraphic division by combining geological principles and mathematical tools, a second purpose of the present invention is to reduce the dependence of the stratigraphic division process on human experience, and a third purpose of the present invention is to provide a stratigraphic division method that takes into account the lithology of the well logging curve and the sedimentary cyclicity of terrigenous clastic rocks.

[0006] In order to achieve the above object, the present invention provides a method for dividing terrigenous clastic rock strata, the method comprising the following steps:

[0007] Analyze geological and logging data, and select well logging curves that are sensitive to the lithology and sedimentary cyclicity of terrigenous clastic rocks;

[0008] The well logging curve Log is decomposed into multiple frequency bands by using maximum overlap wavelet transform, and a decomposition coefficient matrix based on depth domain and frequency band domain is established;

[0009] Starting from the depth domain, the maximum value of the decomposition coefficient matrix and the information entropy curve are calculated, and the calculated curve is used as the basis for the geological stratum division of typical wells in the work area;

[0010] Based on the maximum curve and using the nearby typical wells as templates, the geological strata of other wells in the work area are divided by curve comparison.

[0011] Optionally, the calculation of the maximum value and the information entropy curve includes respectively calculating the information entropy curve of the decomposition coefficient, the information entropy curve of the absolute value of the decomposition coefficient, and the maximum value curve.

[0012] Optionally, the typical well is selected from a set of typical wells.

[0013] Optionally, the typical well set establishment parameters include plane positions and logging curve qualities.

[0014] Optionally, the plane position parameters include plane uniform distribution parameters.

[0015] Optionally, the typical well geological strata division is based on a maximum curve, an information entropy curve and formation sedimentary cyclicity.

[0016] Optionally, the curve comparison method includes overall curve comparison and local zoom comparison.

[0017] Optionally, the basis for dividing the geological strata of other wells also includes layer thickness relationship and stratigraphic isochronism.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0019] 1) The present invention combines geological principles with mathematical methods to extract more effective information that can reflect lithology and sedimentary cycles.

[0020] 2) The present invention highlights the features related to stratigraphic division in the original curve, which can reduce the requirements for personnel experience to a certain extent and has positive significance for the division of terrigenous clastic rock stratigraphic division.

[0021] 3) The present invention radiates from the typical well to the surrounding wells and expands to the entire work area, making greater use of the similarity of logging curves in the same sedimentary environment, and further improving the efficiency of stratigraphic division. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects and / or features of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0023] Figure 1 A schematic flow chart of the stratigraphic division method in Example 1 of the present invention is shown.

[0024] Figure 2 The GR curve in Example 1 of the present invention, the decomposition coefficients of the GR curve after maximum overlap wavelet transform, the information entropy of the absolute values ​​of the decomposition coefficients, the information entropy of the decomposition coefficients and the maximum curve of the absolute values ​​of the decomposition coefficients are shown.

[0025] Figure 3 A stratigraphic division diagram of a typical well in Example 1 is shown.

[0026] Figure 4 A diagram of other new well stratigraphic division plans with reference to adjacent typical wells in Example 1 is shown. DETAILED DESCRIPTION

[0027] Hereinafter, the method for dividing terrigenous clastic rock strata of the present invention will be described in detail in conjunction with exemplary embodiments.

[0028] Exemplary Embodiments

[0029] This exemplary embodiment provides a method for dividing terrigenous clastic rock strata, the method comprising the following steps:

[0030] S10: Analyze geological and logging data, and select the logging curves that are sensitive to the lithology and sedimentary cyclicity of terrigenous clastic rocks.

[0031] In this embodiment, based on the analysis of geological and well logging data, the well logging curve Log that is sensitive to the lithology and sedimentary cyclicity of terrigenous clastic rocks is selected.

[0032] S20: Decomposing the well logging curve Log into multiple frequency bands by using maximum overlap wavelet transform, and establishing a decomposition coefficient matrix based on the depth domain and the frequency band domain.

[0033] In this embodiment, the maximum overlap wavelet transform (MODWT) is used to decompose the well logging curve Log into multiple frequency bands, and a decomposition coefficient matrix based on the depth domain and the frequency band domain is established. The characteristics of this step are that while maintaining the depth and frequency resolution, the accuracy of frequency analysis is improved and the influence of boundary effects is reduced.

[0034] S30: Starting from the depth domain, the maximum value and information entropy curve of the decomposition coefficient matrix are calculated, and the calculated curve is used as a basis for dividing the geological layers of typical wells in the work area.

[0035] In this embodiment, the decomposition coefficient matrix is ​​used to calculate the information entropy curve of the decomposition coefficient, the information entropy curve of the absolute value of the decomposition coefficient and the maximum value curve from the depth domain. From the perspectives of plane position and curve quality, taking into account the principle of uniform plane distribution and excellent logging curve quality, a typical well set A = {A1, A2, ..., A M}(M≥1), using the maximum curve and information entropy curve, combined with the cyclicity of formation sedimentation, the single well geological stratum division is carried out to realize the single well geological stratum division of typical well sets.

[0036] S40: Based on the maximum value curve and using the nearby typical wells as templates, the geological strata of other wells in the work area are divided by curve comparison.

[0037] In this embodiment, for other wells in the work area, reference is made to the typical well A nearby. i Based on the maximum curve, combined with the relationship between layer thickness and stratigraphic isochronism, the geological strata division of the entire area is completed by combining overall curve comparison and local scaling comparison.

[0038] The key to this embodiment is to analyze geological and logging data, select logging curves that are sensitive to the lithology and sedimentary cyclicity of terrigenous clastic rocks, use maximum overlap wavelet transform to decompose the curves into multiple frequency bands, and calculate the maximum value and information entropy curves from the depth domain; on this basis, implement geological strata division for typical wells in the work area, and for other wells in the work area, use adjacent typical wells as reference templates, and use maximum value curves as the basis to complete the geological strata division by curve comparison.

[0039] In order to better understand the above exemplary embodiments of the present invention, they are further described below with reference to specific examples.

[0040] Example 1

[0041] This example provides a method for dividing terrigenous clastic rock strata, which is applied to actual work areas, such as Figure 1 As shown, it is a schematic diagram of the process flow of the method for dividing the terrigenous clastic rock strata.

[0042] Collect geological and logging data in the work area to determine the target layer and main lithology for stratigraphic division. The strata in the area are mainly sandstone and mudstone, so the natural gamma (GR) is selected as the basic curve for stratigraphic division.

[0043] The GR curve is decomposed into multiple frequency bands using maximum overlap wavelet transform {W 1 ,W 2 ,…W L}, construct a 2D decomposition coefficient matrix based on the depth domain and frequency band domain Where N is the number of sample points of the GR curve, L is the number of frequency bands, L≤log2(N), a large L value represents a high frequency, and a small L value represents a low frequency.

[0044] The information entropy is calculated along the rows of the decomposition coefficient matrix W, and the information entropy and maximum curve are calculated along the rows of the matrix using the decomposition coefficient absolute value matrix |W| for later stratigraphic division. Figure 2It is a test curve of a well in the work area, such as Figure 2 As shown in the figure, the marked MD is the depth, the marked GR is the original GR curve, the marked MODWT is the maximum overlap wavelet transform decomposition coefficient of the GR curve, the frequency decreases from left to right, the marked EnM_GR is the information entropy of the absolute value of the decomposition coefficient, the marked EnR_GR is the information entropy of the decomposition coefficient, and the marked ABS_GR is the maximum value of the absolute value of the decomposition coefficient. The maximum value curve ABS_GR is divided into two parts: low frequency band (black curve) and full frequency band (gray filling), that is, the maximum value is obtained in the low frequency band (1-5) and full frequency band (1-L) respectively.

[0045] In this example, Shannon entropy is selected as the information entropy calculation, that is,

[0046]

[0047] Where p represents x i Probability of occurrence.

[0048] Considering factors such as formation collapse during drilling and the principle of uniform plane distribution, multiple wells with good curve quality are selected to establish a typical well set A = {A1, A2, ..., A M}(M≥1), using the maximum value and information entropy curves, combined with the cyclicity of formation sedimentation, the single well geological stratum division of typical wells is realized. Figure 3 This is a typical well stratigraphic division diagram, such as Figure 3 As shown in the figure, area A is divided into four rock stratigraphic groups based on the absolute value maximum curve, showing the depth of each stratigraphic group, the original GR curve, the information entropy of the absolute value of the decomposition coefficient, the information entropy of the decomposition coefficient, the maximum value of the absolute value of the decomposition coefficient and the stratigraphic group division result.

[0049] The maximum absolute value of the decomposition coefficient includes two types: low frequency band and full frequency band. The variation law of the maximum curve within each stratigraphic group is consistent, but there are obvious differences between different stratigraphic groups, which is similar to the concept of geological sedimentary cycle. Figure 3 The middle B area is aimed at the research objectives of this area. The stratigraphic groups ③ and ④ in the A area are taken as the main target stratigraphic groups. According to the information entropy and maximum value curve, the stratigraphic group ③ is further subdivided into 4 stratigraphic sections, and the stratigraphic group ④ is subdivided into 5 stratigraphic sections, so as to meet the requirements of later reservoir description and reserve calculation. Figure 3 It can be seen from the middle B area that the interfaces of various stratigraphic sections basically correspond to obvious information entropy curve change interfaces, and the change rules of the maximum value curves in the same section are similar.

[0050] In this example, the division of stratigraphic segments takes into account the relationship between the inflection point of the information entropy curve, the change of the maximum curve, and the stratigraphic thickness. For example, the bottom boundary of the first segment of stratigraphic group ③ is located at the inflection point of the decomposition coefficient information entropy change. The information entropy below it changes from small to large, and the information entropy above it changes from large to small, and the maximum value in this segment basically shows a trend of changing from large to small.

[0051] In this example, other wells in the work area need to be referenced by typical wells and spread from point to surface. Based on the maximum value curve, combined with the change of formation thickness and formation isochronism, the curve comparison method is used to realize the geological formation division of the whole area. Figure 4 The stratigraphic division plan of a new well without geological strata is shown. First, refer to the adjacent typical wells and directly compare the maximum curves (ABS_GR) of the two wells as a whole to roughly determine the geological stratification; secondly, the reference well ABS_GR curve is segmented and locally scaled, and then compared with the new well ABS_GR curve to refine and adjust the geological stratification; finally, the geological stratification plan for the new well is determined.

[0052] Figure 4 Area A in the middle shows the GR curve and calculated curve of the new well. Figure 4 The black curve in the middle B area is the ABS_GR curve of the new well, and the light gray curve is the ABS_GR curve of the known typical well (the superimposed horizontal line is the geological stratification of the typical well). The two correspond well as a whole, especially in the lower 3695m-3770m section. Figure 4 In the middle C area, the local curve segment of the typical well ABS_GR curve is scaled and compared with the new well ABS_GR curve. For example, around 3741m, the overall similarity of the two curves is high, but there is still an obvious thickness difference. At this time, consider appropriately compressing the reference well ABS_GR curve segment, which can improve the comparability of the two curves and better conform to the consistency of geological stratification in the local area from a planar perspective. Figure 4 The middle D area shows the final geological plan for the new well. The original GR curve does not change significantly between 3695m and 3730m, showing a large section of mudstone. It is not easy to determine the specific position of the stratum interface. However, through the GR curve calculation and reference well comparison method, the specific position of the geological layer can be quickly located. This geological division method takes into account both geological principles and mathematical methods, and highlights the characteristics related to the geological strata in the original logging curve.

[0053] Although the present invention has been described above in conjunction with the exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A method for dividing terrigenous clastic rock strata, characterized in that: The stratigraphic division method comprises the following steps: Analyze geological and logging data, and select well logging curves that are sensitive to the lithology and sedimentary cyclicity of terrigenous clastic rocks; The well logging curve Log is decomposed into multiple frequency bands by using maximum overlap wavelet transform, and a decomposition coefficient matrix based on depth domain and frequency band domain is established; Starting from the depth domain, the maximum value of the decomposition coefficient matrix and the information entropy curve are calculated, and the calculated curve is used as the basis for the geological stratum division of typical wells in the work area; Based on the maximum curve and using the nearby typical wells as templates, the geological strata of other wells in the work area are divided by curve comparison.

2. The method according to claim 1, characterized in that The calculation of the maximum value and the information entropy curve includes respectively calculating the information entropy curve of the decomposition coefficient, the information entropy curve of the absolute value of the decomposition coefficient, and the maximum value curve.

3. The method according to claim 1, characterized in that The typical well is selected from a set of typical wells.

4. The method according to claim 3, characterized in that: The typical well set establishment parameters include plane position and logging curve quality.

5. The method according to claim 4, characterized in that The plane position parameters include plane uniform distribution parameters.

6. The method according to claim 1, characterized in that The basis for the division of the typical well geological strata includes a maximum value curve, an information entropy curve and formation sedimentary cyclicity.

7. The method according to claim 1, characterized in that The curve comparison method includes curve overall comparison and local zoom comparison.

8. The method according to claim 1, characterized in that The basis for the division of geological strata of other wells also includes layer thickness relationship and stratigraphic isochronism.

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