A method for analyzing the vertical evolution of relative paleo-water depth during the deposition of organic-rich shale
By analyzing the ratio of the longest transverse diameter and the longest perpendicular diameter of carbon fluorapatite nodules, the nodule diameter distribution map and the height-to-face ratio curve were drawn, and the multi-solvability and error problems of the ancient water depth recovery method in the existing technology were solved. , and the accurate recovery of the vertical change process of paleowater depth during mud shale sedimentation period was achieved.
Patent Information
- Application Number
- CN202411487563.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-24
- Publication Date
- 2024-12-27
- Estimated Expiration
- 2044-10-24
AI Technical Summary
The existing sedimentary paleowater depth recovery methods have multiple solutions and large errors, making it difficult to accurately obtain the vertical change process of paleowater depth during mud shale sedimentary period.
By performing the ratio analysis of the longest transverse diameter and the longest perpendicular diameter on mud shale core samples containing fluoroapatite nodules, the nodule diameter distribution map and the height-to-face ratio curve are drawn to obtain the vertical change process of paleowater depth.
The accurate vertical change process recovery of the paleowater depth of mud shale sedimentary period was achieved, and the multi-solvency and uncertainty of the traditional methods were overcome. The results were relatively accurate and had good prospects for promotion and application.
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Figure CN119001899B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of petroleum geology, and more specifically to a method for analyzing the vertical evolution of organic-rich shale relative to ancient water depth during its deposition period. Background Art
[0002] Paleo-water depth refers to the water depth in the paleo-geographic environment when the sediments were formed, that is, the depth of the water body where the sediments were located when they were deposited. This concept is of great significance in the study of oil and gas basins because it is directly related to the formation of source rocks, reservoirs and cap rocks, as well as the accumulation conditions of oil and gas. Paleo-water depth is an important indicator for analyzing the genetic environment of sediments and a key factor in revealing the mechanism of organic matter enrichment in shale.
[0003] The restoration of paleo-water depth and its evolution is one of the important contents of the study of oil and gas basins, and plays a vital role in understanding the sedimentary history, oil and gas generation and accumulation process of the basin. The existing methods for restoring sedimentary paleo-water depth can be summarized as follows: (1) analysis of the ratio of major-trace-rare earth elements in the whole rock, such as Mn / Fe, (Ca+Mg) / (Fe+Al), Fe / Co, La / Sm, Th / U; (2) paleo-source / paleo-salinity factors; (3) analysis of microbial diversity and biological relic characteristics; (4) qualitative analysis of sediment color and sedimentary structure; (5) paleo-geomorphological stripping inversion analysis; (6) qualitative restoration of natural gamma-ray logging curves and maximum entropy spectrum analysis curves.
[0004] However, indicator methods such as element ratios and paleo-source / paleo-salinity factors often have significant ambiguity due to differences in the study area and the differences in element test samples, while paleontological relic methods are mostly applicable to specific geological background conditions. Paleogeomorphological backstripping involves seismic stratigraphic interpretation, compaction correction, etc. The scale of paleo-water depth restoration is mainly at the basin level, and the relative error is large. There is randomness in the processing of natural gamma-ray logging curves and maximum entropy spectrum analysis curves, and the restored paleo-water depth is mainly based on the macroscopic trend of increasing and shallowing the water body in the lake basin. How to more intuitively obtain the vertical change process of paleo-water depth during the shale deposition period based on rock and mineral characteristic analysis still requires technical breakthroughs. Summary of the invention
[0005] In view of the above problems, the present invention provides a method for analyzing the vertical evolution of relative ancient water depth during the deposition period of organic-rich shale. Based on the characteristic analysis of carbon-fluoroapatite nodules, the present invention obtains the vertical change process of ancient water depth during the deposition period of shale.
[0006] The purpose of the present invention is to provide a method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale, comprising the following steps:
[0007] Core samples were taken from different depths along the vertical plane of the formation from the shale coring well containing carbon fluoroapatite nodules.
[0008] For core samples in different depth areas, the longest transverse diameter and the longest vertical diameter of carbon fluoroapatite nodules were counted from deep to shallow in the corresponding statistical area, and the ratio of the longest vertical diameter to the longest transverse diameter was calculated.
[0009] By analyzing the changing trends of all the longest lateral diameters and the ratios of all calculated longest vertical diameters to the longest lateral diameters, the vertical variation process of the paleo-water depth during the shale deposition period was obtained.
[0010] Based on the mineral properties of carbon fluoroapatite, the present invention counts the longest lateral diameter and the longest vertical diameter of carbon fluoroapatite nodules, analyzes the vertical distribution characteristic parameters of carbon fluoroapatite nodules at different depths to obtain the ancient water depth change process, and realizes the analysis of the occurrence pattern of carbon fluoroapatite nodules in organic-rich shale to restore the relative ancient water depth of the lake basin during the shale deposition period.
[0011] It is understood that the core samples have a certain depth during the sampling process, and the production depth of the cores with nodules is recorded and the nodules are measured to obtain the required information.
[0012] In a preferred embodiment of the present invention, a nodule diameter distribution diagram is obtained with the depth segment as the ordinate and the longest transverse diameter as the abscissa. It should be noted that since the box plot can intuitively obtain data information, the present invention analyzes the data by drawing a nodule diameter distribution diagram.
[0013] In a preferred embodiment of the present invention, the nodule aspect ratio curve is obtained by taking the depth segment as the ordinate and the ratio of the longest vertical diameter to the longest transverse diameter as the abscissa.
[0014] In a preferred embodiment of the present invention, the shorter the longest transverse diameter in the nodule diameter distribution diagram, the larger the ratio of the longest vertical diameter to the longest transverse diameter in the nodule aspect ratio curve, indicating that the bottom water reducing property is stronger and the water body is deeper.
[0015] In a preferred embodiment of the present invention, the longer the longest transverse diameter in the nodule diameter distribution diagram, the smaller the ratio of the longest vertical diameter to the longest transverse diameter in the nodule aspect ratio curve, indicating that the bottom water reduction is weaker and the water body is shallower.
[0016] In a preferred embodiment of the present invention, the core sample is a core sample cut along the core column and has a continuous and flat surface.
[0017] In a preferred embodiment of the present invention, the depth of the statistical area is 1m~2m. It should be noted that the statistics are performed according to the depth of the 1m~2m statistical area. For example, the core samples are taken from the 3300m~3400m depth area. If the difference between the deepest and shallowest points of the depth area is divided by the 1m statistical area, the 300m~3400m depth area can be divided into 100 statistical segments for statistics, and graphs are drawn based on the statistical results.
[0018] In a preferred embodiment of the present invention, the carbon fluoroapatite nodules are ellipsoidal.
[0019] In a preferred embodiment of the present invention, the depth zone is 3330m~3460m.
[0020] Compared with the prior art, the present invention has the following beneficial effects:
[0021] (1) The present invention aims at core samples of shale coring wells containing carbon fluoroapatite nodules, counts the longest transverse diameter and the longest vertical diameter of the carbon fluoroapatite nodules, and calculates the ratio of the longest vertical diameter to the longest transverse diameter. According to the relative size and change trend of the longest transverse diameter, the longest vertical diameter and the ratio of the longest transverse diameter in different depth areas, the vertical change process of the paleo-water depth during the shale deposition period is obtained. This is because organic-rich shale with huge shale oil potential often has a sedimentary background such as large paleo-water depth, strong paleo-productivity, and stable paleo-water environment. There is often an obvious genetic relationship between increased paleo-water depth and enhanced bottom water reducibility. The formation process of carbon fluoroapatite nodules formed within a few centimeters to tens of centimeters below the sediment and water interface is controlled by the redox conditions of the sediment and water interface, and its occurrence morphology directly reflects the relative lake basin water depth when the nodules are formed. Due to the influence of overlying stratum pressure and liquid surface tension, carbon fluoroapatite nodules are mostly present in the form of bedding ellipsoids. Under shallow water conditions, the redox interface is located in the sediments, and under the pressure of the overlying sediments, the nodules are mostly flat large ellipsoids; under deep water conditions, the redox interface is located at the bottom water or the interface between the sediments and water, and under the strong reduction, the nodules are mostly dispersed small ellipsoids. Therefore, according to the method of the present invention, based on the characteristic analysis of carbon fluoroapatite nodules, the change process of the relative paleo-water depth of the lake basin during the sedimentary evolution of organic-rich mud shale can be characterized.
[0022] (2) Compared with the prior art, the method of the present invention can overcome the ambiguity and uncertainty of the results of random sample selection in the process of restoring ancient water depth by the traditional element ratio method through the quantitative measurement of mineral morphological parameters on the core. The core samples used in the present invention are easy to obtain and have strong operability. It is the first time to restore ancient water depth based on rock and mineral characterization. The results are relatively accurate and have good prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 Schematic diagram of the occurrence of carbon fluoroapatite nodules in the core sample in Example 2 of the present invention.
[0024] Figure 2 Schematic diagram of the statistical mechanism of carbon fluoroapatite nodules in the core samples of the present invention; wherein (A) is a relatively shallow water condition, and (B) is a relatively deep water condition.
[0025] Figure 3 This is a diagram of the vertical variation of paleo-water depth based on the aspect ratio of nodules and the longest lateral diameter of nodules in Example 2 of the present invention.
[0026] Figure numerals: 1 - water body, 2 - interface between sediment and water, 3 - sediment, 4 - redox interface, 5 - carbon fluoroapatite nodules, h - height of carbon fluoroapatite nodules, w - width of carbon fluoroapatite nodules. DETAILED DESCRIPTION
[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0028] The present invention makes full use of detailed continuous coring data of mudstone, and through the measurement and statistics of the carbon fluoroapatite nodules in the core section, selects two key parameters: the longest transverse diameter, the longest vertical diameter and the ratio of the longest transverse diameter of the nodules distributed along the layer, and draws the nodule diameter distribution map and the nodule height-width ratio curve at different depths based on these two key parameters, so as to accurately restore the vertical change process of the ancient water depth within the meter range. The specific technical scheme is as follows.
[0029] Example 1
[0030] Step S1, for the shale continuously cored by drilling, around the coring well where the carbon fluoroapatite nodules 5 are developed, core samples with continuous and smooth surfaces cut along the core column are selected in different depth areas along the vertical surface of the formation.
[0031] Step S2: Count and record the core depth, longest transverse diameter, and longest vertical diameter of the core samples of the continuous coring wells 5. The longest transverse diameter is recorded as the width, the longest vertical diameter is recorded as the height, and the ratio of the longest vertical diameter to the longest transverse diameter is recorded as the aspect ratio.
[0032] The schematic diagram of the mechanism of the occurrence characteristics of the characteristic mineral carbon fluoroapatite nodule 5 indicating the ancient water depth in the present invention is as follows Figure 2 As shown. Figure 2 As shown in (A), under relatively shallow water conditions, the redox interface 4 is located in the sediment 3. The weak reducing conditions during the deposition and diagenesis of the carbon fluoroapatite nodules 5 and the overlying thick sediments 3 result in the carbon fluoroapatite nodules 5 having a large diameter, a small number, and a small aspect ratio.
[0033] Figure 2 As shown in (B), under relatively deep water conditions, the redox interface 4 is located near the interface 2 between sediments and water or in the water body 1. Under strong reducing conditions and weak pressure from overlying sediments 3, the diameter of carbon fluoroapatite nodules 5 is generally small, but the number is large and the aspect ratio is large. Therefore, the longest transverse diameter and aspect ratio of carbon fluoroapatite nodules 5 can be used as effective characteristic parameters of their relative paleo-water depth during the deposition period.
[0034] Step S3, according to the number of statistical data of carbon fluoroapatite nodules 5, with 1m~2m as the statistical area, the longest transverse diameter and the aspect ratio of carbon fluoroapatite nodules 5 at different depths from deep to shallow are counted.
[0035] Step S4, plotting a nodule diameter distribution map with the depth segment as the ordinate and the longest transverse diameter as the abscissa.
[0036] The nodule aspect ratio curve is plotted with the depth segment as the ordinate and the aspect ratio as the abscissa.
[0037] Step S5, obtaining the vertical variation process of the ancient water depth during the shale deposition period through the nodule diameter distribution diagram at different depths and the nodule height-width ratio curve.
[0038] Since the carbon fluoroapatite nodules 5 are in colloidal form and there is formation pressure in the vertical direction, they are flattened in the vertical direction, resulting in the lateral length of the carbon fluoroapatite nodules 5 being larger than the vertical height. Therefore, two situations may occur in the statistical process: one is that the longest lateral diameter of the carbon fluoroapatite nodules 5 is small and the aspect ratio is large; the other is that the longest lateral diameter of the carbon fluoroapatite nodules 5 is large and the aspect ratio is small.
[0039] With the change of depth, when the longest transverse diameter of the nodules distributed along the layer in the nodule diameter distribution diagram is shorter, the height-to-width ratio in the nodule height-to-width ratio curve is larger, indicating that the bottom water reduction is stronger and the water body 1 is deeper. Conversely, the longer the longest transverse diameter of the nodules distributed along the layer, the smaller the height-to-width ratio in the nodule height-to-width ratio curve is, indicating that the bottom water reduction is weaker and the water body 1 is shallower. Thus, the vertical change process of the ancient water depth during the shale deposition period can be obtained.
[0040] The maximum entropy spectrum analysis curve, namely the GR-INPEFA curve, is a frequency trend line obtained by performing synthetic prediction error filtering analysis on the logging curve.
[0041] In order to further verify the method of the present invention, the present invention compared the obtained nodule diameter distribution map and nodule height-width ratio curve with paleo-water depth analysis indicators such as the GR-INPEFA curve or element ratio. The results showed that the results of the nodule diameter distribution map and the nodule height-width ratio curve were consistent with paleo-water depth analysis indicators such as the GR-INPEFA curve or element ratio, indicating that the method of the present invention can be used to determine the vertical change process of paleo-water depth during the shale deposition period.
[0042] Example 2
[0043] Step S1: Take the organic-rich mudstone of Shahejie Formation in Dongying Sag of Jiyang Depression, on which there are key characteristic mineral carbon fluoroapatite nodules 5, such as Figure 1 As shown, the height of the carbon fluoroapatite nodule is recorded as h, and the width of the carbon fluoroapatite nodule is recorded as w.
[0044] Step S2: Based on naked eye observation, the output depth, longest transverse diameter, and longest vertical diameter of the carbon fluoroapatite nodules 5 in the depth area of 3330m-3460m are counted grain by grain. The longest transverse diameter is recorded as the width, and the longest vertical diameter is recorded as the height.
[0045] Step S3, according to the number of statistical data of carbon fluoroapatite nodules 5, with 1.5 meters as the statistical area, the longest transverse diameter and the aspect ratio at different depths are counted.
[0046] Step S4: Draw a nodule diameter distribution map with the depth segment as the ordinate and the longest transverse diameter as the abscissa, such as Figure 3 shown.
[0047] With the depth segment as the ordinate and the aspect ratio as the abscissa, the aspect ratio curve of the nodule is plotted, as shown in Figure 3 shown.
[0048] Step S5: By comparing paleo-water depth analysis indicators such as GR-INPEFA curve or element ratio, the vertical variation process of paleo-water depth during the shale deposition period can be determined.
[0049] In the depth area of 3450m~3363m, the longest lateral diameter from deep to shallow exceeds 20mm and gradually decreases to <2mm upwards, and the aspect ratio from deep to shallow increases from <0.1 to >0.55, indicating that the water depth is gradually deepening; in the depth area of 3363m~3305m, the longest lateral diameter from deep to shallow begins to gradually increase from <2mm upwards, and the aspect ratio from deep to shallow begins to gradually decrease from >0.55 upwards, indicating that the water depth is gradually becoming shallower.
[0050] By comparing the nodule diameter distribution diagram and nodule aspect ratio curve obtained in step S4 with the trend of the GR-INPEFA curve, it can be seen that Figure 3 The nodule diameter distribution diagram, nodule aspect ratio curve and GR-INPEFA curve indicate similar paleo-water depth variation trends, indicating the accuracy and practicability of the method of the present invention.
[0051] Figure 3 The GR-INPEFA curve data in the figure are from the “Sequence Stratigraphy, Depositional Environment and Associated Lithofacies of Lacustrine Shale: A Case From the Upper Fourth Member of Shahejie Formation, Dongying Depression, Bohai Bay Basin” published by the inventors in Frontiers in Earth Science. It should be noted that in order to accurately compare with the results of the present invention, the GR-INPEFA curve data are adjusted to the statistical depth range of the present invention, such as Figure 3 shown.
[0052] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.
[0053] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.
Claims
1. A method for analyzing the vertical evolution of relative paleo-water depth during the deposition of organic-rich shale, characterized in that: The following steps are involved: For a shale coring well containing carbon fluoroapatite nodules (5), core samples are taken from different depths along the vertical plane of the formation; For core samples at different depths, the longest transverse diameter and the longest vertical diameter of carbon fluoroapatite nodules (5) are counted from deep to shallow in the corresponding statistical area, and the ratio of the longest vertical diameter to the longest transverse diameter is calculated; By analyzing the changing trends of all the longest lateral diameters and the ratios of all calculated longest vertical diameters to the longest lateral diameters, the vertical variation process of the paleo-water depth during the shale deposition period was obtained.
2. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 1, characterized in that: The nodule diameter distribution diagram was obtained with the depth segment as the ordinate and the longest transverse diameter as the abscissa.
3. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 2, characterized in that: The nodule height-width ratio curve was obtained by taking the depth segment as the ordinate and the ratio of the longest vertical diameter to the longest transverse diameter as the abscissa.
4. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 3 is characterized in that: The shorter the longest transverse diameter in the nodule diameter distribution diagram, the larger the ratio of the longest vertical diameter to the longest transverse diameter in the nodule aspect ratio curve, indicating that the water body (1) is deeper.
5. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 3, characterized in that: The longer the longest transverse diameter in the nodule diameter distribution diagram, the smaller the ratio of the longest vertical diameter to the longest transverse diameter in the nodule aspect ratio curve, indicating that the water body (1) is shallower.
6. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 1, characterized in that: The core sample is a core sample with a continuous and flat surface cut along the core column.
7. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 1, characterized in that: The depth of the statistical area is 1m~2m.
8. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 1, characterized in that: The carbon fluoroapatite nodules (5) are ellipsoidal in shape.
9. The method for analyzing the vertical evolution of relative paleo-water depth during the deposition period of organic-rich shale according to claim 1, characterized in that: The depth area is 3330m~3460m.