Method for identifying volcanic ash in shale hydrocarbon source rocks

Abstract

The invention relates to the field of petroleum geology research, and discloses a method for identifying volcanic ash in shale hydrocarbon source rocks. Comprising the following steps: acquiring a shale hydrocarbon source rock sample to be identified; analyzing the shale hydrocarbon source rock sample by adopting one or more of a lithofacies analysis method, an X diffraction analysis method and a geochemical analysis method; and identifying the volcanic ash in the shale hydrocarbon source rock sample based on the analysis data. According to the technical scheme, the process is simple, and the operability and the generalizability are extremely high; the volcanic ash in the high-quality hydrocarbon source rock can be accurately identified, the hydrocarbon formation mechanism, the hydrocarbon generation potential and the like of the hydrocarbon source rock can be more accurately judged, and technical support is more effectively provided for oil-gas exploration.

Description

Technical Field

[0001] The invention relates to the field of petroleum geology research, and in particular to a method for identifying volcanic ash in shale source rocks. Background Art

[0002] Volcanism is a common geological phenomenon in nature. Volcanic eruption is the most direct manifestation of the release of heat energy from the earth's interior on the surface. Large-scale volcanic activity is often closely related to crustal movements such as plate subduction, collision and continental rifting. Volcanic eruptions are usually accompanied by a large amount of hot gas, aerosol, volcanic ash and lava flow. During violent eruptions, the eruption height of volcanic materials can reach several thousand meters, and in a short period of time, it will have a significant impact on the climate and natural environment of the affected area. Volcanic materials falling to land can change the structure and chemical composition of surface soil and affect vegetation growth. Volcanic materials from underwater eruptions or terrestrial eruptions falling to the ocean and lakes will affect the paleoecological environment and the growth of organisms to varying degrees. Therefore, people gradually realize that volcanic activity may have an important impact on the growth of lakes and marine organisms and the development of high-quality source rocks in neighboring areas that are coupled in time and space.

[0003] Studies have shown that the impact of volcanism on high-quality source rocks mainly includes the following aspects: First, the aerosols produced by volcanic eruptions refract sunlight, and the high-temperature gases and heavy metal elements can cause pollution to water bodies and plants, causing rapid and large-scale death of organisms, thus laying a preliminary material foundation for the development of source rocks; Second, the intervals between volcanic eruptions provide organisms with time to survive and space for activities. After the volcanic activity stops, a large number of hot springs and large lakes are usually formed near the crater. In addition, volcanic ash contains a large number of minerals and trace elements, which provide rich nutrients for organisms, further promoting the reproduction and development of aquatic organisms and higher terrestrial plants, leading to the re-enrichment of organic matter, and providing a material and energy basis for the flourishing of life; Third, the strongly reducing sedimentary environment rich in organic matter caused by volcanism is conducive to the preservation of organic matter and its conversion to the formation of oil and gas; Fourth, volcanic eruptions can also provide trace elements, which have a catalytic effect in the hydrocarbon generation process of source rocks.

[0004] In view of the above understanding, the identification of volcanic ash (volcanic ash refers to volcanic rocks, minerals and volcanic glass fragments with a particle size of less than 2mm ejected into the atmosphere during volcanic eruptions) in source rocks is of great significance. On the one hand, volcanic materials in source rocks can serve as direct evidence of volcanism and provide more information for studying the formation mechanism of source rocks. On the other hand, since the genetic mechanism of volcanic ash layers determines the isochronism and extensiveness of their spatial distribution, the stratigraphic characteristics and precise dating of volcanic ash have important stratigraphic correlation significance. However, in actual application research, except for volcanic clastic rocks, which are typical rocks formed by the accumulation (or deposition) of volcanic eruption debris and then consolidation or welding, etc., which are relatively easy to distinguish, volcanic materials mixed in other types of source rocks are actually difficult to distinguish. The main reason is that in explosive volcanic activities, volcanic debris with a particle size of >2mm will settle around the crater within a few minutes to a few days after the volcanic eruption, and its distribution range is relatively limited; but volcanic ash with a particle size of <2mm can generally float in the air for months or even years, and spread over a large area and settle in the strata hundreds to thousands of kilometers away from the crater. The deposition and preservation of volcanic ash are closely related to the hydrodynamic environment on the one hand; on the other hand, because volcanic ash will also undergo complex hydrolysis during the deposition process, the mineral existence form will change, which has caused great difficulties for identification.

[0005] Mudstone and shale source rocks are the main types of source rocks. At present, some scholars have also paid attention to the presence of volcanic ash in them. However, since mudstone and shale source rocks are rich in clay minerals, which are similar to the composition of the hydrolysis products of volcanic ash, it is very difficult to identify them. At present, the mainstream method is based on the tuffaceous component in the rock, that is, under a polarizing microscope, the color change is observed in the direction parallel to the gypsum test plate and perpendicular to the gypsum test plate while rotating the stage. If the color changes from orange-red to purple-red, it is mudstone, and if the color does not change, it is a volcanic ash layer. However, this set of methods is too single and has obvious limitations. It is difficult to meet production needs. Many source rock samples containing volcanic ash are ignored in actual production, resulting in the missing of important volcanic material evidence. Therefore, how to establish a universal, practical and effective volcanic ash identification method has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The present application provides a method for identifying volcanic ash in shale source rocks to solve the above-mentioned technical problems in the prior art.

[0007] According to one aspect of the present application, an embodiment provides a method for identifying volcanic ash in shale source rocks, comprising the following steps:

[0008] Step 1. Obtain a shale source rock sample to be identified;

[0009] Step 2. Analyze the shale source rock sample using one or more of a petrographic analysis method, an X-ray diffraction analysis method, and a geochemical analysis method;

[0010] Step 3. Based on the analysis data of step 2, identify the volcanic ash in the shale source rock sample.

[0011] In one embodiment, if volcanic ash is identified by any one of the petrographic analysis method and the X-ray diffraction analysis method, it is directly determined that the shale source rock sample contains volcanic ash;

[0012] If neither the petrographic analysis method nor the X-ray diffraction analysis method identifies volcanic ash, the geochemical analysis method is performed; wherein, if the geochemical analysis method identifies volcanic ash, it means that there is a probability that the mud shale source rock sample contains volcanic ash; if the geochemical analysis method does not identify volcanic ash, it means that the mud shale source rock sample does not contain volcanic ash.

[0013] In one embodiment, the petrographic analysis method comprises the following steps:

[0014] Step 301. Prepare the shale source rock sample according to standard sample preparation to obtain rock thin sections;

[0015] Step 302: Place the rock slice under a polarizing microscope for observation to identify the physical phase composition; the physical phase composition identification includes volcanic debris material analysis and / or volcanic alteration material analysis;

[0016] The pyroclastic material analysis refers to determining whether the rock slice contains pyroclastic material; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash;

[0017] The volcanic alteration analysis refers to determining whether the rock slice contains volcanic alteration; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash.

[0018] In one embodiment, the pyroclastic material includes two categories:

[0019] The first category is relatively large pyroclastic material, including one or more of rock fragments, crystal fragments, and glass fragments;

[0020] The second category is relatively small pyroclastic material, including volcanic dust.

[0021] In one embodiment, the X-ray diffraction analysis method comprises the following steps:

[0022] Step 401. Prepare the shale source rock sample according to the standard to obtain a rock sample;

[0023] Step 402: Perform crystallographic analysis and / or phase analysis on the rock sample;

[0024] The crystallographic analysis refers to determining whether amorphous silicon dioxide is contained in the rock sample; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash;

[0025] The phase analysis refers to determining whether the rock sample contains volcanic alteration products; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash.

[0026] In one embodiment, the volcanic alteration materials include two categories:

[0027] The first category is typical alteration minerals, which are the alteration products unique to volcanic materials;

[0028] The second category is the altered mineral assemblage, which is a set of specific mineral paragenesis formed in a specific environment when volcanic debris undergoes secondary changes.

[0029] In one embodiment, the geochemical analysis method comprises the following steps:

[0030] Step 501. Prepare the shale source rock sample according to the standard to obtain a rock sample;

[0031] Step 502: Perform major element analysis and / or trace element analysis on the rock sample;

[0032] The major element analysis refers to determining whether the major element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, there is no volcanic ash in the rock sample;

[0033] The trace element analysis refers to determining whether the trace element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash.

[0034] In one embodiment, the major element characteristics are judged to be overall comparative chemical composition characteristics, and one or more of SiO2, TiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, CO2, and H2O oxides are compared with existing research data to determine whether the research data is close to shale sedimentary rocks or igneous rocks; and / or,

[0035] The main element characteristics are determined by comparing the relative contents of the oxides and then making a judgment based on empirical knowledge.

[0036] In one embodiment, the trace element characteristics are determined by comparing the abundance values ​​of the trace elements and then making a determination based on empirical knowledge; and / or,

[0037] The trace element characteristics are determined by comparing the relative contents of trace element pairs and then making a judgment based on empirical knowledge.

[0038] In one embodiment, the major element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis;

[0039] The trace element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis.

[0040] The technical solution of the above-mentioned embodiment of the present application first obtains a mudstone source rock sample to be identified, then uses petrographic analysis / X-ray diffraction analysis / geochemical analysis methods to analyze the sample, and finally obtains the volcanic ash identification result of the sample based on the above-mentioned analysis data. The method for identifying volcanic ash in mudstone source rocks in the present application has a simple process and is highly operational and extensible. It can accurately identify volcanic ash in high-quality source rocks, and can make more accurate judgments on the hydrocarbon generation mechanism and hydrocarbon generation potential of source rocks, thereby providing more effective technical support for oil and gas exploration. Specifically, the method of the present application has the following advantages:

[0041] 1. The petrographic characteristics, crystallographic characteristics, phase characteristics and elemental characteristics of volcanic ash mud shale source rocks are comprehensively considered, and the identification angle is more comprehensive.

[0042] 2. The identification technology is more abundant by using various methods such as petrographic analysis, X-diffraction analysis, and geochemical analysis.

[0043] 3. The various methods are logically arranged according to probability and difficulty, making them highly operational and universal.

[0044] 4. The all-round and multi-angle identification method has a higher accuracy rate compared with the traditional method that only relies on optical characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flowchart of a method for identifying volcanic ash in shale source rocks in an embodiment;

[0046] Figure 2 is a flow chart of a method for identifying volcanic ash in shale source rocks in an embodiment;

[0047] Figure 3is a flow chart of a petrographic analysis method in an embodiment;

[0048] Figure 4 is a flow chart of an X-ray diffraction analysis method in an embodiment;

[0049] Figure 5 is a flow chart of a geochemical analysis method in an embodiment;

[0050] Figure 6 This is a schematic diagram of the characteristics of glass fragments in a thin slice of a shale source rock sample A in an embodiment;

[0051] Figure 7 is an X-ray diffraction spectrum of zeolite in a shale source rock sample B in an embodiment;

[0052] Figure 8 It is a scatter plot of a Late Permian profile sample of a basin and three suspected volcanic ash-bearing samples in the PT boundary layer in an embodiment. DETAILED DESCRIPTION

[0053] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0054] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0055] It should be noted that the terms "first", "second" etc. in the present application are used to distinguish similar objects, and need not be used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged in appropriate circumstances, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units need not be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0056] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be an intermediate element. Moreover, in this application, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element through a third element.

[0057] Embodiment 1

[0058] Please refer to Figure 1-Figure 5 An embodiment provides a method for identifying volcanic ash in shale source rocks, comprising the following steps:

[0059] Step 1. Obtain a shale source rock sample to be identified;

[0060] Step 2. Analyze the shale source rock sample using one or more of a petrographic analysis method, an X-ray diffraction analysis method, and a geochemical analysis method;

[0061] Step 3. Based on the analysis data of step 2, identify the volcanic ash in the shale source rock sample.

[0062] Among them, in the analysis of the mud shale source rock sample in step 2, an embodiment is: if any one of the petrographic analysis method and the X-ray diffraction analysis method identifies volcanic ash, it is directly determined that the mud shale source rock sample contains volcanic ash; if neither the petrographic analysis method nor the X-ray diffraction analysis method identifies volcanic ash, the geochemical analysis method is performed; wherein, if the geochemical analysis method identifies volcanic ash, it means that the mud shale source rock sample has a probability of containing volcanic ash; if the geochemical analysis method does not identify volcanic ash, it means that the mud shale source rock sample does not contain volcanic ash.

[0063] In other words, if the petrographic analysis method is effective, it is directly determined that the sample contains volcanic ash; if the X-ray diffraction analysis method is effective, it is directly determined that the sample contains volcanic ash. Generally, there is no priority order between the petrographic analysis method and the X-ray diffraction analysis method. If the geochemical analysis method is effective, it means that there is a certain probability that the sample contains volcanic ash. It can be understood that the petrographic analysis method and the X-ray diffraction analysis method provide a direct basis for the identification of volcanic ash; the geochemical analysis method provides an indirect basis for the identification of volcanic ash.

[0064] In one embodiment, the petrographic analysis method comprises the following steps:

[0065] Step 301. Prepare the shale source rock sample according to the standard to obtain a rock slice; wherein the source rock refers to a rock rich in organic matter, which has generated and discharged or is discharging oil and natural gas in geological history; the shale source rock refers to mudstone and shale source rock, which is a large category of common source rocks and is developed in major continental basins in my country, such as Songliao, Bohai Bay, Junggar, Qaidam and other basins; the characteristics of the shale source rock are: the composition is mainly clay minerals, the appearance is mostly gray-black, dark gray, gray or gray-green, and foliated stratification may be developed;

[0066] Step 302: Place the rock slice under a polarizing microscope for observation to identify the physical phase composition; the physical phase composition identification includes volcanic debris analysis and / or volcanic alteration analysis.

[0067] Among them, the pyroclastic material analysis refers to determining whether the rock slice contains pyroclastic material; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash; the volcanic alteration material analysis refers to determining whether the rock slice contains volcanic alteration materials; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash.

[0068] Specifically, the pyroclastic material refers to the debris from volcanic eruptions, which are traces left in shale source rocks when they are deposited (sedimented) on land or underwater. The pyroclastic material includes two categories:

[0069] The first category is relatively large volcanic debris, including one or more of rock fragments, crystal fragments and glass fragments; the phase identification characteristics under the polarizing microscope are:

[0070] 1. Rock debris: refers to the debris of earlier solidified lava, volcanic channel surrounding rocks and volcanic basement rocks, which are mostly angular and irregular in shape;

[0071] 2. Crystal fragments: refers to the phenocrysts precipitated from the magma in the early underground and the minerals in the surrounding rocks of the volcanic channel, mostly quartz, feldspar and other minerals. Because they are shattered and separated from the semi-solidified magma and surrounding rocks during the eruption, they are often angular. Due to the sudden cooling during the eruption, the minerals generally have cracks, and sometimes dissolution can be seen;

[0072] 3. Glass shavings: refers to the semi-solid porous glass formed when the molten magma rich in volatile components and high viscosity is ejected and rapidly cooled. Because the gas in it suddenly expands, it quickly escapes from the pores, explodes and suddenly cools. Therefore, most of them are in the shape of curved edges and torn shapes. A few of them are in the shape of floating rocks because they are not completely broken into pieces.

[0073] The second category is relatively small pyroclastic material, generally with a particle size of less than 0.0625 mm, including volcanic dust; the phase identification characteristics under a polarizing microscope are:

[0074] 1. Volcanic dust: refers to the smallest volcanic debris. From the perspective of physical phase, it is an aggregate of extremely fine particles such as glass and crystal fragments that are difficult to distinguish even under a high-power polarizing microscope. It is very easy to devitrify and form a cryptocrystalline structure during the diagenesis process. Therefore, it can be distinguished by mineral ductility. That is, under a polarizing microscope, while rotating the stage, observe the color change in the direction parallel to the gypsum test plate and the direction perpendicular to the gypsum test plate. If the color changes, it is not volcanic dust. If the color does not change, it is volcanic dust. Among them, the mineral ductility refers to the relationship between the long direction of the mineral crystal and the long and short radii of the optical body. Since volcanic dust is an aggregate of extremely fine particles, it does not have ductility characteristics under a polarizing microscope.

[0075] Specifically, the volcanic alteration refers to the traces left in the shale source rock after the volcanic debris undergoes secondary changes such as devitrification, hydration, and metasomatic alteration. The volcanic alteration includes two categories:

[0076] 1. The first category is typical alteration minerals, which are the alteration products unique to volcanic materials. Taking zeolite as an example, the newly formed zeolite minerals include high-silicon zeolites (clinoptilolite, mordenite, ferrous zeolite) and low-silicon zeolites (chabazite, sodium zeolite, baculite, and hydrocalcium zeolite).

[0077] 2. The second category is the altered mineral assemblage, which is a set of specific mineral paragenesis formed in a specific environment when volcanic debris undergoes secondary changes. Taking chloriteization as an example, intermediate-basic volcanic debris will undergo replacement and alteration under the action of medium- and low-temperature hydrothermal fluids containing carbon dioxide, hydrogen sulfide, etc., forming a set of mineral assemblage composed of chlorite, epidote, quartz, calcite and pyrite.

[0078] It should be noted that the typical altered minerals referred to in this application include but are not limited to zeolites; the altered mineral assemblages referred to in this application include but are not limited to propylitized mineral assemblages.

[0079] In one embodiment, the X-ray diffraction analysis method (XRD) is a method for structural analysis of the spatial distribution of atoms inside a substance using X-ray diffraction formed by crystals. It is the most commonly used and effective method for crystal structure research and phase analysis. The X-ray diffraction analysis method includes the following steps:

[0080] Step 401. Prepare the shale source rock sample according to the standard to obtain a rock sample;

[0081] Step 402: Perform crystallographic analysis and / or phase analysis on the rock sample;

[0082] Among them, the crystallographic analysis refers to determining whether the rock sample contains amorphous silica; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash; the phase analysis refers to determining whether the rock sample contains volcanic alteration products; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash.

[0083] In detail, the amorphous silica refers to the traces left by volcanic glass in mudstone source rocks. Since the volcanic glass condenses quickly after the volcanic eruption and is not fully crystallized, it presents the phase of amorphous silica and can be presented as evidence of volcanic material.

[0084] The volcanic alteration products are consistent with the concept of volcanic alteration products in petrographic analysis methods, and also include typical alteration minerals and alteration mineral assemblages. Considering that shale source rocks are mostly fine-grained, the petrographic analysis conducted subjectively by identification personnel may become very difficult. X-ray diffraction analysis based on data is relatively more objective, and therefore can serve as a powerful supplement to petrographic analysis.

[0085] In one embodiment, the geochemical analysis method comprises the following steps:

[0086] Step 501. Prepare the shale source rock sample according to the standard to obtain a rock sample;

[0087] Step 502: Perform major element analysis and / or trace element analysis on the rock sample;

[0088] Among them, the major element analysis refers to determining whether the major element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, there is no volcanic ash in the rock sample; the trace element analysis refers to determining whether the trace element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, there is no volcanic ash in the rock sample. Usually, the major element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis; the trace element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis.

[0089] Furthermore, the major elements refer to the elements that are in absolute majority in any rock, and are actually the elements with the highest abundance in the crust and the lithospheric mantle, usually including the oxide forms of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P, and sometimes also including H (H2O) and C (CO2), and the sum of these oxides is 100%. The trace elements are elements that are not present as the main chemical components of any phase in the system relative to the major elements of the research system, and it is generally believed that the content of trace elements in natural systems is less than 0.1%.

[0090] In one embodiment, the major element characteristics are judged by comparing the overall chemical composition characteristics, and one or more of SiO2, TiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, CO2, and H2O oxides are compared with existing research data to determine whether the research data is close to shale sedimentary rocks or igneous rocks.

[0091] In one embodiment, the major element characteristics are determined by comparing the relative contents of the oxides, and then judging based on empirical knowledge. For example, the TiO2 / Al2O3 ratio. Previous studies have shown that the TiO2 / Al2O3 ratio of terrigenous clay rock (shale) is usually 0.035-0.05, while the TiO2 / Al2O3 ratio of acidic volcanic ash is usually <0.02; therefore, the TiO2 / Al2O3 ratio can be used as a reference for whether volcanic ash is contained.

[0092] In one embodiment, the trace element characteristics are determined by comparing the abundance values ​​of the trace elements, and then judging by combining empirical knowledge. For example, previous studies have shown that the abundance values ​​of stable trace elements such as Hf, Nb, Ta, Y, Ga, Th, U, and As in clay formed by volcanic ash alteration are higher than those in clay sediments of non-volcanic origin. Therefore, the abundance of these stable trace elements can be used as an important geochemical marker to determine whether shale source rocks contain volcanic ash.

[0093] In one embodiment, the trace element characteristics are determined by comparing the relative contents of trace element pairs, and then judging based on empirical knowledge. For example, previous studies have shown that the ratios of V / Cr and Fe / Mn in volcanic ash layers are generally high, so the ratios of V / Cr and Fe / Mn can also be used as geochemical markers to determine whether shale source rocks contain volcanic ash.

[0094] The identification method of volcanic ash in mud shale source rocks of the present application first obtains a mud shale source rock sample to be identified, then uses petrographic analysis / X-ray diffraction analysis / geochemical analysis methods to analyze the sample, and finally obtains the volcanic ash identification result of the sample based on the above analysis data. The identification method of volcanic ash in mud shale source rocks can accurately identify volcanic ash in high-quality source rocks, and on this basis, deepen the impact of volcanic activity on the development of high-quality source rocks; in general, it can make more accurate judgments on the hydrocarbon generation mechanism and hydrocarbon generation potential of source rocks, and provide more effective technical support for oil and gas exploration.

[0095] Embodiment 2

[0096] Please refer to Figure 1-Figure 5 An embodiment provides a method for identifying volcanic ash in shale source rocks. The following will explain the technical solution of this application with the ideas of the inventor, which will help those skilled in the art to be familiar with the ideas of this application. Among them, some technical points are explained in detail so that those skilled in the art can fully understand the technical solution of this application.

[0097] like Figure 1 The identification method of volcanic ash in shale source rocks includes the following steps:

[0098] Step 1: Obtain the shale source rock sample to be identified;

[0099] Step 2: Analyze the samples using petrographic analysis, X-ray diffraction analysis, and geochemical analysis; petrographic analysis, X-ray diffraction analysis, and geochemical analysis are three methods for determining whether volcanic ash is contained in shale source rock samples;

[0100] Step 3: Based on the above analysis data, obtain the volcanic ash identification result of the sample.

[0101] Explain the logical relationship. Figure 2 The identification method of volcanic ash in shale source rocks includes the following steps:

[0102] Step 201: preparing a sample to be tested; the sample to be tested refers to a shale source rock sample to be identified; wherein the source rock refers to a rock rich in organic matter, which has generated and discharged or is discharging oil and natural gas in geological history; the shale source rock refers to mudstone and shale source rocks, which belong to a large category of common source rocks and are developed in major continental basins in my country such as Songliao, Bohai Bay, Junggar, Qaidam and other basins; and is characterized by being mainly composed of clay minerals, and having an appearance of mostly gray-black, dark gray, gray or gray-green, and may have leaf-like stratification;

[0103] Step 202: petrographic analysis, performing petrographic analysis on the shale source rock sample; specifically, the petrographic analysis is a method of grinding the shale source rock sample into thin slices and placing them under a polarizing microscope to identify the phase composition;

[0104] Step 203: X-ray diffraction analysis, performing X-ray diffraction analysis on the shale source rock sample; wherein the X-ray diffraction analysis (XRD) is a method for structural analysis of the spatial distribution of atoms inside a substance using X-ray diffraction formed by crystals, and is the most commonly used and effective method for crystal structure research and phase analysis;

[0105] Step 204: geochemical analysis, performing geochemical analysis on the shale source rock sample; wherein the geochemical analysis is to perform elemental analysis on the shale source rock sample after standard sample preparation, and includes major element analysis and trace element analysis.

[0106] Among them, the petrographic analysis method in step 202 and the X-ray diffraction analysis method in step 203 can provide direct evidence for the identification of volcanic ash. Specifically, if the petrographic analysis method in step 202 is effective, it is directly determined that the sample contains volcanic ash; if the X-ray diffraction analysis method in step 203 is effective, it is directly determined that the sample contains volcanic ash. It should be noted that there is no priority order between the petrographic analysis method in step 202 and the X-ray diffraction analysis method in step 203. Furthermore, the geochemical analysis method in step 204 can provide indirect evidence for the identification of volcanic ash. Specifically, if the geochemical analysis method in step 204 is effective, it means that there is a certain probability that the sample contains volcanic ash.

[0107] In other words, the logical relationship between the three methods of petrographic analysis in step 202, X-ray diffraction analysis in step 203, and geochemical analysis in step 204 is: if either the petrographic analysis in step 202 or the X-ray diffraction analysis in step 203 is effective, it is directly determined that the sample contains volcanic ash; if neither method is effective, perform geochemical analysis in step 204; if the geochemical analysis method in step 204 is effective, it means that there is a certain probability that the sample contains volcanic ash; if the geochemical analysis method in step 204 is not effective, it means that the sample does not contain volcanic ash.

[0108] Regarding step 202 petrographic analysis, Figure 3 , including the following steps:

[0109] Step 301: Prepare the sample to be tested according to the standard sample preparation method; specifically, prepare the sample to be tested according to the standard process of petrographic analysis and grind it into a rock slice with a thickness of 30 microns;

[0110] Step 302: observe under a polarizing microscope to identify the phase composition of the rock slice; specifically, place the rock slice obtained in step 301 under a polarizing microscope for observation;

[0111] Step 303: pyroclastic material analysis to determine whether the rock slice contains pyroclastic material;

[0112] In step 303, the pyroclastic material refers to the debris of volcanic eruptions, which are traces left in the shale source rocks when they are accumulated (deposited) on land or underwater. The pyroclastic material mainly includes two categories: one is rock debris, crystal debris, glass debris, and the other is volcanic dust. Specifically, the rock debris, crystal debris, and glass debris are relatively large pyroclastic materials, and the phase identification characteristics under a polarizing microscope are as follows:

[0113] 1. Rock debris: refers to the debris of earlier solidified lava, volcanic channel surrounding rocks and volcanic basement rocks, which are mostly angular and irregular in shape;

[0114] 2. Crystal fragments: refers to the phenocrysts precipitated from the magma in the early underground and the minerals in the surrounding rocks of the volcanic channel, mostly quartz, feldspar and other minerals. Because they are shattered and separated from the semi-solidified magma and surrounding rocks during the eruption, they are often angular. Due to the sudden cooling during the eruption, the minerals generally have cracks, and sometimes dissolution can be seen;

[0115] 3. Glass shavings: refers to the semi-solid porous glass formed when the molten magma rich in volatile components and high viscosity is ejected and rapidly cooled. Because the gas in it suddenly expands, it quickly escapes from the pores, explodes and suddenly cools. Therefore, most of them are in the shape of curved edges and torn shapes. A few of them are in the shape of floating rocks because they are not completely broken into pieces.

[0116] The volcanic dust is a relatively small volcanic debris material, generally with a particle size of less than 0.0625 mm. The phase identification characteristics under a polarizing microscope are:

[0117] 1. Volcanic dust: refers to the smallest volcanic debris. From the perspective of physical phase, it is an aggregate of extremely fine particles such as glass fragments and crystal fragments that are difficult to distinguish even under a high-power polarizing microscope. It is very easy to devitrify and form a cryptocrystalline structure during the diagenesis process. Therefore, it can be distinguished by mineral ductility. That is, under a polarizing microscope, while rotating the stage, observe the color change in the direction parallel to the gypsum test board and perpendicular to the gypsum test board. If the color changes, it is not volcanic dust. If the color does not change, it is volcanic dust. Among them, the mineral ductility refers to the relationship between the long direction of the mineral crystal and the long and short radii of the optical body. Since volcanic dust is an aggregate of extremely fine particles, it does not have ductility characteristics under a polarizing microscope;

[0118] Step 304: Analyze volcanic alteration products to determine whether the rock slice contains volcanic alteration products; wherein the volcanic alteration products refer to the traces left in the shale source rock after the volcanic clastic material undergoes secondary changes such as devitrification, hydration, and metasomatic alteration; the volcanic alteration products mainly include two categories: one is typical alteration minerals, and the other is alteration mineral assemblages;

[0119] Among them, the typical altered minerals refer to the alteration products unique to volcanic materials. Taking zeolite as an example, the newly formed zeolite minerals include high-silicon zeolites (clinoptilolite, mordenite, magnesia zeolite) and low-silicon zeolites (chabazite, sodium zeolite, baculite, and hydrocalcium zeolite); the so-called altered mineral assemblage refers to a set of specific mineral symbiotic assemblages formed in a specific environment when volcanic debris undergoes secondary changes. Taking chloridization as an example, intermediate-basic pyroclastic rocks will undergo replacement alteration under the action of medium- and low-temperature hydrothermal fluids containing carbon dioxide, hydrogen sulfide, etc., forming a set of mineral assemblages composed of chlorite, epidote, quartz, calcite and pyrite. It should be noted that the typical altered minerals referred to in this application include but are not limited to zeolites; the altered mineral assemblage referred to in this application includes but is not limited to chloridization mineral assemblage.

[0120] Among them, the specific logical relationship of petrographic analysis is:

[0121] 1. In step 303, if volcanic debris such as rock fragments, crystal fragments, glass fragments or volcanic dust can be observed under a polarizing microscope, it is directly determined that the sample contains volcanic ash;

[0122] 2. In step 303, if no volcanic debris such as rock debris, crystal debris, glass debris or volcanic dust is observed under the polarizing microscope, it is considered that the sample does not contain volcanic ash;

[0123] 3. In step 304, if volcanic alteration products such as typical altered minerals or altered mineral combinations can be observed under a polarizing microscope, it is directly determined that the sample contains volcanic ash;

[0124] 4. In step 304, if no volcanic alteration products such as typical alteration minerals or alteration mineral assemblages are observed under the polarizing microscope, it is considered that the sample does not contain volcanic ash.

[0125] Regarding step 203X diffraction analysis, Figure 4 , including the following steps:

[0126] Step 401: preparing the sample to be tested according to the standard; specifically, preparing the sample to be tested according to the standard process of X-ray diffraction analysis;

[0127] Step 402: X-ray diffraction analysis, performing X-ray diffraction analysis on the rock sample obtained in step 401; including two types of analysis: one refers to crystallographic analysis 403, and the other refers to phase analysis 404;

[0128] Step 403: The crystallographic analysis refers to determining whether the rock sample contains amorphous silicon dioxide; specifically, the amorphous silicon dioxide refers to the traces left by volcanic glass in shale source rocks. Since volcanic glass condenses quickly after the volcanic eruption and is not fully crystallized, it presents the phase of amorphous silicon dioxide, and can be presented as volcanic material evidence;

[0129] Step 404: The phase analysis refers to determining whether the rock sample contains volcanic alteration products; specifically, the volcanic alteration products are consistent with the concept of volcanic alteration products in step 304, and also include typical alteration minerals and alteration mineral combinations. Considering that the shale source rocks are mostly fine-grained, the petrographic analysis conducted subjectively by the identification personnel may become very difficult, while the data-based X-ray diffraction analysis is relatively more objective, and therefore can serve as a powerful supplement to the petrographic analysis.

[0130] Among them, the specific logical relationship of X-ray diffraction analysis is:

[0131] 1. In step 403, if the result of the crystallographic analysis shows that amorphous silicon dioxide is contained, it is directly determined that the sample contains volcanic ash;

[0132] 2. In step 403, if the result of the crystallographic analysis does not show amorphous silicon dioxide, it is considered that the sample does not contain volcanic ash;

[0133] 3. In the phase analysis of step 404, if the result shows volcanic alteration products such as typical alteration minerals or alteration mineral combinations, it is directly determined that the sample contains volcanic ash;

[0134] 4. In the phase analysis of step 404, if the result shows that there are no volcanic alteration products such as typical alteration minerals or alteration mineral combinations, it is considered that the sample does not contain volcanic ash.

[0135] Regarding the geochemical analysis in step 204, Figure 5 , including the following steps:

[0136] Step 501: Prepare the sample to be tested according to the standard sample preparation method; specifically, prepare the sample to be tested according to the standard process of geochemical analysis;

[0137] Step 502: performing element analysis on the rock sample obtained in step 401; the element analysis includes two types of analysis: one refers to the major element analysis in step 503, and the other refers to the trace element analysis in step 504;

[0138] Step 503: The major element analysis refers to determining whether the major element characteristics of the rock sample are consistent with those of volcanic ash; specifically, the major elements refer to the elements that are in absolute majority in any rock, and are actually the elements with the highest abundance in the crust and the lithospheric mantle, and usually include the oxide forms of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P, and sometimes also include H (H2O) and C (CO2), and the sum of the oxides of these elements is 100%; wherein the major element analysis method includes, but is not limited to, methods such as X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS), etc.;

[0139] Furthermore, to determine whether the major element characteristics are consistent with volcanic ash, it is mainly because the chemical stability and closure of volcanic debris during the sedimentary diagenesis process can effectively preserve the elemental geochemical characteristics of the original rock magma. Therefore, the major element characteristics of volcanic ash alteration and normal sedimentary shale source rocks are significantly different to determine whether the shale source rocks contain volcanic ash. Specifically, there are two ways to determine the major element characteristics. The first method is to compare the chemical composition characteristics as a whole, namely SiO2, TiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, N The specific contents of oxides such as a2O, K2O, P2O5, CO2, and H2O are compared with the research data of previous studies to determine whether they are closer to mudstone sedimentary rocks or igneous rocks. The second method is to compare the relative contents of certain oxides and then make judgments based on empirical knowledge, such as the TiO2 / Al2O3 ratio. Previous studies have shown that the TiO2 / Al2O3 ratio of terrigenous clay rocks (shale) is usually 0.035-0.05, while the TiO2 / Al2O3 ratio of acidic volcanic ash is usually <0.02. Therefore, the TiO2 / Al2O3 ratio can be used as a reference for whether volcanic ash is present.

[0140] Step 504: The trace element analysis refers to determining whether the trace element characteristics of the rock sample are consistent with volcanic ash; specifically, the trace element is an element that is not present as the main chemical component of any phase in the system relative to the major element of the research system, and it is generally believed that the content of trace elements in natural systems is less than 0.1%; wherein, the trace element analysis method includes but is not limited to X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS) and other methods;

[0141] Furthermore, the determination of whether the trace element characteristics are consistent with volcanic ash is mainly based on the consideration that some trace elements such as Nb, Ta, Th, Hf, Y, Ga, Ti, Cr, Co, Ni, etc. are very stable in altered and surface environments, with a small range of variation. Therefore, the trace element characteristics of volcanic ash alteration and normal sedimentary shale source rocks are significantly different to determine whether the shale source rocks contain volcanic ash. Specifically, the determination of trace element characteristics can be carried out in two ways. The first method is to compare the abundance values ​​of certain trace elements, and then combine them with empirical knowledge to make a judgment. For example, previous studies have shown that the trace element characteristics of volcanic ash alteration and normal sedimentary shale source rocks are significantly different to determine whether the shale source rocks contain volcanic ash. The clay formed by ash alteration has higher abundance values ​​of stable trace elements such as Hf, Nb, Ta, Y, Ga, Th, U, and As than clay sediments of non-volcanic origin. Therefore, the abundance of these stable trace elements can be used as an important geochemical marker to determine whether shale source rocks contain volcanic ash. The second method is to compare the relative contents of certain element pairs and then make a judgment based on empirical knowledge. For example, previous studies have shown that the V / Cr and Fe / Mn ratios in volcanic ash layers are generally high. Therefore, the V / Cr and Fe / Mn ratios can also be used as geochemical markers to determine whether shale source rocks contain volcanic ash.

[0142] Among them, the specific logical relationship of geochemical analysis is:

[0143] 1. In step 503, if the result of the major element analysis shows that the major element characteristics of volcanic ash are met, it is directly determined that the sample contains volcanic ash;

[0144] 2. In step 503, if the result of the major element analysis indicates that the sample does not conform to the major element characteristics of volcanic ash, it is considered that the sample does not contain volcanic ash;

[0145] 3. In step 504, if the result of the trace element analysis shows that the sample meets the trace element characteristics of volcanic ash, it is directly determined that the sample contains volcanic ash;

[0146] 4. In step 504, if the results of the trace element analysis indicate that the sample does not conform to the trace element characteristics of volcanic ash, it is considered that the sample does not contain volcanic ash.

[0147] It is important to note that, considering that rock samples generally have strong heterogeneity, if they contain volcanic ash, the distribution and content characteristics of the volcanic ash are also likely to be heterogeneous. Therefore, in step 202 petrographic analysis, step 203 X-ray diffraction analysis, and step 204 geochemical analysis, the sample to be tested is prepared according to the standard, which needs to be comprehensively determined in combination with the specific state of the sample and different analysis purposes.

[0148] The method for identifying volcanic ash in mud shale source rocks of the present application first obtains a mud shale source rock sample to be identified, then uses petrographic analysis / X-diffraction analysis / geochemical analysis methods to analyze the sample, and finally obtains the volcanic ash identification result of the sample based on the above analysis data. This method can be used to accurately identify volcanic ash in high-quality source rocks, and on this basis, deepen the impact of volcanic activity on the development of high-quality source rocks. Overall, a more accurate judgment can be made on the hydrocarbon generation mechanism and hydrocarbon generation potential of the source rock, and more effective technical support can be provided for oil and gas exploration. In general, the method for identifying volcanic ash in mud shale source rocks of the present application has a simple process, is highly operable and extensible, and solves the current problem of identifying volcanic ash in mud shale source rocks.

[0149] Embodiment 3

[0150] A shale source rock sample A is selected, and the volcanic ash identification method in shale source rock in Example 1 and Example 2 is used to identify whether it contains volcanic ash. The specific steps are as follows:

[0151] 1. Prepare the sample A according to the standard process of petrographic analysis and grind it into a rock slice with a thickness of 30 microns;

[0152] According to the steps of sampling - gluing - grinding (coarse grinding - medium grinding - fine grinding - fine grinding) - sticking - grinding (coarse grinding - fine grinding - fine grinding) - cover slice, ordinary rock slices are made, with a standard thickness of 30μ. The specific production process can refer to the industry standard SY-T 5913-2004 "Rock slice preparation method";

[0153] 2. Under a polarizing microscope, use single polarized light and orthogonal polarized transmitted light to identify the phase composition of the rock thin section;

[0154] Observation 1: Preliminary observation under 2.5X and 5X objective lenses showed that the sample was silt-bearing mudstone. However, careful observation under 10X objective lens revealed that the sample contained volcanic debris - glass fragments, which were in the shape of arc polygons and chicken bones, and were strongly altered and residual. Brown volcanic ash was visible on the surface ( Figure 6 );

[0155] Observation 2: Careful observation under 10x and 20x objective lenses revealed that volcanic dust was partially visible in the sample, with a particle size of less than 0.0625 mm, dark color, poor optical properties, and devitrification. Under orthogonal polarization + gypsum test plate, when the stage was rotated, some clay minerals in the thin section were observed to have blue and orange interference color changes in the direction parallel to and perpendicular to the gypsum test plate, but the color of the volcanic dust part did not change;

[0156] 3. Based on the above observations, it can be determined that the sample contains volcanic ash.

[0157] Embodiment 4

[0158] A shale source rock sample B is selected, and the volcanic ash identification method in shale source rock in Example 1 and Example 2 is used to identify whether it contains volcanic ash. The specific steps are as follows:

[0159] 1. Prepare the sample B according to the standard process of petrographic analysis and grind it into a rock slice with a thickness of 30 microns;

[0160] According to the steps of sampling - gluing - grinding (coarse grinding - medium grinding - fine grinding - fine grinding) - sticking - grinding (coarse grinding - fine grinding - fine grinding) - cover slice, ordinary rock slices are made, with a standard thickness of 30μ. The specific production process can refer to the industry standard SY-T 5913-2004 "Rock slice preparation method";

[0161] 2. Under a polarizing microscope, use single polarized light and orthogonal polarized transmitted light to identify the phase composition of the rock thin section;

[0162] Observation 1: No rock fragments, crystal fragments, glass fragments, or volcanic dust or other pyroclastic material was found in the sample;

[0163] Observation 2: No typical volcanic alteration minerals or obvious alteration mineral assemblages were found in this sample;

[0164] 3. Continue to prepare the sample according to the standard process of X-ray diffraction analysis and perform X-ray diffraction analysis;

[0165] 4. X-ray diffraction crystallographic analysis showed that the sample did not contain amorphous silicon dioxide;

[0166] 5. X-ray diffraction phase analysis shows that the sample is mainly composed of clay, quartz, potassium feldspar, plagioclase, calcite, dolomite, siderite, and contains varying amounts of microcrystalline gypsum, pyroxene and zeolite (Table 1, Figure 7 );

[0167] 6. Comprehensive analysis of the above observations shows that the sample contains volcanic ash.

[0168] Table 1 X-ray diffraction component content of shale source rock sample B

[0169]

[0170] Embodiment 5

[0171] The sampling point is a Late Permian section sample in a basin, and the bottom of the Dalong Formation of the section was sampled layer by layer. In addition, since it is suspected that there are traces of volcanic ash at the PT boundary, four key sampling points of the shale source rock at the PT boundary were carried out, namely C1, C2, C3, and C4.

[0172] The four shale source rock samples C1, C2, C3, and C4 were selected, and the volcanic ash identification method in shale source rock in Example 1 and Example 2 was used to identify whether they contained volcanic ash. The specific steps are as follows:

[0173] 1. Prepare the samples C1, C2, C3 and C4 according to the standard process of petrographic analysis and grind them into rock slices with a thickness of 30 microns;

[0174] 2. Under a polarizing microscope, using single polarized light and orthogonal polarized transmitted light illumination, the phase composition of four rock thin sections was identified;

[0175] Observation 1: No rock fragments, crystal fragments, glass fragments, or volcanic dust or other pyroclastic materials were found in any of the four samples;

[0176] Observation 2: No typical volcanic alteration minerals or obvious alteration mineral assemblages were found in any of the four samples;

[0177] 3. Continue to prepare samples of C1, C2, C3 and C4 according to the standard process of X-ray diffraction analysis, and perform X-ray diffraction analysis;

[0178] X-ray diffraction analysis results 1: None of the four samples contained amorphous silicon dioxide;

[0179] X-ray diffraction analysis result 2: none of the four samples contained volcanic alteration materials;

[0180] 4. Continue to prepare samples of the four samples C1, C2, C3, and C4 according to the standard process of geochemical analysis, and perform geochemical analysis; in which, considering the need for comparison, this embodiment also prepares samples of batches of samples taken layer by layer from the bottom of the Dalong Formation according to the standard process of geochemical analysis, and performs geochemical analysis at the same time;

[0181] Taking into account the sample state, the geological background of the study area, and the research results of previous researchers on the area, the geochemical analysis adopted in this embodiment includes major element analysis and trace element analysis, and finally only some major element and trace element analysis results are selected for comparative study;

[0182] Specifically, Cr and Co, TiO2 and V in all sample data were selected for geochemical mapping. The results show that the distribution areas of the data points of three samples C1, C2 and C3 in the shale source rock layer of the PT boundary are significantly different from the normal sedimentary samples sampled layer by layer at the bottom of the Dalong Formation. The three samples C1, C2 and C3 of the PT boundary have low Cr content and high TiO2 content ( Figure 8 );

[0183] 5. Comprehensive analysis of the above results shows that there is a certain probability that samples C1, C2, and C3 contain volcanic ash. Therefore, there is a certain probability that there are traces of volcanic ash at the PT boundary of the profile.

[0184] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for identifying volcanic ash in shale source rocks, characterized in that: The following steps are involved: Step 1. Obtain a shale source rock sample to be identified; Step 2. Analyze the shale source rock sample using one or more of a petrographic analysis method, an X-ray diffraction analysis method, and a geochemical analysis method; Step 3. Based on the analysis data of step 2, identify the volcanic ash in the shale source rock sample.

2. The method for identifying volcanic ash in shale source rocks according to claim 1, characterized in that: If volcanic ash is identified by any one of the petrographic analysis method and the X-ray diffraction analysis method, it is directly determined that the shale source rock sample contains volcanic ash; If neither the petrographic analysis method nor the X-ray diffraction analysis method identifies volcanic ash, the geochemical analysis method is performed; wherein, if the geochemical analysis method identifies volcanic ash, it means that there is a probability that the mud shale source rock sample contains volcanic ash; if the geochemical analysis method does not identify volcanic ash, it means that the mud shale source rock sample does not contain volcanic ash.

3. The method for identifying volcanic ash in shale source rocks according to claim 1, characterized in that: The petrographic analysis method comprises the following steps: Step 301. Prepare the shale source rock sample according to standard sample preparation to obtain rock thin sections; Step 302: Place the rock slice under a polarizing microscope for observation to identify the physical phase composition; the physical phase composition identification includes volcanic debris material analysis and / or volcanic alteration material analysis; The pyroclastic material analysis refers to determining whether the rock slice contains pyroclastic material; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash; The volcanic alteration analysis refers to determining whether the rock slice contains volcanic alteration; if so, the rock slice contains volcanic ash; if not, the rock slice does not contain volcanic ash.

4. The method for identifying volcanic ash in shale source rocks according to claim 3, characterized in that: The pyroclastic materials include two categories: The first category is relatively large pyroclastic material, including one or more of rock fragments, crystal fragments, and glass fragments; The second category is relatively small pyroclastic material, including volcanic dust.

5. The method for identifying volcanic ash in shale source rocks according to claim 1, characterized in that: The X-ray diffraction analysis method comprises the following steps: Step 401. Prepare the shale source rock sample according to the standard to obtain a rock sample; Step 402: Performing crystallographic analysis and / or phase analysis on the rock sample; The crystallographic analysis refers to determining whether amorphous silicon dioxide is contained in the rock sample; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash; The phase analysis refers to determining whether the rock sample contains volcanic alteration products; if so, the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash.

6. The method for identifying volcanic ash in shale source rocks according to any one of claims 3 to 5, characterized in that: The volcanic alteration materials include two categories: The first category is typical alteration minerals, which are the alteration products unique to volcanic materials; The second category is the altered mineral assemblage, which is a set of specific mineral paragenesis formed in a specific environment when volcanic debris undergoes secondary changes.

7. The method for identifying volcanic ash in shale source rocks according to claim 1, characterized in that: The geochemical analysis method comprises the following steps: Step 501. Prepare the shale source rock sample according to the standard to obtain a rock sample; Step 502: Perform major element analysis and / or trace element analysis on the rock sample; The major element analysis refers to determining whether the major element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, there is no volcanic ash in the rock sample; The trace element analysis refers to determining whether the trace element characteristics of the rock sample are consistent with volcanic ash; if so, there is a probability that the rock sample contains volcanic ash; if not, the rock sample does not contain volcanic ash.

8. The method for identifying volcanic ash in shale source rocks according to claim 7, characterized in that: Determine that the major element characteristics are overall comparative chemical composition characteristics, compare one or more of SiO2, TiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, CO2, H2O oxides with existing research data, and determine whether the research data is close to shale sedimentary rocks or igneous rocks; and / or, The main element characteristics are determined by comparing the relative contents of the oxides and then making a judgment based on empirical knowledge.

9. The method for identifying volcanic ash in shale source rocks according to claim 7, characterized in that: Determining the trace element characteristics is to compare the abundance values ​​of the trace elements and then make a judgment based on empirical knowledge; and / or, The trace element characteristics are determined by comparing the relative contents of trace element pairs and then making a judgment based on empirical knowledge.

10. The method for identifying volcanic ash in shale source rocks according to any one of claims 7 to 9, characterized in that: The major element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis; The trace element analysis includes X-ray fluorescence spectrometry analysis or plasma mass spectrometry analysis.

Images