A method for quantitatively calculating the contribution ratio of source rocks using trace elements

Abstract

An embodiment of the present invention provides a method for quantitatively calculating the contribution ratio of source rocks using trace elements, comprising: collecting a crude oil sample, obtaining the content of preset trace elements in the crude oil sample, calculating a first ratio between the preset trace element contents in the crude oil sample, and finding data points corresponding to the first ratio between the preset trace element contents in the crude oil sample in a pre-generated identification index map; the identification index map uses the first ratio between the preset trace element contents as a coordinate axis and includes an area corresponding to at least one type of major source rock; the major source rock type corresponding to the area of ​​the identification index map where the data points corresponding to the crude oil sample are distributed is used as the major source rock type of the oil reservoir, and the contribution ratio of each major source rock in the oil reservoir is quantitatively calculated. This method establishes an identification index map, which can quickly identify the type of major source rock in the oil reservoir and quantitatively calculate the contribution of different types of major source rocks.

Description

Technical Field

[0001] The present invention relates to the field of geological exploration, and in particular to a method for quantitatively calculating the contribution ratio of source rocks using trace elements. Background Art

[0002] Conventional oil-source correlation is primarily based on organic geochemistry, particularly biomarker compounds and organic carbon and hydrogen isotopes. However, with the continued advancement of oil and gas exploration, oil and gas accumulation patterns are becoming increasingly complex. Factors such as high- to overmature organic matter evolution, secondary degradation, and multi-stage and multi-source mixing can cause common organic geochemical indicators to vary non-monotonically, or even become ineffective. Summary of the Invention

[0003] In view of the above problems, the present invention is proposed to provide a method for quantitatively calculating the contribution ratio of source rocks using trace elements, which overcomes the above problems or at least partially solves the above problems.

[0004] In one aspect, an embodiment of the present invention provides a method for quantitatively calculating the contribution ratio of source rocks using trace elements, comprising:

[0005] For each pre-determined reservoir, multiple crude oil samples were collected;

[0006] Obtain the content of preset trace elements in each crude oil sample from each reservoir;

[0007] Calculating a first ratio between preset trace element contents in the crude oil samples according to the preset trace element contents in each crude oil sample of each oil reservoir;

[0008] For each oil reservoir, based on a first ratio between preset trace element contents in each crude oil sample, a data point corresponding to each crude oil sample is found in a pre-generated identification index plate corresponding to the oil reservoir; the identification index plate has the first ratio between preset trace element contents as a coordinate axis and includes an area corresponding to at least one type of major hydrocarbon source rock;

[0009] Determining the main source rock type corresponding to the area where the data points corresponding to the crude oil sample are distributed from the identification index plate corresponding to each oil reservoir, and using the determined main source rock type as the main source rock type of the oil reservoir;

[0010] According to the first ratio between the preset trace element contents of each oil reservoir and the main source rock type of the oil reservoir, the contribution ratio of each main source rock in the oil reservoir is quantitatively calculated.

[0011] In one embodiment, the pre-generated identification indicator chart is generated in the following manner:

[0012] Determining the dimension of the coordinate system in the identification index plate according to the number of the preset first ratio types between the trace element contents, and establishing the identification index coordinate system with each preset first ratio between the trace element contents as the coordinate axis in the identification index plate;

[0013] According to the first ratio between the preset trace element contents in the plurality of source rock samples of each oil reservoir obtained in advance, finding a data point corresponding to each source rock sample in the identification index coordinate system;

[0014] According to the distribution areas of the data points corresponding to all source rock samples, the areas corresponding to different types of main source rocks are divided in the identification index coordinate system.

[0015] In one embodiment, the first ratio between the preset trace element contents in the plurality of source rock samples of each oil reservoir obtained in advance is obtained by:

[0016] For each reservoir, multiple source rock samples were collected;

[0017] For each reservoir, all source rock samples are dissolved and a preset weight of internal standard element is added to obtain a source rock sample solution corresponding to each source rock sample;

[0018] Determine the content of preset trace elements and internal standard elements in each source rock sample solution of each reservoir;

[0019] calculating a second ratio of the content of the internal standard element in each source rock sample solution to a preset weight of the internal standard element;

[0020] Calculating the preset trace element content in the source rock sample based on the second ratio and the preset trace element content in each source rock sample solution of each oil reservoir;

[0021] According to the preset trace element contents in each source rock sample of each oil reservoir, a first ratio between the preset trace element contents is calculated.

[0022] In one embodiment, dissolving all source rock samples for each oil reservoir to obtain a source rock sample solution corresponding to each source rock sample includes:

[0023] The source rock sample is placed in a sealed sample dissolution device, and an appropriate amount of hydrofluoric acid and an appropriate amount of nitric acid are added to obtain a source rock sample stock solution;

[0024] heating the source rock sample solution and evaporating it to dryness, then adding an appropriate amount of nitric acid and evaporating it to dryness to obtain a residue;

[0025] adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the source rock sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element;

[0026] The residue solution is diluted with an appropriate amount of deionized water to obtain the source rock sample solution.

[0027] In one embodiment, determining the content of predetermined trace elements in each source rock sample solution of each oil reservoir includes:

[0028] The source rock sample solution is placed in an inductively coupled plasma mass spectrometer to obtain the content of the trace elements and the content of the internal standard elements.

[0029] In one embodiment, between the steps of collecting the source rock sample and dissolving the source rock sample, the method further comprises:

[0030] The source rock sample is crushed to obtain a crushed source rock sample.

[0031] In one embodiment, the quantitative calculation of the contribution ratio of each major source rock in the oil reservoir based on the first ratio between the preset trace element contents of each oil reservoir and the major source rock type of the oil reservoir includes:

[0032] For each oil reservoir, a characteristic value of a first ratio of trace element contents preset in a crude oil sample that can represent the characteristics of the source rock of the oil reservoir is calculated; based on the identification index plate, the first ratio of trace element contents preset in all main source rock samples of each oil reservoir is obtained, and the characteristic value of the first ratio of trace element contents preset in each type of main source rock in multiple types of main source rock samples of each oil reservoir is calculated;

[0033] According to the main source rock type of each reservoir, determine the calculation formula for quantitatively calculating the contribution ratio of source rock in the reservoir;

[0034] The characteristic value of the first ratio of the trace element content preset in the crude oil sample of each oil reservoir and the characteristic value of the first ratio of the trace element content preset in each type of main hydrocarbon source rock are input into the calculation formula to quantitatively calculate the contribution ratio of each type of main hydrocarbon source rock in the oil reservoir.

[0035] In one embodiment, obtaining the content of predetermined trace elements in each crude oil sample of each oil reservoir includes:

[0036] For each oil reservoir, all crude oil samples were dissolved and a preset weight of internal standard element was added to obtain a crude oil sample solution corresponding to each crude oil sample;

[0037] Determine the content of preset trace elements and internal standard elements in each crude oil sample solution from each reservoir;

[0038] calculating a second ratio of the content of the internal standard element in each crude oil sample solution to a preset weight of the internal standard element;

[0039] The content of the preset trace elements in the crude oil sample is calculated based on the second ratio and the content of the preset trace elements in each crude oil sample of each oil reservoir.

[0040] In one embodiment, for each oil reservoir, dissolving all crude oil samples and adding a preset weight of an internal standard element to obtain a crude oil sample solution corresponding to each crude oil sample includes:

[0041] The crude oil sample is placed in a sealed sample dissolving device, and an appropriate amount of hydrofluoric acid and an appropriate amount of nitric acid are added to obtain a crude oil sample stock solution;

[0042] heating the crude oil sample solution and evaporating it to dryness, then adding an appropriate amount of nitric acid and evaporating it to dryness to obtain a residue;

[0043] adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the crude oil sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element;

[0044] The residue solution was diluted with an appropriate amount of deionized water to obtain a crude oil sample solution.

[0045] In one embodiment, the determination of the content of predetermined trace elements and the content of internal standard elements in each crude oil sample solution of each oil reservoir includes:

[0046] The crude oil sample solution is placed in an inductively coupled plasma mass spectrometer to obtain the content of the trace elements and the content of the internal standard element.

[0047] In one embodiment, the characteristic value is an average value.

[0048] In one embodiment, the preset trace elements include at least two of the following: molybdenum, thorium, vanadium and nickel;

[0049] Correspondingly, the first ratio between the trace element contents is: the molybdenum content divided by the thorium content, and / or the vanadium content divided by the sum of the vanadium content and the nickel content.

[0050] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0051] An embodiment of the present invention provides a method for quantitatively calculating the contribution ratio of source rocks using trace elements, comprising: collecting crude oil samples for each oil reservoir; obtaining the content of trace elements in the crude oil samples of each oil reservoir; calculating a first ratio between the trace element contents in the crude oil samples based on the content of trace elements in the crude oil samples of each oil reservoir; for each oil reservoir, finding data points corresponding to the crude oil samples in a pre-generated identification index plate corresponding to the oil reservoir based on the first ratio between the trace element contents in the crude oil samples; the identification index plate includes an area corresponding to at least one type of main source rock; determining the main source rock type corresponding to the area in the identification index plate where the data points corresponding to the crude oil samples are distributed as the main source rock type of the oil reservoir; and quantitatively calculating the contribution ratio of each main source rock in the oil reservoir based on the first ratio between the preset trace element contents of each oil reservoir and the main source rock type of the oil reservoir.

[0052] Since the composition of trace elements in crude oil records the genetic information of the parent rock and is not easily changed by oil and gas migration, biodegradation, and reservoir destruction, this method is applicable to scenarios of oil source tracing and comparison under conditions of high-overmaturity or secondary degradation, multi-source mixing, etc.; this method is based on the analysis of trace element content in crude oil samples. The testing method is mature, the analysis cycle is short, and the testing price is significantly lower than traditional biomarker compounds, organic carbon and hydrogen isotopes, and traditional and non-traditional metal isotopes such as strontium and chromium, making it easier to promote.

[0053] This method establishes a new index system based on trace element content for oil-source correlation and quantitatively calculates the contribution ratio of different source rocks in the reservoir. Based on the systematic determination of trace element content in crude oil, a trace element ratio index system is established, which can quickly identify the source and genesis of oil and gas and quantitatively calculate the contribution of different types of main source rocks, providing a basis for the study of oil and gas accumulation process and providing technical and theoretical guidance for oil and gas zone evaluation and well location optimization.

[0054] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0055] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0057] Figure 1A flow chart of a method for quantitatively calculating the contribution ratio of source rocks using trace elements provided in an embodiment of the present invention;

[0058] Figure 2 This is a Mo / Th-V / (V+Ni) identification index chart for marine crude oil-source rock in a certain area of ​​a basin provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0060] The embodiment of the present invention provides a method for quantitatively calculating the contribution ratio of source rocks using trace elements, and the flow chart thereof is as follows: Figure 1 As shown, including:

[0061] S11. For each pre-set oil reservoir, multiple crude oil samples are collected;

[0062] S12. Obtaining the content of preset trace elements in each crude oil sample of each oil reservoir;

[0063] S13. Calculating a first ratio between preset trace element contents in the crude oil samples based on the preset trace element contents in each crude oil sample of each oil reservoir;

[0064] S14. For each oil reservoir, based on a preset first ratio between trace element contents in each crude oil sample, find a data point corresponding to each crude oil sample in a pre-generated identification index chart corresponding to the oil reservoir; the identification index chart has the preset first ratio between trace element contents as a coordinate axis and includes an area corresponding to at least one type of major hydrocarbon source rock;

[0065] S15. Determine the main source rock type corresponding to the area where the data points corresponding to the crude oil sample are distributed from the identification index plate corresponding to each oil reservoir, and use the determined main source rock type as the main source rock type of the oil reservoir;

[0066] S16. Quantitatively calculate the contribution ratio of each major source rock in the oil reservoir based on the first ratio between the preset trace element contents of each oil reservoir and the major source rock type of the oil reservoir.

[0067] In step S11, for example, the entire oil field can be used as the preset oil reservoir, and the sampling locations of the crude oil samples are distributed throughout the oil field; or the different oil reservoirs divided into the entire oil field can be used as the preset oil reservoirs, and the sampling locations of the crude oil samples are limited to a single oil reservoir.

[0068] Crude oil samples can be collected, for example, from the wellhead of a normal production well in the oil field, a separator sampling location, or other sampling locations; and in order to make the collected multiple crude oil samples better represent the oil reservoir in which they are located, crude oil samples of different maturity and density can be collected.

[0069] In the above step S12, the preset trace elements may be, for example, elements that are sensitive to the deposition environment, such as non-metallic elements (e.g., boron B, arsenic As, and selenium Se), alkali metal elements (e.g., lithium Li, rubidium Rb, and cesium Cs), alkaline earth metal elements (e.g., beryllium Be, strontium Sr, and barium Ba), transition metal elements (e.g., molybdenum Mo, nickel Ni, vanadium V, and thorium Th), and amphoteric metal elements (e.g., gallium Ga, tin Sn, and lead Pb).

[0070] Nonmetallic elements are those with four or more electrons in their outer shells, making them susceptible to electron acquisition and often existing as anions in ionic compounds. Alkali metals are the six metallic elements in Group IA of the periodic table, excluding hydrogen (H), namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkaline earth elements are those in Group IIA of the periodic table. Transition metals are a series of metallic elements in the d-block and ds-block of the periodic table (the d-block includes elements in Groups IIIB through VIIB and VIII, excluding the lanthanides and actinides; the ds-block includes elements in Groups IB through IIB), also known as transition metals. Amphoteric metals, also known as metalloids or metalloids, are elements with chemical properties intermediate between those of metals and nonmetals. These elements typically exhibit the characteristics of metals, but their chemical properties combine those of both metals and nonmetals. Their oxides and hydroxides typically react with both acids and bases.

[0071] The preset trace element content in each crude oil sample of each reservoir can be obtained, for example, by the following method:

[0072] For each reservoir, all crude oil samples are dissolved and a preset weight of an internal standard element is added to obtain a crude oil sample solution corresponding to each crude oil sample. An internal standard element is an element added during analysis to correct for errors in the analysis. For example, an element that is insensitive to redox reactions, such as rhodium (Rh), can be selected as the internal standard element.

[0073] Determine the content of preset trace elements and internal standard elements in each crude oil sample solution from each reservoir;

[0074] calculating a second ratio of the content of the internal standard element in each crude oil sample solution to a preset weight of the internal standard element;

[0075] The content of the preset trace elements in the crude oil sample is calculated based on the second ratio and the content of the preset trace elements in each crude oil sample of each oil reservoir.

[0076] The aforementioned first ratio and second ratio are only used to distinguish the two ratios and do not have any real meaning.

[0077] For each oil reservoir, all crude oil samples are dissolved and a preset weight of internal standard element is added to obtain a crude oil sample solution corresponding to each crude oil sample. For example, the steps can be as follows:

[0078] Put the crude oil sample into a sealed sample dissolving device, add appropriate amount of hydrofluoric acid and appropriate amount of nitric acid to obtain the crude oil sample stock solution;

[0079] The crude oil sample solution is heated and evaporated to dryness, and then an appropriate amount of nitric acid is added and evaporated to dryness to obtain a residue;

[0080] adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the crude oil sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element;

[0081] The residue solution was diluted with an appropriate amount of deionized water to obtain a crude oil sample solution.

[0082] If the trace element content in the source rock sample or crude oil sample is low in the aforementioned dilution step, resulting in a low content of the preset trace elements in the residual solution, thereby affecting the accuracy of subsequent measurements of the crude oil sample solution, the method of simply reducing the amount of diluent added can be adopted, or the method of weighing the sample multiple times, repeating the above-mentioned dissolution and evaporation process, and then putting the residues together for re-dissolution and dilution, while also reducing the amount of diluent added.

[0083] In one embodiment, the content of preset trace elements and the content of internal standard elements can be determined. For example, an inductively coupled plasma mass spectrometer can be used, where the crude oil sample solution is placed in an inductively coupled plasma mass spectrometer to obtain the content of the trace elements and the content of the internal standard elements. Alternatively, the content of the trace elements and the content of the internal standard elements can be obtained by any other existing method for obtaining the content of elements in a solution. This embodiment of the present invention is not limited to this.

[0084] For the aforementioned step S13, if the preset trace elements are: molybdenum (Mo), nickel (Ni), vanadium (V), and thorium (Th), then the first ratio between the preset trace element contents may be, for example, the molybdenum content divided by the thorium content (Mo / Th), and / or the vanadium content divided by the sum of the vanadium content and the nickel content, that is, and / or, V / (V+Ni).

[0085] The embodiments of the present invention establish for the first time the Mo / Th index, wherein the Mo element is sensitive to redox reactions and the Th element is insensitive to redox environments; and establish the V / (V+Ni) index, wherein the V element is sensitive to sulfidation reactions and the Ni element is insensitive to sulfidation reactions; based on the ratio between sensitive and insensitive elements, not only can crude oils generated from terrestrial and marine source rocks be effectively distinguished, but crude oils produced in sulfidation environments, ironification environments, and conventional strong reducing environments in marine strong reducing environments can also be identified.

[0086] In one embodiment, in the aforementioned step S14, the pre-generated identification indicator chart can be generated, for example, in the following manner:

[0087] Determining the dimension of the coordinate system in the identification index plate based on the number of preset first ratio types between the trace element contents, and establishing the identification index coordinate system using the preset first ratios between the trace element contents as coordinate axes in the identification index plate;

[0088] Finding a data point corresponding to each source rock sample in the identification index coordinate system based on a first ratio of preset trace element contents in a plurality of source rock samples of each oil reservoir obtained in advance;

[0089] According to the distribution area of ​​the data points corresponding to all source rock samples, the areas corresponding to different types of main source rocks are divided in the identification index coordinate system. For example, Figure 2 As shown, in order to facilitate the distinction of four different types of source rocks, in this example, the four different types of source rocks are respectively called black mud shale A, muddy limestone B, black mud shale C and black mud shale D. Figure 2 The area where the red data points are distributed is the area corresponding to the black mudstone A, the area where the purple data points are distributed is the area where the mudstone limestone B is distributed, the area where the blue data points are distributed is the area corresponding to the black mudstone C, and the area where the green data points are distributed is the area corresponding to the black mudstone D.

[0090] Specifically, the first ratio between the preset trace element contents in the plurality of source rock samples of each reservoir obtained in advance is obtained by:

[0091] For each reservoir, multiple source rock samples are collected; for each reservoir, all source rock samples are dissolved and a preset weight of internal standard element is added to obtain a source rock sample solution corresponding to each source rock sample;

[0092] Determine the content of preset trace elements and internal standard elements in each source rock sample solution of each reservoir;

[0093] calculating a second ratio of the content of the internal standard element in each source rock sample solution to a preset weight of the internal standard element;

[0094] Calculating the content of the preset trace elements in the source rock sample according to the second ratio and the content of the preset trace elements in each source rock sample solution of each oil reservoir;

[0095] According to the preset trace element contents in each source rock sample of each oil reservoir, a first ratio between the preset trace element contents is calculated.

[0096] Specifically, before collecting source rock samples from a reservoir, the type of the main source rock of the crude oil in the reservoir can be determined based on drilling, outcrop and seismic data, combined with previous research results;

[0097] The source rock samples collected can include core samples, rock cuttings samples, and field outcrop source rock samples from different depositional environments, lithologies, and maturities. Regardless of whether the source rock is core, rock cuttings, or field outcrop, it is important to ensure that it is free of the influence of secondary fluids and diagenesis, such as calcite veins and quartz veins. For example, if the source rock cuttings are collected, they can be screened, ultrasonically cleaned, manually sorted, or other methods to ensure that drilling mud and debris have not contaminated the source rock samples.

[0098] In one embodiment, for each oil reservoir, dissolving all source rock samples to obtain a source rock sample solution corresponding to each source rock sample includes the following steps:

[0099] The source rock sample is placed in a sealed sample dissolution device, and an appropriate amount of hydrofluoric acid and an appropriate amount of nitric acid are added to obtain a source rock sample stock solution;

[0100] The source rock sample solution is heated and evaporated to dryness, and then an appropriate amount of nitric acid is added and evaporated to dryness to obtain a residue;

[0101] adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the source rock sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element;

[0102] The residue solution was diluted with an appropriate amount of deionized water to obtain a source rock sample solution.

[0103] In one embodiment, the content of preset trace elements in each source rock sample solution of each oil reservoir is determined, for example, the same method as the aforementioned determination of crude oil sample solution or any other existing method of obtaining the element content in the solution can be used, and this embodiment of the present invention is not limited to this.

[0104] In one embodiment, between the steps of collecting the source rock sample and dissolving the source rock sample, in order to make the source rock sample more soluble, the following steps may be further included:

[0105] The source rock sample is crushed to obtain a crushed source rock sample.

[0106] In one embodiment, for example, a hammer can be used to crush the source rock sample until the diameter of the source rock sample is smaller than a preset crushing diameter to obtain a crushed source rock sample; the crushed source rock sample can be ground until the diameter of the crushed source rock sample is smaller than a preset crushing diameter to obtain a crushed source rock sample.

[0107] In one embodiment, in the aforementioned step S16, based on the first ratio between the preset trace element contents of each oil reservoir and the main source rock type of the oil reservoir, quantitatively calculating the contribution ratio of each main source rock in the oil reservoir includes:

[0108] For each oil reservoir, a characteristic value of a first ratio of trace element contents preset in a crude oil sample that can represent the characteristics of the source rock of the oil reservoir is calculated; based on the identification index plate, the first ratio of trace element contents preset in all main source rock samples of each oil reservoir is obtained, and the characteristic value of the first ratio of trace element contents preset in each type of main source rock among multiple types of main source rock samples of each oil reservoir is calculated; the characteristic value can be, for example, an average value;

[0109] According to the main source rock type of each reservoir, determine the calculation formula for quantitatively calculating the contribution ratio of source rock in the reservoir;

[0110] The characteristic value of the first ratio of the trace element content preset in the crude oil sample of each oil reservoir and the characteristic value of the first ratio of the trace element content preset in each type of main source rock are input into the calculation formula to quantitatively calculate the contribution ratio of each type of main source rock in the oil reservoir.

[0111] In order to facilitate understanding of the above method, an embodiment is given below to illustrate in detail:

[0112] 1. 20g of fresh crude oil samples were collected from the oil wellheads of a certain production oil field in a certain area.

[0113] 2. Based on drilling, outcrop and seismic data, combined with previous research results, it is clear that there are four main potential source rocks for marine crude oil in the reservoir, namely black mud shale A, muddy limestone B, black mud shale C and black mud shale D. Source rock samples of black mud shale A, muddy limestone B, black mud shale C and black mud shale D were collected respectively.

[0114] 3. Use a hammer to crush the source rock sample collected in step 2 to a diameter of less than 1 cm. Place the coarsely crushed source rock sample into a grinding jar filled with agate balls. Tighten the grinding jar and place it on the sample crusher. Grind the sample at a speed of 1300 r / min for 3 minutes until the sample is crushed to less than 100 mesh. After completion, pour the source rock sample powder into a sample bag and record the number.

[0115] 4. Weigh 0.05 g of the source rock sample crushed in step 3 or 0.05 g of the crude oil sample collected in step 1, place it in a Teflon sealed sample dissolution device, add 0.5 mL of hydrofluoric acid (HF) and 1 mL of nitric acid (HNO3), seal it, and heat it in an oven at 185°C for 12 h. After taking it out and cooling it, evaporate it to dryness on a hot plate at low temperature, add 1 mL of HNO3 and evaporate it to dryness again; finally, add 6 mL of Rh nitric acid solution, where the Rh concentration is 100 ng / ml and the nitric acid concentration is 5 mol / L, replace the lid, and place it in an oven at 140°C for 5 h to dissolve the residue; after cooling, take 0.4 mL of the residual solution into a 15 mL centrifuge tube and dilute it to 8-10 mL.

[0116] 5. The source rock sample solution or crude oil sample solution obtained in step 4 is subjected to inductively coupled plasma mass spectrometry (ICP-MS) with rhodium as an internal standard to determine the content of preset trace elements and rhodium.

[0117] 6. Based on the trace element analysis results of the source rock samples and crude oil samples in step 5, Mo, an element sensitive to sulfidation and reduction environments, and Th, an element insensitive to redox environments, are selected to establish the Mo / Th ratio. The Mo / Th ratio and V / (V+Ni) ratio of the trace elements of the source rock and crude oil samples are calculated (Table 1), and a Mo / Th-V / (V+Ni) identification index chart for marine crude oil and source rock in a certain basin is further established ( Figure 2 ), we can know that the main source rock of crude oil in a certain area of ​​a basin is black mud shale A, a small amount of crude oil comes from mud limestone B, and black mud shale C and black mud shale D almost make no contribution to the crude oil in a certain area.

[0118] 7. According to the determination in step 6, the main source rock is black mud shale A, whose Mo / Th value is 13.75-920.04, with an average value of 99.11, and V / (V+Ni) value is 0.31-0.95, with an average value of 0.76; the secondary source rock is mud limestone B, whose Mo / Th value is 0.98-7.80, with an average value of 3.46; and V / (V+Ni) value is 0.56-0.87, with an average value of 0.74.

[0119] Since the Mo / Th value range can completely distinguish the two source rocks, and the V / (V+Ni) value of the two source rocks overlaps greatly, the formula corresponding to the Mo / Th value is used to calculate the contribution of the two source rocks. The formula is as follows:

[0120] [Mo / Th] o =[Mo / Th] a ×x1+[Mo / Th] b ×(1-x1)

[0121] In this example, [Mo / Th] o This is a marine crude oil from a certain area in a certain basin, with an average value of 71.50; [Mo / Th] a Black shale A, with an average value of 99.11; [Mo / Th] b The average value is 3.46, which is argillaceous limestone B. According to the above formula, the x1 value is calculated to be 71.13%, that is, the contribution ratio of black shale A to the marine crude oil in a certain area of ​​a certain basin is 71.13%, and the contribution ratio of argillaceous limestone B is 28.87%.

[0122] Table 1 Data of Mo / Th ratio and V / (V+Ni) ratio of marine crude oil and potential source rocks in a certain area of ​​a basin

[0123] Serial number sample Mo / Th V / (V+Ni) 1 Black shale A 13.75-920.04 0.31-0.95 2 Argillaceous limestone B 0.98-7.80 0.56-0.87 3 Black shale C 6.43-7.58 0.24-0.41 4 Black shale D 0.10-1.05 0.54-0.67 5 Marine crude oil in a certain area of ​​a basin 2.49-454.76 0.74-0.87

[0124] According to the data in Table 1, the Mo / Th ratio and V / (V+Ni) ratio of the trace element rocks of marine source rocks of different ages and regions in a certain basin and the crude oil in a certain area are determined, and the Mo / Th-V / (V+Ni) identification index chart based on trace elements is established, such as Figure 2As shown. In the Mo / Th-V / (V+Ni) source rock-crude oil comparative identification index chart, the Mo / Th value of black mud shale A is 13.75-920.04, with an average of 99.11, and the V / (V+Ni) value is 0.31-0.95, with an average of 0.76; the Mo / Th value of early mud limestone B in a certain basin is 0.98-7.80, with an average of 3.46; the V / (V+Ni) value is 0.56-0.87, with an average of 0.74; the Mo / Th value of black mud shale C in a certain basin is The Mo / Th value of black shale D in a certain basin is 0.10-1.05, with an average value of 0.42; the V / (V+Ni) value is 0.54-0.67, with an average value of 0.62; the Mo / Th value of marine crude oil in a certain basin is 0.36-454.76, with an average value of 71.50; the V / (V+Ni) value is 0.43-0.87, with an average value of 0.80.

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for quantitatively calculating the contribution ratio of source rocks using trace elements, characterized in that: include: For each pre-determined reservoir, multiple crude oil samples were collected; Obtain the content of preset trace elements in each crude oil sample from each reservoir; Calculating a first ratio between preset trace element contents in the crude oil samples according to the preset trace element contents in each crude oil sample of each oil reservoir; For each oil reservoir, based on a first ratio between preset trace element contents in each crude oil sample, a data point corresponding to each crude oil sample is found in a pre-generated identification index plate corresponding to the oil reservoir; the identification index plate has the first ratio between preset trace element contents as a coordinate axis and includes an area corresponding to at least one type of major hydrocarbon source rock; Determining the main source rock type corresponding to the area where the data points corresponding to the crude oil sample are distributed from the identification index plate corresponding to each oil reservoir, and using the determined main source rock type as the main source rock type of the oil reservoir; According to the first ratio between the preset trace element contents of each oil reservoir and the main source rock type of the oil reservoir, the contribution ratio of each main source rock in the oil reservoir is quantitatively calculated.

2. The method according to claim 1, wherein The pre-generated identification indicator chart is generated in the following way: Determining the dimension of the coordinate system in the identification index plate according to the number of the preset first ratio types between the trace element contents, and establishing the identification index coordinate system with each preset first ratio between the trace element contents as the coordinate axis in the identification index plate; According to the first ratio between the preset trace element contents in the plurality of source rock samples of each oil reservoir obtained in advance, finding a data point corresponding to each source rock sample in the identification index coordinate system; According to the distribution areas of the data points corresponding to all source rock samples, the areas corresponding to different types of main source rocks are divided in the identification index coordinate system.

3. The method according to claim 2, wherein The first ratio between the preset trace element contents in the plurality of source rock samples of each oil reservoir obtained in advance is obtained by: For each reservoir, multiple source rock samples were collected; For each reservoir, all source rock samples are dissolved and a preset weight of internal standard element is added to obtain a source rock sample solution corresponding to each source rock sample; Determine the content of preset trace elements and internal standard elements in each source rock sample solution of each reservoir; calculating a second ratio of the content of the internal standard element in each source rock sample solution to a preset weight of the internal standard element; Calculating the preset trace element content in the source rock sample based on the second ratio and the preset trace element content in each source rock sample solution of each oil reservoir; According to the preset trace element contents in each source rock sample of each oil reservoir, a first ratio between the preset trace element contents is calculated.

4. The method according to claim 3, wherein For each oil reservoir, dissolving all source rock samples to obtain source rock sample solutions corresponding to each source rock sample includes: The source rock sample is placed in a sealed sample dissolution device, and an appropriate amount of hydrofluoric acid and an appropriate amount of nitric acid are added to obtain a source rock sample stock solution; heating the source rock sample solution and evaporating it to dryness, then adding an appropriate amount of nitric acid and evaporating it to dryness to obtain a residue; adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the source rock sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element; The residue solution is diluted with an appropriate amount of deionized water to obtain the source rock sample solution.

5. The method according to claim 3, wherein The determination of the content of predetermined trace elements in each source rock sample solution of each oil reservoir comprises: The source rock sample solution is placed in an inductively coupled plasma mass spectrometer to obtain the content of the trace elements and the content of the internal standard elements.

6. The method according to claim 3, wherein Between the steps of collecting the source rock sample and dissolving the source rock sample, the method further comprises: The source rock sample is crushed to obtain a crushed source rock sample.

7. The method according to claim 1, wherein The quantitative calculation of the contribution ratio of each major source rock in the oil reservoir based on the first ratio between the preset trace element contents of each oil reservoir and the major source rock type of the oil reservoir includes: For each oil reservoir, a characteristic value of a first ratio of trace element contents preset in a crude oil sample that can represent the characteristics of the source rock of the oil reservoir is calculated; based on the identification index plate, the first ratio of trace element contents preset in all main source rock samples of each oil reservoir is obtained, and the characteristic value of the first ratio of trace element contents preset in each type of main source rock in multiple types of main source rock samples of each oil reservoir is calculated; According to the main source rock type of each reservoir, determine the calculation formula for quantitatively calculating the contribution ratio of source rock in the reservoir; The characteristic value of the first ratio of the trace element content preset in the crude oil sample of each oil reservoir and the characteristic value of the first ratio of the trace element content preset in each type of main hydrocarbon source rock are input into the calculation formula to quantitatively calculate the contribution ratio of each type of main hydrocarbon source rock in the oil reservoir.

8. The method according to claim 1, wherein The method of obtaining the preset trace element content in each crude oil sample of each oil reservoir includes: For each oil reservoir, all crude oil samples were dissolved and a preset weight of internal standard element was added to obtain a crude oil sample solution corresponding to each crude oil sample; Determine the content of preset trace elements and internal standard elements in each crude oil sample solution from each reservoir; calculating a second ratio of the content of the internal standard element in each crude oil sample solution to a preset weight of the internal standard element; The content of the preset trace elements in the crude oil sample is calculated based on the second ratio and the content of the preset trace elements in each crude oil sample of each oil reservoir.

9. The method according to claim 8, wherein For each oil reservoir, all crude oil samples are dissolved and a preset weight of internal standard element is added to obtain a crude oil sample solution corresponding to each crude oil sample, including: The crude oil sample is placed in a sealed sample dissolving device, and an appropriate amount of hydrofluoric acid and an appropriate amount of nitric acid are added to obtain a crude oil sample stock solution; heating the crude oil sample solution and evaporating it to dryness, then adding an appropriate amount of nitric acid and evaporating it to dryness to obtain a residue; adding an appropriate preset volume of a nitric acid solution having a preset internal standard element concentration to dissolve the residue after evaporation of the crude oil sample stock solution to obtain a residual solution; calculating the weight of the internal standard element according to the preset volume and the preset concentration of the internal standard element to obtain a preset weight of the internal standard element; The residue solution was diluted with an appropriate amount of deionized water to obtain a crude oil sample solution.

10. The method according to claim 8, wherein The determination of the content of preset trace elements and the content of internal standard elements in each crude oil sample solution of each oil reservoir includes: The crude oil sample solution is placed in an inductively coupled plasma mass spectrometer to obtain the content of the trace elements and the content of the internal standard element.

11. The method according to claim 7, wherein The characteristic value is an average value.

12. The method according to claim 1, wherein The preset trace elements include at least two of the following: molybdenum, thorium, vanadium and nickel; Correspondingly, the first ratio between the trace element contents is: the molybdenum content divided by the thorium content, and / or the vanadium content divided by the sum of the vanadium content and the nickel content.

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