Method for determining content of organic sulfur in hydrocarbon source rock

Abstract

The invention discloses a method for determining the content of organic sulfur in hydrocarbon source rock, and belongs to the technical field of oil-gas exploration and development. According to the method, the organic sulfur content in the hydrocarbon source rock organic matter is calculated by adopting a method of combining total rock X-ray diffraction analysis and total sulfur analysis. The method comprises the following steps: firstly, obtaining an X-ray diffraction pattern based on a total rock X-ray diffraction test, carrying out phase analysis to obtain mineral composition in a hydrocarbon source rock powder sample, then quantitatively analyzing the mass percent of the sulfur-containing mineral in the hydrocarbon source rock powder sample according to a characteristic peak in the sulfur-containing mineral in the X-ray diffraction pattern, and further obtaining the inorganic sulfur content of the hydrocarbon source rock powder sample. Meanwhile, the total sulfur content of the hydrocarbon source rock powder sample is obtained through an element analysis experiment, and the difference value of the total sulfur content and the inorganic sulfur content in the sample serves as the organic sulfur content. According to the analysis method, kerogen does not need to be prepared, chemical reagents are not used in the whole process, the experiment process is shortened, operation is easy, safety and convenience are achieved, test data are stable and reliable, and repeatability is high.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, and specifically relates to a method for determining the organic sulfur content in source rocks. Background Technology

[0002] In petroleum geological research, the organic sulfur content in the organic matter of source rocks is a crucial factor influencing the hydrocarbon generation threshold and the hydrocarbon generation stages. The activation energies of the "CS" and "SS" bonds in organic matter are significantly lower than those of the "CC" bond. When a large amount of organic sulfur exists in the source rock, especially when sulfur exists in the form of chain sulfides, the "CS" and "SS" bonds break extensively under lower geothermal temperatures and pressures, leading to hydrocarbon generation and significantly lowering the hydrocarbon generation threshold. A reasonable assessment of the organic sulfur content in source rocks has three profound implications for the petroleum industry: First, it expands the scope of conventional oil and gas exploration and development, specifically by further expanding the identification range of effective source rocks and favorable source-reservoir-seal assemblages; second, organic sulfur-rich source rocks generate large quantities of low-maturity, high-viscosity shale oil, increasing the potential for unconventional oil and gas exploration and development; and third, the high-sulfur crude oil generated from sulfur-rich source rocks places higher demands on pipeline corrosion resistance and desulfurization processes. Furthermore, in the field of basic science, accurately determining the content of organic sulfur can provide important evidence for reconstructing the sulfur cycle process and the hydrochemical environment of ancient sedimentary systems (such as lake basins and marine environments) during geological history.

[0003] Currently, there are three main methods for assessing the organic sulfur content in source rock organic matter: The first method requires extracting kerogen with hydrofluoric acid and hydrochloric acid, then calculating the total sulfur and iron content using combustion and chemical precipitation methods respectively, and finally subtracting the pyrite sulfur content from the total sulfur content to obtain the organic sulfur content. The second method requires extracting kerogen with hydrofluoric acid and hydrochloric acid, then using the strong oxidizing properties of chromic acid to remove pyrite from the kerogen, and then using the total sulfur content of the treated kerogen as the organic sulfur content. The third method requires using a Rock-Eval 7s rock pyrolysis instrument manufactured by Vinci Technologies, France, to burn the sulfur-containing compounds in the rock or kerogen into sulfur dioxide through variable-temperature pyrolysis, and directly measuring the organic and inorganic sulfur content in the rock or kerogen using the sulfur dioxide produced at different temperature ranges. However, the first two methods suffer from problems such as complex analytical methods, highly hazardous reagents, and severe damage to the chemical composition of organic matter by chromic acid; the third method suffers from problems such as extremely expensive instruments and a scarcity of such instruments internationally. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, the main objective of this invention is to provide a method for determining the organic sulfur content in source rocks. This method calculates the organic sulfur content in the organic matter of source rocks through whole-rock X-ray diffraction analysis and total sulfur analysis, eliminating the need for chemical reagents, reducing experimental procedures, simplifying operation, making it safer and more convenient, and providing stable, reliable, and highly repeatable data.

[0005] To achieve the above objectives, the present invention provides a method for determining the organic sulfur content in source rocks, comprising the following steps:

[0006] The source rock powder sample was pre-dried and then cooled to room temperature for later use.

[0007] The dried source rock powder sample was subjected to X-ray diffraction test to obtain the X-ray diffraction pattern;

[0008] Phase analysis was performed on the X-ray diffraction pattern to obtain the mineral composition of the source rock powder sample;

[0009] Based on the mineral composition of the source rock powder sample, the total sulfur content of all sulfur-containing minerals in the source rock powder sample is calculated as the inorganic sulfur content of the source rock powder sample.

[0010] Elemental analysis was performed on the dried source rock powder sample to obtain the total sulfur content of the source rock powder sample.

[0011] The difference between the total sulfur content and the inorganic sulfur content of the source rock powder sample is the organic sulfur content of the source rock powder sample.

[0012] Further, the calculation of the total sulfur content of all sulfur-containing minerals in the source rock powder sample based on its mineral composition includes:

[0013] Based on the mineral composition of the source rock powder sample, the mass percentage of sulfur-containing minerals in the total minerals and the molar percentage of sulfur in the sulfur-containing minerals were obtained.

[0014] The sulfur content in sulfur-containing minerals is obtained by multiplying the mass percentage of sulfur-containing minerals in the total minerals by the molar percentage of sulfur in the sulfur-containing minerals.

[0015] The inorganic sulfur content of the source rock powder sample is obtained by summing the sulfur contents of all sulfur-containing minerals.

[0016] Furthermore, the elemental analysis of the dried source rock powder sample includes: heating the source rock powder sample with a combustion accelerant under the action of oxygen and a high-frequency electromagnetic field to burn the source rock powder sample and produce sulfur dioxide and carbon dioxide; and using an infrared detector to detect the sulfur dioxide content to obtain the total sulfur content in the source rock powder sample.

[0017] Furthermore, the heating temperature is 1300±5℃, and the heating time is 40~45s.

[0018] Furthermore, the combustion accelerant includes iron and tungsten.

[0019] Furthermore, the instrument parameters for the X-ray diffraction test include: the operating voltage of the copper target tube CuKα is 40kV, and the operating current is 40mA.

[0020] Furthermore, the phase analysis of the X-ray diffraction pattern includes: the analysis angle range of the X-ray diffraction pattern is 2-92°θ, the step size is 0.02°2θ, and the step interval is 5s.

[0021] Furthermore, the mesh size of the source rock powder sample is 200-230 mesh.

[0022] Furthermore, the pre-drying temperature is 50–70°C, and the drying time is 10–12 hours.

[0023] Furthermore, the source rocks include mudstone, shale, and limestone.

[0024] Compared with existing technologies, this invention has the following advantages: Based on X-ray diffraction analysis and total sulfur analysis of source rocks, this invention provides an efficient and convenient method for determining the organic sulfur content in source rocks. It employs quantitative mineral analysis and chemical calculations to quantitatively analyze the inorganic sulfur content in source rock powder samples, and uses the difference between the total sulfur content and the inorganic sulfur content as the organic sulfur content. This analysis process eliminates the need for kerogen preparation and the use of hazardous chemicals such as chromic acid. The entire process of determining the organic sulfur content of this invention eliminates the use of chemical reagents, reduces experimental procedures, simplifies operation, and is safer and more convenient. Verification with data from a Rock-Eval7s rock pyrolysis instrument shows that the test data of this invention is stable, reliable, and highly repeatable, solving the problems of high testing costs and limited instrumentation in existing rock pyrolysis analysis methods. Attached Figure Description

[0025] Figure 1 This is a correlation diagram comparing the organic sulfur content obtained based on the present invention with the organic sulfur content obtained by the Rock-Eval 7s device in an embodiment of the present invention.

[0026] In the figure, the vertical axis represents the organic sulfur content (wt.%) obtained based on the present invention, and the horizontal axis represents the organic sulfur content (wt.%) obtained by the Rock-Eval7s device. Detailed Implementation

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, regarding numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range. In the description of this invention, it should be noted that the terms "comprising," "including," "having," etc., are open-ended terms, meaning that they include but are not limited to.

[0028] Embodiments of the present invention provide a method for determining the organic sulfur content in a source rock, comprising the following steps:

[0029] The source rock powder sample was pre-dried and then cooled to room temperature for later use.

[0030] The dried source rock powder sample was subjected to whole-rock X-ray diffraction test to obtain the X-ray diffraction pattern;

[0031] Phase analysis was performed on the X-ray diffraction pattern to obtain the mineral composition of the source rock powder sample;

[0032] Based on the mineral composition of the source rock powder sample, the total sulfur content of all sulfur-containing minerals in the source rock powder sample is calculated as the inorganic sulfur content of the source rock powder sample.

[0033] Elemental analysis was performed on the dried source rock powder sample to obtain the total sulfur content of the source rock powder sample.

[0034] The difference between the total sulfur content and the inorganic sulfur content of the source rock powder sample is the organic sulfur content of the source rock powder sample.

[0035] This invention employs a combined method of whole-rock X-ray diffraction (XRD) analysis and total sulfur analysis to calculate the organic sulfur content in the organic matter of source rocks. First, XRD patterns are obtained based on whole-rock XRD testing. Phase analysis is then performed to determine the mineral composition of the source rock powder sample. Next, based on the characteristic peaks of sulfur-containing minerals in the XRD pattern, the mass percentage of sulfur-containing minerals in the source rock powder sample is quantitatively analyzed, thus determining the inorganic sulfur content. Simultaneously, elemental analysis is used to obtain the total sulfur content of the source rock powder sample. The difference between the total sulfur content and the inorganic sulfur content in the sample is taken as the organic sulfur content. This analytical method eliminates the need for kerogen preparation, removes the use of chemical reagents, shortens the experimental procedure, simplifies operation, enhances safety and convenience, and provides stable and reliable experimental data, making it suitable for widespread application.

[0036] In an embodiment of the present invention, calculating the total sulfur content of all sulfur-containing minerals in the source rock powder sample based on its mineral composition includes:

[0037] Based on the mineral composition of the source rock powder sample, the mass percentage of sulfur-containing minerals in the total minerals and the molar percentage of sulfur in the sulfur-containing minerals were obtained.

[0038] The sulfur content in sulfur-containing minerals is obtained by multiplying the mass percentage of sulfur-containing minerals in the total minerals by the molar percentage of sulfur in the sulfur-containing minerals.

[0039] The inorganic sulfur content of the source rock powder sample is obtained by summing the sulfur contents of all sulfur-containing minerals.

[0040] Specifically, the calculation formula is s 无机硫 =∑W 含硫矿物 ×M 含硫矿物 , where s 无机硫 The inorganic sulfur content (wt.%) of the source rock powder sample; W 含硫矿物 The percentage of sulfur-containing minerals in the total mineral mass (wt.%), M 含硫矿物 The percentage of sulfur in sulfur-containing minerals, expressed as %.

[0041] In a preferred embodiment of the present invention, the elemental analysis of the dried source rock powder sample includes: heating the source rock powder sample with a combustion accelerant under the action of oxygen and a high-frequency electromagnetic field to burn the source rock powder sample and produce sulfur dioxide and carbon dioxide; and using a carbon-sulfur analyzer to detect the sulfur dioxide content by an infrared detector to obtain the total sulfur content in the source rock powder sample.

[0042] In a preferred embodiment of the present invention, the heating temperature is 1300±5℃, and the heating time is 40-45s. Controlling the heating temperature and time within this range ensures complete combustion of the source rock powder sample, allowing sulfur-containing compounds to be completely converted into sulfur dioxide, avoiding errors in the total sulfur content determination, and further improving the accuracy of the organic sulfur content test data. More preferably, the heating temperature is 1300℃, and the heating time is 40s.

[0043] In some optional embodiments of the present invention, the combustion accelerant includes iron and tungsten; the instrument parameters for the whole-rock X-ray diffraction test include: a working voltage of 40 kV and a working current of 40 mA for the copper target tube CuKα. The phase analysis of the X-ray diffraction pattern includes: an analysis angle range of 2-92°θ, a step size of 0.02°2θ, and a step interval of 5 s.

[0044] In specific embodiments of the present invention, the X-ray diffraction test method, the analysis of mineral composition, and the analysis process of sulfur-containing mineral content percentage refer to the requirements of the People's Republic of China Petroleum and Natural Gas Industry Standard "SY / T 5163-2018-X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks", and will not be elaborated further here.

[0045] In some preferred embodiments of the present invention, the mesh size of the source rock powder sample is 200-230 mesh. For example, it may include, but is not limited to, 200 mesh, 210 mesh, 220 mesh, and 230 mesh. The pre-drying temperature is 50-70°C, for example, it may include, but is not limited to, 50°C, 55°C, 60°C, 65°C, and 70°C. The drying time is 10-12 hours, for example, it may include, but is not limited to, 10 hours, 10.5 hours, 11 hours, 11.5 hours, and 12 hours. By adopting the above technical solution, it is beneficial to accurately quantify the total sulfur content and inorganic sulfur content of the source rock.

[0046] In embodiments of the present invention, the source rock includes hydrocarbon-generating rocks confirmed by geological studies, such as mudstone, shale, and limestone.

[0047] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0048] Example

[0049] The method for determining the organic sulfur content in source rocks in this embodiment includes the following steps:

[0050] S1. Crush the source rock sample to 200 mesh, dry it in a vacuum drying oven at 60℃ for 12 hours, and cool it to room temperature; do not use any chemical reagents to treat the sample.

[0051] S2. Perform whole-rock X-ray diffraction (XRD) analysis on 3g of the source rock powder sample obtained in step S1 to obtain the X-ray diffraction pattern. Based on the X-ray diffraction pattern, perform phase analysis to quantitatively determine the mass percentage of each sulfur-containing mineral in the source rock powder sample. The specific whole-rock X-ray diffraction experimental method refers to the relevant requirements in the People's Republic of China Petroleum and Natural Gas Industry Standard "SY / T 5163-2018-X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks".

[0052] S3. Analyze the total sulfur content of 3g of source rock powder sample obtained in step S1. The analysis method is as follows: heat the source rock powder sample with a combustion accelerant under the action of oxygen and high-frequency electromagnetic field (1300℃, 40s) to burn the source rock powder sample and produce sulfur dioxide and carbon dioxide. The carbon-sulfur analyzer detects the sulfur dioxide content through an infrared detector to obtain the total sulfur content in the source rock powder sample; wherein, the combustion accelerant includes iron and tungsten.

[0053] S4. Calculate the total sulfur content of all sulfur-containing minerals in the source rock powder sample, and use it as the inorganic sulfur content of the source rock powder sample.

[0054] S5. Subtract the total sulfur content of the source rock powder sample obtained in S3 from the inorganic sulfur content of the source rock powder sample obtained in S4. The difference is the organic sulfur content of the source rock powder sample.

[0055] In the embodiments of the present invention, it should be explained that: in S2 and S3, the amount of experimental sample used is related to the type of experimental instrument. Here, the amount of sample used is the optimal amount that is adapted to the equipment used by the inventor and obtains stable and comparable data; when the model of the experimental instrument changes, the amount of sample used also changes accordingly, so as to achieve the effect of accurately quantifying the sulfur-containing minerals and total sulfur content in the sample.

[0056] In S4, the inorganic sulfur content of the source rock powder sample is calculated as follows: multiply the mass percentage of sulfur-containing minerals by the molar percentage of sulfur in the sulfur-containing minerals to obtain the sulfur content in the sulfur-containing minerals. The sum of the sulfur contents in all sulfur-containing minerals is the inorganic sulfur content of the source rock powder sample.

[0057] The calculation formula is s 无机硫 =∑W 含硫矿物 ×M 含硫矿物 , where s 无机硫 The inorganic sulfur content (wt.%) of the source rock powder sample; W 含硫矿物 The percentage of sulfur-containing minerals in the total mineral mass (wt.%), M 含硫矿物 The percentage of sulfur in sulfur-containing minerals, expressed as %.

[0058] The sulfur-containing minerals detected in the experimental samples included gypsum, pyrite, and jaundice. Therefore, the inorganic sulfur content (wt.%) in the sample = gypsum (wt.%) × 32 / 172 + pyrite (wt.%) × 64 / 120 + jaundice (wt.%) × 64 / 501.

[0059] The test equipment and test conditions are as follows:

[0060] X-ray diffraction analysis was performed using a Bruker D8 X-ray diffraction (XRD) instrument. The copper target tube (CuKα) operated at 40 kV and 40 mA. The diffraction pattern analysis angle range was 2–92°θ, with a step size of 0.02°2θ and a step interval of 5 s.

[0061] The carbon and sulfur analyzer is a Leco CS744 model.

[0062] The organic sulfur content of the above-mentioned samples was tested using multiple source rock powder samples (a to i), and the test data are shown in Table 1.

[0063] Comparative example: The organic sulfur content of source rock powder samples (a to i) was tested using a Rock-Eval 7s rock pyrolysis instrument. The organic sulfur content test data are shown in Table 1.

[0064] Table 1. Comparison of organic sulfur content obtained in the embodiments of the present invention with that obtained by the Rock-Eval 7s device.

[0065]

[0066] Using the organic sulfur content data obtained in the method of the present invention in the above table as the ordinate and the organic sulfur content data obtained by the Rock-Eval 7s rock pyrolysis instrument as the abscissa, a graph is plotted using the above ordinate and abscissa data, as shown below. Figure 1 As shown in the figure, the organic sulfur content obtained by the method of this invention is highly consistent with the organic sulfur content of the sample obtained by the Rock-Eval 7s device, with a correlation coefficient (R0). 2 A value of 0.99 or higher indicates that the test results of this invention are stable, reliable, and accurate.

[0067] In summary, this invention, based on X-ray diffraction analysis and total sulfur content testing, quantitatively analyzes the inorganic and organic sulfur content in source rocks. This analysis eliminates the need for kerogen preparation, avoids the use of chemical reagents, reduces experimental procedures, simplifies operation, enhances safety and convenience, and provides stable, reliable, and highly reproducible data.

[0068] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A method for determining the organic sulfur content in a source rock, characterized in that, Includes the following steps: The source rock powder sample was pre-dried and then cooled to room temperature for later use. The dried source rock powder sample was subjected to whole-rock X-ray diffraction test to obtain the X-ray diffraction pattern. Phase analysis was performed on the X-ray diffraction pattern to obtain the mineral composition of the source rock powder sample; Based on the mineral composition of the source rock powder sample, the total sulfur content of all sulfur-containing minerals in the source rock powder sample is calculated as the inorganic sulfur content of the source rock powder sample. Elemental analysis was performed on the dried source rock powder sample to obtain the total sulfur content of the source rock powder sample. The difference between the total sulfur content and the inorganic sulfur content of the source rock powder sample is the organic sulfur content of the source rock powder sample.

2. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The calculation of the total sulfur content of all sulfur-containing minerals in the source rock powder sample based on its mineral composition includes: Based on the mineral composition of the source rock powder sample, the mass percentage of sulfur-containing minerals in the total minerals and the molar percentage of sulfur in the sulfur-containing minerals were obtained. The sulfur content in sulfur-containing minerals is obtained by multiplying the mass percentage of sulfur-containing minerals in the total minerals by the molar percentage of sulfur in the sulfur-containing minerals. The inorganic sulfur content of the source rock powder sample is obtained by summing the sulfur contents of all sulfur-containing minerals.

3. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The elemental analysis of the dried source rock powder sample includes: The source rock powder sample is heated with a combustion accelerant under the influence of oxygen and a high-frequency electromagnetic field to burn the source rock powder sample and produce sulfur dioxide and carbon dioxide. The carbon-sulfur analyzer detects the sulfur dioxide content through an infrared detector to obtain the total sulfur content in the source rock powder sample.

4. The method for determining the organic sulfur content in source rocks according to claim 3, characterized in that, The heating temperature is 1300±5℃, and the heating time is 40~45s.

5. The method for determining the organic sulfur content in source rocks according to claim 3, characterized in that, The combustion aid includes iron and tungsten.

6. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The instrument parameters for the whole-rock X-ray diffraction test include: the working voltage of the copper target tube CuKα is 40kV and the working current is 40mA.

7. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The phase analysis of the X-ray diffraction pattern includes: the analysis angle range of the X-ray diffraction pattern is 2-92°θ, the step size is 0.02°2θ, and the step interval is 5s.

8. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The mesh size of the source rock powder sample is 200-230 mesh.

9. The method for determining the organic sulfur content in source rocks according to claim 1, characterized in that, The pre-drying temperature is 50–70°C, and the drying time is 10–12 hours.

10. The method for determining the organic sulfur content in source rocks according to any one of claims 1 to 9, characterized in that, The source rocks include mudstone, shale, and limestone.

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