Method for representing heterogeneity of millimeter-level shale oil and gas reservoir

Abstract

The invention provides a method for characterizing the heterogeneity of a millimeter-level shale oil and gas reservoir. The method mainly solves the problem that the reliability and accuracy of a reservoir evaluation result of an existing volume sampling method are low. The method is characterized by comprising the following steps that S1, shale millimeter-level mineral components are recognized and drilled; s2, based on the obtained powdery sample, oil-containing and non-oil-containing tests are carried out; determining occurrence pore size distribution to carry out reservoir characterization through comparison before and after pumping; s3, on the basis of the obtained powdery sample, carrying out oiliness characterization on different lamina / layered components; and S4, carrying out millimeter-level shale oil reservoir heterogeneity characterization on the basis of the reservoir property and oiliness results of the different strata / layered components. According to the method provided by the invention, the identification precision of the shale formation / stratified structure can be enhanced, millimeter-level fine representation of lithology of different formation / strata is realized, and favorable support is provided for shale oil enrichment mechanism, sweet spot prediction and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas resource evaluation, and in particular to a method for characterizing the heterogeneity of millimeter-level shale oil and gas reservoirs. Background Art

[0002] As the recoverable resources of shale oil in my country increase year by year, shale oil has become a strategic component of China's oil and gas reserves and production. However, the geological characteristics of my country's continental shales are relatively complex, and the main sedimentary process is affected by multiple factors, resulting in obvious differences in rock structure and mineral composition. As we all know, continental shales are usually produced in a thin lamellar stacking style with well-developed lamellae, which are interspersed with thin layers such as sand and carbonate. In addition, the shale reservoir itself is dense, which makes it show strong heterogeneity. Only by naked eye observation, it can be seen that there are significant differences in mineral composition, color brightness, thin layer thickness, particle size and other characteristics at the millimeter scale. These differences will undoubtedly directly cause differences in reservoir and oil content. In the past, when preparing samples to characterize shale reservoir and oil content, predecessors usually divided a whole piece (full / half diameter specification) of core samples into different areas, and then designed corresponding characterization experiments for different areas. Some experiments may require sample crushing and grinding, and some may require drill strings. In order to reduce the impact of heterogeneity on the results, previous researchers usually mixed the powder samples obtained from the same rock thoroughly and then weighed and sampled them for experiments. However, when conducting different experiments according to this volume sampling, the experimental results may be inconsistent due to differences in mineral composition and structure within the rock, which reduces the reliability of the experimental evaluation results of the reservoir and restricts the exploration effect of shale oil. Therefore, how to more accurately evaluate shale oil reservoirs at the millimeter scale and reduce the impact of heterogeneity to a greater extent is the focus of current research on shale oil reservoir evaluation. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the problem of low reliability and accuracy of the results of reservoir evaluation by the existing volume sampling method in the background technology, and to provide a method for characterizing the heterogeneity of shale oil and gas reservoirs at the millimeter level. The method for characterizing the heterogeneity of shale oil and gas reservoirs at the millimeter level can enhance the accuracy of identification and evaluation of different laminae / layered structures of shale by accurately comparing the differences in reservoir properties and oil content between various lithologies at the millimeter scale of shale, and realize the millimeter-level fine characterization of different laminae / layered lithologies, providing favorable support for shale oil enrichment mechanism, "sweet spot" prediction, etc.

[0004] The present invention solves the problem through the following technical solution: The method for characterizing the heterogeneity of millimeter-level shale oil and gas reservoirs comprises the following steps:

[0005] S1: Identification and drilling of millimeter-scale mineral components in shale;

[0006] Accurately locate the distribution of different laminae / layer components, finely identify different laminae / layered components, and realize the identification of millimeter-level mineral components of shale;

[0007] With the help of a micro-drill sampler, drilling is performed on the thin layers of different identified laminae / laminated components to obtain corresponding powdered samples, so that the content of the obtained samples meets the requirements of subsequent supporting experiments;

[0008] S2: Based on the obtained powdered samples, oil-containing and oil-free tests are carried out; by comparing before and after extraction, the pore size distribution is determined to characterize the reservoir properties;

[0009] S3: Based on the obtained powder samples, characterize the oil content of different laminae / layered components;

[0010] S4: Based on the reservoir and oil content results of different laminae / layered components, the heterogeneity of shale oil reservoirs at the millimeter level is characterized;

[0011] Based on the reservoir properties and oil content of different laminae / layered components, the free oil, oil saturation index, proportion of light and heavy oil components, pore size distribution, and pore size distribution characteristics are comprehensively compared with different laminae / layered components to finally achieve millimeter-level shale oil reservoir heterogeneity characterization.

[0012] Preferably, the method for identifying millimeter-scale mineral components of shale in step S1 comprises:

[0013] The full-diameter (original cylindrical shape obtained by drilling) shale core with laminae / layers is cut perpendicular to the bedding direction by an anhydrous diamond wire cutting machine to prepare a half-diameter (semi-cylindrical) shale sample with a smooth cutting surface;

[0014] The cut shale sample section is placed upward in the Bruker M4 TORNADO spectrometer and after it is in a vacuum state, it is scanned point by point using the beam excited by the multi-guide capillary focusing mirror (resolution 20 μm). The scanning time of each point is 3 to 5 ms, and it is repeated once after the scanning of the entire core section is completed;

[0015] After scanning, the element type is determined point by point, and specific elements are selected for combination with reference to the common mineral types of shale. After the combination, the different laminae / layered components are finely identified according to the proportion of the specific element content, thereby realizing the identification of millimeter-level mineral components of shale.

[0016] Preferably, the shale sample is mainly composed of felsic minerals, calcite, dolomite, clay and pyrite, wherein the proportion of felsic minerals, calcite, dolomite, clay and pyrite in the shale sample is greater than 90%; the main elements of the felsic minerals are: Si, O, Al; the main elements of calcite are: Ca, C, O, Fe, Mn; the main elements of dolomite are Ca, C, O, Fe, Mg, Mn; the main elements of clay are Si, Al, O; the main elements of pyrite are: S, Fe.

[0017] Preferably, the S1 is based on a high-performance micro-area X-ray fluorescence spectrometer to accurately locate the distribution positions of different laminae / layer components and finely identify different laminae / layer components;

[0018] Preferably, the high performance micro-area X-ray fluorescence spectrometer is a Bruker M4 TORNADO spectrometer.

[0019] Preferably, the specific method of performing reservoir characterization based on the obtained powdered sample in step S2 includes:

[0020] 1) Test the powdered samples obtained by the millimeter-level drill micro-drill prototype with and without oil;

[0021] 2) The pore size distribution characteristics are determined by using the nitrogen adsorption results after extraction, and then the pore size distribution and specific surface area are derived respectively; the pore size distribution is determined by performing difference processing on the pore size distribution curves before and after extraction, thereby characterizing the reservoir properties of different laminae / layered components.

[0022] Preferably, the method for testing the oil content of the powder sample obtained by the millimeter-level drill bit micro-drill prototype is: weigh the powder sample, dry it in a vacuum dryer at 60°C for 12 hours, and then perform nitrogen optimization. The method for testing the oil-free state of the obtained powder sample is:

[0023] Weigh the powdered sample, extract it with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and dry it at 60℃ for 12h to fully remove the residual fluid inside the sample. After degreasing, conduct a nitrogen adsorption experiment to obtain the pore size distribution characteristics in the oil-free state.

[0024] Preferably, the method for deriving the pore size distribution and specific surface area is:

[0025] The pore size distribution and specific surface area were derived using the BJH (Barrette Joynere Halenda) model and the BET (Brunauer Emmette Teller) model respectively.

[0026] Preferably, step S3 is a method for characterizing the oil content of different laminae / lamellar components based on the obtained powdered sample, comprising:

[0027] 1) Weigh 1-5 mg of powdered sample for rock pyrolysis experiment to obtain information on free oil content;

[0028] 2) Weigh 1-5 mg of powdered sample for TOC analysis, and combine the TOC analysis results with the free oil content to calculate the oil saturation index;

[0029] 3) Weigh 50 mg of powdered sample and conduct pyrolysis-gas chromatography experiment to obtain the proportion of light and heavy oil components;

[0030] 4) Based on the above results, the oil content of different laminae / layered components was characterized by obtaining three parameters: information on free oil content, oil saturation index, and the proportion of light and heavy oil components.

[0031] Preferably, the specific method of performing millimeter-scale shale oil reservoir heterogeneity characterization based on the reservoir properties and oil content results of different laminae / layered components in step S4 includes:

[0032] The reservoir and oil-bearing characterization parameters of different laminae / layered components were sorted out, and the pore volume, specific surface area, TOC, free oil content, and oil saturation index of each component were summarized;

[0033] By comparing the same parameters of different laminae / stratified components, the differences in reservoir and oil content between components at millimeter scale conditions are revealed;

[0034] Based on the differences in reservoir and oil content among components under millimeter scale conditions, the heterogeneity of reservoir and oil content of millimeter-scale shale oil is revealed.

[0035] Compared with the above background technology, the present invention has the following beneficial effects:

[0036] The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity has the following technical effects:

[0037] (1) High evaluation accuracy

[0038] Based on high-performance micro-area X-ray fluorescence spectroscopy, the distribution positions of different laminae / layer components are accurately located. With the help of a millimeter-level micro-drill sampler, drilling is carried out on thin layers of different lithologies to obtain corresponding powdered samples, and then conventional pyrolysis, total organic carbon analysis, pyrolysis-gas chromatography, low-temperature nitrogen adsorption and other experiments are carried out. From the experimental results, it can be seen that there are obvious differences in the pore volume, specific surface area, TOC, free oil content, and oil saturation index of different lithologies at the millimeter scale. Compared with the previous method of obtaining samples by volume method and then conducting corresponding experiments, this method greatly improves the accuracy of the evaluation results, realizes the millimeter-level fine evaluation of different laminae / layer lithologies, and provides favorable support for shale oil exploration and development.

[0039] (2) Economical and universal

[0040] The sampler equipped with a millimeter-level micro-drill is easy to obtain and cheap on the market. At the same time, considering that shale itself is mostly composed of clay minerals, with well-developed foliation, small and easily broken particles, the sampler can easily obtain the number of samples required for the experiment in a short time during the process of acting on the shale, ensuring the smooth progress of subsequent experiments. The operation during the drilling process is simple, convenient and fast, and there is no need to adjust the operation process and means according to the properties of shale in different regions and different layers. This shows that this method has good application prospects in characterizing millimeter-level shale reservoirs and is suitable for promotion and application to other continental / marine shales.

[0041] (3) Strong recognition and representativeness

[0042] Previous methods based on volume sampling were too rough, and the experimental results obtained from the samples usually only represented the information of the entire sample (half / full diameter specifications). Shale usually has irregularly distributed lamination / layered structures and lithology, and favorable shale reservoir and oil content information is often contained therein. However, previous methods were unable to obtain it effectively and accurately. The present invention can quickly and effectively obtain experimental samples by utilizing high-performance micro-area X-ray fluorescence spectroscopy and micro-drilling sampling technology, and more finely identify and characterize millimeter-level reservoirs. At the same time, the method can refine the internal information of the entire shale sample, with a more detailed measurement range and a smaller scale, greatly improving the representativeness of the experimental results. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a distribution characteristic diagram of different laminae components according to an embodiment of the present invention;

[0044] Figure 2 is a diagram of the locations of the micro-drill sampling points and the corresponding components in an embodiment of the present invention;

[0045] Figure 3 is a pore size distribution curve diagram of low temperature nitrogen adsorption (BJH model) after extraction in an embodiment of the present invention;

[0046] Figure 4 Graph showing the relationship between TOC and pore volume (left) and specific surface area (right) of an embodiment of the present invention;

[0047] Figure 5 : is a graph showing the relationship between free oil content S1 and TOC in an embodiment of the present invention;

[0048] Figure 6 is the pore size distribution curve obtained based on the BJH model in the embodiment of the present invention;

[0049] Figure 7 This is a spider diagram for evaluating the reservoir and oil content of different components in the embodiment of the present invention;

[0050] Figure 8 1 is a graph showing the relationship between the free hydrocarbon content and the pore volume of different components in the examples of the present invention. Specific implementation method:

[0051] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0052] The present invention discloses a method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity, comprising the following steps:

[0053] S1: Identification and drilling of millimeter-scale mineral components in shale;

[0054] Based on the high-performance micro-area X-ray fluorescence spectrometer, the distribution positions of different lamina / layer components are accurately located, the different lamina / layered components are finely identified, and the identification of millimeter-level mineral components of shale is realized; the high-performance micro-area X-ray fluorescence spectrometer is a BrukerM4 TORNADO spectrometer.

[0055] With the help of a micro-drill sampler, drilling is performed on the thin layers of different identified laminae / laminated components to obtain corresponding powdered samples, so that the content of the obtained samples meets the requirements of subsequent supporting experiments;

[0056] The method for identifying millimeter-scale mineral components of shale comprises:

[0057] The full-diameter (original cylindrical shape obtained by drilling) shale core with laminae / layers is cut perpendicular to the bedding direction by an anhydrous diamond wire cutting machine to prepare a half-diameter (semi-cylindrical) shale sample with a smooth cutting surface;

[0058] The cut shale sample section is placed upward in the Bruker M4 TORNADO spectrometer and after it is in a vacuum state, it is scanned point by point using the beam excited by the multi-guide capillary focusing mirror (resolution 20 μm). The scanning time of each point is 3 to 5 ms, and it is repeated once after the scanning of the entire core section is completed;

[0059] After scanning, the element type is determined point by point, and specific elements are selected for combination with reference to the common mineral types of shale. After the combination, the different laminae / layered components are finely identified according to the proportion of the specific element content, thereby realizing the identification of millimeter-level mineral components of shale.

[0060] S2: Based on the obtained powdered samples, oil-containing and oil-free tests are carried out; by comparing before and after extraction, the pore size distribution is determined to characterize the reservoir; the specific methods include:

[0061] 1) Test the powdered samples obtained by the millimeter-level drill micro-drill prototype with and without oil;

[0062] The method for testing the oil content of the powder sample obtained by the millimeter-level drill bit micro-drill prototype is as follows: weigh the powder sample, dry it in a vacuum dryer at 60°C for 12 hours, and then perform nitrogen optimization. The method for testing the oil-free state of the obtained powder sample is as follows:

[0063] Weigh the powdered sample, extract it with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and dry it at 60℃ for 12h to fully remove the residual fluid inside the sample. After degreasing, conduct a nitrogen adsorption experiment to obtain the pore size distribution characteristics in the oil-free state.

[0064] 2) The pore size distribution characteristics are determined by the nitrogen adsorption results after extraction, and the pore size distribution and specific surface area are derived using the BJH (Barrette Joynere Halenda) model and the BET (Brunauer Emmette Teller) model respectively; the pore size distribution is determined by performing difference processing on the pore size distribution curves before and after extraction, thereby characterizing the reservoir properties of different laminar / layered components.

[0065] S3: Based on the obtained powder samples, characterize the oil content of different laminae / layered components. The specific methods include:

[0066] 1) Weigh 1-5 mg of powdered sample for rock pyrolysis experiment to obtain information on free oil content;

[0067] 2) Weigh 1-5 mg of powdered sample for TOC analysis, and combine the TOC analysis results with the free oil content to calculate the oil saturation index;

[0068] 3) Weigh 50 mg of powdered sample and conduct pyrolysis-gas chromatography experiment to obtain the proportion of light and heavy oil components;

[0069] 4) Based on the above results, the oil content of different laminae / layered components was characterized by obtaining three parameters: information on free oil content, oil saturation index, and the proportion of light and heavy oil components.

[0070] S4: Based on the reservoir and oil content results of different laminae / layered components, the heterogeneity of shale oil reservoirs at the millimeter level is characterized;

[0071] Based on the reservoir properties and oil content of different laminae / layered components, the free oil, oil saturation index, proportion of light and heavy oil components, pore size distribution, and pore size distribution characteristics are comprehensively compared with different laminae / layered components to finally achieve millimeter-level shale oil reservoir heterogeneity characterization.

[0072] Based on the reservoir and oil content results of different laminae / layered components, the specific methods for characterizing the heterogeneity of shale oil reservoirs at the millimeter level include:

[0073] The reservoir and oil-bearing characterization parameters of different laminae / layered components were sorted out, and the pore volume, specific surface area, TOC, free oil content, and oil saturation index of each component were summarized;

[0074] By comparing the same parameters of different laminae / stratified components, the differences in reservoir and oil content between components at millimeter scale conditions are revealed;

[0075] Based on the differences in reservoir and oil content among components under millimeter scale conditions, the heterogeneity of reservoir and oil content of millimeter-scale shale oil is revealed.

[0076] Example 1

[0077] This experiment takes the full-diameter mudstone with laminar development in a typical continental shale oil key exploration layer in my country as an example. First, an anhydrous corundum (Φ0.38mm) wire cutting machine is used to cut perpendicular to the bedding development direction to prepare a half-diameter sample with a smooth cut surface. The length and width of the shale profile in this example are generally about 10cm. First, the shale sample with the profile facing up is placed in the BrukerM4 TORNADO spectrometer and waited until it is in a vacuum state. The beam excited by the multi-guide capillary focusing mirror (resolution 20μm) is scanned from point to line and then to surface. By measuring multiple elements and their combinations, different laminar / layered components are finely identified. Then, different components were drilled with the help of a micro-drill sampler. The content of the samples must meet the needs of subsequent supporting experiments. Among them, 2 mg of powdered samples were subjected to rock pyrolysis experiments to obtain information on the amount of free oil; 2 mg of powdered samples were subjected to TOC analysis and the results were combined with the free oil content to calculate the oil saturation index; 50 mg of powdered samples were subjected to PY-GC experiments to obtain the proportion of light and heavy oil components; 4 g of powdered samples were further divided into two equal parts, one of which needed to be dried at 60°C in a vacuum dryer for 12 hours before a nitrogen adsorption experiment; the other needed to be extracted with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and dried at 60°C for 12 hours to fully remove the residual fluid inside the sample, and then a nitrogen adsorption experiment was carried out. The pore size distribution was determined by comparing before and after extraction, and the pore result characteristics were determined using the nitrogen adsorption results after extraction, and then the reservoir properties of different laminar / layered components were evaluated. The free oil, oil saturation index, proportion of light and heavy oil components, and pore size distribution characteristics are comprehensively used to evaluate the oil content of different strata / layer components, and ultimately achieve millimeter-scale characterization of shale oil reservoir heterogeneity.

[0078] In the embodiment, the PY-GC analysis experiment operation process can be seen in the industry standard (SY / T6188-2016 Rock pyrolysis gas chromatography analysis method); the low-temperature nitrogen adsorption experiment operation process can be seen in the national standard (GB / T 21650.2-2008 Determination of pore size distribution and porosity of solid materials by mercury injection and gas adsorption method Part 2: Analysis of mesopores and macropores by gas adsorption method).

[0079] 1. Identification and drilling of millimeter-scale mineral components

[0080] The distribution characteristics of different laminae components in this example are shown in Figure 1 .

[0081] Shale oil and gas are generally enriched in black / gray-black shale formations with well-developed laminae / layers. Therefore, this example uses a gray-black shale with well-developed laminae and a key exploration interval as the experimental object (see Figure 1 a). The shale in this example is mainly composed of felsic minerals (elements: Si, O, Al, etc.), calcite (elements: Ca, C, O, Fe, Mn, etc.), dolomite (elements: Ca, C, O, Fe, Mg, Mn, etc.), clay (elements: Si, Al, O, etc.), pyrite (elements: S, Fe), etc. Based on the XRF analysis results (usually the elements after Al can be accurately identified), multiple elements that may constitute the shale components are combined (see Figure 1 b~e), by the content / color code of element combination ( Figure 1 f) It is clear that the shale is mainly composed of calcite laminae, felsic laminae and clay laminae. Considering the characteristics of the sample's rapid vertical changes in components, 11 micro-drilling sampling locations were determined for oil-bearing and reservoir evaluation. Figure 2 Micro-drill sampling locations and corresponding components.

[0082] The samples obtained by micro-drilling include calcite + clay, clay, felsic minerals and calcite, a total of four types. Through rock pyrolysis and TOC analysis, three parameters for evaluating oil content can be obtained: free hydrocarbon S1 (mg / g), TOC (wt%) and oil saturation index OSI (S1 / TOC×100, mg / g). Among them, S1 is often used to characterize the oil content of shale, TOC is often used to reflect the necessary conditions for shale hydrocarbon generation, and OSI represents the oil production capacity of shale. The higher the value, the higher the oil production capacity. The proportion of light and heavy hydrocarbon components is obtained through PY-GC experiments, showing the difference in the adsorption capacity of different components for hydrocarbons, thereby reflecting the mobility of shale oil. The higher the light component, the stronger the mobility, and the easier it is to extract shale oil. By comparing the results of nitrogen adsorption experiments before and after extraction, the pore size distribution characteristics of shale oil storage of different components are revealed. The larger the pore size of shale oil storage, the more movable the shale oil is, and the easier it is to obtain. In addition, nitrogen adsorption experiments after extraction can obtain two parameters for evaluating reservoir properties: pore volume (cm3 / g) and specific surface area (m 2 / g). The larger the pore volume, the larger the reservoir space and the stronger the reservoir performance; the specific surface area often reflects the number of micropores. When the specific surface area is smaller, it means that the pore volume provided by the micro-scale pores is smaller, the pore volume provided by the meso-macro pores is larger, and the movable proportion of shale oil is larger. The results obtained from the above experiments can be seen in Table 1.

[0083] Table 1 Results of supporting experiments based on micro-drill sampling

[0084]

[0085] 2. Reservoir Characterization

[0086] Through low-temperature nitrogen adsorption experiments, the pore volume and specific surface area can be calculated using the BJH model and BET theory (Table 1). Overall, the pore volume (V) and specific surface area (S) of each component in the millimeter scale range vary greatly, reflecting a strong heterogeneity. 3 / g~0.091cm 3 / g, S specific surface area is between 17.041m 2 / g~30.495m 2 / g, among which the pore volume and specific surface area corresponding to clay are larger than those of calcite + clay, felsic, calcite, pyrite, etc.

[0087] Figure 3 This is the pore size distribution curve of low temperature nitrogen adsorption (BJH model) after extraction. Figure 3 It can be seen that based on the pore size distribution characteristics obtained from the nitrogen adsorption experiment, the pore volume of pyrite at different scales is the smallest compared with calcite, felsic, clay, and calcite + clay, and the largest for clay and calcite + clay, which further shows that the increase in clay mineral content contributes to the increase in the total pore volume and the pore volume corresponding to pores of different scales. As a shale in the middle and high maturity stage, it belongs to the main stage of organic matter degradation and hydrocarbon generation to increase pores. The difference in TOC greatly causes the difference in pore structure. Figure 4 The relationship between TOC and pore volume (left) and specific surface area (right). Figure 4 It can be seen that TOC has a good positive correlation with pore volume and specific surface area.

[0088] 3. Characterization of Oil Content

[0089] According to Table 1, the oil content between millimeter-scale mineral layers varies significantly (2.88-4.45 mg / g), showing strong heterogeneity. Figure 5 is the relationship between free oil content S1 and TOC; Figure 5It can be seen that S1 and TOC have a good positive correlation and the S1 of the clay layer is higher than that of other components. This is because high TOC is not only a necessary condition for the large-scale hydrocarbon generation of medium- and high-maturity shale, but also a necessary condition for the degradation and formation of a large number of organic pores to provide crude oil storage space ( Figure 4 ). Combined with the reservoir evaluation, it is inferred that the organic-clay mineral complex can guarantee the generation and storage of more hydrocarbons to a great extent. In addition, the oil-containing components between different components in shale are also different. The ratio of light and heavy oil components (C1-C15) / (C15+) is 0.449-0.609. Such differences are mainly caused by the different reservoir characteristics of mineral components and the different adsorption capacity of pore walls for oil molecules. Since clay and calcite + clay components contain more organic-clay complexes, the adsorption capacity for hydrocarbon substances is greatly enhanced. It can be seen from Table 1 that S1 of some calcite layers shows low values ​​while (C1~C15) / (C15+) shows high values. This is because in the mature hydrocarbon generation stage of organic matter, some pore walls are in contact with hydrocarbon molecules for a long time, causing the pore walls to change from hydrophilic to oil-wet, and the oil-wet pore network continues to develop. Calcite is more likely to become oil-wet when in contact with hydrocarbon molecules, which increases the enrichment of light components.

[0090] Figure 6 is the pore size distribution curve based on the BJH model. By subtracting the pore size distribution curve (BJH model) obtained from the low-temperature nitrogen adsorption experiment after extraction from the corresponding pore size distribution curve (BJH model) before extraction, the pore size distribution characteristics of the retained oil can be obtained. Under laboratory conditions, the retained oil is mainly stored in pores of about 3nm and 10-100nm in shale. By comparison, Figure 6 The retained oil components and main pore size range of the clay components in the shale are concentrated in 10-100nm. Usually, the retained oil inside the shale is not all free oil, but also contains adsorbed oil. This part of the oil is often concentrated in pores of a few nanometers, which makes it impossible to mine it and has no meaning for actual production. The larger the pore size scale of the residual oil, the higher the proportion of free oil in the residual oil, and the greater the amount of movable oil. It can be seen that shales with high organic matter and clay mineral content have higher movable oil content than other shales, which is of great significance for the evaluation of shale oil "sweet spots".

[0091] 4. Characterization of millimeter-scale shale oil reservoir heterogeneity

[0092] Based on the experimental results of reservoir properties and oil content, five evaluation parameters including V, S, S1, OSI and TOC were used to evaluate the heterogeneity of shale oil reservoirs at the millimeter level. Figure 7 Spider diagram for evaluating reservoir and oil content of different components, Figure 7The characterization results of reservoir and oil content of different components show (parameters of the same lithology are averaged) that clay has larger / higher reservoir space and oil content than other lithologies, followed by calcite+clay and felsic, and calcite has the worst reservoir and oil content. Figure 8 is the relationship between the free hydrocarbon content and pore volume of different components, Figure 8 It can be seen that according to the intersection relationship of S1 and V of different components, S1 and V have an obvious positive correlation, among which TOC and mineral components are the key factors affecting the reservoir and oil content of shale. The higher the clay content and TOC, the higher the corresponding S1 and V. Based on the above evaluation results, it can be inferred that for shales in the medium and high maturity stages, the higher the TOC and clay content, the higher the corresponding shale oil storage capacity and oil content. At the same time, OSI is greater than 100 mg / g, which also reflects a higher movable oil content, and can be used as the first choice for exploration. That is, through the quantitative characterization of the oil content and reservoir properties of different mineral components in the millimeter scale range, a more refined and representative evaluation of the heterogeneity of shale oil reservoirs can be achieved.

[0093] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Therefore, the content of the present invention is not limited to the examples listed, and any equivalent changes taken by ordinary technicians in the field of the present invention by reading the specification of the present invention to the technical solution of the present invention are all covered by the claims of the present invention.

Claims

1. A method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity, characterized by: The following steps are involved: S1: Identification and drilling of millimeter-scale mineral components in shale; Accurately locate the distribution of different laminae / layer components, finely identify different laminae / layered components, and realize the identification of millimeter-level mineral components of shale; With the help of a micro-drill sampler, drilling is performed on the thin layers of different identified laminae / laminated components to obtain corresponding powdered samples, so that the content of the obtained samples meets the requirements of subsequent supporting experiments; S2: Based on the obtained powdered samples, oil-containing and oil-free tests are carried out; by comparing before and after extraction, the pore size distribution is determined to characterize the reservoir properties; S3: Based on the obtained powder samples, characterize the oil content of different laminae / layered components; S4: Based on the reservoir and oil content results of different laminae / layered components, the heterogeneity of shale oil reservoirs at the millimeter level is characterized; Based on the reservoir properties and oil content of different laminae / layered components, the free oil, oil saturation index, proportion of light and heavy oil components, pore size distribution, and pore size distribution characteristics are comprehensively compared with different laminae / layered components to finally achieve millimeter-level shale oil reservoir heterogeneity characterization.

2. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 1, characterized in that: Step S1: a method for identifying millimeter-scale mineral components of shale, comprising: The full-diameter mudstone core with laminae / layers is cut perpendicular to the bedding direction by an anhydrous diamond wire cutting machine to prepare a half-diameter shale sample with a smooth cutting surface; The cut shale sample section is placed upward in a Bruker M4 TORNADO spectrometer and after it is in a vacuum state, a light beam excited by a multi-guide capillary focusing mirror is used to scan point by point. The scanning time of each point is 3 to 5 ms, and the scanning is repeated once after the entire core section is scanned. The resolution of the light beam excited by the multi-guide capillary focusing mirror is 20 μm. After scanning, the element type is determined point by point, and specific elements are selected for combination with reference to the common mineral types of shale. After the combination, the different laminae / layered components are finely identified according to the proportion of the specific element content, thereby realizing the identification of millimeter-level mineral components of shale.

3. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 2, characterized in that: The shale sample is mainly composed of felsic minerals, calcite, dolomite, clay, and pyrite; the felsic minerals include the elements: Si, O, Al; calcite includes the elements: Ca, C, O, Fe, Mn; dolomite includes the elements Ca, C, O, Fe, Mg, Mn; clay includes the elements Si, Al, O; Pyrite includes the elements: S and Fe.

4. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 1, characterized in that: The S1 is based on a high-performance micro-area X-ray fluorescence spectrometer to accurately locate the distribution positions of different laminae / layer components and finely identify different laminae / layer components; Preferably, the high performance micro-area X-ray fluorescence spectrometer is a Bruker M4 TORNADO spectrometer.

5. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 1, characterized in that: Step S2: Based on the obtained powdered sample, a specific method for performing reservoir characterization includes: 1) Test the powdered samples obtained by the millimeter-level drill micro-drill prototype with and without oil; 2) The pore size distribution characteristics are determined by using the nitrogen adsorption results after extraction, and then the pore size distribution and specific surface area are derived respectively; the pore size distribution is determined by performing difference processing on the pore size distribution curves before and after extraction, thereby characterizing the reservoir properties of different laminae / layered components.

6. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 5, characterized in that: The method for testing the oil content of the powdered sample obtained by the millimeter-level drill bit micro-drill prototype is as follows: weigh the powdered sample, dry it at 60°C in a vacuum dryer for 12 hours, and then conduct a nitrogen adsorption experiment to obtain the pore size distribution characteristics under the oil-containing state.

7. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 5, characterized in that: The oil-free test method for the obtained powdered sample is: Weigh the powdered sample, extract it with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and dry it at 60℃ for 12h to fully remove the residual fluid inside the sample. After degreasing, conduct a nitrogen adsorption experiment to obtain the pore size distribution characteristics in the oil-free state.

8. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 5, characterized in that: The method to derive the pore size distribution and specific surface area is: The pore size distribution and specific surface area were derived using the BJH model and the BET model respectively.

9. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 1, characterized in that: Step S3 is a method for characterizing the oil content of different laminae / layered components based on the obtained powdered sample, including: 1) Weigh 1-5 mg of powdered sample for rock pyrolysis experiment to obtain information on free oil content; 2) Weigh 1-5 mg of powdered sample for TOC analysis, and combine the TOC analysis results with the free oil content to calculate the oil saturation index; 3) Weigh 50 mg of powdered sample and conduct pyrolysis-gas chromatography experiment to obtain the proportion of light and heavy oil components; 4) Based on the above results, the oil content of different laminae / layered components was characterized by obtaining three parameters: information on free oil content, oil saturation index, and the proportion of light and heavy oil components.

10. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity according to claim 1, characterized in that: The specific method of performing millimeter-level shale oil reservoir heterogeneity characterization based on the reservoir properties and oil content results of different laminae / layered components in step S4 includes: The reservoir and oil-bearing characterization parameters of different laminae / layered components were sorted out, and the pore volume, specific surface area, TOC, free oil content, and oil saturation index of each component were summarized; By comparing the same parameters of different laminae / stratified components, the differences in reservoir and oil content between components at millimeter scale conditions are revealed; Based on the differences in reservoir and oil content among components under millimeter scale conditions, the heterogeneity of reservoir and oil content of millimeter-scale shale oil is revealed.

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