A method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity

Abstract

The application provides a method for characterizing millimeter shale oil and gas reservoir heterogeneity, which mainly solves the problem of low reliability and precision of existing volume sampling method for evaluating reservoir results. Its characteristics are as follows: S1: mud shale millimeter mineral component identification and drilling; S2: based on the obtained powder sample, oil and non-oil tests are carried out; by comparing before and after extraction, the occurrence pore size distribution is determined to characterize the reservoir property; S3: based on the obtained powder sample, the oiliness of different lamina / laminated components is characterized; S4: based on the reservoir property and oiliness of different lamina / laminated components, the millimeter shale oil reservoir heterogeneity is characterized. The method can enhance the identification accuracy of shale lamina / laminated structure, realize millimeter fine characterization of different lamina / laminated properties, and provide favorable support for shale oil enrichment mechanism and "sweet spot" prediction.

Description

Technical Field

[0001] This invention relates to the field of oil and gas resource evaluation technology, and in particular to a method for characterizing the heterogeneity of millimeter-scale shale oil and gas reservoirs. Background Technology

[0002] With the recoverable resources of shale oil in my country increasing year by year, shale oil has become a strategic component for increasing China's oil and gas reserves and production. However, the geological characteristics of my country's continental shale are quite complex, mainly due to the influence of multiple factors during the sedimentary process, resulting in significant differences in rock structure and mineral composition. As is well known, continental shale usually occurs in a sheet-like stacked pattern with well-developed foliation, containing thin layers of sand and carbonates. In addition, the shale reservoir itself is dense, making it exhibit strong heterogeneity. Even by visual observation, there are significant differences in mineral composition, color brightness, thin layer thickness, and grain size at the millimeter scale. Undoubtedly, these differences will directly cause differences in reservoir properties and oil-bearing capacity. In the past, when preparing samples to characterize the reservoir properties and oil-bearing capacity of shale, researchers usually first divided a whole core sample (full / half diameter) into different regions, and then designed corresponding characterization experiments for different regions. Some experiments may require sample crushing and grinding, while others may require drilling. To mitigate the impact of heterogeneity on results, previous researchers typically thoroughly mixed powdered samples from the same rock before weighing and dividing them for experiments. However, conducting different experiments using this volumetric sampling method is highly susceptible to inconsistencies due to variations in mineral composition and structure within the rock, leading to inconsistent results, reduced reliability of reservoir evaluations, and limitations on shale oil exploration outcomes. Therefore, how to more accurately evaluate shale oil reservoirs at the millimeter scale and further reduce the impact of heterogeneity is a key research focus in shale oil reservoir evaluation. Summary of the Invention

[0003] The technical problem to be solved by this invention is to overcome the low reliability and accuracy of existing volumetric sampling methods for reservoir evaluation in the background art. Instead, it provides a method for characterizing the heterogeneity of shale oil and gas reservoirs at the millimeter level. This method enhances the accuracy of identifying and evaluating different laminar / layered structures of shale by accurately comparing the differences in reservoir and oil-bearing properties among different lithologies at the millimeter scale. It achieves millimeter-level fine characterization of different laminar / layered lithologies, providing favorable support for shale oil enrichment mechanisms and "sweet spot" prediction.

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

[0005] S1: Millimeter-level mineral composition identification and drilling of mudstone and shale;

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

[0007] Using a micro-drill sampler, drilling was performed on thin layers of different identified laminar / layered components to obtain corresponding powdered samples, ensuring that the content of the obtained samples met the requirements of subsequent supporting experiments.

[0008] S2: Based on the obtained powdered samples, oil-containing and oil-free tests are conducted; by comparing the pre- and post-extraction conditions, the storage capacity is characterized by determining the pore size distribution.

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

[0010] S4: Based on the above results of reservoir properties and oil-bearing properties of different laminar / layered components, the heterogeneity of shale oil reservoirs at the millimeter level is characterized.

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

[0012] Preferably, the method for identifying millimeter-scale mineral components of mudstone and shale in step S1 includes...

[0013] The full-diameter (original cylindrical) mudstone and shale core with layered / stratified development was cut with an anhydrous diamond wire cutter perpendicular to the direction of bedding development to prepare shale samples with smooth cut surfaces in the shape of half-diameter (semi-cylindrical).

[0014] After the cut shale sample is placed face up in the Bruker M4 TORNADO spectrometer and the vacuum state is reached, the beam excited by the multi-conductor capillary focusing lens (resolution 20 μm) is used to scan point by point. The scanning time for each point is 3 to 5 ms. After the entire core profile is scanned, the process is repeated once.

[0015] After scanning, the element types are determined point by point. Referring to the common mineral types of mudstone and shale, specific elements are selected and combined. Based on the content ratio of specific elements, different laminar / layered components are precisely identified, thereby achieving the identification of millimeter-level mineral components in mudstone and shale.

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

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

[0018] The preferred high-performance micro-area X-ray fluorescence spectrometer is the Bruker M4 TORNADO spectrometer.

[0019] Preferably, step S2, based on the acquired powdered sample, includes the following specific methods for characterizing its storage properties:

[0020] 1) Test the oil content and oil-free content of powdered samples obtained from a millimeter-level drill bit micro-drilling sampler;

[0021] 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 respectively. The storage pore size distribution is determined by subtracting the pore size distribution curves before and after extraction, thereby characterizing the storage capacity of different lamellar / layered components.

[0022] Preferably, the method for testing the oil content of powdered samples obtained from a millimeter-level drill bit micro-drilling sampler is as follows: weigh the powdered sample, dry it in a vacuum dryer at 60°C for 12 hours, and then perform nitrogen gas drying. Preferably, the method for testing the oil-free nature of the obtained powdered sample is as follows:

[0023] To obtain the pore size distribution characteristics of the powdered sample, it is necessary to first extract the sample with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and then dry it at 60°C for 12 hours to fully remove the residual fluid inside the sample and remove the oil. Then, a nitrogen adsorption experiment is performed to obtain the pore size distribution characteristics in the oil-free state.

[0024] The preferred method for deriving pore size distribution and specific surface area is as follows:

[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, based on the obtained powdered sample, involves a method for characterizing the oil content of different lamellar / layered components, including:

[0027] 1) Weigh 1-5 mg of powdered sample and conduct rock pyrolysis experiments to obtain information on the amount of free oil;

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

[0029] 3) Weigh 50mg of powdered sample and perform 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 lamellar / layered components was characterized by three parameters: the information on free oil content, oil saturation index, and the proportion of light and heavy oil components.

[0031] Preferably, the specific method for characterizing the heterogeneity of shale oil reservoirs at the millimeter level based on the reservoir properties and oil-bearing properties of different laminar / layered components in step S4 includes:

[0032] The reservoir and oil content characterization parameters of different lamellar / 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 lamellar / layered components, the differences in storage and oil content among components under millimeter-scale conditions are revealed.

[0034] Based on the differences in reservoir and oil-bearing properties among components at the millimeter scale, the heterogeneity of reservoir and oil-bearing properties in millimeter-scale shale oil is revealed.

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

[0036] This method for characterizing the heterogeneity of millimeter-scale shale oil and gas reservoirs has the following technical advantages:

[0037] (1) High evaluation accuracy

[0038] High-performance micro-area X-ray fluorescence spectroscopy accurately locates the distribution of different laminae / layer components. Using a millimeter-scale micro-drill bit, samples are obtained by drilling into thin layers of different lithologies, yielding corresponding powdered samples. Conventional pyrolysis, total organic carbon analysis, pyrolysis-gas chromatography, and low-temperature nitrogen adsorption experiments are then performed. The results show significant differences in pore volume, specific surface area, TOC, free oil content, and oil saturation index among different lithologies at the millimeter scale. Compared to previous methods of obtaining samples using volumetric methods and then conducting corresponding experiments, this method greatly improves the accuracy of the evaluation results, achieving millimeter-scale fine evaluation of different laminae / layer lithologies, providing strong support for shale oil exploration and development.

[0039] (2) Economical and universally applicable

[0040] The millimeter-scale micro-drill bit sampler is readily available and inexpensive. Considering the inherent characteristics of shale—primarily composed of clay minerals, with well-developed foliation and fine, easily fragmented grains—the sampler can quickly obtain the required sample quantity during shale drilling, ensuring the smooth progress of subsequent experiments. The drilling process is simple, convenient, and quick, requiring no adjustments to procedures or methods based on the specific properties of shale in different regions or strata. Therefore, this method demonstrates promising application prospects in characterizing millimeter-scale shale reservoirs and is suitable for wider application to other continental / marine shale formations.

[0041] (3) Highly identifiable and representative

[0042] Traditional volumetric sampling methods are too coarse, and the experimental results obtained from the acquired sample typically represent the information of the entire sample (half / full diameter). Shale often develops irregularly distributed lamellar / layered structures and lithologies, containing valuable information about shale reservoirs and oil-bearing potential. However, previous methods have been unable to effectively and accurately obtain this information. This invention utilizes high-performance micro-area X-ray fluorescence spectroscopy and micro-drilling sampling technology to rapidly and effectively acquire experimental samples, enabling more precise identification and characterization of reservoirs down to the millimeter level. Simultaneously, this method can refine the internal information of the entire shale sample, providing a more detailed measurement range and smaller scale, significantly improving the representativeness of the experimental results. Attached Figure Description

[0043] Figure 1 This is a distribution feature diagram of different laminar components in an embodiment of the present invention;

[0044] Figure 2 This is a diagram showing the location of micro-drill sampling points and their corresponding composition in an embodiment of the present invention;

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

[0046] Figure 4 This is a graph showing the relationship between TOC and pore volume (left) and specific surface area (right) in an embodiment of the present invention.

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

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

[0049] Figure 7 This is a spider diagram of the evaluation of the storage properties and oil content of different components in embodiments of the present invention;

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

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

[0052] This invention discloses a method for characterizing the heterogeneity of millimeter-scale shale oil and gas reservoirs, comprising the following steps:

[0053] S1: Millimeter-level mineral composition identification and drilling of mudstone and shale;

[0054] Based on the high-performance micro-area X-ray fluorescence spectrometer, the distribution of different lamellar / layered components can be accurately located, and different lamellar / layered components can be finely identified, realizing the identification of millimeter-level mineral components in mudstone and shale; the high-performance micro-area X-ray fluorescence spectrometer is a Bruker M4 TORNADO spectrometer.

[0055] Using a micro-drill sampler, drilling was performed on thin layers of different identified laminar / layered components to obtain corresponding powdered samples, ensuring that the content of the obtained samples met the requirements of subsequent supporting experiments.

[0056] The method for identifying millimeter-scale mineral components of mudstone and shale includes:

[0057] The full-diameter (original cylindrical) mudstone and shale core with layered / stratified development was cut with an anhydrous diamond wire cutter perpendicular to the direction of bedding development to prepare shale samples with smooth cut surfaces in the shape of half-diameter (semi-cylindrical).

[0058] After the cut shale sample is placed face up in the Bruker M4 TORNADO spectrometer and the vacuum state is reached, the beam excited by the multi-conductor capillary focusing lens (resolution 20 μm) is used to scan point by point. The scanning time for each point is 3 to 5 ms. After the entire core profile is scanned, the process is repeated once.

[0059] After scanning, the element types are determined point by point. Referring to the common mineral types of mudstone and shale, specific elements are selected and combined. Based on the content ratio of specific elements, different laminar / layered components are precisely identified, thereby achieving the identification of millimeter-level mineral components in mudstone and shale.

[0060] S2: Based on the obtained powdered samples, oil-containing and oil-free tests are performed; by comparing the pre- and post-extraction conditions, the storage capacity is characterized by determining the pore size distribution; specific methods include:

[0061] 1) Test the oil content and oil-free content of powdered samples obtained from a millimeter-level drill bit micro-drilling sampler;

[0062] The method for testing the oil content of powdered samples obtained from a millimeter-level drill bit micro-drilling sampler is as follows: Weigh the powdered sample, dry it in a vacuum dryer at 60℃ for 12 hours, and then perform nitrogen purification. The method for testing the oil-free nature of the obtained powdered sample is as follows:

[0063] To obtain the pore size distribution characteristics of the powdered sample, it is necessary to first extract the sample with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week and then dry it at 60°C for 12 hours to fully remove the residual fluid inside the sample and remove the oil. Then, a nitrogen adsorption experiment is performed to obtain the pore size distribution characteristics in the oil-free state.

[0064] 2) The pore size distribution characteristics were determined by the nitrogen adsorption results after extraction. The pore size distribution and specific surface area were derived by using the BJH (Barrette Joynere Halenda) model and the BET (Brunauer Emmette Teller) model, respectively. The storage pore size distribution was determined by subtracting the pore size distribution curves before and after extraction, thereby characterizing the storage capacity of different lamellar / layered components.

[0065] S3: Based on the obtained powdered samples, characterize the oil content of different lamellar / layered components. Specific methods include:

[0066] 1) Weigh 1-5 mg of powdered sample and conduct rock pyrolysis experiments to obtain information on the amount of free oil;

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

[0068] 3) Weigh 50mg of powdered sample and perform 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 lamellar / layered components was characterized by three parameters: the information on free oil content, oil saturation index, and the proportion of light and heavy oil components.

[0070] S4: Based on the above results of reservoir properties and oil-bearing properties of different laminar / layered components, the heterogeneity of shale oil reservoirs at the millimeter level is characterized.

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

[0072] Based on the reservoir and oil-bearing properties of different laminar / layered components, specific methods for characterizing the heterogeneity of millimeter-scale shale oil reservoirs include:

[0073] The reservoir and oil content characterization parameters of different lamellar / 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 lamellar / layered components, the differences in storage and oil content among components under millimeter-scale conditions are revealed.

[0075] Based on the differences in reservoir and oil-bearing properties among components at the millimeter scale, the heterogeneity of reservoir and oil-bearing properties in millimeter-scale shale oil is revealed.

[0076] Example 1

[0077] This experiment uses a full-diameter mudstone shale with lamellar development from a key exploration section of a typical continental shale oil field in my country as an example. First, an anhydrous diamond wire cutter (Φ0.38mm) was used to cut the shale along the direction perpendicular to the bedding development, preparing samples with smooth cut surfaces and a half-diameter specification. The length and width of the shale profile in this example are generally around 10cm. The shale sample with the profile facing upwards was placed in a Bruker M4 TORNADO spectrometer and brought to a vacuum state. Then, a beam of light excited by a multi-channel capillary focusing lens (resolution 20μm) was used to scan from point to line to surface. By measuring various elements and their combinations, different lamellar / layered components were precisely identified. Then, using a micro-drill sampler, different components were drilled. The sample content had to meet the requirements of subsequent supporting experiments. Among them, 2 mg of powdered sample was used for rock pyrolysis experiments to obtain information on free oil content; 2 mg of powdered sample was used for TOC analysis, and the results were combined with free oil content to calculate the oil saturation index; 50 mg of powdered sample was used for PY-GC experiments to obtain the proportion of light and heavy oil components; 4 g of powdered sample was further divided into two equal parts. One part needed to be dried at 60℃ for 12 h in a vacuum dryer and then subjected to nitrogen adsorption experiments; the other part needed to be extracted with a CH2Cl2 and C3H6O solution in a 3:1 volume ratio for one week and dried at 60℃ for 12 h to fully remove residual fluid inside the sample before nitrogen adsorption experiments. By comparing the extraction time and time, the pore size distribution was determined, and the porosity characteristics were determined using the nitrogen adsorption results after extraction, thereby evaluating the reservoir properties of different laminar / layered components. The oil-bearing properties of different laminae / layer components are evaluated by comprehensively considering free oil, oil saturation index, proportion of light and heavy oil components, and distribution characteristics of pore size, ultimately achieving millimeter-level characterization of shale oil reservoir heterogeneity.

[0078] In the examples, the PY-GC analysis experimental procedure can be found in the industry standard (SY / T6188-2016 Gas Chromatography Analysis Method for Rock Pyrolysis); the low-temperature nitrogen adsorption experimental procedure can be found in the national standard (GB / T 21650.2-2008 Mercury Intrusion Porosimetry and Gas Adsorption Method for Determination of Pore Size Distribution and Porosity of Solid Materials Part 2: Gas Adsorption Method for Analysis of Mesopores and Macropores).

[0079] I. Millimeter-level mineral component identification and drilling

[0080] The distribution characteristics of different laminar components in this embodiment are shown in [reference needed]. Figure 1 .

[0081] Shale oil and gas are generally enriched in black / grayish-black shale formations with well-developed lamellar / layered structures. Therefore, this example uses a grayish-black shale formation with well-developed lamellar structures, representing a key exploration stratum, as the experimental subject (see...). Figure 1 a). In this embodiment, the shale 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 (which can usually accurately identify elements after Al), multiple elements that may constitute the shale components are combined (see...). Figure 1 b~e), the content of element combinations / color scale ( Figure 1 f) It was determined that the shale was mainly composed of superimposed calcite lamellar, felsic lamellar, and clay lamellar. Considering the rapid vertical variation in the composition of this sample, 11 micro-drilling sampling locations were selected for oil-bearing and reservoir evaluation. Figure 2 This shows the sampling locations and corresponding components of the micro-drill.

[0082] The samples obtained from the micro-drilling included four types: calcite + clay, clay, felsic minerals, and calcite. Through rock pyrolysis and TOC analysis, three parameters for evaluating oil content were obtained: free hydrocarbons (S1) (mg / g), TOC (wt%), and the oil saturation index (OSI) (S1 / TOC×100, mg / g). S1 is commonly used to characterize shale oil content, TOC often reflects the necessary conditions for shale hydrocarbon generation, and OSI represents the oil-producing capacity of shale; a higher OSI value indicates a higher oil-producing capacity. PY-GC experiments were used to obtain the proportion of light and heavy hydrocarbon components, showing the differences in the adsorption capacity of different components for hydrocarbons, thus reflecting the mobility of shale oil. Higher light hydrocarbon content indicates stronger mobility, and easier shale oil extraction. By comparing the results of nitrogen adsorption experiments before and after extraction, the pore size distribution characteristics of shale oil with different components were revealed. Larger pore sizes indicate greater mobility and easier extraction of shale oil. In addition, nitrogen adsorption experiments after extraction can obtain two parameters for evaluating storage capacity: pore volume (cm³).3 / g) and specific surface area (m²) 2 / g). Larger pore volume indicates larger reservoir space and stronger reservoir performance; specific surface area often reflects the number of micropores. The smaller the specific surface area, the less pore volume is provided by micropores, while the larger the pore volume provided by meso-macropores, the greater the movable proportion of shale oil. The results obtained from the above experiments are shown in Table 1.

[0083] Table 1. Experimental results based on micro-drilling sampling

[0084]

[0085] II. Storage Characterization

[0086] Through low-temperature nitrogen adsorption experiments, the pore volume and specific surface area were calculated using the BJH model and BET theory (Table 1). Overall, the pore volume (V) and specific surface area (S) of each component varied significantly within the millimeter scale, reflecting strong heterogeneity. V was between 0.054 cm⁻¹. 3 / g~0.091cm 3 / g, the specific surface area of ​​S is between 17.041m² 2 / g~30.495m 2 / g, where the pore volume and specific surface area of ​​clay are larger than those of calcite + clay, felsic materials, calcite, pyrite, etc.

[0087] Figure 3 This is a pore size distribution curve of nitrogen adsorption at low temperature after extraction (BJH model). Figure 3 As can be seen from the pore size distribution characteristics obtained from nitrogen adsorption experiments, pyrite has the smallest pore volume at different scales compared to calcite, felsic materials, clay, and calcite + clay, while clay and calcite + clay have the largest. This further indicates that increasing clay mineral content contributes to the increase in total pore volume and the corresponding pore volume at different scales. As shale in its medium-to-high maturity stage, it belongs to the main stage of organic matter degradation, hydrocarbon generation, and porosimetry. Differences in total organic matter (TOC) significantly contribute to differences in pore structure. Figure 4 This is a graph showing the relationship between TOC and pore volume (left) and specific surface area (right). Figure 4 It can be seen that TOC has a strong positive correlation with both pore volume and specific surface area.

[0088] III. Characterization of Oil Content

[0089] As shown in Table 1, the oil content varies significantly between the millimeter-scale mineral layers (2.88–4.45 mg / g), indicating strong heterogeneity. Figure 5 The relationship between free oil content S1 and TOC; Figure 5It is evident that S1 and TOC show a strong positive correlation, with the S1 of the clay layer being higher than that of other components. This is because high TOC is not only a necessary condition for the large-scale hydrocarbon generation in medium-to-high maturity shale, but also a necessary condition for degradation to form numerous organic pores to provide storage space for crude oil. Figure 4 Based on reservoir evaluation, it is inferred that the organic matter-clay mineral complex can significantly ensure the simultaneous generation and storage of more hydrocarbons. Furthermore, the oil-bearing components within the shale exhibit differences, with the ratio of light to heavy oil components (C1–C15) / (C15+) ranging from 0.449 to 0.609. This difference is primarily due to the varying reservoir characteristics of the mineral components and the different adsorption capacities of the pore walls for oil molecules. Because clay and calcite+clay components contain more organic matter-clay complexes, their adsorption capacity for hydrocarbons is greatly enhanced. Table 1 shows that some calcite layers have low S1 values ​​and high (C1~C15) / (C15+) values. This is because during the mature hydrocarbon generation stage, some pore walls change from hydrophilic to oleophilic after prolonged contact with hydrocarbon molecules, and the oil-wet pore network continues to develop. Calcite is more likely to become oil-wetted when in contact with hydrocarbon molecules, which increases the enrichment of light components.

[0090] Figure 6 The image shows the pore size distribution curve obtained based on the BJH model. The pore size distribution characteristics of the retained oil can be obtained 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. Under laboratory conditions, the retained oil is mainly found in shale pores of approximately 3 nm and 10–100 nm. Through comparison, Figure 6 The clay components in shale contain retained oil components, and their main pore size range is concentrated in the 10–100 nm range. Typically, the retained oil within shale is not entirely free oil; it also contains adsorbed oil. This adsorbed oil often accumulates in pores of a few nanometers, making it unrecoverable and meaningless for actual production. The larger the pore size of the residual oil, the higher the proportion of free oil and the greater the amount of mobile oil. Therefore, shale with high organic matter and clay mineral content has a higher amount of mobile oil compared to other shale types, which is significant for evaluating the "sweet spot" of shale oil.

[0091] IV. Characterization of Heterogeneity in Millimeter-Scale Shale Oil Reservoirs

[0092] Based on the results of reservoir and oil-bearing experiments, the heterogeneity of millimeter-scale shale oil reservoirs was evaluated by comprehensively considering five evaluation parameters: V, S, S1, OSI, and TOC. Figure 7 Spider diagrams for evaluating the reservoir properties and oil content of different components, by Figure 7The reservoir and oil-bearing properties of different components are shown in the results (parameters of the same lithology are averaged). Clay has a larger / higher reservoir space and oil content than other lithologies, followed by calcite + clay and felsic materials. Calcite has the worst reservoir and oil-bearing properties. Figure 8 To illustrate the relationship between free hydrocarbon content and pore volume for different components, from Figure 8 As can be seen from the cross-correlation relationship between S1 and V of different components, S1 and V have a significant positive correlation. TOC and mineral composition are key factors affecting shale reservoir properties and oil content. Higher clay content and TOC correspond to higher S1 and V values. Based on the evaluation results, it can be inferred that for shale at medium to high maturity stages, higher TOC and clay content generally correspond to higher shale oil reservoir capacity and oil content. Simultaneously, an OSI greater than 100 mg / g also reflects higher movable oil content, making it a preferred exploration target. In other words, by quantitatively characterizing the oil-bearing and reservoir properties of different mineral components within a millimeter-scale range, a more refined and representative evaluation of shale oil reservoir heterogeneity can be achieved.

[0093] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the terms used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Therefore, the content of the present invention is not limited to the embodiments listed, and any equivalent modifications made to the technical solutions of the present invention by those skilled in the art through reading the present invention specification are covered by the claims of the present invention.

Claims

1. A method of characterizing millimeter-scale shale oil and gas reservoir heterogeneity, the method comprising: The method comprises the following steps: S1: mud shale millimeter level mineral component identification and drilling; accurately positioning the distribution position of different lamina / laminated components, finely identifying different lamina / laminated components, and realizing the identification of mud shale millimeter level mineral components; with the help of a micro drill sampler, drilling is carried out on the identified different lamina / laminated component thin layers and corresponding powdered samples are obtained, so that the content of the obtained samples meets the needs of subsequent supporting experiments; S2: based on the obtained powdered samples, oil-containing and oil-free tests are carried out; by comparison before and after extraction, the occurrence pore size distribution is determined to characterize the reservoir property; the specific method comprises: 1) oil-containing and oil-free tests are carried out on the powdered samples obtained by the millimeter level drill sample machine; 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; the occurrence pore size distribution is determined by difference processing of the pore size distribution curves before and after extraction, and the reservoir property of different lamina / laminated components is characterized; S3: based on the obtained powdered samples, the oil-bearing property of different lamina / laminated components is characterized; the specific method comprises: 1) 1-5 mg of powdered sample is weighed for rock pyrolysis experiment to obtain free oil content information; 2) 1-5 mg of powdered sample is weighed for TOC analysis, and the TOC analysis result is combined with the free oil content to calculate the oil saturation index; 3) 50 mg of powdered sample is weighed for pyrolysis-gas chromatography experiment to obtain the proportion of light and heavy oil components; 4) based on the above results, the oil-bearing property of different lamina / laminated components is characterized by the three parameters of obtained free oil content information, oil saturation index and proportion of light and heavy oil components; S4: based on the reservoir property and oil-bearing property of different lamina / laminated components, the millimeter level shale oil reservoir heterogeneity is characterized; specifically, it comprises: the obtained reservoir property and oil-bearing property characterization parameters of different lamina / laminated components are arranged, and the pore volume, specific surface area, TOC, free oil content and oil saturation index of each component are summarized; by comparing the same parameters of different lamina / laminated components, the differences in reservoir property and oil-bearing property among the components under millimeter scale conditions are revealed; based on the differences in reservoir property and oil-bearing property among the components under millimeter scale conditions, the heterogeneity of millimeter level shale reservoir property and oil-bearing property is revealed.

2. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 1, wherein: The method for identifying the millimeter level mineral components of mud shale in step S1 comprises: a full-diameter mud shale core with developed lamina / lamination is cut by an anhydrous diamond wire cutting machine perpendicular to the development direction of the bedding, and a shale sample with a smooth cut surface and a half-diameter sample style is prepared; the cut shale sample is placed with the section upward in a Bruker M4 TORNADO spectrometer and scanned point by point after the vacuum state is reached, the scanning time of each point is 3-5 ms, and the scanning is repeated once after the scanning of the whole core section is completed; the resolution of the light beam excited by the multi-guide capillary focusing mirror is 20 μm. After scanning, the element type of each point is determined, the common mineral types of shale are referred to, specific elements are selected for combination, and after combination, the specific element content ratio is used to finely and clearly distinguish different lamellar / laminated components, thereby realizing the identification of millimeter-level mineral components of shale.

3. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 2, wherein: The shale sample is composed of felsic minerals, calcite, dolomite, clay, and pyrite; the felsic minerals include elements Si, O, and Al; the calcite includes elements Ca, C, O, Fe, and Mn; the dolomite includes elements Ca, C, O, Fe, Mg, and Mn; the clay includes elements Si, Al, and O; and the pyrite includes elements S and Fe. The S1 is based on accurate positioning of the distribution positions of different lamellar / laminated components by a high-performance micro-area X-ray fluorescence spectrometer, and fine identification of different lamellar / laminated components.

4. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 1, wherein: 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 of claim 4, wherein: The method for testing the oil content of the powder sample obtained by the millimeter-level drill bit micro-drill sample machine is as follows: the powder sample is weighed, dried at 60 DEG C in a vacuum drying machine for 12 hours, and then subjected to nitrogen adsorption experiment to obtain the pore size distribution characteristics under the oil-containing state.

6. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 1, wherein: The method for testing the oil-free state of the obtained powder sample is as follows:

7. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 1, wherein: The powder sample is weighed, extracted with a solution of CH2Cl2 and C3H6O in a volume ratio of 3:1 for one week, dried at 60 DEG C for 12 hours, and then subjected to nitrogen adsorption experiment to obtain the pore size distribution characteristics under the oil-free state. The method for deriving the pore size distribution and specific surface area is as follows:

8. The method for characterizing millimeter-scale shale oil and gas reservoir heterogeneity of claim 1, wherein: The BJH model and the BET model are used to derive the pore size distribution and specific surface area, respectively. ​

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