A method for measuring hydrocarbon content of different occurrence states of shale based on imbibition and pyrolysis

Abstract

The application discloses a shale hydrocarbon content measurement method based on imbibition and pyrolysis of different occurrence states, and the method comprises the following steps: establishing a two-dimensional nuclear magnetic resonance fluid identification chart and a conversion equation between mass and nuclear magnetic signal quantity for shale in a research area; measuring two-dimensional nuclear magnetic resonance signals of original samples and samples in a dried state to determine the amount of medium free hydrocarbon; combining two-dimensional nuclear magnetic resonance signals of pyrolysis and dried samples to distinguish bound hydrocarbon and adsorbed hydrocarbon; carrying out imbibition of crude oil at formation temperature on the dried samples to determine the amount of light free hydrocarbon; selecting shale samples of different lithofacies in the research area, quantifying oil components of different occurrence states of the shale samples of different lithofacies, counting proportions of different components, and selecting shale lithology with good mobility. The application realizes accurate quantification of shale hydrocarbon of different occurrence states by combining two-dimensional nuclear magnetic resonance, imbibition and pyrolysis technology, and provides key technical support for shale oil reservoir evaluation and development plan formulation.

Description

Technical Field

[0001] This invention relates to a method for measuring hydrocarbon content in shale under different occurrence states, specifically a method for measuring hydrocarbon content in shale under different occurrence states based on infiltration and pyrolysis. Background Technology

[0002] Shale oil "sweet spots" refer to high-quality source rocks or reservoir segments within shale oil formations that possess high oil content, good reservoir properties, and excellent fracturing resilience. These are key target formations for achieving large-scale, efficient development. The occurrence characteristics of shale oil and the hydrocarbon content in different occurrence states are core evaluation parameters for selecting optimal shale oil sweet spots. Clarifying the mobility differences and distribution characteristics of hydrocarbons in different occurrence states provides a scientific basis for distinguishing between total resources and recoverable resources, thereby maximizing the benefits of shale oil development.

[0003] The hydrocarbon occurrence states of shale oil can be broadly classified into three categories: free state, adsorbed state, and swollen state. Free hydrocarbons refer to hydrocarbons freely occurring within the pores, fractures, and other reservoir spaces of shale, and are the most valuable type of occurrence in shale oil development. Based on mobility differences, free hydrocarbons can be further divided into mobile hydrocarbons and bound hydrocarbons. Mobile hydrocarbons are further subdivided into light free hydrocarbons and medium free hydrocarbons; the former has a lower carbon number and higher mobility, while the latter has a higher carbon number but still possesses mobility. Bound hydrocarbons are hydrocarbons that are restricted by pore throats and capillary confinement, and cannot flow freely under conventional development conditions. Adsorbed hydrocarbons are hydrocarbons that adhere to the surface of shale mineral particles, the interlayer of clay minerals, or the surface of kerogen through physical or chemical processes; these hydrocarbons have extremely poor mobility. Swollen hydrocarbons refer to a type of occurrence in which hydrocarbon molecules are dissolved inside the kerogen, and have the worst mobility.

[0004] Currently, experimental methods for characterizing hydrocarbons in different occurrence states in shale include multi-temperature-step pyrolysis and two-dimensional nuclear magnetic resonance (NMR). Multi-temperature-step pyrolysis utilizes the differences in the degree of binding between hydrocarbons in different occurrence states and the pores of the shale matrix, as well as the differences in the thermal stability of hydrocarbon molecules. By setting a gradient heating program, hydrocarbons are released sequentially in a certain order. Based on the content and composition of products in different temperature ranges, the occurrence states can be distinguished and quantitatively characterized. Multi-temperature-step pyrolysis is widely applicable to organic-rich mudstone and shale formations and can measure hydrocarbons in different occurrence states, such as free oil and adsorbed oil. However, due to limitations in experimental principles and geological conditions, the actual operation and measurement results of multi-temperature-step pyrolysis are subject to certain limitations.

[0005] 1) Samples are usually stored for a long time. Even frozen and sealed samples will lose some light hydrocarbons during the sample crushing process, and the measurement results will underestimate the actual amount of free hydrocarbons. 2) Relying solely on temperature gradients to distinguish between free oil and adsorbed oil lacks an absolutely reliable theoretical basis, leading to deviations in free hydrocarbon measurement results; 3) For continental shale reservoirs with strong heterogeneity, the multi-temperature-stage pyrolysis model based on pyrolysis data to evaluate mobile hydrocarbons is difficult to adapt to such complex reservoir characteristics.

[0006] Two-dimensional nuclear magnetic resonance (2D NMR) is based on the differences in the relaxation signals of hydrogen nuclei in hydrocarbon molecules. By combining two-dimensional NMR spectra (vertical relaxation time T1 and transverse relaxation time T2), it utilizes the differences in relaxation signals corresponding to hydrocarbons in different occurrence states to achieve the identification and quantification of their occurrence states. 2D NMR can accurately characterize hydrocarbons in different occurrence states and can perform non-destructive testing of samples. However, it can only distinguish between free oil and adsorbed oil, and cannot finely differentiate between mobile and bound oil within free oil. Furthermore, the measurement results are affected by the sample condition; for commonly placed shale samples, the volatilization of light hydrocarbons leads to lower free hydrocarbon measurement results.

[0007] Therefore, traditional single multi-temperature-level pyrolysis method and two-dimensional nuclear magnetic resonance method are difficult to effectively characterize the hydrocarbon content of shale oil reservoirs under different occurrence states. There is an urgent need to propose a quantitative characterization method for hydrocarbon content of shale oil reservoirs under different occurrence states.

[0008] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to provide a method for measuring hydrocarbon content in shale under different occurrence states based on percolation and pyrolysis. This method solves the problems of easy volatility of light free hydrocarbons and poor adaptability to complex reservoirs in the measurement of hydrocarbon content in shale under different occurrence states by traditional single experimental methods. The method of this invention achieves accurate identification and quantitative characterization of hydrocarbons in different occurrence states such as light free hydrocarbons, medium free hydrocarbons, bound hydrocarbons and adsorbed hydrocarbons in shale, providing scientific and reliable experimental data support for the selection of sweet spots and resource evaluation of shale oil.

[0010] To achieve the above objectives, this invention provides a method for measuring hydrocarbon content in shale under different occurrence states based on infiltration and pyrolysis, the method comprising: A two-dimensional nuclear magnetic resonance (NMR) fluid identification chart and a mass-NMR signal conversion equation were established for shale in the study area. The two-dimensional NMR fluid identification chart was constructed from the distribution areas of organic matter, free oil, and adsorbed oil. The two-dimensional NMR signals of the original sample and the dried sample were measured to determine the amount of medium-quality free hydrocarbons. The bound hydrocarbons and adsorbed hydrocarbons were distinguished by combining the two-dimensional NMR signals of the pyrolysis and dried samples. Crude oil permeation experiments were conducted on the dried sample at formation temperature to determine the amount of light-quality free hydrocarbons. Shale samples of different lithofacies in the study area were selected, and the oil components of different occurrence states of shale samples of different lithofacies were quantified, the proportion of different components was statistically analyzed, and shale lithologies with good mobility were selected.

[0011] Preferably, the establishment of the two-dimensional nuclear magnetic resonance fluid identification chart and the conversion equation between mass and nuclear magnetic resonance signal quantity is based on samples covering different lithologies in the study area.

[0012] Preferably, the establishment of the two-dimensional nuclear magnetic resonance fluid identification chart and the conversion equation between mass and NMR signal quantity includes: performing wash oil drying and saturated crude oil operations on the original sample to obtain wash oil dried sample and saturated crude oil sample, and measuring the two-dimensional NMR signal quantity and mass of each sample, converting the two-dimensional NMR signal quantity of each state onto the two-dimensional NMR T1~T2 chart; comparing the two-dimensional NMR charts of the original state and the wash oil dried state to determine the distribution area of ​​organic matter; comparing the two-dimensional NMR charts of the wash oil dried state and the saturated formation crude oil state to determine the distribution areas of free oil and adsorbed oil; establishing a two-dimensional NMR fluid identification chart for the shale in the study area to identify the positions of kerogen, adsorbed oil and free oil in the two-dimensional chart; based on the two-dimensional NMR signal quantity and mass of the saturated formation crude oil column sample under the two-dimensional NMR signal quantity and mass states of wash oil dried state and saturated crude oil, obtaining the two-dimensional NMR signal quantity and mass of the crude oil, establishing a mathematical equation with the fluid mass difference and signal quantity difference, and obtaining the conversion equation between the two-dimensional NMR signal quantity and mass of the crude oil.

[0013] Preferably, the determination of the median free hydrocarbon content includes: selecting a shale sample to be studied, measuring the two-dimensional nuclear magnetic resonance signal of the original rock column sample, drying the column sample to obtain a dried column sample, conducting a two-dimensional nuclear magnetic resonance experiment on the dried column sample, measuring the nuclear magnetic signal and mass of the dried column sample; identifying the nuclear magnetic signal of the oil region using the two-dimensional nuclear magnetic resonance fluid identification chart, determining the reduction in oil signal after drying, calculating the reduction in oil in the sample according to the mass-NMR signal conversion equation, and dividing the result by the mass of the dried sample to obtain the median free hydrocarbon content in the sample.

[0014] Preferably, the distinction between bound hydrocarbons and adsorbed hydrocarbons includes: identifying the signal quantity of the oil region based on the two-dimensional nuclear magnetic resonance (NMR) signal of the dried column sample of the shale sample under study, combined with a two-dimensional NMR fluid identification chart; obtaining the mass of residual oil in the sample according to the mass-NMR signal quantity conversion equation; dividing the mass of the dried sample by the mass of the sample to obtain the residual oil content per unit mass of rock; pulverizing the dried sample of the shale sample under study, mixing it evenly, and then performing multi-temperature-stage pyrolysis on a portion of the pulverized sample, with the temperature points set at 300℃, 450℃, and 600℃, maintaining the temperature at each temperature point for a period of time, and measuring the free hydrocarbon content S1 and the adsorbed hydrocarbon content S2 respectively. 2-1 and the amount of hydrocarbons cracked from kerogen S 2-2 Parameters; then subtract the amount of adsorbed hydrocarbons per unit mass from the amount of residual rock oil per unit mass obtained from the dried sample to obtain the amount of bound hydrocarbons in the sample.

[0015] More preferably, the dried shale sample to be studied is pulverized to 100 mesh; or / and, the heating rate of the multi-temperature-stage pyrolysis is 25℃ / min; or / and, the temperature of the single temperature point is maintained for 3min.

[0016] Preferably, the determination of the amount of light free hydrocarbons includes: measuring the two-dimensional nuclear magnetic resonance (NMR) signal quantity and mass of the shale sample under study in its original state; immersing it in formation crude oil at a high temperature of 70°C; taking it out at regular intervals to measure the two-dimensional NMR signal; when the NMR signal no longer changes, the permeation reaches equilibrium; measuring the two-dimensional NMR signal after permeation with crude oil; extracting the oil region signal based on the original state and the two-dimensional NMR signal after permeation with crude oil; calculating the change in oil NMR signal quantity; calculating the recovered oil quantity based on the mass-NMR signal quantity conversion equation; and dividing the recovered oil quantity by the original state sample mass to obtain the amount of light free hydrocarbons.

[0017] More preferably, the sample is immersed in formation crude oil at a high temperature of 70°C, and the sample is taken out every 24 hours to measure the two-dimensional nuclear magnetic resonance signal.

[0018] Preferably, the oil components of different occurrence states of shale samples of different lithofacies are quantified, and at least 5 shale samples of each lithofacies are selected from the study area.

[0019] Preferably, the selected shale lithology has good mobility and is selected from lithologies with a high proportion of light and medium free hydrocarbons.

[0020] The method for measuring hydrocarbon content in shale under different occurrence states based on percolation and pyrolysis, as proposed in this invention, solves the problems of easy volatility of light free hydrocarbons and poor adaptability to complex reservoirs in the measurement of hydrocarbon content in shale under different occurrence states by traditional single experimental methods. It has the following advantages: (1) The method of the present invention combines the percolation experiment with pyrolysis and two-dimensional nuclear magnetic resonance technology, which breaks through the limitations of the traditional single method. The percolation experiment is carried out under simulated formation temperature conditions, which can effectively recover the light free hydrocarbons volatilized due to sample placement, and make up for the shortcomings of two-dimensional nuclear magnetic resonance in measuring light hydrocarbons. The multi-temperature-level pyrolysis provides a reliable basis for the identification of adsorbed hydrocarbons through precise temperature gradient settings. Combined with the residual oil data obtained by two-dimensional nuclear magnetic resonance, it realizes the accurate distinction between bound hydrocarbons and adsorbed hydrocarbons. (2) The two-dimensional nuclear magnetic resonance fluid identification chart and the conversion equation between mass and nuclear magnetic signal quantity established by the method of the present invention provide a unified standard for the quantification of hydrocarbons in different occurrence states. The chart can clearly define the distribution areas of organic matter, free oil and adsorbed oil in the two-dimensional nuclear magnetic spectrum, and the conversion equation ensures the accurate conversion of nuclear magnetic signal quantity to actual mass, thereby improving the reliability and comparability of measurement results. (3) The method of the present invention has a rigorous logic and standardized operation throughout the entire measurement process, from sample pretreatment to step-by-step determination of hydrocarbons in various occurrence states. It clearly specifies key parameters such as the particle size of dried sample, pyrolysis heating rate and temperature holding time, which reduces the error in the experimental process and ensures the consistency and scientific nature of the measurement data of shale samples of different lithofacies. It lays a solid data foundation for the subsequent selection of sweet spot areas of shale oil and resource evaluation. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the method for measuring hydrocarbon content in shale oil under different occurrence states based on infiltration and pyrolysis, according to the present invention.

[0022] Figure 2 This is a schematic diagram of a two-dimensional nuclear magnetic resonance fluid identification plate, which is an application example of the present invention.

[0023] Figure 3 This is a schematic diagram illustrating the correlation between fluid mass and two-dimensional NMR signal quantity in an application example of the present invention.

[0024] Figure 4 This is a schematic diagram illustrating the content of shale oil in different lithologies under different occurrence states, which is an application example of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that: Unless otherwise specified in the examples, conditions should be followed according to standard conditions or the manufacturer's recommendations. Instruments whose manufacturers are not specified are all commercially available products. Raw materials and reagents whose manufacturers are not specified are all commercially available goods or can be prepared using known methods.

[0027] In this invention, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are used only for simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0028] The features mentioned in this invention can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification, provided that there is no contradiction in the combination of these features. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0029] In the description of this invention, it should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Currently, the technical methods face three main challenges: First, light free hydrocarbons in shale oil reservoirs are highly volatile, leading to experimental measurements that are less than the actual formation reserves. Second, there is a lack of reliable theoretical basis for distinguishing shale oil in different formation states based on temperature gradients. Third, two-dimensional nuclear magnetic resonance (NMR) cannot differentiate between mobile oil (i.e., mobile hydrocarbons) and bound oil (i.e., bound hydrocarbons) within free hydrocarbons, making it difficult to accurately evaluate the different components of free hydrocarbons in shale oil reservoirs. Therefore, it is necessary to effectively recover light free hydrocarbons to obtain the original reserves of light free oil under formation conditions, while simultaneously developing experimental methods to distinguish between bound and mobile hydrocarbons. This would allow for an accurate and systematic characterization of the content of light, medium, bound, and adsorbed hydrocarbons in shale oil.

[0031] This invention provides a method for measuring hydrocarbon content in shale under different occurrence states based on infiltration and pyrolysis, such as... Figure 1 As shown, it includes: S101: Establish a two-dimensional nuclear magnetic resonance fluid identification chart and a conversion equation between mass and nuclear magnetic resonance signals for shale in the study area; S102: Measure the two-dimensional nuclear magnetic resonance signal of the original sample and the dried sample to determine the amount of medium-quality free hydrocarbons; S103: By combining the two-dimensional nuclear magnetic resonance signals of pyrolysis and dried samples, bound hydrocarbons and adsorbed hydrocarbons can be distinguished. S104: Conduct crude oil permeation experiments at formation temperature on dried samples to determine the amount of light free hydrocarbons; S105: Select shale samples of different lithofacies in the study area, quantify the oil components of different occurrence states of shale samples of different lithofacies, count the proportion of different components, and select shale lithologies with good mobility.

[0032] The following examples illustrate in detail the method for measuring hydrocarbon content in shale under different occurrence states based on infiltration and pyrolysis provided by the present invention.

[0033] Example 1 Jimsar Lucao Gou Formation shale oil, as my country's first national-level continental shale oil demonstration area, has accumulated a production exceeding 5 million tons. However, due to the complex reservoir lithology and pore structure, the occurrence characteristics of Jimsar shale oil vary considerably. This embodiment takes two reservoirs in the Jimsar Depression, the second section (upper sweet spot) and the first section (lower sweet spot), as examples to further determine the dominant lithology of the sweet spots and explain the specific steps of the method for measuring hydrocarbon content in different occurrence states of shale based on permeation and pyrolysis, including:

[0034] (1) Establish a two-dimensional nuclear magnetic resonance fluid identification chart and a conversion equation between mass and nuclear magnetic resonance signals for shale in the study area. Core samples of Permian Lucaogou Formation sweet spot shale were collected in the Jimsar Depression at a depth of 4000-4500m to ensure that the samples covered different lithologies in the selected study area (including silty shale, dolomitic silty shale, dolomitic silty shale, silty dolomitic shale, and micritic dolomitic shale). The cores were drilled parallel to the strata. The collected samples were cut into regular columns (5cm in length and 2.5cm in diameter), and then each column was cut into two original core columns of 2.5cm in length.

[0035] Five original core samples of 2.5 cm were selected, with each sample representing a different lithology. This ensured that the selected samples covered as much of the lithology in the study area as possible. The original samples were subjected to wash-oil drying and saturated crude oil operations to obtain wash-oil dried samples and saturated crude oil samples. The two-dimensional nuclear magnetic resonance (NMR) signal intensity and mass of the original samples (i.e., samples in their original state), wash-oil dried samples (i.e., samples in the wash-oil dried state, dried at 110℃ for 48 h), and saturated crude oil samples (i.e., samples in the saturated formation crude oil state, saturated at 25 MPa for 72 h) were measured. The two-dimensional NMR signal intensity of each state was converted onto two-dimensional NMR T1~T2 plates.

[0036] By comparing the two-dimensional nuclear magnetic resonance (NMR) maps of the original state and the washed-oil-dried state, the distribution area of ​​organic matter was determined. Similarly, by comparing the two-dimensional NMR maps of the washed-oil-dried state and the state of saturated formation crude oil, the distribution areas of free oil and adsorbed oil were determined. Based on this, a two-dimensional NMR fluid identification map for the shale in the study area was established. Figure 2 The positions of kerogen (i.e., organic matter), adsorbed oil (i.e., adsorbed hydrocarbons), and free oil (i.e., free hydrocarbons) in the two-dimensional plate were identified, as shown in Table 1.

[0037] Table 1 shows the positions of the fluid in the two-dimensional diagram. Based on the two-dimensional NMR signal quantity and mass of crude oil under two conditions—washed oil drying and saturated crude oil—the two-dimensional NMR signal quantity and mass of crude oil in saturated rock column samples were obtained. A mathematical equation was established using the fluid mass difference and signal quantity difference. Figure 3 The following equations for the conversion of crude oil two-dimensional NMR signal quantity and mass are derived:

[0038] y=7012x (1) In equation (1), x represents the fluid quality difference; y represents the signal difference.

[0039] (2) Measure the two-dimensional nuclear magnetic resonance signals of the original sample and the dried sample to determine the amount of medium-quality free hydrocarbons. The same sample from the same study area was reselected as the shale sample to be studied. The sample was cut into two parallel cylindrical samples with a length of 2.5 cm by wire cutting. The two-dimensional nuclear magnetic resonance signal of the original rock cylindrical sample was measured. The cylindrical sample was then dried (110℃, 24h) to obtain a dried cylindrical sample. Two-dimensional nuclear magnetic resonance experiments were carried out on the dried cylindrical sample to measure the nuclear magnetic signal and mass of the dried cylindrical sample. Based on the two-dimensional nuclear magnetic resonance fluid identification chart obtained above, the nuclear magnetic signal of the oil region was identified, and the amount of oil signal reduction after drying (i.e., signal difference) was obtained. Then, according to the conversion equation between oil mass and nuclear magnetic signal, the amount of oil reduction in the sample (i.e., fluid mass difference) was calculated. Divided by the mass of the dried sample, the median free hydrocarbon content in the sample was obtained.

[0040] (3) Combine the two-dimensional nuclear magnetic resonance signals of pyrolysis and drying samples to distinguish between bound hydrocarbons and adsorbed hydrocarbons. Based on the two-dimensional nuclear magnetic resonance (NMR) signal of the dried column of the shale sample to be studied, combined with the two-dimensional NMR fluid identification chart, the signal quantity of the oil region is identified. According to the conversion equation between oil signal quantity and mass, the mass of residual oil in the sample is obtained. Dividing it by the mass of the dried sample, the residual oil content per unit mass of rock is obtained (unit: mg / g).

[0041] The dried sample was pulverized to 100 mesh, mixed evenly, and a portion of the pulverized sample was subjected to multi-temperature-stage pyrolysis (heating rate 25℃ / min). The temperature points were set at 300℃, 450℃, and 600℃, and each temperature point was maintained for 3 minutes. The amount of free hydrocarbon S1 and adsorbed hydrocarbon S2 were measured respectively. 2-1 and the amount of hydrocarbons cracked from kerogen S 2-2 The parameters are then calculated; the amount of adsorbed hydrocarbons per unit mass is subtracted from the amount of residual rock oil per unit mass obtained from the dried sample to obtain the amount of bound hydrocarbons in the sample (unit: mg / g).

[0042] (4) Conduct a formation temperature-based crude oil percolation test on the dried sample to determine the amount of light free hydrocarbons. Another 2.5cm parallel column sample was used to measure the two-dimensional nuclear magnetic resonance (NMR) signal quantity and mass in its original state. It was then immersed in the formation crude oil at a high temperature (70℃). The sample was taken out every 24 hours to measure the two-dimensional NMR signal. When the NMR signal did not change, the permeation reached equilibrium, and the two-dimensional NMR signal after the crude oil permeation was measured. Based on the two-dimensional NMR signals in the original state and after the crude oil permeation, the oil region signal was extracted, and the change in oil NMR signal quantity was calculated. According to the conversion equation between oil mass and NMR signal quantity in equation (1), the amount of oil recovered by permeation was calculated, and then divided by the mass of the original sample to obtain the amount of light free hydrocarbons (unit: mg / g).

[0043] (5) Quantify the oil components in different occurrence states and statistically analyze the proportion of different components. Select shale samples of different lithofacies from the study area, ensuring at least 5 samples for each lithology, and repeat steps (2) to (4) above. Measure the amount of light free hydrocarbons, medium free hydrocarbons, adsorbed hydrocarbons, and bound hydrocarbons in each sample (all in mg / g). Analyze the proportion of hydrocarbons in different occurrence states according to lithology, and select lithologies with high proportions of light and medium free hydrocarbons as the preferred lithologies. See Table 2. For the Lucaogou Formation shale reservoir in the Jimsar Depression, dolomitic silty shale and silty shale have higher proportions of light and medium free hydrocarbons, followed by dolomitic silty shale. That is, silty shale and dolomitic silty shale are the lithologies with good occurrence characteristics in the Lucaogou Formation. Figure 4 ).

[0044] Table 2. Lithological statistics on the proportion of hydrocarbons in different occurrence states Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for measuring hydrocarbon content in shale under different occurrence states based on percolation and pyrolysis, characterized in that, The method includes: Two-dimensional nuclear magnetic resonance fluid identification charts and mass-NMR signal conversion equations were established for shale samples of different lithofacies in the study area. The two-dimensional nuclear magnetic resonance fluid identification charts were constructed from the distribution regions of organic matter, free oil and adsorbed oil. The two-dimensional nuclear magnetic resonance signal of the original core sample and the dried core sample under drying conditions were measured to determine the amount of medium-quality free hydrocarbons. By combining the two-dimensional nuclear magnetic resonance signal quantities of the pyrolysis and dried column samples of the shale samples under study, bound hydrocarbons and adsorbed hydrocarbons can be distinguished. To determine the amount of light free hydrocarbons, a crude oil permeation experiment was conducted on the dried column sample at formation temperature. This included immersing the sample in formation crude oil at a high temperature of 70°C, taking it out at intervals to measure the two-dimensional nuclear magnetic resonance (NMR) signal, and measuring the two-dimensional NMR signal after the crude oil permeation reached equilibrium when the NMR signal did not change. Shale samples of different lithofacies in the study area were selected as shale samples to be studied. The oil components of different occurrence states of shale samples of different lithofacies were quantified, the proportion of different components was statistically analyzed, and shale lithology with good mobility was selected. The distinction between bound hydrocarbons and adsorbed hydrocarbons includes: Based on the two-dimensional nuclear magnetic resonance signal of the dried column of the shale sample to be studied, combined with the two-dimensional nuclear magnetic resonance fluid identification chart, the signal of the oil region is identified. According to the mass-NMR signal conversion equation, the mass of residual oil in the shale sample to be studied is obtained. Dividing it by the mass of the dried column, the amount of residual oil per unit mass of rock is obtained. The dried columnar sample of the shale to be studied was pulverized and mixed evenly. A portion of the pulverized sample was then subjected to multi-temperature pyrolysis at 300℃, 450℃, and 600℃. Each temperature point was maintained for a period of time, and the amount of free hydrocarbons S1 and adsorbed hydrocarbons S2 were measured respectively. 2-1 and the amount of hydrocarbons cracked from kerogen S 2-2 Parameters; then subtract the amount of adsorbed hydrocarbons per unit mass from the amount of residual oil per unit mass of rock obtained from the dried column sample to obtain the amount of bound hydrocarbons in the shale sample under study.

2. The measurement method according to claim 1, characterized in that, The establishment of the two-dimensional nuclear magnetic resonance fluid identification chart and the conversion equation between mass and nuclear magnetic resonance signal quantity was carried out using different lithofacies shale samples covering different lithologies in the study area.

3. The measurement method according to claim 1, characterized in that, The establishment of the two-dimensional nuclear magnetic resonance fluid identification chart and the conversion equation between mass and nuclear magnetic resonance signal quantities includes: The original core samples were subjected to oil washing and drying and saturated formation crude oil operations to obtain oil washing and drying samples and saturated formation crude oil samples. The two-dimensional nuclear magnetic resonance signal quantity and mass of each sample were measured, and the two-dimensional nuclear magnetic resonance signal quantity of each state was converted onto two-dimensional nuclear magnetic resonance T1~T2 plates. By comparing the two-dimensional nuclear magnetic resonance fluid identification maps of the original state and the washed oil-dried state, the distribution area of ​​organic matter was determined; by comparing the two-dimensional nuclear magnetic resonance fluid identification maps of the washed oil-dried state and the saturated formation crude oil state, the distribution areas of free oil and adsorbed oil were determined; a two-dimensional nuclear magnetic resonance fluid identification map of the shale in the study area was established to identify the positions of organic matter, adsorbed oil and free oil in the two-dimensional nuclear magnetic resonance fluid identification map; Based on the two-dimensional nuclear magnetic resonance signal quantity and mass of the core sample under two conditions: washed oil drying and saturated formation crude oil, the two-dimensional nuclear magnetic resonance signal quantity and mass of the crude oil under the saturated crude oil condition are obtained. Mathematical equations are established based on the fluid mass difference and the two-dimensional nuclear magnetic resonance signal quantity difference, and the conversion equation between mass and nuclear magnetic resonance signal quantity is obtained.

4. The measurement method according to claim 1, characterized in that, The determination of the amount of medium-quality free hydrocarbons includes: A shale sample to be studied was selected, and the two-dimensional nuclear magnetic resonance (NMR) signal of the original core column was measured. The original core column was then dried to obtain a dried core column. A two-dimensional NMR experiment was conducted on the dried core column to measure the two-dimensional NMR signal and mass. Using the two-dimensional NMR fluid identification chart, the two-dimensional NMR signal of the oil region was identified, and the reduction in the two-dimensional NMR signal of the oil after drying was obtained. Then, according to the mass-NMR signal conversion equation, the reduction in the oil mass in the shale sample to be studied was calculated. Dividing this by the mass of the dried core column yielded the amount of medium-quality free hydrocarbons in the shale sample to be studied.

5. The measurement method according to claim 1, characterized in that, In the pyrolysis, the dried columnar sample of the shale sample to be studied is pulverized into 100 mesh; Or / and, the heating rate of the multi-temperature-stage pyrolysis is 25℃ / min; Or / and, the temperature at the single temperature point is maintained for 3 minutes.

6. The measurement method according to claim 1, characterized in that, The determination of the amount of light free hydrocarbons includes: The two-dimensional nuclear magnetic resonance (NMR) signal quantity and mass of the shale sample under study were measured in its original state. The dried column sample was immersed in the formation crude oil at a high temperature of 70°C. The sample was taken out at regular intervals to measure the two-dimensional NMR signal quantity. When the two-dimensional NMR signal quantity did not change, the permeation reached equilibrium, and the two-dimensional NMR signal quantity after permeation with crude oil was measured. Based on the two-dimensional NMR signal quantity in the original state and after permeation with crude oil, the two-dimensional NMR signal quantity of the oil region was extracted, and the change in the two-dimensional NMR signal quantity of the oil was calculated. According to the mass-NMR signal quantity conversion equation, the amount of oil recovered by permeation was calculated, and then divided by the mass of the shale sample under study in its original state to obtain the amount of light free hydrocarbons.

7. The measurement method according to claim 6, characterized in that, The sample was immersed in crude oil at a high temperature of 70°C, and the sample was taken out every 24 hours to measure the two-dimensional nuclear magnetic resonance signal.

8. The measurement method according to claim 1, characterized in that, The oil components of different occurrence states of shale samples of different lithofacies were quantified. At least five shale samples of each lithofacies were selected from the study area.

9. The measurement method according to any one of claims 1 to 8, characterized in that, The selection of shale lithology with good mobility refers to selecting lithologies with a high proportion of light and medium free hydrocarbons.

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