A shale oil rock sample effective porosity determination method based on two-dimensional nuclear magnetic technology

Abstract

This invention relates to the field of experimental testing technology in oil and gas exploration and development, and particularly to a method for determining the effective porosity of shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) technology. The method involves: preparing the target NMR sample using a freezing method, and calibrating the water and oil content values ​​separately; conducting water and oil distribution experiments on the sample, followed by pore characteristic experiments; calibrating the effective and ineffective pore regions and water and oil distribution regions of the sample's NMR signal, and providing different boundary delineation methods; calibrating the NMR signal obtained from the two-dimensional NMR, and delineating the effective and ineffective pore regions and oil and water distribution regions of the tested sample according to the boundary delineation methods; based on the shale pore properties, recovering the sample pore volume and performing two-dimensional NMR measurement to determine the total volume of the sample; obtaining data using oil-water data extraction methods, and combining this data with the total volume to obtain the effective porosity. The method provided by this invention is convenient, fast, has a short experimental cycle, and high production efficiency.

Description

Technical Field

[0001] This invention relates to the field of experimental testing technology for oil and gas exploration and development, and in particular to a method for determining the effective porosity of shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) technology. Background Technology

[0002] Nuclear magnetic resonance (NMR) is a non-destructive, pollution-free, and rapid measurement technique that has been widely used in core testing within the petroleum industry both domestically and internationally. Core porosity is an indispensable parameter for reservoir research and reserve evaluation, and NMR technology is a primary means of addressing the issue of effective reservoir porosity. Previously, NMR measurements were based on NMR T2 spectroscopy, which determined the pore volume of the sample using T2 spectroscopy with fully saturated water, while the total volume was obtained through conventional saturation methods.

[0003] In recent years, with the deepening of shale oil and gas exploration and development, the combined testing of longitudinal relaxation time T1 and transverse relaxation time T2 (i.e., two-dimensional NMR) has been developed. This aims to address issues related to the reservoir properties and oil content of shale oil reservoirs. In the combined T1-T2 NMR testing, the NMR signals on the T1-T2 MAP spectrum after inversion are represented by color intensity, or energy groups. These energy groups indicate the amount of fluid or hydrogen content within the sample. Determining the effective porosity of shale oil samples using two-dimensional NMR requires not only interpreting the meaning of the T1-T2 NMR signal distribution spectrum and identifying the different properties and characteristics of hydrogen-bearing substances represented by the NMR signals at each position within the spectrum, but also performing quantitative calculations from qualitative analysis of the NMR signals representing different hydrogen-bearing substances within the spectrum. Shale oil reservoirs contain various hydrogen-containing compounds, including crystalline water, structural water, clay-adsorbed water, pore-bound water, organic matter, and hydrocarbons. They also contain both effective and ineffective porosity. The accuracy of the effective porosity of shale oil samples is directly affected by the correct quantitative analysis of the physical properties of NMR signals on T1-T2 NMR spectra. Effective porosity in shale is a crucial parameter for oil reservoir research and reserve evaluation. Shale oil and gas exploration and development urgently require NMR porosity data that accurately reflects the storage capacity of shale oil. However, the current lack of analytical techniques for two-dimensional NMR spectra of shale samples makes it impossible to identify the physicochemical properties of different NMR signals on the two-dimensional NMR spectrum, hindering accurate quantitative calculation and making it impossible to accurately determine the effective porosity of shale rock samples. Therefore, a method for determining the effective porosity of shale oil samples based on two-dimensional NMR technology is proposed. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] This invention provides a method for determining the effective porosity of shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) technology. It mainly solves the problem in the prior art that the lack of methods for classifying effective and ineffective porosity, extracting oil and water data, and measuring effective pore volume during two-dimensional NMR measurement makes it difficult to interpret two-dimensional NMR spectra, thus making it impossible to accurately determine porosity using two-dimensional NMR.

[0006] (II) Technical Solution

[0007] Step 1: Determine the target study area, obtain shale oil samples from the target study area, prepare the samples into target NMR samples using the freezing method, and calibrate the water content and oil content of the target NMR samples respectively.

[0008] Step 2: Perform water distribution experiments and oil distribution experiments on the target NMR sample, and perform pore property characteristic experiments on the target NMR sample after natural oil and water loss, low-temperature water removal, and low-temperature oil removal.

[0009] Step 3: Based on the results of the water distribution experiment and the oil distribution experiment, the target NMR sample is divided into an effective porosity region and an ineffective porosity region, and the NMR signal boundary and oil-water boundary are defined for the effective porosity region and the ineffective porosity region respectively.

[0010] Step 4: Recover the pore volume of the target NMR sample, measure the pore volume of the target NMR sample, and obtain the total volume of the target NMR sample using Archimedes' principle;

[0011] Step 5: Based on the boundary division results of the NMR signal and the oil-water boundary division results, extract the data corresponding to the two-dimensional NMR signal of the sample under test, and calculate the porosity of the target NMR sample by combining the total volume.

[0012] Preferably, the method for preparing the target NMR sample is as follows:

[0013] Liquid nitrogen or a cryogenic freezer, with a temperature range of ≤-40°C, is used to freeze the full-diameter shale oil sample to be taken, ensuring the shale oil sample is completely frozen.

[0014] Use core cutting tools or core-specific machetes to prepare sheet-like shale oil samples with the required thickness of 15mm to 20mm along the bedding plane of the core. Then freeze them again to keep them frozen.

[0015] The flaky shale oil sample was cut into block-shaped samples with geometrical requirements by using a core cutting tool along a direction perpendicular to the bedding and the end face of the bedding.

[0016] Preferably, in step one, the method for calibrating the water volume value is as follows:

[0017] Seven oil-free target NMR samples were selected. The moisture in the target NMR samples was removed at a high temperature of 120℃. Different amounts of deionized water or distilled water were dripped into each rock sample. The different amounts of water dripped into the seven target NMR samples were then used to perform NMR T1-T2 combined measurements on each target NMR sample to obtain two-dimensional NMR data for different target NMR samples.

[0018] Using NMR signal as the x-axis and water volume as the y-axis, a functional relationship between water volume and NMR signal is established.

[0019] Preferably, in step one, the method for calibrating the oil content value is as follows: select 7 rock sample test glasses, put the target NMR test sample into the rock sample test glass, add unequal amounts of kerosene into the rock sample test glass, and perform NMR T1-T2 joint NMR measurement on each target NMR test sample to obtain two-dimensional NMR measurement data under different oil contents;

[0020] Using NMR signal as the x-axis and oil quantity as the y-axis, a functional relationship between water quantity and NMR signal is established.

[0021] Preferably, in step two, the water distribution experiment includes a water distribution experiment of the target NMR sample and a water distribution experiment of the target NMR sample after oil content calibration. The method for the water distribution experiment of the target NMR sample is as follows:

[0022] Select any target NMR sample, place it in a 700℃ dry distillation oven to remove hydrogen-containing substances, and perform a two-dimensional NMR experiment until the hydrogen-containing substances in the target NMR sample are completely removed.

[0023] The target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After the mass of the target NMR sample remained unchanged, a two-dimensional NMR experiment was carried out again to obtain the T1-T2 distribution spectrum and determine the water distribution area.

[0024] Preferably, in step two, the experimental method for measuring the water distribution of the target NMR sample after oil quantity value calibration is as follows:

[0025] A target NMR sample with calibrated oil content was selected, and two-dimensional NMR was performed to obtain a two-dimensional NMR spectrum.

[0026] The oil was removed by alcohol and benzene solvent, and after dehumidification at 115℃ to constant weight, a two-dimensional nuclear magnetic resonance experiment was conducted to obtain the T1-T2 distribution spectrum under the conditions of oil removal and dehumidification.

[0027] After the oil content value was calibrated, the target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After weighing it to a constant mass, two-dimensional NMR was performed again to obtain a water-saturated two-dimensional NMR spectrum.

[0028] The target NMR sample, after being calibrated for oil content, was broken open and then re-moistened. Once the mass was constant, a two-dimensional NMR measurement was performed to obtain its water-absorbing two-dimensional NMR spectrum under external force destruction conditions.

[0029] By comparing the two-dimensional NMR results of the target NMR sample after oil quantity calibration under different conditions, the location of water distribution can be determined.

[0030] Preferably, in step two, the oil distribution experiment is performed as follows:

[0031] Select any target NMR sample, remove oil with alcohol and benzene solvent, dehumidify at 115℃, and conduct a two-dimensional NMR experiment; obtain the two-dimensional NMR spectrum of the target NMR sample under the conditions of oil removal and dehumidification.

[0032] After the target NMR sample was placed in an environment with a humidity of not less than 85% and absorbed water, two-dimensional NMR measurement was carried out to obtain the two-dimensional NMR spectrum of the target NMR sample under water absorption conditions.

[0033] The target NMR sample was immersed in kerosene to absorb saturated kerosene. After the quality stabilized, two-dimensional NMR was performed to obtain the two-dimensional NMR spectrum of the target NMR sample under water and oil absorption conditions. Based on the experimental results, the oil distribution area was determined.

[0034] Preferably, in step two, the process of the oil-water natural loss sample pore property characteristic experiment is as follows: two target NMR samples are selected from the center of the frozen and pressurized core. After two-dimensional NMR measurement, the target NMR samples are placed in a rock sample bottle and allowed to thaw slowly under natural conditions. Some fluid is lost. One target NMR sample is first placed in kerosene and then in water, allowing it to absorb oil and water on its own. After the mass remains unchanged, two-dimensional NMR measurements are carried out on both samples. The other target NMR sample is first placed in water and then in kerosene. After the mass remains unchanged, two-dimensional NMR measurements are carried out on both samples.

[0035] Preferably, in step two, the process of the low-temperature dehydration sample pore property characteristic experiment is as follows: select the target NMR sample, perform two-dimensional NMR measurement, place the target NMR sample under vacuum low temperature of 60℃ for 8 hours to remove pore water, and then perform two-dimensional NMR measurement. Then, place the target NMR sample in a constant humidity chamber with humidity greater than 85%, and after the mass remains unchanged, perform two-dimensional NMR measurement again. Compare and analyze the two-dimensional NMR measurement data under different conditions to determine the reproducibility of pore water.

[0036] Preferably, in step two, the experimental procedure for the porosity characteristic experiment of the sample after low-temperature oil removal is as follows: Select the target NMR sample, perform two-dimensional NMR measurement, and then perform low-temperature oil removal using chloroform for at least 70 hours, followed by two-dimensional NMR experiment; immerse the target NMR sample in kerosene until the rock sample is saturated with kerosene by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR experiment; place the target NMR sample under constant humidity conditions with a humidity greater than 85%, until the rock sample is saturated with water by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR measurement to obtain two-dimensional NMR spectra under different conditions.

[0037] Preferably, in step three, the method for determining the distribution locations of ineffective pore regions and effective pore regions is as follows: the target NMR sample is degreased with alcohol and benzene solvent, and then dehumidified at 115°C to constant weight. A two-dimensional NMR experiment is then performed to obtain the T1-T2 distribution spectrum of solids or near-solid hydrogen-containing substances that cannot be removed under the degreasing and dehumidification conditions. The sample is then saturated with oil and water by self-absorption, and after the mass is kept constant, two-dimensional NMR measurements are performed to obtain the pore oil-water distribution spectrum.

[0038] The region containing the T1-T2 distribution spectrum of solid or near-solid hydrogen-containing substances such as crystalline water or structural water, organic matter, and bituminous matter within clay minerals is defined as the ineffective porosity distribution region, while the region containing saturated oil and water is defined as the effective porosity distribution region.

[0039] Preferably, in step three, the method for defining the NMR signal boundary between the effective porosity region and the ineffective porosity region is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest point of the NMR signal between the ineffective porosity region of the solid or near-solid region and the effective porosity region of the pore water region is selected, corresponding to a ms in T2 coordinates. A perpendicular line is drawn to the T2 axis (horizontal coordinate), i.e., T2 = a ms. The straight line T2 = ams is selected as the boundary line between the effective porosity region and the ineffective porosity region, where T2 ≤ a ms represents the ineffective porosity region, and T2 > a ms represents the effective porosity region. Where there is no obvious weakest point of the NMR signal between the effective porosity region and the ineffective porosity region, T2 ≤ 0.2ms in the T1-T2 rectangular coordinate system is selected as the ineffective porosity region, and T2 > 0.2ms as the effective porosity region.

[0040] When the NMR signal between the effective pore region and the ineffective pore region is continuously without NMR signal, that is, when the NMR signal is all in the background area of ​​the spectrum, the value of a is a = (a1 + a2) / 2, where a1 is the left boundary T2 value of the continuous absence of NMR signal and a2 is the right boundary T2 value of the continuous absence of NMR signal.

[0041] Preferably, in step three, the method for delineating the boundary between the oil and water distribution areas is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest NMR signal between the pore water distribution area and the oil distribution area is selected, corresponding to a T1 coordinate value of b ms. A perpendicular line is drawn to the T1 axis (vertical coordinate), i.e., T1 = b ms. The line T1 = b is selected as the boundary line between the oil and water NMR signals. T1 ≤ b ms indicates water distribution, and T1 > b ms indicates oil distribution. Since there is no obvious weakest NMR signal between the oil and water distribution areas, T1 < 10 ms is selected as water distribution, and T1 ≥ 10 ms as oil distribution in the T1-T2 rectangular coordinate system. When there are consecutive areas of no NMR signal in the spectrum between the pore water and oil distribution areas, b is taken as b = (b1 + b2) / 2, where b1 is the lower boundary T1 value of the continuous no NMR signal, and b2 is the upper boundary T1 value of the continuous no NMR signal.

[0042] Water is basically distributed in the range of T1 / T2 = 10⁻¹, while oil is distributed in the range of T1 / T2 > 10. The boundary between the water distribution area and the oil distribution area is T1 = b ms, that is, in the effective pore area of ​​T2 > a ms. Between the water distribution area and the oil distribution area, T1 > b ms is considered oil, and T1 ≤ b ms is considered water.

[0043] Preferably, in step four, the experimental process for restoring the pore volume of the target NMR sample is as follows: the target NMR sample is immersed in kerosene, and the mass of the target NMR sample is weighed periodically until the mass of the target NMR sample is constant; then the target NMR sample is placed in a constant humidity chamber with a humidity of not less than 85% to allow the target NMR sample to absorb water, and the mass of the target NMR sample is weighed periodically.

[0044] Preferably, in step four, the method for determining the pore volume of the target NMR sample is as follows: after the target NMR sample has absorbed oil and water, the mass of the target NMR sample is weighed, and two-dimensional NMR measurement is performed to obtain the NMR data of the target NMR sample after water absorption.

[0045] Preferably, in step four, the method for determining the total volume of the target NMR sample is as follows: after absorbing water and oil, the target NMR sample is immersed again in kerosene for 30 minutes, and the total volume of the target NMR sample is determined according to Archimedes' principle.

[0046] Preferably, in step five, the effective porosity calculation formula for the target NMR sample is:

[0047]

[0048] Among them, V water The volume of water measured by nuclear magnetic resonance in the sample is in ml; Voil V represents the amount of oil and gas measured by nuclear magnetic resonance in the sample, in ml; φ represents the effective porosity of the sample, in %; tatal The total volume of the sample being tested is expressed in cm³. 3 .

[0049] (III) Beneficial Effects

[0050] This invention provides a method for determining the effective porosity of shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) technology. This method calculates porosity conveniently, quickly, simply, and easily understood, avoiding confusion caused by unclear oil-water distribution. It effectively distinguishes between effective and ineffective porosity regions, preventing inaccurate measurements of oil-water content and effective pore volume due to unclear delineation. This makes oil-water content determination more precise, significantly improving the accuracy of effective porosity determination using two-dimensional NMR. The method also features a short testing cycle, high production efficiency, and is non-toxic and harmless, conforming to HSE (Health, Safety, and Environmental) principles. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating the method for determining the oil content of organic and inorganic pores in shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) according to an embodiment of the present invention.

[0052] Figure 2 This is a schematic diagram illustrating the relationship between the water content of the target sample determined by NMR and the NMR signal in an embodiment of the present invention.

[0053] Figure 3 This is a schematic diagram illustrating the relationship between the oil content and NMR signal of the target NMR sample in an embodiment of the present invention.

[0054] Figure 4 This is a schematic diagram of the two-dimensional NMR distribution spectrum of the target sample for water distribution determination in an embodiment of the present invention. In the diagram, a is the two-dimensional NMR spectrum of hydrogen-containing substances removed at high temperature, and b is the two-dimensional NMR spectrum of water after adding an appropriate amount of water.

[0055] Figure 5 This is a schematic diagram of the two-dimensional NMR distribution spectrum of the target NMR sample under different conditions in an embodiment of the present invention. In the diagram, a is the two-dimensional NMR spectrum of the original sample, b is the two-dimensional NMR spectrum after dehumidification at 115℃, c is the two-dimensional NMR spectrum after dehumidification at 115℃ with the addition of an appropriate amount of water, and d is the two-dimensional NMR spectrum after dehumidification at 115℃ with the addition of sufficient water and after the sample has cracks.

[0056] Figure 6 This is a schematic diagram of the two-dimensional NMR distribution spectrum of the target NMR sample oil distribution experiment in an embodiment of the present invention. In this diagram, a is the two-dimensional NMR spectrum after dehumidification at 115℃, b is the two-dimensional NMR spectrum after dehumidification at 115℃ with the addition of an appropriate amount of water, and c is the two-dimensional NMR spectrum of oil saturated after dehumidification at 115℃ with the addition of an appropriate amount of water.

[0057] Figure 7This is a schematic diagram of the two-dimensional NMR distribution spectrum of the target NMR sample oil for low-temperature dehydration pore property verification experiment in an embodiment of the present invention. In the diagram, a is the two-dimensional NMR spectrum of the original sample, b is the two-dimensional NMR spectrum of the sample after low-temperature dehydration, and c is the two-dimensional NMR spectrum of the resaturated water after low-temperature dehydration.

[0058] Figure 8 This is a schematic diagram of the two-dimensional NMR distribution spectrum of the target NMR sample oil for low-temperature oil removal pore property verification experiment in an embodiment of the present invention. In the diagram, a is the two-dimensional NMR spectrum of the original sample, b is the two-dimensional NMR spectrum of the sample after low-temperature oil removal and dehumidification, c is the two-dimensional NMR spectrum of the self-absorbed oil-saturated sample, and d is the two-dimensional NMR spectrum of the sample after oil saturation and subsequent self-absorption and water saturation.

[0059] Figure 9 This is a schematic diagram of the oil-water distribution region division in the two-dimensional NMR spectra of the target NMR sample in an embodiment of the present invention. In this diagram, a is a boundary delineation diagram of the NMR signal for a sample with a relatively clear boundary between effective and ineffective pores and between oil and water distributions; b is a boundary delineation diagram of the NMR signal for a sample with an indistinct boundary between effective and ineffective pores and a continuous no-signal area between oil and water distributions; and c is a boundary delineation diagram of the NMR signal for a sample with a clear boundary between effective and ineffective pores and an indistinct boundary between oil and water distributions.

[0060] Figure 10 This is a boundary delineation diagram for two-dimensional nuclear magnetic resonance (NMR) measurement of oil and water NMR signals according to an embodiment of the present invention.

[0061] 1-Ineffective pore zone; 2-Effective pore zone for oil and water; 3-Porous water distribution zone; 4-Oil and gas distribution zone; A-Boundary between ineffective and effective pores; B-Boundary between oil and water distribution; C-Any perpendicular line from the lower edge of the water distribution zone to the T1 axis; N-Any perpendicular line from the right edge of the water distribution zone to the T2 axis; D-Any perpendicular line from the upper edge of the oil distribution zone to the T1 axis; M-Any perpendicular line from the right edge of the oil distribution zone to the T2 axis. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0063] Figure 1 This is a flowchart illustrating the method for determining the oil content of organic and inorganic pores in shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) according to an embodiment of the present invention. Figure 1 As shown, this invention provides a method for determining the oil-bearing properties of organic and inorganic pores in shale oil samples based on two-dimensional nuclear magnetic resonance (NMR), including:

[0064] Step 1: Determine the target study area, obtain shale oil samples from the target study area, prepare the samples into target NMR samples using the freezing method, and calibrate the water content and oil content of the target NMR samples respectively.

[0065] Step 2: Perform water distribution experiments and oil distribution experiments on the target NMR sample, and perform pore property characteristic experiments on the target NMR sample after natural oil and water loss, low-temperature water removal, and low-temperature oil removal.

[0066] Step 3: Based on the results of the water distribution experiment and the oil distribution experiment, the target NMR sample is divided into an effective porosity region and an ineffective porosity region, and the NMR signal boundary and oil-water boundary are defined for the effective porosity region and the ineffective porosity region respectively.

[0067] Step 4: Recover the pore volume of the target NMR sample, measure the pore volume of the target NMR sample, and obtain the total volume of the target NMR sample using Archimedes' principle;

[0068] Step 5: Based on the boundary division results of the NMR signal and the oil-water boundary division results, extract the data corresponding to the two-dimensional NMR signal of the sample under test, and calculate the porosity of the target NMR sample by combining the total volume.

[0069] In step one, the sample preparation process for the target NMR measurement is as follows:

[0070] In practical applications, liquid nitrogen or cryogenic freezers are used, with a temperature range of ≤-40°C, to freeze the full-diameter or large-block shale oil samples to be taken, ensuring that the shale oil samples are completely frozen.

[0071] Use core cutting tools or core-specific machetes to cut large shale oil samples into sheet-like pieces along the bedding plane of the core, with a thickness of 15mm to 20mm required for the measurement. Then freeze them again to keep them frozen.

[0072] The flaky shale oil sample was cut into block-shaped samples with geometrical requirements by using a core cutting tool along a direction perpendicular to the bedding and the end face of the bedding.

[0073] In practical applications, the target NMR sample cannot be prepared by crushing. In order to improve the success rate of sample preparation and reduce breakage, a special cutting tool is required to prepare the target NMR sample. This also avoids the formation of cracks in the prepared sample, which would affect the shale test results.

[0074] In this embodiment, the target study area is determined, shale oil samples from the target study area are obtained, and after the target NMR sample is prepared, the water content and oil content of the target NMR sample are calibrated respectively.

[0075] If the target NMR sample cannot be measured immediately after preparation, it should be frozen in a -60°C freezer to prevent a large loss of fluid from the sample due to poor connection between sample preparation and sample testing.

[0076] In this method, the method for calibrating the water volume value in step one is as follows:

[0077] Seven oil-free target NMR samples were selected. The moisture in the target NMR samples was removed at a high temperature of 120℃. Different amounts of deionized water or distilled water were dripped into each rock sample. The different amounts of water dripped into the seven target NMR samples were then used to perform NMR T1-T2 combined measurements on each target NMR sample to obtain two-dimensional NMR data for different target NMR samples.

[0078] Using NMR signal as the x-axis and water volume as the y-axis, a functional relationship between water volume and NMR signal is established.

[0079] In practical applications, the method for calibrating the oil content value in step one is as follows: select 7 rock sample test glasses, put the target NMR test sample into the rock sample test glass, add unequal amounts of kerosene into the rock sample test glass, and perform NMR T1-T2 joint NMR measurement on each target NMR test sample to obtain two-dimensional NMR measurement data under different oil contents.

[0080] Using NMR signal as the x-axis and oil quantity as the y-axis, a functional relationship between water quantity and NMR signal is established.

[0081] In this embodiment, the water volume calibration process is as follows:

[0082] Oil-free rock samples were selected, and the water content in the target NMR samples was removed at high temperature. Different amounts of deionized water or distilled water were added to each target NMR sample. The water volumes added to the seven rock samples were 0.100 ml, 0.200 ml, 0.300 ml, 0.400 ml, 0.500 ml, 0.700 ml, and 0.900 ml, respectively. Two-dimensional NMR T1-T2 combined spectral analysis was performed on each rock sample to obtain the relationship between water content and NMR signal.

[0083] like Figure 2 As shown, the horizontal axis represents the NMR signal, and the vertical axis represents water content. Water content and NMR signal have a directly proportional linear relationship. Using the NMR signal as the independent variable, regression analysis yields the corresponding relationship between water content and NMR signal intensity. The regression equation is: V water =k water X nmr The correlation coefficient R = 0.9999, where the proportionality coefficient k after regression is... water =0.9213, Xnmr V represents the signal value measured by two-dimensional NMR, in mL. water The water content corresponding to the two-dimensional NMR signal value is expressed in mL. It can be seen that the NMR signal value and water content have a very good linear relationship, and the correlation is fully applicable to NMR measurements. Therefore, this NMR technique has high accuracy and reliability, and the water content in rock samples can be accurately obtained by measuring the NMR signal.

[0084] In this embodiment, the specific process of oil quantity calibration is as follows:

[0085] Select the target NMR sample and add a fixed amount of kerosene to the rock sample test cup. In actual testing, the reservoir in-situ oil also needs to be calibrated, and the method is the same, so it will not be described here. The amount of kerosene in the rock sample cup is 0.500ml, 1.000ml, 1.500ml, 2.000ml, 2.500ml, 3.000ml and 3.500ml respectively. NMR is performed on each rock sample to obtain the relationship between the amount of kerosene and the NMR signal.

[0086] like Figure 3 As shown, the horizontal axis represents the NMR signal, and the vertical axis represents the kerosene content. The kerosene content and the NMR signal have a directly proportional linear relationship. Using the NMR signal as the independent variable, a polynomial regression was used to obtain the correspondence between oil content and NMR signal intensity. The regression equation is: V oil =k oil X nmr The correlation coefficient R = 0.9999, where the proportionality coefficient k after regression is... oil =1.2246, X nmr V represents the signal value measured by two-dimensional NMR, in mL. oil The corresponding oil content, expressed in mL, is obtained from the two-dimensional NMR signal values. It can be seen that the oil content and the NMR signal exhibit a direct linear relationship, and this correlation is fully applicable to NMR measurements. Therefore, this NMR technique has high accuracy and reliability, and the oil content in rock samples can be accurately obtained by measuring the NMR signal.

[0087] In this method, step two includes the water distribution experiment of the target NMR sample and the water distribution experiment of the target NMR sample after oil content calibration. The method for the water distribution experiment of the target NMR sample is as follows:

[0088] Select any target NMR sample, place it in a 700℃ dry distillation oven to remove hydrogen-containing substances, and perform a two-dimensional NMR experiment until the hydrogen-containing substances in the target NMR sample are completely removed.

[0089] The target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After the mass of the target NMR sample remained unchanged, a two-dimensional NMR experiment was carried out again to obtain the T1-T2 distribution spectrum and determine the water distribution area.

[0090] In practical applications, the experimental method for determining the water distribution of the target NMR sample after oil quantity value calibration in step two is as follows:

[0091] A target NMR sample with calibrated oil content was selected, and two-dimensional NMR was performed to obtain a two-dimensional NMR spectrum.

[0092] The oil was removed by alcohol and benzene solvent, and after dehumidification at 115℃ to constant weight, a two-dimensional nuclear magnetic resonance experiment was conducted to obtain the T1-T2 distribution spectrum under the conditions of oil removal and dehumidification.

[0093] After the oil content value was calibrated, the target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After weighing it to a constant mass, two-dimensional NMR was performed again to obtain a water-saturated two-dimensional NMR spectrum.

[0094] The target NMR sample, after being calibrated for oil content, was broken open and then re-moistened. Once the mass was constant, a two-dimensional NMR measurement was performed to obtain its water-absorbing two-dimensional NMR spectrum under external force destruction conditions.

[0095] By comparing the two-dimensional NMR results of the target NMR sample after oil quantity calibration under different conditions, the location of water distribution can be determined.

[0096] In this method, the oil distribution experiment in step two is as follows:

[0097] Select any target NMR sample, remove oil with alcohol and benzene solvent, dehumidify at 115℃, and conduct a two-dimensional NMR experiment; obtain the two-dimensional NMR spectrum of the target NMR sample under the conditions of oil removal and dehumidification.

[0098] After the target NMR sample was placed in an environment with a humidity of not less than 85% and absorbed water, two-dimensional NMR measurement was carried out to obtain the two-dimensional NMR spectrum of the target NMR sample under water absorption conditions.

[0099] The target NMR sample was immersed in kerosene to absorb saturated kerosene. After the quality stabilized, two-dimensional NMR was performed to obtain the two-dimensional NMR spectrum of the target NMR sample under water and oil absorption conditions. Based on the experimental results, the oil distribution area was determined.

[0100] In this embodiment, the specific process of the water distribution experiment is as follows:

[0101] In practical applications, such as Figure 4 (a) and Figure 4As shown in (b), the target NMR sample after the oil content value was calibrated was selected and placed in a 700℃ dry distillation oven to remove hydrogen-containing substances. Then, a two-dimensional NMR experiment was performed to confirm that the hydrogen-containing substances in the sample were completely removed. Then, the target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. When the rock sample mass remained unchanged, a two-dimensional NMR experiment was carried out again to determine the location of water distribution.

[0102] Select the target NMR sample after oil volume value calibration, such as Figure 5 As shown in (a), two-dimensional NMR measurements were performed and a two-dimensional NMR spectrum was obtained. Oil was removed using alcohol and benzene solvents, and the mixture was dehumidified at 115℃ to constant weight before the two-dimensional NMR experiment was conducted. Figure 5 As shown in (b), the T1-T2 distribution spectrum under degreasing and dehumidification conditions was obtained. The target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture, and after being weighed to a constant mass, two-dimensional NMR measurements were performed again. Figure 5 As shown in (c), a two-dimensional NMR spectrum of water-saturated sample was obtained. The target NMR sample was then broken open and re-moistened. After the mass was stabilized, two-dimensional NMR measurements were performed. Figure 5 As shown in (d), the water absorption two-dimensional NMR spectrum of the target NMR sample under external force damage conditions was obtained.

[0103] like Figure 4 As shown in (a), the two-dimensional NMR spectrum shows no NMR signal, indicating that the hydrogen-containing compounds in the target NMR sample were essentially removed after passing through a 700℃ dry distillation chamber. After adding water to the target NMR sample, as shown... Figure 4 As shown in (b), the NMR signals in the two-dimensional NMR T1-T2 spectrum are distributed near the diagonal of the T1-T2 map, and the newly added NMR signals are the NMR signals of water.

[0104] like Figure 5 As shown in (a), the original target NMR sample had different hydrogen-containing compounds. After being dehumidified at 115℃ to constant weight, the target NMR sample was as follows: Figure 5 As shown in (b), there is an NMR signal on the left edge of the two-dimensional NMR T1-T2 map spectrum. This NMR signal belongs to hydrogen-containing compounds that could not be removed by solvent degreasing and dehumidification at 115℃. These unremovable hydrogen-containing compounds are mainly crystalline water or structural water within clay minerals, organic matter, and asphaltenes; they are solid or near-solid hydrogen-containing compounds. The NMR measurement of the target sample shows water absorption, such as... Figure 5 As shown in (c), there is a new NMR signal, with a basic distribution similar to... Figure 4 (b) Similarly, near the diagonal of the spectrum, i.e., in the region where T1 / T2 = 10⁻¹, this signal belongs to the water signal category; such as Figure 5 As shown in (d), the target NMR sample was resaturated with water after being subjected to external force, resulting in a new two-dimensional NMR spectrum, which is basically distributed along the region T1 / T2 = 10⁻¹. Figure 4 and Figure 5 As can be seen, the water sample measured by the target NMR is basically distributed along the region of T1 / T2 = 10⁻¹.

[0105] The above experimental process shows that in the two-dimensional NMR distribution spectrum of the target NMR sample, water is distributed along the diagonal of the T1-T2 two-dimensional spectrum, that is, the two-dimensional NMR distribution region of water is basically in the range of T1 / T2 = 10-1.

[0106] In this embodiment, the specific process of the oil distribution experiment is as follows:

[0107] In practical applications, the target NMR sample is selected, degreased with alcohol and benzene solvent, and then dehumidified at 115℃. Figure 6 As shown in (a), a two-dimensional nuclear magnetic resonance (NMR) experiment was conducted. After adding an appropriate amount of water, the shale oil reservoir was immersed in kerosene until it became saturated with kerosene. This indicates that the shale oil reservoir contains original water, thus the experiment is consistent with the reservoir. After saturation with water and the oil content stabilizes, the quality of the shale oil reservoir tends to stabilize. Figure 6 (b) and Figure 6 As shown in (c), two-dimensional nuclear magnetic resonance (NMR) measurements were performed to obtain two-dimensional NMR oil and gas distribution spectra under different conditions.

[0108] This experiment shows that, Figure 6 As shown in (a), the two-dimensional NMR spectrum of the target sample after degreasing and 115℃ only retains the NMR signal at the left edge, indicating hydrogen-containing substances that could not be removed by degreasing and humidification, while the pore fluid has been removed; Figure 6 As shown in (b), the two-dimensional NMR spectrum after water absorption shows a new signal detected on the right side of the original, unremovable NMR spectrum. This signal belongs to the NMR signal of the absorbed water, and its distribution range is consistent with the water distribution experiment described earlier, basically distributed in the T1 / T2 = 10⁻¹ region. The NMR signal belongs to the absorbed water. Figure 6 As shown in (c), the two-dimensional NMR analysis after oil absorption detected a new signal, which is the two-dimensional NMR signal of the absorbed oil. This signal is distributed in the region with a high T1 value, above the water signal, and with a slightly increased T2, i.e., T1 / T2>10, indicating a stratification phenomenon with the water. This experiment shows that under the condition of a two-phase medium containing both water and oil, the oil and water in the two-dimensional NMR distribution spectrum of the target NMR sample exhibit stratification, with the oil distributed in the region of T1 / T2>10 and the water similarly distributed in the range of T1 / T2=10⁻¹.

[0109] The above experimental process shows that when the target NMR sample is in a two-phase medium containing both water and oil, the two-dimensional NMR distribution spectrum of the target NMR sample exhibits oil-water stratification, and the oil is distributed in the region where T1 / T2 > 10.

[0110] In this method, the process of the experiment on the pore property characteristics of the oil-water naturally lost sample in step two is as follows: Two target NMR samples are selected from the center of the frozen and pressurized core. After two-dimensional NMR measurement, the target NMR samples are placed in a rock sample bottle and thawed slowly under natural conditions. Some fluid is lost. One target NMR sample is first placed in kerosene and then in water to allow it to absorb oil and water without changing its mass. Two-dimensional NMR measurements are then carried out on the other sample. The other target NMR sample is first placed in water and then in kerosene. After the mass remains unchanged, two-dimensional NMR measurements are carried out on the other sample.

[0111] In practical applications, the process of the experiment on the pore property characteristics of the sample after low-temperature water removal in step two is as follows: Select the target NMR sample, perform two-dimensional NMR measurement, place the target NMR sample under vacuum low temperature of 60℃ for 8 hours to remove pore water, and then perform two-dimensional NMR measurement. Then, place the target NMR sample in a constant humidity chamber with humidity greater than 85%, and after the mass remains unchanged, perform two-dimensional NMR measurement again. Compare and analyze the two-dimensional NMR measurement data under different conditions to determine the reproducibility of pore water.

[0112] In this method, the experimental procedure for the porosity characteristic experiment of the sample after low-temperature oil removal in step two is as follows: Select the target NMR sample, perform two-dimensional NMR measurement, and then perform low-temperature oil removal with chloroform for no less than 70 hours, followed by two-dimensional NMR experiment; immerse the target NMR sample in kerosene until the rock sample is saturated with kerosene by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR experiment; place the target NMR sample under constant humidity conditions with a humidity greater than 85%, until the rock sample is saturated with water by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR measurement to obtain two-dimensional NMR spectra under different conditions.

[0113] In this embodiment, the specific process of the natural loss of porosity properties experiment is as follows:

[0114] Target NMR samples were collected from the center of the pressurized core samples of shale oil reservoirs. Two-dimensional NMR measurements were performed before the samples were fully thawed. The samples were then placed in sample bottles and allowed to thaw naturally for 4 hours to ensure complete thawing. Two-dimensional NMR measurements were then performed again, with the two samples placed in water and kerosene, respectively, without changing their mass. Note that the media used here must be different from those used previously. Based on the experimental results of the two-dimensional NMR measurements and the division of oil-water distribution areas in the two-dimensional NMR spectra, the pore water and oil content of the samples were calculated. Table 1 shows the NMR analysis data of the water-absorbing and re-absorbing oil samples. Table 1 shows the calculated NMR analysis results of the target NMR samples for water-absorbing and re-absorbing oil.

[0115] Table 1. NMR analysis data of water-absorbing and oil-absorbing samples.

[0116]

[0117] As shown in Table 1, after sample 1 was saturated with water, the water content increased by 0.045 ml, and the oil and gas content remained basically unchanged. After saturating with oil, the oil and gas content increased by 0.027 ml, and the water content remained unchanged. For sample 2, after saturating with oil, the oil content increased by 0.034 ml, and the pore water content remained basically unchanged. After saturating with water, the pore water content increased by 0.047 ml, and the oil and gas content remained unchanged. The oil and water content measured after the rock sample absorbed oil and water was slightly greater than that measured during pressure holding and freezing.

[0118] Therefore, when a target NMR sample containing oil and water in its pores is saturated with oil and water through self-absorption, water can only enter the water-containing pore space under the action of capillary force, which is the water-wetted pore. The oil-containing pore is oil-wetted and has a repulsive force on water, so water cannot enter the oil-containing pore. Similarly, oil can be self-absorbed into the oil-containing pore under the action of capillary force, while the water-containing pore, because it contains water in the capillary and has water adsorption on the pore surface, is water-wetted and has a repulsive force on oil, so oil cannot enter the water-containing pore space. Therefore, the pores of the target NMR sample containing some oil and water are selective for the oil and water absorbed. In other words, the pores of the original sample with some oil and water loss are selective for the oil and water absorbed. Oil can only enter the pores where oil is present, and water can only enter the pores where water is present. Moreover, the naturally lost sample can be filled with oil and water through self-absorption saturation. That is, the oil and water loss sample can be restored to a water and oil distribution close to that under reservoir conditions through self-absorption saturation.

[0119] In this embodiment, the specific process of the low-temperature dehydration experiment is as follows:

[0120] Select target NMR samples from the pressure-maintaining core locations of shale oil reservoirs, such as... Figure 7 As shown in (a), two-dimensional nuclear magnetic resonance (NMR) measurements were performed to obtain the original target NMR spectrum of the sample. The rock sample was then subjected to a vacuum low-temperature (60℃) environment for 8 hours to remove pore water, and two-dimensional NMR analysis was conducted on the dewatered rock sample. Figure 7 As shown in (b), the two-dimensional NMR spectrum of the target NMR sample after pore water removal was obtained; the dehydrated rock sample was placed under constant humidity conditions (greater than 85%) to allow it to self-absorb water to become saturated. After maintaining its mass, the rock sample underwent two-dimensional NMR analysis again. Figure 7 As shown in (c), the T1-T2 combined NMR spectrum of the target NMR sample that has been reabsorbed water was obtained.

[0121] By comparing the T1-T2 combined spectral data, it can be seen that the target NMR sample collected from the pressure-maintaining core location of the shale oil reservoir contains a good oil-water distribution. After the sample is placed under vacuum low temperature of 60℃ for 8 hours, the pore water is basically removed and some oil is also removed. After the sample is saturated with moisture, it can reabsorb water into the pores where the pore water has been removed, while water cannot enter the pores where oil is present.

[0122] from Figure 7 As can be seen, Figure 7 As shown in (a), the selected target NMR sample has a good oil-water distribution. The target NMR sample was dehumidified under vacuum low temperature (60°C) conditions for 8 hours. Figure 7 As shown in (b), the pore water was mostly removed, and some oil was also removed. The target NMR sample was then rehydrated and saturated. Figure 7 As shown in (c), the target NMR sample can reabsorb water from the pores where pore water has been removed, while water cannot enter the pores where oil is present.

[0123] Therefore, pore water is reproducible, meaning that under capillary action, water can enter the pores originally occupied by pore water, but water cannot enter the pores where oil is present.

[0124] In this embodiment, the specific process of the low-temperature oil removal pore property experiment is as follows:

[0125] In addition, two-dimensional nuclear magnetic resonance (NMR) measurements were performed on target NMR samples collected from pressurized core locations in shale oil reservoirs. Figure 8 As shown in (a), the original two-dimensional NMR spectrum of the target NMR sample was obtained; chloroform (boiling point 60℃) was used for low-temperature oil removal, generally for no less than 70 hours. Then, the target NMR sample was dehumidified under vacuum at 60℃ for 8 hours, and then two-dimensional NMR experiments were performed on the sample. Figure 8 As shown in (b), a two-dimensional NMR spectrum of the target NMR sample under deoiling and dehumidification conditions was obtained. The target NMR sample was then immersed in kerosene to allow the rock sample to self-absorb and become saturated with kerosene while maintaining its mass. Following this, a two-dimensional NMR experiment was conducted. Figure 8 As shown in (c), a two-dimensional NMR spectrum of the target NMR sample under oil-saturated conditions was obtained; then, the target NMR sample was placed under constant humidity conditions (greater than 85%) to allow it to self-absorb water and remain saturated with constant mass, and two-dimensional NMR measurements were performed on the sample again, as shown in (c). Figure 8 As shown in (d), a two-dimensional NMR spectrum, i.e., the combined T1-T2 NMR spectrum, was obtained under the water absorption conditions of the target NMR sample.

[0126] The oil and water distribution experiments show that water is distributed between T1 / T2 = 1 and 10, while oil is mainly distributed between T1 / T2 > 10. Figure 8As shown in (a), the selected target NMR sample has a good oil-water distribution; after low-temperature oil and moisture removal, the target NMR sample is as follows: Figure 8 As shown in (b), the NMR signal in the oil-water distribution area basically disappeared, indicating that the oil and water in the pores were essentially removed; after the target NMR sample was immersed in kerosene and saturated by self-absorption, as shown... Figure 8 As shown in (c), the strong NMR signals near the original water and oil distribution areas indicate that, under conditions without pore water, oil can enter not only the pore space where the original sample contains oil, but also the pore space occupied by the original sample's pore water. This means that, under dry or oil-only conditions, the target NMR sample can allow oil to enter pores with different properties. After the target NMR sample undergoes self-absorption saturation with no change in mass, as shown in [the diagram]... Figure 8 As shown in (d), the two-dimensional NMR oil-water distribution is the same as that of the original target NMR sample, indicating that the sample is saturated with water and displaces the oil at the same time. That is, the water displaces the self-absorbed saturated oil that occupies the water distribution area of ​​the original sample. In other words, the water reoccupies the pore space that it occupies, but the water cannot displace the oil in the pore space where the original sample oil is located.

[0127] Water can displace oil in water-distributed areas because the capillary surface tension of water in these areas is greater than that of oil. In other words, the capillary force exerted by the water on the water is greater than that exerted by the oil, making the capillary pores hydrophilic. Conversely, water cannot displace oil in oil-distributed areas, as the capillary force exerted by the oil on the oil is greater than that exerted by the water, making the capillary pores oleophilic. We can define a hydrophilic phase that can only absorb water as the water-wetting phase, and the corresponding pores as inorganic pores. Similarly, an oleophilic phase that can only absorb oil is the oil-wetting phase, and the corresponding pores are organic pores. By utilizing the difference in surface tension between oleophilic organic pores and hydrophilic inorganic pores, and through the absorption of oil and water, the size and distribution of organic and inorganic pores can be determined.

[0128] Based on the conclusions obtained from the water distribution experiment, after removing pore water and oil from the target NMR sample, and considering the oil distribution experiment, even with pre-saturation with water, water will not enter the pore space occupied by oil. This indicates that the target NMR sample can self-absorb and saturate with both oil and water; water can only enter the pore space occupied by water, not the pores where oil is present. In the absence of pore water, oil can enter both the pores occupied by pore water and the pores where oil is present in the original target NMR sample. However, water can displace the oil in the pore space occupied by pore water in the original sample, but cannot displace the pores where oil is present. In the presence of pore water, oil can only enter the pores where oil is present; oil cannot displace the pores occupied by water that belong to pore water. Therefore, the pore properties can be utilized to restore the pore space occupied by oil and water in the sample, enabling the determination of organic and inorganic pores and their oil content.

[0129] Therefore, oil is reproducible, meaning that oil can enter the pore space where it resides under capillary force.

[0130] In this method, the method for determining the distribution location of ineffective pore regions and effective pore regions in step three is as follows: the target NMR sample is degreased with alcohol and benzene solvent, and then dehumidified at 115℃ to constant weight. Two-dimensional NMR experiments are then performed to obtain the T1-T2 distribution spectrum of solids or near-solid hydrogen-containing substances that cannot be removed under the degreasing and dehumidification conditions. The sample is then saturated with oil and water by self-absorption, and after the mass is kept constant, two-dimensional NMR measurements are performed to obtain the pore oil-water distribution spectrum.

[0131] The region containing the T1-T2 distribution spectrum of solid or near-solid hydrogen-containing substances such as crystalline water or structural water, organic matter, and bituminous matter within clay minerals is defined as the ineffective porosity distribution region, while the region containing saturated oil and water is defined as the effective porosity distribution region.

[0132] In practical applications, in step three, the method for defining the boundary line of the NMR signal between the effective porosity region and the ineffective porosity region is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest point of the NMR signal between the ineffective porosity region of the solid or near-solid region and the effective porosity region of the pore water region is selected, corresponding to a ms in T2 coordinates. A perpendicular line is drawn to the T2 axis (horizontal coordinate), i.e., T2 = a ms. The straight line T2 = ams is selected as the boundary line between the effective porosity region and the ineffective porosity region. Where T2 ≤ a ms indicates the ineffective porosity region, and T2 > a ms indicates the effective porosity region. If there is no obvious weakest point of the NMR signal between the effective porosity region and the ineffective porosity region, T2 ≤ 0.2ms in the T1-T2 rectangular coordinate system is selected as the ineffective porosity region, and T2 > 0.2ms as the effective porosity region.

[0133] When the NMR signal between the effective pore region and the ineffective pore region is continuously without NMR signal, that is, when the NMR signal is all in the background area of ​​the spectrum, the value of a is a = (a1 + a2) / 2, where a1 is the left boundary T2 value of the continuous absence of NMR signal and a2 is the right boundary T2 value of the continuous absence of NMR signal.

[0134] In this method, the method for delineating the boundary between the oil and water distribution areas in step three is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest NMR signal between the pore water distribution area and the oil distribution area is selected, corresponding to a T1 coordinate value of b ms. A perpendicular line is drawn to the T1 axis (vertical coordinate), i.e., T1 = b ms. The line T1 = b is selected as the boundary line between the oil and water NMR signals. T1 ≤ b ms indicates water distribution, and T1 > b ms indicates oil distribution. Since there is no obvious weakest NMR signal between the oil and water distribution areas, T1 < 10 ms is selected as water distribution, and T1 ≥ 10 ms as oil distribution in the T1-T2 rectangular coordinate system. When there are consecutive areas of no NMR signal in the spectrum between the pore water and oil distribution areas, b is taken as b = (b1 + b2) / 2, where b1 is the lower boundary T1 value of the consecutive no NMR signal, and b2 is the upper boundary T1 value of the consecutive no NMR signal.

[0135] Water is basically distributed in the range of T1 / T2 = 10⁻¹, while oil is distributed in the range of T1 / T2 > 10. The boundary between the water distribution area and the oil distribution area is T1 = b ms, that is, in the effective pore area of ​​T2 > a ms. Between the water distribution area and the oil distribution area, T1 > b ms is considered oil, and T1 ≤ b ms is considered water.

[0136] In this embodiment, the specific process of dividing the region into effective porosity and ineffective porosity is as follows:

[0137] In practical applications, based on oil-water distribution experiments, in the T1-T2 two-dimensional NMR spectrum, the distribution location of the H2-containing energy clusters that were not removed at 115℃ is a difficult-to-flow hydrogen-containing substance, which is mainly clay mineral crystal water, solid organic matter, and asphalt, etc. It does not have the storage capacity of oil and gas, and is therefore located as an ineffective pore region.

[0138] The target NMR sample was degreased with alcohol and benzene solvent, and then dehumidified to constant weight at 115℃. The sample was then self-absorbed to saturate oil and water, and its mass was measured using a two-dimensional NMR combined T1-T2 assay. Figure 9 (b) and Figure 9 As shown in (c), the NMR T1-T2 oil-water distribution spectrum was obtained, and compared with... Figure 9 (a) By comparison, the newly emerging nuclear magnetic resonance signal is oil and water. Oil and water and the pores they contain are the main research objects. The pores occupied by oil and water are the oil, gas and water storage space of shale reservoirs, which belong to the effective pore area.

[0139] In this embodiment, the specific process of determining the partition boundary is as follows:

[0140] In practical applications, the purpose of delineating the boundary between effective and ineffective porosity regions for NMR signals is to extract the desired signal data. Specifically, such as... Figure 10As shown, the lower boundary line of the water data area is any perpendicular line to the T1 axis outside the lower boundary of the water data area, i.e., the area without NMR signals, such as line C. The T1 coordinate value is c. The right boundary line of the water data area is any perpendicular line to the T2 axis outside the right boundary of the water data area, such as line N. The T1 coordinate value is n. The right boundary line of the oil data area is any perpendicular line to the T2 axis outside the right boundary of the oil data area, such as line M. The T1 coordinate value is m. The upper boundary line of the oil data area is any perpendicular line to the T1 axis outside the upper boundary of the oil data area, such as line D. The T1 coordinate value is d.

[0141] In this method, the experimental process for restoring the pore volume of the target NMR sample in step four is as follows: the target NMR sample is immersed in kerosene, and the mass of the target NMR sample is weighed at regular intervals until the mass of the target NMR sample is constant; then the target NMR sample is placed in a constant humidity chamber with a humidity of not less than 85% to allow the target NMR sample to absorb water, and the mass of the target NMR sample is weighed at regular intervals.

[0142] In this embodiment, the two-dimensional NMR measurement after self-absorption of oil and water shows that the oil and water volume is close to the true pore volume of the rock sample of the target NMR measurement sample. Therefore, the accuracy of calculating the pore volume of the sample by using the amount of oil and water after self-absorption saturation is higher than that of calculating the pore volume by using the amount of oil and water before self-absorption saturation.

[0143] In practical applications, in step four, the method for determining the pore volume of the target NMR sample is as follows: after the target NMR sample has absorbed oil and water, the mass of the target NMR sample is weighed, and two-dimensional NMR measurement is performed to obtain the NMR data of the target NMR sample after water absorption.

[0144] In this method, the method for determining the total volume of the target NMR sample in step four is as follows: after absorbing water and oil, the target NMR sample is immersed again in kerosene for 30 minutes, and the total volume of the target NMR sample is determined according to Archimedes' principle.

[0145] In this embodiment, the specific calculation process in step five is as follows:

[0146] Based on the NMR signal values ​​of the known water and oil distribution regions, and combined with the total volume, the effective porosity is calculated using the following formula:

[0147]

[0148] Among them, V water The volume of water measured by nuclear magnetic resonance in the sample is in ml; V oil V represents the amount of oil and gas measured by nuclear magnetic resonance in the sample, in ml; φ represents the effective porosity of the sample, in %; tatal The total volume of the sample being tested is expressed in cm³. 3 .

[0149] In this embodiment, the samples were selected from core samples of shale oil reservoirs in the exploration area, and the target NMR samples were prepared using a freezing technique to avoid sample fractures. Table 2 shows the effective porosity measurement data of shale samples using NMR. As shown in Table 2, two-dimensional NMR identifies different fluids through spectral NMR signal maps, distinguishing between shale clay water and pore water. The samples do not require processing at a plant, and any sample does not affect the NMR measurements. Therefore, the accuracy of NMR data is higher than that obtained by other methods, and the data has been well applied in practice. The NMR porosity measurement method provided in this embodiment is highly accurate, simple, convenient, and quick, making it of significant value for shale oil reservoir research.

[0150] Table 2. Data on effective porosity determination of shale samples by nuclear magnetic resonance (NMR)

[0151]

[0152] This invention provides a method for determining the effective porosity of shale oil samples based on two-dimensional nuclear magnetic resonance (NMR) technology. Through experiments, a two-dimensional NMR spectrum analysis technique is established, clarifying the oil-water distribution in the two-dimensional NMR spectrum. This avoids the serious distortion caused by unclear oil-water distribution leading to confusion in the pore volume determination results of the two-dimensional NMR method. The distribution of effective and ineffective pore regions is also clarified experimentally, avoiding inaccurate pore volume determination due to unclear delineation between the two. Through shale oil sample property characteristic experiments, it is confirmed that the pores of shale oil reservoir samples have dual oil-water wettability. The self-absorption of oil and water solves the problem of inaccurate pore volume determination in shale oil, improving the accuracy of determining the oil content of organic and inorganic pores in shale samples. The two-dimensional NMR analysis technique provides a technical means for the determination of effective porosity in other shale oil samples, providing a comparable benchmark for the determination of effective porosity in other shale samples. The porosity determination method provided in this embodiment is convenient, quick, simple, and highly accurate. It has a short experimental cycle, high production efficiency, and is non-toxic and harmless, in line with the HSE (Health, Safety, and Environmental Protection) concept.

[0153] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for determining effective porosity of a shale oil rock sample based on two-dimensional nuclear magnetic technology, characterized in that, include: Step 1: Determine the target study area, obtain shale oil samples from the target study area, prepare the samples into target NMR samples using the freezing method, and calibrate the water content and oil content of the target NMR samples respectively. Step 2: Perform water distribution experiments and oil distribution experiments on the target NMR sample, and perform pore property characteristic experiments on the target NMR sample after natural oil and water loss, low-temperature water removal, and low-temperature oil removal. Step 3: Based on the results of the water distribution experiment and the oil distribution experiment, the target NMR sample is divided into an effective porosity region and an ineffective porosity region, and the NMR signal boundary and oil-water boundary are defined for the effective porosity region and the ineffective porosity region respectively. Step 4: Recover the pore volume of the target NMR sample, measure the pore volume of the target NMR sample, and obtain the total volume of the target NMR sample using Archimedes' principle; Step 5: Based on the boundary division results of the NMR signal and the oil-water boundary division results, extract the data corresponding to the two-dimensional NMR signal of the sample under test, and calculate the porosity of the target NMR sample by combining the total volume.

2. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, The preparation method of the target NMR sample is as follows: Liquid nitrogen or a cryogenic freezer, with a temperature range of ≤-40°C, is used to freeze the full-diameter shale oil sample to be taken, ensuring the shale oil sample is completely frozen. Use core cutting tools or core-specific machetes to prepare sheet-like shale oil samples with the required thickness of 15mm to 20mm along the bedding plane of the core. Then freeze them again to keep them frozen. The flaky shale oil sample was cut into block-shaped samples with geometrical requirements by using a core cutting tool along a direction perpendicular to the bedding and the end face of the bedding.

3. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step one, the method for calibrating the water volume value is as follows: Seven oil-free target NMR samples were selected. The moisture in the target NMR samples was removed at a high temperature of 120℃. Different amounts of deionized water or distilled water were dripped into each rock sample. The different amounts of water dripped into the seven target NMR samples were then used to perform NMR T1-T2 combined measurements on each target NMR sample to obtain two-dimensional NMR data for different target NMR samples. Using NMR signal as the x-axis and water volume as the y-axis, a functional relationship between water volume and NMR signal is established.

4. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step one, the method for calibrating the oil content value is as follows: select 7 rock sample test glasses, put the target NMR test sample into the rock sample test glass, add unequal amounts of kerosene into the rock sample test glass, and perform NMR T1-T2 combined NMR measurement on each target NMR test sample to obtain two-dimensional NMR measurement data under different oil contents. Using NMR signal as the x-axis and oil quantity as the y-axis, a functional relationship between water quantity and NMR signal is established.

5. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step two, the water distribution experiment includes a water distribution experiment of the target NMR sample and a water distribution experiment of the target NMR sample after oil content calibration. The method for the water distribution experiment of the target NMR sample is as follows: Select any target NMR sample, place it in a 700℃ dry distillation oven to remove hydrogen-containing substances, and perform a two-dimensional NMR experiment until the hydrogen-containing substances in the target NMR sample are completely removed. The target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After the mass of the target NMR sample remained unchanged, a two-dimensional NMR experiment was carried out again to obtain the T1-T2 distribution spectrum and determine the water distribution area.

6. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 5, characterized in that, In step two, the experimental method for determining the water distribution of the target NMR sample after oil quantity value calibration is as follows: A target NMR sample with calibrated oil content was selected, and two-dimensional NMR was performed to obtain a two-dimensional NMR spectrum. The oil was removed by alcohol and benzene solvent, and after dehumidification at 115℃ to constant weight, a two-dimensional nuclear magnetic resonance experiment was conducted to obtain the T1-T2 distribution spectrum under the conditions of oil removal and dehumidification. After the oil content value was calibrated, the target NMR sample was placed in a humidifier with a humidity of not less than 85% to absorb moisture. After weighing it to a constant mass, two-dimensional NMR was performed again to obtain a water-saturated two-dimensional NMR spectrum. The target NMR sample, after being calibrated for oil content, was broken open and then re-moistened. Once the mass was constant, a two-dimensional NMR measurement was performed to obtain its water-absorbing two-dimensional NMR spectrum under external force destruction conditions. By comparing the two-dimensional NMR results of the target NMR sample after oil quantity calibration under different conditions, the location of water distribution can be determined.

7. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step two, the oil distribution experiment is performed as follows: Select any target NMR sample, remove oil with alcohol and benzene solvent, dehumidify at 115℃, and conduct a two-dimensional NMR experiment; obtain the two-dimensional NMR spectrum of the target NMR sample under the conditions of oil removal and dehumidification. After the target NMR sample was placed in an environment with a humidity of not less than 85% and absorbed water, two-dimensional NMR measurement was carried out to obtain the two-dimensional NMR spectrum of the target NMR sample under water absorption conditions. The target NMR sample was immersed in kerosene to absorb saturated kerosene. After the quality stabilized, two-dimensional NMR was performed to obtain the two-dimensional NMR spectrum of the target NMR sample under water and oil absorption conditions. Based on the experimental results, the oil distribution area was determined.

8. The method for determining effective porosity of shale oil rock sample based on two- dimensional nuclear magnetic technology according to claim 1, characterized in that, In step two, the process of the oil-water natural loss sample pore property characteristic experiment is as follows: Two target NMR samples are selected from the center of the frozen and pressurized core. After two-dimensional NMR measurement, the target NMR samples are placed in a rock sample bottle and allowed to thaw slowly under natural conditions. Some fluid is lost. One target NMR sample is first placed in kerosene and then in water, allowing it to absorb oil and water on its own. After the mass remains unchanged, two-dimensional NMR measurements are carried out on both samples. The other target NMR sample is first placed in water and then in kerosene. After the mass remains unchanged, two-dimensional NMR measurements are carried out on both samples.

9. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step two, the process of the low-temperature dehydration sample pore property characteristic experiment is as follows: Select the target NMR sample, perform two-dimensional NMR measurement, place the target NMR sample under vacuum low temperature of 60℃ for 8 hours to remove pore water, and then perform two-dimensional NMR measurement. Then, place the target NMR sample in a constant humidity chamber with humidity greater than 85%, and after the mass remains unchanged, perform two-dimensional NMR measurement again. Compare and analyze the two-dimensional NMR measurement data under different conditions to determine the reproducibility of pore water.

10. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step two, the experimental procedure for the porosity characteristic experiment of the sample after low-temperature oil removal is as follows: Select the target NMR sample, perform two-dimensional NMR measurement, and then perform low-temperature oil removal with chloroform for no less than 70 hours, followed by two-dimensional NMR experiment; immerse the target NMR sample in kerosene until the rock sample is saturated with kerosene by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR experiment; place the target NMR sample under constant humidity conditions with a humidity greater than 85%, until the rock sample is saturated with water by self-absorption, and after the mass remains unchanged, perform two-dimensional NMR measurement to obtain two-dimensional NMR spectra under different conditions.

11. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step three, the method for determining the distribution locations of ineffective and effective pore regions is as follows: the target NMR sample is degreased with alcohol and benzene solvent, and then dehumidified at 115°C to constant weight. A two-dimensional NMR experiment is then performed to obtain the T1-T2 distribution spectrum of solids or near-solid hydrogen-containing substances that cannot be removed under the degreasing and dehumidification conditions. The sample is then saturated with oil and water by self-absorption, and after the mass is kept constant, two-dimensional NMR measurements are performed to obtain the pore oil-water distribution spectrum. The region containing the T1-T2 distribution spectrum of solid or near-solid hydrogen-containing substances such as crystalline water or structural water, organic matter, and bituminous matter within clay minerals is defined as the ineffective porosity distribution region, while the region containing saturated oil and water is defined as the effective porosity distribution region.

12. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 6 or 7, characterized in that, In step three, the method for defining the boundary line of the NMR signal between the effective porosity region and the ineffective porosity region is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest point of the NMR signal between the ineffective porosity region where the solid or near-solid region is located and the effective porosity region where the pore water is located is selected, with a corresponding T2 coordinate value of ams. A perpendicular line is drawn to the T2 axis (horizontal coordinate), i.e., T2 = ams. The straight line T2 = ams is selected as the boundary line between the effective porosity region and the ineffective porosity region. Where T2 ≤ ams indicates the ineffective porosity region, and T2 > ams indicates the effective porosity region. If there is no obvious weakest point of the NMR signal between the effective porosity region and the ineffective porosity region, T2 ≤ 0.2ms in the T1-T2 rectangular coordinate system is selected as the ineffective porosity region, and T2 > 0.2ms as the effective porosity region. When the NMR signal between the effective pore region and the ineffective pore region is continuously without NMR signal, that is, when the NMR signal is all in the background area of ​​the spectrum, the value of a is a = (a1 + a2) / 2, where a1 is the left boundary T2 value of the continuous absence of NMR signal and a2 is the right boundary T2 value of the continuous absence of NMR signal.

13. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 6 or 7, characterized in that, In step three, the method for delineating the boundary between the oil and water distribution areas is as follows: The two-dimensional NMR spectrum T1-T2 is treated as a rectangular coordinate system. The weakest NMR signal between the pore water distribution area and the oil distribution area is selected, corresponding to a T1 coordinate value of b ms. A perpendicular line is drawn to the T1 axis (vertical coordinate), i.e., T1 = b ms. The line T1 = b is selected as the boundary line between the oil and water NMR signals. T1 ≤ b ms indicates water distribution, and T1 > b ms indicates oil distribution. Since there is no obvious weakest NMR signal between the oil and water distribution areas, T1 < 10 ms is selected for water distribution, and T1 ≥ 10 ms for oil distribution in the T1-T2 rectangular coordinate system. When there are consecutive areas of no NMR signal in the spectrum between the pore water and oil distribution areas, b is taken as b = (b1 + b2) / 2, where b1 is the lower boundary T1 value of the consecutive no NMR signal, and b2 is the upper boundary T1 value of the consecutive no NMR signal. Water is basically distributed in the range of T1 / T2 = 10⁻¹, while oil is distributed in the range of T1 / T2 > 10. The boundary between the water distribution area and the oil distribution area is T1 = b ms, that is, in the effective pore area of ​​T2 > a ms. Between the water distribution area and the oil distribution area, T1 > b ms is considered oil, and T1 ≤ b ms is considered water.

14. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step four, the experimental process for restoring the pore volume of the target NMR sample is as follows: the target NMR sample is immersed in kerosene, and the mass of the target NMR sample is weighed periodically until the mass of the target NMR sample is constant; then the target NMR sample is placed in a constant humidity chamber with a humidity of not less than 85% to allow the target NMR sample to absorb water, and the mass of the target NMR sample is weighed periodically.

15. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step four, the method for determining the pore volume of the target NMR sample is as follows: after the target NMR sample has absorbed oil and water, the mass of the target NMR sample is weighed, and two-dimensional NMR measurement is performed to obtain the NMR data of the target NMR sample after water absorption.

16. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step four, the method for determining the total volume of the target NMR sample is as follows: after absorbing water and oil, the target NMR sample is immersed again in kerosene for 30 minutes, and the total volume of the target NMR sample is determined according to Archimedes' principle.

17. The method for determining effective porosity of shale oil rock sample based on two-dimensional nuclear magnetic technology according to claim 1, characterized in that, In step five, the effective porosity of the target NMR sample is calculated using the following formula: Wherein, V water is the water content of the sample determined by nuclear magnetic resonance, ml; V oil is the oil and gas content of the sample determined by nuclear magnetic resonance, ml; φ is the effective porosity of the sample, %; V tatal is the total volume of the sample, cm 3 .

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