Method for testing minimum using pore throat of oil-gas modified fluid

Abstract

The invention provides a method for testing a minimum utilization pore throat of oil and gas modified fluid, and relates to the technical field of oil and gas development, and the method comprises the following steps: carrying out a high-pressure mercury injection experiment on a first rock sample to obtain a quantitative relationship between the mercury injection pressure and the pore throat radius; performing a nuclear magnetic resonance T2 spectrum test on the second rock sample to obtain an original T2 relaxation spectrum; establishing a conversion relation between nuclear magnetic resonance T2 relaxation time and aperture by using high-pressure mercury injection data; applying formation pressure to the second rock sample, carrying out constant-temperature reaction, putting into a centrifugal machine, and applying centrifugal force to simulate a strong driving process; and performing nuclear magnetic resonance T2 spectrum test on the centrifuged second rock sample, and calculating the minimum operating aperture according to the conversion relation. According to the method, the temperature and pressure environment and the strong driving process of reservoir in-situ modification are effectively simulated, the minimum using pore throat of the fluid is obtained through quantitative calculation, the precision of the micro-nano pore diameter section is improved through the conversion relation established through the fractal theory, skeleton signal interference is removed, and the accurate fluid occurrence state change rule is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas development, and particularly relates to a test method for minimum producing pore throat of oil and gas modified fluid. BACKGROUND

[0002] Low maturity source rock type oil and gas resources (such as low maturity coal rock gas, shale oil, etc.) have huge resource quantity, but the reservoir physical property is extremely poor, nanoscale pores are developed, and fluid flowability is extremely poor, so in-situ modification technology (such as electric heating, catalytic cracking, etc.) needs to be used to convert bound organic matter into free state for further effective exploitation. Accurate measurement of the minimum producing pore diameter is of great significance for predicting recoverable reserves, and the minimum producing pore diameter directly determines the effective pore size and pore volume that can participate in flow under specific driving conditions, and further affects the calculation result of recoverable reserves. By quantitatively characterizing this parameter, key basis can be provided for oil and gas reservoir economic evaluation, development plan design and recovery prediction, avoiding the estimation deviation of reserves and development risk caused by unclear producing pore diameter, and also providing reference for the development of development measures.

[0003] At present, the technologies for evaluating reservoir pore structure mainly include mercury injection method and nuclear magnetic resonance method. Although the existing methods can test the pore size distribution of the reservoir, they cannot distinguish the state (movable and immovable) of the fluid in the pore and the minimum pore diameter of the movable fluid in the reservoir.

[0004] Chinese patent document CN115728202A discloses a method for determining the lower limit of shale movable throat radius, discloses a technical scheme for determining the lower limit of movable throat radius by combining full-pore-range characterization through low-temperature nitrogen adsorption, high-pressure mercury injection and nuclear magnetic resonance, and movable oil extraction experiment, solves the problem of describing the occurrence space characteristics of complex pore structure shale, but this scheme uses normal temperature and pressure experimental conditions, determines the movable oil saturation through petroleum ether heating extraction, cannot simulate the high temperature and high pressure environment and strong driving conditions of the in-situ modification process of low maturity source rock, and does not consider the change of fluid state from bound organic matter to free state, is only suitable for conventional shale oil evaluation, and is not suitable for low maturity source rock type oil and gas resources that need in-situ modification development.

[0005] The Chinese patent document CN120628933A discloses a method for determining the lower limit of movable fluid pore diameter and the effective pore volume ratio, discloses a technical solution for calculating reservoir temperature according to the geothermal gradient and burial depth theory, correcting the water surface tension coefficient, and calculating the lower limit of movable water pore diameter through the principle of equalizing capillary force and reservoir fluid pressure, fully considering the influence of in-situ temperature and pressure conditions of the reservoir on the fluid mobility, but this solution is a pure theoretical calculation method, lacks experimental verification, and is aimed at the original water in the original state of the reservoir, without considering the fluid state change caused by the conversion of bound organic matter during the in-situ upgrading of low-maturity source rock, and without involving the influence of the strong driving effect generated by in-situ upgrading on fluid power, so it cannot be directly applied to the evaluation of the in-situ upgrading development process of low-maturity source rock type oil and gas resources. SUMMARY

[0006] The purpose of the present application is to provide a test method for the minimum producing pore throat of oil and gas upgrading fluid, which can improve the conversion accuracy and quantitative calculation of the micro-nano pore diameter section to obtain the minimum producing pore throat of fluid in the rock after in-situ upgrading of the reservoir.

[0007] To achieve the above-mentioned purpose, the present application realizes the following technical solutions: A test method for the minimum producing pore throat of oil and gas upgrading fluid, comprising the following steps: S1: sample preparation is performed on the core sample drilled from the target reservoir, the sample is divided into a first rock sample and a second rock sample, the first rock sample is subjected to oil washing and drying treatment, and then high-pressure mercury injection experiment is performed to obtain high-pressure mercury injection data, the high-pressure mercury injection data including the quantitative relationship between mercury injection pressure and pore throat radius; S2: nuclear magnetic resonance T2 spectrum test is performed on the second rock sample to obtain the original T2 relaxation spectrum; S3: the conversion relationship between nuclear magnetic resonance T2 relaxation time and pore diameter is established by using the high-pressure mercury injection data; S4: the second rock sample is placed in a reaction kettle, the formation pressure is applied and the temperature is raised to a set temperature, and then constant temperature reaction is performed to a set time, after that, the second rock sample is loaded into a centrifuge tube and sealed, and then put into a centrifuge to apply centrifugal force to simulate the strong driving process; S5: nuclear magnetic resonance T2 spectrum test is performed on the second rock sample after centrifugation, the T2 spectrum before and after centrifugation is compared to determine the T2 cutoff value, and the minimum producing pore diameter is calculated according to the conversion relationship.

[0008] Further, in S1, the sample preparation is performed by a diamond wire cutting machine under water-free conditions.

[0009] Further, before S2, the pulse sequence parameters of the low-field nuclear magnetic resonance equipment are corrected, the pulse sequence parameters including echo interval time, sampling bandwidth, preamplifier gain, repetition waiting time, scan number and echo number.

[0010] Further, the method of removing the rock skeleton base signal in S2 is implemented by heating the second rock sample at high temperature, then centrifuging, and then performing nuclear magnetic resonance scanning to obtain the rock skeleton spin echo train as the base signal, and removing the base signal from the spin echo train of the second rock sample containing fluid to obtain the T2 spectrum reflecting only the relaxation characteristics of the pore fluid.

[0011] Further, the heating temperature when removing the skeleton base signal is greater than or equal to 600 DEG C, and the heating time is greater than or equal to 30 minutes.

[0012] Further, in S3, a conversion relationship between the T2 relaxation time and the pore size is established based on the fractal geometry theory, and the conversion relationship is:

[0013] wherein, is the pore throat radius, is the nuclear magnetic resonance relaxation time; is the proportional coefficient, is the fractal control index.

[0014] Further, when the nuclear magnetic resonance spectrum is multi-peak or the fractal dimension is significantly different at different scale sections, a segmented function is used to determine the conversion parameters of each scale section, and the segmented function is:

[0015] wherein, is the pore throat radius, is the nuclear magnetic resonance relaxation time, is the adsorbed state zone proportional coefficient, controlling the pore size conversion scale of the nanometer pore throat section, is the free state zone proportional coefficient, controlling the pore size conversion scale of the micro-fracture or channel section, is the fractal control index of the first pore interval, is the fractal control index of the second pore interval, is the relaxation time corresponding to the demarcation point.

[0016] Further, in S4, the formation pressure applied by the reaction kettle is 25-60 MPa, the set temperature is 200-450 DEG C, and the constant temperature reaction time is 1 hour, wherein the formation pressure applied by the reaction kettle is 25-60 MPa, in order to better simulate the actual environment pressure of the formation pressure, the set temperature is the temperature point of the in-situ modification, which is usually 200-450 DEG C.

[0017] Further, in S4, the centrifuge speed is determined according to the target driving pressure gradient.

[0018] Further, in S5, the T2 cutoff value is the T2 value at which the signal in the T2 spectrum after centrifugation begins to decrease obviously.

[0019] Compared with the prior art, the present application has the following beneficial effects: The present application establishes a nonlinear conversion relationship between T2 relaxation time and pore diameter based on fractal geometry theory, introduces a surface fractal dimension to represent the multi-scale roughness characteristics of the pore surface of low maturity source rock, and obtains a conversion formula of throat radius and T2 by combining with a power law relationship of pore throat ratio, which more accurately reflects the complex pore structure characteristics of organic matter and inorganic matter interweaving than a traditional linear conversion relationship, significantly improves the conversion accuracy of micro-nano pore diameter section, and can adapt to the case of multi-peak spectrum and fractal dimension change of different scale sections through a segmented function.

[0020] The present application provides a method for determining a T2 cutoff value by comparing the T2 spectra before and after centrifugation, and quantitatively calculating the minimum producing pore throat of fluid in the rock after in-situ modification of the reservoir, which can directly evaluate the improvement effect of in-situ modification on the minimum producing pore diameter, and provides a key technical means for the recoverable reserves evaluation and development plan design of low maturity source rock type oil and gas resources.

[0021] The present application can accurately reproduce the in-situ modification process, including heat treatment and chemical treatment, by simulating the temperature and pressure environment of low maturity source rock samples under in-situ conditions in a reaction kettle, which overcomes the limitation that the prior art cannot restore the real temperature and pressure conditions of the reservoir, so that the test results are more consistent with the actual formation development conditions.

[0022] The present application can simulate the high pore fluid pressure and overpressure conditions of deep shale gas reservoirs by simulating the strong driving process generated by in-situ modification through a centrifuge, and calculating and determining the centrifugal speed according to the target driving pressure gradient, which overcomes the restriction of the upper limit of the speed of conventional centrifugation. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The present application provides a test method for the minimum producing pore throat of oil and gas modification fluid; Figure 2 A pressure mercury result graph of a low maturity rock sample in an embodiment of the present application; Figure 3 A corresponding result graph of pore throat radius and T2 relaxation time of a low maturity rock sample in an embodiment of the present application; Figure 4 A fitting result graph of relaxation time and pore throat radius of a low maturity rock sample in an embodiment of the present application; Figure 5 A movable fluid characterization result graph of a low maturity rock sample in an embodiment of the present application; Figure 6 A nuclear magnetic resonance test result graph of a low maturity rock sample before and after in-situ modification in an embodiment of the present application; Figure 7 This is a diagram showing the mobile fluid characterization results of an in-situ modified low-maturity rock sample in an embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0025] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] Example 1 like Figure 1 As shown, this invention provides a test method for the minimum pore throat movement of oil and gas reforming fluids, comprising the following steps: S1: Sample preparation is carried out on the core samples drilled from the target reservoir. The samples are divided into the first rock sample and the second rock sample. After washing and drying the first rock sample, a high pressure mercury intrusion test is carried out to obtain high pressure mercury intrusion data. The high pressure mercury intrusion data includes the quantitative relationship between mercury intrusion pressure and pore throat radius. Specifically, rock samples are drilled from full-diameter cores of the target reservoir, with diameters ranging from 25mm to 100mm. Sample preparation requires drilling under waterless conditions using a diamond wire cutter to prevent hydration reactions that could damage the original pore structure. Next, each drilled sample is cut into two pieces. One piece is washed with oil, dried, and subjected to high-pressure mercury intrusion porosimetry (HIP) tests, standard for low-maturity source rock oil and gas resources, to obtain a quantitative relationship curve between the mercury intrusion pressure and the pore throat radius.

[0027] S2: Perform nuclear magnetic resonance T2 spectrum testing on the second rock sample to obtain the original T2 relaxation spectrum; Specifically, another rock sample obtained from the above-mentioned wire cutting was subjected to nuclear magnetic resonance T2 spectrum testing. Before the test, the pulse sequence parameters of the low-field nuclear magnetic resonance equipment need to be corrected to be applicable to different types of samples. The following uses a tight rock sample of low-maturity source rock type oil and gas resources as an example to further explain the pulse sequence parameters that need to be corrected. The echo interval (TE) plays a decisive role in signal acquisition. A shorter TE helps to obtain rapid relaxation information of fluids in nanoscale pores. Therefore, in experiments with low-maturity tight reservoir samples, the TE is set to the minimum allowable value of the equipment to improve detection sensitivity.

[0028] The sampling bandwidth (SW) not only limits the frequency range of the receiver, but also affects the sampling rate. If it is set too small, it may cause the fast relaxation signal to be missed; if it is set too large, it will increase the noise. In order to ensure that the characteristics of the nanopore can be effectively recorded, a larger SW is selected in the low-porosity and low-permeability core test to improve the sampling frequency and improve the identification ability of the fast relaxation component.

[0029] The preamplifier gain (PRG) is used to enhance the amplitude of the detected signal, thereby improving the signal-to-noise ratio. However, if the value is too high, distortion may occur, so a balance needs to be maintained between the gain and the signal fidelity.

[0030] The repetition time (TW) determines whether the protons return to the initial polarization state. If it is set too short, the polarization will be insufficient, which will affect the test results, so a TW greater than three times the relaxation time of the pore fluid is usually selected to ensure complete recovery.

[0031] Increasing the number of scans (NS) helps to improve the signal-to-noise ratio, but too many will significantly prolong the experimental period and reduce overall efficiency. Therefore, when the signal-to-noise ratio is high, a moderate NS value should be selected to balance accuracy and efficiency.

[0032] Too many echoes (NECH) will accumulate redundant noise, causing the T2 spectrum quality to decline and increasing unnecessary acquisition. Its impact on the results is relatively limited, so the NECH value when the signal tends to be stable can usually be selected.

[0033] In order to eliminate the interference of hydrogen nuclei in the rock skeleton on the T2 spectrum and accurately characterize the production characteristics of the fluid in the confined space, the present application establishes an implementation method for removing the base signal of the rock skeleton. The specific process is as follows: the sample is placed in a high-temperature and high-pressure reaction kettle, heated at a temperature greater than or equal to 600°C for more than or equal to 30 minutes, then subjected to high-speed centrifugation, and then subjected to nuclear magnetic resonance scanning to obtain the spin echo train of the rock skeleton as the base. Then, the spin echo train of the sample containing the fluid is subtracted from the base signal, and the T2 spectrum reflecting only the relaxation characteristics of the pore fluid is obtained by inversion.

[0034] S3: Establish the conversion relationship between the nuclear magnetic resonance T2 relaxation time and the pore size using high-pressure mercury injection data; Specifically, using the information such as specific surface area of pores obtained from high-pressure mercury injection data, the nuclear magnetic resonance T2 relaxation time is converted into pore radius, and the conversion basis is as follows: According to the principle of nuclear magnetic resonance: (1) In a porous medium, the bulk relaxation effect of the fluid itself is much weaker than the surface relaxation, so 1 / T 2B can be ignored. At the same time, under ideal uniform magnetic field conditions, the effect of diffusion on nuclear magnetic resonance measurement can also be ignored. Therefore, the surface relaxation dominant approximation can be used: (2) In Euclidean geometry, the surface area of a regular sphere is proportional to the square of the radius, i.e. Then, , Then, (3) For complex, multi-scale rock pore types, the pore surface is not a normal Euclidean smooth surface or a regular sphere, but is composed of extremely rough, organic and inorganic interwoven pore walls. The shale pore system presents a multi-scale rough structure, and at this time, the physical or geometric approximation is that the surface has a fractal scale law, so the relationship between the pore structure parameters and the nuclear magnetic resonance signal can be established.

[0035] For a fractal surface, the scale of the surface area is not but, (4) ( represents a smooth Euclidean surface, The larger the surface is rougher, and the limit means that the surface area is infinite) The corresponding volume is still a Euclidean three-dimensional So (5) Therefore: (6) where is a constant (approximately constant at this scale).

[0036] Substitute 6 into 1 and treat as a constant to get (7) Rearranged as: (8) Take the power of both sides (assuming ; and, usually ) to get the power-law relationship of pore size about : (9) Here, it needs to be explained that is determined by the surface fractal dimension ; if (smooth surface), then (linear relationship); if , then . is the front factor, which contains and the geometric scale constant .

[0037] Considering the relationship between pore size and throat size: (10) In engineering and fractal / statistical geometry, the power law of pore throat ratio is often used, that is: (11) Where represents the change in scale of the pore throat ratio with pore size; if the pore throat ratio is constant. From (10)-(11), we get: (12) Substitute (9) into (12): (13) Define (14) Then, we can get:

[0038] Where, is the pore throat radius, is the nuclear magnetic resonance relaxation time; is the proportionality coefficient, is the fractal control index. From equation (14), and are constants.

[0039] If the NMR spectrum is multi-peak or fractal analysis shows is significantly different at different scale segments, follow the above steps to derive each segment (consider , , as a constant in the segment), and get the segmented function: (15) Where , is the pore throat radius, is the nuclear magnetic resonance relaxation time, is the proportionality coefficient of the small pore or adsorption state region, which controls the pore size conversion scale of the nanopore throat segment, is the proportionality coefficient of the large pore or free state region, which controls the pore size conversion scale of the micro-fracture or channel segment, is the fractal control index of the first pore interval, is the fractal control index of the second pore interval, is the relaxation time corresponding to the dividing point. The dividing The spectrum valley, fractal dimension mutation or cross validation can be determined; at the junction, a smoothing function can be used to connect to ensure continuity; at this time, at the small pore, nitrogen adsorption method or SEM measured pore size relationship fitting can also be introduced, and the large pore section adopts high pressure mercury measured pore size fitting.

[0040] S4: Put the second rock sample into the reaction kettle, apply the formation pressure and heat to the set temperature, and after constant temperature reaction to the set time, seal the second rock sample into the centrifuge tube and put it into the centrifuge to apply the centrifugal force, simulate the strong driving process; Specifically, the in-situ core scanned by nuclear magnetic resonance T2 spectrum after cutting is put into a high temperature and high pressure reaction kettle, the formation pressure is applied by a high pressure plunger pump, and the reaction kettle is heated to a set temperature to simulate the in-situ modification process of the reservoir. After constant temperature reaction reaches the set time, the core is sealed in a specially designed heat-resistant and pressure-resistant metal centrifuge tube, and then put into a high-speed centrifuge to apply a high centrifugal force calculated according to the target driving pressure gradient for a certain period of time to simulate the strong driving process of the in-situ modification to produce movable fluid in the pore; It should be noted that a large driving pressure gradient will be generated during the in-situ modification development process, and the fluid will migrate from the reservoir matrix to the artificial fracture. The centrifugal force applied by the centrifuge needs to simulate this strong driving condition. The centrifugal force corresponds to the driving force of the fluid in the pore. According to the formula of centrifugal force, the centrifugal force is equal to the mass multiplied by the square of angular velocity multiplied by the radius of rotation. The pressure gradient generated by the centrifugal force can be calculated by dividing the centrifugal force by the column height of the fluid. According to the numerical value of the target driving pressure gradient, the required centrifugal force is back calculated, and then the speed of the centrifuge is calculated. The centrifugal time also needs to be determined according to the actual situation to ensure that the movable fluid is fully driven out. The speed of the centrifuge is adjusted to match the driving effect of the centrifugal force with the strong driving conditions in the actual reservoir modification development process, which improves the accuracy of the test. The adjustability of the speed of the centrifuge makes the test method adaptable to the evaluation needs under different driving conditions.

[0041] S5: Perform nuclear magnetic resonance T2 spectrum test on the second rock sample after centrifugation, compare the T2 spectrum before and after centrifugation, determine the T2 cutoff value, and calculate the minimum producing pore size according to the conversion relationship; Specifically, the metal centrifuge tube is opened, the core after centrifugation is taken out immediately, and nuclear magnetic resonance T2 spectrum scanning is performed to obtain the distribution of residual fluid that has not been driven out; the T2 spectrum before and after centrifugation is compared. The fluid corresponding to the T2 interval where the signal decreases significantly after centrifugation is the fluid that has been produced. The T2 cutoff value (T 2c ) at which the signal begins to decrease significantly is determined. The conversion method obtained in step three is used to calculate the minimum pore radius r min that has been successfully produced by the formula. This radius is the minimum producing pore size of the fluid under the simulated driving conditions.

[0042] Example 2 As shown in Figure 2 - Figure 7 The specific implementation steps are as follows, taking the minimum pore throat of in-situ modified fluid of bound state crude oil in a rock sample of a low maturity source rock type reservoir in a certain block as an example: Step one: use a diamond wire cutting machine to drill two cylindrical rock samples with a diameter of 25 mm under waterless conditions to avoid the destruction of pore structure by hydration reaction. One of the two rock samples is washed with an organic solvent (such as toluene / methanol azeotropic mixture) to remove movable oil, and then vacuum dried at 180°C for 48 hours. High-pressure mercury injection experiment is performed on the dried rock sample to obtain the relationship curve of mercury injection pressure and pore throat radius, which is used for the conversion of nuclear magnetic T2 spectrum and pore size in the future. Figure 2 ).

[0043] Step two: place the other rock sample without oil washing in a low-field nuclear magnetic resonance instrument (such as a 2MHz nuclear magnetic resonance analyzer), and set the following parameters: echo interval (TE): 0.1ms (minimum value of the instrument); sampling frequency (SW): 333kHz; preamplifier gain (PRG): 1, repetition waiting time (TW): 1000s (more than 3 times T1); number of scans (NS): 64 times; number of echoes (NECH): 8000.

[0044] Start the nuclear magnetic resonance scanning system to collect the original T2 relaxation spectrum of the rock sample.

[0045] Step three: according to the high-pressure mercury injection data, apply the above deduced formula result to fit the relationship between T2 and pore size r (such as Figure 3 and Figure 4 ).

[0046] Step four: open the upper end cover of the high-temperature and high-pressure reaction kettle, put the rock sample into the high-temperature and high-pressure reaction kettle, apply 45MPa confining pressure through the confining pressure loading port to simulate the formation pressure. Increase the temperature of the reaction kettle to 350°C through the electric heating disc to simulate the in-situ pyrolysis process, and continue for 1 hour. After the reaction is completed, use the mechanical arm to quickly transfer the rock sample to the specially designed metal centrifugal tube along the slide rail. Put the centrifugal tube into the high-speed centrifuge, calculate the required centrifugal force according to the target driving pressure gradient and optimize the optimal speed and centrifugation time, and in this embodiment, 12000r / min is adopted, and the centrifugation time is 30min, to simulate the fluid production process under strong driving conditions and determine the movable pore size before modification. Figure 5 ).

[0047] Step five: after the centrifugation is completed, open the metal centrifugal tube, use the mechanical arm to quickly transfer the rock sample to the nuclear magnetic resonance test system 14 along the slide rail for nuclear magnetic resonance T2 spectrum test, and the parameters are the same as before. Compare the T2 spectra before and after modification (such as Figure 6 , Figure 7The T2 cut-off value (T2c) is determined, i.e. the T2 value at which the signal starts to decrease significantly, by identifying the T2 interval in which the signal decreases significantly (as shown in FIG. 2). The minimum drainage aperture of the oil reservoir before and after in-situ upgrading is calculated to be 0.367 microns and 0.043 microns, respectively.

[0048] The present application can be applied to shale oil and gas reservoirs, coal rock gas reservoirs, and can be extended to fluid minimum drainage aperture testing in low-permeability oil and gas reservoirs such as tight oil and oil shale, thereby providing important technical support for economic evaluation and development plan optimization of oil and gas reservoirs.

[0049] The above-described embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A test method for the minimum pore throat movement of oil and gas reforming fluids, characterized in that: Includes the following steps; S1: Sample preparation is carried out on the core samples drilled from the target reservoir. The samples are divided into the first rock sample and the second rock sample. After washing and drying the first rock sample, a high pressure mercury intrusion test is carried out to obtain high pressure mercury intrusion data. The high pressure mercury intrusion data includes the quantitative relationship between mercury intrusion pressure and pore throat radius. S2: Perform nuclear magnetic resonance T2 spectrum testing on the second rock sample to obtain the original T2 relaxation spectrum; S3: Establish the conversion relationship between nuclear magnetic resonance T2 relaxation time and aperture using high-pressure mercury intrusion data; S4: Place the second rock sample in the reactor, apply formation pressure and heat to the set temperature, react at a constant temperature for the set time, then put the second rock sample into a centrifuge tube and seal it, put it into a centrifuge and apply centrifugal force to simulate a strong driving process. S5: Perform nuclear magnetic resonance T2 spectrum testing on the second rock sample after centrifugation, compare the T2 spectra before and after centrifugation, determine the T2 cutoff value, and calculate the minimum usable aperture based on the conversion relationship.

2. The test method for the minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: In S1, sample preparation was carried out using a diamond wire cutter under anhydrous conditions.

3. The test method for the minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: Before S2, the pulse sequence parameters of the low-field nuclear magnetic resonance equipment are calibrated. These pulse sequence parameters include echo interval time, sampling bandwidth, preamplifier gain, repetition wait time, number of scans, and number of echoes.

4. The test method for minimum pore throat movement of oil and gas reforming fluid according to claim 1, characterized in that: S2 is achieved by removing the basic signal of the rock skeleton. The method of removing the basic signal of the rock skeleton is to heat the second rock sample at high temperature, centrifuge it, and then perform nuclear magnetic resonance scanning to obtain the spin echo train of the rock skeleton as the base signal. After removing the base signal from the spin echo train of the second rock sample containing fluid, the T2 spectrum that only reflects the relaxation characteristics of pore fluid is obtained.

5. The test method for minimum active pore throat of oil and gas reforming fluid according to claim 4, characterized in that: The heating temperature for removing the basic skeleton signal is greater than or equal to 600℃, and the heating time is greater than or equal to 30 minutes.

6. The test method for the minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: In S3, the conversion relationship between T2 relaxation time and aperture is established based on fractal geometry theory. The conversion relationship is as follows: in, Where is the throat radius, For nuclear magnetic resonance relaxation time, This is the proportionality coefficient. It is the fractal control index.

7. The test method for minimum pore throat movement of oil and gas reforming fluid according to claim 1, characterized in that: When the nuclear magnetic resonance spectrum exhibits multiple peaks or its fractal dimension differs significantly across different scale segments, a piecewise function is used to determine the transformation parameters for each scale segment. The piecewise function is as follows: in, Where is the throat radius, For nuclear magnetic resonance relaxation time, The ratio of adsorbed states is used to control the pore size transition scale of the nanopore throat. The free-state region scaling factor controls the pore size conversion scale of microcracks or channel sections. This is the fractal control index for the first pore region. This represents the fractal control index for the second pore region. This represents the relaxation time corresponding to the dividing point.

8. The test method for minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: In S4, the formation pressure applied to the reactor is 25MPa-60MPa, the set temperature is 200℃-450℃, and the constant temperature reaction time is 1 hour.

9. The test method for the minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: In S4, the centrifuge speed is determined based on the target driving pressure gradient.

10. The test method for the minimum active pore throat of oil and gas reforming fluid according to claim 1, characterized in that: In S5, the T2 cutoff value is the T2 value at which the signal in the T2 spectrum begins to decrease significantly after centrifugation.

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