CN107271346A - The measuring method of oil-containing tight sand pore-size distribution feature - Google Patents

Abstract

The invention provides a kind of measuring method of oil-containing tight sand pore-size distribution feature, belong to geology field, more particularly to tight sand field, probe liquid is used as using octamethylcy-clotetrasiloxane, oil-containing tight sand nanoscale hole completely can be quantitatively portrayed, the accuracy of oil-containing tight sand pore-size distribution numerical representation method is improved.The measuring method of the oil-containing tight sand pore-size distribution feature, comprises the following steps：Oil-containing tight sand sample is pre-processed；Using nuclear magnetic resonance freeze-thaw method test oil-containing tight sand as former state；To oil-containing tight sand former state saturation octamethylcy-clotetrasiloxane, saturated sample is tested using nuclear magnetic resonance freeze-thaw method；Data by above-mentioned oil-containing tight sand as former state with oil-containing tight sand saturated sample calculate the pore-size distribution of oil-containing tight sand.

Description

Measuring method of pore size distribution characteristics of oil-bearing tight sandstone

technical field

The invention relates to the field of geology, in particular to the field of tight sandstone, and in particular to a method for measuring the pore size distribution characteristics of oil-bearing tight sandstone.

Background technique

In recent years, with the continuous in-depth development of oil and gas exploration and development, the focus of oil and gas resources research at home and abroad has gradually shifted from shallow layers to deep layers, from conventional oil and gas reservoirs to unconventional oil and gas reservoirs, tight gas, shale gas, coalbed methane, tight oil, etc. Unconventional oil and gas have shown great potential under the current economic and technological conditions. China's conventional oil and gas resources are relatively poor, but unconventional oil and gas resources are abundant, especially tight oil and gas development and utilization potential is huge. Therefore, tight sandstone oil and gas are of great significance to our country. The rapid development of tight sandstone oil and gas exploration and development has broken through the lower limit of physical properties of conventional reservoirs in the traditional sense, and it has been discovered that nanopores in tight sandstone can also store rich oil and gas resources. Therefore, the research on the nano-pore structure of tight sandstone is very important for the exploration and development of tight oil and gas.

The pores of conventional reservoirs are generally on the millimeter-micron scale, while the pores of tight sandstone are mainly nano-scale pores. The physical properties of nanoscale pores are obviously different from pores above micron scale, which makes the characterization techniques and methods of conventional reservoir pores less applicable to unconventional reservoirs. There are many technical means to characterize the nanopore characteristics of tight sandstone reservoirs, including mercury porosimetry, gas isothermal adsorption, and nuclear magnetic resonance T ₂ spectrum and other technical methods. Among them, mercury porosimetry and gas adsorption method are the most widely used. However, there are still many limitations in the characterization of tight sandstone by mercury porosimetry and gas adsorption. The Washburn formula used by mercury intrusion porosimetry is more accurate in the analysis of pores larger than 50nm, but there is a large error in the analysis of pores smaller than 50nm. At the same time, when the mercury porosimetry is used to measure nano-scale pores, the excessive pressure required may damage the pores of tight sandstone. The characterization of gas adsorption for material pore size depends on computational models. For the same sample, using different calculation models, the obtained pore size distribution characteristics are quite different. At the same time, the gas adsorption test takes a long time, and the pores in the range of 0.4-100nm are mainly accurately characterized. None of these methods can completely characterize the nanoscale pore structure characteristics of tight sandstone. Therefore, how to accurately and quantitatively analyze the nanoscale pores of tight sandstone has become a difficult point in the evaluation of tight sandstone reservoirs.

There are two mature methods for measuring the pore size distribution characteristics of oil-bearing tight sandstone. The first method uses organic reagents to wash off the residual oil in tight sandstone, and then uses mercury porosimetry to measure. The problem with this method is that on the one hand The use of simple organic reagents cannot thoroughly clean the residual oil and gas in the semi-open pores and some open pores, so that the mercury porosimetry will lead to small test results; Excessive mercury injection pressure will change part of the pore structure, thus making the test results deviate from the true value. The second method is to use organic solvents to extract the residual oil in tight sandstone, and then use gas adsorption method to measure it. This method also has limitations similar to the first method. The nanopore size distribution of oil-bearing tight sandstone cannot be completely measured. These two methods have certain defects and application limitations, and both of them will lead to a smaller pore size content determined.

Contents of the invention

The purpose of the present invention is to provide a method for measuring the pore size distribution characteristics of oil-bearing tight sandstone, using octamethylcyclotetrasiloxane as a probe liquid, which can completely and quantitatively describe the nano-scale pores of oil-bearing tight sandstone, and improve the pore size distribution value of oil-bearing tight sandstone Accuracy of representation.

The invention provides a method for measuring the pore size distribution characteristics of oil-bearing tight sandstone, comprising the following steps:

Pretreatment of oil-bearing tight sandstone samples; use nuclear magnetic resonance freeze-thaw method to test the original oil-bearing tight sandstone; for oil-bearing tight sandstone original saturated octamethylcyclotetrasiloxane, use nuclear magnetic resonance freeze-thaw method to test saturated samples; through the above oil-bearing tight sandstone The pore size distribution of the oil tight sandstone was calculated from the data of the original sandstone and the saturated sample of the oil tight sandstone.

As a preferred technical solution, the step of pretreating the oil-bearing tight sandstone sample includes: mechanically pulverizing the oil-bearing tight sandstone sample, taking a sample of 20-35 mesh, drying, weighing, recording the mass M, and loading the sample into Chromatography vials.

As a more preferred technical solution, the mechanical pulverization is pulverization using an agate mortar, and the drying is drying in a vacuum box.

As a preferred technical solution, the steps of using NMR freeze-thaw method to test the original sample of oil-bearing tight sandstone include: using a sample with strong NMR signal to determine the center frequency of the permanent magnet, correcting the frequency of the radio frequency signal, and determining the radio frequency pulse width; Test alcohol, determine the temperature correction coefficient λ of the NMR signal intensity; determine the relationship between the NMR signal intensity and the content of octamethylcyclotetrasiloxane; determine the NMR experimental parameters of oil-bearing tight sandstone, set the temperature plan, Determination of oil-bearing tight sandstone samples by fusion method.

As a more preferred technical scheme, utilize nuclear magnetic resonance freeze-thaw method to test alcohol, determine the temperature correction coefficient λ of nuclear magnetic resonance signal intensity to be the signal intensity of test alcohol standard sample at different temperatures in the range of -30 ℃ ~ 20 ℃, according to the formula (1 ), calculate λ, the formula (1) is

In formula (1), SI is the NMR signal intensity, T is the temperature, α and β are the resistivity parameters, and λ is the temperature correction coefficient of the NMR signal intensity.

As a preferred technical scheme, the step of saturating the oil-bearing tight sandstone with octamethylcyclotetrasiloxane as it is is to use a vacuum saturation device to process, place the sample to be tested in a vacuum box, and vacuumize it for 12 hours; Add octamethylcyclotetrasiloxane to the original chromatographic bottle of oily tight sandstone, and equilibrate for 6 hours; centrifuge the chromatographic bottle for 2 hours

As a preferred technical solution, the same experimental parameters and the same temperature plan as the test sample are set when using the NMR freeze-thaw method to test the saturated sample.

As a preferred technical solution, the specific steps of calculating the pore size distribution of the oil-bearing tight sandstone include:

Use the data of each temperature point of the saturated sample to subtract the data of the corresponding temperature point after the original correction; the NMR signal intensity is corrected by using the NMR signal intensity temperature correction coefficient λ; use the corrected data of each temperature point of the saturated sample Subtract the data corresponding to the temperature point after the original correction; use the relationship between the nuclear magnetic resonance signal intensity and the content of octamethylcyclotetrasiloxane to convert the signal intensity into the liquid volume of octamethylcyclotetrasiloxane; The Booth-Thomas equation converts the temperature into the pore size to obtain the relationship between the pore volume and the pore size; according to the relationship between the pore volume and the pore size, the differential pore size distribution curve and the logarithmic differential pore size distribution curve of the sample are calculated and drawn.

As a more preferred technical solution, the calculation formulas of the differential pore size distribution and the logarithmic differential pore size distribution are:

In formulas (2)-(3), V is the pore volume; D is the pore diameter; T is the temperature; K _GT is the Gibbs-Thomas constant, a constant related to the thermodynamic properties of the probe liquid.

Compared with prior art, the beneficial effect of the present invention is:

1, the measuring method of the present invention adopts nuclear magnetic resonance freeze-thaw method to have following advantage:

① The theoretical basis of NMR freeze-thaw method is Gibbs-Thomson equation, which can directly reveal the relationship between melting point and pore volume, and the complex pore structure of oil-bearing tight sandstone has little influence on it;

②The information of the pore size distribution curve obtained by the NMR freeze-thaw method is richer and more delicate; compared with the conventional NMR T2 method, the NMR freeze-thaw method can accurately detect the nanopore size of oil-bearing tight sandstone, and the effective pore size range that can be tested is Up to 4-1500nm;

③ The nuclear magnetic resonance freeze-thaw method not only has unique technical advantages over the mercury intrusion method in the quantitative identification of "full pores" in tight sandstone, but also has the advantages of not polluting the sample, not destroying the sample structure, and the test is convenient and fast;

2. The measurement method of the present invention adopts octamethylcyclotetrasiloxane as the NMR probe liquid, which has amphiphilicity, which is conducive to entering the pores of organic matter and the pores of inorganic minerals, and can dissolve the residues in the pores. Organic matter such as oil and asphalt can better saturate pores; it is beneficial to improve the experimental accuracy of NMR freeze-thaw method; it will not frostbite the sample to be tested during the test, and will not change the original pore structure of the sample; compared with commonly used The probe liquid water and cyclohexane are more conducive to testing for oil-bearing tight sandstone.

Description of drawings

Fig. 1 is the schematic flow sheet of measurement method of the present invention;

Figure 2a. The relationship between temperature and signal intensity; b. Relationship diagram with -SI _K T _K ;

Fig. 3 is a linear relationship diagram between standard sample quality and signal strength;

Fig. 4 is the original nuclear magnetic resonance signal intensity and the relationship diagram between the signal intensity and temperature after correction;

Fig. 5 is a graph showing the relationship between cumulative pore volume and pore diameter of oil-bearing tight sandstone samples;

Fig. 6 is the pore size distribution curve of oil-bearing tight sandstone samples.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The embodiment of the present invention provides a method for measuring the pore size distribution characteristics of oil-bearing tight sandstone, referring to Fig. 1, Fig. 1 is a schematic flow chart of the measuring method of the present invention, the method comprises the following steps:

S101. Pretreatment of oil-bearing tight sandstone samples;

S102, using nuclear magnetic resonance freeze-thaw method to test the original sample of oil-bearing tight sandstone;

S103. For oily tight sandstone saturated with octamethylcyclotetrasiloxane as it is, the saturated sample is tested by nuclear magnetic resonance freeze-thaw method;

S104. Calculate the pore size distribution of the oil-bearing tight sandstone based on the above data of the oil-bearing tight sandstone original sample and the oil-bearing tight sandstone saturated sample.

Specifically, before the actual test, several samples are selected from the oil-bearing tight sandstone reservoir, and the sample that best represents the physical properties of the oil-bearing tight sandstone reservoir is determined from these core samples as the optimal sample, so that the heterogeneity of the oil-bearing tight sandstone can be avoided. Due to the qualitative nature, the test results cannot reflect the real reservoir physical properties.

As a preferred embodiment, in step S101, the step of pretreating the oil-bearing tight sandstone sample includes: mechanically pulverizing the oil-bearing tight sandstone sample, taking a sample of 20-35 mesh and drying it, weighing it with an analytical balance, and recording After mass M, the sample is loaded into the chromatographic vial.

In this embodiment, when the oil-bearing tight sandstone sample to be tested is mechanically crushed, it is preferable to use an agate mortar, and metal grinding bodies such as copper bowls and stainless steel bowls cannot be used to avoid the influence of metal on the test results of the sample to be tested. After the sample is pulverized, use a sieve for sorting, and select a 20-35 mesh sample to be tested. Generally speaking, the size of the sample particles is determined according to the mineral composition of the sample to be tested and the cementation degree of the tight sandstone. In the embodiment of the present invention, a sample of 20-35 mesh is used. If the sample is too large, it is not conducive to the later saturation of the probe liquid, which will affect the test results; if the sample particles are too small, they will accumulate a large number of pores between micron-nano particles, which will also affect the test results.

In this embodiment, for the drying process, it is preferable to place the selected samples in a vacuum box, set the temperature at 100° C., and dry them for 24 hours. If it is not a vacuum environment, some minerals may be oxidized and other phenomena may occur, thereby changing the original sample. The dried sample is weighed with an analytical balance, and a sample of about 0.5-1.5 g can be selected. The specific mass and volume can be adjusted according to the size of the chromatographic plane, and the mass M of the test sample can be recorded.

In this embodiment, the weighed sample to be tested is packed into a chromatographic bottle to prepare for the next test. Preferably, the inner diameter of the NMR instrument coil is 10mm, so a 2.5ml glass chromatographic bottle is used to hold the sample, but it can be understood What's more, depending on the instrument used, different sizes or materials of chromatographic vials can be used.

As a preferred embodiment, in step S102, the step of using nuclear magnetic resonance freeze-thaw method to test the original sample of oil-bearing tight sandstone includes: using a sample with a strong nuclear magnetic signal to determine the center frequency of the permanent magnet, correcting the frequency of the radio frequency signal, and determining the pulse width of the radio frequency; Test alcohol by NMR freeze-thaw method, determine the temperature correction coefficient λ of NMR signal intensity; determine the relationship between NMR signal intensity and octamethylcyclotetrasiloxane content; determine the NMR experimental parameters of oil-bearing tight sandstone, and set the temperature plan , Determination of oil-bearing tight sandstone samples by NMR freeze-thaw method.

In this embodiment, the magnet used in the nuclear magnetic resonance equipment is a permanent magnet with a natural magnetic field strength B ₀ , which corresponds to a natural frequency of hydrogen nuclei according to ω=γB ₀ . Only when the radio frequency pulse frequency is the same as the natural frequency of the permanent magnet, the sample placed in the magnet will undergo nuclear magnetic resonance. The natural frequency is called the resonance frequency, also known as the center frequency. Permanent magnets are sensitive to changes in the external environment such as temperature, and the natural frequency of the magnet may drift slightly, so it is necessary to adjust the RF pulse frequency to make it consistent with the current natural frequency of the magnet, that is, to find the center frequency, which needs to be adjusted before performing experimental tests. The invention uses samples with strong nuclear magnetic signals such as vegetable oil to determine the center frequency of the permanent magnet and correct the frequency of the radio frequency signal.

In addition, to obtain NMR signals is inseparable from radio frequency pulse excitation, because the size of the radio frequency coil and the power of the radio frequency power amplifier are different, so the pulse energy required to excite the sample is also different. The pulse energy is determined by the pulse amplitude and pulse width. Therefore, changing the hard pulse width is essentially changing the hard pulse energy. The more commonly used pulse sequences are 90-degree hard pulses and 180-degree hard pulses. Similarly, the NMR instrument can be used to test substances with strong signals such as vegetable oil, and the radio frequency pulse width can be determined.

The NMR signal is very sensitive to temperature changes, and the signal intensity must be corrected before converting the NMR signal to the liquid volume. The impact on the signal strength is mainly manifested in two aspects: the change of Zeeman level particle number distribution with temperature and the change of quality factor of probe coil with temperature. Considering the influence of temperature on the particle occupancy number distribution and the quality factor of the probe coil, the formula for converting the signal intensity at a certain temperature into the standard temperature signal intensity is:

In formula (1), SI is the NMR signal intensity, T is the temperature, α and β are the resistivity parameters, and λ is the temperature correction coefficient of the NMR signal intensity, which is measured before the experiment.

The temperature range of the test in the present invention is -30°C to 20°C, and the liquid standard sample with a low freezing point is used for measurement. The present invention uses alcohol to test the signal strength of the standard sample at different temperatures in the range of -30°C to 20°C. . Thus, according to formula (1), λ can be calculated.

The NMR signal intensity SI is proportional to the volume V of the probe liquid. The NMR freeze-thaw method was used to measure the probe content in the sample at different temperatures, that is, the content of octamethylcyclotetrasiloxane. Therefore, the standard sample should be used to calibrate the relationship between the content of octamethylcyclotetrasiloxane and the NMR signal. When testing the sample, the NMR signal intensity at each temperature point can be converted into the content of octamethylcyclotetrasiloxane through the fitted linear equation.

The NMR parameter setting is the prerequisite for the experiment. If the parameter setting is good, the experimental result will be close to the actual situation. If the parameter setting is poor, the experimental result may deviate from the original nature of the measured sample, and even the experimental result cannot be obtained. Therefore, it is necessary to determine the optimal parameters of the NMR experiment of oil-bearing tight sandstone. After determining the parameters, set the temperature plan, and use the NMR freeze-thaw method to measure the original oil-bearing tight sandstone.

As a preferred embodiment, in step S103, the step of saturating the oil-bearing tight sandstone with octamethylcyclotetrasiloxane as it is is to use a vacuum saturation device to process, place the sample to be tested in a vacuum box, and vacuumize it for 12 hours; Add octamethylcyclotetrasiloxane to the chromatographic bottle in which the oil-bearing tight sandstone sample is placed after vacuuming, and equilibrate for 6 hours; centrifuge the chromatographic bottle for 2 hours.

In this embodiment, the oil-bearing tight sandstone is treated with a vacuum saturation device, which is simple and convenient, and the operation is convenient. The specific steps are preferably as follows: place the sample to be tested in a vacuum box and vacuumize it for 12 hours; Add octamethylcyclotetrasiloxane liquid into the 2.5ml chromatographic bottle of the sample, and equilibrate for 6 hours, so that the oil-bearing tight sandstone can be fully saturated with octamethylcyclotetrasiloxane as it is. As a preferred embodiment, the centrifugation step is to use a centrifuge to centrifuge the 2.5ml chromatographic bottle at a speed of 5000r/min for 2h to ensure sufficient centrifugation. However, it can be understood that the above vacuuming, balancing and centrifuging time can be routinely adjusted according to the needs of actual experiments.

As a preferred embodiment, the same experimental parameters and the same temperature plan as the test sample are set when using the nuclear magnetic resonance freeze-thaw method to test the saturated sample. In this example, the data obtained under the same experimental parameters and the same temperature plan are more rigorous and usable for subsequent analysis.

As a preferred embodiment, in step S104, the specific steps of calculating and drawing the original differential pore size distribution curve and logarithmic differential pore size distribution curve of the oil-bearing tight sandstone include:

Use the data of each temperature point of the saturated sample to subtract the number of the corresponding temperature point after the original correction

According to the data; the nuclear magnetic resonance signal strength is corrected by the temperature correction coefficient λ of the nuclear magnetic resonance signal strength; the corrected data of each temperature point of the saturated sample is used to subtract the data of the corresponding temperature point after the original correction; the difference between the nuclear magnetic resonance signal strength and eight The relationship between the content of methylcyclotetrasiloxane, the signal intensity is converted into the liquid volume of octamethylcyclotetrasiloxane; the temperature is converted into the pore size by using the Gibbs-Thomas equation, and the relationship between the pore volume and the pore diameter is obtained ; Calculate the differential pore size distribution curve and the logarithmic differential pore size distribution curve of the sample according to the relationship between the pore volume and the pore size, so as to measure the pore size distribution characteristics of the oil-bearing tight sandstone.

In this embodiment, the direct data of the experiment is the change of the signal intensity of the sample to the temperature. First, the data of each temperature point of the saturated sample is used to subtract the data of the corresponding temperature point after the original correction; The intensity temperature correction coefficient λ is used for correction; the signal intensity is converted into the liquid volume of octamethylcyclotetrasiloxane by using the relationship between the nuclear magnetic resonance signal intensity and the content of octamethylcyclotetrasiloxane; using Gibbs The Thomas equation converts the temperature into the pore size, thereby obtaining the relationship between the cumulative pore volume and the pore size; according to the relationship between the pore volume and the pore size, calculate and draw the differential pore size distribution curve and the logarithmic differential pore size distribution curve of the sample,

Among them, the calculation method of the differential pore size distribution P _d (D) of the sample is

The logarithmic differential pore size distribution P _log (D) of the sample is calculated as

In formulas (2)-(3), V is the pore volume; D is the pore diameter; T is the temperature; K _GT is the Gibbs-Thomas constant, a constant related to the thermodynamic properties of the probe liquid.

In order to more clearly and in detail describe the method for measuring the pore size distribution characteristics of oil-bearing tight sandstone provided by the embodiments of the present invention, the following will be described in conjunction with specific examples.

A sample of oil-bearing tight sandstone is selected.

The oil-bearing tight sandstone samples were mechanically pulverized in an agate mortar, dried in a vacuum box with 20-35 mesh samples, weighed with an analytical balance, and the recorded mass M was 0.607g; the weighed sample to be tested was loaded into 2.5 ml chromatographic vials.

The steps of testing the original sample of oil-bearing tight sandstone by nuclear magnetic resonance freeze-thaw method include: using a sample with a strong nuclear magnetic signal to determine the center frequency of the permanent magnet, correcting the frequency of the radio frequency signal, and determining the pulse width of the radio frequency; Signal intensity temperature correction coefficient λ; Determine the relationship between NMR signal intensity and octamethylcyclotetrasiloxane content; Determine the NMR experimental parameters of oil-bearing tight sandstone, set the temperature plan, and use NMR freeze-thaw method to determine oil-bearing tight sandstone as is.

Use vegetable oil to determine the center frequency of the permanent magnet, correct the frequency of the radio frequency signal, and use vegetable oil to determine the pulse width of the radio frequency, P1 is 3.2μs, P2 is 6.6μs;

Use the NMR freeze-thaw method to test alcohol, determine the temperature correction coefficient λ of the NMR signal intensity, set it from 253.15K to 293.15K, and test a CPMG sequence every 10K to obtain the relationship between signal intensity and temperature, see Figure 2a , combined with SI _K The relationship with -S _IK T _K can be calculated as 507.38 through linear fitting, see Figure 2b;

Use the standard sample to calibrate the relationship between the octamethylcyclotetrasiloxane content and the nuclear magnetic signal, see Figure 3, when testing the sample, the CPMG signal intensity at each temperature point can be converted into eight Methylcyclotetrasiloxane content.

When octamethylcyclotetrasiloxane is used as the probe liquid to measure the pore size distribution of oil-bearing tight sandstone by NMR freeze-thaw method, the CPMG sequence parameters are as follows: waiting time Tw is 2500ms, echo time TE is 1ms, and the number of echoes is 2000. The temperature plan is 250.55-280.55K with a temperature interval of 2K; 280.55-285.55K with a temperature interval of 1K; 285.55-288.55K with a temperature interval of 0.5K; 288.55-289.55K with a temperature interval of 0.2K; Data were collected using CPMG sequences after a waiting time of 20 minutes at each temperature point. The oil-bearing tight sandstone samples were then tested by NMR freeze-thaw method.

Using a vacuum saturation device, place the sample to be tested in a vacuum box and vacuumize for 12 hours; add octamethylcyclotetrasiloxane to the chromatographic bottle containing the oil-containing dense sandstone sample after vacuuming, and balance for 6 hours; centrifuge the chromatographic bottle 2h. The saturated samples were tested using the NMR freeze-thaw method, setting the same experimental parameters and the same temperature schedule as the original samples.

The pore size distribution of the oil-bearing tight sandstone is calculated from the above data of the oil-bearing tight sandstone original sample and the oil-bearing tight sandstone saturated sample:

Use the data of each temperature point of the saturated sample to subtract the number of the corresponding temperature point after the original correction

According to; the nuclear magnetic resonance signal intensity, using the temperature correction coefficient λ of the nuclear magnetic resonance signal intensity, using the above formula (1) for temperature correction. The NMR signal intensities at all temperature points were corrected to 290.15K, and the corrected data are shown in Figure 4. Then perform subsequent calculations. It can be found that the lower the temperature, the more the deviation between the original signal strength and the corrected signal strength.

Using the relationship between the NMR signal intensity and the content of octamethylcyclotetrasiloxane, the signal intensity is converted into the liquid volume of octamethylcyclotetrasiloxane, and the temperature is converted into the pore size using the Gibbs-Thomas equation, thereby The relationship between cumulative pore volume and pore diameter is obtained, as shown in Figure 5. From the relationship between cumulative pore volume and pore diameter, according to formulas (2) and (3), the logarithmic differential pore size distribution curve of the sample can be calculated and drawn, as shown in Figure 6. It can be seen from Fig. 6 that the pores of oil-bearing tight sandstone are mainly nano-scale pores, and the nano-scale pores of tight sandstone are rich in a large amount of crude oil. Therefore, the measurement method of the present invention can more accurately measure the pore size distribution characteristics of the oil-bearing tight sandstone, and is more conducive to the oil and gas research of the tight sandstone.

Claims (9)

1. the measuring method of oil-containing tight sand pore-size distribution feature, it is characterised in that comprise the following steps：

Oil-containing tight sand sample is pre-processed；Using nuclear magnetic resonance freeze-thaw method test oil-containing tight sand as former state；To containing Oily tight sand former state saturation octamethylcy-clotetrasiloxane, saturated sample is tested using nuclear magnetic resonance freeze-thaw method；Contained by above-mentioned Oily tight sand calculates the pore-size distribution of oil-containing tight sand with the data of oil-containing tight sand saturated sample as former state.

2. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 1, it is characterised in that described right The step of oil-containing tight sand sample is pre-processed includes：Mechanical crushing is carried out to oil-containing tight sand sample, 20-35 was taken Purpose sample is dried, and is weighed, and sample is loaded into chromatogram bottle after record mass M.

3. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 2, it is characterised in that the machine Tool is crushed to crush using agate mortar, and the drying is drying in vacuum tank.

4. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 1, it is characterised in that utilize core The step of magnetic resonance freeze-thaw method tests oil-containing tight sand former state includes：Determined using the strong sample of nuclear magnetic signal in permanent magnet Frequency of heart, corrects radio frequency signal frequency, determines radio frequency pulsewidth；Alcohol is tested using nuclear magnetic resonance freeze-thaw method, nuclear magnetic resonance is determined Signal intensity temperature correction coefficient λ；Determine the relation of NMR signal intensity and octamethylcy-clotetrasiloxane content；It is determined that containing The nuclear magnetic resonance experiment parameter of oily tight sand, design temperature plan determines oil-containing tight sand using nuclear magnetic resonance freeze-thaw method As former state.

5. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 4, it is characterised in that utilize core Magnetic resonance freeze-thaw method tests alcohol, determines NMR signal strength temperature correction factor λ to test alcohol at -30 DEG C~20 DEG C In the range of under different temperatures standard specimen signal intensity, according to formula (1), calculate λ, the formula (1) is

<mrow> <msub> <mi>SI</mi> <mi>S</mi> </msub> <mo>=</mo> <msub> <mi>SI</mi> <mi>K</mi> </msub> <mfrac> <mrow> <msub> <mi>T</mi> <mi>K</mi> </msub> <mrow> <mo>(</mo> <mi>&amp;alpha;</mi> <mo>+</mo> <mi>&amp;beta;</mi> <mo>&amp;CenterDot;</mo> <msub> <mi>T</mi> <mi>K</mi> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>T</mi> <mi>S</mi> </msub> <mrow> <mo>(</mo> <mi>&amp;alpha;</mi> <mo>+</mo> <mi>&amp;beta;</mi> <mo>&amp;CenterDot;</mo> <msub> <mi>T</mi> <mi>S</mi> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>=</mo> <msub> <mi>SI</mi> <mi>K</mi> </msub> <mfrac> <mrow> <msub> <mi>T</mi> <mi>K</mi> </msub> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mo>+</mo> <msub> <mi>T</mi> <mi>K</mi> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>T</mi> <mi>S</mi> </msub> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mo>+</mo> <msub> <mi>T</mi> <mi>S</mi> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>,</mo> </mrow>

SI is NMR signal intensity in formula (1), and T is temperature, and α and β is resistance parameter, and λ is NMR signal intensity Temperature correction coefficient.

6. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 1, it is characterised in that to oil-containing The step of tight sand former state saturation octamethylcy-clotetrasiloxane, to be handled using vacuum saturation device, testing sample is put It is placed in vacuum tank, vacuumizes 12h；Prestox ring is added in the chromatogram bottle for vacuumizing rear oil-containing tight sand former state to being placed with Tetrasiloxane, balances 6h；Chromatogram bottle is centrifuged into 2h.

7. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 6, it is characterised in that utilize core Setting and test former state identical experiment parameter and identical temperature plan when magnetic resonance freeze-thaw method tests saturated sample.

8. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 1, it is characterised in that the meter Calculating the specific steps of the pore-size distribution of oil-containing tight sand includes：

The data of corresponding temperature point after correcting as former state are subtracted using the data of each temperature spot of saturated sample；By NMR signal Intensity, using NMR signal strength temperature correction factor λ, is modified；After each temperature spot amendment of saturated sample Data subtract as former state correct after corresponding temperature point data；Contained using NMR signal intensity and octamethylcy-clotetrasiloxane Relation between amount, signal intensity is converted into the liquid volume of octamethylcy-clotetrasiloxane；Utilize gibbs Thomas's equation By temperature conversion pore size, the correlation in pore volume and aperture is obtained；According to pore volume and the relation in aperture, calculate and paint The differential pore size distribution curve and logarithmic differentiation pore size distribution curve of sample preparation product.

9. the measuring method of oil-containing tight sand pore-size distribution feature according to claim 8, it is characterised in that described micro- The calculation formula of point pore-size distribution and logarithmic differentiation pore-size distribution is：

<mrow> <msub> <mi>P</mi> <mi>d</mi> </msub> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mi>V</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>D</mi> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mi>V</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>T</mi> </mrow> </mfrac> <mo>&amp;CenterDot;</mo> <mfrac> <mrow> <mi>d</mi> <mi>T</mi> </mrow> <mrow> <mi>d</mi> <mi>D</mi> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mi>V</mi> <mrow> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>T</mi> </mrow> </mfrac> <mo>&amp;CenterDot;</mo> <mfrac> <msub> <mi>K</mi> <mrow> <mi>G</mi> <mi>T</mi> </mrow> </msub> <msup> <mi>D</mi> <mn>2</mn> </msup> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>

<mrow> <msub> <mi>P</mi> <mi>log</mi> </msub> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mi>V</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>log</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>d</mi> <mi>V</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>D</mi> </mrow> </mfrac> <mo>&amp;CenterDot;</mo> <mfrac> <mrow> <mi>d</mi> <mi>D</mi> </mrow> <mrow> <mi>d</mi> <mi>log</mi> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>=</mo> <msub> <mi>P</mi> <mi>d</mi> </msub> <mrow> <mo>(</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>&amp;CenterDot;</mo> <mi>D</mi> <mo>&amp;CenterDot;</mo> <mi>l</mi> <mi>n</mi> <mrow> <mo>(</mo> <mn>10</mn> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> <mo>,</mo> </mrow>

V is pore volume in formula (2)-(3)；D is aperture；T is temperature；K_GTFor gibbs Thomas's constant.