Method for calculating shale movable oil saturation based on nuclear magnetic-centrifugal principle

Abstract

The present application relates to the technical field of reservoir evaluation in petroleum geological exploration and deposition reservoir, in particular to a method for calculating shale movable oil saturation based on nuclear magnetic-centrifugal principle, comprising: obtaining a sample after oil washing; based on real gas-oil ratio in the ground, using crude oil and natural gas to configure, obtaining configured crude oil; pressurizing and saturating the configured crude oil to obtain a saturated oil core sample; calculating the total pore volume V of the core under real underground temperature and pressure conditions; obtaining the total volume V1 of the saturated oil core sample under normal temperature and pressure, calculating the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions; calculating the ground movable fluid saturation S2, and finally calculating the real movable oil saturation S of the shale. Through the method, the gas-oil ratio under the geological real conditions is recovered, the crude oil viscosity is reduced, the real situation is closer, the experimental error is minimized, and the calculation result is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reservoir evaluation in petroleum geological exploration and deposition reservoir, in particular to a method for calculating shale movable oil saturation based on nuclear magnetic-centrifugal principle. BACKGROUND

[0002] The increasing demand for energy and the continuous consumption of conventional oil and gas resources make the contradiction between supply and demand of oil and gas increasingly prominent. Therefore, unconventional energy is increasingly valued by people, and shale oil is an important part of it. At present, shale oil has become a hot spot of unconventional exploration and development. Compared with conventional reservoirs, shale oil reservoirs are rich in organic matter, have diverse pore types, and have multi-scale distribution of pores and complex spatial structure. Therefore, exploration efforts have been strengthened at home and abroad. Shale oil is a typical unconventional resource, and its mobility is an important factor affecting whether the reservoir can be put into development and production. As an important part of oil and gas exploration, shale oil mobility evaluation is one of the necessary steps for shale oil exploration. The ultimate goal of shale oil exploration is to guide the large-scale development of soluble organic matter in shale series. Therefore, the mobility evaluation of shale oil is one of the key reference elements for determining the favorable shale oil enrichment section.

[0003] At present, research believes that shale oil mainly exists in three forms: free state, adsorbed state and dissolved state in shale series. Under the current technical conditions, the main part that can be exploited is free shale oil, and bound oil is difficult to have actual utilization value. Therefore, the quantitative evaluation of free shale oil (movable oil) saturation is the most core content in the study of shale oil. The commonly used methods for quantitative characterization of shale oil mobility currently include empirical method, multi-temperature stage pyrolysis, geochemical parameter method, adsorption-free oil model method, nuclear magnetic resonance-high speed centrifugation method, numerical simulation method, gas chromatography-mass spectrometry (GC-MS) technology.

[0004] Among them, the multi-temperature pyrolysis method, geochemical parameter method and gas chromatography-mass spectrometry (GC-MS) technology need a large amount of geochemical experimental data to draw the parameter trend chart, and then to quantitatively characterize the movable oil saturation of shale oil in different evolution stages. The required data volume is large and the cost is high, and the application effect is better in mature exploration areas. The adsorption-free oil model method, numerical simulation method and molecular dynamics simulation are all based on idealized state simulation, with large artificial factors and poor representativeness. The movable oil calculated by the empirical method is the theoretical value, and the oil saturation index is a shale oil mobility evaluation parameter proposed based on the exploration and development practice of North American marine shale oil. There are great differences in mineral composition and organic matter between the shale layer series in China and North America. Whether the limit of 100 mg / g of oil saturation index is applicable to the mobility evaluation of continental shale oil is still controversial. The multi-temperature pyrolysis method requires a small amount of sample (2 mg) for experiment, the powdered sample destroys the original structure of the rock, and it cannot simulate the real underground environment under high temperature and high pressure conditions, so it is difficult to judge the seepage performance of crude oil underground, and thus the movable conditions of crude oil cannot be determined.

[0005] Nuclear magnetic resonance technology is an important research means for calculating reservoir porosity and characterizing pore structure. The value of movable porosity can be obtained by nuclear magnetic measurement before and after core centrifugation, but it is less used in saturation research. Nuclear magnetic resonance technology is a kind of pore classification method based on the relationship between rock transverse relaxation time T2 and pore radius r, and according to the T2 spectrum distribution map. Based on the fluid relaxation characteristics, the pore size distribution law inside the rock can be analyzed, and the basic physical characteristics of the rock can be accurately measured. The principle is that when the oil (or water) containing sample is in a uniform static magnetic field, the hydrogen nucleus 1H in the fluid will be polarized by the magnetic field, and a magnetization vector will be formed macroscopically. At this time, if a radio frequency field of a certain frequency (Larmor frequency) is applied to the sample, nuclear magnetic resonance will be produced. After the radio frequency field is removed, an amplitude signal that decays with time in an exponential function can be received, which can be described by the transverse relaxation time T2. After high-speed centrifugation experiment, the crude oil remaining in the core after centrifugation is regarded as immovable oil, and the crude oil removed by high-speed centrifugation is regarded as movable oil. The value of movable porosity is obtained by nuclear magnetic measurement before and after core centrifugation. The method of testing movable oil saturation by combining nuclear magnetic and centrifugation experiments is economical, efficient and executable, and it is the best solution to shale movable oil saturation under current technical conditions. For example, in the Jimsar shale oil reservoir, the nuclear magnetic resonance results were measured by applying oil displacement water experiment of rock sample, three types of adsorbed water, adsorbed oil and free oil of shale oil were proposed, and the wettability characteristics of large pore oil-wet oil and small pore water-wet water and the oil occurrence mode were proposed. The cutoff value is determined by using nuclear magnetic experiment results to calculate the free oil saturation, and the application effect is good. However, this method saturates water or chemical reagents (such as MnCl2) in the core, which does not reduce the real situation underground, so there is a certain difference between the calculation results and the actual situation.

[0006] In the study of tight reservoirs such as shale, scholars have developed nuclear magnetic resonance-centrifugation method to study the mobility of crude oil, and the crude oil still existing in the core after high-speed centrifugation is regarded as immobile oil, and the crude oil centrifuged out is regarded as mobile oil, but in these studies, nuclear magnetic resonance is usually carried out under the condition of saturating the core with n-dodecane fluid, although it has a similar composition to oil, but it is not directly used with oil, and natural gas is not added, so it cannot determine the influence of gas-oil ratio on the flowability of oil. In addition, under the high temperature and high pressure environment in the underground, the viscosity and density of shale oil will change significantly, as shown in the accompanying drawings of the specification Figure 4 and the accompanying drawings of the specification Figure 5 It is found that the current experimental method cannot obtain a more real underground actual environment, and the results obtained have a large gap with the actual results in the underground. SUMMARY

[0007] To solve the above technical problems, the present application provides a method for calculating the movable oil saturation of shale based on the principle of nuclear magnetic resonance-centrifugation, which restores the gas-oil ratio closer to the real geological conditions, reduces the viscosity of crude oil, and is closer to the real situation, minimizes experimental errors, and makes the calculation results more accurate.

[0008] The present application is realized by adopting the following technical solutions:

[0009] A method for calculating the movable oil saturation of shale based on the principle of nuclear magnetic resonance-centrifugation, comprising the following steps:

[0010] Step 1. Obtain the original core sample, wash and dry the oil to obtain the washed oil sample; based on the real gas-oil ratio in the underground, use crude oil and natural gas to prepare a sample to obtain the prepared crude oil, the volume of the prepared crude oil is V0;

[0011] Step 2. Vacuumize the washed oil sample and pressurize to saturate the prepared crude oil to obtain the oil-saturated core sample;

[0012] Step 3. Take out the oil-saturated core sample, measure the volume V' of the remaining prepared crude oil, and calculate the total pore volume V of the core under the real underground temperature and pressure conditions:

[0013] V=V0-V';

[0014] Step 4. Perform nuclear magnetic resonance experiment on the oil-saturated core sample under room temperature conditions, and obtain the T2 relaxation time spectrum by inversion, obtain the total pore volume V1 of the oil-saturated core sample under normal temperature and pressure, compare the difference between the pore volume under room temperature conditions and the real underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

[0015] S1=(V-V1) / V;

[0016] Step five. The same oil-saturated core sample is subjected to high-speed centrifugation at different centrifugal speeds respectively, and nuclear magnetic resonance test is performed after each centrifugation to obtain the optimal centrifugal speed;

[0017] Step six. All the oil-saturated core samples are subjected to centrifugation at the optimal centrifugal speed selected in step five, and then nuclear magnetic resonance test is performed to obtain the total pore volume V2 of the core after centrifugation, which is compared with the total pore volume V1 of the oil-saturated core sample at normal temperature and pressure in step four to calculate the ground movable fluid saturation S2:

[0018] S2=(V1-V2) / V1;

[0019] Step seven. The real movable oil saturation S of the shale is calculated:

[0020] S=S1+S2.

[0021] The oil washing in step one specifically refers to washing oil by extraction with chloroform.

[0022] The oil-washed sample obtained in step one specifically refers to: drilling an original core sample, washing oil by extraction with chloroform, then drying the core sample in a vacuum drying oven at a temperature of 60℃ for 4 hours, sealing it with plastic wrap after cooling, and obtaining the oil-washed sample.

[0023] Washing oil by extraction with chloroform specifically refers to: wrapping the original core sample with filter paper, loading it into the sample chamber of an extractor, then adding chloroform to the extractor, extracting the original core sample at a temperature of 75-80℃, until the reflux liquid is colorless, then taking out the core sample and completely volatilizing the chloroform at room temperature.

[0024] The obtained configuration crude oil in step one specifically refers to: calculating the amount of crude oil and natural gas based on the real gas-oil ratio underground, and transporting them to a high-temperature and high-pressure sample preparation device, setting the corresponding temperature and pressure according to the real underground conditions, and keeping them constant for 1 hour to obtain the configuration crude oil.

[0025] Step two specifically refers to: vacuumizing the oil-washed sample for more than 12 hours, the pressure P during vacuumizing is <-0.098 MPa, the vacuum degree reaches 0.1 Pa, pressurizing and saturating the configuration crude oil, and keeping it for 12 hours to obtain the oil-saturated core sample.

[0026] The optimal centrifugal speed obtained in step five specifically refers to: if the porosity obtained by the previous nuclear magnetic resonance test is less than 5% of the porosity obtained by the subsequent nuclear magnetic resonance test, then the centrifugal speed corresponding to the previous nuclear magnetic resonance test is determined as the optimal centrifugal speed, and the corresponding centrifugal force is the optimal centrifugal force.

[0027] The step five specifically refers to: the oil-saturated core sample is centrifuged once at a centrifugal speed of 5000 r / min, one nuclear magnetic resonance experiment is carried out, the T2 relaxation time spectrum is obtained by inversion, and the porosity is obtained; then the oil-saturated core sample is centrifuged once at a centrifugal speed of 6000 r / min, one nuclear magnetic resonance experiment is carried out, the T2 relaxation time spectrum is obtained by inversion, and the porosity is obtained; and the like is sequentially carried out until the optimal centrifugal speed is obtained.

[0028] In the step five, the centrifugal time is 60 min each time.

[0029] Compared with the prior art, the beneficial effects of the present application are shown in:

[0030] 1. The calculation method of the present application can obtain more accurate movable oil saturation calculation values after fully considering the influence of similar solubility and gas-driven crude oil, reduces experimental errors, and is more consistent with actual geological conditions. Specifically, compared with the old method, the movable oil saturation calculated by the present method is 3-4 percentage points higher.

[0031] 2. The present application uses a high-temperature and high-pressure sample preparation device to inject natural gas into crude oil with high viscosity in proportion, restores the gas-oil ratio close to the real geological conditions, reduces the viscosity of the crude oil, and is closer to the real situation, thereby minimizing experimental errors. In the process of directly filling methane gas into the core sample, the gas-oil ratio is directly changed, which leads to inaccurate calculation and cannot reflect the real mobility of underground crude oil.

[0032] 3. The present application first performs oil washing operation on the original core sample, which can remove the original hydrocarbons in the original core sample, so that the core can be saturated with oil, which is closer to the real gas-oil ratio underground. Trichloromethane is used for oil washing, and trichloromethane is an anionic surfactant with strong solubility and easy evaporation, and is easy to remove.

[0033] 4. The oil saturation of the core is different under different centrifugal speeds, and the oil saturation of the core gradually decreases when the centrifugal speed gradually increases. The present application calculates the optimal centrifugal speed, so that the movable fluid saturation measured is closer to the real movable oil saturation. BRIEF DESCRIPTION OF DRAWINGS

[0034] The present application will be further described in detail below in combination with the drawings and specific embodiments of the present application, in which:

[0035] Figure 1 The flowchart is a flowchart of the present application;

[0036] Figure 2 The movable oil saturation calculated by different methods in the present application is shown in the contrast diagram;

[0037] Figure 3The T2 relaxation time spectrum of the oil-saturated core sample is obtained by inversion calculation under different centrifugal speeds in the present application.

[0038] Figure 4 The density of the ground shale oil changes with temperature.

[0039] Figure 5 The viscosity of the ground shale oil changes with temperature. DETAILED DESCRIPTION

[0040] Embodiment 1

[0041] As a basic embodiment of the present application, the present application comprises a method for calculating the shale movable oil saturation based on the nuclear magnetic-centrifugal principle, comprising the following steps:

[0042] Step one. Obtain the original core sample, wash the oil and dry to obtain the oil-washed sample; based on the real gas-oil ratio underground, use crude oil and natural gas to configure the sample to obtain the configured crude oil, and the volume of the configured crude oil is V0.

[0043] Step two. Vacuumize the oil-washed sample and pressurize to saturate the configured crude oil to obtain the oil-saturated core sample.

[0044] Step three. Take out the oil-saturated core sample, measure the volume V' of the remaining configured crude oil, and calculate the total pore volume V of the core under the real underground temperature and pressure conditions:

[0045] V = V0-V'.

[0046] Step four. Perform nuclear magnetic resonance experiment on the oil-saturated core sample under room temperature conditions, and obtain the T2 relaxation time spectrum by inversion to obtain the total pore volume V1 of the oil-saturated core sample under normal temperature and pressure, compare the difference in pore volume between the room temperature conditions and the real underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under the room temperature conditions:

[0047] S1 = (V-V1) / V.

[0048] Step five. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal speed.

[0049] Step six. Use the optimal centrifugal speed selected in step five to centrifuge all the oil-saturated core samples, and then perform nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation, and compare it with the total pore volume V1 of the oil-saturated core sample under normal temperature and pressure in step four to calculate the ground movable fluid saturation S2:

[0050] S2 = (V1-V2) / V1.

[0051] Step seven. Calculate the true movable oil saturation S of the shale:

[0052] S = S1 + S2.

[0053] Example 2

[0054] As a preferred embodiment of the present application, the present application comprises a method for calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation, comprising the following steps:

[0055] Step one. Obtain the original core sample, wash the oil by extracting with chloroform and dry to obtain the oil-washed sample. Calculate the amount of crude oil and natural gas based on the true gas-oil ratio in the underground and transport them to a high-temperature high-pressure sample mixer, set the corresponding temperature and pressure according to the true underground conditions, and maintain for 1 h to obtain the configured crude oil. The volume of the configured crude oil is V0.

[0056] Step two. Vacuumize the oil-washed sample and pressurize to saturate the configured crude oil to obtain the oil-saturated core sample.

[0057] Step three. Take out the oil-saturated core sample, measure the volume V' of the remaining configured crude oil, and calculate the total pore volume V of the core under the true underground temperature and pressure conditions:

[0058] V = V0 - V'.

[0059] Step four. Perform nuclear magnetic resonance experiment on the oil-saturated core sample under room temperature conditions, and obtain the T2 relaxation time spectrum by inversion to obtain the total pore volume V1 of the oil-saturated core sample under normal temperature and normal pressure. Compare the difference in pore volume between room temperature conditions and true underground temperature and pressure conditions to calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

[0060] S1 = (V - V1) / V.

[0061] Step five. Perform high-speed centrifugation on the same oil-saturated core sample using different centrifugal speeds, and perform nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal speed. Specifically, if the porosity obtained by the previous nuclear magnetic resonance test is less than 5% of the porosity obtained by the subsequent nuclear magnetic resonance test, then the centrifugal speed corresponding to the previous nuclear magnetic resonance test is determined as the optimal centrifugal speed, and the corresponding centrifugal force is the optimal centrifugal force.

[0062] Step six. Perform centrifugation on all oil-saturated core samples using the optimal centrifugal speed selected in step five, and then perform nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total pore volume V1 of the oil-saturated core sample under normal temperature and pressure in step four to calculate the surface movable fluid saturation S2:

[0063] S2 = (V1-V2) / V1.

[0064] Step seven. Calculate the real movable oil saturation S of the shale:

[0065] S = S1 + S2.

[0066] Example 3

[0067] As another preferred embodiment of the present application, the present application comprises a method for calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation, comprising the following steps:

[0068] Step one. Obtain the original core sample, wash the oil and dry to obtain the oil-washed sample. Specifically, first wrap the original core sample, i.e. the plunger sample, with filter paper and then put it into the sample chamber of the Soxhlet extractor, then add chloroform to the extractor, and extract the original core sample at a temperature of 75-80°C until the reflux liquid is colorless, then take out the core sample and completely volatilize the chloroform at room temperature.

[0069] Based on the real gas-oil ratio underground, use crude oil and natural gas to make a sample, and obtain the configuration crude oil, the volume of which is V0. Specifically, use a CP-2 type high-temperature and high-pressure sample preparation instrument to inject a certain volume of crude oil into the oil storage cylinder and a certain volume of natural gas into the gas storage cylinder, calculate the amount of crude oil and natural gas based on the real gas-oil ratio underground, use a constant-speed and constant-pressure metering pump to deliver the calculated amount of crude oil and natural gas to the high-temperature and high-pressure sample preparation instrument, and set the temperature and pressure according to the real underground conditions of the shale oil reservoir being studied, and keep them constant for 1 hour.

[0070] Step two. Vacuumize the oil-washed sample and pressurize to saturate the configuration crude oil to obtain the oil-saturated core sample. Specifically, vacuumize the oil-washed sample for more than 12 hours, the pressure during vacuumization is P<-0.098Mpa, and the vacuum degree reaches 0.1Pa. Connect the high-temperature and high-pressure sample preparation instrument and the core vacuumization and pressurization saturation experimental device to directly pressurize and saturate the configuration oil, and keep it for 12 hours to obtain the oil-saturated sample.

[0071] Step three. Take out the oil-saturated core sample, measure the volume V' of the remaining configuration crude oil, and calculate the total pore volume V of the core sample under the real underground temperature and pressure conditions:

[0072] V = V0-V'.

[0073] Step four. Perform nuclear magnetic resonance experiment on the oil-saturated core sample at room temperature, and obtain the T2 relaxation time spectrum by inversion, obtain the total pore volume V1 of the oil-saturated core sample at room temperature and pressure, compare the difference in pore volume between room temperature conditions and real underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

[0074] S1=(V-V1) / V.

[0075] Step 5. High-speed centrifuge the same oil-saturated core sample at different centrifugal speeds. Perform a nuclear magnetic resonance (NMR) test after each centrifugation to determine the optimal centrifugal speed. Specifically, the oil-saturated core sample is first centrifuged once at 5000 r / min, followed by a NMR test. The T2 relaxation time spectrum is then inverted to obtain the porosity. Next, the sample is centrifuged once at 6000 r / min, followed by a NMR test. The T2 relaxation time spectrum is then inverted to obtain the porosity. This process is repeated repeatedly. Each centrifugation can last for 60 minutes.

[0076] If the porosity obtained by the previous nuclear magnetic resonance test - the porosity obtained by the next nuclear magnetic resonance test) / the porosity data obtained by the previous nuclear magnetic resonance test × 100% is less than 5%, then the centrifugal speed corresponding to the previous nuclear magnetic resonance test is determined to be the optimal centrifugal speed, and the corresponding centrifugal force is determined to be the optimal centrifugal force.

[0077] Step 6. Centrifuge all oil-saturated core samples using the optimal centrifugal speed selected in Step 5, then perform nuclear magnetic resonance experiments to obtain the total pore volume V2 of the core after centrifugation. Compare this with the total pore volume V1 of the oil-saturated core sample at room temperature and pressure in Step 4 to calculate the surface movable fluid saturation S2:

[0078] S2 = (V1 - V2) / V1.

[0079] Step 7. Calculate the true movable oil saturation S of the shale:

[0080] S=S1+S2.

[0081] Example 4

[0082] As another embodiment of the present invention, refer to the attached Figure 1 The present invention includes a method for calculating the movable oil saturation of shale based on the nuclear magnetic-centrifugal principle, comprising the following steps:

[0083] Step 1. Drill a core sample to obtain an original core sample, extract the oil with chloroform, and then dry the core sample in a vacuum drying oven at 60°C for 4 hours. After cooling, seal it with plastic wrap.

[0084] Using a CP-2 high-temperature, high-pressure sample preparation instrument, a certain volume of crude oil and natural gas was injected into the instrument. The crude oil and natural gas quantities were calculated based on the actual underground gas-oil ratio. The calculated crude oil and natural gas quantities were then pumped into the high-temperature, high-pressure sample preparation instrument using a constant-speed, constant-pressure metering pump. The temperature and pressure were set according to the actual underground conditions of the shale oil reservoir being studied and maintained constant for 1 hour to obtain the prepared crude oil. The volume of the prepared crude oil was designated as V0.

[0085] Step two. The oil-washed sample is vacuumed for more than 12 hours, the pressure P is less than -0.098 MPa, the vacuum degree reaches 0.1 Pa, and the core sample is saturated with crude oil by pressurization for 12 hours to obtain a saturated oil core sample.

[0086] Step three. The saturated oil core sample is taken out, the volume V' of the remaining configured crude oil is measured, and the volume difference V0-V' of the crude oil in the sample preparation barrel before and after saturation is the total pore volume V of the core under the real underground temperature and pressure conditions, which is also the total pore volume V of the pressure-maintained core.

[0087] Step four. The saturated oil core sample is subjected to nuclear magnetic resonance experiment at room temperature, and the T2 relaxation time spectrum is obtained by inversion, and the total pore volume V1 of the saturated oil core sample at room temperature and normal pressure is obtained, that is, the total pore volume V1 of the core at normal pressure. The difference between the pore volumes under the room temperature condition and the real underground temperature and pressure condition is calculated to obtain the oil saturation S1 of the light hydrocarbon loss part under the room temperature condition:

[0088] S1=(V-V1) / V.

[0089] Step five. The same saturated oil core sample is subjected to high-speed centrifugation using different centrifugal speeds (5000 r / min, 6000 r / min, 7000 r / min, etc.), and nuclear magnetic resonance test is performed after each centrifugation. The nuclear magnetic resonance T2 relaxation time spectrum obtained by inversion calculation under different centrifugal speeds is shown in detail in the specification. Figure 3 The last centrifugal speed is selected as the standard centrifugal speed, that is, the nuclear magnetic volume after the previous centrifugation-the nuclear magnetic volume after the next centrifugation) / the nuclear magnetic volume after the previous centrifugation×100%<5%, to obtain the optimal centrifugal speed.

[0090] Step six. All saturated oil core samples are subjected to centrifugation using the optimal centrifugal speed selected in step five, and then subjected to nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. The total pore volume V1 of the saturated oil core sample at room temperature and normal pressure in step four is compared to calculate the ground movable fluid saturation S2:

[0091] S2=(V1-V2) / V1.

[0092] Step seven. The real movable oil saturation S of the shale is calculated:

[0093] S=S1+S2.

[0094] Referring to the specification Figure 2, the old method refers to the method mentioned in the background art, scholars developed nuclear magnetic resonance-centrifugation method to study the mobility of crude oil, the crude oil still existing in the core after high-speed centrifugation is regarded as immobile oil, and the crude oil centrifuged out is regarded as mobile oil, but in these studies, nuclear magnetic resonance is usually used to obtain the mobile oil saturation under the condition of saturating the core with n-dodecane fluid. The new method refers to the method adopted in the embodiment. From the attached figures of the specification Figure 2 It can be seen that the mobile oil saturation obtained by the method of the present application is obviously 3-4 percentage points higher than that obtained by the old method, which is a more accurate calculation value of mobile oil saturation obtained after fully considering the effects of similar solubility and gas-driven crude oil, reduces experimental errors, and is more consistent with actual geological conditions.

[0095] In summary, various corresponding transformation schemes made by those skilled in the art after reading the present application file without creative mental effort according to the technical solutions and technical concepts of the present application all belong to the scope protected by the present application.

Claims

1. A method for calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation, characterized in that: The method comprises the following steps: Step one: obtaining an original core sample, washing oil and drying to obtain a washed oil sample; Based on the real gas-oil ratio in the underground, the crude oil and natural gas are used for sample matching to obtain the matching crude oil, and the volume of the matching crude oil is V0; Step two: vacuumizing the washed oil sample, pressurizing and saturating the matching crude oil to obtain a saturated oil core sample; Step three: taking out the saturated oil core sample, measuring the volume V' of the remaining matching crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure conditions: V = V0-V'; Step four: performing a nuclear magnetic resonance experiment on the saturated oil core sample under room temperature conditions, and inversely calculating a T2 relaxation time spectrum to obtain the total pore volume V1 of the saturated oil core sample under normal temperature and pressure, comparing the pore volume difference between the room temperature conditions and the real underground temperature and pressure conditions, and calculating the oil saturation S1 of the light hydrocarbon loss part under the room temperature conditions: S1 = (V-V1) / V; Step five: using different centrifugal speeds to centrifuge the same saturated oil core sample, respectively, and performing a nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal speed; Step six: using the optimal centrifugal speed selected in step five to centrifuge all the saturated oil core samples, and then performing a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation, comparing the total pore volume V2 with the total pore volume V1 of the saturated oil core sample under normal temperature and pressure in step four, and calculating the ground movable fluid saturation S2: S2 = (V1-V2) / V1; Step seven: calculating the real movable oil saturation S of the shale: S = S1+S2.

2. The method of claim 1, wherein the method is based on the principle of NMR- centrifuge to calculate the mobile oil saturation of shale. The washing oil in step one specifically refers to using chloroform to extract and wash oil.

3. The method of claim 2, wherein the method is based on the principle of NMR- centrifuge to calculate the mobile oil saturation of shale. The washed oil sample obtained in step one specifically refers to: drilling an original core sample, extracting and washing oil with chloroform, then drying the core sample in a vacuum drying oven at a temperature of 60 DEG C for 4 hours, sealing with plastic wrap after cooling, and obtaining the washed oil sample.

4. The method of claim 3, wherein the method is based on the principle of NMR- centrifuge to calculate the mobile oil saturation of shale. The chloroform extraction and washing oil specifically refers to: wrapping the original core sample with filter paper, loading it into the sample chamber of the extractor, then adding chloroform to the extractor, extracting the original core sample at a temperature of 75-80 DEG C, until the reflux liquid is colorless, then taking out the core sample, and completely volatilizing the chloroform at room temperature.

5. The method of claim 1, wherein: The matching crude oil obtained in step one specifically refers to: calculating the amount of crude oil and natural gas based on the real gas-oil ratio in the underground, and conveying it to a high-temperature and high-pressure sample matching device, setting the corresponding temperature and pressure according to the real underground conditions, and keeping constant for 1 hour to obtain the matching crude oil.

6. The method of calculating the movable oil saturation of shale based on the principle of NMR-centrifugation of claim 1, wherein: The step two specifically refers to: vacuumizing the washed oil sample for more than 12 hours, the pressure P during vacuumizing is <-0.098 Mpa, the vacuum degree reaches 0.1 Pa, pressurizing and saturating the matching crude oil, and keeping for 12 hours to obtain the saturated oil core sample.

7. The method of calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation of claim 1, wherein: The optimal centrifugal speed obtained in step five specifically refers to: if the porosity obtained by the previous nuclear magnetic resonance test minus the porosity obtained by the subsequent nuclear magnetic resonance test / the porosity obtained by the previous nuclear magnetic resonance test x 100% <5%, then the centrifugal speed corresponding to the previous nuclear magnetic resonance test is the optimal centrifugal speed, and the corresponding centrifugal force is the optimal centrifugal force.

8. The method of calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation of claim 7, characterized in that: The step five specifically refers to: centrifuging the oil-saturated core sample once at a centrifugal speed of 5000 r / min, performing a nuclear magnetic resonance experiment once, inverting to obtain a T2 relaxation time spectrum, and obtaining porosity; then centrifuging once at a centrifugal speed of 6000 r / min, performing a nuclear magnetic resonance experiment once, inverting to obtain a T2 relaxation time spectrum, and obtaining porosity; and the like, until the optimal centrifugal speed is obtained.

9. The method of calculating the movable oil saturation of shale based on the principle of nuclear magnetic centrifugation of claim 8, wherein: In the step five, the centrifugation time is 60 min each time.

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