Method for calculating shale movable oil saturation based on nuclear magnetism-centrifugation principle

Abstract

The invention relates to the technical field of reservoir evaluation in petroleum geological exploration sedimentary reservoirs, in particular to a method for calculating shale movable oil saturation based on a nuclear magnetism-centrifugation principle, which comprises the following steps: processing to obtain a sample after oil washing; based on the underground real gas-oil ratio, crude oil and natural gas are used for sample preparation, and prepared crude oil is obtained; pressurizing and saturating the prepared crude oil to obtain an oil-saturated rock core sample; calculating the total pore volume V of the rock core under the real underground temperature and pressure condition; obtaining the total volume V1 of the oil-saturated rock core sample at normal temperature and normal pressure, and calculating the oil saturation S1 of the light hydrocarbon lost part at room temperature; the ground movable fluid saturation S2 is obtained through calculation, and finally the real movable oil saturation S of the shale is obtained through calculation. By means of the method, the gas-oil ratio closer to the real geological condition is recovered, the viscosity of crude oil can be reduced, the viscosity is closer to the real condition, the experimental error is reduced to the maximum extent, and the calculation result is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of reservoir evaluation in sedimentary reservoirs in petroleum geological exploration, and in particular to a method for calculating movable oil saturation of shale based on the nuclear magnetic resonance-centrifugation principle. Background Art

[0002] The increasing demand for energy and the continuous consumption of conventional oil and gas resources have made the contradiction between oil and gas supply and demand increasingly prominent. Therefore, unconventional energy has received more and more attention, and shale oil is an important component of it. At present, shale oil has become a hot spot for unconventional exploration and development. Compared with conventional oil reservoirs, shale oil reservoirs are rich in organic matter, with diverse pore types, multi-scale distribution of pores, and complex spatial structure. Both at home and abroad have strengthened their exploration efforts. Shale oil is a typical unconventional resource. Its mobility is an important factor affecting whether the reservoir can be put into development and production. As an important link in oil and gas exploration, shale oil mobility evaluation is one of the indispensable steps in shale oil exploration. The ultimate goal of shale oil exploration is to guide the large-scale development of soluble organic matter in shale formations. Therefore, shale oil mobility evaluation is one of the key reference factors for determining favorable shale oil enrichment intervals.

[0003] Current research suggests that shale oil exists in shale formations in three forms: free, adsorbed, and dissolved. Under current technical conditions, the main form of shale oil that can be mined is free shale oil, and bound oil is unlikely to have practical value. Therefore, the quantitative evaluation of the saturation of free shale oil (mobile oil) is the core of shale oil research. The commonly used quantitative characterization methods for shale oil mobility currently include empirical methods, multi-step pyrolysis, geochemical parameter methods, adsorption-free oil model methods, nuclear magnetic resonance-high-speed centrifugation methods, numerical simulation methods, and gas chromatography-mass spectrometry (GC-MS) technology.

[0004] Among them, the multi-stage pyrolysis method, geochemical parameter method, and gas chromatography-mass spectrometry (GC-MS) technology require a large amount of geochemical experimental data to draw parameter change trend diagrams, and then quantitatively characterize the movable oil saturation of shale oil at different evolutionary stages. The amount of data required is large and the cost is high. 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 states for simulation, with large human factors and poor representativeness. The movable oil volume calculated by the empirical method is a theoretical value, and the oil saturation index is a shale oil mobility evaluation parameter proposed based on the exploration and development practice of marine shale oil in North America. It has great differences in mineral composition, organic matter, etc. with my country's continental shale formations. Whether the oil saturation index limit of 100 mg / g is applicable to the evaluation of continental shale oil mobility is still controversial. The multi-stage pyrolysis method requires a small amount of sample (2 mg) for the 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. It is difficult to judge the seepage performance of crude oil underground, and therefore it is impossible to determine the movable conditions of crude oil.

[0005] Nuclear magnetic resonance technology is an important research method 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 based on the relationship between the transverse relaxation time T2 of the rock and the pore radius r, and a pore classification method is formulated based on the T2 energy spectrum distribution diagram. Based on the fluid relaxation characteristics, the pore size distribution law inside the rock can be analyzed, and the basic physical properties of the rock can be accurately measured. The principle is that when the oil (or water) sample is in a uniform static magnetic field, the hydrogen nucleus 1H contained in the fluid will be polarized by the magnetic field, and a magnetization vector will be shown macroscopically. At this time, if a radio frequency field of a certain frequency (Lamor frequency) is applied to the sample, nuclear magnetic resonance will be generated. After the radio frequency field is removed, a signal with an amplitude that decays exponentially with time can be received. The attenuation degree of the signal can be described by the transverse relaxation time T2. After the high-speed centrifugation experiment, the crude oil still in the core after centrifugation can be regarded as immobile oil, and the crude oil removed by high-speed centrifugation can be regarded as movable oil. The value of movable porosity can be obtained by nuclear magnetic resonance measurement before and after the core centrifugation. The method of testing movable oil saturation by combining nuclear magnetic resonance and centrifugation experiments is economical, efficient and executable, and is the best solution to solve the movable oil saturation of shale under current technical conditions. For example, in the Jimusar shale oil reservoir, by measuring the nuclear magnetic resonance results of the oil-water drive experiment of the rock sample, three types of shale oil occurrence, adsorbed water, adsorbed oil and free oil were proposed, and the wettability characteristics and crude oil occurrence mode of large pore oil-wet oil-bearing and small pore water-wet water-bearing were proposed. The cutoff value was determined by using the nuclear magnetic resonance experiment results to calculate the free oil saturation, and the application effect was good. However, this method saturates the core with water or chemical reagents (such as MnCl2), and does not restore the actual situation underground, so there is a certain difference between the calculated results and the actual situation.

[0006] In the study of tight reservoirs such as shale, scholars have developed the nuclear magnetic resonance-centrifugation method to study the mobility of crude oil. The crude oil that remains in the core after high-speed centrifugation is regarded as immobile oil, and the crude oil removed by high-speed centrifugation is regarded as movable oil. However, these studies usually use NMR under the condition of saturated core with n-dodecane fluid. Although it has a similar composition to petroleum, it does not directly use petroleum, and no natural gas is added, so it is impossible to determine the effect of gas-oil ratio on the fluidity of petroleum. In addition, under the high temperature and high pressure environment underground, the viscosity and density of shale oil will undergo significant changes, as shown in the attached manual. Figure 4 And the instruction manual Figure 5 As shown, the current experimental methods are unable to obtain a more realistic underground environment, and the results obtained are far from the actual underground results. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a method for calculating the movable oil saturation of shale based on the nuclear magnetic resonance-centrifuge principle, which restores the gas-oil ratio closer to the actual geological conditions, can reduce the viscosity of crude oil, and is closer to the actual situation, thereby minimizing experimental errors and making the calculation results more accurate.

[0008] The present invention is achieved by adopting the following technical solutions:

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

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

[0011] Step 2. Vacuum the sample after oil washing, pressurize and saturate the crude oil to obtain an oil-saturated core sample;

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

[0013] V = V0 - V';

[0014] Step 4. Under room temperature conditions, perform a nuclear magnetic resonance experiment on the oil-saturated core sample, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core sample at room temperature and pressure. Compare the difference in pore volume under room temperature conditions and the actual 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 5. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance testing after each centrifugation to obtain the optimal centrifugal speed;

[0017] Step 6. Centrifuge all the oil-saturated core samples using the optimal centrifugal speed selected in step 5, and then perform a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total volume V1 of the oil-saturated core sample at normal temperature and pressure in step 4, and calculate the ground movable fluid saturation S2:

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

[0019] Step 7. Calculate the real movable oil saturation S of the desired shale:

[0020] S=S1+S2.

[0021] The washing oil in step 1 specifically refers to extracting the washing oil using chloroform.

[0022] Obtaining the oil-washed sample in step 1 specifically refers to: drilling an original core sample, extracting the wash oil with chloroform, and then drying the core sample in a vacuum drying oven at 60° C. for 4 hours, and sealing it with plastic wrap after cooling to obtain the oil-washed sample.

[0023] The specific method of extracting the washing oil with chloroform is as follows: wrap the original core sample with filter paper, put it into the sample chamber of the extractor, then add chloroform into the extractor, extract the original core sample at a temperature of 75-80°C, extract until the reflux liquid is colorless, then take out the core sample, and completely evaporate the chloroform at room temperature.

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

[0025] The step 2 specifically refers to: vacuuming the sample after oil washing for more than 12 hours, the pressure during vacuuming P<-0.098Mpa, the vacuum degree reaches 0.1Pa, pressurizing and saturating the crude oil, maintaining for 12 hours, and obtaining an oil-saturated core sample.

[0026] Obtaining the optimal centrifugal speed in step five specifically refers to: if the porosity obtained from the previous nuclear magnetic resonance test - the porosity obtained from the next nuclear magnetic resonance test) / the porosity data obtained from 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 the optimal centrifugal force.

[0027] The step five specifically refers to: centrifuging the oil-saturated core sample once at a centrifugal speed of 5000 r / min, conducting a nuclear magnetic resonance experiment, and inverting to obtain a T2 relaxation time spectrum, and obtaining the porosity; then centrifuging once at a centrifugal speed of 6000 r / min, and conducting a nuclear magnetic resonance experiment, inverting to obtain a T2 relaxation time spectrum, and obtaining the porosity; and so on, until the optimal centrifugal speed is obtained.

[0028] In the step 5, each centrifugation time is 60 min.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The calculation method of the present invention fully considers the influence of similar miscibility and gas-driven crude oil, and can obtain a more accurate movable oil saturation calculation value, reduce experimental errors, and be more in line with actual geological conditions. Specifically, compared with the old method, the movable oil saturation calculated by this method is 3-4 percentage points higher.

[0031] 2. The present invention uses a high-temperature and high-pressure sample dispenser to inject natural gas into crude oil with high viscosity in proportion to restore the gas-oil ratio close to the actual geological conditions, which can not only reduce the viscosity of crude oil, but also be closer to the actual situation and minimize experimental errors. However, the process of directly filling the core sample with methane gas will directly change its gas-oil ratio, resulting in an inability to accurately calculate and cannot reflect the actual mobility of underground crude oil.

[0032] 3. The present invention first performs an oil washing operation on the original core sample to remove the original hydrocarbons in the original core sample, so that after the core is saturated with oil, it can be closer to the actual gas-oil ratio underground. Chloroform is used to extract the oil washing. Chloroform is an anionic surfactant with strong dissolving ability, easy to volatilize, and easy to remove.

[0033] 4. The oil saturation of the core is different at different centrifugal speeds. When the centrifugal speed gradually increases, the oil saturation in the core gradually decreases. The present invention calculates the optimal centrifugal speed so that the measured movable fluid saturation is closer to the real movable oil saturation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0035] Figure 1 It is a schematic diagram of the process of the present invention;

[0036] Figure 2 It is a schematic diagram comparing movable oil saturation calculated by different methods in the present invention;

[0037] Figure 3The nuclear magnetic resonance T2 relaxation time spectrum obtained by inversion calculation of the oil-saturated core sample at different centrifugal speeds in the present invention;

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

[0039] Figure 5 This is the viscosity curve of ground shale oil changing with temperature. DETAILED DESCRIPTION

[0040] Example 1

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

[0042] Step 1. Obtain an original core sample, wash the oil and dry it to obtain an oil-washed sample; based on the actual gas-oil ratio underground, use crude oil and natural gas to perform sampling to obtain configured crude oil, where the volume of the configured crude oil is V0.

[0043] Step 2. Evacuate the oil-washed sample, pressurize and saturate it with crude oil to obtain an oil-saturated core sample.

[0044] Step 3. Take out the oil-saturated core sample, measure the volume V' of the remaining crude oil, and calculate the total pore volume V of the core under the actual underground temperature and pressure conditions:

[0045] V=V0-V'.

[0046] Step 4. Under room temperature conditions, perform a nuclear magnetic resonance experiment on the oil-saturated core sample, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core sample at room temperature and pressure. Compare the difference in pore volume under room temperature conditions and the actual underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

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

[0048] Step 5. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance testing after each centrifugation to obtain the optimal centrifugal speed.

[0049] Step 6. Centrifuge all the oil-saturated core samples using the optimal centrifugal speed selected in step 5, and then perform a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total volume V1 of the oil-saturated core sample at normal temperature and pressure in step 4, and calculate the ground movable fluid saturation S2:

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

[0051] Step 7. Calculate the real movable oil saturation S of the desired shale:

[0052] S=S1+S2.

[0053] Example 2

[0054] As a preferred embodiment of the present invention, the present invention includes a method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifugal principle, comprising the following steps:

[0055] Step 1. Obtain the original core sample, extract the washed oil with chloroform and dry it to obtain the washed oil sample. Based on the actual gas-oil ratio underground, calculate the amount of crude oil and natural gas and transport them to the high-temperature and high-pressure sampler. According to the actual underground conditions, set the corresponding temperature and pressure, and keep them constant for 1 hour to obtain the configured crude oil. The volume of the configured crude oil is V0.

[0056] Step 2. Evacuate the oil-washed sample, pressurize and saturate it with crude oil to obtain an oil-saturated core sample.

[0057] Step 3. Take out the oil-saturated core sample, measure the volume V' of the remaining crude oil, and calculate the total pore volume V of the core under the actual underground temperature and pressure conditions:

[0058] V=V0-V'.

[0059] Step 4. Under room temperature conditions, perform nuclear magnetic resonance experiments on the oil-saturated core samples, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core samples at room temperature and pressure differential. Compare the difference in pore volume under room temperature conditions and the actual underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

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

[0061] Step 5. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance tests after each centrifugation to obtain the optimal centrifugal speed. Specifically, 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% < 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 the optimal centrifugal force.

[0062] Step 6. Centrifuge all the oil-saturated core samples using the optimal centrifugal speed selected in step 5, and then perform a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total volume V1 of the oil-saturated core sample at normal temperature and pressure in step 4, and calculate the ground movable fluid saturation S2:

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

[0064] Step 7. Calculate the real movable oil saturation S of the desired shale:

[0065] S=S1+S2.

[0066] Example 3

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

[0068] Step 1. Obtain the original core sample, wash the oil and dry it to obtain the washed oil sample. Specifically, at room temperature, first wrap the original core sample with filter paper, i.e., the plunger sample, and 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 evaporate the chloroform at room temperature.

[0069] Based on the real gas-oil ratio underground, crude oil and natural gas are used for sample preparation to obtain the prepared crude oil, and the volume of the prepared crude oil is V0. Specifically, a certain volume of crude oil is injected into the oil storage cylinder and a certain volume of natural gas is injected into the gas storage cylinder using a CP-2 high-temperature and high-pressure sample preparation instrument. Based on the real gas-oil ratio underground, the amount of crude oil and natural gas is calculated, and a constant speed and constant pressure metering pump is used to transport the calculated amount of crude oil and natural gas to the high-temperature and high-pressure sample preparation device. The temperature and pressure are set according to the real underground conditions of the shale oil reservoir under study, and are kept constant for 1 hour.

[0070] Step 2. Vacuum the washed oil sample, pressurize and saturate the crude oil to obtain an oil-saturated core sample. Specifically, vacuum the washed oil sample for more than 12 hours, the pressure during vacuuming P<-0.098Mpa, and the vacuum degree reaches 0.1Pa. Connect the high-temperature and high-pressure sample preparation instrument and the core vacuuming and pressurizing saturation experimental device, directly pressurize and saturate the oil, and keep it for 12 hours to obtain an oil-saturated sample.

[0071] Step 3. Take out the oil-saturated core sample, measure the volume V' of the remaining crude oil, and calculate the total pore volume V of the core under the actual underground temperature and pressure conditions:

[0072] V=V0-V'.

[0073] Step 4. Under room temperature conditions, perform a nuclear magnetic resonance experiment on the oil-saturated core sample, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core sample at room temperature and pressure. Compare the difference in pore volume under room temperature conditions and the actual 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. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance tests after each centrifugation to obtain the optimal centrifugal speed. Specifically, the oil-saturated core sample is first centrifuged once at a centrifugal speed of 5000r / min, a nuclear magnetic resonance experiment is performed, and the T2 relaxation time spectrum is inverted to obtain the porosity; then the sample is centrifuged once at a centrifugal speed of 6000r / min, and a nuclear magnetic resonance experiment is performed, the T2 relaxation time spectrum is inverted to obtain the porosity; and so on. Each centrifugation time can be 60min.

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

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

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

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

[0080] S=S1+S2.

[0081] Example 4

[0082] As another embodiment of the present invention, refer to the attached specification 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 column 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 the CP-2 high-temperature and high-pressure sample preparation instrument, a certain volume of crude oil and natural gas are respectively injected into the sample preparation instrument, and the amount of crude oil and natural gas is calculated based on the actual gas-oil ratio underground. The calculated amount of crude oil and natural gas is transported to the high-temperature and high-pressure sample preparation device using a constant speed and constant pressure metering pump. According to the actual underground conditions of the shale oil reservoir being studied, the temperature and pressure are set and kept constant for 1 hour to obtain the configured crude oil. The volume of the configured crude oil is V0.

[0085] Step 2. Evacuate the oil-washed sample for more than 12 hours, the pressure during evacuation P<-0.098Mpa, the vacuum degree reaches 0.1Pa, pressurize and saturate the crude oil, maintain for 12 hours, and obtain the saturated oil core sample.

[0086] Step 3. Take out the oil-saturated core sample and measure the volume V' of the remaining crude oil. The difference in crude oil volume in the sample barrel before and after oil saturation is V0-V', which is the total pore volume V of the core under the actual underground temperature and pressure conditions, and is also the total pore volume V of the pressure-maintaining core.

[0087] Step 4. Under room temperature conditions, perform nuclear magnetic resonance experiments on the oil-saturated core samples, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core samples at normal temperature and pressure, that is, the total pore volume V1 of the normal pressure core. Compare the difference in pore volume under room temperature conditions and the actual underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions:

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

[0089] Step 5. Use different centrifugal speeds (5000r / min, 6000r / min, 7000r / min, etc.) to centrifuge the same oil-saturated core sample at high speed. Perform NMR test after each centrifugation. The NMR T2 relaxation time spectra obtained by inversion calculation at different centrifugal speeds are detailed in the attached manual. Figure 3 The last centrifugal speed was selected as the centrifugal standard, that is, the NMR volume of the previous centrifugation - the NMR volume of the next centrifugation) / the NMR volume of the previous centrifugation × 100% < 5%, and the optimal centrifugal speed was obtained.

[0090] Step 6. Centrifuge all the oil-saturated core samples using the optimal centrifugal speed selected in step 5, and then perform a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total volume V1 of the oil-saturated core sample at normal temperature and pressure in step 4, and calculate the ground movable fluid saturation S2:

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

[0092] Step 7. Calculate the real movable oil saturation S of the desired shale:

[0093] S=S1+S2.

[0094] Refer to the instruction manual Figure 2In the figure, the old method specifically refers to the one mentioned in the background technology. Scholars developed the nuclear magnetic resonance-centrifugation method to study the mobility of crude oil. The crude oil still in the core after high-speed centrifugation is regarded as immobile oil, and the crude oil removed by high-speed centrifugation is regarded as movable oil. However, in these studies, nuclear magnetic resonance is usually performed under the condition of saturated core with n-dodecane fluid to obtain the movable oil saturation. The new method refers to the method used in this embodiment. Figure 2 It can be seen that the movable oil saturation obtained by the method of the present invention is significantly 3-4 percentage points higher than that obtained by the old method. This is a more accurate movable oil saturation calculation value obtained after fully considering the influence of similar solubility and gas-driven crude oil, which reduces experimental errors and is more in line with actual geological conditions.

[0095] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. A method for calculating movable oil saturation of shale based on nuclear magnetic resonance-centrifugation principle, characterized in that: The following steps are involved: Step 1. Obtain the original core sample, wash the oil and dry it to obtain the oil-washed sample; Based on the actual gas-oil ratio underground, crude oil and natural gas are used for sample preparation to obtain prepared crude oil, where the volume of the prepared crude oil is V0; Step 2. Vacuum the washed oil sample and pressurize it to saturate the crude oil to obtain an oil-saturated core sample; Step 3. Take out the oil-saturated core sample, measure the volume V' of the remaining crude oil, and calculate the total pore volume V of the core under the actual underground temperature and pressure conditions: V = V0 - V'; Step 4. Under room temperature conditions, perform a nuclear magnetic resonance experiment on the oil-saturated core sample, and invert the T2 relaxation time spectrum to obtain the total volume V1 of the oil-saturated core sample at room temperature and pressure. Compare the difference in pore volume under room temperature conditions and the actual underground temperature and pressure conditions, and calculate the oil saturation S1 of the light hydrocarbon loss part under room temperature conditions: S1=(V-V1) / V; Step 5. Use different centrifugal speeds to perform high-speed centrifugation on the same oil-saturated core sample, and perform nuclear magnetic resonance testing after each centrifugation to obtain the optimal centrifugal speed; Step 6. Centrifuge all the oil-saturated core samples using the optimal centrifugal speed selected in step 5, and then perform a nuclear magnetic resonance experiment to obtain the total pore volume V2 of the core after centrifugation. Compare it with the total volume V1 of the oil-saturated core sample at normal temperature and pressure in step 4, and calculate the ground movable fluid saturation S2: S2 = (V1-V2) / V1; Step 7. Calculate the real movable oil saturation S of the desired shale: S=S1+S2.

2. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 1, characterized in that: The washing oil in step 1 specifically refers to extracting the washing oil using chloroform.

3. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 2, characterized in that: Obtaining the oil-washed sample in step 1 specifically refers to: drilling an original core sample, extracting the wash oil with chloroform, and then drying the core sample in a vacuum drying oven at 60° C. for 4 hours, and sealing it with plastic wrap after cooling to obtain the oil-washed sample.

4. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 3 is characterized in that: The specific method of extracting the washing oil with chloroform is as follows: wrap the original core sample with filter paper, put it into the sample chamber of the extractor, then add chloroform into the extractor, extract the original core sample at a temperature of 75-80°C, extract until the reflux liquid is colorless, then take out the core sample, and completely evaporate the chloroform at room temperature.

5. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 1, characterized in that: The step 1 of obtaining the configured crude oil specifically refers to: based on the actual gas-oil ratio underground, calculating the amount of crude oil and natural gas, and transporting them to a high-temperature and high-pressure sample preparation device, setting the corresponding temperature and pressure according to the actual underground conditions, and maintaining them constant for 1 hour to obtain the configured crude oil.

6. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 1, characterized in that: The step 2 specifically refers to: vacuuming the sample after oil washing for more than 12 hours, the pressure during vacuuming P<-0.098Mpa, the vacuum degree reaches 0.1Pa, pressurizing and saturating the crude oil, maintaining for 12 hours, and obtaining an oil-saturated core sample.

7. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 1, characterized in that: Obtaining the optimal centrifugal speed in step five specifically refers to: if (porosity obtained from the previous nuclear magnetic resonance test - porosity obtained from the next nuclear magnetic resonance test) / porosity data obtained from the previous nuclear magnetic resonance test × 100% < 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 the optimal centrifugal force.

8. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to 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, conducting a nuclear magnetic resonance experiment, and inverting to obtain a T2 relaxation time spectrum, and obtaining the porosity; then centrifuging once at a centrifugal speed of 6000 r / min, and conducting a nuclear magnetic resonance experiment, inverting to obtain a T2 relaxation time spectrum, and obtaining the porosity; and so on, until the optimal centrifugal speed is obtained.

9. The method for calculating movable oil saturation of shale based on the nuclear magnetic-centrifuge principle according to claim 8, characterized in that: In the step 5, each centrifugation time is 60 min.

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