Displacement method of rock core and method for detecting physical properties of rock core by using nuclear magnetic resonance and imaging technology

Abstract

The invention provides a rock core displacement method and a method for detecting physical properties of a rock core by using nuclear magnetic resonance and imaging technologies, and relates to the technical field of rock core crude oil exploitation. According to the method, heavy water without H proton signals is used for displacing the rock core, then oil is saturated in the mode that oil displaces the heavy water, at the moment, the occurrence state of the rock core is a water-oil coexistence state, the state of the rock core in the stratum is better met, and the indoor experiment condition is the same as the oilfield exploitation site condition. According to the method provided by the invention, relaxation spectrum detection and imaging detection can be combined in the displacement process, so that the state of the rock core in each time period in the whole displacement process can be precisely monitored, reservoir information can be better known on an oil field site, the recovery efficiency is improved, and technical support is provided for exploration and development of the on-site oil and gas field. Moreover, the method provided by the invention can be suitable for rapidly measuring the unconventional gas and oil storage rock stratum, and has the advantages of rapidness, accuracy and no damage detection.

Description

Technical Field

[0001] The invention relates to the technical field of core crude oil exploitation, and in particular to a core displacement method and a method for detecting the physical properties of the core by utilizing nuclear magnetic resonance and imaging technology. Background Art

[0002] As an indispensable and non-renewable resource for the development of modern industry, oil is called "the blood of industry". At present, oil energy is still an important resource to ensure industrial development and people's lives. At present, there are problems with the exploitation of oil energy such as low exploitation efficiency and long project cycle. Therefore, it is of great significance to study the fluidity characteristics and distribution laws of crude oil in cores with different porosity and permeability, use displacement experiments to simulate the specific conditions of crude oil exploitation in oil fields, establish corresponding models, and improve crude oil recovery rates. The main research method for improving recovery rate is laboratory simulation displacement experiments, which can also be used to study the lithology of the target layer.

[0003] As an analytical method, nuclear magnetic resonance technology has the advantages of rich information and accurate results. It has been reported that the flow law of crude oil in cores is detected by nuclear magnetic resonance technology. The core displacement methods used before the existing nuclear magnetic resonance technology analysis mainly include vacuum pressure saturation oil treatment, water saturation treatment and manganese saturation treatment. However, the displacement efficiency of the displacement core obtained by the above displacement method is different from the actual displacement efficiency of the core crude oil during the on-site production process of the oil field, and it is impossible to provide accurate data for the on-site production activities of the oil field. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a core displacement method and a method for detecting the physical properties of the core using nuclear magnetic resonance and imaging technology. The oil-water saturated core obtained by the displacement method provided by the present invention is the same as the conditions at the oil field production site, and the displacement efficiency obtained by gas displacement is basically the same as the actual displacement efficiency of the core crude oil during the on-site production process, providing accurate data support for oil field on-site production activities.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a core displacement method, comprising the following steps:

[0007] The dried core samples are sequentially subjected to heavy water flooding and oil flooding saturation to obtain water-oil saturated cores;

[0008] The water-oil saturated core is gas-displaced by using a hydrogen-free gas to obtain a displaced core.

[0009] Preferably, the porosity of the dried core sample is 5-12%;

[0010] The process parameters of heavy water displacement saturation include: the applied confining pressure is 10-15 MPa, the displacement pressure is 5 MPa, and the displacement flow rate of heavy water at the end of heavy water displacement saturation is 20-25 PV.

[0011] Preferably, the process parameters of the oil displacement saturation include: an applied confining pressure of 10-15 MPa, a displacement pressure of 3-7 MPa, and an oil displacement flow rate of 50-55 PV at the end of the oil displacement saturation.

[0012] Preferably, the hydrogen-free gas comprises at least one of carbon dioxide and nitrogen;

[0013] The gas displacement includes constant pressure displacement and gradient flow displacement in sequence; the pressure of the constant pressure displacement is 1-5MPa, and the volume of oil displaced by the constant pressure displacement accounts for 8-12% of the total oil volume; the total displacement flow of the gradient flow displacement is 5PV; the confining pressure applied during the gas displacement is 10-15MPa.

[0014] Preferably, the total displacement flow rate of hydrogen-free gas during the gradient flow displacement process is 0.4PV, 0.8PV, 1.2PV, 1.6PV and 5PV respectively.

[0015] The present invention also provides a method for detecting the physical properties of a core using nuclear magnetic resonance and imaging technology, comprising the following steps:

[0016] Obtain the volume of the dried core sample to be tested;

[0017] The dried core sample to be tested is saturated with oil to obtain an oil-saturated core;

[0018] The dried core sample to be tested is subjected to heavy water displacement saturation and oil displacement saturation in sequence to obtain a water-oil saturated core; and the quality of the water-oil saturated core is tested;

[0019] Using a hydrogen-free gas to perform gas displacement on the water-oil saturated core to obtain a displacement core; recording the time of the gas displacement and the total volume of the driven oil;

[0020] Performing nuclear magnetic resonance detection on the dried core sample to be tested, the oil-saturated core, the saturated core and the displacement core, respectively, to obtain the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil-saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core and the displacement core;

[0021] Performing nuclear magnetic resonance imaging on the displacement core to obtain a nuclear magnetic resonance imaging image of the displacement core;

[0022] Providing an oil index line, wherein the oil index line takes the volume of the oil standard sample as an independent variable and the amount of the nuclear magnetic signal as a dependent variable; the standard oil sample is of the same type as the oil used for the oil displacement saturation;

[0023] Data processing is performed on the volume of the dried core sample, the mass of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the displacement core and the oil mark line to obtain the core physical property detection results.

[0024] Preferably, the nuclear magnetic resonance detection is a low-field high-frequency nuclear magnetic resonance detection, and the magnet frequency of the low-field high-frequency nuclear magnetic resonance detection is ≥12MHz and the echo time is ≤0.15ms.

[0025] Preferably, the conditions of the nuclear magnetic resonance detection include: a sampling frequency of 200KHz, a waiting time of 4000ms, an analog gain of 20db, a digital gain of 2, an accumulation number of 32, an echo time of 0.08ms, an echo number of 15000, and a pre-amplification gear of 1.

[0026] Preferably, the conditions of the nuclear magnetic resonance imaging include: the sampling sequence is a hard pulse echo sequence, the frequency offset is 12.796619 MHz, the X-direction gradient is 70, the Y-direction gradient is 160, the Z-direction gradient is -170, the waiting time is 500 ms, the echo time is 5.885 ms, the analog gain is 10 db, and the number of accumulations is 8.

[0027] Preferably, the core physical properties include one or more of core porosity, core oil saturation, core residual saturation, core displacement efficiency and displacement efficiency spectrum;

[0028] The calculation formula of the core porosity is shown in Formula 1:

[0029]

[0030] In formula 1, is the total porosity of the core, V 孔 V is the total pore volume of the dried core sample to be tested, 样 is the total volume of the dried core sample to be tested, S 油 is the nuclear magnetic signal of the oil-saturated core, k is the slope of the oil mark line;

[0031] The calculation formula of the core oil saturation is shown in Formula 2:

[0032] S o =(S 油-水 / k / V 孔 )×100% Formula 2;

[0033] In formula 2, S o is the oil saturation of the oil-saturated core, S 油-水is the nuclear magnetic signal of the water-oil saturated core, k is the slope of the oil mark line, V 孔 is the total pore volume of the dried core sample to be tested;

[0034] The calculation formula of the core residual saturation is shown in Formula 3:

[0035] S or =S n / (k×V 油 )×100% Formula 3;

[0036] In formula 3, S or is the residual saturation of the core, S n is the nuclear magnetic signal of the displacement core, k is the slope of the oil mark line, V 油 is the volume of oil in the pores of the oil-saturated core;

[0037] The calculation formula of the core displacement efficiency is shown in Formula 4:

[0038] E=(S 油-水- S n ) / S 油-水 ×100% Formula 4;

[0039] In formula 4, E is the core displacement efficiency, S n is the nuclear magnetic signal of the displacement core, S 油-水 is the NMR signal of the water-oil saturated core;

[0040] The displacement efficiency spectrum line takes the displacement flow rate of hydrogen-free gas as the independent variable and the core displacement efficiency as the dependent variable.

[0041] The present invention firstly displaces the core with heavy water containing no H proton signal, and then saturates the core with oil by displacing the heavy water with oil. In the case of saturated heavy water, when the oil enters the pore channel, only part of the heavy water will be displaced. At this time, the occurrence state of the core is a state of coexistence of water and oil, which is more consistent with the state of the core in the formation, thereby achieving the same conditions of indoor experiments as those at the oil field mining site, and the displacement efficiency obtained by gas displacement is basically the same as the actual displacement efficiency of the core crude oil during the on-site mining process, providing accurate data support for on-site production activities of the oil field.

[0042] The present invention provides a method for detecting the physical properties of the core using nuclear magnetic resonance and imaging technology, and using nuclear magnetic resonance technology T2 spectrum and nuclear magnetic resonance imaging detection technology to comprehensively monitor and analyze the distribution of each fluid in each core sample. First, the core drying sample is subjected to nuclear magnetic resonance detection to obtain the nuclear magnetic T2 spectrum of the core drying sample; then a displacement experiment (heavy water displacement saturation, oil displacement saturation, gas displacement) is carried out, and the nuclear magnetic resonance T2 spectrum and imaging detection are carried out during the experiment; data processing uses an oil mark line for nuclear magnetic resonance calibration, and the nuclear magnetic resonance signal is converted. The method provided by the present invention can combine relaxation spectrum detection and imaging detection during the displacement process, and can obtain the movement mode and law of various types of fluids in the core during the displacement process of the sample, realize the precise monitoring of the state of the core in each time period during the entire displacement experiment, and study the fluid migration situation and core pore information, which is helpful for the oil field site to better understand the reservoir information, help to improve the recovery rate, and provide technical support for the exploration and development of on-site oil and gas fields. Moreover, the method provided by the present invention can quickly obtain measurement results within a short experimental period. The method is suitable for rapid measurement of unconventional gas and oil storage formations and has the advantages of rapid, accurate and non-destructive detection.

[0043] The present invention utilizes nuclear magnetic resonance detection technology to calculate parameters such as sample oil saturation and displacement efficiency by converting nuclear magnetic resonance signals into oil volume. Based on the excellent ability of nuclear magnetic resonance to capture hydrogen signals, the fluctuation ability of different media in different pore sizes and pore types and the mobilization law of crude oil can be visualized to achieve comprehensive monitoring of the core displacement process. Compared with traditional displacement methods, the detection data provided by the present invention has higher accuracy.

[0044] The nuclear magnetic resonance method used in the present invention requires a small amount of core samples, greatly reduces the consumption and damage to the full-diameter cores taken out on site, and can achieve non-destructive testing.

[0045] The present invention performs nuclear magnetic resonance detection on a dried core sample to obtain a nuclear magnetic resonance T2 spectrum of the dried core sample, and obtains a sample base signal amount according to the nuclear magnetic resonance T2 spectrum of the dried core sample. After the base signal is removed from the nuclear magnetic resonance T2 spectrum of other core samples, the data processing result is more accurate.

[0046] The method adopted by the present invention has a simple test process, a single nuclear magnetic resonance test time of 20 to 30 minutes, and the entire process can be completed within 24 hours and a data report can be issued, which is time-saving.

[0047] Furthermore, compared with the soft pulse echo sequence, the present invention adopts the hard pulse echo sequence in nuclear magnetic resonance imaging, which can collect more short relaxation signals, making the imaging clearer. The present invention adopts a shorter echo time and a relatively long waiting time, which can collect more H proton signals, thereby improving the accuracy of the detection results. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the gas displacement experimental device of the present invention;

[0049] Figure 2 The process flow chart of the method for detecting the physical properties of the core using nuclear magnetic resonance and imaging technology of the present invention;

[0050] Figure 3 The NMR T2 spectra of the displacement core and the water-oil saturated core at each total displacement flow rate in Example 1;

[0051] Figure 4 The nuclear magnetic resonance imaging images of the displacement core and the saturated core at each total displacement flow rate in Example 1;

[0052] Figure 5 The simulated oil mark line in Example 1;

[0053] Figure 6 is the displacement efficiency spectrum in Example 1;

[0054] Figure 7 The NMR T2 spectra of the displacement core and the saturated core at various displacement flow rates in Comparative Example 1;

[0055] Figure 8 The nuclear magnetic resonance imaging images of the displacement core and the saturated core at each total displacement flow rate in Comparative Example 1;

[0056] Fig. 9 This is the displacement efficiency spectrum in Comparative Example 1. DETAILED DESCRIPTION

[0057] The present invention provides a core displacement method, comprising the following steps:

[0058] The dried core samples are sequentially subjected to heavy water flooding and oil flooding saturation to obtain water-oil saturated cores;

[0059] The water-oil saturated core is gas-displaced by using a hydrogen-free gas to obtain a displaced core.

[0060] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0061] The present invention sequentially performs heavy water displacement saturation and oil displacement saturation on a dried core sample to obtain a water-oil saturated core.

[0062] In the present invention, the core drying sample is preferably obtained by washing oil, washing salt and drying fresh core in sequence. In the present invention, the fresh core preferably includes a core obtained by drilling on-site in an oil field. The present invention has no special limitation on the oil washing, and washing is performed until no oil remains in the oil washing device. The present invention has no special limitation on the salt washing, and washing is performed until no salt remains in the device. In the present invention, the purpose of the oil washing and salt washing is to remove impurities in the core. In the present invention, the drying temperature is preferably 100-105°C, and in a specific embodiment, it can be 100°C, 101°C, 102°C, 103°C, 104°C or 105°C; the present invention has no special limitation on the drying time, and drying to constant weight is sufficient, such as 24h. In the present invention, the porosity of the core drying sample is preferably 5-12%, and in a specific embodiment, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%.

[0063] In the present invention, the process parameters for heavy water displacement saturation preferably include: an applied confining pressure of 10 to 15 MPa, which may be 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa or 15 MPa in a specific embodiment; a displacement pressure of 5 MPa; and a displacement flow rate of heavy water at the end of heavy water displacement saturation of 20 to 25 PV, which may be 20 PV, 21 PV, 22 PV, 23 PV, 24 PV or 25 PV in a specific embodiment.

[0064] In the present invention, the process parameters of the oil displacement saturation preferably include: the applied confining pressure is 10-15MPa, which can be 10MPa, 11MPa, 12MPa, 13MPa, 14MPa or 15MPa in a specific embodiment; the displacement pressure is 5MPa; the oil displacement flow rate at the end of the oil displacement saturation is 50-55PV, which can be 50PV, 5PV, 52PV, 53PV, 54PV or 55PV in a specific embodiment. In the present invention, the oil for oil displacement saturation preferably includes simulated oil, and the simulated oil preferably includes n-dodecane and on-site crude oil, and the volume ratio of n-dodecane to on-site crude oil is preferably 3:1.

[0065] In the present invention, the step of sequentially saturating the dried core sample with heavy water and oil preferably comprises: placing the dried core sample in a holder, applying a confining pressure of 10 to 15 MPa, and using a horizontal flow pump to displace the heavy water in the container into the core under a constant pressure of 5 MPa, with a final displacement flow rate of 20 to 25 PV, to obtain a heavy water-saturated core; removing the front end pipeline of the holder, connecting a container filled with oil, and injecting oil into the heavy water-saturated core at the same displacement pressure until no heavy water is driven out from the rear end of the holder, with a final displacement flow rate of 50 to 55 PV, to obtain a water-oil saturated core; water and oil coexist in the water-oil saturated core.

[0066] After obtaining the water-oil saturated core, the present invention uses a hydrogen-free gas to perform gas displacement on the water-oil saturated core to obtain a displacement core.

[0067] In the present invention, the hydrogen-free gas preferably includes at least one of carbon dioxide and nitrogen.

[0068] In the present invention, the confining pressure applied during the gas displacement is 10-15 MPa, and in specific embodiments may be 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa or 15 MPa.

[0069] In the present invention, the gas displacement includes constant pressure displacement and gradient flow displacement in sequence. In the present invention, the pressure of the constant pressure displacement is preferably 1-5MPa, and in specific embodiments it can be 1MPa, 2MPa, 3MPa, 4MPa or 5MPa; the volume of oil displaced by the constant pressure displacement accounts for 8-12% of the total volume of oil, and in specific embodiments it can be 8%, 9%, 10%, 11% or 12%. In the present invention, the total displacement flow of the gradient flow displacement is 5PV; the total displacement flow of hydrogen-free gas during the gradient flow displacement process (the total displacement flow of the first few times) is preferably 0.2PV, 0.4PV9, 0.6PV, 0.8PV, 1.2PV, 1.6PV and 5PV in sequence. The present invention adopts the above-mentioned gas displacement method, and the oil displacement efficiency is higher than that of liquid displacement.

[0070] In the present invention, the gas displacement operation preferably includes: placing the water-oil saturated core into the coil, opening the confining pressure valve, setting a certain confining pressure, turning on the gas source switch, turning on the air inlet switch and the balance switch, injecting hydrogen-free gas into the nuclear magnetic coil at a certain pressure through the pipeline, and controlling the gas flow and pressure through the pressure regulating valve. In the present invention, the material of the coil preferably includes polytetrafluoroethylene.

[0071] The present invention firstly displaces the core with heavy water containing no H proton signal, and then saturates the core with oil by displacing the heavy water with oil. In the case of saturated heavy water, when the oil enters the pore channel, only part of the heavy water will be displaced. At this time, the occurrence state of the core is a state of coexistence of water and oil, which is more consistent with the state of the core in the formation, thereby achieving the same conditions of indoor experiments as those at the oil field mining site, and the displacement efficiency obtained by gas displacement is basically the same as the actual displacement efficiency of the core crude oil during the on-site mining process, providing accurate data support for on-site production activities of the oil field.

[0072] The present invention provides a method for detecting the physical properties of a rock core using nuclear magnetic resonance and imaging technology, comprising the following steps:

[0073] Obtain the volume of the dried core sample to be tested;

[0074] The dried core sample to be tested is saturated with oil to obtain an oil-saturated core;

[0075] The dried core sample to be tested is subjected to heavy water displacement saturation and oil displacement saturation in sequence to obtain a water-oil saturated core; and the quality of the water-oil saturated core is tested;

[0076] Using a hydrogen-free gas to perform gas displacement on the water-oil saturated core to obtain a displacement core; recording the time of the gas displacement and the total volume of the driven oil;

[0077] Performing nuclear magnetic resonance detection on the dried core sample to be tested, the oil-saturated core, the saturated core and the displacement core, respectively, to obtain the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil-saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core and the displacement core;

[0078] Performing nuclear magnetic resonance imaging on the displacement core to obtain a nuclear magnetic resonance imaging image of the displacement core;

[0079] Providing an oil index line, wherein the oil index line takes the volume of the oil standard sample as an independent variable and the amount of the nuclear magnetic signal as a dependent variable; the standard oil sample is of the same type as the oil used for the oil displacement saturation;

[0080] Data processing is performed on the volume of the dried core sample, the mass of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the displacement core and the oil mark line to obtain the core physical property detection results.

[0081] The present invention detects the mass and volume (denoted as V) of the dried core sample to be tested. 样 ) and density. In the present invention, the volume is preferably detected using a density balance.

[0082] The present invention performs oil displacement saturation on the dried core sample to be tested to obtain an oil-saturated core.

[0083] In the present invention, the process conditions for oil displacement saturation preferably include: the applied confining pressure is 10-15MPa, which may be 10MPa, 11MPa, 12MPa, 13MPa, 14MPa or 15MPa in a specific embodiment; the displacement pressure is 3-7MPa, which may be 3MPa, 4MPa, 5MPa, 6MPa or 7MPa in a specific embodiment; the displacement flow rate of oil at the end of oil displacement saturation is 20-25PV, which may be 20-25PV in a specific embodiment. In the present invention, the oil for oil displacement saturation preferably includes simulated oil, and the composition of the simulated oil preferably includes n-dodecane and on-site crude oil, and the volume ratio of n-dodecane to on-site crude oil is preferably 3:1.

[0084] In the present invention, the oil displacement saturation preferably includes: placing the dried core sample to be tested in a clamp, applying a confining pressure of 10 to 15 MPa, and using a horizontal flow pump to displace the oil in the container into the core under a constant pressure of 5 MPa, with a final displacement flow rate of 20 PV to obtain an oil-saturated core.

[0085] After the oil displacement is saturated, the present invention preferably further comprises: washing the oil-saturated core with oil, washing the salt and drying it in sequence to obtain an oil-saturated core pretreatment sample.

[0086] The present invention sequentially performs heavy water displacement saturation and oil displacement saturation on the dried core sample to be tested to obtain a saturated core; detects the mass of the saturated core; performs gas displacement on the water-oil saturated core using a hydrogen-free gas to obtain a displacement core; and records the time of the gas displacement and the total volume of the driven oil. In the present invention, the process conditions of heavy water displacement saturation, oil displacement saturation and gas displacement are the same as the process conditions of heavy water displacement saturation, oil displacement saturation and gas displacement in the displacement method of the core in the above technical scheme, and are not repeated here. In the present invention, the mass is preferably detected using a density balance. In the present invention, the time of the gas displacement is preferably the time of constant pressure displacement. In the present invention, the dried core sample to be tested uses a core obtained by washing oil, washing salt and drying a fresh core or the oil-saturated core pretreatment sample.

[0087] The present invention performs nuclear magnetic resonance detection on the dried core sample to be tested, the oil-saturated core, the saturated core and the displacement core, respectively, and obtains the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil-saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core and the displacement core. In the present invention, the nuclear magnetic resonance T2 spectrum of the oil-saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core and the displacement core nuclear magnetic resonance T2 spectrum are all the results after removing the nuclear magnetic signal of the nuclear magnetic resonance T2 spectrum (base) of the dried core sample. .

[0088] In the present invention, the nuclear magnetic resonance detection is preferably low-field high-frequency nuclear magnetic resonance detection, the magnet frequency of the low-field high-frequency nuclear magnetic resonance detection is preferably ≥12MHz, and the echo time of the low-field high-frequency nuclear magnetic resonance detection is preferably ≤0.15ms, and in a specific embodiment, it can be 0.08-0.15ms. The present invention uses a low-field high-frequency nuclear magnetic resonance device to set a shorter echo time, and has a higher acquisition accuracy for fluids in nanopores of unconventional reservoirs. Compared with conventional low-field nuclear magnetic resonance devices, it has obvious advantages in signal-to-noise ratio, acquisition accuracy, and acquisition stability.

[0089] In the present invention, the conditions of the nuclear magnetic resonance detection preferably include: the sampling frequency (SW) is 200KHz, the waiting time (TW) is 4000ms, the analog gain (RG1) is 20db, the digital gain (DRG1) is 2, the cumulative number (NS) is 32, the echo time (TE) is 0.08ms, the number of echoes (NECH) is 15000, and the pre-release gear (PRG) is 1.

[0090] The present invention performs nuclear magnetic resonance imaging on the displacement core to obtain a nuclear magnetic resonance imaging image of the displacement core. In the present invention, the conditions of the nuclear magnetic resonance imaging include: the sampling sequence is a hard pulse (H_SE) echo sequence, the frequency offset (SFO1) is 12.796619MHz, the X-direction gradient (GxOffset) is 70, the Y-direction gradient (GyOffset) is 160, the Z-direction gradient (GzOffset) is -170, the waiting time (TR) is 500ms, the echo time (TE) is 5.885ms, the analog gain (RG1) is 10db, and the number of accumulations (Averages) is 8.

[0091] The present invention provides an oil mark line, wherein the oil mark line takes the volume of an oil standard sample as an independent variable and takes the amount of a nuclear magnetic signal as a dependent variable; the standard oil sample is of the same type as the oil used for oil displacement saturation.

[0092] In the present invention, the method for obtaining the oil mark line preferably includes the following steps: performing nuclear magnetic resonance detection on a series of oil standard samples of different volumes to obtain T2 spectra of oil of different volumes, drawing a scatter plot with the volume of the oil standard sample as the independent variable and the nuclear magnetic signal as the dependent variable, adding a trend line with an intercept of zero, and obtaining the oil mark line; the oil mark line is preferably y=kx, wherein k is the slope, x is the oil volume, and y is the nuclear magnetic signal of the corresponding volume of oil. In the present invention, the volumes of the series of oil standard samples of different volumes are preferably 0.1mL, 0.2mL, 0.3mL, 0.4mL and 0.5mL, respectively.

[0093] In the present invention, the principle of calibration of the oil mark line is: the amount of nuclear magnetic resonance signal is proportional to the amount of water in the sample under the same detection parameters. A group of standard samples with known water content are detected, and a curve of the amount of nuclear magnetic resonance signal is fitted. The amount of water contained in the sample can be calculated by substituting the measured signal of the detected sample into the curve equation, and the porosity of the sample can be obtained by dividing it by the sample volume.

[0094] The present invention processes data on the volume of the dried core sample, the mass of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the displacement core and the oil mark line to obtain the core physical property detection results.

[0095] In the present invention, the core physical properties preferably include one or more of core porosity, core oil saturation, core residual saturation, core displacement efficiency and displacement efficiency spectrum.

[0096] In the present invention, the calculation formula of the core porosity is shown in Formula 1:

[0097]

[0098] In formula 1, is the total porosity of the core, V 孔 V is the total pore volume of the dried core sample to be tested, 样 is the total volume of the dried core sample to be tested, S 油 is the nuclear magnetic signal of the oil-saturated core, and k is the slope of the oil mark line.

[0099] In the present invention, the calculation formula of the core oil saturation is shown in Formula 2:

[0100] S o =(S 油-水 / k / V 孔 )×100% Formula 2;

[0101] In formula 2, S o is the oil saturation of the oil-saturated core, k is the slope of the oil mark line, V 孔 is the total pore volume of the dried core sample to be tested, S 油-水 is the nuclear magnetic signal of the water-oil saturated core. The oil saturation at this time is the maximum oil saturation.

[0102] In the present invention, the calculation formula of the core residual saturation (the amount of oil remaining in the core after each gas displacement is completed) is shown in Formula 3:

[0103] S or =S n / (k×V 油 )×100% Formula 3;

[0104] In formula 3, S or is the residual saturation of the core, S n is the nuclear magnetic signal of the displacement core, k is the slope of the oil mark line, V 油 is the volume of oil in the pores of the oil-saturated core.

[0105] In the present invention, the calculation formula of the core displacement efficiency is shown in Formula 4:

[0106] E=(S 油-水- S n ) / S 油-水 ×100% Formula 4;

[0107] In formula 4, E is the core displacement efficiency, S n is the nuclear magnetic signal of the displacement core, S 油-水 is the NMR signal of the water-oil saturated core.

[0108] In the present invention, the displacement efficiency spectrum preferably takes the displacement flow rate of hydrogen-free gas as the independent variable and the core displacement efficiency as the dependent variable.

[0109] The present invention utilizes nuclear magnetic resonance detection technology to calculate parameters such as sample oil saturation and displacement efficiency by converting nuclear magnetic resonance signals into oil volume. Based on the excellent ability of nuclear magnetic resonance to capture hydrogen signals, the fluctuation ability of different media in different pore sizes and pore types and the mobilization law of crude oil can be visualized to achieve comprehensive monitoring of the core displacement process. Compared with traditional displacement methods, the detection data provided by the present invention has higher accuracy.

[0110] The nuclear magnetic resonance method used in the present invention requires a small amount of core samples, greatly reduces the consumption and damage to the full-diameter cores taken out on site, and can achieve non-destructive testing.

[0111] The present invention performs nuclear magnetic resonance detection on a dried core sample to obtain a nuclear magnetic resonance T2 spectrum (baseline) of the dried core sample, and obtains a sample basement signal amount according to the nuclear magnetic resonance T2 spectrum of the dried core sample. After the basement signal is removed from the nuclear magnetic resonance T2 spectrum of other core samples, the data processing result is more accurate.

[0112] The method adopted by the present invention has a simple test process, a single nuclear magnetic resonance test time of 20 to 30 minutes, and the entire process can be completed within 24 hours and a data report can be issued, which is time-saving.

[0113] Furthermore, compared with the soft pulse echo sequence, the present invention adopts the hard pulse echo sequence in nuclear magnetic resonance imaging, which can collect more short relaxation signals, making the imaging clearer. The present invention adopts a shorter echo time and a relatively long waiting time, which can collect more H proton signals, thereby improving the accuracy of the detection results.

[0114] In order to further illustrate the present invention, the core displacement method provided by the present invention and the method for detecting the physical properties of the core using nuclear magnetic resonance and imaging technology are described in detail below in combination with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0115] Experimental materials: simulated oil (the volume ratio of n-dodecane to on-site crude oil is preferably 3:1), carbon dioxide cylinder.

[0116] Experimental instruments: Large aperture nuclear magnetic resonance imaging analyzer, resonance frequency of 12 MHz, probe coil diameter of 1 inch, magnet temperature of 32 ° C. The saturated sample volume was detected by a density balance;

[0117] Magnetic resonance equipment parameter debugging: Turn on the nuclear magnetic resonance instrument, turn on the temperature control system to start temperature control, wait for the temperature on the instrument display to stabilize at 40°C for a period of time, then open the analysis and detection software, turn on the radio frequency, turn on the FID sequence to calibrate the instrument center frequency, find the pulse width, and turn on the CPMG sequence to set appropriate parameters.

[0118] Debugging of imaging parameters of nuclear magnetic resonance equipment: Place the standard oil sample into the nuclear magnetic resonance coil made of tetrafluoroethylene, open the imaging detection software, click the "PRESCAN" button to calibrate the center frequency, find the pulse width and amplitude, and open the H_SE sequence to set appropriate parameters.

[0119] During the nuclear magnetic resonance imaging detection process, when the total displacement flow of the gas displacement reaches a certain amount, the axial pressure is suspended, the nuclear magnetic resonance imaging measurement software is opened to set the main frequency, the nuclear magnetic resonance forming parameters are set, the scan button is clicked, and the imaging data is saved in the target folder after waiting for 30 minutes, completing one imaging data acquisition.

[0120] Example 1 (experimental group)

[0121] use Figure 1 The device is according to Figure 2 The flow chart shown uses low-field high-frequency nuclear magnetic resonance and imaging technology to detect the distribution characteristics of crude oil in the core.

[0122] NMR parameter settings: sampling frequency SW = 200KHz; waiting time TW = 4000ms; analog gain RG1 = 20db; digital gain DRG1 = 2; accumulation times NS = 32; echo time TE = 0.08ms; number of echoes NECH = 15000; preamplifier position PRG = 1.

[0123] Magnetic resonance imaging parameter settings: the sampling sequence is a hard pulse (H_SE) echo sequence, frequency offset SFO1 = 12.796619 MHz, X-direction gradient GxOffset = 70, Y-direction gradient GyOffset = 160, Z-direction gradient GzOffset = -170, waiting time TR = 500 ms, echo time TE = 5.885 ms, analog gain RG1 = 10 db, and accumulation times Averages = 8.

[0124] S1 Sample pretreatment: Select a core sample with a diameter of 25 mm and a length of 6 cm, wash it with oil, wash it with salt, and dry it at 105℃ for 24 hours, put it in a drying dish and cool it to room temperature to obtain a core drying sample. Detect the volume of the core drying sample (V 样 ), perform nuclear magnetic resonance detection on the dried core sample to obtain the nuclear magnetic resonance T2 spectrum of the dried core sample.

[0125] S2 Sample oil saturation: The dried core sample is placed in a holder, a confining pressure of 13 MPa is applied, and a heavy water is used with a horizontal flow pump to displace the simulated oil into the dried core sample at a constant pressure of 5 MPa. The final displacement flow rate is 20 PV to obtain an oil-saturated core. The saturated simulated oil sample is tested by nuclear magnetic resonance to obtain the nuclear magnetic signal of the oil-saturated core (S 油 ), after the test, the sample is washed with oil, washed with salt and dried to obtain an oil-saturated core pretreatment sample.

[0126] S3 sample is saturated with water and oil: the oil-saturated core pretreatment sample is placed in a clamp, and a confining pressure of 13MPa is applied. The heavy water in the intermediate container is saturated with heavy water into the dried core sample at a constant pressure of 5MPa using a horizontal flow pump. The final displacement flow rate is 20PV to obtain a saturated heavy water core; the front end pipeline of the clamp is removed, and an intermediate container filled with simulated oil is connected. The simulated oil is injected into the saturated heavy water core at the same displacement pressure until no heavy water is driven out from the tail end of the clamp. The final displacement flow rate is 50PV, and the core is in a state of water and oil coexistence, and a water-oil saturated core is obtained. Take out the water-oil saturated core, wipe off the floating oil on the surface (avoid sucking out the oil in the core when wiping dry), wrap it with raw tape and put it into the nuclear magnetic resonance instrument for nuclear magnetic resonance detection to obtain the water-oil saturated core nuclear magnetic resonance T2 spectrum, see Figure 3 After the test, remove the raw material belt and measure the quality of the water-oil saturated core.

[0127] S4 sample constant pressure gas displacement: place the water-oil saturated core into the core holder, turn on the peripheral horizontal flow pump of the large aperture nuclear magnetic resonance imaging analyzer, inject a confining pressure of 12MPa, and when the display on the horizontal flow pump shows the upper limit (20MPa), connect the inlet end of the holder to the carbon dioxide gas cylinder, set the displacement pressure to 1MPa, and continuously and stably drive out the carbon dioxide gas in the gas cylinder, observe the liquid discharge at the tail end of the holder, and when the total volume of oil driven out in the measuring cylinder accounts for 10% of the pore volume of the sample, close the air inlet channel of the inlet section of the holder, suspend the displacement, and obtain the constant pressure displacement core; record the total volume of oil driven out in the measuring cylinder, and record the duration of this displacement. Perform nuclear magnetic resonance detection on the constant pressure displacement core to obtain the nuclear magnetic resonance T2 spectrum of the constant pressure displacement core (the nuclear magnetic signal value is recorded as S n ), and the nuclear magnetic resonance T2 spectrum and imaging data of the constant pressure displacement core were processed using nuclear magnetic resonance analysis software and nuclear magnetic resonance imaging software, respectively.

[0128] S5 Sample gradient flow displacement: Set the total carbon dioxide displacement flow rate to 0.4PV, 0.8PV, 1.2PV, 1.6PV, and 5PV in 7 gradient experiments, repeat step S4 until no simulated oil is displaced from the end of the clamp, and obtain the displacement core. The NMR T2 spectra of the displacement core at each total displacement flow rate are shown in Figure 3 , Magnetic resonance imaging is shown in Figure 4 , Figure 4 The displacement directions of carbon dioxide in each graph are the same, and the direction of the arrow is the displacement direction of carbon dioxide.

[0129] S6 simulated oil calibration: Use a pipette to drop 0.1mL, 0.2mL, 0.3mL, 0.4mL and 0.5mL of simulated oil into the sample bottle, and perform NMR detection on the sample bottles with different volumes of simulated oil to obtain the NMR T2 spectra of simulated oil with different volumes. Draw a scatter plot with simulated oil volume as the independent variable and NMR signal as the dependent variable, add a trend line with zero intercept, and obtain the simulated oil calibration line, see Figure 5 , the simulated oil line equation y = kx, where k is the slope, x is the simulated oil volume, and y is the nuclear magnetic signal of the corresponding volume of simulated oil. y = kx is specifically y = 10020x, R 2 =0.9936.

[0130] S7 data processing: draw T2 spectrum, process the data of core porosity, core displacement efficiency, core oil saturation and remaining core oil saturation, and process the raw data of imaging detection into image results through imaging processing software. The data processing process is as follows:

[0131] ① Calculate the core porosity

[0132] Core porosity Definition: The ratio of the sum of the volumes of all pore spaces in a rock sample to the volume of the rock sample.

[0133] V 孔 =V 油 , V 油 is the simulated oil volume in the oil-saturated core in step S2. The simulated oil volume can be calculated using the corresponding simulated oil mark line, that is, V 孔 =V 油 =S 油 / k, the core porosity calculation formula is: in, is the total porosity of the core, V 孔 V is the total pore volume of the dried core sample to be tested, 样 is the total volume of the dried core sample to be tested, S 油 is the nuclear magnetic signal of the oil-saturated core, and k is the slope of the oil mark line. The core porosity calculation results are shown in Table 1.

[0134] ② Calculate the oil saturation of the core

[0135] The oil saturation of the oil-saturated core in step S2 is defined as 100%, and the residual saturation of the core after gas displacement is: S or =(S n / k / V油 )×100%=S n / (k×V 油 )×100%, where S n is the nuclear magnetic signal of the displacement core.

[0136] The calculation formula for core oil saturation is: S o =(S 油-水 / k / V 孔 )×100%, where S o is the oil saturation of the oil-saturated core, S 油-水 is the nuclear magnetic signal of the water-oil saturated core, k is the slope of the oil mark line, V 孔 is the total pore volume of the dried core sample to be tested.

[0137] ③ Calculate the core displacement efficiency: E = (S 油-水- S n ) / S 油-水 × 100%, where E is the core displacement efficiency, S n is the nuclear magnetic signal of the displacement core, S 油-水 is the NMR signal of the water-oil saturated core. Figure 6 .

[0138] ④ Draw the displacement efficiency spectrum: Draw the gas-to-oil displacement efficiency spectrum with the total displacement flow (carbon dioxide) as the independent variable and the displacement efficiency as the dependent variable.

[0139] ⑤ Import the raw imaging data into the magnetic resonance imaging processing software to complete the processing and export the imaging image.

[0140] Comparative Example 1 (control group)

[0141] The only difference from Example 1 is:

[0142] In the NMR parameter setting, the waiting time TW=3000ms and the echo time TE=0.15ms.

[0143] In the MRI parameter setting, the sampling sequence is a soft pulse (SE) echo sequence, the frequency offset SFO1 = 12.796619 MHz, the X-direction gradient GxOffset = 70, the Y-direction gradient GyOffset = 160, the Z-direction gradient GzOffset = -170, the waiting time TR = 500 ms, the echo time TE = 5.885 ms, the analog gain RG1 = 10 db, and the accumulation number Averages = 8. The data processing results are shown in Tables 1, 3 and Figures 7 to 9 ,in, Figure 7 The NMR T2 spectra of the displacement core and saturated core at each displacement flow rate are shown in Figure 2. Figure 8The NMR images of the displacement core and saturated core at each total displacement flow rate are shown in Figure 2. Figure 8 The displacement directions of each carbon dioxide are the same, and the arrow direction is the carbon dioxide displacement direction. Fig. 9 is the displacement efficiency spectrum.

[0144] Table 1 Comparison of core properties in Example 1 and Comparative Example 1

[0145] serial number Core dry sample volume / mL Core dry sample pore volume / mL Porosity / % Example 1 24.008 2.480 10.33 Comparative Example 1 23.496 2.461 10.48

[0146] Table 2 Test results of core samples in Example 1

[0147]

[0148] Table 3 Test results of core samples in comparative example 1

[0149]

[0150] From Tables 1 to 3 and Figures 3 to 9 It can be seen that according to the comparative analysis of the T2 spectra of Example 1 and Comparative Example 1, the detection conditions selected by the present invention can measure more signal amounts, and the specific signal amount increases in the medium and short relaxation parts, indicating that the method provided by the present invention can collect more crude oil signals stored in small and medium pores.

[0151] According to the comparison of the nuclear magnetic resonance imaging of Example 1 and Comparative Example 1, the imaging image detected by the H_SE sequence is brighter, can collect more short relaxation signals, and can reflect more information of small holes.

[0152] As the total displacement flow of carbon dioxide continues to increase, the signal volume in the core shows a step-down trend, and the displacement efficiency at the final equilibrium point is 49.97%; according to the analysis of the nuclear magnetic imaging diagram, the pore size distribution of the core in this layer is relatively uniform, with medium and large pores being the majority, the crude oil is evenly distributed, and there are no obvious cracks in the core. The detection data provided by the present invention can provide accurate data information for on-site oil production in oil fields.

[0153] The present invention uses low-field high-frequency nuclear magnetic resonance technology T2 spectrum and nuclear magnetic resonance imaging detection technology to comprehensively monitor and analyze the distribution of each fluid in each core sample. First, nuclear magnetic resonance detection is performed on the core drying sample to obtain the nuclear magnetic T2 spectrum of the core drying sample; then the core drying sample is placed in a coil made of polytetrafluoroethylene, and the confining pressure and displacement flow are applied according to the experimental requirements to carry out the displacement experiment, and the nuclear magnetic resonance T2 spectrum and imaging detection are carried out during the experiment; data processing adopts nuclear magnetic resonance calibration (oil mark line), and the nuclear magnetic resonance signal is converted to calculate the porosity, oil saturation, displacement efficiency and imaging map of the sample, and then the monitoring of the state of the core in each time period in the whole displacement process (heavy water displacement saturation, oil displacement saturation, gas displacement) is realized. Moreover, the present invention first displaces the core with heavy water that does not contain H proton signals, and then saturates the simulated oil by using simulated oil to displace heavy water. In the case of saturated heavy water, when the simulated oil enters the pore channel, only part of the heavy water will be displaced. At this time, the occurrence state of the core is a state of coexistence of water and oil, which is more consistent with the state of the core in the formation, thereby achieving the same conditions of the indoor experiment as the conditions at the oil field production site. The detection data provided by the present invention can provide accurate data information for on-site oil production in the oil field.

[0154] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A core displacement method, characterized in that: The following steps are involved: The core dried samples were subjected to heavy water flooding and oil flooding saturation in sequence to obtain water-oil saturated cores; The water-oil saturated core is gas-displaced by using a hydrogen-free gas to obtain a displaced core.

2. The displacement method according to claim 1, characterized in that: The porosity of the dried core sample is 5-12%; The process parameters of heavy water displacement saturation include: an applied confining pressure of 10-15 MPa, a displacement pressure of 3-7 MPa, and a displacement flow rate of heavy water of 20-25 PV at the end of heavy water displacement saturation.

3. The displacement method according to claim 1, characterized in that: The process parameters of the oil displacement saturation include: the applied confining pressure is 10-15 MPa, the displacement pressure is 5 MPa, and the oil displacement flow rate at the end of the oil displacement saturation is 50-55 PV.

4. The displacement method according to claim 1, characterized in that: The hydrogen-free gas includes at least one of carbon dioxide and nitrogen; The gas displacement includes constant pressure displacement and gradient flow displacement in sequence; the pressure of the constant pressure displacement is 1-5MPa, and the volume of oil displaced by the constant pressure displacement accounts for 8-12% of the total oil volume; the total displacement flow of the gradient flow displacement is 5PV; the confining pressure applied during the gas displacement is 10-15MPa.

5. The displacement method according to claim 1 or 4, characterized in that: The total displacement flow rate of hydrogen-free gas during the gradient flow displacement process is 0.4PV, 0.8PV, 1.2PV, 1.6PV and 5PV respectively.

6. A method for detecting the physical properties of a core using nuclear magnetic resonance and imaging technology, characterized in that: The following steps are involved: Obtain the volume of the dried core sample to be tested; The dried core sample to be tested is saturated with oil to obtain an oil-saturated core; The dried core sample to be tested is subjected to heavy water displacement saturation and oil displacement saturation in sequence to obtain a water-oil saturated core; and the quality of the water-oil saturated core is tested; Using a hydrogen-free gas to perform gas displacement on the water-oil saturated core to obtain a displacement core; recording the time of the gas displacement and the total volume of the driven oil; Performing nuclear magnetic resonance detection on the dried core sample to be tested, the oil-saturated core, the saturated core and the displacement core, respectively, to obtain the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil-saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core and the displacement core; Performing nuclear magnetic resonance imaging on the displacement core to obtain a nuclear magnetic resonance imaging image of the displacement core; Providing an oil index line, wherein the oil index line takes the volume of the oil standard sample as an independent variable and the amount of the nuclear magnetic signal as a dependent variable; the standard oil sample is of the same type as the oil used for the oil displacement saturation; Data processing is performed on the volume of the dried core sample, the mass of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the dried core sample, the nuclear magnetic resonance T2 spectrum of the oil saturated core, the nuclear magnetic resonance T2 spectrum of the water-oil saturated core, the nuclear magnetic resonance T2 spectrum of the displacement core and the oil mark line to obtain the core physical property detection results.

7. The method according to claim 1, characterized in that The nuclear magnetic resonance detection is a low-field high-frequency nuclear magnetic resonance detection, and the magnet frequency of the low-field high-frequency nuclear magnetic resonance detection is ≥12MHz, and the echo time is ≤0.15ms.

8. The method according to claim 6 or 7, characterized in that: The conditions of the nuclear magnetic resonance detection include: a sampling frequency of 200KHz, a waiting time of 4000ms, an analog gain of 20db, a digital gain of 2, an accumulation number of 32, an echo time of 0.08ms, an echo number of 15000, and a preamplifier gear of 1.

9. The method according to claim 6, characterized in that The conditions of the nuclear magnetic resonance imaging include: the sampling sequence is a hard pulse echo sequence, the frequency offset is 12.796619 MHz, the X-direction gradient is 70, the Y-direction gradient is 160, the Z-direction gradient is -170, the waiting time is 500 ms, the echo time is 5.885 ms, the analog gain is 10 db, and the number of accumulations is 8.

10. The method according to claim 6, characterized in that The core physical properties include one or more of core porosity, core oil saturation, core residual saturation, core displacement efficiency and displacement efficiency spectrum; The calculation formula of the core porosity is shown in Formula 1: φ=S 油 / (k×V 样 )×100% Formula 1; In formula 1, φ is the total porosity of the core, V 孔 V is the total pore volume of the dried core sample to be tested, 样 is the total volume of the dried core sample to be tested, S 油 is the nuclear magnetic signal of the oil-saturated core, k is the slope of the oil mark line; The calculation formula of the core oil saturation is shown in Formula 2: S o =(S 油-水 / k / V 孔 )×100% Formula 2; In formula 2, S o is the oil saturation of the oil-saturated core, S 油-水 is the nuclear magnetic signal of the water-oil saturated core, k is the slope of the oil mark line, V 孔 is the total pore volume of the dried core sample to be tested; The calculation formula of the core residual saturation is shown in Formula 3: S or =S n / (k×V 油 )×100% Formula 3; In formula 3, S or is the residual saturation of the core, S n is the nuclear magnetic signal of the displacement core, k is the slope of the oil mark line, V 油 is the volume of oil in the pores of the oil-saturated core; The calculation formula of the core displacement efficiency is shown in Formula 4: E=(S 油-水- S n ) / S 油-水 ×100% Formula 4; In formula 4, E is the core displacement efficiency, S n is the nuclear magnetic signal of the displacement core, S 油-水 is the NMR signal of the water-oil saturated core; The displacement efficiency spectrum line takes the displacement flow rate of hydrogen-free gas as the independent variable and the core displacement efficiency as the dependent variable.

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