CN112505084A - Evaluation model, evaluation method and application for improving shale oil mobility through gas injection - Google Patents

Evaluation model, evaluation method and application for improving shale oil mobility through gas injection Download PDF

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CN112505084A
CN112505084A CN202011373009.9A CN202011373009A CN112505084A CN 112505084 A CN112505084 A CN 112505084A CN 202011373009 A CN202011373009 A CN 202011373009A CN 112505084 A CN112505084 A CN 112505084A
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shale
oil
nuclear magnetic
gas injection
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CN112505084B (en
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王民
李明
张金旭
卢双舫
李进步
许承武
胡慧婷
李婷婷
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China University of Petroleum East China
Northeast Petroleum University
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Northeast Petroleum University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
    • G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
    • G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/34—Purifying; Cleaning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
    • G01N2001/2873—Cutting or cleaving

Abstract

The invention relates to the technical field of petroleum development, and particularly discloses an evaluation model, an evaluation method and application for improving shale oil mobility through gas injection. The evaluation model for improving the mobility of the shale oil by gas injection provided by the invention is based on the fact that a nuclear magnetic resonance instrument is used in a gas injection displacement experiment, nuclear magnetic signals of samples can be measured in real time, nuclear magnetic resonance detection is carried out on the samples in different states in the experiment process, and the distribution characteristics of crude oil in the samples in different stages are further analyzed according to the variation characteristics of a nuclear magnetic spectrum, so that the mobility of the shale oil under the gas injection condition is evaluated, and the problem that the conventional evaluation method for improving the mobility of the shale oil by gas injection mostly adopts a numerical simulation method and has poor persuasion is solved. The evaluation method provided by the time is strong in operability, can analyze the mobility change of crude oil with different apertures under the condition of shale oil gas injection, provides guidance opinions for later-stage mine tests, is high in reproducibility, and has practical significance for effective development of shale oil.

Description

Evaluation model, evaluation method and application for improving shale oil mobility through gas injection
Technical Field
The invention relates to the technical field of petroleum development, in particular to an evaluation model, an evaluation method and application for improving shale oil mobility through gas injection.
Background
With the continuous development of science and technology, the demand of people for energy is also increasing. Among them, shale oil is a petroleum resource contained in shale layers, and the resource amount thereof is huge, so that the exploration and development of shale oil is considered as an important strategic measure for solving the shortage of oil and gas resources. Although the amount of shale oil resources in China is huge, two same problems are faced in the development process: i.e., short well life (typically less than 10 years), extremely low recovery (3% -10%). Due to the small pore diameter of shale, the complex pore throat structure and the high content of organic matters, in addition, the stratum pressure of part of shale intervals is low, the pressure conduction efficiency is poor, shale oil is difficult to seep out of shale (or an interlayer) only depending on self energy, or the productivity is limited, so that the shale oil has the characteristics of rapid attenuation of stratum energy and rapid reduction of yield in the mining process. How to improve the shale oil recovery ratio by supplementing the formation energy and efficiently and economically increase the micro and macro movable oil quantity of the shale oil is a technical bottleneck to be solved urgently in the development of the shale oil.
At present, in order to improve the recovery rate of shale oil by supplementing formation energy and efficiently and economically increase the micro and macro movable oil quantity of the shale oil,numerous solutions have been proposed, among which the supplementation of shale oil intervals with gas injection is considered to be the most promising. Commonly used implant dielectrics include N2、CO2、CH4And a hydrocarbon-rich gas. However, for improving the mobility of shale oil through gas injection, a numerical simulation method is mainly adopted for research at present, and the research in the related field is weak due to the lack of indoor physical experiment support. Therefore, numerical simulation methods are mostly adopted in evaluation methods for improving shale oil mobility based on gas injection in the prior art, and the evaluation results are poor in persuasion and the like.
Disclosure of Invention
The embodiment of the invention aims to provide an evaluation model for improving shale oil mobility through gas injection, so as to solve the problems that most of the existing evaluation methods for improving shale oil mobility based on gas injection in the background art adopt numerical simulation methods, and the evaluation results are poor in persuasion and the like.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
an evaluation model for improving shale oil mobility by gas injection is shown as the following formula (1):
Figure BDA0002807347500000021
wherein, in the formula (1)
ηtXRepresenting the movable proportion of shale oil of the shale rock sample at the time x; the method comprises the following steps that a shale rock sample to be evaluated is obtained by sequentially cutting an original core sample of shale or shale to be evaluated, removing residual oil in pores and drying the original core sample to obtain a dry shale sample, then performing nuclear magnetic resonance test on the dry shale sample, vacuumizing and pressurizing saturated oil, aging the dry shale sample, then taking out the aged saturated oil sample, performing nuclear magnetic resonance test on the aged saturated oil sample, then performing a gas injection displacement experiment on the aged saturated oil sample, and performing nuclear magnetic resonance test on the aged saturated oil sample at different moments in the gas injection displacement process;
a1 is NMR T obtained by NMR test of shale dried sample2Semaphore, A2, is NMR T obtained by NMR testing of aged saturated oil samples2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2And (4) signal quantity.
As a further scheme of the invention: the evaluation model for improving the shale oil mobility by gas injection further comprises the calculation of the movable oil quantity of shale oil at the time x of the shale rock sample shown in the following formula (2):
Figure BDA0002807347500000022
in the formula (2), VtX is movableRepresenting the movable oil quantity of shale oil of the shale rock sample at the time x; a2 is NMR T obtained by NMR measurement of aged saturated oil sample2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2A semaphore; and a, fitting the linear relation between corresponding signal amplitudes obtained by performing nuclear magnetic resonance tests on crude oil fluids under different volume conditions respectively during vacuumizing and pressurizing saturated oil by using a statistical linear regression method to obtain the slope of a graticule equation.
It should be noted that Nuclear Magnetic Resonance (NMR) has been widely used in well logging and core analysis, and compared with the conventional gas injection enhanced recovery evaluation method, NMR can reflect the porosity, pore throat structure and the pore diameters of different fluids, and the technique is less affected by factors and is not substantially affected by mud shale cracks, clay minerals and sample specifications. However, research on the evaluation of shale gas injection mobility enhancement by nuclear magnetic resonance is still in the beginning. The evaluation model for improving the shale oil mobility through gas injection provided by the embodiment of the invention is combined with a nuclear magnetic-displacement device, and the nuclear magnetic resonance device is adopted to evaluate the gas injection and improve the shale oil mobility, so that the parameters in the development process of shale oil resources can be determined, and compared with a numerical simulation method, the evaluation result is more visual and accurate.
Another object of an embodiment of the present invention is to provide an evaluation method for improving shale oil mobility by using the above-mentioned gas injection model, which specifically includes the following steps: sequentially cutting an original core sample of shale or mud shale to be evaluated, removing residual oil in pores and drying to obtain a dry shale sample, performing nuclear magnetic resonance test on the dry shale sample, vacuumizing and pressurizing saturated oil, aging for 25-30 days, taking out the aged saturated oil sample, performing nuclear magnetic resonance test on the aged saturated oil sample, putting the aged saturated oil sample into a nuclear magnetic resonance-displacement device for gas injection displacement experiment, performing nuclear magnetic resonance test on the aged saturated oil sample at different moments in the gas injection displacement process, and performing nuclear magnetic resonance T-shaped (T-shaped) test on the dry shale sample, the aged saturated oil sample and the aged saturated oil sample in the gas injection displacement process2And (4) signal quantity, calculating the movable proportion of shale oil of the shale rock sample at different moments so as to evaluate the mobility of the shale oil under the condition of gas injection.
Another object of the embodiments of the present invention is to provide an application of the evaluation method in shale oil exploration and development.
Compared with the prior art, the invention has the beneficial effects that:
the evaluation model for improving shale oil mobility through gas injection provided by the embodiment of the invention is based on the fact that nuclear magnetic resonance instruments are used in a gas injection displacement experiment, nuclear magnetic signals of samples can be measured in real time, nuclear magnetic resonance detection is carried out on samples in different states in the experiment process, processing and analysis are carried out according to the change characteristics of nuclear magnetic spectrums, and the distribution characteristics of crude oil in the samples in different stages can be obtained, so that mobility of shale oil under the gas injection condition is evaluated, and the problem that the evaluation result is inaccurate due to the fact that numerical simulation methods are mostly adopted in existing evaluation methods for improving shale oil mobility through gas injection is solved. The provided evaluation method is strong in operability, evaluates the shale oil gas injection effect based on an indoor physical simulation experiment by means of a nuclear magnetic resonance instrument, is clear in experimental thought and strict in experimental process, can perform nuclear magnetic resonance test on a sample at any moment, analyzes the change of the mobility of crude oil with different apertures under the shale oil gas injection condition, provides guidance for later-stage mine field tests, is high in reproducibility, has practical significance on effective development of shale oil, and has wide application prospects.
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Fig. 1 is a schematic flow chart of an evaluation model for improving shale oil mobility through gas injection according to an embodiment of the present invention.
Fig. 2 is a schematic view of an nmr displacement apparatus according to another embodiment of the present invention.
Fig. 3 is a schematic diagram of the interior of a magnet housing in an nmr displacement apparatus according to another embodiment of the invention.
Fig. 4 is a schematic cross-sectional view of the inside of a magnet housing in an nmr displacement apparatus according to another embodiment of the invention.
FIG. 5 shows NMR T of shale in dry sample, saturated oil and gas injection displacement states at different times according to another embodiment of the present invention2Spectra.
FIG. 6 shows NMR T of n-dodecane in different volumes2Spectra.
FIG. 7 is a graph of the plot equation between n-dodecane fluid volume and nuclear magnetic signal volume.
FIG. 8 is a schematic diagram showing the variation of crude oil content in shale with different pore size ranges in another embodiment of the present invention.
Wherein, in the schematic diagram of the nuclear magnetic resonance-displacement device: 1-a gas cylinder; 2-an air compressor; 3-gas booster pump; 4-confining pressure liquid container; 5-a first circulation pump; 6-a magnet box; 7-a second circulation pump; 8-a back pressure valve; 9-a pump body; 10-a radio frequency device; 11-a computer; 12-a receiving member.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Aiming at the prior technical scheme, the evaluation model for improving the mobility of shale oil through gas injection provided by the embodiment of the invention is shown as the following formula (1):
Figure BDA0002807347500000051
wherein, the formula (1) is used for calculating the movable proportion of shale oil (the proportion of the movable reserve of crude oil to the total content of crude oil);
in the formula (1), etatXRepresenting the movable proportion of shale oil of the shale rock sample at the time x (in the process of gas injection displacement); the shale rock sample is obtained by sequentially cutting an original core sample of shale or mud shale to be evaluated, removing residual oil in pores and drying to obtain a shale dry sample, and then performing nuclear magnetic resonance test on the shale dry sample to obtain a corresponding nuclear magnetic resonance T2Measuring signal amount, vacuumizing and pressurizing saturated oil, aging for 25-30 days, taking out an aged saturated oil sample, and performing nuclear magnetic resonance test on the aged saturated oil sample to obtain corresponding nuclear magnetic resonance T2Measuring the signal quantity, then putting the aged saturated oil sample into a nuclear magnetic resonance-displacement device for gas injection displacement experiment, wherein in the gas injection displacement experiment, the nuclear magnetic resonance instrument is used for measuring the nuclear magnetic signals of the sample in real time, namely, the nuclear magnetic resonance test is carried out on the aged saturated oil sample at different moments in the gas injection displacement process to obtain the nuclear magnetic resonance T at the corresponding moment2A semaphore; after the gas injection displacement experiment is finished, processing and analyzing the data to obtain the distribution characteristics of the crude oil in the samples at different stages, so as to evaluate the mobility of the shale oil under the gas injection condition;
a1 is NMR T obtained by NMR test of shale dried sample2Semaphore, A2, is NMR T obtained by NMR testing of aged saturated oil samples2The signal quantity Ax is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2And (4) signal quantity.
As another preferred embodiment of the present invention, the removing of the residual oil in the pores is performed by using a soxhlet extraction method or an ultrasonic method, wherein the soxhlet extraction method or the ultrasonic method is used to remove the residual oil in the pores of the cut sample after the original core sample of the shale or mud shale to be evaluated is cut to obtain the cut sample, and the solvent used in the soxhlet extraction method or the ultrasonic method is a mixed organic solvent of dichloromethane and acetone, wherein the volume ratio of dichloromethane to acetone is 3: 1.
Preferably, the solvent used in the Soxhlet extraction method or the ultrasonic method is a mixed organic solvent of dichloromethane and acetone in a volume ratio of 3: 1.
In another preferred embodiment of the present invention, the crude oil fluid used for the saturated oil may be n-dodecane, or other organic solvent, such as any one of benzene, toluene, xylene, pentane, hexane, cyclohexane, octane, n-octadecane, and dichloromethane, and n-dodecane is preferred.
As another preferred embodiment of the present invention, the evaluation model for improving the mobility of shale oil by gas injection further comprises a calculation process of the amount of the mobile oil of shale oil at the time x of the shale rock sample as shown in the following formula (2):
Figure BDA0002807347500000061
in the formula (2), VtX is movableRepresenting the movable oil quantity of shale oil of the shale rock sample at the time x; a2 is NMR T obtained by NMR measurement of aged saturated oil sample2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2A semaphore; and a, fitting the linear relation between corresponding signal amplitudes obtained by performing nuclear magnetic resonance tests on different volumes of crude oil fluid adopted in the process of vacuumizing and pressurizing saturated oil by using a statistical linear regression method to obtain the slope of a graticule equation.
As another preferred embodiment of the invention, the data is processed and analyzed after the gas injection displacement experiment is finished, and the data is processed and analyzed through VtX is movableIs calculated byThe corresponding crude oil variable quantity in the samples at different stages is obtained through an etatXThe distribution characteristics of the crude oil in the samples at different stages are obtained through the calculation formula, and the content and the distribution characteristics of the crude oil in the samples at different stages can be obtained, so that the mobility of the shale oil under the gas injection condition is evaluated.
As another preferred embodiment of the present invention, the method for obtaining a in formula (2) is to perform NMR test on different volumes of crude oil fluid (preferably n-dodecane) to obtain NMR T corresponding to each volume2Fitting the linear relation between the volume of the crude oil fluid and the corresponding signal amplitude by utilizing a statistical linear regression method to obtain a marked line equation system represented by the following formula (3):
Figure BDA0002807347500000071
wherein in formula (3), a is the slope of the (fluid-calibrated) reticle equation represented by formula (3), M0The total nuclear magnetic signal of the crude oil fluid (preferably the total nuclear magnetic signal of n-dodecane), VOilRepresents the volume of the crude oil fluid; the linear relation between the volume of the crude oil fluid and the corresponding signal quantity of the crude oil fluid for nuclear magnetic resonance measurement is fitted by utilizing a statistical linear regression method to obtain a graticule line equation represented by the formula (3), so that a can be substituted into a calculation formula of the movable oil quantity of the shale oil to calculate the movable oil quantity of the corresponding shale oil.
The embodiment of the invention also provides a shale oil mobility evaluation method of the evaluation model for improving shale oil mobility by adopting the gas injection, in particular to a method for improving shale oil mobility by utilizing a nuclear magnetic resonance device to evaluate gas injection, which comprises the following steps:
sequentially cutting an original core sample of shale or shale to be evaluated, removing residual oil in pores, and drying to obtain a shale dry sample, and performing nuclear magnetic resonance test on the shale dry sample to obtain a corresponding nuclear magnetic resonance T2Measuring signal amount, vacuumizing, pressurizing saturated oil, and aging for 25-3Taking out the aged saturated oil sample after 0 day, and performing nuclear magnetic resonance test on the aged saturated oil sample to obtain corresponding nuclear magnetic resonance T2Measuring the signal quantity, then placing the aged saturated oil sample into a nuclear magnetic resonance-displacement device to perform a gas injection displacement experiment, wherein in the displacement experiment, a nuclear magnetic resonance instrument is used for measuring the nuclear magnetic signals of the sample in real time, namely, the nuclear magnetic resonance test is performed on the aged saturated oil sample at different moments in the gas injection displacement process to obtain the nuclear magnetic resonance T at the corresponding moment2Signal amount according to nuclear magnetic resonance T of dry shale sample, aged saturated oil sample and aged saturated oil sample in the gas injection displacement process2And (3) semaphore, calculating the movable proportion of shale oil of the shale sample at different moments to obtain the distribution characteristics of crude oil in samples at different stages, and evaluating the mobility of the shale oil under the gas injection condition.
As another preferred embodiment of the present invention, the nmr-displacement apparatus includes a displacement system and a confining pressure system for gas injection displacement experiment, and a nuclear magnetic system for nmr test.
As another preferred embodiment of the present invention, specifically, the nuclear magnetic resonance-displacement device includes a displacement system, a confining pressure system, a control system, and a nuclear magnetic system, and the displacement system, the confining pressure system, the control system, the nuclear magnetic system, and the data acquisition system are connected to ensure smooth operation of the instrument.
As another preferred embodiment of the present invention, the displacement system includes a gas cylinder 1, an air compressor 2 and a gas booster pump 3, the gas cylinder 1 and the air compressor 2 are both connected to the gas booster pump 3, and an output end of the gas booster pump 3 is connected to the nuclear magnetic system; the nuclear magnetic system comprises a magnet box 6, wherein the magnet box 6 comprises a heat-shrinkable tube for placing a core sample and a top rod arranged in the heat-shrinkable tube, and an axial through hole for ventilation is formed in the center of the top rod; confining pressure system is including confining pressure liquid (fluoridizing liquid) splendid attire ware 4, first circulating pump 5 (confining pressure (fluoridizing liquid) circulating pump promptly), second circulating pump 7 (cooling liquid (fluoridizing liquid) circulating pump promptly) and backpressure valve 8, confining pressure liquid splendid attire ware 4 is connected with magnet case 6 through first circulating pump 5, second circulating pump 7 with magnet case 6 is connected, magnet case 6 still is connected with pump body 9 (hand pump) through backpressure valve 8, the output of backpressure valve 8 still with hold 12 (specifically can be the beaker) be connected.
As another preferred embodiment of the present invention, the control system includes V1, V2, V3, V4, V5, V6 and V7 valves disposed on the connecting lines, the data acquisition system includes a computer 11, the computer 11 is connected to the magnet box 6 through the radio frequency device 10, and the data acquisition system is used for processing and analyzing the data after the gas injection displacement experiment is finished, so as to obtain the distribution characteristics of the crude oil in the samples at different stages, thereby evaluating the mobility of the shale oil under the gas injection condition.
As another preferred embodiment of the present invention, in the evaluation method, the transverse relaxation time T of the nuclear magnetic resonance test2Mainly controlled by the surface relaxation mechanism, transverse relaxation time T2Can be expressed as shown in the following formula (4):
Figure BDA0002807347500000091
wherein in the formula (4), rho is the surface relaxation rate of the rock (shale or mud shale), V is the pore volume of the rock, S is the rock surface area, T is2Is the transverse relaxation time of the nuclear magnetic resonance test.
As another preferred embodiment of the present invention, in the evaluation method, the ratio V/S of the pore volume of the rock to the rock surface area based on the formula (4) is proportional to the pore radius r of the rock, so that the pore radius of the rock is proportional to the transverse relaxation time T of the NMR test2Can be expressed as shown in the following formula (5):
Figure BDA0002807347500000092
wherein in the formula (5), rho is the surface relaxation rate of the rock, c is the pore shape factor of the rock, r is the pore radius of the rock, and T is2Is the transverse relaxation time of the nuclear magnetic resonance measurement.
In particular, according to nuclear magnetic resonance, high pressure mercury injection and low temperature N2The experiment such as adsorption can establish the correlation of the specific surface area (S/V), the accumulated pore volume or the pore size distribution, and further the surface relaxation rate rho of the rock can be obtained through calibration. Knowing the surface relaxation rate ρ of the rock and the pore shape factor c of the rock, using nuclear magnetism T2The spectrum yields the pore size distribution. Combining the calibration of the fluid volume with the nuclear magnetic resonance T2The response can finally obtain the distribution of the fluid in the pores with different sizes. It should be noted that, because the nuclear magnetic response mechanism of shale is complex, there are many uncertainties in converting the transverse relaxation time into the pore size, and in the practical analysis, the nuclear magnetic T can be directly used2And (4) analyzing the occurrence pore diameter of the crude oil at different displacement moments by a spectrogram.
As another preferred embodiment of the invention, in the evaluation method, the variation trend of the crude oil distribution of the shale at different times can be obtained by comparing the difference of nuclear magnetic spectra of the sample in a saturated oil state and at different gas injection displacement times; the pore size is divided into different intervals according to the pore size division standard, and the change condition of the crude oil content along with the displacement time in different pore size ranges can be evaluated.
As another preferred embodiment of the invention, the evaluation method is specifically a method for evaluating gas injection to improve the mobility of shale oil by using a nuclear magnetic resonance-displacement device, and the used experimental instruments mainly comprise an MR-dd high-temperature high-pressure displacement device and a mesoscopic low-field nuclear magnetic resonance analyzer of meso MR23-060H-I, and specifically comprise a gas cylinder, a displacement system, a confining pressure system, a control system, a nuclear magnetic system (a magnet box and a radio frequency device) and a data acquisition system; the nuclear magnetic resonance coil adopts a 70mm coil; the sample may be analyzed at any stage during the experiment by nmr testing. Different experimental schemes are designed, so that the soaking and well opening processes in the gas injection displacement process can be simulated. And processing and analyzing the data after the gas injection displacement experiment is finished, so that the content and distribution characteristics of the crude oil in the samples at different stages can be obtained, and the mobility of the shale oil under the gas injection condition can be evaluated.
Preferably, the evaluation method comprises the steps of:
step one, preparing an experimental device;
step two, preprocessing a sample;
step three, the displacement process is realized;
step four, calibrating the fluid;
and step five, processing experimental data.
The specific process of the step one is as follows:
(1) ferrous metal ware around the nmr magnet box is removed. The instrument power is turned on, the magnet control temperature is set to 35 ℃ according to the instrument requirements, and the probe and the magnet are kept at constant temperature. The instrument is preheated for more than 16 h.
(2) According to the research purpose of the experiment, the gas cylinder, the displacement system, the confining pressure system, the control system, the nuclear magnetic system and the data acquisition system are connected in sequence, and the smooth operation of the instrument is guaranteed.
(3) And opening the computer, entering measurement control analysis software, and checking whether the communication between the software and the instrument is normal or not.
The specific process of the second step is as follows:
(1) sample preparation: performing linear cutting on the obtained original core sample of the shale (or mud shale) to be evaluated, wherein the sample is cylindrical, the diameter of the sample is 2cm-3cm, and the height of the sample is 1cm-4 cm; numbering samples in sequence, removing residual oil in pores by a Soxhlet extraction method or an ultrasonic method, and adopting a mixed organic solvent of dichloromethane and acetone with a volume ratio of 3:1 as a solvent; placing the sample after oil washing in a vacuum oven with controllable dry humidity for drying, wherein the relative humidity is set to be 40%, the temperature is set to be 65 ℃, the drying time is 8h, and the dried sample is placed in a drying dish for later use; the porosity and the permeability of the shale sample are respectively measured by a helium method and a pulse attenuation method, and the specific operation method is GB/T34533-2017 (the measurement of the porosity and the permeability of the shale helium method by the pulse attenuation method).
(2) Setting nuclear magnetic resonance parameters: according to SY/T6490-2014 (rock sample nuclear magnetic resonance parameter laboratory measurement specification) and in combination with the properties of the sample, the nuclear magnetic resonance measurement transverse relaxation time T of the shale is set2The acquisition parameters are as follows: the diameter of the coil is 70mm, the waiting Time (TW) is 3000ms, the echo interval (TE) is 0.25ms, the Number of Echoes (NECH) is 8000, and the superposition times (NS) is 64 times; and (3) measuring the NMR spin echo train of the sample by using a spin echo pulse sequence (CPMG), and inverting the nuclear magnetic resonance relaxation signal by using a SIRT method.
(3) Nuclear magnetic resonance testing: firstly, standard sample preparation: will contain 0.05% CuSO4A standard sample (25mL-30mL) of the solution is sent to the middle position of a glass test tube (a non-magnetic container), and the central position of the standard sample is positioned at the central position of a magnetic field for standard sample; measuring a dry sample signal of the shale sample: the prepared rock sample (dry sample) to be measured is well packed by a glass test tube and is placed into a measurement cavity; transverse relaxation time T of sample measured by CPMG pulse sequence2After setting the parameters of the measuring system, starting to measure twice after confirming that the current parameters are accurate; ③ saturated oil of the sample: placing the dry sample after the test in a vacuumizing saturation device, and saturating oil; firstly, opening a vacuumizing switch, and vacuumizing air in a sample chamber and a rock sample pore throat until the relative vacuum degree reaches 75kPa for 12-24 h; then closing the vacuum pump, opening a switch of a fluid saturation device, and injecting n-dodecane into the sample chamber, wherein the pressure is kept at about 15MPa, and the saturation time is 24-48 h; taking out the saturated sample from the sample chamber, placing the sample in a beaker containing n-dodecane, sealing and aging for 20-30 days; and measuring the nuclear magnetic signal characteristics of the sample twice after the aging is finished.
The concrete process of the third step is as follows:
(1) preparation before experiment: the apparatus was examined and a sufficient amount of the fluorination liquid (no hydrogen signal) was added to the fluorination liquid holding bottle 4 and the cooling liquid (fluorination liquid) circulation pump 7.
(2) Displacement experiment: putting the aged core into a heat-shrinkable tube, and placing the aged core into a measuring chamber to enable the core to be positioned in the center of a magnet. The valves V4, V5 and V6 are opened to set the temperature, pressure, circulation flow rate of the confining pressure fluorinated liquid and the circulation flow rate of the cooling fluorinated liquid. After the temperature of the fluoride liquid rises to the designated temperature, keeping for more than 1 hour, and measuring the nuclear magnetism T of the rock core2Spectra. ② the valves of V1, V2, V3 and V7 are opened in turn, the outlet of the gas booster pump 3 is arrangedPressure (inlet pressure of core chamber) and pump body 9 (hand pump) pressure (back pressure). And designing corresponding experimental schemes aiming at different experimental purposes. By controlling experimental parameters such as gas injection pressure, back pressure, displacement time and the like, and by means of a nuclear magnetic resonance instrument, according to specific research of experiments, the nuclear magnetic resonance T of a sample is measured at regular intervals2And (4) spectrum analysis is further carried out on the change rule of the movable oil proportion of the shale sample. And thirdly, after the experiment is finished, closing the valves V2, V1, V3, V7, V6, V5 and V4 in sequence, and finishing the experimental instrument.
The concrete process of the step four is as follows:
(1) taking out five small bottles with the volume of about 1.2mL and matched bottle caps, and weighing the mass of 5 empty bottles respectively after screwing the bottle caps; after weighing, the sample is respectively placed in a nuclear magnetic resonance apparatus to measure T2The spectrum is used as the base of the empty bottle; in view of the pore volume of the sample of this experiment, 0.2mL, 0.4mL, 0.6mL, 0.8mL and 1.0mL of n-dodecane was measured as a standard sample by taking out the pipette and dropping it into 5 empty bottles.
(2) After weighing, putting the standard sample into a glass test tube for nuclear magnetic resonance test; after the test is finished, respectively removing the corresponding empty bottle bases for inversion; after the inversion is completed, corresponding T to each volume2The free fluid signal amplitudes of the spectra are accumulated respectively; fitting the linear relation between the n-dodecane volume of the standard sample and the corresponding signal amplitude by using a statistical linear regression method; because the magnitude order difference between the fluid volume and the signal amplitude is large, in order to ensure the accuracy of the coefficient as much as possible, the signal amplitude is reduced by 10000 times and then is fitted with the fluid volume; obtaining a scale equation shown in formula (3), wherein a is the slope of the (fluid-calibrated) scale equation shown in formula (3), M0The total nuclear magnetic signal of the crude oil fluid (preferably the total nuclear magnetic signal of n-dodecane).
Step five comprises calculation of the shale oil movable proportion and the movable oil quantity and evaluation of the change of the shale oil movable proportion in different aperture ranges, and the specific process is as follows:
(1) setting A1 as the NMR T obtained by NMR test of shale dry sample2Semaphore, A2 oldNuclear magnetic resonance T obtained by performing nuclear magnetic resonance test on saturated oil sample2Semaphore, gas injection displacement process t1The nuclear magnetic signal quantity of the aged saturated oil sample at the moment is A3, and t is obtained in the process of gas injection displacement2(t2＞t1) The NMR signal of the aged saturated oil sample at that time was A4. Then t1、t2Moment shale oil movable proportion etat1Eta andt2sequentially comprises the following steps:
Figure BDA0002807347500000131
Figure BDA0002807347500000132
t1、t2movable oil quantity V of time shale oilt1 MovableAnd Vt2 Movable: sequentially comprises the following steps:
Figure BDA0002807347500000133
Figure BDA0002807347500000134
(2) change of shale oil movable proportion in different aperture ranges: transverse relaxation time T of nuclear magnetic resonance measurement2Mainly controlled by the surface relaxation mechanism, transverse relaxation time T2Evaluation was performed according to the formulae (4) and (5).
The embodiment of the invention also provides application of the evaluation method in shale oil exploration and development.
The technical effects of the evaluation model for improving shale oil mobility by gas injection according to the present invention will be further described below by referring to specific examples.
Example 1
An evaluation model for improving shale oil mobility by gas injection is shown as the following formula (1):
Figure BDA0002807347500000141
wherein, the formula (1) is used for calculating the movable proportion of shale oil (the proportion of the movable reserve of crude oil to the total content of crude oil);
in the formula (1), etatXRepresenting the movable proportion of shale oil of the shale rock sample at the time x (in the process of gas injection displacement); the shale rock sample is obtained by sequentially cutting an original core sample of shale or mud shale to be evaluated, removing residual oil in pores and drying to obtain a shale dry sample, and then performing nuclear magnetic resonance test on the shale dry sample to obtain a corresponding nuclear magnetic resonance T2Measuring signal amount, vacuumizing and pressurizing saturated oil, aging for 25-30 days, taking out an aged saturated oil sample, and performing nuclear magnetic resonance test on the aged saturated oil sample to obtain corresponding nuclear magnetic resonance T2Measuring the signal quantity, then putting the aged saturated oil sample into a nuclear magnetic resonance-displacement device for gas injection displacement experiment, wherein in the gas injection displacement experiment, the nuclear magnetic resonance instrument is used for measuring the nuclear magnetic signals of the sample in real time, namely, the nuclear magnetic resonance test is carried out on the aged saturated oil sample at different moments in the gas injection displacement process to obtain the nuclear magnetic resonance T at the corresponding moment2A semaphore; after the gas injection displacement experiment is finished, processing and analyzing the data to obtain the distribution characteristics of the crude oil in the samples at different stages, so as to evaluate the mobility of the shale oil under the gas injection condition;
a1 is NMR T obtained by NMR test of shale dried sample2Semaphore, A2, is NMR T obtained by NMR testing of aged saturated oil samples2The signal quantity Ax is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2And (4) signal quantity.
Example 2
The method for establishing the evaluation model for improving the shale oil mobility by gas injection in the embodiment 1 is specifically shown in the figure 1 and comprises the following steps:
taking the original shale sampleCutting, washing oil, drying at low temperature, saturating oil (n-dodecane) and aging in sequence, then putting into a nuclear magnetic resonance-displacement device, and displacing the crude oil in the pore throat by using different gas media (nitrogen, carbon dioxide, methane, air and the like). Different experimental schemes are designed, so that the process of soaking and well opening under the gas injection condition of a mine field can be simulated. In the experiment, nuclear magnetic resonance hydrogen signals (T) of shale samples under different states are measured by a nuclear magnetic resonance device2Spectrum), the content and the distribution characteristics of the crude oil in the pore throats of the samples at different moments can be monitored in real time, and further the change of the movable oil proportion of the shale under different gas injection conditions can be evaluated. The invention has clear experimental principle, compliant experimental device and reliable experimental result. The experimental method established at this time not only fills the blank of evaluating the shale oil gas injection effect based on the physical simulation experiment indoors, but also can provide guidance for efficient development of the shale oil in the mine field.
Example 3
As shown in fig. 1, the embodiment of the invention discloses a method for improving shale oil mobility by evaluating gas injection by using a nuclear magnetic resonance device. According to the method, the evaluation of the shale oil gas injection mobility effect is realized by means of a nuclear magnetic resonance device. By carrying out gas injection displacement after oil washing, low-temperature drying and oil saturation of the sample, the stewing and well opening processes in the gas injection process are simulated, and the nuclear magnetic signal characteristics of the sample at different experimental stages are compared. And after the experiment is finished, processing and analyzing the data to obtain the content and distribution characteristics of the crude oil in the samples at different stages, and evaluating the movable proportion of the shale oil under the gas injection condition.
Specifically, an original core sample of shale or mud shale to be evaluated is sequentially cut, residual oil in pores is removed, and the original core sample is dried to obtain a shale dry sample, and then the shale dry sample is subjected to nuclear magnetic resonance test to obtain a corresponding nuclear magnetic resonance T2Measuring signal amount, vacuumizing and pressurizing saturated oil, aging for 25-30 days, taking out an aged saturated oil sample, and performing nuclear magnetic resonance test on the aged saturated oil sample to obtain corresponding nuclear magnetic resonance T2Measuring signal amount, placing the aged saturated oil sample in a nuclear magnetic resonance-displacement device, performing gas injection displacement experiment, and displacingIn the replacement experiment, the nuclear magnetic signals of the sample can be measured in real time by means of a nuclear magnetic resonance instrument, namely, the nuclear magnetic resonance test is carried out on the aged saturated oil sample at different moments in the gas injection displacement process to obtain the nuclear magnetic resonance T at the corresponding moment2Signal amount according to nuclear magnetic resonance T of dry shale sample, aged saturated oil sample and aged saturated oil sample in the gas injection displacement process2And (3) semaphore, calculating the movable proportion of shale oil of the shale sample at different moments to obtain the distribution characteristics of crude oil in samples at different stages, and evaluating the mobility of the shale oil under the gas injection condition.
Example 4
Compared with the example 3, the method also comprises the calculation of the movable oil quantity of the shale oil, in particular to the calculation process of the movable oil quantity of the shale oil at the time x of the shale rock sample shown in the following formula (2):
Figure BDA0002807347500000161
in the formula (2), VtX is movableRepresenting the movable oil quantity of shale oil of the shale rock sample at the time x; a2 is NMR T obtained by NMR measurement of aged saturated oil sample2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2A semaphore; and a, fitting the linear relation between corresponding signal amplitudes obtained by performing nuclear magnetic resonance tests on different volumes of crude oil fluid adopted in the process of vacuumizing and pressurizing saturated oil by using a statistical linear regression method to obtain the slope of a graticule equation.
Example 5
The acquisition method of a in embodiment 4 is: taking out five small bottles with the volume of about 1.2mL and matched bottle caps, and weighing the mass of 5 empty bottles respectively after screwing the bottle caps; after weighing, the sample is respectively placed in a nuclear magnetic resonance apparatus to measure T2The spectrum is used as the base of the empty bottle; in view of the pore volume of the sample of the experiment, the pipette is taken out and 0.2mL, 0.4mL, 0.6mL, 0.8mL and 1.0mL of n-dodecane is respectively measured and dropped into 5 empty bottles as standard samples; is divided intoRespectively weighing and then placing the weighed materials into a glass test tube for nuclear magnetic resonance testing; after the test is finished, respectively removing the corresponding empty bottle bases for inversion; after the inversion is completed, corresponding T to each volume2The free fluid signal amplitudes of the spectra are accumulated respectively; fitting the linear relation between the n-dodecane volume of the standard sample and the corresponding signal amplitude by using a statistical linear regression method;
because the magnitude order difference between the fluid volume and the signal amplitude is large, in order to ensure the accuracy of the coefficient as much as possible, the signal amplitude is reduced by 10000 times and then is fitted with the fluid volume; obtaining a reticle equation set
Figure BDA0002807347500000171
Where a is the slope of the graticule equation, M0Fitting the volume V of n-dodecane as a standard sample to the total nuclear magnetic signal of the crude oil fluid, preferably n-dodecane, by means of statistical linear regressionOil。
Example 6
An evaluation method, in particular to a method for evaluating gas injection and improving shale oil mobility by using a nuclear magnetic resonance-displacement device, as shown in figure 1, the experimental apparatus used in the method mainly comprises an MR-dd high-temperature high-pressure displacement device and a MesoMR23-060H-I medium-size low-field nuclear magnetic resonance analyzer, which jointly form the nuclear magnetic resonance-displacement device; the nuclear magnetic resonance coil adopts a 70mm coil; the sample may be analyzed at any stage during the experiment by nmr testing. Different experimental schemes are designed, so that the soaking and well opening processes in the gas injection displacement process can be simulated. And processing and analyzing the data after the gas injection displacement experiment is finished, so that the content and distribution characteristics of the crude oil in the samples at different stages can be obtained, and the mobility of the shale oil under the gas injection condition can be evaluated.
In this embodiment, referring to fig. 2 to 4, the nuclear magnetic resonance-displacement device includes a displacement system, a confining pressure system, a control system, and a nuclear magnetic system, and the displacement system, the confining pressure system, the control system, the nuclear magnetic system, and the data acquisition system are connected to ensure smooth operation of the instrument. The displacement system comprises a gas cylinder 1, an air compressor 2 and a gas booster pump 3, wherein the gas cylinder 1 and the air compressor 2 are both connected with the gas booster pump 3, and the output end of the gas booster pump 3 is connected with the nuclear magnetic system; the nuclear magnetic system comprises a magnet box 6, the magnet box comprises a heat-shrinkable tube for placing a core sample and a mandril arranged in the heat-shrinkable tube, and an axial through hole for ventilation is formed in the center of the mandril; confining pressure system is including confining pressure liquid (fluoridizing liquid) splendid attire ware 4, first circulating pump 5 (confining pressure (fluoridizing liquid) circulating pump promptly), second circulating pump 7 (cooling liquid (fluoridizing liquid) circulating pump promptly) and backpressure valve 8, confining pressure liquid splendid attire ware 4 is connected with magnet case 6 through first circulating pump 5, second circulating pump 7 with magnet case 6 is connected, magnet case 6 still is connected with pump body 9 (hand pump) through backpressure valve 8, the output of backpressure valve 8 still with hold 12 (specifically can be the beaker) be connected.
In this embodiment, the control system includes V1, V2, V3, V4, V5, V6 and V7 valves disposed on the connecting lines, the data acquisition system includes a computer 11, the computer 11 is connected to the magnet box 6 through a radio frequency device 10, and the data acquisition system is used for processing and analyzing data after the gas injection displacement experiment is finished, so as to obtain distribution characteristics of crude oil in samples at different stages, and thus evaluate the mobility of the shale oil under the gas injection condition.
In this embodiment, the evaluation method specifically includes the following steps:
step one, preparing an experimental device;
step two, preprocessing a sample;
step three, the displacement process is realized;
step four, calibrating the fluid;
and step five, processing experimental data.
Example 7
In example 6, the specific procedure of step one is as follows:
(1) ferrous metal ware around the nmr magnet box is removed. The instrument power is turned on, the magnet control temperature is set to 35 ℃ according to the instrument requirements, and the probe and the magnet are kept at constant temperature. The instrument is preheated for more than 16 h.
(2) According to the research purpose of the experiment, the gas cylinder, the displacement system, the confining pressure system, the control system, the nuclear magnetic system and the data acquisition system are connected in sequence, and the smooth operation of the instrument is guaranteed.
(3) And opening the computer, entering measurement control analysis software, and checking whether the communication between the software and the instrument is normal or not.
Example 8
In example 6, the specific procedure of step two is as follows:
(1) sample preparation: the shale sample to be evaluated is taken from three lower layers of Yang-depression and sand-dip of Bohai Bay basin, and the maturity RoThe obtained shale (original core) sample to be evaluated is subjected to line cutting, wherein the sample is cylindrical, the diameter of the sample is 2.5cm, and the height of the sample is 2.8 cm; removing residual oil in pores by a Soxhlet extraction method or an ultrasonic method, and using a mixed organic solvent of dichloromethane and acetone with a volume ratio of 3:1 as a solvent; placing the sample after oil washing in a vacuum oven with controllable dry humidity for drying, wherein the relative humidity is set to be 40%, the temperature is set to be 65 ℃, the drying time is 8h, and the dried sample is placed in a drying dish for later use; the porosity and the permeability of the shale sample are respectively measured by a helium method and a pulse attenuation method, the specific operation method is GB/T34533-2017 (the porosity and the permeability of the shale helium method are measured), the porosity of the sample is 5.8%, and the permeability is 0.0084 mD.
(2) Setting nuclear magnetic resonance parameters: according to SY/T6490-2014 (rock sample nuclear magnetic resonance parameter laboratory measurement specification) and in combination with the properties of the sample, the nuclear magnetic resonance measurement transverse relaxation time T of the shale is set2The acquisition parameters are as follows: the diameter of the coil is 70mm, the waiting Time (TW) is 3000ms, the echo interval (TE) is 0.25ms, the Number of Echoes (NECH) is 8000, and the superposition times (NS) is 64 times; and (3) measuring the NMR spin echo train of the sample by using a spin echo pulse sequence (CPMG), and inverting the nuclear magnetic resonance relaxation signal by using a SIRT method. The interior of the magnet housing 6 of the nuclear magnetic system is schematically shown in fig. 3 and 4.
(3) Nuclear magnetic resonance testing: firstly, standard sample preparation: will contain 0.05% CuSO4Standards of the solution(25mL-30mL) is sent to the middle position of a glass test tube (non-magnetic container), and the central position of a standard sample is positioned at the central position of a magnetic field for standard sample; measuring a dry sample signal of the shale sample: the prepared rock sample (dry sample) to be measured is well packed by a glass test tube and is placed into a measurement cavity; transverse relaxation time T of sample measured by CPMG pulse sequence2After setting the parameters of the measuring system, starting to measure twice after confirming that the current parameters are accurate; ③ saturated oil of the sample: placing the dry sample after the test in a vacuumizing saturation device, and saturating oil; firstly, opening a vacuumizing switch, and vacuumizing air in a sample chamber and a rock sample pore throat until the relative vacuum degree reaches 75kPa for 16.5 h; then, the vacuum pump is closed, the switch of the fluid saturation device is opened, n-dodecane is injected into the sample chamber, the pressure is kept at about 15MPa, and the saturation time is 40 h; taking out the saturated sample from the sample chamber, placing the sample in a beaker containing n-dodecane, sealing and aging for 23 days; and measuring the nuclear magnetic signal characteristics of the sample twice after the aging is finished.
Example 9
In example 6, the specific procedure of step three is as follows:
(1) preparation before experiment: the apparatus was examined and a sufficient amount of the fluorination liquid (no hydrogen signal) was added to the fluorination liquid holding bottle 4 and the cooling liquid (fluorination liquid) circulation pump 7.
(2) Displacement experiment: putting the aged core into a heat-shrinkable tube, and placing the aged core into a measuring chamber to enable the core to be positioned in the center of a magnet. The valves V4, V5 and V6 are opened to set the temperature, pressure, circulation flow rate of the confining pressure fluorinated liquid and the circulation flow rate of the cooling fluorinated liquid. After the temperature of the fluoride liquid rises to the designated temperature, keeping for more than 1 hour, and measuring the nuclear magnetism T of the rock core2Spectra. And secondly, opening valves V1, V2, V3 and V7 in sequence, setting the outlet pressure (the inlet pressure of a core chamber) of the gas (carbon dioxide) booster pump 3 to be 5.0MPa, and simulating a gas injection soaking state by noting that the valve V7 is in a closed state. And measuring the nuclear magnetic signals of the samples at regular intervals (adopting the principle of density before density and density after density) and soaking for 60 minutes by gas injection. Setting the pressure (back pressure) of the pump body 9 (hand pump) to be 4.0MPa, then opening the V7 valve, simulating the gas injection well opening process, and measuring at regular intervalsNuclear magnetic signal of the quantitative sample. The NMR T of the sample is measured at regular intervals by means of an NMR instrument, according to the specific purpose of the study of the experiment2And (4) spectrum analysis is further carried out on the change rule of the movable oil proportion of the shale sample. And thirdly, after the experiment is finished, closing valves V2, V1, V3, V7, V6, V5 and V4 in sequence, finishing the experimental instrument, and obtaining a nuclear magnetic spectrogram shown in figure 5.
Example 10
In example 6, the specific procedure of step four is as follows:
(1) taking out five small bottles with the volume of about 1.2mL and matched bottle caps, and weighing the mass of 5 empty bottles respectively after screwing the bottle caps; after weighing, the sample is respectively placed in a nuclear magnetic resonance apparatus to measure T2The spectrum is used as the base of the empty bottle; in view of the pore volume of the sample of this experiment, the pipette was removed and 0.2ml, 0.4ml, 0.6ml, 0.8ml and 1.0ml of n-dodecane was measured in 5 empty vials as standard samples.
(2) After weighing, putting the standard sample into a glass test tube for nuclear magnetic resonance test; after the test is finished, respectively removing the corresponding empty bottle bases for inversion; after the inversion is completed, corresponding T to each volume2The free fluid signal amplitudes of the spectra are accumulated respectively; fitting the linear relation between the n-dodecane volume of the standard sample and the corresponding signal amplitude by using a statistical linear regression method; because the magnitude order difference between the fluid volume and the signal amplitude is large, in order to ensure the accuracy of the coefficient as much as possible, the signal amplitude is reduced by 10000 times and then is fitted with the fluid volume; obtaining a scale equation shown in formula (3), wherein a is the slope of the (fluid-calibrated) scale equation shown in formula (3), M0The total nuclear magnetic signal of the crude oil fluid (preferably the total nuclear magnetic signal of n-dodecane).
Specifically, as shown in FIG. 6 and FIG. 7, FIG. 6 shows the NMR T of n-dodecane in different volumes2Spectrum, fig. 7 is a plot of the line equation between the n-dodecane fluid volume and the nuclear magnetic semaphore; by measuring the nuclear magnetic signal, the a-0.6797 can be calculated according to the calibrated marking equation of the fluid shown in the formula (3);
example 11
In example 6, the step five includes calculation of the shale oil mobility ratio, the amount of the mobile oil, and evaluation of the change of the shale oil mobility ratio in different aperture ranges, and the specific process is as follows:
(1) setting A1 as the NMR T obtained by NMR test of shale dry sample2Semaphore, A2, is NMR T obtained by NMR testing of aged saturated oil samples2Semaphore, nuclear magnetic resonance T of shale dry sample2The signal quantity is A1-1280.32 a.u., the nuclear magnetic signal quantity of the aged saturated oil sample is A2-5082.86 a.u., and t is measured in the gas injection displacement process1The nuclear magnetic signal quantity of the aged saturated oil sample at the moment is A3, and t is obtained in the process of gas injection displacement2(t2＞t1) The NMR signal of the aged saturated oil sample at that time was A4. Then t1、t2Moment shale oil movable proportion etat1Eta andt2sequentially comprises the following steps:
Figure BDA0002807347500000211
Figure BDA0002807347500000212
t1、t2movable oil quantity V of time shale oilt1 MovableAnd Vt2 MovableThe following components are sequentially:
Figure BDA0002807347500000213
Figure BDA0002807347500000221
(2) characterization of shale oil mobility at different pore sizes: by comparing the changes of the nuclear magnetic resonance spectrums of the samples in the saturated oil state and the gas drive state at different moments, the occurrence content, the occurrence pore diameter and the mobility of the crude oil in the shale can be evaluated, and the specific shale has different propertiesThe variation of crude oil content over the pore size range is shown in FIG. 8. In FIG. 8, the A region in hatching indicates t1To t2Time aperture (T)21ms) crude oil reduction, while the B region represents the macropores (1ms < T)2100ms) indicates an increase from t1To t2At that time, the injected carbon dioxide displaces the crude oil in the small pores to the large pores.
Example 12
Compared with the example 11, the fifth step also comprises the analysis and summary of the change and the mobility of the crude oil-borne pore diameter under the gas injection condition by converting the transverse relaxation time into the pore diameter size:
transverse relaxation time T of nuclear magnetic resonance measurement2Mainly controlled by the surface relaxation mechanism, transverse relaxation time T2Can be expressed as shown in the following formula (4):
Figure BDA0002807347500000222
wherein in the formula (4), rho is the surface relaxation rate of the rock (shale or mud shale), V is the pore volume of the rock, S is the rock surface area, T is2Is the transverse relaxation time of the nuclear magnetic resonance test.
Based on the fact that the ratio V/S of the pore volume of the rock to the surface area of the rock in the formula (4) is in direct proportion to the pore radius r of the rock, the pore radius of the rock is in direct proportion to the transverse relaxation time T of the nuclear magnetic resonance test2Can be expressed as shown in the following formula (5):
Figure BDA0002807347500000223
wherein in the formula (5), rho is the surface relaxation rate of the rock, c is the pore shape factor of the rock, r is the pore radius of the rock, and T is2Is the transverse relaxation time of the nuclear magnetic resonance measurement.
While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims (10)

1. An evaluation model for improving shale oil mobility by gas injection, which is characterized in that the evaluation model for improving shale oil mobility by gas injection is shown as the following formula (1):
Figure FDA0002807347490000011
wherein, in the formula (1)
Figure FDA0002807347490000013
Representing the movable proportion of shale oil of the shale rock sample at the time x; the method comprises the following steps that a shale rock sample to be evaluated is obtained by sequentially cutting an original core sample of shale or shale to be evaluated, removing residual oil in pores and drying the original core sample to obtain a dry shale sample, then performing nuclear magnetic resonance test on the dry shale sample, vacuumizing and pressurizing saturated oil, aging the dry shale sample, then taking out the aged saturated oil sample, performing nuclear magnetic resonance test on the aged saturated oil sample, then performing a gas injection displacement experiment on the aged saturated oil sample, and performing nuclear magnetic resonance test on the aged saturated oil sample at different moments in the gas injection displacement process;
a1 is NMR T obtained by NMR test of shale dried sample2Semaphore, A2, is NMR T obtained by NMR testing of aged saturated oil samples2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2And (4) signal quantity.
2. The evaluation model for improving shale oil mobility through gas injection according to claim 1, wherein the residual oil in the pores is removed by using a Soxhlet extraction method or an ultrasonic method after a cutting sample is obtained by cutting an original core sample of the shale or mud shale to be evaluated.
3. The evaluation model for improving shale oil mobility through gas injection according to claim 1, further comprising calculation of the amount of oil moved by shale oil at time x of the shale rock sample as shown in the following formula (2):
Figure FDA0002807347490000012
in the formula (2), the reaction mixture is,
Figure FDA0002807347490000014
representing the movable oil quantity of shale oil of the shale rock sample at the time x; a2 is NMR T obtained by NMR measurement of aged saturated oil sample2The signal quantity, Ax, is the nuclear magnetic resonance T obtained by performing the nuclear magnetic resonance test on the aged saturated oil sample at the time x in the gas injection displacement process2A semaphore; and a, fitting the linear relation between corresponding signal amplitudes obtained by performing nuclear magnetic resonance tests on crude oil fluids under different volume conditions respectively during vacuumizing and pressurizing saturated oil by using a statistical linear regression method to obtain the slope of a graticule equation.
4. The model for evaluating shale oil mobility through gas injection according to claim 3, wherein a in the formula (2) is obtained by performing nmr test on crude oil fluid with different volumes to obtain nmr T corresponding to each volume2Fitting the linear relation between the volume of the crude oil fluid and the corresponding signal amplitude by using a statistical linear regression method to obtain a marking line equation represented by the following formula (3):
Figure FDA0002807347490000021
wherein in the formula (3), a is the slope of the reticle equation expressed by the formula (3), M0Is the total nuclear magnetic signal of the crude oil fluid, VOilRepresenting the volume of the crude fluid.
5. An evaluation method, characterized in that the evaluation model for improving shale oil mobility by gas injection according to any of claims 1-4 is adopted, and the evaluation method specifically comprises the following steps: sequentially cutting an original core sample of shale or mud shale to be evaluated, removing residual oil in pores and drying to obtain a dry shale sample, performing nuclear magnetic resonance test on the dry shale sample, vacuumizing and pressurizing saturated oil, aging for 25-30 days, taking out the aged saturated oil sample, performing nuclear magnetic resonance test on the aged saturated oil sample, putting the aged saturated oil sample into a nuclear magnetic resonance-displacement device for gas injection displacement experiment, performing nuclear magnetic resonance test on the aged saturated oil sample at different moments in the gas injection displacement process, and performing nuclear magnetic resonance T-shaped (T-shaped) test on the dry shale sample, the aged saturated oil sample and the aged saturated oil sample in the gas injection displacement process2And (4) signal quantity, calculating the movable proportion of shale oil of the shale rock sample at different moments so as to evaluate the mobility of the shale oil under the condition of gas injection.
6. The evaluation method according to claim 5, wherein the NMR-displacement device comprises a displacement system and a confining pressure system for gas injection displacement experiments, and a nuclear magnetic system for NMR testing.
7. The evaluation method according to claim 6, wherein the displacement system comprises a gas cylinder, an air compressor and a gas booster pump, the gas cylinder and the air compressor are both connected with the gas booster pump, and the output end of the gas booster pump is connected with the nuclear magnetic system; the nuclear magnetic system comprises a magnet box, the magnet box comprises a heat-shrinkable tube for placing a core sample and a mandril arranged in the heat-shrinkable tube, and an axial through hole for ventilation is formed in the center of the mandril; the confining pressure system comprises a confining pressure liquid containing device, a first circulating pump, a second circulating pump and a back pressure valve, the confining pressure liquid containing device is connected with a magnet box through the first circulating pump, the second circulating pump is connected with the magnet box, the magnet box is further connected with a pump body through the back pressure valve, and the output end of the back pressure valve is further connected with a containing part.
8. The method of claim 5, wherein the transverse relaxation time T of the NMR measurement is measured in the method2Can be expressed as shown in the following formula (4):
Figure FDA0002807347490000031
wherein in the formula (4), rho is the surface relaxation rate of the rock, V is the pore volume of the rock, S is the surface area of the rock, and T is2Is the transverse relaxation time of the nuclear magnetic resonance test.
9. The evaluation method according to claim 8, wherein in the evaluation method, the ratio V/S of the pore volume of the rock to the rock surface area based on the formula (4) is proportional to the pore radius r of the rock, so that the pore radius of the rock is proportional to the transverse relaxation time T of the NMR test2Can be expressed as shown in the following formula (5):
Figure FDA0002807347490000032
wherein in the formula (5), rho is the surface relaxation rate of the rock, c is the pore shape factor of the rock, r is the pore radius of the rock, and T is2Is the transverse relaxation time of the nuclear magnetic resonance test.
10. Use of the evaluation method according to any one of claims 5 to 9 in shale oil development.
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