CN115788373B - CO (carbon monoxide)2Evaluation method for oil-gas displacement rule of shale oil reservoir - Google Patents
CO (carbon monoxide)2Evaluation method for oil-gas displacement rule of shale oil reservoir Download PDFInfo
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- 238000006073 displacement reaction Methods 0.000 title claims abstract description 124
- 239000003079 shale oil Substances 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 31
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title 1
- 229910002091 carbon monoxide Inorganic materials 0.000 title 1
- 239000003921 oil Substances 0.000 claims abstract description 83
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 82
- 238000005481 NMR spectroscopy Methods 0.000 claims abstract description 67
- 238000001228 spectrum Methods 0.000 claims abstract description 61
- 239000010779 crude oil Substances 0.000 claims abstract description 44
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 44
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 41
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 37
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- 238000002474 experimental method Methods 0.000 claims abstract description 23
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- 238000009826 distribution Methods 0.000 claims description 16
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 claims description 15
- 239000008398 formation water Substances 0.000 claims description 14
- 238000005406 washing Methods 0.000 claims description 13
- 239000011572 manganese Substances 0.000 claims description 12
- 230000008569 process Effects 0.000 claims description 12
- 230000035699 permeability Effects 0.000 claims description 11
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 9
- 229910052748 manganese Inorganic materials 0.000 claims description 9
- 238000004364 calculation method Methods 0.000 claims description 7
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 5
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
- Y02P90/70—Combining sequestration of CO2 and exploitation of hydrocarbons by injecting CO2 or carbonated water in oil wells
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Abstract
The invention belongs to the technical field of oil reservoir development, and particularly relates to a method for evaluating the oil-gas displacement rule of a CO 2 and shale oil reservoir. A method for evaluating the oil-gas displacement rule of CO 2 and shale oil deposit includes such steps as respectively fully saturating the core sample with simulated stratum water and saturated simulated crude oil, performing nuclear magnetic resonance T 2 spectrum test, using carbon dioxide to perform displacement experiment on core sample, performing nuclear magnetic resonance T 2 spectrum test, comparing, quantitatively calculating the CO 2 displacement efficiency under different constant-flow displacement conditions, and evaluating the oil-gas displacement rule of CO 2 and shale oil deposit, so as to determine the injection condition for optimizing the CO 2 displacement of shale oil deposit. According to the invention, a core sample is displaced at a constant flow rate through an indoor simulation experiment, and the nuclear magnetic resonance online monitoring technology is utilized to analyze the influence factors of the oil gas effect of CO 2 replacement and reveal the replacement rule of CO 2 and the oil gas of the shale oil reservoir, so that the on-site injection and technological parameters are optimized, and the recovery ratio of the shale oil reservoir is improved.
Description
Technical Field
The invention belongs to the technical field of oil reservoir development, and particularly relates to a method for evaluating the oil-gas displacement rule of a CO 2 and shale oil reservoir.
Background
Water flooding is a method of improving recovery efficiency common to conventional reservoirs at present, but after water flooding development, part of crude oil still exists in the formation pores and cannot be extracted, and is generally called residual oil. For this part of the remaining oil, gas flooding is a common tertiary oil recovery method, the mechanism is to displace crude oil remained in the reservoir by injecting gas into the stratum, and CO 2 is one of the common gases of gas flooding, and the effect obtained in the aspect of improving the recovery ratio is widely accepted.
CO 2 flooding projects are developed in China in a plurality of large oil fields such as Daqing. However, due to the lack of a CO 2 gas source, the development of China in the aspect of CO 2 oil displacement is severely limited, the technology is developed until a few CO 2 gas fields with smaller scale are discovered in the later period, the CO 2 gas displacement project is developed gradually in various large oil fields in China, and theoretical research is also broken suddenly. Indoor experiments and field experiments show that compared with water flooding, the CO 2 oil displacement can remarkably improve the development effects of low-permeability oil reservoirs and small-fault-block oil reservoirs. CO 2 is easy to break through early CO 2 by non-miscible displacement of oil, and under the condition of miscible phase, CO 2 and crude oil can be mixed in any proportion, and interfacial tension is eliminated, so that high-efficiency CO 2 displacement of oil is obtained. In addition, the CO 2 is fully dissolved in the crude oil, the viscosity of the crude oil is reduced, the advantages of CO 2 flooding such as surface tension reduction are fully developed in a mixed phase flooding stage, and more CO 2 enters into the small pore throat for flooding. The shale oil reservoir has fine pore throats, micro-nano pore throats develop, and the CO 2 miscible flooding has adaptability to the shale oil reservoir.
Shale oil resources of various basins in China have huge potential, and along with the increasing maturity and perfection of exploitation technology, shale oil becomes a realistic strategic alternative resource. The CO 2 oil displacement technology is applied to the development of domestic shale oil reservoirs, and has the great advantages of no consumption of water resources, no damage to the reservoir, rapid flowback and strong seam making capability. CN201810886910.2 discloses a CO 2 fracturing oil displacement integrated oil extraction method for a tight oil reservoir, CN201921121815.X discloses a CO 2 displacement device for a tight oil core, CN202010456667.8 discloses a characteristic evaluation method for a tight oil reservoir CO 2 driving reservoir, and CN202010456442.2 discloses a method for evaluating the CO 2 driving of different mineral components of the tight oil reservoir to improve the recovery ratio. The research object for CO 2 oil displacement is focused on compact sandstone, so that the research on the action rule of CO 2 oil displacement and shale is less, and the replacement mechanism of CO 2 and shale oil is not revealed from the microscopic pore scale. The evaluation of the current CO 2 oil displacement technical effect is mainly realized through reservoir geologic modeling and oil reservoir numerical simulation, but some actual blocks of a mine do not have the conditions of numerical modeling and geologic modeling, for example, some blocks which are just developed have fewer wells, the oil reservoir data of the blocks are not complete, the knowledge degree of the blocks is low, and the method is not suitable for analyzing and evaluating the CO 2 oil displacement technical effect of the blocks by directly adopting the numerical modeling and the geologic modeling.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a method for evaluating the oil-gas displacement law of a CO 2 and shale oil reservoir, which is characterized in that the influence factors of the oil-gas displacement effect under the mixed phase and the non-mixed phase state of CO 2 are analyzed by using an on-line nuclear magnetic resonance monitoring technology through an indoor simulation experiment, and the oil-gas displacement law of CO 2 and the shale oil reservoir is revealed, so that the on-site injection and technological parameters are optimized, and the recovery ratio of the shale oil reservoir is improved.
The technical scheme of the invention is as follows: a method for evaluating the oil-gas displacement rule of a CO 2 and shale oil reservoir comprises the following steps:
S1: preparing a core sample and numbering;
S2: selecting the core samples numbered in the step S1, sequentially washing oil, drying, weighing, and measuring the air permeability of the core samples;
S3: fully saturating the core sample treated in the step S2 with simulated formation water;
S4: using manganese water to displace the core sample fully saturated with simulated formation water in the S3 at a constant flow rate, and performing a nuclear magnetic resonance T 2 spectrum test when the displacement is finished;
S5: performing saturated simulated crude oil displacement on the core sample in the step S4 at a constant flow rate until the produced liquid at the outlet of the core sample is free of water, establishing stratum original oil-water distribution, and performing nuclear magnetic resonance T 2 spectrum test on the core sample when the displacement is finished;
S6: displacing the core sample of the saturated simulated crude oil in the step S5 with carbon dioxide at a constant flow rate until the core sample outlet production fluid does not contain crude oil, and performing nuclear magnetic resonance T 2 spectrum test on the core sample at the end of displacement;
s7: and (3) re-selecting core samples with different numbers in the step (S1), repeating the steps (S2-S6), performing at least 5 groups of carbon dioxide displacement experiments, quantitatively calculating carbon dioxide displacement efficiency according to nuclear magnetic resonance T 2 spectrums of carbon dioxide displacement core samples with different constant flow rates, evaluating the oil-gas displacement rule of the CO 2 and the shale oil reservoir, and further optimizing the injection parameters of carbon dioxide displacement of the shale oil reservoir, wherein the calculation formula of the carbon dioxide displacement efficiency b is as follows:
Wherein: s i is the difference of the T 2 spectrum frequency area after the initial saturated simulated crude oil and the carbon dioxide are replaced, and S o is the T 2 spectrum frequency area after the carbon dioxide are replaced.
The diameter of the core samples in the step S1 is 25mm, and the number of the core samples is more than or equal to 5.
The specific process of the core sample wash oil in the step S2 is as follows: and (3) placing the core sample in an extraction container with the volume ratio of benzene to alcohol of 1:3 for washing oil.
The specific process of drying the core sample in the step S2 is as follows: and after the oil washing is finished, placing the core sample into an incubator to be heated to 100-105 ℃, keeping the temperature unchanged for 24-48 hours, and taking out to measure the dry weight of the core.
And S2, measuring the air permeability of the core sample by adopting a steady-state method.
The concentration of Mn 2+ of the manganese water in the S4 is larger than the mineralization degree of the stratum water, the constant flow rate of the core sample fully saturated with the simulated stratum water in the displacement S3 is 0.1-0.2 ml/min, the injection rate is 3-4 PV, and the PV is the pore volume.
And the constant flow rate of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 is 0.1-0.2 ml/min.
The simulated crude oil in S5 is prepared by crude oil and refined kerosene according to a volume ratio of 1:1, and the viscosity of the simulated crude oil in S5 is 6.5-8 mPa.s at the normal temperature of 20 ℃.
In the step S7, at least 5 groups of carbon dioxide displacement experiments are performed, and the number of experimental groups in which carbon dioxide is in a mixed phase state is at least 2.
The invention has the technical effects that: 1. according to the invention, by combining a displacement experiment with a nuclear magnetic resonance test technology and displacing the nuclear magnetic resonance T 2 spectrum of a core sample with different constant flow rates, the carbon dioxide displacement efficiency is quantitatively calculated, and compared with reservoir geological modeling and reservoir numerical simulation, the calculation result of the invention is accurate and reliable; 2. according to the invention, through analyzing nuclear magnetic resonance T 2 spectra before and after the replacement of CO 2 and shale oil reservoir oil gas, the microscopic mechanism and key control factors of the oil gas replacement of different pore diameters and pore throats in the replacement process of CO 2 are revealed, and the evaluation result is more visual and accurate; 3. according to the invention, by combining a displacement experiment with a nuclear magnetic resonance test technology, compared with the traditional displacement experiment, the method uses the nuclear magnetic resonance T 2 spectrum to quantitatively calculate the carbon dioxide oil displacement efficiency, does not need to collect and meter the displaced output, reduces the contact between experimenters and chemical substances, and is safer; 4. according to the invention, through evaluating the oil-gas displacement rule of the CO 2 and the shale oil reservoir, the injection parameters of the carbon dioxide displacement of the shale oil reservoir can be optimized, so that the best effect is achieved when CO 2 is injected into the reservoir for displacing crude oil.
Further description will be made below with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram showing calculation of oil displacement efficiency in a 10 1ms-102 ms interval of pore size distribution in an embodiment of the invention.
Fig. 2 is a nuclear magnetic resonance T 2 spectrum of a core N1 according to an example of the present invention.
Fig. 3 is a nuclear magnetic resonance T 2 spectrum of core N2 according to the example of the present invention.
Fig. 4 is a nuclear magnetic resonance T 2 spectrum of core N3 according to the example of the present invention.
Fig. 5 is a nuclear magnetic resonance T 2 spectrum of core N4 according to the example of the present invention.
Fig. 6 is a nuclear magnetic resonance T 2 spectrum of a core according to example N5 of the present invention.
Detailed Description
Example 1
A method for evaluating the oil-gas displacement rule of a CO 2 and shale oil reservoir comprises the following steps:
S1: preparing a core sample and numbering;
S2: selecting the core samples numbered in the step S1, sequentially washing oil, drying, weighing, and measuring the air permeability of the core samples;
S3: fully saturating the core sample treated in the step S2 with simulated formation water;
S4: using manganese water to displace the core sample fully saturated with simulated formation water in the S3 at a constant flow rate, and performing a nuclear magnetic resonance T 2 spectrum test when the displacement is finished;
S5: performing saturated simulated crude oil displacement on the core sample in the step S4 at a constant flow rate until the produced liquid at the outlet of the core sample is free of water, establishing stratum original oil-water distribution, and performing nuclear magnetic resonance T 2 spectrum test on the core sample when the displacement is finished;
S6: displacing the core sample of the saturated simulated crude oil in the step S5 with carbon dioxide at a constant flow rate until the core sample outlet production fluid does not contain crude oil, and performing nuclear magnetic resonance T 2 spectrum test on the core sample at the end of displacement;
s7: and (3) re-selecting core samples with different numbers in the step (S1), repeating the steps (S2-S6), performing at least 5 groups of carbon dioxide displacement experiments, quantitatively calculating carbon dioxide displacement efficiency according to nuclear magnetic resonance T 2 spectrums of carbon dioxide displacement core samples with different constant flow rates, evaluating the oil-gas displacement rule of the CO 2 and the shale oil reservoir, and further optimizing the injection parameters of carbon dioxide displacement of the shale oil reservoir, wherein the calculation formula of the carbon dioxide displacement efficiency b is as follows:
Wherein: s i is the difference of the T 2 spectrum frequency area after the initial saturated simulated crude oil and the carbon dioxide are replaced, and S o is the T 2 spectrum frequency area after the carbon dioxide are replaced.
The principle of nuclear magnetic resonance technology in the invention is that after rock sample is saturated with oil or water, nuclear magnetic moment of hydrogen nuclei in the oil and water is split in energy level in an evenly distributed external static magnetic field, at the moment, a radio frequency field with specific frequency is applied, the nuclear magnetic moment is absorbed and transited, nuclear magnetic resonance is generated, and nuclear magnetic resonance signal intensity is in direct proportion to the number of hydrogen nuclei in a tested sample. The process by which the magnetization vector returns to the equilibrium state after being displaced from the equilibrium state upon nuclear magnetic resonance under excitation of a radio frequency field is called relaxation, and a signal whose relaxation motion amplitude decays with time can be received. The rate of signal decay can be described by the T 1 longitudinal relaxation time and the T 2 transverse relaxation time. Although both reflect reservoir rock Dan Wuxing and fluid properties, the latter measurement is typically used in nuclear magnetic resonance measurements because the T 1 measurement speed is slower compared to the T 2 measurement speed. The relaxation time is determined by the petrophysical properties and the fluid characteristics, and for the same fluid, the relaxation rate depends only on the petrophysical properties. The environment and the effect between atomic nuclei of each hydrogen nucleus in pure material samples, such as pure water, are the same, and a relaxation time T 2 can be used to describe the physical properties of the samples.
The physical properties of the rock fluid system are different, and the distribution of T 2 is different, and in turn, the physical properties of the rock fluid can be determined by the distribution of T 2 obtained by a nuclear magnetic resonance apparatus. Because the simulated oil does not contain hydrogen core 1H, the T 2 distribution curve of the bound water state measured after the oil drives water to the core does not produce water is characterized by the distribution of the bound fluid, and compared with the T 2 distribution curve of the saturated water state, the part with the reduced ordinate of the curve is the movable fluid part.
It is known from the theory of seepage mechanics that when the radius of the pore of the reservoir is small to a certain extent, the fluid in the pore is restrained by capillary force or viscous force and cannot flow. From previous studies, shale reservoir tie-up fluids are predominantly distributed within smaller radius pores, with only a small portion being present at the wall of the larger pore throat, while mobile fluids are predominantly distributed within the larger radius pore throat. An exact pore throat radius cut-off value exists in the porous medium, the fluid which is endowed in the porous medium is divided into two parts, and the fluid in all pores smaller than the value is in a constraint state and is difficult to flow under the existing conditions; while the fluid in the pores above this value is mobile.
According to the nuclear magnetic resonance principle, nuclear magnetic resonance measurement T 2 spectra of core saturated water states with different permeabilities has a one-to-one correspondence with pore radii in rock, namely, a longer T 2 relaxation time corresponds to larger pores in a rock sample, and a shorter T 2 relaxation time corresponds to smaller pores. Then there is also a demarcation point on the T 2 spectrum where the fluid is mobile when the T 2 relaxation time of the pore fluid is greater than a certain value, and otherwise bound.
According to the invention, by combining a displacement experiment with a nuclear magnetic resonance test technology and measuring the core oil signal T 2 spectrum when the water content of the liquid outlet end is 100%, the displacement efficiency under different experimental conditions is calculated, so that the displacement rule of CO 2 and shale oil is defined, and the experiment execution standards SY/T5336-2006 and SY/T6490-2016 are obtained.
The diameter of the core samples in the step S1 is 25mm, and the number of the core samples is more than or equal to 5.
The specific process of the core sample wash oil in the step S2 is as follows: and (3) placing the core sample in an extraction container with the volume ratio of benzene to alcohol of 1:3 for washing oil. Residual oil in the core sample can be washed out through extraction with the volume ratio of benzene to alcohol being 1:3, interference to subsequent experimental results is prevented, and the pore volume is measured more accurately.
The specific process of drying the core sample in the step S2 is as follows: and after the oil washing is finished, placing the core sample into an incubator to be heated to 100-105 ℃, keeping the temperature unchanged for 24-48 hours, and taking out to measure the dry weight of the core.
And in the step S2, a steady-state method is adopted to measure the air permeability of the core sample, and the GB/T29172-2012 standard is specifically implemented.
The concentration of Mn 2+ of the manganese water in the S4 is larger than the mineralization degree of the formation water, the constant flow rate of a core sample of the fully saturated simulated formation water in the S3 is 0.1-0.2 ml/min, the injection rate is 3-4 PV, the PV is the pore volume, and the effect of the manganese water in the S4 is to fully inhibit the hydrogen ion signal in the formation water, so that the T 2 spectrum only represents the hydrogen ion signal of the simulated crude oil, thereby evaluating the oil displacement efficiency.
And the constant flow rate of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 is 0.1-0.2 ml/min.
The simulated crude oil in S5 is prepared by crude oil and refined kerosene according to a volume ratio of 1:1, and the viscosity of the simulated crude oil in S5 is 6.5-8 mPa.s at the normal temperature of 20 ℃.
In the step S7, at least 5 groups of carbon dioxide displacement experiments are performed, and the number of experimental groups in which carbon dioxide is in a mixed phase state is at least 2.
Example 2
The evaluation method provided by the invention is used for evaluating the substitution rule of CO 2 and shale oil for the core sample of the shale oil reservoir of a certain oil field. The specific process is as follows:
S1: preparing a core sample and numbering;
Drilling a core with a diameter of 25mm on a standard core, and measuring the diameter and the length of the core respectively by core numbers N1, N2, N3, N4 and N5;
S2: sequentially washing oil, drying and weighing the core sample obtained in the step S1, and measuring the air permeability of the core sample; the specific process of the core sample wash oil is as follows: placing the core sample in an extraction container with the volume ratio of benzene to alcohol of 1:3 for washing oil, and drying the core sample, wherein the specific process comprises the following steps: after oil washing is finished, placing the core sample into an incubator to be heated to 105 ℃, keeping the temperature unchanged for 48 hours, taking out to measure the dry weight of the core, and measuring the air permeability of the core sample by adopting a steady-state method, wherein the physical parameters of the core are shown in table 1;
Table 1 core physical properties table for nmr displacement experiments
S3: fully saturating the core sample treated by the step S2 with simulated formation water, and testing the equipment: oxford Geospec/53 nuclear magnetic resonance apparatus; LDY-150 high-temperature high-pressure dynamic displacement system;
S4: core samples of the simulated formation water are displaced by using manganese water at a constant flow rate, nuclear magnetic resonance T 2 spectrum test is carried out at the end of displacement, the concentration of the manganese water is 30000mg/L, the constant flow rate of the core samples of the simulated formation water is 0.1ml/min, and the injection rate is 3-4 PV.
S5: performing saturated simulated crude oil displacement on the core sample in the step S4 at a constant flow rate until the produced liquid at the outlet of the core sample is free of water, and establishing stratum original oil-water distribution; performing nuclear magnetic resonance T 2 spectrum test on the core sample at the end of displacement, wherein the constant flow rate of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 is 0.1ml/min, and the viscosity of the simulated crude oil in S5 is 6.5-8 mPa.s at the normal temperature of 20 ℃;
s6: displacing the core sample of the saturated simulated crude oil in the step S5 with carbon dioxide at a constant flow rate until the core sample outlet production fluid does not contain crude oil, and performing nuclear magnetic resonance T2 spectrum test on the core sample at the end of displacement;
S7: repeating the steps S2-S6, performing a displacement experiment on the core sample in a CO2 miscible and immiscible state, wherein the nuclear magnetic resonance displacement experiment in the CO2 miscible state is 2 groups, the nuclear magnetic resonance displacement experiment in the CO2 immiscible state is 3 groups, the parameter setting of the nuclear magnetic resonance displacement experiment in the experiment is shown in a table 2, and nuclear magnetic resonance T2 spectrum test is performed at the end of each group of experiments, and the nuclear magnetic resonance T2 spectrum is shown in fig. 2-5;
Table 2 nmr displacement experiment parameter settings
Comparing the nuclear magnetic resonance T 2 spectrum of the core sample in the mixed phase and non-mixed phase state of the CO 2 in the S7, quantitatively calculating the oil displacement efficiency in the mixed phase and non-mixed phase state of the CO 2, and as shown in FIG. 1, a pore throat oil displacement efficiency calculation method with the aperture of 10 1ms-102 ms is shown. Assuming that the initial saturated crude oil quantity in the pore throat with the radius of 10 1ms-102 ms is represented by (Si), the crude oil quantity of the region after water flooding is represented by So, and the calculation formula of the carbon dioxide oil displacement efficiency b can be calculated by comparing the frequency area difference of the spectra of the saturated crude oil T 2 before and after the experiment:
Wherein: s i is the difference of the T 2 spectrum frequency area after the initial saturated simulated crude oil and the carbon dioxide are replaced, and S o is the T 2 spectrum frequency area after the carbon dioxide are replaced.
The displacement efficiency of CO 2 in the miscible and immiscible state with crude oil is shown in table 3.
The initial state nuclear magnetic resonance result of the N1 core sample is shown in fig. 2, the nuclear magnetic resonance T 2 spectrum and the horizontal axis envelope area are 32504.54, and the pore throat application range is 0.01-505.26 ms. The nuclear magnetic resonance T 2 spectrum is approximately bimodal in the initial oil-water distribution state, the left peak is slightly higher than Yu Youfeng, most of detected signals are in the range that the relaxation time is not more than 100ms, and after the nuclear magnetic resonance relaxation time is more than 100ms, a lower peak appears in the curve. Therefore, sample N1 has three types of pore throats in the initial oil-water relation state, namely a smaller pore throats ranging from 0.01 to 1.20ms, a medium pore throats ranging from 1.20 to 191.16ms and a larger pore throats ranging from 191.16 to 505.26ms, and the relative contents of 3 types of pore throats are 46.96%, 52.12% and 0.92%.
The experimental result of the N1 core sample CO 2 after displacement is shown in fig. 2, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 13880.82, the pore throat movement range is 0.01-622.26 ms, and the oil displacement efficiency is 57.30%. The core sample T 2 spectrum after CO 2 is driven approximately shows a unimodal state, wherein the right peak of the initial state is obviously reduced, the left peak is reduced by a small amplitude, and most of detected signals are in a range of not more than 30ms in relaxation time. According to the 3 kinds of pore throats range divided in the initial state, the oil displacement efficiency of CO 2 flooding is 16.50%, 40.29% and 0.51% respectively in the ranges of 0.01-1.20 ms, 1.20-191.16 ms and 191.16-505.26 ms, the oil displaced by CO 2 mainly comes from a larger pore throats, and a certain amount of residual oil is still reserved in smaller pore throats.
The nuclear magnetic resonance displacement experimental result of the N2 core sample is shown in fig. 3, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 50946.28, and the pore throat application range is 0.01-880.49 ms. The nuclear magnetic resonance T 2 spectrum is bimodal in the initial oil-water distribution state, the right peak is higher than Zuo Feng, and most of detected signals are in the range that the relaxation time is not more than 1000 ms. Therefore, in the initial oil-water relation state, the sample N2 has a smaller pore throat of 0.01-1.20 ms, a relative content of 33.87%, and a larger pore throat of 1.20-880.49 ms, and a relative content of 66.13%.
The experimental result of the N2 core sample CO 2 after displacement is shown in fig. 3, the envelope area of the nuclear magnetic resonance T 2 spectrum and the horizontal axis is 20960.78, the pore throat movement range is 0.01-622.26 ms, and the oil displacement efficiency is 58.86%. The core sample T 2 spectrum after CO 2 is driven is in a bimodal state, wherein the right peak is obviously reduced, the left peak is reduced in amplitude, the whole curve is shifted left, and most of detected signals are in a range that the relaxation time is not more than 144.81 ms. According to the range of class 2 pore throats divided in the initial state, the displacement efficiency of CO 2 flooding is 17.75 percent and 41.11 percent respectively in the range of 0.01-1.20 ms and 1.20-880.49 ms, and the oil displaced by CO 2 mainly comes from larger pore throats and a certain amount of residual oil is still reserved in smaller pore throats.
The minimum miscible phase pressure MMP of the long 7 shale oil reservoir measured according to the early-stage experiment is 23.3MPa, the injection pressure of the N2 sample and the N1 sample is 25MPa, and the two are the displacement under the miscible phase displacement condition, so that the displacement efficiency is higher. Different, the constant flow rate of the sample No. N1 is 0.2mL/min, the oil displacement efficiency is 53.03%, the constant flow rate of the sample No. N2 is 0.4mL/min, and the oil displacement efficiency is 58.86%, which indicates that the oil displacement efficiency of the core sample can be improved to a certain extent by the improvement of the constant flow rate.
The nuclear magnetic resonance displacement experimental result of the N3 core sample is shown in fig. 4, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 49421.66, and the pore throat application range is 0.01-439.76 ms. The nuclear magnetic resonance T 2 spectrum is bimodal in the initial oil-water distribution state, the right peak is higher than Zuo Feng, and most of detected signals are in the range that the relaxation time is not more than 1000 ms. Therefore, in the initial oil-water relation state, the sample N3 has a smaller pore throat of 0.01-1.38 ms, a relative content of 31.97%, and a larger pore throat of 1.38-439.76 ms, and a relative content of 68.03%.
The experimental result of the N3 core sample CO 2 after displacement is shown in fig. 4, the envelope area of the nuclear magnetic resonance T 2 spectrum and the horizontal axis is 20938.63, the pore throat movement range is 0.01-580.52 ms, and the oil displacement efficiency is 57.63%. The core sample T 2 spectrum after CO 2 is driven is in a bimodal state, wherein the right peak is obviously reduced, the left peak is reduced in amplitude, the whole curve is shifted left, and most of detected signals are in a range that the relaxation time is not more than 580.52 ms. According to the range of class 2 pore throats divided in the initial state, the displacement efficiency of CO 2 flooding is 9.39% and 48.24% respectively in the range of 0.01-1.48 ms and 1.48-580.52 ms, the oil driven by CO2 mainly comes from larger pore throats, and a certain amount of residual oil is still reserved in smaller pore throats.
The nuclear magnetic resonance displacement experimental result of the N4 core sample is shown in fig. 5, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 34004.59, and the pore throat application range is 0.01-1431.46 ms. The nuclear magnetic resonance T 2 spectrum is bimodal in the initial oil-water distribution state, the right peak is higher than Zuo Feng, and most of detected signals are in the range that the relaxation time is not more than 1000 ms. Therefore, in the initial oil-water relation state, the sample N4 has a smaller pore throat of 0.01-1.59 ms, a relative content of 35.92%, and a larger pore throat of 1.59-1431.46 ms, and a relative content of 64.08%.
The experimental result of the N4 core sample CO 2 after displacement is shown in fig. 5, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 15942.98, the pore throat movement range is 0.01-580.52 ms, and the oil displacement efficiency is 53.12%. The spectrum of the core sample T 2 after CO 2 is bimodal, zuo Feng is slightly higher than Yu Youfeng, the right peak is obviously reduced, the left peak is reduced in amplitude, the whole curve is shifted left, and most of detected signals are in the range that the relaxation time is not more than 580.52 ms. According to the range of 2 types of pore throats divided in the initial state, the oil displacement efficiency of the CO 2 drive is 5.50 percent and 47.62 percent respectively in the range of 0.01-1.70 ms and 1.70-580.52 ms, and the oil driven by the CO 2 mainly comes from a larger pore throat, and a certain amount of residual oil is still reserved in a smaller pore throat.
The nuclear magnetic resonance displacement experimental result of the N5 core sample is shown in fig. 6, the envelope area of the nuclear magnetic resonance T 2 spectrum and the transverse axis is 43992.00, and the pore throat application range is 0.01-1245.88 ms. The nuclear magnetic resonance T2 spectrum is bimodal in the initial oil-water distribution state, the left peak is higher than the right peak, and most of detected signals are in the range that the relaxation time is not more than 1000 ms. Therefore, in the initial oil-water relation state, the sample N5 has a smaller pore throat of 0.01-1.70 ms, a relative content of 47.56%, and a larger pore throat of 1.70-1245.88 ms, and a relative content of 52.44%.
The experimental result of the N5 core sample CO 2 after displacement is shown in fig. 6, the envelope area of the nuclear magnetic resonance T 2 spectrum and the horizontal axis is 23456.70, the pore throat movement range is 0.01-622.26 ms, and the oil displacement efficiency is 53.32%. The spectrum of the core sample T 2 after CO 2 is bimodal, zuo Feng is slightly higher than Yu Youfeng, the right peak is obviously reduced, the left peak is reduced in amplitude, the whole curve is shifted left, and most of detected signals are in the range that the relaxation time is not more than 622.26 ms. According to the range of the class 2 pore throats divided in the initial state, the oil displacement efficiency of the CO 2 flooding is 17.76 and 35.56% respectively in the range of 0.01-1.48 ms and 1.48-622.26 ms, and unlike the 4 samples, the oil displaced by the CO 2 of the sample N5 mainly comes from the smaller pore throats, and a certain amount of residual oil is still reserved in the larger pore throats.
Referring to Table 3, the minimum miscible pressure MMP of the long 7 shale oil reservoir is 23.3MPa, the injection pressure of samples No. N3, no. N4 and No. N5 is 17MPa, and the oil displacement efficiency is 53.12-57.63% under the condition of non-miscible flooding, and is 54.69% on average, and is lower than that under the condition of miscible flooding. Different, the permeability of the sample No. N3 is higher, and the oil displacement efficiency is higher than that of the sample No. N4 under the same experimental conditions; the permeability of the sample No. N5 is higher, the displacement temperature is higher, and the displacement efficiency is lower than that of the samples No. N3 and No. N4, but the use degree of the sample to smaller pore throats is higher.
Table 3 CO 2 oil displacement characteristics for displacing different pore throats
According to the invention, through an indoor simulation experiment, injection pressure, constant flow, injection quantity and action time are changed, the distribution characteristics of fluid in porous media with different scales in the CO 2 fracturing process are evaluated by using a nuclear magnetic resonance online monitoring technology, the replacement rule of CO 2 and shale oil is defined, and a foundation is laid for improving the recovery ratio of shale oil reservoirs.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that are easily contemplated by those skilled in the art within the scope of the present invention are intended to be included in the scope of the present invention.
Claims (2)
1. A method for evaluating the oil-gas displacement rule of a CO 2 and shale oil reservoir is characterized by comprising the following steps: the method comprises the following steps:
s1: preparing core samples, numbering, wherein the diameter of the core samples is 25mm, and the number of the core samples is more than or equal to 5;
S2: selecting the core sample numbered in the step S1, sequentially washing oil, drying and weighing, and measuring the air permeability of the core sample, wherein the specific process of washing oil of the core sample is as follows: placing the core sample in an extraction container with the volume ratio of benzene to alcohol of 1:3 for washing oil, wherein the core sample is dried by the following concrete process: after oil washing is finished, placing the core sample in an incubator to heat to 100-105 ℃, keeping the temperature unchanged for 24-48 hours, and taking out to measure the dry weight of the core;
S3: fully saturating the core sample treated in the step S2 with simulated formation water;
S4: using manganese water to displace the core sample fully saturated with simulated formation water in S3 at a constant flow, performing nuclear magnetic resonance T2 spectrum test when the displacement is finished, wherein the concentration of Mn 2+ of the manganese water is larger than the mineralization degree of the formation water, the constant flow rate of the core sample of the fully saturated simulated formation water in the displacement S3 is 0.1-0.2 ml/min, the injection rate is 3-4 PV, and the PV is the pore volume;
S5: performing saturated simulated crude oil displacement on the core sample in the S4 at a constant flow rate until the produced liquid at the outlet of the core sample is free of water, establishing stratum original oil-water distribution, performing nuclear magnetic resonance T2 spectrum test on the core sample when the displacement is finished, performing saturated simulated crude oil displacement on the core sample in the S4 at a constant flow rate of 0.1-0.2 ml/min, configuring the simulated crude oil and refined kerosene according to a volume ratio of 1:1, wherein the viscosity of the simulated crude oil in the S5 is 6.5-8 mPa.s at the normal temperature of 20 ℃;
S6: displacing the core sample of the saturated simulated crude oil in the S5 with carbon dioxide at a constant flow rate until the core sample outlet production fluid does not contain crude oil, and performing nuclear magnetic resonance T2 spectrum test on the core sample at the end of displacement;
S7: re-selecting core samples with different numbers in the step S1, repeating the steps S2-S6, performing at least 5 groups of carbon dioxide displacement experiments, wherein the number of the experimental groups of carbon dioxide in a miscible state is at least 2, quantitatively calculating the carbon dioxide displacement efficiency according to nuclear magnetic resonance T 2 spectrums of the carbon dioxide displacement core samples with different constant flow rates, evaluating the oil-gas displacement rule of the CO 2 and the shale oil reservoir, and further optimizing the injection parameters of the carbon dioxide displacement of the shale oil reservoir, wherein the calculation formula of the carbon dioxide displacement efficiency b is as follows:
（1）
Wherein: s i is the difference of the T 2 spectrum frequency area after the initial saturated simulated crude oil and the carbon dioxide are replaced, and S o is the T 2 spectrum frequency area after the carbon dioxide is replaced.
2. The method for evaluating the oil-gas displacement law of the CO 2 and shale oil reservoirs according to claim 1, which is characterized by comprising the following steps: and S2, measuring the air permeability of the core sample by adopting a steady-state method.
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