CN115788373A - CO (carbon monoxide) 2 Evaluation method for oil-gas displacement rule of shale oil reservoir - Google Patents
CO (carbon monoxide) 2 Evaluation method for oil-gas displacement rule of shale oil reservoir Download PDFInfo
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- 238000011156 evaluation Methods 0.000 title claims abstract description 19
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- 229910052748 manganese Inorganic materials 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 5
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention belongs to the technical field of oil reservoir development, and particularly relates to CO 2 And a shale oil reservoir oil-gas replacement rule evaluation method. CO (carbon monoxide) 2 The evaluation method of oil-gas replacement rule of shale oil reservoir comprises the steps of fully saturating a simulated formation water and a saturated simulated crude oil respectively for a rock core sample, and performing nuclear magnetic resonance T 2 Performing spectrum test, performing displacement experiment on the rock core sample by using carbon dioxide with different injection parameters, and performing nuclear magnetic resonance T 2 Spectrum testing and comparison, quantitative calculation of CO under different constant flow displacement conditions 2 Oil displacing efficiency to CO 2 Evaluating the oil-gas replacement rule of the shale oil reservoir, thereby ensuring the optimization of the shale oil reservoir CO 2 And (4) injection conditions of oil displacement. The invention changes a constant flow displacement rock core sample through an indoor simulation experiment, and analyzes CO by utilizing a nuclear magnetic resonance online monitoring technology 2 The influence factors of oil gas displacement effect reveal CO 2 With shaleThe oil and gas replacement rule of the oil reservoir optimizes the on-site injection and process parameters and improves the recovery ratio of the shale oil reservoir.
Description
Technical Field
The invention belongs to the technical field of oil reservoir development, and particularly relates to CO 2 And a shale oil reservoir oil-gas replacement rule evaluation method.
Background
Waterflooding is a common method of enhanced recovery for conventional reservoirs at present, but after waterflood development, there is still a portion of crude oil in the formation pores that cannot be recovered, which we generally refer to as residual oil. For this part of the remaining oil, gas flooding is a commonly used tertiary oil recovery method, the mechanism of which is to displace the crude oil, CO, remaining in the reservoir by injecting gas into the formation to displace the water 2 Is one of the common gases in gas flooding, and the effect of the gas flooding on the aspect of improving the recovery efficiency is widely accepted.
China also develops CO in several oil fields in turn 2 And (5) driving items. However, due to CO 2 The problem of gas source shortage makes China in CO 2 The development of oil displacement is severely limited until some CO with smaller scale is discovered in the later period 2 Gas field, the technology has been developed, CO 2 The gas drive project is developed gradually in various large oil fields in China, and has a burst on theoretical research. Indoor experiments and field experiments show that compared with water flooding, CO is 2 The oil displacement can obviously improve the development effect of low-permeability oil reservoirs and small fault block oil reservoirs. CO2 2 The non-miscible flooding is easy to cause early CO 2 Break through, while under miscible conditions, CO 2 Can be mixed with crude oil at any ratio to eliminate interfacial tension and obtain high-efficiency CO 2 Oil displacement efficiency. In addition, CO 2 Fully dissolved in crude oil, reduces the viscosity of the crude oil, reduces the surface tension and other CO 2 The advantages of flooding are fully shown in the miscible flooding stage, so that more CO is generated 2 Entering a small throat to drive oil. Shale oil reservoir pore throat is fine, micro-nano pore throat develops, CO 2 The miscible flooding has adaptability to shale oil reservoirs.
Shale oil resources in each basin in China have great potential, and as the mining technology becomes more mature and perfect, shale oil must become a realistic strategic take-over resource. CO2 2 The oil displacement technology is applied to the development of domestic shale oil reservoirs, and has the great advantages of no water resource consumption, no damage to the reservoirs, rapid flowback and strong fracture-making capability. CN201810886910.2 discloses CO aiming at tight oil reservoir 2 A fracturing oil displacement integrated oil production method is disclosed, and CN201921121815.X discloses CO of a compact oil core 2 Displacement devices, CN202010456667.8, disclose dense reservoir CO 2 Evaluation method of reservoir driving characteristics, CN202010456442.2 discloses a rock core CO of different mineral components of a tight reservoir 2 An evaluation method for improving recovery efficiency. The above special interest to CO 2 The research object of oil displacement is mostly concentrated on compact sandstone and for CO 2 The research on the action rules of oil displacement and shale is less, and especially, CO is not revealed from the microscopic pore scale 2 A mechanism of displacement with shale oil. Current CO 2 Evaluation of oil displacement technical effect is mainly carried out through reservoir geological modeling and oil reservoirThe numerical simulation is realized, but some actual blocks of the mine field do not have the conditions of numerical simulation and geological modeling, for example, some blocks which are just developed have few wells, incomplete block oil deposit data and low block recognition degree, and are not suitable for directly adopting the numerical simulation and the geological modeling to carry out CO on the blocks 2 And analyzing and evaluating the oil displacement technical effect.
Disclosure of Invention
In view of the above problems, it is an object of the present invention to provide a CO 2 The evaluation method of oil-gas replacement rule of shale oil reservoir analyzes CO through indoor simulation experiment and by utilizing nuclear magnetic resonance on-line monitoring technology 2 The influence factors of the oil-gas displacement effect under the mixed phase and non-mixed phase states reveal CO 2 And the replacement rule of oil gas of the shale oil reservoir, thereby optimizing the injection and process parameters on site and improving the recovery ratio of the shale oil reservoir.
The technical scheme of the invention is as follows: CO (carbon monoxide) 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir comprises the following steps:
s1: preparing a core sample and numbering;
s2: selecting the core sample numbered in the S1, sequentially performing oil washing, drying and weighing, and measuring the air permeability of the core sample;
s3: fully saturating the core sample treated in the S2 with simulated formation water;
s4: using manganese water to displace the rock core sample of the fully saturated simulated formation water in the S3 at a constant flow, and performing nuclear magnetic resonance T after the displacement is finished 2 Testing a spectrum;
s5: performing saturated simulation crude oil displacement on the core sample in the S4 at a constant flow until the produced fluid at the core sample outlet does not contain water, establishing the original oil-water distribution of the stratum, and performing nuclear magnetic resonance T on the core sample when the displacement is finished 2 Testing a spectrum;
s6: displacing the saturated rock core sample simulating the crude oil in the S5 with carbon dioxide at a constant flow until the produced fluid at the outlet of the rock core sample does not contain the crude oil, and performing nuclear magnetic resonance T on the rock core sample when the displacement is finished 2 Testing a spectrum;
s7: reselecting S1, repeating the steps S2-S6, performing at least 5 groups of carbon dioxide displacement experiments, and displacing the nuclear magnetic resonance T of the rock core samples at different constant flow rates according to carbon dioxide 2 Spectrum, quantitative calculation of carbon dioxide oil displacement efficiency, for CO 2 Evaluating an oil-gas replacement rule of the shale oil reservoir so as to optimize injection parameters of carbon dioxide flooding of the shale oil reservoir, wherein the calculation formula of the carbon dioxide flooding efficiency b is as follows:
in the formula: s. the i Simulating T after crude oil and carbon dioxide displacement for initial saturation 2 Spectral frequency area difference, S o For post-carbon dioxide replacement T 2 Spectral frequency area.
The diameter of the core sample in the S1 is 25mm, and the number of the core samples is more than or equal to 5.
The specific process of washing the oil of the core sample in the S2 comprises the following steps: the core sample was placed in an extraction vessel with a volume ratio of benzene to alcohol of 1.
The specific process of drying the core sample in the S2 comprises the following steps: and after the oil washing is finished, placing the core sample in a thermostat, heating 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 S2, measuring the air permeability of the core sample by adopting a steady state method.
Mn of manganese water in S4 2+ The concentration of the displacement agent is greater than the mineralization degree of the formation water, the constant flow of a rock core sample of the fully saturated simulated formation water in the displacement S3 is 0.1-0.2 ml/min, the injection amount is 3-4 PV, and PV is the pore volume.
The constant flow of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 in the S5 is 0.1-0.2 ml/min.
The simulated crude oil in the S5 is prepared by mixing crude oil and refined kerosene according to the volume ratio of 1, and the viscosity of the simulated crude oil in the S5 is 6.5-8 mPa & S at the normal temperature of 20 ℃.
In the step S7, at least 5 carbon dioxide displacement experiments are performed, and the number of experimental groups in which carbon dioxide is in a miscible state is at least 2.
The invention has the technical effects that: 1. the invention combines the displacement experiment and the nuclear magnetic resonance testing technology, and displaces the nuclear magnetic resonance T of the rock core sample through different constant flows 2 Spectrum, the carbon dioxide oil displacement efficiency is calculated quantitatively, and compared with reservoir geological modeling and reservoir numerical simulation, the method has accurate and reliable calculation results; 2. the invention analyzes CO 2 Nuclear magnetic resonance T before and after oil and gas replacement with shale oil reservoir 2 Spectrum, revealing CO 2 In the replacement process, the evaluation result is more visual and accurate due to the oil-gas replacement micro mechanism and key control factors of pore throats with different apertures; 3. the invention combines the displacement experiment and the nuclear magnetic resonance testing technology, and compared with the traditional displacement experiment, the nuclear magnetic resonance T is used 2 The carbon dioxide oil displacement efficiency is calculated quantitatively by spectrum, and the product after displacement does not need to be collected and metered, so that the contact between experimenters and chemicals is reduced, and the method is safer; 4. the invention is through the reaction of CO 2 The evaluation is carried out with the oil-gas displacement rule of the shale oil reservoir, so that the injection parameters of the carbon dioxide displacement of the shale oil reservoir can be optimized, and CO is enabled to be 2 Injection into the reservoir displaces the crude oil for best results.
The following will be further described with reference to the accompanying drawings.
Drawings
FIG. 1 shows an exemplary pore size distribution of 10 1 ms-10 2 And (4) a schematic diagram of oil displacement efficiency calculation in the ms interval.
FIG. 2 shows the nuclear magnetic resonance T of the N1 core in the embodiment of the invention 2 Spectral curves.
FIG. 3 shows the nuclear magnetic resonance T of N2 core in the embodiment of the present invention 2 Spectral curves.
FIG. 4 shows the nuclear magnetic resonance T of the core No. N3 in the embodiment of the invention 2 Spectral curves.
FIG. 5 shows nuclear magnetic resonance T of N4 core in example of the present invention 2 Spectral curves.
FIG. 6 shows the nuclear magnetic resonance T of the core No. N5 in the embodiment of the invention 2 Spectral curves.
Detailed Description
Example 1
CO (carbon monoxide) 2 The method for evaluating the oil-gas displacement rule of the shale oil reservoir comprises the following steps:
s1: preparing a core sample and numbering;
s2: selecting the core sample numbered in the S1, sequentially performing oil washing, drying and weighing, and measuring the air permeability of the core sample;
s3: fully saturating the core sample treated in the step S2 to simulate formation water;
s4: using manganese water to displace the rock core sample of fully saturated simulated formation water in the S3 at a constant flow, and performing nuclear magnetic resonance T at the end of displacement 2 Testing a spectrum;
s5: performing saturated simulated crude oil displacement on the core sample in the S4 at a constant flow until produced fluid at the core sample outlet does not contain water, establishing the original oil-water distribution of the stratum, and performing nuclear magnetic resonance T on the core sample when the displacement is finished 2 Testing a spectrum;
s6: displacing the saturated rock core sample simulating the crude oil in the S5 with carbon dioxide at a constant flow until the produced fluid at the outlet of the rock core sample does not contain the crude oil, and performing nuclear magnetic resonance T on the rock core sample when the displacement is finished 2 Testing a spectrum;
s7: re-selecting core samples with different numbers in the S1, repeating the steps S2-S6, performing at least 5 groups of carbon dioxide displacement experiments, and displacing the core samples at different constant flows according to the nuclear magnetic resonance T of the carbon dioxide 2 Spectrum, quantitative calculation of carbon dioxide oil displacement efficiency, for CO 2 Evaluating an oil-gas replacement rule of the shale oil reservoir so as to optimize injection parameters of carbon dioxide flooding of the shale oil reservoir, wherein the calculation formula of the carbon dioxide flooding efficiency b is as follows:
in the formula: s. the i Simulating T after crude oil and carbon dioxide displacement for initial saturation 2 Spectral frequency area difference, S o For post carbon dioxide T 2 Spectral frequency area.
The principle of the nuclear magnetic resonance technology in the invention is that after the rock sample is saturated with oil or water, the nuclear magnetic moments of hydrogen nuclei in the oil or water are subjected to energy level splitting in an external static magnetic field which is uniformly distributed, at the moment, a radio frequency field with specific frequency is additionally applied, the nuclear magnetic moments are subjected to absorption transition to generate nuclear magnetic resonance, and the nuclear magnetic resonance signal intensity is in direct proportion to the number of the hydrogen nuclei contained in the sample to be detected. The process that the magnetization vector deviates from the equilibrium state and then returns to the equilibrium state when nuclear magnetic resonance occurs under the excitation of the radio frequency field is called relaxation, and a signal that the amplitude of relaxation motion of the relaxation motion decays along with time can be received. Can use T 1 Longitudinal relaxation time and T 2 Transverse relaxation time describes how fast the signal decays. Although both reflect reservoir petrophysical and fluid properties, due to T 1 Measurement of velocity vs. T 2 The measurement speed is slow, so the latter measurement is generally used in nuclear magnetic resonance measurement. The relaxation time is determined by the petrophysical properties and the fluid characteristics, and for the same fluid, the relaxation speed depends only on the petrophysical properties. The environment and the function between the atomic nuclei of each hydrogen nucleus in a pure substance sample such as pure water are the same, and a relaxation time T can be used 2 Physical properties of the samples are described.
The rock fluid systems have different physical properties and have T 2 The distribution is also different, in turn T can be obtained by NMR 2 The distribution determines the physical properties of the rock fluid. Because the simulated oil does not contain hydrogen nuclei 1H, T in the bound water state measured after the oil drives water to the rock core and does not produce water 2 The distribution curve, which is characterized by the distribution of the bound fluid, and T in the saturated water state 2 The portion of the distribution curve with the ordinate reduced from that of the distribution curve is the mobile fluid portion.
It is known from the theory of seepage mechanics that when the radius of the pores in the reservoir is small to a certain extent, the fluid in the pores is bound by capillary force or viscous force and cannot flow. According to previous researches, the shale reservoir bound fluid is mainly distributed in pores with small radius, only a small part of the shale reservoir bound fluid exists on the wall surface of a pore throat with large radius, and the mobile fluid is mainly distributed in the pore throat with large radius. An exact pore throat radius cutoff value exists in the porous medium, the fluid existing in the porous medium is divided into two parts, and the fluid in all pores smaller than the cutoff value is in a bound state and is difficult to flow under the existing conditions; whereas the fluid in the pores above this value is mobile.
According to the principle of nuclear magnetic resonance, nuclear magnetic resonance T measurement of saturated water states of cores with different permeabilities 2 The spectrum has a one-to-one correspondence with the pore radius in the rock, i.e. a longer T 2 Relaxation times correspond to larger pores in the rock sample and shorter T 2 The relaxation time corresponds to a smaller pore. Then at T 2 There is also a cut-off point on the spectrum, when T of the pore fluid 2 When the relaxation time is larger than a certain value, the fluid is mobile fluid, and the fluid is bound fluid on the contrary.
The invention combines displacement experiment and nuclear magnetic resonance testing technology, and measures the core oil signal T when the water content of the liquid outlet end is 100 percent 2 Spectrum, calculating oil displacement efficiency under different experimental conditions, thereby defining CO 2 The replacement rule with shale oil is carried out according to the standard SY/T5336-2006 and SY/T6490-2016.
The diameter of the core sample in the S1 is 25mm, and the number of the core samples is more than or equal to 5.
The specific process of washing the oil of the core sample in the S2 comprises the following steps: the core sample was placed in an extraction vessel with a volume ratio of benzene to alcohol of 1. Through the extraction that benzene and alcohol volume ratio are 1.
The specific process of drying the core sample in the S2 comprises the following steps: and after the oil washing is finished, placing the core sample in a thermostat, heating 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 S2, measuring the air permeability of the core sample by adopting a steady state method, and specifically executing the GB/T29172-2012 standard.
Mn of manganese water in S4 2+ The concentration of (2) is greater than the mineralization degree of the formation water, and the fully saturated simulated formation water in S3 is displacedThe constant flow rate of the rock core sample is 0.1-0.2 ml/min, the injection amount is 3-4 PV, PV is the pore volume, and the manganese water in S4 is used for fully inhibiting hydrogen ion signals in formation water to ensure that T is subjected to 2 The spectrum only represents the hydrogen ion signal of the simulated crude oil, so that the oil displacement efficiency is evaluated.
The constant flow of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 in the S5 is 0.1-0.2 ml/min.
The simulated crude oil in the S5 is prepared from crude oil and refined kerosene according to a volume ratio of 1, and the viscosity of the simulated crude oil in the S5 is 6.5-8 mPa & S at the normal temperature of 20 ℃.
In the step S7, at least 5 carbon dioxide displacement experiments are performed, and the number of experimental groups in which carbon dioxide is in a miscible state is at least 2.
Example 2
The evaluation method of the invention is adopted to carry out CO treatment on the core sample of the shale oil deposit in the oil field 2 Evaluating the replacement rule of the shale oil. The specific process is as follows:
s1: preparing a core sample and numbering;
drilling a rock core with the diameter of 25mm on the standard rock core, numbering the rock core by numbers N1, N2, N3, N4 and N5, and respectively measuring the diameter and the length of the rock core;
s2: sequentially carrying out oil washing, drying and weighing on the core sample obtained in the step S1, and measuring the air permeability of the core sample; the specific process of oil washing of the core sample comprises the following steps: placing the core sample into an extraction container with the volume ratio of benzene to alcohol being 1: after the oil washing is finished, placing the rock core sample in a constant temperature box, heating to 105 ℃, keeping the temperature unchanged for 48 hours, taking out the measured rock core dry weight, and measuring the air permeability of the rock core sample by adopting a steady state method, wherein the physical property parameters of the rock core are shown in table 1;
table 1 nuclear magnetic resonance displacement experiment core physical property table
S3: fully saturating the core sample treated by the S2 with simulated formation water, and carrying out experimental equipment: oxford Geospec2/53 NMR; an LDY-150 high-temperature high-pressure dynamic displacement system;
s4: using manganese water to displace the rock core sample of the fully saturated simulated formation water in the S3 at a constant flow, and performing nuclear magnetic resonance T after the displacement is finished 2 The manganese water is Mn in the spectrum test 2+ The concentration of (A) is 30000mg/L, the constant flow of the core sample of the fully saturated simulated formation water in the displacement S3 is 0.1ml/min, and the injection amount is 3-4 PV.
S5: performing saturated simulated crude oil displacement on the core sample in the step S4 at a constant flow until the produced fluid at the core sample outlet does not contain water, and establishing the original oil-water distribution of the stratum; performing nuclear magnetic resonance T on the rock core sample at the end of displacement 2 Performing spectrum test, wherein the constant flow of a 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 saturated in the simulated crude oil in the S5 with carbon dioxide at a constant flow until the produced fluid at the outlet of the core sample does not contain the crude oil, and carrying out a nuclear magnetic resonance T2 spectrum test on the core sample when the displacement is finished;
s7: repeating the steps S2 to S6, and performing a displacement experiment on the rock core sample in a CO2 miscible phase and immiscible phase state, wherein the nuclear magnetic resonance displacement experiment 2 group in the CO2 miscible phase state and the nuclear magnetic resonance displacement experiment 3 group in the CO2 immiscible phase state are performed, the nuclear magnetic resonance displacement experiment parameters in the experiment are set as shown in the table 2, the nuclear magnetic resonance T2 spectrum test is performed when each group of experiments are finished, and the nuclear magnetic resonance T2 spectrum is shown in the figures 2 to 5;
TABLE 2 NMR Displacement experiment parameter settings
Comparison of CO in S7 2 Nuclear magnetic resonance T of core sample in miscible and immiscible states 2 Spectrum, quantitative calculation of CO 2 Oil displacement efficiency in a mixed phase and non-mixed phase state, as shown in FIG. 1, the pore diameter is determined to be 10 1 ms-10 2 The ms pore throat flooding efficiency calculation method is shown schematically. Assuming a radius of 10 1 ms-10 2 The initial saturated crude oil amount in the pore throat of ms is represented by (Si), the crude oil amount in the region after water flooding is represented by So, and the saturated crude oil T before and after the comparative experiment 2 The difference value of the frequency area of the spectrum can be calculated, and the carbon dioxide oil displacement efficiency b can be calculated according to the following formula:
in the formula: s i Simulating T after crude oil and carbon dioxide displacement for initial saturation 2 Spectral frequency area difference, S o For post-carbon dioxide replacement T 2 Spectral frequency area.
CO 2 The displacement efficiency of the displacement with crude oil in miscible and immiscible states is shown in table 3.
The initial nuclear magnetic resonance result of the N1 core sample is shown in FIG. 2, and the nuclear magnetic resonance T 2 The envelope area of the spectrum and the horizontal axis is 32504.54, and the aperture throat dynamic range is between 0.01 and 505.26ms. Nuclear magnetic resonance T in initial oil-water distribution state 2 The spectrum is approximately bimodal, the left peak is slightly higher than the right peak, most of the detected signals have a lower peak value in the range that the relaxation time does not exceed 100ms, and after the nuclear magnetic resonance relaxation time exceeds 100 ms. Thus, the N1 sample has three types of pore throats, a small pore throat between 0.01 and 1.20ms, a medium pore throat between 1.20 and 191.16ms, and a large pore throat between 191.16 and 505.26ms in the initial oil water relationship state, and the relative contents of the class 3 pore throats are calculated to be 46.96%, 52.12%, and 0.92%.
N1 core sample CO 2 The results of the experiment after displacement are shown in FIG. 2, NMR T 2 The envelope area of the spectrum and the horizontal axis is 13880.82, the pore throat using range is 0.01-622.26 ms, and the oil displacement efficiency is 57.30%. CO2 2 Post-flood core sample T 2 The spectrum is approximately in a single peak state, wherein the right peak of the initial state is obviously reduced, the reduction amplitude of the left peak is smaller, and most of the detected signals are in the range that the relaxation time does not exceed 30 ms. Class 3 pore throat ranges divided according to initial state, CO ranges from 0.01 to 1.20ms, 1.20 to 191.16ms, 191.16 to 505.26ms 2 Oil displacement efficiency of the flooding is respectively 16.50%, 40.29% and 0.51%, and CO 2 The oil that is driven off comes primarily from the larger pore throats, with a certain amount of remaining oil remaining in the smaller pore throats.
The result of the nuclear magnetic resonance displacement experiment of the N2 core sample is shown in FIG. 3, and the nuclear magnetic resonance T 2 The envelope area of the spectrum and the horizontal axis is 50946.28, and the pore throat movement range is between 0.01 and 880.49ms. Nuclear magnetic resonance T in initial oil-water distribution state 2 The spectrum is bimodal, with the right peak higher than the left, and most of the detected signal is within a relaxation time of no more than 1000 ms. Therefore, in the initial oil-water relationship state of the sample No. N2, the smaller pore throat is 0.01-1.20 ms, the relative content is 33.87%, the larger pore throat is 1.20-880.49 ms, and the relative content is 66.13%.
N2 core sample CO 2 The results of the experiment after displacement are shown in FIG. 3, NMR T 2 The envelope area of the spectrum and the horizontal axis is 20960.78, the pore throat utilization range is 0.01-622.26 ms, and the oil displacement efficiency is 58.86%. CO2 2 Post-flood core sample T 2 The spectrum is in a double peak state, wherein the right peak is obviously reduced, the reduction amplitude of the left peak is smaller, the curve is integrally shifted to the left, and most of detected signals are in the range that the relaxation time does not exceed 144.81 ms. Class 2 pore throat ranges divided according to initial state, CO in the range of 0.01-1.20 ms, 1.20-880.49 ms 2 Oil displacement efficiency of oil displacement is 17.75 percent and 41.11 percent respectively, and CO 2 The oil displaced is primarily from the larger pore throat, with a certain amount of remaining oil remaining in the smaller pore throat.
According to the early-stage experiment, the minimum miscible phase pressure MMP of the long 7 shale oil reservoir is 23.3MPa, the injection pressure of the No. 2 sample and the No. 1 sample is 25MPa, the two samples are both displacement under the miscible phase displacement condition, and the oil displacement efficiency is higher. The difference is that the constant flow of the N1 sample is 0.2mL/min, the oil displacement efficiency is 53.03%, the constant flow of the N2 sample is 0.4mL/min, and the oil displacement efficiency is 58.86%, which indicates that the improvement of the constant flow can improve the oil displacement efficiency of the core sample to a certain extent.
The result of the nuclear magnetic resonance displacement experiment of the N3 core sample is shown in FIG. 4, and the nuclear magnetic resonance T 2 The envelope area of the spectrum and the horizontal axis is 49421.66, and the pore throat dynamic range is between 0.01 and 439.76ms. Nuclear magnetic resonance T in initial oil-water distribution state 2 The spectrum is bimodal, with the right peak higher than the left, and most of the detected signal is within a relaxation time of no more than 1000 ms. Therefore, in the initial oil-water relationship state of the sample N3, the smaller pore throat is 0.01-1.38 ms, the relative content is 31.97%, the larger pore throat is 1.38-439.76 ms, and the relative content is 68.03%.
N3 core sample CO 2 The results of the experiment after displacement are shown in FIG. 4, NMR T 2 The envelope area of the spectrum and the horizontal axis is 20938.63, the pore throat mobility range is 0.01-580.52 ms, and the oil displacement efficiency is 57.63%. CO2 2 Post-flood core sample T 2 The spectrum is in a bimodal state, wherein the right peak is obviously reduced, the reduction amplitude of the left peak is small, the curve is integrally shifted left, and most of detected signals are in the range that the relaxation time does not exceed 580.52 ms. Class 2 pore throat range divided according to initial state, CO in the range of 0.01-1.48 ms, 1.48-580.52 ms 2 The oil displacement efficiency of the oil displacement is respectively 9.39% and 48.24%, the oil displaced by CO2 mainly comes from a larger pore throat, and a certain amount of residual oil is still present in a smaller pore throat.
The result of the nuclear magnetic resonance displacement experiment of the N4 core sample is shown in FIG. 5, and the nuclear magnetic resonance T 2 The envelope area of the spectrum and the horizontal axis is 34004.59, and the pore throat dynamic range is between 0.01 and 1431.46ms. Nuclear magnetic resonance T in initial oil-water distribution state 2 The spectrum is bimodal, with the right peak higher than the left, and most of the detected signal is within a relaxation time of no more than 1000 ms. Therefore, in the initial oil-water relationship state, the small pore throat of the sample N4 is 0.01-1.59 ms, the relative content is 35.92%, the large pore throat is 1.59-1431.46 ms, and the relative content is 64.08%.
N4 core sample CO 2 The results of the experiment after displacement are shown in FIG. 5, NMR T 2 The envelope area of the spectrum and the horizontal axis is 15942.98, the pore throat using range is 0.01-580.52 ms, and the oil displacement efficiency is 53.12%. CO2 2 Post-flood core sample T 2 The spectrum is in a double peak state, the left peak is slightly higher than the right peak, the right peak is obviously reduced, the reduction amplitude of the left peak is small, the curve is integrally shifted to the left, and most of detected signals are in the range that the relaxation time does not exceed 580.52 ms. Class 2 pore throat ranges divided according to initial state, CO ranges from 0.01-1.70 ms and 1.70-580.52 ms 2 The oil displacement efficiency of the flooding is 5.50 percent and 47.62 percent respectively, and the CO content is 2 The oil that is driven off comes primarily from the larger pore throats, with a certain amount of remaining oil remaining in the smaller pore throats.
The result of the nuclear magnetic resonance displacement experiment of the N5 core sample is shown in FIG. 6, and the nuclear magnetic resonance T 2 The envelope area of the spectrum and the horizontal axis is 43992.00, and the throat area is between 0.01 and 1245.88ms. The nuclear magnetic resonance T2 spectrum is in a bimodal state under 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 does not exceed 1000 ms. Therefore, in the initial oil-water relationship state of the sample No. N5, the smaller pore throat is 0.01-1.70 ms, the relative content is 47.56%, the larger pore throat is 1.70-1245.88 ms, and the relative content is 52.44%.
N5 core sample CO 2 The results of the experiment after displacement are shown in FIG. 6, NMR T 2 The envelope area of the spectrum and the horizontal axis is 23456.70, the pore throat using range is 0.01-622.26 ms, and the oil displacement efficiency is 53.32%. CO2 2 Post-flood core sample T 2 The spectrum is in a double-hump state, the left peak is slightly higher than the right peak, the right peak is obviously reduced, the reduction amplitude of the left peak is small, the curve is integrally shifted left, and most of detected signals are in the range that the relaxation time does not exceed 622.26 ms. Class 2 pore throat ranges divided according to initial state, CO ranges from 0.01-1.48 ms, 1.48-622.26 ms 2 The oil displacement efficiency of the flooding is 17.76 percent and 35.56 percent respectively, and the sample is different from the 4 samples, namely, the No. N5 sample CO 2 The oil displaced is primarily from the smaller pore throats with some residual oil remaining in the larger pore throats.
Referring to table 3, the minimum miscible phase pressure MMP of the long 7 shale reservoir is 23.3MPa, the injection pressures of samples No. 3, N4 and N5 are 17MPa, the displacement is performed under the immiscible phase displacement condition, the displacement efficiency is 53.12-57.63%, the average displacement efficiency is 54.69%, and the displacement efficiency is lower than that under the miscible phase displacement condition. The difference is that the permeability of the N3 sample is higher, and the oil displacement efficiency is higher than that of the N4 sample under the same experimental conditions; the N5 sample has higher permeability and higher displacement temperature, and the oil displacement efficiency is not as good as that of the N3 and N4 samples, but the mobility degree of smaller pore throats is higher.
TABLE 3 CO 2 Displacement of oil characteristics for displacing different pore throats
The invention changes the injection pressure, the constant flow, the injection amount and the action time through an indoor simulation experiment, and utilizes the nuclear magnetic resonance on-line monitoring technology to evaluate CO 2 The distribution characteristics of the fluid in the porous media with different scales in the fracturing process are determined, and CO is determined 2 And the replacement rule with shale oil lays a foundation for improving the recovery ratio of the shale oil reservoir.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (9)
1. CO (carbon monoxide) 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: the method comprises the following steps:
s1: preparing a core sample and numbering;
s2: selecting the core sample numbered in the S1, sequentially performing oil washing, drying and weighing, and measuring the air permeability of the core sample;
s3: fully saturating the core sample treated in the S2 with simulated formation water;
s4: using manganese water to displace a rock core sample of the fully saturated simulated formation water in the S3 at a constant flow, and carrying out nuclear magnetic resonance T after the displacement is finished 2 Testing a spectrum;
s5: performing saturated simulated crude oil displacement on the core sample in the S4 at constant flow until the produced fluid at the core sample outlet does not contain water, establishing the original oil-water distribution of the stratum, and performing nuclear magnetic resonance T on the core sample when the displacement is finished 2 Testing a spectrum;
s6: displacing the core sample saturated in the S5 simulated crude oil by using carbon dioxide at a constant flow until the produced fluid at the outlet of the core sample does not contain the crude oil, and performing nuclear magnetic resonance T on the core sample when the displacement is finished 2 Testing a spectrum;
s7: reselecting the core samples with different numbers in the step S1, repeating the steps S2-S6, performing at least 5 groups of carbon dioxide displacement experiments, and displacing the core samples at different constant flow rates according to the nuclear magnetic resonance T of the carbon dioxide 2 Spectrum, quantitative calculation of carbon dioxide oil displacement efficiency, for CO 2 Evaluating an oil-gas replacement rule of the shale oil reservoir so as to optimize injection parameters of carbon dioxide flooding of the shale oil reservoir, wherein the calculation formula of the carbon dioxide flooding efficiency b is as follows:
in the formula: S i simulating T after crude oil and carbon dioxide displacement for initial saturation 2 The difference in the area of the spectral frequency area,S o is T after carbon dioxide replacement 2 Spectral frequency area.
2. CO according to claim 1 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: the diameter of the core sample in the S1 is 25mm, and the number of the core samples is more than or equal to 5.
3. CO according to claim 1 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: in said S2The specific process of oil washing of the core sample comprises the following steps: the core sample was placed in an extraction vessel with a volume ratio of benzene to alcohol of 1.
4. CO according to claim 1 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: the specific process of drying the core sample in the S2 comprises the following steps: and after the oil washing is finished, placing the core sample in a constant temperature box, heating to 100-105 ℃, keeping the temperature unchanged for 24-48 hours, and taking out to measure the dry weight of the core.
5. CO according to claim 1 2 The method for evaluating the oil-gas displacement rule of the shale oil reservoir is characterized by comprising the following steps of: and in the S2, measuring the air permeability of the core sample by adopting a steady state method.
6. The method for evaluating the oil-gas replacement law of the CO2 and shale oil reservoir according to claim 1, which is characterized by comprising the following steps: mn of manganese water in S4 2+ The concentration of the core is greater than the mineralization degree of formation water, the constant flow of a core sample fully saturated with simulated formation water in the displacement S3 is 0.1-0.2ml/min, the injection amount is 3-4 PV, and PV is pore volume.
7. CO according to claim 1 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: and the constant flow of the saturated simulated crude oil core sample in the simulated crude oil displacement S4 in the S5 is 0.1-0.2ml/min.
8. CO according to claim 1 2 The evaluation method of the oil-gas replacement rule of the shale oil reservoir is characterized by comprising the following steps: the simulated crude oil in the S5 is prepared by mixing crude oil and refined kerosene according to the volume ratio of 1, and the viscosity of the simulated crude oil in the S5 is 6.5-8mPa & S at the normal temperature of 20 ℃.
9. CO according to claim 1 2 The method for evaluating the oil-gas displacement rule of the shale oil reservoir is characterized by comprising the following steps of: at least 5 groups of carbon dioxide are performed in the step S7In the displacement experiment, the number of experimental groups of carbon dioxide in a miscible state is at least 2.
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