A heterogeneous core miscible flooding experimental device and method based on layered nuclear magnetic T2 testing

Abstract

The present invention discloses a heterogeneous core miscible flooding experimental device and method based on layered nuclear magnetic resonance (NMR) T2 testing, belonging to the technical field of miscible flooding development in low-permeability heterogeneous oil reservoirs. The device comprises a liquid supply system, a temperature control system, a 1.5-inch online NMR core holder, a pressure loading system, a 1.5-inch core barrel, a nuclear magnetic resonance instrument, and a metering device. The device utilizes spliced ​​1.5-inch core samples to simulate rock heterogeneity within a reservoir. During the experiment, layered T2 scanning is performed to obtain T2 spectrum distributions in regions with different permeabilities in the heterogeneous formation, thereby achieving accurate simulation of heterogeneous oil reservoirs and the effect of miscible flooding on improving oil recovery. This method is beneficial for studying the distribution of residual oil within rocks during miscible flooding, and provides a basis for improving the ultimate recovery of oil reservoirs and increasing the productivity and recovery rate of oil wells.

Description

Technical Field

[0001] The present invention belongs to the technical field of miscible flooding development of low-permeability heterogeneous oil reservoirs, and particularly relates to a heterogeneous core miscible flooding experimental device and method based on layered nuclear magnetic resonance T2 testing. Background Art

[0002] CO2 miscible flooding enhances oil recovery (ERR) by not only increasing oil production but also achieving geological sequestration of the greenhouse gas CO2, offering both economic and environmental benefits. It is an effective method for ensuring energy security and mitigating the greenhouse effect. However, reservoirs formed under different sedimentary processes have varying structural properties, leading to reservoir heterogeneity that affects fluid distribution and migration, thereby impacting development outcomes. The effectiveness of CO2 miscible flooding within porous media is governed by the complex pore structure, and the mechanisms of miscible flooding within heterogeneous porous media are currently poorly understood. Therefore, in-depth research into the impact of reservoir heterogeneity on oilfield production is crucial for enhancing oil recovery and CO2 displacement and storage efficiency.

[0003] Current laboratory physical simulation experiments studying miscible flooding in heterogeneous cores typically employ parallel core holders or sand-filled small core cylinder models to simulate intralayer heterogeneity. These methods can generally replicate rock heterogeneity, but significant challenges remain: the parallel holders affect the CO2 miscibility during the experiment, the sand-filled small core cylinder models cannot accurately measure the various parameters of the permeable layers, and the intralayer heterogeneity of thick oil reservoirs cannot be accurately simulated. Furthermore, these methods are only suitable for measuring the ultimate recovery of miscible flooding and cannot be used to study the miscible displacement mechanism within heterogeneous porous media. Therefore, it is urgent to propose a heterogeneous core miscible flooding experimental process and method based on layered nuclear magnetic resonance T2 testing to accurately obtain the specific distribution of remaining oil at each stage of the CO2 miscible flooding process in heterogeneous cores and to study the miscible displacement mechanism within heterogeneous cores. Summary of the Invention

[0004] In response to the above-mentioned problems existing in the prior art, the present invention proposes a heterogeneous core miscible flooding experimental device and method based on layered nuclear magnetic resonance T2 testing, which realizes the true simulation of the miscible development process of heterogeneous reservoirs in oil fields, provides technical support for studying the specific distribution of oil and water in each stage of the CO2 miscible flooding process, and is conducive to studying the miscible flooding mechanism in heterogeneous cores. The design is reasonable, solves the shortcomings of the prior art, and has good results.

[0005] A heterogeneous core miscible flooding experimental device based on layered nuclear magnetic resonance T2 testing, including a fluid supply system, a temperature control system, a 1.5-inch online nuclear magnetic resonance core holder, a pressure loading system, a 1.5-inch core barrel, a nuclear magnetic resonance instrument, and a metering device;

[0006] The fluid supply system includes a constant speed and constant pressure pump and three intermediate containers, namely a manganese water intermediate container, a formation oil intermediate container and a CO2 intermediate container, which are used to inject fluid into the 1.5-inch online nuclear magnetic core holder;

[0007] The 1.5-inch online nuclear magnetic resonance core holder is used to clamp the core sample and is equipped with a nuclear magnetic resonance instrument to monitor the specific T2 spectrum of the core sample in real time during the pressure drive process;

[0008] The pressure loading system includes a confining pressure circulation pump and a manual high-pressure pump. The confining pressure circulation pump is used to apply confining pressure to the core sample in the 1.5-inch online nuclear magnetic core holder, obtain the confining pressure value in real time, and circulate and keep warm;

[0009] The temperature control system is used to control the temperature of the fluid injected into the core sample;

[0010] The metering device is used to measure the water output from the outflow end of the 1.5-inch online nuclear magnetic core holder.

[0011] Furthermore, the constant speed and constant pressure pump is respectively connected to the high-pressure injection pipes of the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container through a four-way valve; the outflow ends of the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container are all connected to a high-pressure liquid outlet pipe, and each high-pressure liquid outlet pipe is connected to the injection pipe arranged at the injection end of the 1.5-inch online nuclear magnetic core clamp through a six-way valve, and the outflow end of the 1.5-inch online nuclear magnetic core clamp is connected to the metering device through a discharge pipe, and the discharge pipe is provided with a back pressure valve and an outlet control valve.

[0012] Furthermore, an injection pressure gauge is provided on the six-way valve for obtaining the injection pressure of the fluid in the core sample in real time.

[0013] Furthermore, the confining pressure pump circulates through the pressure injection pipeline and the fluorine oil intermediate container and is connected to the 1.5-inch online nuclear magnetic core holder, using fluorine oil to avoid the influence of the confining pressure liquid on the nuclear magnetic signal; the manual high-pressure pump is connected to the back pressure valve through the pressure injection pipeline.

[0014] Furthermore, the 1.5-inch online nuclear magnetic core holder includes a cylinder, a sealing cover and an external coil. The cylinder contains a core sample and is sealed at both ends with a sealing cover. The core sample is covered with a rubber sleeve and a radio frequency coil is provided outside the sealing cover to measure the T2 signal of the internal core.

[0015] Furthermore, the temperature control system is configured to have electric heating insulation sleeves on the outer walls of the manganese water intermediate container, the formation oil intermediate container, the CO2 intermediate container and the fluorine oil intermediate container, and an electric heater is provided in the clamp for adjusting the internal temperature of the clamp.

[0016] A heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing, using the heterogeneous core miscible flooding experimental device based on layered nuclear magnetic T2 testing as described above, comprises the following steps:

[0017] Step 1: Prepare core samples. The core samples are divided into heterogeneous artificial core cementation and natural heterogeneous core splicing cementation;

[0018] Step 2: injecting manganese water, formation oil and CO2 into the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container respectively, and injecting fluorine oil into the fluorine oil intermediate container;

[0019] Step 3: Control the confining pressure circulation pump to apply an initial confining pressure to the cavity of the 1.5-inch online nuclear magnetic core holder. The initial confining pressure ranges from 2 to 5 MPa. At the same time, the temperature of the fluid in each intermediate container and the temperature of the core sample in the 1.5-inch online nuclear magnetic core holder are kept consistent with the formation temperature of the reservoir to be simulated. After the temperature is constant at the formation temperature, adjust the four-way valve and use a constant speed and constant pressure pump to increase the pressure of the formation oil intermediate container and the CO2 intermediate container to the formation pressure and stabilize it;

[0020] Step 4: Adjust the four-way valve and the six-way valve to control the constant-speed, constant-pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Use the manganese water to displace the core sample. Obtain the manganese water injection pressure based on the injection pressure gauge. Measure the water flow rate from the discharge pipe using a metering device. After the formation water injection pressure and water flow rate stabilize, calculate the initial water permeability of the core.

[0021] Step 5: Control the manual high-pressure pump to slowly apply back pressure to the back-pressure valve until the pressure reaches the formation pressure. Observe the injection pressure gauge and control the confining pressure circulation pump to ensure that the confining pressure is always higher than the injection pressure. After the injection pressure indicator stabilizes, adjust the four-way valve and the six-way valve to control the constant-speed constant-pressure pump to inject the formation oil in the formation oil intermediate container into the 1.5-inch online nuclear magnetic core holder at the preset flow rate. After water stops flowing out of the outflow end, close the inlet and outlet switches of the holder. After the formation oil has aged for a period of time, perform a layered test of the initial core T2 signal.

[0022] Step 6: Adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Use the manganese water to displace the core sample. Test the core T2 signal in layers every time a certain pore volume of manganese water is injected. As soon as manganese water appears in the metering device, adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject a certain pore volume of CO2 at a preset flow rate. During this period, the core T2 signal is continuously tested in layers, and the oil output from the discharge pipe is measured using the metering device to obtain a curve of injection pressure and recovery factor changing with time.

[0023] Step 7: Adjust the four-way valve and the six-way valve, and control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Each time a certain pore volume of manganese water is injected, the core T2 signal is tested in layers; and the oil output of the discharge pipe is measured using a metering device to obtain a curve of the injection pressure and recovery rate over time. The experiment is stopped when oil stops flowing from the outlet; based on the obtained layered test core T2 signal, the oil distribution in the heterogeneous core formation at different displacement stages is analyzed, and the miscible displacement mechanism in the heterogeneous core is studied.

[0024] Furthermore, in step 1, the heterogeneous artificial core cementing preparation process is as follows: injecting different purpose sands into two beakers respectively, and then adding 5% epoxy resin to each beaker and stirring thoroughly to obtain two different mixed sands; placing a semi-cylindrical spacer into a 1.5-inch core barrel, filling the 1.5-inch core barrel with one type of mixed sand in small amounts and multiple times, removing the spacer and filling the 1.5-inch core barrel with another type of mixed sand in small amounts and multiple times, fully compacting with a press, placing in a constant temperature box for drying, and then measuring the specific porosity and permeability of the core samples;

[0025] The natural heterogeneous core splicing and cementing process is as follows: existing natural cores are cut and spliced ​​together, and the specific porosity and permeability of the spliced ​​core samples are measured; the spliced ​​core samples are vacuumed, saturated with formation water, and placed in a 1.5-inch online nuclear magnetic core holder;

[0026] If the effect of gravity is not considered, the core splicing surface is made perpendicular to the length direction of the core;

[0027] If the effect of gravity is considered, the core splicing surface is made parallel to the length direction of the core. For positive rhythm research, the core with low permeability is placed on the top, and for negative rhythm research, the core with low permeability is placed on the bottom.

[0028] Furthermore, in steps 5 to 7, if the effect of gravity is not considered, the core T2 signal is tested layer by layer perpendicular to the length direction of the core; if the effect of gravity is considered, the core T2 signal is tested layer by layer parallel to the length direction of the core.

[0029] Beneficial technical effects brought about by the present invention:

[0030] The present invention proposes a 1.5-inch multi-layer spliced ​​core test method, which avoids the influence of the parallel clamp experiment on the CO2 miscibility effect and the inability to accurately measure the various parameters of each permeable layer in the sand-filled small core column model and accurately simulate the intra-layer heterogeneity of thick oil layers, and truly restores the heterogeneity of the rock in the reservoir.

[0031] The present invention proposes a heterogeneous core miscible flooding experimental process and method based on layered nuclear magnetic resonance T2 testing. The process uses spliced ​​1.5-inch core samples to simulate the rock heterogeneity within the reservoir. During the experiment, layered T2 scanning is used to obtain the T2 spectrum distribution of different permeability areas in the heterogeneous formation. This achieves accurate simulation of heterogeneous oil reservoirs and the effect of miscible flooding on improving oil recovery. This is beneficial for studying the distribution of residual oil in the rock during miscible flooding, and provides a basis for improving the ultimate recovery rate of the reservoir and increasing the productivity and recovery rate of the oil well. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a heterogeneous core miscible flooding experimental device based on layered nuclear magnetic T2 testing in the present invention;

[0033] Figure 2 This is a top view of the 1.5-inch core barrel used during the experiment;

[0034] In the figure, 1-constant speed and constant pressure pump; 2-four-way valve; 3-manganese water intermediate container; 4-formation oil intermediate container; 5-CO2 intermediate container; 6-six-way valve; 7-injection pressure gauge; 8-circulating confining pressure pump; 9-fluorine oil intermediate container; 10-1.5-inch online nuclear magnetic resonance core holder; 11-nuclear magnetic resonance instrument; 12-manual high-pressure pump; 13-back pressure valve; 14-outlet control valve; 15-metering device; 16-temperature control system. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention will be further described below with reference to specific embodiments:

[0036] A heterogeneous core miscible flooding experimental device based on layered nuclear magnetic T2 testing, such as Figure 1 As shown, it includes a fluid supply system, a temperature control system 16, a 1.5-inch online nuclear magnetic core holder, a pressure loading system, a 1.5-inch core barrel, a nuclear magnetic resonance instrument 11 and a metering device 15;

[0037] The fluid supply system includes a constant speed and constant pressure pump 1 and three intermediate containers, namely a manganese water intermediate container 3, a formation oil intermediate container 4 and a CO2 intermediate container 5, which are used to inject fluid into a 1.5-inch online nuclear magnetic core holder 10;

[0038] A constant-speed, constant-pressure pump 1 is connected to the high-pressure injection pipelines of the manganese water intermediate container 3, the formation oil intermediate container 4, and the CO2 intermediate container 5, respectively, through a four-way valve 2. The outflow ends of the manganese water intermediate container 3, the formation oil intermediate container 4, and the CO2 intermediate container 5 are all connected to high-pressure liquid outlet pipelines. Each high-pressure liquid outlet pipeline is connected to the injection pipeline installed at the injection end of the 1.5-inch online nuclear magnetic core holder 10 through a six-way valve 6. The outflow end of the 1.5-inch online nuclear magnetic core holder 10 is connected to a metering device 15 via a discharge pipeline. The discharge pipeline is equipped with a back-pressure valve 13 and an outlet control valve 14. An injection pressure gauge 7 is installed on the six-way valve 6 to obtain real-time injection pressure of the fluid in the core sample.

[0039] The 1.5-inch online nuclear magnetic resonance core holder 10 is used to clamp the core sample and is equipped with a nuclear magnetic resonance instrument 11 to monitor the specific T2 spectrum of the core sample in real time during the pressure-driven process. The 1.5-inch online nuclear magnetic resonance core holder 10 includes a cylinder, a sealing cover and an external coil. The cylinder contains the core sample and is sealed at both ends with a sealing cover. The core sample is covered with a rubber sleeve, and a coil is set outside the sealing cover to measure the internal core T2 signal.

[0040] The pressure loading system includes a confining pressure circulation pump and a manual high-pressure pump 12. The confining pressure circulation pump is used to apply confining pressure to the core sample in the 1.5-inch online nuclear magnetic core holder 10, obtain the confining pressure value in real time, and circulate and keep warm. The confining pressure pump circulates through the pressure injection pipeline and the fluorine oil intermediate container 9 and then connects to the 1.5-inch online nuclear magnetic core holder 10, using fluorine oil to avoid the influence of the confining pressure liquid on the nuclear magnetic signal. The manual high-pressure pump 12 is connected to the back pressure valve 13 through the pressure injection pipeline.

[0041] The temperature control system 16 is used to control the temperature of the fluid injected into the core sample; the temperature control system 16 is configured to have an electric heating insulation sleeve on the outer walls of the manganese water intermediate container 3, the formation oil intermediate container 4, the CO2 intermediate container 5 and the fluorine oil intermediate container 9, and a temperature controller is provided inside the cylinder to monitor and adjust the internal temperature of the cylinder.

[0042] The metering device 15 is used to measure the water output from the outflow end of the 1.5-inch online nuclear magnetic core holder 10.

[0043] A heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing, using the heterogeneous core miscible flooding experimental device based on layered nuclear magnetic T2 testing as described above, comprises the following steps:

[0044] Step 1: Prepare core samples. The core samples are divided into heterogeneous artificial core cementation and natural heterogeneous core splicing cementation;

[0045] The preparation process of heterogeneous artificial core cementation is as follows: inject a certain mesh sand and 5% epoxy resin into two beakers and stir them thoroughly to obtain two different mixed sands; put a semi-cylindrical spacer into the 1.5-inch core barrel, such as Figure 2 As shown, the 1.5-inch core barrel consists of two semi-hollow cylindrical structures. A well-mixed sand mixture is added to the 1.5-inch core barrel in small amounts multiple times. The spacer is removed and another mixed sand mixture is added to the 1.5-inch core barrel in small amounts multiple times. The core sample is fully compacted with a press and dried in a constant temperature oven. The specific porosity and permeability of the core sample are then measured to predict fluid flow rates, calculate pore volumes, and analyze and compare displacement effects on cores with different porosity and permeability.

[0046] The natural heterogeneous core splicing and cementing process is as follows: existing natural cores are cut and spliced ​​together, and the specific porosity and permeability of the spliced ​​core samples are measured; the spliced ​​core samples are vacuumed, saturated with formation water, and placed in a 1.5-inch online nuclear magnetic core holder;

[0047] If the effect of gravity is not considered, the core splicing surface is made perpendicular to the length direction of the core;

[0048] If the effect of gravity is considered, the core splicing surface is made parallel to the length direction of the core. For positive rhythm research, the core with low permeability is placed on the top, and for negative rhythm research, the core with low permeability is placed on the bottom.

[0049] Step 2: injecting manganese water, formation oil and CO2 into the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container respectively, and injecting fluorine oil into the fluorine oil intermediate container;

[0050] Step 3: Control the confining pressure circulation pump to apply an initial confining pressure to the cavity of the 1.5-inch online nuclear magnetic core holder. The initial confining pressure ranges from 2 to 5 MPa. At the same time, the temperature of the fluid in each intermediate container and the temperature of the core sample in the 1.5-inch online nuclear magnetic core holder are kept consistent with the formation temperature of the reservoir to be simulated. After the temperature is constant at the formation temperature, adjust the four-way valve and use a constant speed and constant pressure pump to increase the pressure of the formation oil intermediate container and the CO2 intermediate container to the formation pressure and stabilize it;

[0051] Step 4: Adjust the four-way valve and the six-way valve to control the constant speed and pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at the preset flow rate. For cores with worse porosity and permeability, use a smaller flow rate to avoid pressure buildup caused by excessive inlet flow. Use manganese water to displace the core sample, obtain the manganese water injection pressure based on the reading of the injection pressure gauge, and use a metering device to measure the water flow rate from the discharge pipe. After the formation water injection pressure and water flow rate stabilize, calculate the initial water permeability of the core;

[0052] Step 5: Control the manual high-pressure pump to slowly apply back pressure to the back-pressure valve until the pressure reaches the formation pressure. Observe the injection pressure gauge and control the confining pressure circulation pump to ensure that the confining pressure is always higher than the injection pressure. After the injection pressure indicator stabilizes, adjust the four-way valve and the six-way valve to control the constant-speed constant-pressure pump to inject the formation oil in the formation oil intermediate container into the 1.5-inch online nuclear magnetic core holder at the preset flow rate. After water stops flowing out of the outflow end, close the inlet and outlet switches of the holder. After the formation oil has aged for a period of time, perform a layered test of the initial core T2 signal.

[0053] Step 6: Adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Use the manganese water to displace the core sample. Test the core T2 signal in layers every time a certain pore volume of manganese water is injected. As soon as manganese water appears in the metering device, adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject a certain pore volume of CO2 at a preset flow rate. During this period, the core T2 signal is continuously tested in layers, and the oil output from the discharge pipe is measured using the metering device to obtain a curve of injection pressure and recovery factor changing with time.

[0054] Step 7: Adjust the four-way valve and the six-way valve, and control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Each time a certain pore volume of manganese water is injected, the core T2 signal is tested in layers; and the oil output of the discharge pipe is measured using a metering device to obtain a curve of the injection pressure and recovery rate over time. The experiment is stopped when oil stops flowing from the outlet; based on the obtained layered test core T2 signal, the oil distribution in the heterogeneous core formation at different displacement stages is analyzed, and the miscible displacement mechanism in the heterogeneous core is studied.

[0055] In steps 5 to 7, if the effect of gravity is not considered, the core T2 signal is tested layer by layer perpendicular to the length direction of the core; if the effect of gravity is considered, the core T2 signal is tested layer by layer parallel to the length direction of the core.

[0056] Example 1

[0057] This example proposes a heterogeneous core miscible flooding experimental method based on layered nuclear magnetic resonance T2 testing. Using the apparatus described above, the specific distribution of remaining oil at each stage of the miscible flooding process under heterogeneous and different rhythmic conditions is measured by taking gravity into account. The method includes the following steps:

[0058] Step 1: Prepare core samples. The core samples are divided into heterogeneous artificial core cementation and natural heterogeneous core splicing cementation;

[0059] The heterogeneous artificial core cementing preparation process is as follows: Sample 1: 200-mesh quartz sand and 5% epoxy resin are injected into a beaker and thoroughly mixed. Sample 2: 40-mesh quartz sand and 5% epoxy resin are injected into a beaker and thoroughly mixed. Two different sand mixtures are obtained. A semi-cylindrical spacer is placed in a 1.5-inch core barrel. Small amounts of one well-mixed sand are then added to the barrel in multiples. The spacer is removed and the other mixed sand is then added to the barrel in multiples. The core samples are then fully compacted using a press and dried in a constant temperature oven for 24 hours. The porosity and permeability of the core samples are then measured.

[0060] The natural heterogeneous core splicing and cementing process is as follows: existing natural cores are cut and spliced ​​together, and the specific porosity and permeability of the spliced ​​core samples are measured; the spliced ​​core samples are vacuumed, saturated with formation water, and placed in a 1.5-inch online nuclear magnetic core holder;

[0061] The core splicing surface is made parallel to the length direction of the core. For the positive rhythm study, the core of the low permeability part is placed on the top, and for the negative rhythm study, the core of the low permeability part is placed on the bottom.

[0062] Step 2: injecting manganese water, formation oil and CO2 into the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container respectively, and injecting fluorine oil into the fluorine oil intermediate container;

[0063] Step 3: Control the confining pressure circulation pump to apply an initial confining pressure of 5 MPa to the cavity of the 1.5-inch online nuclear magnetic core holder. At the same time, the temperature of the fluid in each intermediate container and the temperature of the core sample in the 1.5-inch online nuclear magnetic core holder are kept consistent with the formation temperature of the reservoir to be simulated. After the temperature is constant at the formation temperature, adjust the four-way valve and use a constant speed and constant pressure pump to increase the pressure of the formation oil intermediate container and the CO2 intermediate container to the formation pressure and stabilize it;

[0064] Step 4: Adjust the four-way valve and the six-way valve to control the constant-speed, constant-pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a flow rate of 1 ml / min. Use the manganese water to displace the core sample. Obtain the manganese water injection pressure based on the reading on the injection pressure gauge. Measure the water output from the discharge pipe using a metering device. After the formation water injection pressure and water output stabilize, calculate the initial water-tested permeability of the core.

[0065] Step 5: Control the manual high-pressure pump to slowly apply back pressure to the back-pressure valve until the pressure reaches the formation pressure. Observe the injection pressure gauge and control the confining pressure circulation pump to ensure that the confining pressure is always 3 MPa higher than the injection pressure. After the injection pressure indicator stabilizes, adjust the four-way valve and the six-way valve to control the constant-speed constant-pressure pump to inject the formation oil in the formation oil intermediate container into the 1.5-inch online nuclear magnetic resonance core holder at a flow rate of 0.08 ml / min. After the outflow end stops producing water, close the inlet and outlet switches of the holder. After the formation oil has aged for 24 hours, test the initial core T2 signal using layers parallel to the core length.

[0066] Step 6: Adjust the four-way valve and the six-way valve, control the constant speed and pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a flow rate of 0.08 ml / min, and use the manganese water to displace the core sample. Every time 0.1 PV of manganese water is injected, the core T2 signal is tested in layers parallel to the length of the core. After the metering device just appears manganese water, adjust the four-way valve and the six-way valve, control the constant speed and pressure pump to inject 0.3 PV of CO2 at a flow rate of 0.08 ml / min, and every time 0.1 PV is injected, the core T2 signal is tested in layers parallel to the length of the core. The metering device is used to measure the oil output of the discharge pipe to obtain the injection pressure and recovery factor change curve over time.

[0067] Step 7: Adjust the four-way valve and the six-way valve, and control the constant speed and pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a flow rate of 0.08 ml / min. Every time 0.1 PV of manganese water is injected, the core T2 signal is tested in layers parallel to the length direction of the core; and the oil output of the discharge pipe is measured using a metering device to obtain the injection pressure and recovery rate change curve with time. When the outlet stops producing oil, stop the experiment; based on the obtained core T2 signal tested in layers parallel to the length direction of the core, analyze the oil distribution in the heterogeneous core formation at different displacement stages, and study the miscible displacement mechanism in the heterogeneous core.

[0068] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A heterogeneous core miscible flooding experimental method based on layered nuclear magnetic resonance T2 testing, characterized in that: A heterogeneous core miscible flooding experimental device based on layered NMR T2 testing was used, including a fluid supply system, a temperature control system, a 1.5-inch online NMR core holder, a pressure loading system, a 1.5-inch core barrel, an NMR instrument, and a metering device. The fluid supply system includes a constant speed and constant pressure pump and three intermediate containers, namely a manganese water intermediate container, a formation oil intermediate container and a CO2 intermediate container, which are used to inject fluid into the 1.5-inch online nuclear magnetic core holder; The 1.5-inch online nuclear magnetic resonance core holder is used to clamp the core sample and is equipped with a nuclear magnetic resonance instrument to monitor the specific T2 spectrum of the core sample in real time during the pressure drive process; The pressure loading system includes a confining pressure circulation pump and a manual high-pressure pump. The confining pressure circulation pump is used to apply confining pressure to the core sample in the 1.5-inch online nuclear magnetic core holder, obtain the confining pressure value in real time, and circulate and keep warm; The temperature control system is used to control the temperature of the fluid injected into the core sample; The metering device is used to measure the water output from the outflow end of the 1.5-inch online nuclear magnetic core holder; The method comprises the following steps: Step 1: Prepare core samples. The core samples are divided into heterogeneous artificial core cementation and natural heterogeneous core splicing cementation; Step 2: injecting manganese water, formation oil and CO2 into the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container respectively, and injecting fluorine oil into the fluorine oil intermediate container; Step 3: Control the confining pressure circulation pump to apply an initial confining pressure to the cavity of the 1.5-inch online nuclear magnetic core holder. The initial confining pressure ranges from 2 to 5 MPa. At the same time, the temperature of the fluid in each intermediate container and the temperature of the core sample in the 1.5-inch online nuclear magnetic core holder are kept consistent with the formation temperature of the reservoir to be simulated. After the temperature is constant at the formation temperature, adjust the four-way valve and use a constant speed and constant pressure pump to increase the pressure of the formation oil intermediate container and the CO2 intermediate container to the formation pressure and stabilize it; Step 4: Adjust the four-way valve and the six-way valve to control the constant-speed, constant-pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Use the manganese water to displace the core sample. Obtain the manganese water injection pressure based on the injection pressure gauge. Measure the water flow rate from the discharge pipe using a metering device. After the formation water injection pressure and water flow rate stabilize, calculate the initial water permeability of the core. Step 5: Control the manual high-pressure pump to slowly apply back pressure to the back-pressure valve until the pressure reaches the formation pressure. Observe the injection pressure gauge and control the confining pressure circulation pump to ensure that the confining pressure is always higher than the injection pressure. After the injection pressure indicator stabilizes, adjust the four-way valve and the six-way valve to control the constant-speed constant-pressure pump to inject the formation oil in the formation oil intermediate container into the 1.5-inch online nuclear magnetic core holder at the preset flow rate. After water stops flowing out of the outflow end, close the inlet and outlet switches of the holder. After the formation oil has aged for a period of time, perform a layered test of the initial core T2 signal. Step 6: Adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Use the manganese water to displace the core sample. Test the core T2 signal in layers every time a certain pore volume of manganese water is injected. As soon as manganese water appears in the metering device, adjust the four-way valve and the six-way valve to control the constant speed and constant pressure pump to inject a certain pore volume of CO2 at a preset flow rate. During this period, the core T2 signal is continuously tested in layers, and the oil output from the discharge pipe is measured using the metering device to obtain a curve of injection pressure and recovery factor changing with time. Step 7: Adjust the four-way valve and the six-way valve, and control the constant speed and constant pressure pump to inject the manganese water in the manganese water intermediate container into the 1.5-inch online nuclear magnetic core holder at a preset flow rate. Each time a certain pore volume of manganese water is injected, the core T2 signal is tested in layers; and the oil output of the discharge pipe is measured using a metering device to obtain a curve of the injection pressure and recovery rate over time. The experiment is stopped when oil stops flowing from the outlet; based on the obtained layered test core T2 signal, the oil distribution in the heterogeneous core formation at different displacement stages is analyzed, and the miscible displacement mechanism in the heterogeneous core is studied.

2. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 1 is characterized in that: The constant speed and constant pressure pump is respectively connected to the high-pressure injection pipelines of the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container through a four-way valve; the outflow ends of the manganese water intermediate container, the formation oil intermediate container and the CO2 intermediate container are all connected to a high-pressure liquid outlet pipeline, and each high-pressure liquid outlet pipeline is connected to the injection pipeline arranged at the injection end of the 1.5-inch online nuclear magnetic core clamp through a six-way valve, and the outflow end of the 1.5-inch online nuclear magnetic core clamp is connected to the metering device through a discharge pipeline, and the discharge pipeline is provided with a back pressure valve and an outlet control valve.

3. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 2 is characterized in that: The six-way valve is provided with an injection pressure gauge for obtaining the injection pressure of the fluid in the core sample in real time.

4. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 3 is characterized in that: The confining pressure circulation pump is connected to a pressure injection pipeline and a fluorine oil intermediate container and then connected to a 1.5-inch online nuclear magnetic core holder, using fluorine oil to avoid the influence of the confining pressure liquid on the nuclear magnetic signal; the manual high-pressure pump is connected to the back-pressure valve through the pressure injection pipeline.

5. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 4 is characterized in that: The 1.5-inch online nuclear magnetic core holder includes a cylinder, a sealing cover, and an external coil. The cylinder contains a core sample, and both ends of the cylinder are sealed with sealing covers. The core sample is covered with a rubber sleeve, and a radio frequency coil is provided outside the sealing cover to measure the T2 signal of the internal core.

6. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 5 is characterized in that: The temperature control system is configured to have electric heating insulation sleeves on the outer walls of the manganese water intermediate container, the formation oil intermediate container, the CO2 intermediate container and the fluorine oil intermediate container, and an electric heater inside the clamp for adjusting the internal temperature of the clamp.

7. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 1 is characterized in that: In step 1, the heterogeneous artificial core cementing preparation process is as follows: injecting different purpose sands into two beakers respectively, and then adding 5% epoxy resin to each beaker and stirring thoroughly to obtain two different mixed sands; placing a semi-cylindrical spacer into a 1.5-inch core barrel, filling the 1.5-inch core barrel with one type of mixed sand in small amounts and multiple times, removing the spacer and filling the 1.5-inch core barrel with another type of mixed sand in small amounts and multiple times, fully compacting with a press, placing in a constant temperature box for drying, and then measuring the specific porosity and permeability of the core samples; The natural heterogeneous core splicing and cementing process is as follows: existing natural cores are cut and spliced ​​together, and the specific porosity and permeability of the spliced ​​core samples are measured; the spliced ​​core samples are vacuumed, saturated with formation water, and placed in a 1.5-inch online nuclear magnetic core holder; If the effect of gravity is not considered, the core splicing surface is made perpendicular to the length direction of the core; If the effect of gravity is considered, the core splicing surface is made parallel to the length direction of the core. For positive rhythm research, the core with low permeability is placed on the top, and for negative rhythm research, the core with low permeability is placed on the bottom.

8. The heterogeneous core miscible flooding experimental method based on layered nuclear magnetic T2 testing according to claim 1 is characterized in that: In steps 5 to 7, if the effect of gravity is not considered, the core T2 signal is tested layer by layer perpendicular to the length direction of the core; if the effect of gravity is considered, the core T2 signal is tested layer by layer parallel to the length direction of the core.

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