Experimental device and method for evaluating sensitivity of ultra-low permeability reservoir based on nuclear magnetic resonance

Abstract

The invention discloses an ultra-low permeability reservoir sensitivity evaluation experiment device and method based on nuclear magnetic resonance. The problems that an existing experimental method is long in experimental period, effective seepage cannot be achieved, and various sensitive coupling phenomena are prone to occurring when an ultra-low permeability reservoir is experimented are mainly solved. The device is characterized by comprising a nuclear magnetic resonance magnet (10), a clamp holder (9) is arranged in the nuclear magnetic resonance magnet (10), a confining pressure device (12) is connected to the clamp holder (9), the two ends of the clamp holder (9) are connected with six-way valves respectively, the two six-way valves are connected with a vacuum system and a liquid supply system respectively, a first six-way valve (5) is further connected with a gas supply system and a heavy water test tube (6), and a second six-way valve (6) is further connected with a second six-way valve (6). And the second six-way valve (18) is connected with a constant-pressure pump (20) through a back-pressure valve (19). The experimental device is simple in structure, convenient to operate and short in experimental period, avoids the occurrence of various occasional sensitivity problems during single sensitivity test, and improves the accuracy of reservoir sensitivity experimental evaluation.

Description

Technical Field

[0001] The invention relates to the field of oil and gas development experiments, in particular to an ultra-low permeability reservoir sensitivity evaluation experimental device and method based on nuclear magnetic resonance. Background Art

[0002] At present, reservoir sensitivity experiments in China are often conducted based on the existing industry standard SY / T5358-2010, which is mainly applicable to rock samples with a permeability greater than 1mD, and is not applicable to low-permeability and ultra-low-permeability tight sandstone or shale reservoirs. In the process of conducting experiments based on the reference standard, a very high displacement pressure difference is required to achieve stability, and the experimental cycle is long, and there are problems such as fluid "unable to drive"; or when conducting constant-speed experiments, pressure is held back, resulting in a simultaneous increase in internal pressure and confining pressure, and multiple sensitivity coupling phenomena occur, thereby affecting the accuracy of the experiment. Summary of the invention

[0003] In order to overcome the problems of existing experimental methods in ultra-low permeability reservoir experiments, such as long experimental cycle, inability to achieve effective seepage, and easy occurrence of multiple sensitivity coupling phenomena, the present invention provides an ultra-low permeability reservoir sensitivity evaluation experimental device and method based on nuclear magnetic resonance. The experimental device has a simple structure, convenient operation, and a short experimental cycle, and avoids the occurrence of occasional problems of multiple sensitivities when performing a single sensitivity test, thereby improving the accuracy of reservoir sensitivity experimental evaluation.

[0004] The technical solution of the present invention is: an ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance, including a liquid supply system, an air supply system, a vacuum system, and a nuclear magnetic resonance magnet. A clamp is arranged inside the nuclear magnetic resonance magnet, and a confining pressure device is connected to the clamp. The two ends of the clamp are respectively connected to a first six-way valve and a second six-way valve, and the first six-way valve and the second six-way valve are respectively connected to the vacuum system and the liquid supply system, the first six-way valve is also connected to the air supply system and the heavy water test tube, and the second six-way valve is connected to a constant pressure pump through a back pressure valve.

[0005] Furthermore, the vacuum system includes a vacuum pump, the vacuum pump is connected to a first drying tube and a second drying tube via a four-way joint, the first drying tube is connected to a first six-way valve, and the second drying tube is connected to a second six-way valve.

[0006] Furthermore, the gas supply system includes a methane gas cylinder, the methane gas cylinder is connected to a booster pump, and the booster pump outlet is connected to the first six-way valve via a high-pressure valve.

[0007] Furthermore, the liquid supply system includes a double-bar constant speed and constant pressure pump, which is connected to several parallel intermediate containers. The other end of the intermediate container is connected to a third six-way valve, and the third six-way valve is respectively connected to the first six-way valve and the second six-way valve through a three-way joint.

[0008] An ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance includes the following steps:

[0009] (1) Prepare core samples and prepare 8% potassium chloride solution for the experiment;

[0010] (ii) Saturate the core with 8% potassium chloride solution and place the core in a holder under an NMR magnet to test the core NMR porosity;

[0011] (iii) performing sensitivity tests on the cores respectively, wherein the sensitivity tests are stress sensitivity tests and / or acid sensitivity tests and / or alkali sensitivity tests and / or salt sensitivity tests and / or water-acid sensitivity tests, and each test is conducted using different core samples;

[0012] (iv) Calculate the nuclear magnetic permeability of the core under different conditions based on the experimental results in step (iii), and calculate the damage rate of the core under different media.

[0013] Further, the stress sensitivity experiment includes the following steps:

[0014] S1.1. Take out the core that has been tested for nuclear magnetic porosity and dry it;

[0015] S1.2, put the core into the holder, apply confining pressure to the holder through the confining pressure device, apply back pressure to the core outlet through the constant pressure pump, and evacuate the core through the vacuum pump;

[0016] S1.3. Alternately increase the internal pressure and back pressure of the core by increasing the pump and the constant pressure pump until the internal pressure reaches P1, and then conduct the first NMR T2 spectrum test;

[0017] S1.4, continue to increase the internal pressure to P2, P3, P4, P5, etc., and perform nuclear magnetic resonance T2 spectrum test at each pressure;

[0018] S1.5. Adjust the constant pressure pump to gradually reduce the back pressure at the core outlet, and perform NMR T2 spectrum test at each back pressure;

[0019] S1.6. Calculate the nuclear magnetic permeability of the core based on the nuclear magnetic T2 spectrum, and calculate the change rate of the nuclear magnetic permeability of the core under different net stresses based on the nuclear magnetic permeability.

[0020] Further, the water sensitivity experiment comprises the following steps:

[0021] S2.1. Place the core saturated with 8% potassium chloride solution in a holder, apply confining pressure to the holder through a confining pressure device, and add 4% potassium chloride solution and distilled water into intermediate container A and intermediate container B respectively;

[0022] S2.2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution;

[0023] S2.3, allowing the heavy water in the heavy water test tube to enter the holder, and performing nuclear magnetic resonance T2 spectrum testing in real time;

[0024] S2.4, dry the core and evacuate it; then saturate the core with 4% potassium chloride solution in the intermediate container A from both ends of the clamp, perform nuclear magnetic resonance scanning in real time, test the nuclear magnetic resonance porosity in the state of 4% potassium chloride solution, and calculate the nuclear magnetic resonance permeability;

[0025] S2.5. Repeat steps S2.3 and S2.4, and replace the intermediate container A in step S2.4 with the intermediate container B to obtain the nuclear magnetic porosity in the distilled water state, thereby calculating the nuclear magnetic permeability and permeability change rate in the distilled water state.

[0026] Further, the acid sensitivity experiment comprises the following steps:

[0027] S3.1. Place the core saturated with 8% potassium chloride solution in a holder, apply confining pressure to the holder through a confining pressure device, and add 15% HCl and 8% potassium chloride solution into intermediate container A and intermediate container B respectively;

[0028] S3.2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution;

[0029] S3.3, allowing the heavy water in the heavy water test tube to enter the holder, and performing nuclear magnetic resonance T2 spectrum testing in real time;

[0030] S3.4, dry the core and evacuate the core; then saturate the core with 15% HCl solution in the intermediate container A from both ends of the holder, and keep both ends of the holder closed for at least one hour;

[0031] S3.5, repeat steps S3.3 and S3.4, and replace the intermediate container in step S3.4 with the 8% potassium chloride solution in the intermediate container B, and calculate the nuclear magnetic permeability in the state of 8% potassium chloride solution;

[0032] S3.6. Calculate the rate of change of permeability under acidic conditions.

[0033] Further, the alkali sensitivity experiment comprises the following steps:

[0034] S4.1. Place the core saturated with 8% potassium chloride solution in a holder, apply confining pressure to the holder through a confining pressure device, and add sodium hydroxide solutions with different pH values ​​of 7-13 into intermediate container A, intermediate container B, intermediate container C, and intermediate container D respectively;

[0035] S4.2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution;

[0036] S4.3, allowing the heavy water in the heavy water test tube to enter the holder, and performing nuclear magnetic resonance T2 spectrum testing in real time;

[0037] S4.4, dry the core and evacuate the core; saturate the core with sodium hydroxide solution in the intermediate container A from both ends of the holder, perform nuclear magnetic resonance scanning in real time, wait for at least 12 hours, and then test the nuclear magnetic porosity and nuclear magnetic permeability in the state of sodium hydroxide solution with a pH value of 7;

[0038] S4.5, repeat steps S4.3 and S4.4, replace the intermediate container A in step S4.4 with intermediate container B, intermediate container C, and intermediate container D in sequence, and test the nuclear magnetic porosity and nuclear magnetic permeability under sodium hydroxide solutions with different pH values;

[0039] S4.6. Calculate the permeability change rate under sodium hydroxide solutions with different pH values.

[0040] Further, the salt sensitivity experiment comprises the following steps:

[0041] S5.1. Place the saturated core into a holder, apply confining pressure to the holder through a confining pressure device, and add potassium chloride solutions of different concentrations into intermediate container A, intermediate container B, intermediate container C, and intermediate container D respectively;

[0042] S5.2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution;

[0043] S5.3, allowing the heavy water in the heavy water test tube to enter the holder, and performing nuclear magnetic resonance T2 spectrum testing in real time;

[0044] S5.4, dry the core and evacuate it; then saturate the solution in the intermediate container A into the core from both ends of the holder, perform nuclear magnetic resonance scanning in real time, and test the nuclear magnetic resonance porosity and nuclear magnetic resonance permeability;

[0045] S5.5, repeat steps S5.3 and S5.4, and replace the intermediate container A in step S5.4 with intermediate container B, intermediate container C, and intermediate container D in sequence, and calculate the nuclear magnetic permeability of potassium chloride solutions of different concentrations;

[0046] S5.6. Calculate the permeability change rate under different concentrations of potassium chloride solution.

[0047] The present invention has the following beneficial effects: due to the adoption of the above scheme, the experimental device has a simple structure, convenient operation and a short experimental cycle; compared with the traditional reservoir sensitivity evaluation experimental method, the experimental method is more suitable for the evaluation of reservoirs where low permeability, ultra-low permeability and other fluids are difficult to flow, making up for the shortcomings of the current reservoir sensitivity flow experimental evaluation method, and greatly shortening the test time and reducing human errors. In the process of a single sensitivity experiment, the occurrence of the reservoir sensitivity coupling effect caused by speed sensitivity is eliminated, and the stress sensitivity effect caused by high confining pressure during acid sensitivity, alkali sensitivity, salt sensitivity and water sensitivity tests due to core density can be prevented, thereby improving the accuracy of the reservoir sensitivity experimental evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the structure of the present invention;

[0049] Figure 2 This is the NMR T2 spectrum before and after the shale acid sensitivity experiment;

[0050] Figure 3 This is a diagram of the permeability change before and after the shale acid sensitivity experiment.

[0051] In the figure, 1-methane gas cylinder, 2-boosting pump, 3-control valve, 4-pressure regulating valve, 5-first six-way valve, 6-heavy water test tube, 7-inlet pressure sensor, 8-outlet pressure sensor, 9-clamp, 10-nuclear magnetic resonance magnet, 11-tee joint, 12-confining pressure device, 13-first drying tube, 14-vacuum pressure gauge, 15-four-way joint, 16-vacuum pump, 17-second drying tube, 18-second six-way valve, 19-back pressure valve, 20-constant pressure pump, 21-data acquisition device, 22-third six-way valve, 23-intermediate container A, 24-intermediate container B, 25-intermediate container C, 26-intermediate container D, 27-fourth six-way valve, 28-double-bar constant speed and constant pressure pump. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the accompanying drawings:

[0053] Depend on Figure 1 As shown, an ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance includes a liquid supply system, a gas supply system, a vacuum system, and a nuclear magnetic resonance magnet 10. A clamp 9 is provided in the nuclear magnetic resonance magnet 10, and the core is placed in the clamp 9. The clamp 9 is connected to a confining pressure device 12, which can apply confining pressure to the clamp 9. The two ends of the clamp 9 are respectively connected to a first six-way valve 5 and a second six-way valve 18.

[0054] The vacuum system includes a vacuum pump 16, which is connected to a first drying tube 13, a second drying tube 17 and a vacuum pressure gauge 14 through a four-way joint 15, wherein the other end of the first drying tube 13 is connected to a first six-way valve 5, and the other end of the second drying tube 17 is connected to a second six-way valve 18. The gas supply system includes a methane cylinder 1, which is connected to a booster pump 2, and the outlet of the booster pump 2 is connected to a control valve 3 and a high-pressure valve 4, and the other end of the high-pressure valve 4 is connected to the first six-way valve 5. The liquid supply system includes a double-bar constant speed and pressure pump 28, which is connected to a plurality of parallel intermediate containers through a fourth six-way valve 27, and the other end of the intermediate container is connected to a third six-way valve 22, and the third six-way valve 22 is respectively connected to the first six-way valve 5 and the second six-way valve 18 through a three-way joint 11.

[0055] The first six-way valve 5 is also connected to a heavy water test tube 6 and an inlet pressure sensor 7, the second six-way valve 18 is connected to a back pressure valve 19 and an outlet pressure sensor 8, the back pressure valve 19 is connected to a constant pressure pump 20, and the inlet pressure sensor 7 and the outlet pressure sensor 8 are both connected to a data acquisition device 21.

[0056] An ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance, the experimental method adopts the above-mentioned experimental device and comprises the following steps:

[0057] (I) Select the rock blocks required for the experiment, and drill several parallel samples of core columns with a diameter of 25 mm. Dry the rock samples to constant weight, take out the cores, place them in a cooler, cool them to room temperature, test the length and diameter of the cores for later use; prepare the 8% potassium chloride solution used in the experiment.

[0058] (ii) evacuating the core and pressurizing it with a saturated 8% potassium chloride solution, and placing the core in a holder 9 under a nuclear magnetic resonance magnet 10 to test the core nuclear magnetic resonance porosity;

[0059] (iii) performing sensitivity tests on the cores respectively. According to the needs, the sensitivity test may be one or more of a stress sensitivity test, an acid sensitivity test, an alkali sensitivity test, a salt sensitivity test, and a water-acid sensitivity test. Different core samples are tested in each test;

[0060] (iv) Calculate the nuclear magnetic permeability of the core under different conditions based on the experimental results in step (iii), and calculate the permeability change rate of the core under different media, that is, the core damage rate.

[0061] The specific steps of the stress sensitivity experiment, acid sensitivity experiment, alkali sensitivity experiment, salt sensitivity experiment, and water-acid sensitivity experiment are described below.

[0062] The stress sensitivity experiment includes the following steps:

[0063] S1.1. Prepare the core, prepare the 8% potassium chloride solution used in the experiment, vacuum and pressurize the core to saturate it with 8% potassium chloride solution, test the nuclear magnetic porosity; then take out the core and dry it.

[0064] S1.2, place the dried core into the clamp 9, apply confining pressure to the clamp 9 through the confining pressure device 12, open the back pressure valve 19, and apply a certain back pressure to the core outlet through the constant pressure pump 20; open the valve on the first six-way valve 5 corresponding to the clamp 9 and the first drying tube 13, open the second six-way valve 18 and the valve corresponding to the clamp 9 and the second drying tube 17, close the other valves, and start the vacuum pump 16 to evacuate the core.

[0065] S1.3. After the vacuuming is completed, the vacuum pump 16 is turned off, and the confining pressure is raised to the pressure of the overburden formation. The confining pressure is kept constant during the experiment. The valves corresponding to the pressure regulating valve 4, the inlet pressure sensor 7, the clamp 9, the outlet pressure sensor 8, and the back pressure valve 19 on the first six-way valve 5 and the second six-way valve 18 are opened, and the internal pressure and back pressure of the core are alternately increased by increasing the pump 2 and the constant pressure pump 20. Each time the pressure is increased, the internal pressure is required to be equal to the back pressure. When the internal pressure reaches P1, the pressure is stopped, and the first nuclear magnetic T2 spectrum test is performed after the pressure is stable.

[0066] S1.4. After the scan is completed, the pressure regulating valve 4 and the back pressure valve 19 are adjusted to continue to increase the internal pressure to P2, P3, P4, P5, etc., and the nuclear magnetic resonance T2 spectrum test is performed at each pressure. During the experiment, the difference between the confining pressure and the maximum internal pressure is ensured to be no less than 2MPa.

[0067] S1.5, adjust the constant pressure pump 20 to gradually reduce the back pressure at the core outlet, ... P5, P4, P3, P2, P1, so that the back pressure corresponds to the internal pressure in step S1.4, and perform nuclear magnetic resonance T2 spectrum test at each back pressure.

[0068] S1.6. Calculate the nuclear magnetic permeability of the core based on the nuclear magnetic T2 spectrum, and calculate the rate of change of the nuclear magnetic permeability of the core under different net stresses based on the nuclear magnetic permeability.

[0069] The core nuclear magnetic permeability is calculated using the SDR model in the field of nuclear magnetic resonance core analysis and well logging. The nuclear magnetic permeability is:

[0070] K NMR =30φ 4 T 2g 2

[0071] Where: K NMR is the nuclear magnetic permeability, φ is the nuclear magnetic porosity, T 2g is the geometric mean of the relaxation times, and

[0072]

[0073] Where: T Ai 2i is the i-th relaxation time in the T2 amplitude coordinate system;

[0074] The change rate of core nuclear magnetic permeability is:

[0075]

[0076] Where: D is the change rate of core nuclear magnetic permeability, K o is the nuclear magnetic permeability of the core when the net stress is 0 MPa, K i is the nuclear magnetic permeability of the core under different net stresses.

[0077] The water sensitivity test includes the following steps:

[0078] S2.1. Place the core saturated with 8% potassium chloride solution into the holder 9, apply confining pressure to the holder 9 through the confining pressure device 12, and add 4% potassium chloride solution and distilled water into the intermediate container A23 and the intermediate container B24 respectively.

[0079] S2.2. Test the nuclear magnetic T2 spectrum of the core in 8% potassium chloride solution and calculate the nuclear magnetic permeability based on the T2 spectrum. The specific steps are the same as S1.6.

[0080] S2.3. Turn on the vacuum pump 16, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the heavy water test tube 6, the clamp 9, and the second drying tube 17, and close the other valves, so that the heavy water in the heavy water test tube 6 is sucked from the left end of the clamp 9 to the right end, and perform nuclear magnetic resonance scanning in real time until the peak of the T2 spectrum signal disappears.

[0081] S2.4, open the confining pressure device 12, open the vacuum pump 16, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the clamp 9, the first drying pipe 13, and the second drying pipe 17, and evacuate the core from both ends of the clamp 9 again, and cool it to room temperature after it is completely evacuated.

[0082] Open the double-bar constant speed and constant pressure pump 28, open the valves on the third six-way valve 22 and the fourth six-way valve 27 connected to the intermediate container 23 and the double-bar constant speed and constant pressure pump 28, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the three-way connection 11 and the clamp 9, so that the 4% potassium chloride solution in the intermediate container A23 is saturated into the core from both ends of the clamp 9, and a nuclear magnetic resonance scan is performed in real time. When the peak value remains unchanged, it indicates complete saturation, test the nuclear magnetic porosity in the state of 4% potassium chloride solution, and calculate the nuclear magnetic permeability.

[0083] S2.5. Repeat steps S2.3 and S2.4, and replace the intermediate container A23 in step S2.4 with the intermediate container B24. The intermediate container B24 contains distilled water, so the nuclear magnetic porosity in the distilled water state can be obtained, and the nuclear magnetic permeability and permeability change rate in the distilled water state can be calculated.

[0084] The acid sensitivity test includes the following steps:

[0085] S3.1. Place the core saturated with 8% potassium chloride solution into the holder 9, apply confining pressure to the holder 9 through the confining pressure device 12, and add 15% HCl and 8% potassium chloride solution into the intermediate container A23 and the intermediate container B24 respectively.

[0086] S3.2. Test the nuclear magnetic T2 spectrum of the core in 8% potassium chloride solution and calculate the nuclear magnetic permeability based on the T2 spectrum. The specific steps are the same as S1.6.

[0087] S3.3, the heavy water in the heavy water test tube 6 enters the holder 9, and the nuclear magnetic T2 spectrum test is performed in real time. The specific steps are the same as S2.3.

[0088] S3.4, open the confining pressure device 12, open the vacuum pump 16, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the clamp 9, the first drying pipe 13, and the second drying pipe 17, and evacuate the core from both ends of the clamp 9 again, and cool it to room temperature after it is completely evacuated.

[0089] Open the double-bar constant speed and constant pressure pump 28, open the valves on the third six-way valve 22 and the fourth six-way valve 27 connected to the intermediate container 23 and the double-bar constant speed and constant pressure pump 28, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the three-way connection 11 and the clamp 9, so that the 15% HCl in the intermediate container A23 is saturated into the core from both ends of the clamp 9, and the two ends of the clamp 9 are closed for at least one hour.

[0090] S3.5, after the reaction is completed, repeat step S3.3;

[0091] Open the double-bar constant speed and constant pressure pump 28, open the valves on the third six-way valve 22 and the fourth six-way valve 27 connected to the intermediate container 23 and the double-bar constant speed and constant pressure pump 28, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the three-way connection 11 and the clamp 9, so that the 8% potassium chloride solution in the intermediate container B24 is saturated into the core from both ends of the clamp 9, and a nuclear magnetic resonance scan is performed in real time. When the peak value remains unchanged, it indicates complete saturation, and the nuclear magnetic porosity and nuclear magnetic permeability in the state of 8% potassium chloride solution are tested.

[0092] S3.6. Calculate the rate of change of permeability under acidic conditions.

[0093] The alkaline sensitivity test includes the following steps:

[0094] S4.1. Place the core saturated with 8% potassium chloride solution in the holder 9, apply confining pressure to the holder 9 through the confining pressure device 12, and add sodium hydroxide solutions with different pH values ​​of 7-13 into the intermediate container A23, the intermediate container B24, the intermediate container C25, and the intermediate container D26 respectively;

[0095] S4.2, test and calculate the nuclear magnetic permeability in the state of 8% potassium chloride solution, and calculate the nuclear magnetic permeability according to the T2 spectrum, the specific steps are the same as S1.6;

[0096] S4.3, allowing the heavy water in the heavy water test tube 6 to enter the holder 9, and performing a nuclear magnetic resonance T2 spectrum test in real time, the specific steps are the same as S2.3;

[0097] S4.4, dry the core and evacuate the core; saturate the core with sodium hydroxide solution in the intermediate container A23 from both ends of the holder 9, perform nuclear magnetic resonance scanning in real time, wait for at least 12 hours, and test the nuclear magnetic porosity and nuclear magnetic permeability in the state of sodium hydroxide solution with a pH value of 7;

[0098] S4.5, repeat steps S4.3 and S4.4, replace the intermediate container A23 in step S4.4 with intermediate container B24, intermediate container C25, and intermediate container D26 in sequence, and test the nuclear magnetic porosity and nuclear magnetic permeability under sodium hydroxide solutions with different pH values;

[0099] S4.6. Calculate the permeability change rate under sodium hydroxide solutions with different pH values.

[0100] The salt sensitivity experiment includes the following steps:

[0101] S5.1. Place the saturated core into the holder 9, apply confining pressure to the holder 9 through the confining pressure device 12, and add potassium chloride solutions of different concentrations into the intermediate container A23, the intermediate container B24, the intermediate container C25, and the intermediate container D26 respectively;

[0102] S5.2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution. The specific steps are the same as S1.6.

[0103] S5.3, allowing the heavy water in the heavy water test tube 6 to enter the holder 9, and performing a nuclear magnetic resonance T2 spectrum test in real time, the specific steps are the same as S2.3;

[0104] S5.4, dry the core and evacuate it; then saturate the solution in the intermediate container A23 into the core from both ends of the holder 9, perform nuclear magnetic scanning in real time, and test the nuclear magnetic porosity and nuclear magnetic permeability;

[0105] S5.5, repeat steps S5.3 and S5.4, and replace the intermediate container A23 in step S5.4 with intermediate container B24, intermediate container C25, and intermediate container D26 in sequence, and calculate the nuclear magnetic permeability of potassium chloride solutions of different concentrations;

[0106] S5.6. Calculate the permeability change rate under different concentrations of potassium chloride solution.

[0107] Example:

[0108] Shale was selected as the experimental rock sample to simulate its acid sensitivity experimental process. The specific operation steps are as follows:

[0109] (1) Select shale blocks, drill and process several core columns with a size of 25*50 mm, dry the core samples at 60°C to constant weight, take out the cores, place them in a cooler, cool them to room temperature, test the length and diameter of the cores, and set them aside for use. Prepare the standard brine solution of 8% potassium chloride solution and 15% HCl required for the experiment.

[0110] (2) The core to be tested is evacuated and pressurized to be saturated with 8% potassium chloride solution, and then the saturated core is placed in a core holder 9 under a nuclear magnetic resonance magnet 10 to test the nuclear magnetic resonance porosity.

[0111] (3) A confining pressure of 2.5 MPa is applied to the core holder 9 through the confining pressure device 12, and 15% HCl and 8% potassium chloride solutions are added to the intermediate container A23 and the intermediate container B24, respectively.

[0112] (4) The nuclear magnetic permeability of the core is calculated using the SDR model in the field of nuclear magnetic resonance core analysis and logging. The expression of this model is:

[0113] K NMR =30φ 4 T 2g 2 ,

[0114] Where: K NMR is the nuclear magnetic permeability;

[0115] T 2g The geometric mean of the relaxation times, and

[0116] φ is the nuclear magnetic porosity, and the initial permeability is 0.0136 mD obtained by calculation.

[0117] (5) Turn on the vacuum pump 16, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the heavy water test tube 6, the holder 9, and one side of the drying tube 17, close the other valves, and suck the heavy water in the test tube from the left end to the right end of the holder 9, and perform nuclear magnetic resonance scanning in real time until the peak of the T2 spectrum signal disappears.

[0118] (6) Turn on the heating system of the confining pressure device 12, raise the temperature to 60°C, turn on the vacuum pump 16, open the corresponding valves on the first six-way valve 5 and the second six-way valve 18 connected to the clamp 9 and the first drying tube 13 and the second drying tube 17, and evacuate the core from both ends of the clamp 9 again. After the core is completely evacuated, turn off the heating system and cool it to room temperature.

[0119] (7) Open the double-bar constant speed and constant pressure pump 28, open the valves on the third six-way valve 22 and the fourth six-way valve 27 connected to the intermediate container A23 and the constant speed and constant pressure pump 28, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the three-way connector 11 and the clamp 9, and saturate the 15% HCl in the intermediate container A23 into the core from both ends of the clamp 9 to saturate 1 times the pore volume, close the inlet and outlet valves on the first six-way valve 5 and the second six-way valve 18 at both ends of the clamp 9, and react for 1 hour.

[0120] (8) After the reaction is completed, repeat steps (5) to (6), then open the double-bar constant speed and constant pressure pump 28, open the valves on the third six-way valve 22 and the fourth six-way valve 27 connected to the intermediate container B24 and the constant speed and constant pressure pump 28, open the valves on the first six-way valve 5 and the second six-way valve 18 connected to the three-way connector 11 and the clamp 9, and saturate the core with 8% potassium chloride solution in the intermediate container B24 from both ends of the clamp 9, perform nuclear magnetic resonance scanning in real time, and when the peak value remains unchanged, it indicates complete saturation, test the nuclear magnetic porosity and nuclear magnetic permeability in the state of 8% potassium chloride solution after the acid injection reaction, and calculate the core permeability after acid injection to be 0.1461mD.

[0121] (9) By comparing the nuclear magnetic resonance T2 spectra before and after acid injection, it can be seen that after the acid reaction, the T2 spectrum curve moves to the right and the peak on the right increases. This indicates that after acid injection, some substances in the shale sample react with the acid, the number of macropores inside the core increases, and the permeability increases, achieving the effect of improving the reservoir. The experimental results are shown in Figure 2 , Figure 3 shown.

Claims

1. An ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance, comprising a liquid supply system, a gas supply system, and a vacuum system, characterized in that: The invention also comprises a nuclear magnetic resonance magnet (10), wherein a clamp (9) is provided inside the nuclear magnetic resonance magnet (10), the clamp (9) is connected to a confining pressure device (12), two ends of the clamp (9) are respectively connected to a first six-way valve (5) and a second six-way valve (18), the first six-way valve (5) and the second six-way valve (18) are respectively connected to a vacuum system and a liquid supply system, the first six-way valve (5) is also connected to an air supply system and a heavy water test tube (6), and the second six-way valve (18) is connected to a constant pressure pump (20) via a back pressure valve (19).

2. The ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance according to claim 1, characterized in that: The vacuum system comprises a vacuum pump (16), the vacuum pump (16) being connected to a first drying pipe (13) and a second drying pipe (17) via a four-way joint (15), the first drying pipe (13) being connected to a first six-way valve (5), and the second drying pipe (17) being connected to a second six-way valve (18).

3. The ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance according to claim 1, characterized in that: The gas supply system comprises a methane gas cylinder (1), the methane gas cylinder (1) is connected to a booster pump (2), and the outlet of the booster pump (2) is connected to a first six-way valve (5) via a high-pressure valve (4).

4. The ultra-low permeability reservoir sensitivity evaluation experimental device based on nuclear magnetic resonance according to claim 1, characterized in that: The liquid supply system comprises a double-bar constant speed and constant pressure pump (28), the double-bar constant speed and constant pressure pump (28) is connected to a plurality of parallel intermediate containers, the other end of the intermediate container is connected to a third six-way valve (22), and the third six-way valve (22) is respectively connected to the first six-way valve (5) and the second six-way valve (18) through a three-way connector (11).

5. An experimental method for evaluating the sensitivity of ultra-low permeability reservoirs based on nuclear magnetic resonance, characterized in that The following steps are involved: (1) Prepare core samples and prepare 8% potassium chloride solution for the experiment; (ii) saturating the core with 8% potassium chloride solution and placing the core in a holder (9) under a nuclear magnetic resonance magnet (10) to test the nuclear magnetic resonance porosity of the core; (iii) performing sensitivity tests on the cores respectively, wherein the sensitivity tests are stress sensitivity tests and / or acid sensitivity tests and / or alkali sensitivity tests and / or salt sensitivity tests and / or water-acid sensitivity tests, and each test is conducted using different core samples; (iv) Calculate the nuclear magnetic permeability of the core under different conditions based on the experimental results in step (iii), and calculate the damage rate of the core under different media.

6. The ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance according to claim 5, characterized in that: The stress sensitivity experiment includes the following steps: S1.

1. Take out the core that has been tested for nuclear magnetic porosity and dry it; S1.2, placing the core in the holder (9), applying confining pressure to the holder (9) through the confining pressure device (12), applying back pressure to the core outlet through the constant pressure pump (20), and evacuating the core through the vacuum pump (16); S1.3, alternately increasing the internal pressure and back pressure of the core by increasing the pump (2) and the constant pressure pump (20) until the internal pressure reaches P1, and performing the first nuclear magnetic resonance T2 spectrum test; S1.4, continue to increase the internal pressure to P2, P3, P4, P5, etc., and perform nuclear magnetic resonance T2 spectrum test at each pressure; S1.5, adjusting the constant pressure pump (20) to gradually reduce the back pressure at the core outlet, and performing a nuclear magnetic resonance T2 spectrum test at each back pressure; S1.

6. Calculate the nuclear magnetic permeability of the core based on the nuclear magnetic T2 spectrum, and calculate the change rate of the nuclear magnetic permeability of the core under different net stresses based on the nuclear magnetic permeability.

7. The ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance according to claim 5, characterized in that: The water sensitivity test comprises the following steps: S2.

1. Place the core saturated with 8% potassium chloride solution into a holder (9), apply confining pressure to the holder (9) through a confining pressure device (12), and add 4% potassium chloride solution and distilled water into intermediate container A (23) and intermediate container B (24), respectively; S2.

2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution; S2.3, allowing the heavy water in the heavy water test tube (6) to enter the holder (9), and performing a nuclear magnetic resonance T2 spectrum test in real time; S2.4, the core is dried and vacuumed; then the 4% potassium chloride solution in the intermediate container A (23) is saturated into the core from both ends of the clamp (9), and a nuclear magnetic resonance scan is performed in real time to test the nuclear magnetic resonance porosity in the state of 4% potassium chloride solution, and the nuclear magnetic resonance permeability is calculated; S2.

5. Repeat steps S2.3 and S2.4, and replace the intermediate container A (23) in step S2.4 with the intermediate container B (24), and obtain the nuclear magnetic porosity under distilled water conditions, thereby calculating the nuclear magnetic permeability and permeability change rate under distilled water conditions.

8. The ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance according to claim 5, characterized in that: The acid sensitivity experiment comprises the following steps: S3.

1. Place the core saturated with 8% potassium chloride solution into a holder (9), apply confining pressure to the holder (9) through a confining pressure device (12), and add 15% HCl and 8% potassium chloride solution into intermediate container A (23) and intermediate container B (24), respectively; S3.

2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution; S3.3, allowing the heavy water in the heavy water test tube (6) to enter the holder (9), and performing a nuclear magnetic resonance T2 spectrum test in real time; S3.4, dry the core and evacuate the core; then allow the 15% HCl solution in the intermediate container A (23) to saturate the core from both ends of the holder (9), and keep both ends of the holder (9) closed for at least one hour; S3.5, repeat steps S3.3 and S3.4, and replace the intermediate container in step S3.4 with the 8% potassium chloride solution in the intermediate container B (24), and calculate the nuclear magnetic permeability in the state of 8% potassium chloride solution; S3.

6. Calculate the rate of change of permeability under acidic conditions.

9. The ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance according to claim 5, characterized in that: The alkali sensitivity experiment comprises the following steps: S4.

1. Place the core saturated with 8% potassium chloride solution into a holder (9), apply confining pressure to the holder (9) through a confining pressure device (12), and add sodium hydroxide solutions with different pH values ​​of 7-13 into intermediate container A (23), intermediate container B (24), intermediate container C (25), and intermediate container D (26) respectively; S4.

2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution; S4.3, allowing the heavy water in the heavy water test tube (6) to enter the holder (9), and performing a nuclear magnetic resonance T2 spectrum test in real time; S4.4, drying the core and evacuating the vacuum; saturating the core with sodium hydroxide solution in the intermediate container A (23) from both ends of the holder (9), performing real-time nuclear magnetic resonance scanning, and after reacting for at least 12 hours, testing the nuclear magnetic porosity and nuclear magnetic permeability in the state of sodium hydroxide solution with a pH value of 7; S4.5, repeat steps S4.3 and S4.4, replace the intermediate container A (23) in step S4.4 with intermediate container B (24), intermediate container C (25), and intermediate container D (26) in sequence, and test the nuclear magnetic porosity and nuclear magnetic permeability under sodium hydroxide solutions with different pH values; S4.

6. Calculate the permeability change rate under sodium hydroxide solutions with different pH values.

10. The ultra-low permeability reservoir sensitivity evaluation experimental method based on nuclear magnetic resonance according to claim 5, characterized in that: The salt sensitivity experiment comprises the following steps: S5.

1. Place the saturated core into a holder (9), apply confining pressure to the holder (9) through a confining pressure device (12), and add potassium chloride solutions of different concentrations into intermediate container A (23), intermediate container B (24), intermediate container C (25), and intermediate container D (26); S5.

2. Test and calculate the nuclear magnetic permeability in 8% potassium chloride solution; S5.3, allowing the heavy water in the heavy water test tube (6) to enter the holder (9), and performing a nuclear magnetic resonance T2 spectrum test in real time; S5.4, the core is dried and evacuated; then the solution in the intermediate container A (23) is saturated into the core from both ends of the holder (9), and a nuclear magnetic resonance scan is performed in real time to test the nuclear magnetic porosity and nuclear magnetic permeability; S5.5, repeat steps S5.3 and S5.4, and replace the intermediate container A (23) in step S5.4 with intermediate container B (24), intermediate container C (25), and intermediate container D (26) in sequence, and calculate the nuclear magnetic permeability of potassium chloride solutions with different concentrations; S5.

6. Calculate the permeability change rate under different concentrations of potassium chloride solution.

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