A nuclear magnetic resonance testing device and method for pressure-coated pore structures

Abstract

The present invention relates to a nuclear magnetic resonance testing device and method for a pressurized pore structure. A full-diameter nuclear magnetic clamp for pressurized pores comprises a clamp housing, a cavity is provided inside the clamp housing, and a front support and a rear support are provided at both ends of the cavity respectively; a coil skeleton is located in the cavity and between the rear support and the front support; a through hole is provided in the middle of the coil skeleton along the radial direction; a front block and a rear block are respectively located at both ends of the internal channel of the coil skeleton; a heat shrink tube is provided outside the front block and the rear block, and the front block and the rear block are respectively connected to the front support and the rear support; a coil is wound around the outside of the coil skeleton, and the coil connector is connected to the pin seal after passing through the hole; a heating plate is provided on the outside of the clamp housing. The present invention proposes a full-diameter nuclear magnetic clamp for pressurized pores, which realizes the measurement of porosity under pressurization by nuclear magnetic resonance. The experimental operation is simple and reflects its microscopic characteristics, and the experimental results are reliable.

Description

Technical Field

[0001] The invention relates to a nuclear magnetic resonance testing device and method for a pressure-coated pore structure. Background Art

[0002] The relationship between rock porosity and net overburden pressure under reservoir conditions is a crucial aspect of reserve calculation and oil and gas field development research. Currently, overburden porosity experiments primarily utilize conventional gas flooding methods, using helium porosimeters. This method only measures porosity changes at a macroscopic level, but fails to reflect pore changes and distribution characteristics under microscopic conditions, nor can it mechanistically analyze stress sensitivity damage.

[0003] In addition, when using existing experimental equipment, nuclear magnetic resonance, overburden pressure and pore permeability measurements need to be separated. The experimental steps are complicated and difficult to control, which can easily cause data distortion. Summary of the Invention

[0004] The present invention proposes a full-diameter nuclear magnetic holder for overburden pores, which realizes the measurement of porosity and permeability under overburden pressure by nuclear magnetic resonance. The experimental operation is simple and reflects its microscopic characteristics. The experimental results are reliable, achieving the purpose of quickly, effectively and conveniently testing the porosity and permeability of cores under overburden pressure.

[0005] The technical solution of the present invention to solve the above problems is: a full-diameter nuclear magnetic clamp with a covered pore, which is special in that:

[0006] The invention comprises a holder housing, wherein a cavity is provided inside the holder housing, and outlets communicating with the outside are provided at both ends of the cavity, wherein a front end support is provided in one outlet and a rear end support is provided in the other outlet; the coil bobbin is located in the cavity and between the rear end support and the front end support, and the coil bobbin is a cylindrical structure, wherein the outer diameters at both ends are larger than the outer diameter in the middle, and slots are provided in the axial direction at the ends of the coil bobbin for threading; a through hole is provided in the radial direction in the middle of the coil bobbin;

[0007] The front end block and the rear end block are respectively located at the two ends of the internal channel of the coil skeleton, and the core is placed between the front end block and the rear end block; the front end block and the rear end block are provided with heat shrink tubes on the outside, and the front end block and the rear end block are respectively connected to the front end support and the rear end support; the rear end support, the front end support, the heat shrink tube and the inner wall of the clamp housing cavity form a pressure cavity, and the end of the clamp housing is provided with a pressure hole, which is connected to the pressure cavity;

[0008] A hole is provided on the housing of the holder near one end of the front support, a pin seal is provided in the hole, a coil is wound around the outside of the coil frame, and the coil connector passes through the hole and is connected to the pin seal;

[0009] A rear end support fixing nut is provided on the clamp housing near one end of the rear end support for positioning the rear end support;

[0010] The centers of the rear support and the rear block are both provided with a hole, and the holes of the two correspond to each other; the centers of the front support and the front block are both provided with a hole, and the holes of the two correspond to each other; the hole of the front support is the displacement hole, and the hole of the rear support is the outlet;

[0011] A heating plate is provided on the outside of the holder housing.

[0012] Furthermore, an annular groove is provided on the outside of the holder housing, and the heating plate is arranged in the annular groove.

[0013] Furthermore, there is a slotted hole on the end face of the rear end support fixing nut, which is used to tighten it according to the designed preload force using a torque wrench during installation, and a threaded section is provided on the outside of the rear end support fixing nut for threaded connection with the clamp housing.

[0014] Furthermore, one end of the above-mentioned rear end support is a small diameter end, and the other end is a large diameter end. A tapered threaded hole is provided inside the small diameter end for connecting the displacement pipeline; a sealing groove is provided on the outside of the large diameter section for installing the seal at the rear end support; a sealing hole is provided inside the large diameter section for connecting with the rear end block.

[0015] Furthermore, one end of the above-mentioned rear end block is a small diameter end, and the other end is a large diameter end. The small diameter end extends into a sealing hole provided inside the large diameter section of the rear end support, and a sealing groove for installing a seal is provided on the outside of the small diameter end of the rear end block, and a seal for the rear end block is provided in the sealing groove.

[0016] Furthermore, the end face of the coil skeleton is provided with a pin hole, and the clamp housing is provided with a stepped pin that matches the pin hole.

[0017] Furthermore, the front end support comprises a supporting section, a sealing section, a connecting section and a mounting section which are connected in sequence;

[0018] The end of the support section is provided with a sealing hole, one end of the front end block is a small diameter end, and the other end is a large diameter end, the small diameter end of the front end block extends into the sealing hole at the end of the support section, and the outer side of the small diameter end of the front end block is provided with a sealing groove for installing a seal, and the sealing groove is provided with a seal for the front end block;

[0019] There is a sealing groove on the outside of the sealing section for installing the seal at the front support; there is a thread on the outside of the connecting section for threaded connection with the clamp housing;

[0020] A parallel surface is provided on the outside of the installation section for tightening with a torque wrench according to a set pre-tightening force, and a tapered threaded hole is provided on the end face of the installation section for connecting a displacement pipeline.

[0021] Furthermore, the rear end block and the front end block are made of polyimide material; the rear end support fixing nut, the rear end support, the clamp housing and the front end support are made of titanium alloy material.

[0022] In addition, the present invention also proposes a nuclear magnetic resonance testing device for a pressed pore structure, which is special in that:

[0023] It comprises a full-diameter nuclear magnetic resonance clamp with a covered pore, which is installed in a full-diameter nuclear magnetic resonance online detection system. The coil on the coil skeleton is connected to the full-diameter nuclear magnetic resonance online detection system through a pin seal; the full-diameter nuclear magnetic resonance online detection system is connected to a computer; an intermediate container is connected to the covered pore hole on the clamp housing by a pipeline, a pressure transmitter is installed on its pipeline and connected to a pressure patrol meter, and a manual pump is connected to the intermediate container by a pipeline; another intermediate container is connected to the displacement hole at the front support by a pipeline, another pressure transmitter is installed on its pipeline and connected to another pressure patrol meter, and an ISO pump is connected to the intermediate container by a pipeline; the outlet end of the full-diameter nuclear magnetic resonance clamp with a covered pore is connected to a calibrated test tube.

[0024] In addition, the present invention also proposes a test method based on the above-mentioned pressure-coated pore structure nuclear magnetic resonance test device, which is special in that it includes the following steps:

[0025] Step 1: Use a vacuum and pressure saturation device to vacuum the core and saturate it with formation water, where the formation water is determined according to the water type and salinity of the area where the core is located;

[0026] Step 2: Place the core into the full-diameter NMR holder of the overburden pore, and place the whole into the NMR online detection system, setting the required temperature;

[0027] Step 3: Use a nuclear magnetic resonance instrument to conduct nuclear magnetic resonance testing on the core, test the nuclear magnetic T2 spectrum curve when the core water saturation is 100%, and determine its permeability;

[0028] Step 4: Apply overburden pressure to the core using a manual pump, set the inlet pressure, and simultaneously displace the core using an ISCO pump. After the outlet flow and overburden pressure stabilize, perform nuclear magnetic resonance testing on the core and determine its permeability.

[0029] Step 5: Keep the inlet pressure constant and change the overburden pressure. After the outlet flow and overburden pressure are stable, perform nuclear magnetic resonance testing on the core and determine its permeability.

[0030] Step 6: Repeat step 5 until the end of the experiment;

[0031] Step 7: Release the inlet pressure and overburden pressure, remove the core, and end the experiment.

[0032] Compared with the prior art, the beneficial effects of the nuclear magnetic resonance testing device and method for overburden pore structure provided by the present invention are:

[0033] (1) The test device and method place the core overburden pore in a full-diameter nuclear magnetic holder, and realize the measurement of porosity and permeability under overburden pressure by nuclear magnetic resonance. The experimental operation is simple and reflects its microscopic characteristics. The experimental results are reliable, achieving the purpose of quickly, effectively and conveniently testing the core overburden porosity and permeability. The final test results also provide basic data for oil and gas reservoir productivity evaluation and water production dynamic analysis.

[0034] (2) The nuclear magnetic resonance testing device and method for overburden pore structure provided by the present invention are capable of conducting nuclear magnetic resonance testing experiments on cores under different overburden pressure conditions, establishing the relationship between overburden pressure and porosity, and ultimately obtaining the damage rate and microscopic pore distribution characteristics, thereby clarifying the microscopic change law.

[0035] (3) The present invention provides an overburden pore structure nuclear magnetic resonance testing device and method, which realizes a variable overburden pore permeability experiment under a high temperature and high pressure environment for a full-diameter nuclear magnetic resonance online detection system. The present invention has an overburden pore full-diameter nuclear magnetic clamp, which can be connected to a displacement pump to displace the clamped core, and is combined with a full-diameter nuclear magnetic resonance online detection system to conduct experiments;

[0036] (4) The present invention provides a device and method for testing a pressurized pore structure NMR. The present invention provides a device and method for testing a pressurized pore structure. The device and method are designed to eliminate magnetic interference. The pressurized pore structure and full-diameter NMR holder have reasonable material selection and structural layout.

[0037] (5) The present invention provides a pressurized pore structure NMR testing device and method. Considering the position of the NMR system receiver and the radio frequency coil, the inner wall of the holder housing in the pressurized pore full-diameter NMR holder of the present invention has a structure that has a certain degree of shielding against interference noise.

[0038] (6) The present invention provides a device and method for testing a nuclear magnetic resonance (NMR) of a pressed porous structure. Considering that a specific temperature can be applied, the outer wall of the holder housing of the pressed porous full-diameter NMR holder of the present invention is provided with a heating plate to achieve temperature control.

[0039] (6) The present invention provides a pressurized pore structure nuclear magnetic resonance testing device and method. Considering the possible interference problem of the size of the signal device of the existing full-diameter nuclear magnetic resonance online detection system, the present invention provides a pressurized pore full-diameter nuclear magnetic resonance clamp with a coil skeleton and a sealing pin installed on the end face inside the clamp, which can meet the requirements of transmitting radio frequency pulses and receiving signals during the experiment;

[0040] (7) The present invention provides a new method for testing a pressurized porous structure nuclear magnetic resonance device and method, which aims to realize a high-temperature and high-pressure environment in an existing full-diameter nuclear magnetic resonance online detection system and to conduct such a test. The present invention systematically designs the overall layout, sealing and bearing components, and proposes a reasonable skeleton structure in terms of material selection and stress analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the assembly structure of the full-diameter nuclear magnetic clamp with a covered pressure hole according to the present invention;

[0042] Figure 2 1. It is an exploded schematic diagram of the structure of the full-diameter nuclear magnetic clamp with a covered pressure hole according to the present invention;

[0043] Figure 3 It is a schematic diagram of the experimental connection of the present invention;

[0044] Figure 4 Schematic diagram of core nuclear magnetic T2 spectrum curves under different overburden pressures;

[0045] Figure 5 Schematic diagram of core nuclear magnetic porosity curves under different overburden pressures;

[0046] Figure 6 Schematic diagram of the equivalent elastic strain cloud diagram of the front support end;

[0047] Figure 7 Schematic diagram of the equivalent stress cloud diagram at the front support end;

[0048] Figure 8 Schematic diagram of the total displacement cloud diagram of the front support end;

[0049] Figure 9 Schematic diagram of the safety factor cloud diagram of the front support end.

[0050] In the figure: rear end support fixing nut 1, rear end support 2, rear end block 3, coil skeleton 4, heat shrink tube 5, core 6, front end block 7, clamp housing 8, front end support 9, pin seal 10, pin seal 11, front end support seal 12, front end block seal 13, rear end block seal 14, rear end support seal 15, heating plate 16, full diameter nuclear magnetic resonance online detection system 17, computer 18, intermediate container 19, intermediate container 20, ISCO pump 21, pressure transmitter 22, pressure patrol meter 23, manual pump 24. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is claimed, but merely represents selected embodiments of the present invention.

[0052] See also Figure 1 and Figure 2 The present invention designs a full-diameter nuclear magnetic clamp with a covered pore, comprising a clamp housing 8, wherein a cavity is provided inside the clamp housing 8, and outlets communicating with the outside are provided at both ends of the cavity, wherein a front end support 9 is provided in one outlet, and a rear end support 2 is provided in the other outlet; the coil skeleton 4 is located in the cavity and between the rear end support 2 and the front end support 9, and the coil skeleton 4 is a cylindrical structure, the outer diameters of both ends of the coil skeleton 4 are larger than the outer diameter of the middle part, and slots are provided at the ends of both ends of the coil skeleton 4 along the axial direction for threading; a through hole is provided in the middle of the coil skeleton 4 along the radial direction.

[0053] The front end block 7 and the rear end block 3 are respectively located at the two ends of the internal channel of the coil skeleton 4, and the core is placed between the front end block 7 and the rear end block 3; the front end block 7 and the rear end block 3 are fixed by heat shrinkage tube 5, and the front end block 7 and the rear end block 3 are respectively connected to the front end support 9 and the rear end support 2; the rear end support 2, the front end support 9, the heat shrinkage tube 5 and the inner wall of the clamp housing 8 cavity form a covering pressure cavity, and the end of the clamp housing 8 is provided with a covering pressure hole, which is connected to the covering pressure cavity; a hole is provided on the clamp housing 8 near one end of the front end support 9, and the hole is connected to the covering pressure cavity. A pin seal 10 is provided, a coil is wound around the outside of the coil skeleton 4, and the coil joint is connected to the pin seal 10 after passing through the hole; a rear end support fixing nut 1 is provided on the clamp housing 8 near one end of the rear end support 2, which is used to position the rear end support 2; the centers of the rear end support 2 and the rear end block 3 are both provided with channels, and the channels of the two correspond to each other; the centers of the front end support 9 and the front end block 7 are both provided with channels, and the channels of the two correspond to each other; the channel of the front end support 9 is a displacement hole, and the channel of the rear end support 2 is an outlet; a heating plate 16 is provided on the outside of the clamp housing 8.

[0054] As a preferred embodiment of the present invention, an annular groove is provided on the outside of the holder housing 8, and the heating plate 16 is adhered to the annular groove.

[0055] As a preferred embodiment of the present invention, a slotted hole is provided on the end face of the rear end support fixing nut 1, which is used to tighten it according to the designed pre-tightening force using a torque wrench during installation, and a threaded section is provided on the outer side of the rear end support fixing nut 1 for threaded connection with the clamp housing 8.

[0056] As a preferred embodiment of the present invention, one end of the rear end support 2 is a small diameter end, and the other end is a large diameter end. A tapered threaded hole is provided inside the small diameter end for connecting the displacement pipeline; a sealing groove is provided on the outside of the large diameter section for installing the seal 15 at the rear end support; a sealing hole is provided inside the large diameter section for connecting with the rear end block 3.

[0057] Furthermore, one end of the above-mentioned rear end block 3 is a small diameter end, and the other end is a large diameter end. The small diameter end extends into a sealing hole provided inside the large diameter section of the rear end support 2, and a sealing groove for installing a seal is provided on the outside of the small diameter end of the rear end block 3, and a rear end block seal 14 is provided in the sealing groove.

[0058] As a preferred embodiment of the present invention, the end surface of the coil skeleton 4 is provided with a pin hole, and the clamp housing is provided with a stepped pin that matches the pin hole.

[0059] As a preferred embodiment of the present invention, the front end support 9 includes a support section, a sealing section, a connecting section and an installation section connected in sequence; a sealing hole is provided at the end of the support section, one end of the front end block 7 is a small diameter end, and the other end is a large diameter end, and its small diameter end extends into the sealing hole at the end of the support section, and a sealing groove for installing a seal is provided on the outside of the small diameter end of the front end block 7, and a front end block seal 13 is provided in the sealing groove; a sealing groove is provided on the outside of the sealing section for installing the front end support seal 12; a thread is provided on the outside of the connecting section for threaded connection with the clamp housing 8; a parallel surface is provided on the outside of the installation section for tightening with a torque wrench according to the set preload force, and a tapered threaded hole is provided on the end face of the installation section for connecting the displacement pipeline.

[0060] As a preferred embodiment of the present invention, the rear end block 3 and the front end block 7 are made of polyimide material; the rear end support fixing nut 1, the rear end support 2, the clamp housing 8 and the front end support 9 are made of titanium alloy material.

[0061] The assembly process of the full-diameter nuclear magnetic clamp structure with a covered pore is as follows:

[0062] The coil is wound on the coil skeleton 4, and the wire end is connected to the pin seal 10 through the hole of the clamp housing 8. The pin seal 11 is installed on the pin seal 10. At this time, the threaded section of the pin seal 10 is screwed into the threaded hole in the clamp housing 8. Since two wire ends need to be led out here, the pin seal 10, the pin seal 11 and the hole positions on the clamp housing 8 are also corresponding; the coil skeleton 4 is installed in the clamp housing 8, and the pin hole on the coil skeleton 4 is installed corresponding to the step pin on the clamp housing 8; the heating plate 16 is pasted on the outer groove of the clamp housing 8, and can be wrapped with insulation foam after installation; the treated core 6 is connected with the rear end block 3 and The front end block 7 is docked, the heat shrink tube 5 is put on the outside and heat shrunk, the rear end block seal 14 is installed at the rear end block 3, and the front end block seal 13 is installed at the front end block 7; at this time, the other end of the front end block 7 is installed into the front end support 9, the front end support seal 12 is installed at the front end support 9, and the whole is installed in the clamp housing 8, and the threads at the position of the front end support 9 and the clamp housing 8 are tightened; the rear end support seal 15 is installed on the rear end support 2, and then the rear end support 2 is installed in the clamp housing 8. At this time, the hole position of the rear end support 2 is just connected to the sealed end of the rear end block 3; finally, the rear end support fixing nut 1 is screwed into the clamp housing 8 with a special wrench.

[0063] The rear pin seal 11, the front support seal 12, the front block seal 13, the rear block seal 14 and the rear support seal 15 are lubricated with high-temperature silicone grease when installed.

[0064] According to the design of this embodiment, there is no magnetic interference with the nuclear magnetic signal and it is resistant to high temperature. In this example, the rear end block 3 is made of polyimide material, the coil skeleton 4 is made of polytetrafluoroethylene material, the heat shrink tube 5 is made of polytetrafluoroethylene material, and the front end block 7 is made of polyimide material.

[0065] According to the consideration that the design of this embodiment has no magnetic interference with the nuclear magnetic signal and is resistant to high temperature and has a certain hardness, in this example, the seal 11 at the rear pin, the seal 12 at the front support, the seal 13 at the front block, the seal 14 at the rear block and the seal 15 at the rear support are made of fluororubber material, and the pin seal 10 is a Dianthus SZP series single-core high-pressure sealed pin.

[0066] Based on the design of this embodiment to prevent magnetic interference with nuclear magnetic signals and to withstand temperature and pressure, in this example, the rear end support fixing nut 1, the rear end support 2, the clamp housing 8, and the front end support 9 are made of titanium alloy material, and the pipeline is made of micro-magnetic stainless steel material.

[0067] It is worth noting that in this embodiment, the threads at the front support 9 and the rear support fixing nut are both connected by a single tight bolt, and σ should be solved according to the following formula caFor mechanical property verification, the allowable stress [σ] in this example is 983.33 MPa.

[0068]

[0069]

[0070]

[0071]

[0072] Where C b 、C m They represent the stiffness of the bolt and the connected parts respectively, F0 is the preload force, F1 is the residual preload force, and F2 is the total tension.

[0073] It is worth noting that for the main load-bearing components, the finite element method in mechanical calculation can be simplified to the method of thermal-solid coupling to solve the displacement, stress and safety factor caused by external loads. Figure 6-9 As shown, in this embodiment, the front support end 9 is subjected to an overburden of 60 MPa and a temperature of 120°C. The maximum displacement is only 0.021606 mm, meeting the design requirements. The maximum equivalent elastic strain is 0.0027488 mm, within the elastic allowable range. The maximum equivalent stress is 308.67 MPa. At stress concentration points, optimized chamfers can be used to reduce stress concentration. The allowable safety stress is 983.33 MPa, verifying safety. The minimum safety factor is 3.6738, which is greater than the predetermined safety factor of 1.2, indicating safe use.

[0074] Also, see Figure 3The present invention also proposes a nuclear magnetic resonance testing device for a pressurized pore structure, comprising a full-diameter nuclear magnetic resonance clamp for a pressurized pore, wherein the full-diameter nuclear magnetic resonance clamp for the pressurized pore is installed in a full-diameter nuclear magnetic resonance online detection system 17, and the coil on the coil skeleton 4 is connected to the full-diameter nuclear magnetic resonance online detection system 17 through a pin seal 10; the full-diameter nuclear magnetic resonance online detection system 17 is connected to a computer 18; an intermediate container 19 is connected to the pressurized hole at the clamp housing 8 by a pipeline, a pressure transmitter 22 is installed on its pipeline and connected to a pressure patrol meter 23, and a manual pump 24 is connected to the intermediate container 19 by a pipeline; another intermediate container 20 is connected to the displacement hole at the front support 9 by a pipeline, another pressure transmitter 22 is installed on its pipeline and connected to another pressure patrol meter 23, and an ISO pump 21 is connected to the intermediate container 20 by a pipeline; the outlet end of the full-diameter nuclear magnetic resonance clamp for the pressurized pore is connected to a calibrated test tube. The full-diameter NMR clamp for overburden pores is used to clamp the core and provide temperature and pressure environment; the full-diameter NMR online detection system is used to test the core T2 spectrum; the manual pump is mainly used to apply overburden pressure to the core, the ISCO pump is mainly used to apply displacement pressure to the core, the pressure patrol meter is mainly used to display pressure data; the pressure transmitter is mainly used to measure overburden pressure and inlet pressure. The computer is mainly used for NMR data processing and overburden porosity data calculation, such as Figure 4 and Figure 5 shown.

[0075] It is worth noting that in this embodiment, a six-way valve or a one-way valve can be added for use according to actual experimental conditions, and the sealing of pipelines and joints and whether they are blocked should also be tested in advance.

[0076] It is worth noting that in this embodiment, formation water can be loaded into the intermediate container 20 and fluorine oil can be loaded into the intermediate container 19 according to actual experimental conditions.

[0077] The present invention also proposes a test method based on the above-mentioned pressure-coated pore structure nuclear magnetic resonance test device, see Figure 3 , including the following steps:

[0078] Step 1: Use a vacuum and pressure saturation device to vacuum the core and saturate it with formation water, where the formation water is determined according to the water type and salinity of the area where the core is located;

[0079] Step 2: Place the core into the full-diameter NMR holder of the overburden pore, and place the whole into the NMR online detection system, setting the required temperature;

[0080] Step 3: Use a nuclear magnetic resonance instrument to conduct nuclear magnetic resonance testing on the core, test the nuclear magnetic T2 spectrum curve when the core water saturation is 100%, and determine its permeability;

[0081] Step 4: Apply overburden pressure to the core using a manual pump, set the inlet pressure, and simultaneously displace the core using an ISCO pump. After the outlet flow and overburden pressure stabilize, perform nuclear magnetic resonance testing on the core and determine its permeability.

[0082] Step 5: Keep the inlet pressure constant and change the overburden pressure. After the outlet flow and overburden pressure are stable, perform nuclear magnetic resonance testing on the core and determine its permeability.

[0083] Step 6: Repeat step 5 until the end of the experiment;

[0084] Step 7: Release the inlet pressure and overburden pressure, remove the core, and end the experiment.

[0085] The permeability can be determined according to the following formula:

[0086]

[0087] Where:

[0088] K l — Rock liquid permeability, in units of ten to the negative cube of the second micrometer (10 -3 μm 2 );

[0089] μ—Fluid viscosity under test conditions, in millipascals seconds (mPa.s);

[0090] L—rock sample length, in centimeters (cm);

[0091] A is the cross-sectional area of the rock sample, in square centimeters (cm 3 );

[0092] Δp—pressure difference between the two ends of the rock sample, in megapascals (MPa);

[0093] Q—The volume of fluid passing through the rock sample per unit time, in cubic centimeters per second (cm 3 / s).

[0094] Furthermore, the permeability change rate of the rock sample under different overburden stresses during the overburden stress increase process is calculated according to the following formula:

[0095]

[0096] Where:

[0097] D stn —Permeability change rate under different overburden stresses during overburden stress increase;

[0098] K i —Initial permeability (core permeability under initial overburden stress), in units of ten to the negative cube of micrometers (103 μm 2 );

[0099] K n —Core permeability (under different overburden stresses during overburden stress increase), in units of ten to the negative cube of the second micrometer (10 3 μm 2 ).

[0100] Furthermore, the maximum core permeability damage rate is calculated according to the following formula:

[0101] D st =max(D st1 ,D st2 ,…,D stn )

[0102] Where:

[0103] D st —stress sensitivity damage rate;

[0104] D stn —Permeability change rate under different net stresses during overburden stress increase.

[0105] Furthermore, referring to the damage degree evaluation index table:

[0106] Table 1 Damage degree evaluation indicators

[0107]

[0108]

[0109] Finally, the original data was processed and calculated. The damage degree evaluation was referred to Table 1. The pore distribution law processing results were as follows: Figure 4 As shown in the figure, the relationship between the core nuclear magnetic porosity and the different overburden pressures is as follows: Figure 5 As shown;

[0110] The present invention provides a nuclear magnetic resonance testing device and method for overburden pore structure, which is equipped with a vacuum pressurization and saturation device, a full-diameter nuclear magnetic resonance online detection system, a manual pump, an ISCO pump, a pressure patrol meter, a high-precision pressure transmitter, a computer and other equipment to perform nuclear magnetic resonance core online detection of different overburden pressures in a simulated high-temperature environment, and establish a relationship between overburden pressure and porosity, and finally obtain the damage rate and microscopic pore distribution characteristics, and clarify its microscopic change law. Compared with the existing solution of testing the porosity change from a macroscopic perspective, the present invention provides a method for obtaining the damage rate and microscopic pore distribution characteristics and clarifying its microscopic change law. The overall structure of the device is compatible with conventional laboratory equipment, and it also provides a reasonable nuclear magnetic resonance testing device and method for overburden pore structure for further research on multi-dimensional nuclear magnetic resonance online detection systems, research on gas reservoir development plans, and providing basic data and references.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may adjust the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Therefore, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A full-diameter nuclear magnetic clamp with a covered pore, characterized by: The invention comprises a holder housing (8), wherein a cavity is provided inside the holder housing (8), and outlets communicating with the outside are provided at both ends of the cavity, wherein a front end support (9) is provided in one of the outlets, and a rear end support (2) is provided in the other outlet; a coil frame (4) is located in the cavity and between the rear end support (2) and the front end support (9); the coil frame (4) is a cylindrical structure, wherein the outer diameters at both ends are larger than the outer diameter of the middle part; slots are provided at the ends of the coil frame (4) along the axial direction for threading; a through hole is provided in the middle part of the coil frame (4) along the radial direction; The front end block (7) and the rear end block (3) are respectively located at the two ends of the internal channel of the coil skeleton (4), and the core is placed between the front end block (7) and the rear end block (3); the front end block (7) and the rear end block (3) are provided with a heat shrink tube (5) on the outside, and the front end block (7) and the rear end block (3) are respectively connected to the front end support (9) and the rear end support (2); the rear end support (2), the front end support (9), the heat shrink tube (5) and the inner wall of the cavity of the clamp housing (8) form a pressure cavity, and the end of the clamp housing (8) is provided with a pressure hole, and the pressure hole is connected to the pressure cavity; A hole is provided on the holder housing (8) near one end of the front support (9), a pin seal (10) is provided in the hole, a coil is wound around the outside of the coil frame (4), and a coil connector is connected to the pin seal (10) after passing through the hole; A rear end support fixing nut (1) is provided on the clamp housing (8) near one end of the rear end support (2) for positioning the rear end support (2); The centers of the rear support (2) and the rear block (3) are both provided with a hole, and the holes of the two correspond to each other; the centers of the front support (9) and the front block (7) are both provided with a hole, and the holes of the two correspond to each other; the hole of the front support (9) is a displacement hole, and the hole of the rear support (2) is an outlet; A heating plate (16) is provided on the outside of the holder housing (8); The front end support (9) comprises a supporting section, a sealing section, a connecting section and a mounting section which are connected in sequence; The end of the support section is provided with a sealing hole, one end of the front end block (7) is a small diameter end, and the other end is a large diameter end, and the small diameter end thereof extends into the sealing hole at the end of the support section, and a sealing groove for installing a sealing member is provided on the outer side of the small diameter end of the front end block (7), and a front end block seal (13) is provided in the sealing groove; The outer side of the sealing section is provided with a sealing groove for installing a sealing member (12) at the front end support; the outer side of the connecting section is provided with a thread for threaded connection with the clamp housing (8); A parallel surface is provided on the outside of the installation section for tightening with a torque wrench according to a set pre-tightening force, and a tapered threaded hole is provided on the end face of the installation section for connecting a displacement pipeline.

2. The full-diameter nuclear magnetic clamp with a covered pore according to claim 1, characterized in that: An annular groove is provided on the outside of the holder housing (8), and the heating plate (16) is arranged in the annular groove.

3. The full-diameter nuclear magnetic clamp with a covered pore according to claim 2, characterized in that: The end surface of the rear end support fixing nut (1) is provided with a slotted hole for tightening it according to the designed pre-tightening force using a torque wrench during installation, and the outer side of the rear end support fixing nut (1) is provided with a threaded section for threaded connection with the clamp housing (8).

4. The full-diameter nuclear magnetic clamp with a covered pore according to claim 3, characterized in that: One end of the rear end support (2) is a small diameter end, and the other end is a large diameter end. The small diameter end is provided with a tapered threaded hole for connecting a displacement pipeline; a sealing groove is provided on the outside of the large diameter section for installing a sealing member (15) at the rear end support; and a sealing hole is provided inside the large diameter section for connecting to the rear end block (3).

5. The full-diameter nuclear magnetic clamp with a covered pore according to claim 4, characterized in that: One end of the rear end block (3) is a small diameter end, and the other end is a large diameter end. The small diameter end extends into a sealing hole provided inside the large diameter section of the rear end support (2), and a sealing groove for installing a sealing member is provided on the outer side of the small diameter end of the rear end block (3), and a rear end block sealing member (14) is provided in the sealing groove.

6. The full-diameter nuclear magnetic clamp with a covered pore according to claim 5, characterized in that: The end surface of the coil frame (4) is provided with a pin hole, and the clamp housing is provided with a step pin that matches the pin hole.

7. The full-diameter nuclear magnetic clamp with a covered pore according to claim 6, characterized in that: The rear end block (3) and the front end block (7) are made of polyimide material; the rear end support fixing nut (1), the rear end support (2), the clamp housing (8), and the front end support (9) are made of titanium alloy material.

8. A nuclear magnetic resonance testing device for a pressure-coated pore structure, characterized in that: The invention comprises a full-diameter nuclear magnetic resonance clamp with a pressurized pore as described in any one of claims 1 to 7, wherein the full-diameter nuclear magnetic resonance clamp with a pressurized pore is installed in a full-diameter nuclear magnetic resonance online detection system (17), and the coil on the coil skeleton (4) is connected to the full-diameter nuclear magnetic resonance online detection system (17) through a pin seal (10); the full-diameter nuclear magnetic resonance online detection system (17) is connected to a computer (18); an intermediate container is connected to the pressurized hole at the clamp housing (8) by a pipeline, a pressure transmitter (22) is installed on its pipeline and connected to a pressure patrol meter (23), and a manual pump (24) is connected to the intermediate container by a pipeline; another intermediate container is connected to the displacement hole at the front support (9) by a pipeline, another pressure transmitter (22) is installed on its pipeline and connected to another pressure patrol meter (23), and an ISCO pump (21) is connected to the intermediate container by a pipeline; the outlet end of the full-diameter nuclear magnetic resonance clamp with a pressurized pore is connected to a calibrated test tube.

9. A test method based on the nuclear magnetic resonance test device for overburden pore structure according to claim 8, characterized in that: The following steps are involved: Step 1: Use a vacuum and pressure saturation device to vacuum the core and saturate it with formation water, where the formation water is determined according to the water type and salinity of the area where the core is located; Step 2: Place the core into the full-diameter NMR holder of the overburden pore, and place the whole into the NMR online detection system, setting the required temperature; Step 3: Use a nuclear magnetic resonance instrument to conduct nuclear magnetic resonance testing on the core, test the nuclear magnetic T2 spectrum curve when the core water saturation is 100%, and determine its permeability; Step 4: Apply overburden pressure to the core using a manual pump, set the inlet pressure, and simultaneously displace the core using an ISCO pump. After the outlet flow and overburden pressure stabilize, perform nuclear magnetic resonance testing on the core and determine its permeability. Step 5: Keep the inlet pressure constant and change the overburden pressure. After the outlet flow and overburden pressure are stable, perform nuclear magnetic resonance testing on the core and determine its permeability. Step 6: Repeat step 5 until the end of the experiment; Step 7: Release the inlet pressure and overburden pressure, remove the core, and end the experiment.

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