Nuclear magnetism-resistivity combined measurement method for occurrence and migration of fluid in rock core

Abstract

The invention provides a nuclear magnetism-resistivity combined measurement method for occurrence and migration of fluid in a rock core. The nuclear magnetism-resistivity combined measurement method comprises the steps that the rock core is dried and cooled to the room temperature; applying a specified confining pressure to the rock core and keeping the confining pressure constant; measuring background resistivity distribution of the rock core, and closing the resistivity analyzer; opening a liquid pump and a liquid inlet valve, and stopping pumping when the liquid level of the fluid is flush with the upper surface of the sponge; performing nuclear magnetic resonance imaging on the rock core, dividing the rock core into a plurality of observation sections in the longitudinal direction, and ensuring that at least one observation section is formed at the place with the conductivity probe; turning off the nuclear magnetic analysis system and the nuclear magnetic resonance imaging system, and measuring the resistivity of the rock core; nuclear magnetic measurement and resistivity measurement are carried out alternately; calculating a fluid migration rule in a spontaneous imbibition process to simulate a soaking process; and calculating a fluid migration rule in a gas driving process, and realizing nuclear magnetism-resistivity combined measurement of fluid occurrence and migration. The method can effectively avoid the interference of magnetic polarization on the resistivity test in the nuclear magnetic measurement process, and is high in measurement precision.

Description

Technical Field

[0001] The present application relates to the field of oil production, and in particular to a nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores. Background Art

[0002] The original formation pressure coefficient of normal pressure shale gas wells is low. Some gas wells can achieve self-flow after fracturing and energy enhancement, but there are still a few gas wells that cannot self-flow after fracturing. After a large amount of fracturing fluid enters the reservoir, under some conditions, the fracturing fluid can block small pores and cause water lock damage. Under some conditions, the fracturing fluid can supplement the pore pressure in the near-well area and achieve an energy enhancement effect. The interaction mechanism between fracturing fluid and reservoir is unclear. The interaction between fracturing fluid and reservoir is one of the key issues in research. Especially in microscopic pore space, micro-nano pores, and micro-fracture systems, the occurrence and migration laws of fluids are the focus and difficulty of research. It is of great engineering significance to realize quantitative evaluation and real-time monitoring of the interaction between fracturing fluid and reservoir.

[0003] At present, the commonly used equipment for indoor evaluation of fluid storage and migration in cores is mainly nuclear magnetic resonance, CT, resistivity testing and other devices. The testing methods based on different principles have their own advantages and disadvantages, and the effectiveness of the test is not the same under different experimental conditions. For example, nuclear magnetic resonance has high accuracy for large-pore sandstone, but it is difficult to quantitatively evaluate the storage state in micro-nano pores in shale, especially it is difficult to provide an accurate correspondence between relaxation experiments and pore size. CT is not accurate enough for observing shale matrix pores and can only observe large cracks; in addition, resistivity testing has high requirements for the matrix minerals and fluid types of rock samples. Therefore, there is an urgent need for a method that can combine the advantages of multiple measurement methods to achieve high-precision real-time monitoring of fluid storage and migration processes in cores. Summary of the invention

[0004] The present application provides a nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores, aiming to solve the problem of inaccurate judgment of fluid storage and migration in rock cores in the prior art.

[0005] The technical solution of this application is:

[0006] A nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a rock core, using a fluid joint measurement device in a rock core for measurement, comprising the following steps:

[0007] A1, place the core in a 60°C drying oven for 12 hours, cool the core to room temperature and place it in a core holder for clamping; close the liquid inlet valve and the air inlet valve on the fluid joint measurement device in the core, and open the vent valve on the fluid joint measurement device in the core;

[0008] A2, turning on the confining pressure pump on the fluid joint measurement device in the core to apply a specified confining pressure to the core and keep it constant; turning on the resistivity analyzer on the fluid joint measurement device in the core to measure the background resistivity distribution of the core; and turning off the resistivity analyzer after the measurement is completed;

[0009] A3, turning on the liquid pump and the liquid inlet valve on the fluid joint measurement device in the core, pumping liquid into the core holder at a constant pressure, and stopping the pumping when the fluid level is flush with the upper surface of the sponge; at the same time, turning on the nuclear magnetic resonance imaging system on the fluid joint measurement device in the core, performing nuclear magnetic resonance imaging on the core, and dividing it into a plurality of observation sections in the longitudinal direction, so that at least one observation section is formed where the conductivity probe is provided on the side of the core, and analyzing and recording the nuclear magnetic spectrum of each section in the longitudinal direction; after time t1, turning off the nuclear magnetic resonance imaging system, turning on the resistivity analyzer, measuring the resistivity of the core, and subtracting the background resistivity to obtain the distribution of resistivity changes; the resistivity measurement time of the core is t2, and t1 is greater than t2, and t1-t2 constitute a measurement cycle;

[0010] A4, alternately performing nuclear magnetic resonance measurement and resistivity measurement on the core using the method in step A3;

[0011] A5, the distribution of resistivity changes measured in each measurement cycle is coupled with the spectrum peak of nuclear magnetic resonance to calculate the fluid migration law during spontaneous imbibition to simulate the soaking process;

[0012] A6, after time t3, close the liquid inlet valve, open the air inlet valve on the fluid joint measurement device in the core, and pump gas into the core holder for displacement, so as to simulate the production gas drive and the self-release process of water lock; during the gas drive process, use the method in step A3 to alternately perform nuclear magnetic resonance measurement and resistivity measurement on the core, and use the method in step A5 to calculate the fluid migration law during the gas drive process of the core.

[0013] As a technical solution of the present application, in step A5, the coupling algorithm includes the following steps:

[0014] The area enclosed by the nuclear magnetic spectrum curve and the horizontal axis is calculated within a given relaxation time range on each observation section, which is recorded as S1; the average value of the resistivity change distribution on the observation section is calculated based on the resistivity change distribution value of the corresponding observation section, which is recorded as S2, and the saturation coefficient ρ on the observation section can be obtained by ρ=S1×S2; the saturation coefficient on each observation section is calculated, and then spatial interpolation is performed to obtain the saturation spatial distribution; the saturation coefficient on each observation section is calculated in each measurement cycle, and the saturation spatial distribution is obtained by spatial interpolation, and the saturation spatial distribution is calculated by the same method in the next measurement cycle; this step is repeated to obtain the change of the spatial saturation distribution over time.

[0015] As a technical solution of the present application, the fluid joint measurement device in the core includes a liquid pump, a gas pump, an inverted T-shaped connecting pipe, a core clamp, a sponge, a confining pressure pump, a conductivity probe, a resistivity analyzer, a nuclear magnetic resonance imaging system, a venting pipe and a pressure-controlled venting system; the core is clamped in the inner cavity of the core clamp, and a rubber film is sealed between the inner wall and the core; the nuclear magnetic resonance imaging system is arranged on the periphery of the core clamp for performing nuclear magnetic resonance imaging on the core; the first end of the inverted T-shaped connecting pipe is connected to the liquid pump, the second end is connected to the gas pump, and the third end in the middle passes through the bottom of the nuclear magnetic resonance imaging system, the core clamp, and the bottom of the core clamp in sequence. The core holder is connected to the sponge at the bottom of the core holder, and the sponge is at the bottom of the core; one end of the confining pressure pump passes through one side of the nuclear magnetic resonance imaging system and is connected to the gap between the core holder and the rubber membrane, and is used to inject liquid into the gap and apply confining pressure to the core; a plurality of conductivity probes are attached to one of the outer walls of the core, and the resistivity analyzer is electrically connected to the plurality of conductivity probes, and is used to measure the distribution of the conductivity of the core in real time; one end of the vent pipe is connected to the pressure-controlled venting system, and the other end passes through the top of the nuclear magnetic resonance imaging system and the top of the core holder in sequence and is connected to the top of the core.

[0016] As a technical solution of the present application, a liquid inlet valve is installed on the first end of the inverted T-shaped connecting pipe, and an air inlet valve is installed on the second end.

[0017] As a technical solution of the present application, a vent valve is installed on the vent pipe.

[0018] As a technical solution of the present application, the inverted T-shaped connecting pipe is made of non-metallic material.

[0019] As a technical solution of the present application, the core holder is made of non-metallic material.

[0020] As a technical solution of the present application, the venting pipe includes a horizontal pipe and a vertical pipe that are integrally formed and vertically connected. One end of the horizontal pipe is connected to the pressure-controlled venting system, and the other end passes through the top of the nuclear magnetic resonance imaging system and the top of the core clamp in sequence and is connected to the top of the core.

[0021] Beneficial effects of this application:

[0022] The present application provides a nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores, which can effectively avoid the interference of magnetic polarization on resistivity testing during nuclear magnetic resonance measurement by introducing a measurement cycle, thereby ensuring measurement accuracy during the nuclear magnetic resonance-resistivity joint measurement process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show the following technical solutions of the present application.

[0024] Certain embodiments of the application should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A schematic diagram of a process flow of a nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a rock core provided in an embodiment of the present application;

[0026] Figure 2 Schematic diagram of the fluid joint measurement device in the core provided in an embodiment of the present application.

[0027] Icons: 1-liquid pump; 2-gas pump; 3-inverted T-shaped connecting pipe; 4-core holder; 5-sponge; 6-confining pressure pump; 7-conductivity probe; 8-resistivity analyzer; 9-nuclear magnetic resonance imaging system; 10-vent pipe; 11-pressure-controlled venting system; 12-core; 13-rubber membrane; 14-liquid inlet valve; 15-gas inlet valve; 16-vent valve. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0030] Example:

[0031] Please refer to Figure 1 , with reference Figure 2 In the embodiment of the present application, a nuclear magnetic resonance-resistivity joint measurement method for the occurrence and migration of fluid in a core is provided, and a fluid joint measurement device for the core is used for measurement. The fluid joint measurement device for the core comprises a liquid pump 1, a gas pump 2, an inverted T-shaped connecting pipe 3, a core clamp 4, a sponge 5, a confining pressure pump 6, a conductivity probe 7, a resistivity analyzer 8, a nuclear magnetic resonance imaging system 9, a venting pipe 10 and a pressure-controlled venting system 11; a core 12 is clamped in the inner cavity of the core clamp 4, and a rubber film 13 is sealed between the inner wall and the core 12; the nuclear magnetic resonance imaging system 9 is arranged on the outer periphery of the core clamp 4 for performing nuclear magnetic resonance imaging on the core 12; the first end of the inverted T-shaped connecting pipe 3 is connected to the liquid pump 1, the second end is connected to the gas pump 2, and the third end in the middle passes through the nuclear magnetic resonance imaging system 9 in sequence. 9, the bottom of the core holder 4 and connected to the sponge 5 below the core holder 4, the sponge 5 is at the bottom of the core 12; one end of the confining pressure pump 6 passes through one side of the nuclear magnetic resonance imaging system 9 and is connected to the gap between the core holder 4 and the rubber membrane 13, for injecting liquid into the gap and applying confining pressure to the core 12; a plurality of conductivity probes 7 are attached to one of the outer walls of the core 12, and the resistivity analyzer 8 is electrically connected to the plurality of conductivity probes 7, for real-time measurement of the distribution of the conductivity of the core 12; one end of the vent pipe 10 is connected to the pressure-controlled venting system 11, and the other end passes through the top of the nuclear magnetic resonance imaging system 9, the top of the core holder 4 and is connected to the top of the core 12 in sequence; the nuclear magnetic-resistivity joint measurement method for fluid storage and migration in the core mainly includes the following steps:

[0032] A1, place the core 12 in a 60°C drying oven for 12 hours, then cool it to room temperature, place the core 12 in the core holder 4; close the liquid inlet valve 14 and the air inlet valve 15, and open the vent valve 16;

[0033] A2, turn on the confining pressure pump 6, apply a specified confining pressure to the core 12 and keep it constant; turn on the resistivity analyzer 8, measure the background resistivity distribution of the core 12, and then turn off the resistivity analyzer 8;

[0034] A3, open the liquid pump 1 and the liquid inlet valve 14, pump the liquid into the core holder 4 at a constant pressure, and stop pumping when the liquid level is flush with the upper surface of the sponge 5; at the same time, open the nuclear magnetic resonance imaging system 9, perform nuclear magnetic resonance imaging on the core 12, and divide it into multiple observation sections in the longitudinal direction, so that at least one observation section is formed where the conductivity probe 7 is set on the side of the core 12, and analyze and record the nuclear magnetic spectrum of each section in the longitudinal direction; after time t1, close the nuclear magnetic resonance imaging system 9, open the resistivity analyzer 8, measure the resistivity of the core 12, and subtract the background resistivity to obtain the distribution of resistivity changes; the resistivity measurement time of the core 12 is t2, and t1 is greater than t2, and t1-t2 constitute a measurement cycle;

[0035] A4, using the method in step A3 to alternately perform nuclear magnetic resonance measurement and resistivity measurement on the core 12 to prevent the magnetic polarization effect generated during the resistivity measurement from affecting the resistivity measurement;

[0036] A5, the distribution of resistivity changes measured in each measurement cycle is coupled with the spectrum peak of nuclear magnetic resonance to calculate the fluid migration law during spontaneous imbibition to simulate the soaking process;

[0037] A6, after a certain period of time, close the liquid inlet valve 14, open the air inlet valve 15, and pump gas into the core holder 4 for displacement, so as to simulate the production gas drive and the self-release process of water lock; during the gas drive process, the method in step A3 is used to alternately perform nuclear magnetic resonance measurement and resistivity measurement on the core 12, and the method in step A5 is used to calculate the fluid migration law during the gas drive process of the core 12, and finally realize the nuclear magnetic resonance-resistivity joint measurement of fluid occurrence and migration.

[0038] It should be noted that, in step A5, the coupling algorithm includes the following steps:

[0039] Since there are nuclear magnetic spectrum curves based on nuclear magnetic resonance and resistivity change distribution based on the spatial distribution of resistivity change on each observation section, therefore, within a given relaxation time range on each observation section, the area enclosed by the nuclear magnetic spectrum curve and the horizontal axis is calculated, recorded as S1; the average value of the resistivity change distribution on the plane is calculated based on the corresponding resistivity change distribution value of the plane, recorded as S2; the saturation coefficient on the observation section can be obtained by the following formula ρ = S1 × S2; the saturation coefficient on each observation section is calculated, and then spatial interpolation is performed to obtain the saturation spatial distribution. Therefore, in each measurement cycle, the saturation coefficient on each observation section is calculated, and the saturation spatial distribution is obtained by spatial interpolation; in the next measurement cycle, the same method is used to calculate the saturation spatial distribution; the method is repeated to obtain the change of spatial saturation distribution over time, and then the fluid occurrence and migration law in the core is obtained.

[0040] It should be noted that, in this embodiment, the inverted T-shaped connecting pipe 3 and the core clamp 4 are made of non-metallic materials. At the same time, the vent pipe 10 includes a horizontal pipe and a vertical pipe that are integrally formed and vertically connected. One end of the horizontal pipe is connected to the pressure-controlled venting system 11, and the other end passes through the top of the nuclear magnetic resonance imaging system 9 and the top of the core clamp 4 in sequence and is connected to the top of the core 12. The liquid inlet valve 14 controls the fluid flow state in the liquid pump 1, and the air inlet valve 15 controls the fluid flow state in the gas pump 2. The confining pressure pump 6 injects liquid into the gap between the rubber membrane 13 and the inner wall of the core clamp 4, and then the rubber membrane 13 applies confining pressure to the core 12. A sponge 5 is provided at the bottom of the core 12. After the fluid flows out of the inverted T-shaped connecting tube 3, it can seep through the sponge 5 and then contact the core 12. A plurality of conductivity probes 7 are attached to the outside of the core 12. The resistivity analyzer 8 is electrically connected to the conductivity probes 7, and can measure the conductivity distribution of the core 12 in real time; the nuclear magnetic resonance imaging system 9 adopts the structure in the prior art, and its specific structure and working principle are not repeated here, and it is located outside the core clamp 4, and can perform nuclear magnetic resonance imaging of the core 12; a vent pipe 10 is connected to the top of the core 12, and a pressure-controlled vent system 11 is connected to the end of the vent pipe 10, which can control the pressure of the vent pipe 10, and the vent valve 16 can control the connection state of the vent pipe 10.

[0041] In summary, the method of nuclear magnetic resonance-resistivity joint measurement in the present application can effectively avoid the interference of magnetic polarization on resistivity testing during nuclear magnetic resonance measurement by mainly introducing a measurement cycle, and can also ensure measurement accuracy during nuclear magnetic resonance-resistivity joint measurement.

[0042] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores, characterized in that: The measurement is carried out using a fluid joint measurement device in the core, including the following steps: A1, placing the core in a drying box for drying, cooling the core to room temperature and placing it in a core holder for clamping and fixing; closing the liquid inlet valve and the air inlet valve on the fluid joint measuring device in the core, and opening the vent valve on the fluid joint measuring device in the core; A2, turning on the confining pressure pump on the fluid joint measurement device in the core to apply a specified confining pressure to the core and keep it constant; turning on the resistivity analyzer on the fluid joint measurement device in the core to measure the background resistivity distribution of the core; and turning off the resistivity analyzer after the measurement is completed; A3, turning on the liquid pump and the liquid inlet valve on the fluid joint measurement device in the core, pumping liquid into the core holder at a constant pressure, and stopping the pumping when the fluid level is flush with the upper surface of the sponge; at the same time, turning on the nuclear magnetic resonance imaging system on the fluid joint measurement device in the core, performing nuclear magnetic resonance imaging on the core, and dividing it into a plurality of observation sections in the longitudinal direction, so that at least one observation section is formed where the conductivity probe is provided on the side of the core, and analyzing and recording the nuclear magnetic spectrum of each section in the longitudinal direction; after time t1, turning off the nuclear magnetic resonance imaging system, turning on the resistivity analyzer, measuring the resistivity of the core, and subtracting the background resistivity to obtain the distribution of resistivity changes; the resistivity measurement time of the core is t2, and t1 is greater than t2, and t1-t2 constitute a measurement cycle; A4, alternately performing nuclear magnetic resonance measurement and resistivity measurement on the core using the method in step A3; A5, the distribution of resistivity changes measured in each measurement cycle is coupled with the spectrum peak of nuclear magnetic resonance to calculate the fluid migration law during spontaneous imbibition to simulate the soaking process; A6, after time t3, close the liquid inlet valve, open the air inlet valve on the fluid joint measurement device in the core, and pump gas into the core holder for displacement, so as to simulate the production gas drive and the self-release process of water lock; during the gas drive process, use the method in step A3 to alternately perform nuclear magnetic resonance measurement and resistivity measurement on the core, and use the method in step A5 to calculate the fluid migration law during the gas drive process of the core.

2. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores according to claim 1, characterized in that: In step A5, the coupling algorithm includes the following steps: The area enclosed by the nuclear magnetic spectrum curve and the horizontal axis is calculated within a given relaxation time range on each observation section, which is recorded as S1; the average value of the resistivity change distribution on the observation section is calculated based on the resistivity change distribution value of each corresponding observation section, which is recorded as S2, and the saturation coefficient ρ on the observation section can be obtained by ρ=S1×S2; the saturation coefficient on each observation section is calculated, and then spatial interpolation is performed to obtain the saturation spatial distribution; the saturation coefficient on each observation section is calculated in each measurement cycle, and the saturation spatial distribution is obtained by spatial interpolation, and the saturation spatial distribution is calculated by the same method in the next measurement cycle; this step is repeated to obtain the change of spatial saturation distribution over time.

3. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in rock cores according to claim 1, characterized in that: The fluid joint measurement device in the core comprises a liquid pump, a gas pump, an inverted T-shaped connecting pipe, a core clamp, a sponge, a confining pressure pump, a conductivity probe, a resistivity analyzer, a nuclear magnetic resonance imaging system, a venting pipe and a pressure-controlled venting system; the core is clamped in the inner cavity of the core clamp, and a rubber film is sealed between the inner wall and the core; the nuclear magnetic resonance imaging system is arranged on the outer periphery of the core clamp for performing nuclear magnetic resonance imaging on the core; the first end of the inverted T-shaped connecting pipe is connected to the liquid pump, the second end is connected to the gas pump, and the third end in the middle passes through the bottom of the nuclear magnetic resonance imaging system, the bottom of the core clamp and is connected to the gas pump. A sponge is connected to the inner bottom of the core holder, and the sponge is at the bottom of the core; one end of the confining pressure pump passes through one side of the nuclear magnetic resonance imaging system and is connected to the gap between the core holder and the rubber membrane, so as to inject liquid into the gap and apply confining pressure to the core; a plurality of conductivity probes are attached to one of the outer walls of the core, and the resistivity analyzer is electrically connected to the plurality of conductivity probes, so as to measure the distribution of the conductivity of the core in real time; one end of the vent pipe is connected to the pressure-controlled venting system, and the other end passes through the top of the nuclear magnetic resonance imaging system and the top of the core holder in sequence and is connected to the top of the core.

4. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a core according to claim 3, characterized in that: A liquid inlet valve is installed on the first end of the inverted T-shaped connecting pipe, and an air inlet valve is installed on the second end.

5. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a core according to claim 3, characterized in that: A vent valve is installed on the vent pipe.

6. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a core according to claim 3, characterized in that: The inverted T-shaped connecting pipe is made of non-metallic material.

7. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a core according to claim 3, characterized in that: The core holder is made of non-metallic material.

8. The nuclear magnetic resonance-resistivity joint measurement method for fluid storage and migration in a core according to claim 3, characterized in that: The venting pipe includes a horizontal pipe and a vertical pipe that are integrally formed and vertically connected. One end of the horizontal pipe is connected to the pressure-controlled venting system, and the other end passes through the top of the nuclear magnetic resonance imaging system and the top of the core holder in sequence and is connected to the top of the core.

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