A method for nuclear magnetic-resistivity combined measurement of fluid occurrence and migration in a core

Abstract

The application provides a method for nuclear magnetic-resistivity combined measurement of fluid occurrence and migration in a core, which comprises the following steps: drying the core and cooling it to room temperature; applying a specified confining pressure to the core and keeping it constant; measuring the background resistivity distribution of the core and closing the resistivity analyzer; opening the liquid pump and the liquid inlet valve, and stopping the pumping when the liquid surface is flush with the upper surface of the sponge; performing nuclear magnetic resonance imaging on the core, dividing it into multiple observation sections in the longitudinal direction, and ensuring that at least one observation section is formed in the place where the conductivity probe is located; closing the nuclear magnetic analysis system and the nuclear magnetic resonance imaging system, and measuring the resistivity of the core; alternately performing nuclear magnetic measurement and resistivity measurement; calculating the fluid migration law in the spontaneous imbibition process to simulate the well soaking process; and calculating the fluid migration law in the gas drive process to realize the nuclear magnetic-resistivity combined measurement of fluid occurrence and migration. The method can effectively avoid the interference of magnetic polarization on the resistivity test during the nuclear magnetic measurement process, and has high measurement accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil exploitation, in particular to a nuclear magnetic-resistivity combined measurement method for fluid occurrence and migration in a core. BACKGROUND

[0002] The original formation pressure coefficient of a shale gas well under normal pressure is low, and some gas wells can realize self-flowing after fracturing energy increase, but a few gas wells cannot realize self-flowing after fracturing, and the fracturing fluid can block small pores under some conditions to cause water lock damage, and the fracturing fluid can also supplement the pore pressure near the wellbore under some conditions to realize energy increase effect, and the interaction mechanism between the fracturing fluid and the reservoir is unknown. The interaction between the fracturing fluid and the reservoir is one of the key problems to be studied. In particular, in the micro-pore space, the fluid occurrence and migration law in the micro-nano pore and micro-fracture system is the focus and difficulty of the study. It has important engineering significance to realize quantitative evaluation and real-time monitoring of the interaction between the fracturing fluid and the reservoir.

[0003] At present, the commonly used equipment for evaluating fluid occurrence and migration in a core in the laboratory mainly includes nuclear magnetic resonance, CT, resistivity testing and the like. The testing methods of different principles have advantages and disadvantages, and the effectiveness of the testing is not the same under different experimental conditions. For example, nuclear magnetic resonance has high precision for large-pore sandstone, but it is difficult to quantitatively evaluate the occurrence state in the micro-nano pore of shale, especially it is difficult to provide an accurate corresponding relationship between the relaxation experiment and the pore size. The precision of CT observation on shale matrix pores is not enough, and it can only observe large fractures; in addition, the resistivity testing has high requirements for the matrix minerals of the rock sample and the type of fluid. Therefore, it is urgent to develop a method which can combine the advantages of multiple measurement methods to realize high-precision real-time monitoring of the fluid occurrence and migration process in a core. SUMMARY

[0004] The present application provides a nuclear magnetic-resistivity combined measurement method for fluid occurrence and migration in a core, which aims to solve the problem of inaccurate judgment of fluid occurrence and migration in a core.

[0005] The technical scheme of the present application is as follows:

[0006] A nuclear magnetic-resistivity combined measurement method for fluid occurrence and migration in a core, which is measured by using a core fluid combined measurement device, and includes the following steps:

[0007] A1, placing a core in a 60℃ drying oven for drying for 12 hours, cooling the core to room temperature and placing it in a core holder for clamping and fixing; closing the liquid inlet valve and the gas inlet valve on the core fluid combined measurement device, and opening the vent valve on the core fluid combined measurement device;

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

[0009] A3, open the liquid pump and liquid inlet valve on the core fluid measuring device, pump liquid into the core holder at a constant pressure, and stop pumping when the liquid surface is level with the upper surface of the sponge; at the same time, open the nuclear magnetic resonance imaging system on the core fluid measuring device, perform nuclear magnetic resonance imaging on the core and divide it into multiple observation sections in the longitudinal direction, so that the place where the conductivity probe is arranged on the side surface of the core forms at least one observation section, analyze and record the nuclear magnetic spectrum of each section in the longitudinal direction; after a period of time t1, close the nuclear magnetic resonance imaging system and open the resistivity analyzer to measure the resistivity of the core and subtract the background resistivity to obtain the distribution of resistivity change; the resistivity measurement time of the core is t2, and t1 is greater than t2, t1-t2 constitutes a measurement period;

[0010] A4, use the method in step A3 to alternately measure the core with nuclear magnetic resonance and resistivity;

[0011] A5, couple the measured resistivity change distribution and the nuclear magnetic spectrum peak in each measurement period to calculate the fluid migration rule in the spontaneous imbibition process, which is used to simulate the huff and puff process;

[0012] A6, after a period of time t3, close the liquid inlet valve and open the gas inlet valve on the core fluid measuring device to pump gas into the core holder for displacement, which is used to simulate the production gas drive and water lock self-release process; during the gas drive process, use the method in step A3 to alternately measure the core with nuclear magnetic resonance and resistivity, and use the method in step A5 to calculate the fluid migration rule in the core gas drive process.

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

[0014] The area surrounded by the nuclear magnetic spectrum curve and the horizontal axis in the given relaxation time range on each observation section is calculated and recorded as S1; the average value of the resistivity variation distribution on the observation section is calculated on the corresponding resistivity variation distribution value, recorded as S2, and the saturation coefficient p on the observation section can be obtained by p=S1*S2; the saturation coefficient on each observation section is calculated, then spatial interpolation is performed to obtain the spatial distribution of the saturation; the saturation coefficient on each observation section is calculated in each measurement period, the spatial distribution of the saturation is obtained by spatial interpolation, and the same method is used to calculate the spatial distribution of the saturation in the next measurement period; the spatial saturation distribution changes with time by repeating the step.

[0015] As a technical scheme of the present application, the core fluid combined measurement device comprises a liquid pump, a gas pump, an inverted T-shaped connecting pipe, a core holder, a sponge, a confining pressure pump, an electrical conductivity probe, a resistivity analyzer, a nuclear magnetic resonance imaging system, a venting pipe and a pressure control venting system; the core holder holds a core in the inner cavity, and a rubber film is sealingly arranged between the inner wall and the core; the nuclear magnetic resonance imaging system is arranged on the outer periphery of the core holder and is used 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 sequentially passes through the bottom of the nuclear magnetic resonance imaging system, the bottom of the core holder and is connected to the sponge below the core holder, and the sponge is located 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 communicated with the gap between the core holder and the rubber film, and is used for injecting liquid into the gap and applying confining pressure to the core; a plurality of electrical conductivity probes are attached to one of the outer side walls of the core, and the resistivity analyzer is electrically connected to the plurality of electrical conductivity probes and is used for measuring the distribution of the electrical conductivity of the core in real time; one end of the venting pipe is connected to the pressure control venting system, and the other end sequentially passes through the top of the nuclear magnetic resonance imaging system, the top of the core holder and is connected to the top of the core.

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

[0017] As a technical scheme of the present application, the venting pipe is provided with a venting valve.

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

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

[0020] As a technical scheme of the present application, the vent pipe comprises a horizontal pipe and a vertical pipe which are integrally formed and vertically communicated, one end of the horizontal pipe is connected to the pressure control vent system, and the other end sequentially penetrates through the top of the nuclear magnetic resonance imaging system, the top of the core holder and is connected to the top of the core.

[0021] Advantages of the present application:

[0022] The present application provides a nuclear magnetic-resistivity combined measurement method for fluid occurrence and migration in a core, which can effectively avoid the interference of magnetic polarization on resistivity testing in the nuclear magnetic measurement process by introducing a measurement period, and ensure the measurement accuracy in the nuclear magnetic-resistivity combined measurement process. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced below, and it should be understood that the following drawings only show,

[0024] Some embodiments of the application should not be considered as limiting the scope, and other related drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1 The nuclear magnetic-resistivity combined measurement method for fluid occurrence and migration in a core provided by the embodiments of the present application is shown in the flowchart.

[0026] Figure 2 The core fluid combined measurement device provided by the embodiments of the present application is shown in the schematic diagram.

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

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all 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] The following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application claimed, but merely represents selected embodiments of the application. Based upon the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present application.

[0030] Embodiments:

[0031] Please refer to Figure 1 , please refer to Figure 2 , a core fluid occurrence and migration of nuclear magnetic-resistivity combined measurement method is provided in the embodiments of the application, which is measured by using a core fluid combined measurement device, the core fluid combined measurement device comprises a liquid pump 1, a gas pump 2, a reverse T-shaped connecting pipe 3, a core holder 4, a sponge 5, a confining pressure pump 6, an electrical conductivity probe 7, a resistivity analyzer 8, a nuclear magnetic resonance imaging system 9, a venting pipe 10 and a pressure control venting system 11; the core 12 is clamped in the inner cavity of the core holder 4, and a rubber film 13 is sealingly arranged between the inner wall and the core 12; the nuclear magnetic resonance imaging system 9 is arranged on the outer periphery of the core holder 4 and is used for performing nuclear magnetic resonance imaging on the core 12; the first end of the reverse 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 sequentially passes through the bottom of the nuclear magnetic resonance imaging system 9, the bottom of the core holder 4 and is connected to the sponge 5 below the core holder 4, and the sponge 5 is located 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 communicated with the gap between the core holder 4 and the rubber film 13, and is used for injecting liquid into the gap and applying confining pressure to the core 12; a plurality of electrical conductivity probes 7 are attached to one of the outer side walls of the core 12, and the resistivity analyzer 8 is electrically connected to the plurality of electrical conductivity probes 7 and is used for measuring the distribution of the electrical conductivity of the core 12 in real time; one end of the venting pipe 10 is connected to the pressure control venting system 11, and the other end sequentially 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; the core fluid occurrence and migration of nuclear magnetic-resistivity combined measurement method mainly comprises the following steps:

[0032] A1, the core 12 is placed in a 60℃ drying oven for 12 hours, and then cooled to room temperature, the core 12 is placed in the core holder 4; the liquid inlet valve 14 and the gas inlet valve 15 are closed, and the venting valve 16 is opened;

[0033] A2, the confining pressure pump 6 is opened, a specified confining pressure is applied to the core 12 and kept constant; the resistivity analyzer 8 is opened, the background resistivity distribution of the core 12 is measured, and then the resistivity analyzer 8 is closed;

[0034] A3, open the liquid pump 1 and the liquid inlet valve 14, pump liquid into the core holder 4 at a constant pressure, stop pumping when the liquid level is flush with the upper surface of the sponge 5; meanwhile, open the nuclear magnetic resonance imaging system 9, perform nuclear magnetic resonance imaging on the core 12, and divide the core 12 into multiple observation sections in the longitudinal direction, so that at least one observation section is formed at the place where the conductivity probe 7 is arranged on the side surface of the core 12, analyze and record the nuclear magnetic spectrum of each section in the longitudinal direction; after a 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 the resistivity change; the resistivity measurement time of the core 12 is t2, and t1 is greater than t2, t1-t2 constitutes a measurement period;

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

[0036] A5, couple the measured resistivity change distribution and the nuclear magnetic spectrum peak in each measurement period, calculate the fluid migration law in the spontaneous imbibition process, and use it to simulate the huff and puff process;

[0037] A6, after a certain time, close the liquid inlet valve 14, open the gas inlet valve 15, pump gas into the core holder 4 for displacement, to simulate the production gas displacement and self-release of water lock; during the gas displacement process, alternately perform nuclear magnetic measurement and resistivity measurement on the core 12 by using the method in step A3, and calculate the fluid migration law in the gas displacement process of the core 12 by using the method in step A5, to finally realize the nuclear magnetic-resistivity combined 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 and resistivity change distribution results based on resistivity change spatial distribution on each observation section, the area surrounded by the nuclear magnetic spectrum curve and the horizontal axis is calculated within a given relaxation time range on each observation section, and is denoted as S1; the average value of the resistivity change distribution on the plane is calculated on the resistivity change distribution value of the corresponding plane, and is denoted 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, so that the saturation spatial distribution is obtained. Therefore, the saturation coefficient on each observation section is calculated in each measurement period, the saturation spatial distribution is obtained through spatial interpolation; in the next measurement period, the saturation spatial distribution is calculated by using the same method; the spatial saturation distribution changes with time by repeatedly using the method, and then the fluid occurrence and migration law in the core is obtained.

[0040] It should be noted that in the present embodiment, the inverted T-shaped connecting pipe 3 and the core holder 4 are made of non-metallic materials. Meanwhile, the vent pipe 10 comprises a horizontally integrated and vertically connected horizontal pipe and vertical pipe, one end of the horizontal pipe is connected to the pressure control vent system 11, and the other end sequentially 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. The inlet valve 14 controls the fluid flow state in the liquid pump 1, and the 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 holder 4, and then the rubber membrane 13 applies confining pressure to the core 12. The bottom of the core 12 is provided with a sponge 5, and after the fluid flows out of the inverted T-shaped connecting pipe 3, it can seep through the sponge 5 and then contact the core 12. A plurality of electrical conductivity probes 7 are attached to the outside of the core 12, and the electrical resistivity analyzer 8 is electrically connected to the electrical conductivity probes 7, which can measure the electrical 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 will not be repeated here. It is located outside the core holder 4 and can perform nuclear magnetic resonance imaging on the core 12. The vent pipe 10 is connected to the top of the core 12, and the vent pipe 10 is connected to the pressure control vent system 11 at the end, 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 for combined nuclear magnetic-electrical resistivity measurement in the present application can effectively avoid the interference of magnetic polarization on resistivity testing during nuclear magnetic measurement by introducing a measurement period, and can also ensure measurement accuracy during combined nuclear magnetic-electrical resistivity measurement.

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

Claims

1. A nuclear magnetic resonance-resistivity combined measurement method for fluid storage and migration in rock cores, characterized in that: The measurement is performed using a fluid joint measurement device in the core, which 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 vent pipe, and a pressure-controlled venting system; the core clamp has a core in its inner cavity, and a rubber membrane is provided between the inner wall and the core for sealing; the nuclear magnetic resonance imaging system is provided 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 and the bottom of the core clamp in sequence and is connected to the sponge at the bottom of the core clamp. The sponge is located 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, for injecting liquid into the gap and applying confining pressure to the core; a plurality of conductivity probes are attached to one outer wall of the core, and the resistivity analyzer is electrically connected to the plurality of conductivity probes for real-time measurement of the distribution of core conductivity; one end of the vent pipe is connected to the pressure-controlled vent 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; 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; a vent valve is installed on the vent pipe; the process comprises the following steps: A1: drying the core in a drying oven, cooling the core to room temperature, and clamping the core in the core holder; closing the liquid inlet valve and the air inlet valve on the fluid joint measurement device in the core, and opening the vent valve on the fluid joint measurement 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 keeping 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; simultaneously 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 the core 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 surface of the core, and analyzing and recording the nuclear magnetic resonance 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 a distribution of resistivity changes; the resistivity measurement time of the core is t2, and t1 is greater than t2, and t1-t2 constitutes a measurement cycle; A4, alternately performing nuclear magnetic resonance (NMR) measurement and resistivity measurement on the core using the method in step A3; A5, couples the distribution of resistivity changes measured within each measurement cycle with the NMR spectrum peak to calculate the fluid migration law during spontaneous imbibition and use it 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 of water lock. During the gas drive process, nuclear magnetic resonance measurement and resistivity measurement are alternately performed on the core using the method in step A3, and the fluid migration law during the gas drive process of the core is calculated using the method in step A5.

2. The nuclear magnetic resonance-resistivity combined 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, and 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, and is recorded as S2. 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. The saturation spatial distribution is calculated using the same method in the next measurement cycle; this step is repeated to obtain the change of the spatial saturation distribution over time.

3. The nuclear magnetic resonance-resistivity combined measurement method for fluid occurrence and migration in rock cores according to claim 1, characterized in that: The inverted T-shaped connecting pipe is made of non-metallic material.

4. The nuclear magnetic resonance-resistivity combined measurement method for fluid occurrence and migration in rock cores according to claim 1, characterized in that: The core holder is made of non-metallic material.

5. The nuclear magnetic resonance-resistivity combined measurement method for fluid storage and migration in rock cores according to claim 1, characterized in that: The vent 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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