Experimental method for quantitative evaluation of fault core structure evolution using nuclear magnetic resonance

Abstract

The present invention provides an experimental method for quantitatively evaluating the structural evolution law of fault cores by using nuclear magnetic resonance, and relates to the field of nuclear magnetic resonance technology. Nuclear magnetic resonance technology has been widely used in the field of rock mechanics in recent years because of its advantages of simple operation, non-destructiveness, and rapidity, and is an important means for characterizing rock pore structure. According to the characteristics of the fault cores of natural fault zones, the present invention configures a similar fault core model indoors, uses a nuclear magnetic resonance analyzer to study the changes in the fault core T2 spectrum and nuclear magnetic resonance imaging under conditions such as different compaction degrees, and semi-quantitatively and qualitatively analyzes the structural evolution mechanism of the fault core.

Description

Technical Field

[0001] The invention relates to the field of nuclear magnetic resonance technology, and in particular to an experimental method for quantitatively evaluating the evolution law of fault nuclear structure by using nuclear magnetic resonance. Background Art

[0002] Fault core is an important component structure of well-sealed faults, and plays an important role in the closure of oil and gas reservoirs and gas storage facilities. Faults have undergone extremely complex structural evolution over a long geological history. The consolidated or unconsolidated materials in the upper and lower plates of the fault are filled by the fault drag and are drawn into the fault zone after being squeezed, displaced and worn to become fault cores. Fault cores undergo compaction, cementation and other evolutionary processes under the action of heat, chemistry and stress. However, since the reservoir-controlling faults or the boundary faults of gas storage facilities are deeply buried underground, it is difficult to obtain fault cores, and it is difficult to track the structural evolution of fault cores in the process of complex physical and chemical reactions. It is necessary to use a configured fault core model to carry out physical simulation to study its structural evolution law. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide an experimental method for quantitatively evaluating the structural evolution law of fault cores using nuclear magnetic resonance, and to use a nuclear magnetic resonance analyzer to study the changes in the T2 spectrum and nuclear magnetic resonance imaging of fault cores under conditions such as different compaction degrees, so as to semi-quantitatively and qualitatively analyze the structural evolution mechanism of fault cores.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] An experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance, comprising:

[0006] Sampling the fault zone containing the fault core and placing it in a sample storage tube to obtain the target fault core and the rock physical parameters of the target fault core;

[0007] Performing nuclear magnetic resonance scanning on the sample storage cylinder to obtain a T2 spectrum of the sample storage cylinder;

[0008] Measuring the mass of each component of the sample storage cylinder, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters;

[0009] Performing saturated water treatment and nuclear magnetic resonance scanning on the target tomographic core to obtain a T2 spectrum of the target tomographic core;

[0010] According to the mass of soil particles and water in the target fault core, the target fault core treated with saturated water is subjected to low-temperature drying and compaction treatment until the compaction depth is greater than 50 mm;

[0011] Determining the T2 spectrum of the target fault core under different compaction degrees according to the T2 spectrum of the sample cylinder and the T2 spectrum of the target fault core;

[0012] The T2 spectra of the target fault core under different compaction degrees are superimposed on one graph, and the changes of T2 spectra during the compaction process are compared and analyzed to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects.

[0013] Preferably, sampling is performed on the fault zone containing the fault core to obtain the target fault core and the rock physical parameters of the target fault core, including:

[0014] Determine the fault strike of the fault zone containing the fault core on site, and determine multiple fault core sampling points at different locations along the fault strike;

[0015] At each of the fault core sampling points, three target fault core samples are taken at several different orientations using an electric soil sampler;

[0016] After the sampling is completed, the sample of the target fault core is removed from the soil sampler together with the sample storage tube, and the taken out complete target fault core is sealed and stored;

[0017] The water content, components and particle size distribution of the broken target fault core are measured to obtain the rock physical parameters.

[0018] Preferably, measuring the mass of each component of the sample storage cylinder, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters, comprises:

[0019] Weigh the mass m2 of the sample cylinder, the mass m3 of the upper cover of the sample cylinder, the mass m4 of the lower cover of the sample cylinder, the mass m5 of the lower cover with holes of the sample cylinder, the initial mass m of the target fault core and the sample cylinder and the upper and lower covers respectively. a ;

[0020] According to the formula m1 = m a -m2-m3-m4 calculate the mass m1 of the target fault core;

[0021] The mass m of the soil particles in the target fault core is calculated based on the moisture content of the target fault core. 1土 , the mass of the water m 1水 .

[0022] Preferably, the target tomographic core is subjected to saturated water treatment and nuclear magnetic resonance scanning to obtain a T2 spectrum of the target tomographic core, including:

[0023] Based on the capillary saturation method, samples of the target fault core at each of the fault core sampling points are taken for saturated water treatment;

[0024] When the sample of the target fault core is saturated, weigh the sample mass m b ;

[0025] The saturated sample is subjected to nuclear magnetic resonance scanning to obtain the T2 spectrum of the target tomographic nucleus.

[0026] Preferably, according to the mass of soil particles and water in the target fault core, the target fault core after saturated water treatment is subjected to low-temperature drying and compaction treatment until the compaction depth is greater than 50 mm, comprising:

[0027] The scanned target tomographic core is dried at low temperature. When the mass of the target tomographic core is reduced to m a When , it is determined that the water content of the target fault core returns to the initial state;

[0028] Remove the upper cover of the sample storage cylinder and replace the lower cover of the sample storage cylinder with a perforated lower cover with drainage holes;

[0029] The target fault core is compacted with a compaction rod. During the compaction process, the mass of the discharged water and soil particles is measured for every 10% compaction, and the moisture content and dry density of the target fault core after compaction are calculated;

[0030] The steps of saturated water treatment, nuclear magnetic resonance scanning and low-temperature drying are repeated until the compaction depth reaches 50 mm.

[0031] Preferably, determining the T2 spectrum of the target fault core under different compaction degrees according to the T2 spectrum of the sample cylinder and the T2 spectrum of the target fault core comprises:

[0032] Subtracting the analysis result of the T2 spectrum of the sample cylinder from the T2 spectrum of the target fault core to obtain the T2 spectrum of the target fault core under different compaction degrees;

[0033] The distribution law of the aperture is inverted by using the relationship between the T2 spectrum of the target tomographic core and the aperture; the distribution law is: Where ρ2 is the transverse surface relaxation strength of rock, T 2表面 is the lateral duration of the surface, r is the pore radius, F s is the geometric factor, spherical pore F s =3, columnar pores F s =2.

[0034] Preferably, the T2 spectra of the target fault core under different compaction degrees are superimposed into one graph, and the changes of the T2 spectra during the compaction process are compared and analyzed to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects, including:

[0035] The T2 spectrum of nuclear magnetic relaxation time is obtained by using a low-field nuclear magnetic resonance sequence, and the T2 spectra of the fault core under different compaction degrees are superimposed on a graph, and the changes of the T2 spectrum during the compaction process are compared and analyzed to obtain the analysis results; the analysis results include: the minimum and maximum relaxation times, the relaxation times corresponding to the spectrum peaks, and the signal intensity corresponding to each relaxation time accounts for the total signal intensity; the minimum and maximum relaxation times reflect the range of the pore structure of the fault core; the relaxation time corresponding to the spectrum peak reflects the most concentrated pore size in the fault core; the ratio of the signal intensity corresponding to each relaxation time to the total signal intensity reflects the component proportion of the porosity in the fault core;

[0036] By studying the analysis results, the changes in pore size and distribution of the target fault core during the compaction process are determined, and the pore size and distribution are further verified by combining high-pressure mercury injection, as well as the changes in nuclear magnetic resonance imaging, to quantitatively evaluate the structural evolution of the fault core under complex physical and chemical effects.

[0037] The present invention discloses the following technical effects:

[0038] The present invention provides an experimental method for quantitatively evaluating the structural evolution law of fault cores by using nuclear magnetic resonance, comprising: sampling a fault zone containing fault cores and placing the sample in a sample storage tube to obtain a target fault core and rock physical parameters of the target fault core; performing nuclear magnetic resonance scanning on the sample storage tube to obtain a T2 spectrum of the sample storage tube; measuring the mass of each component of the sample storage tube, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters; performing saturated water treatment and nuclear magnetic resonance on the target fault core. Vibration scanning is performed to obtain the T2 spectrum of the target fault core; the target fault core treated with saturated water is subjected to low-temperature drying and compaction treatment according to the mass of soil particles and water in the target fault core, until the compaction depth is greater than 50 mm; the T2 spectrum of the target fault core under different compaction degrees is determined according to the T2 spectrum of the sample storage tube and the T2 spectrum of the target fault core; the T2 spectrum of the target fault core under different compaction degrees is superimposed on a graph, and the change of the T2 spectrum during the compaction process is compared and analyzed to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects. According to the fault core characteristics of the natural fault zone, the present invention configures a similar fault core model indoors, uses a nuclear magnetic resonance analyzer to study the changes of the fault core T2 spectrum and nuclear magnetic resonance imaging under conditions such as different compaction degrees, and semi-quantitatively and qualitatively analyzes the structural evolution mechanism of the fault core. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 A flow chart of a method provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of an experimental process provided by an embodiment of the present invention;

[0042] Figure 3 A fault core sampling location map of a natural fault zone provided by an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of an electric soil extractor provided in an embodiment of the present invention;

[0044] Figure 5 A schematic diagram of a sample storage cartridge provided in an embodiment of the present invention;

[0045] Figure 6 A schematic diagram of a hydraulic device provided in an embodiment of the present invention;

[0046] Figure 7 A schematic diagram of a step-by-step compaction process of a fault core provided by an embodiment of the present invention;

[0047] Figure 8 A nuclear magnetic resonance analyzer provided by an embodiment of the present invention;

[0048] Fig. 9 A schematic diagram of changes in the nuclear magnetic resonance T2 spectrum of a fault core during the compaction process provided by an embodiment of the present invention.

[0049] Description of reference numerals:

[0050] 1. Fault zone, 2. Crack, 3. Fault core, 4. Sampling position, 5. Sample storage tube, 6. Mold upper cover, 7. Mold lower cover, 8. Mold lower cover with holes, 9. Removable spiral blade, 10. Displacement sensor, 11. Hydraulic push rod with size scale, 12. Nuclear magnetic resonance apparatus. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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 creative work are within the scope of protection of the present invention.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Figure 1 A flow chart of a method provided by an embodiment of the present invention, such as Figure 1 As shown, the present invention provides an experimental method for quantitatively evaluating the evolution law of fault nuclear structure using nuclear magnetic resonance, comprising:

[0054] Step 100: sampling the fault zone containing the fault core and placing the sample into a sample storage tube to obtain a target fault core and rock physical parameters of the target fault core;

[0055] Step 200: performing nuclear magnetic resonance scanning on the sample storage cylinder to obtain a T2 spectrum of the sample storage cylinder;

[0056] Step 300: measuring the mass of each component of the sample storage cylinder, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters;

[0057] Step 400: performing saturated water treatment and nuclear magnetic resonance scanning on the target tomographic core to obtain a T2 spectrum of the target tomographic core;

[0058] Step 500: performing low-temperature drying and compaction treatment on the target fault core after saturated water treatment according to the mass of soil particles and water in the target fault core, until the compaction depth is greater than 50 mm;

[0059] Step 600: determining the T2 spectrum of the target fault core under different compaction degrees according to the T2 spectrum of the sample cylinder and the T2 spectrum of the target fault core;

[0060] Step 700: superimpose the T2 spectra of the target fault core under different compaction degrees into one graph, and compare and analyze the changes of the T2 spectrum during the compaction process to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects.

[0061] like Figure 2 As shown, the technical route of this embodiment is as follows:

[0062] 1) Cross-section core sampling

[0063] like Figure 3 As shown in FIG. 1 , for a fault zone 1 (with multiple fractures 2) containing a fault core 3, the fault strike is measured on site, and four fault core sampling points (sampling positions 4) are determined at different positions (A, B, C, and D) along the fault strike. Figure 3 The red oval shown) is used with an electric soil extractor (such as Figure 4As shown in the figure, three fault core samples are taken at several different positions. The electric soil sampler is composed of a detachable spiral blade 9 and a sample storage tube 5, and the sample storage tube has an inner diameter of 25 mm and a height of 100 mm. After sampling, the fault core sample is removed from the soil sampler together with the sample storage tube. The complete fault core sample after taking out is sealed and stored with the mold lower cover 7 and the mold upper cover 6. Some broken samples are taken to carry out the determination of rock physical parameters such as water content, composition, and particle grading.

[0064] 2) Magnetic resonance scanning of sample tube

[0065] The sample storage tube is composed of a sample storage tube 5, a mold upper cover 6 and a sealed mold lower cover 7. Figure 5 The sample cylinder is scanned by nuclear magnetic resonance to obtain its T2 spectrum, which is used as the reference value for subsequent tomographic nuclear magnetic resonance analysis.

[0066] 3) Compaction of fault core and NMR structural analysis

[0067] Weigh the mass of the sample tube m2, the mass of the upper cover m3, the mass of the lower cover m4, the mass of the lower cover 8 with holes of the mold m5, and the initial mass of the tomographic nuclear analysis sample (including the sample tube and the upper and lower covers) m a From this, we can calculate the fault core mass m1 = m a -m2-m3-m4, and then calculate the mass m of dry soil in the fault core based on the sample moisture content measured in step 1 1土 , water mass m 1水 .

[0068] Take the fault core sample of area A for saturated water treatment. According to the standard of geotechnical test method, considering the weak structure of the fault core, in order to avoid the disturbance caused by vacuum saturation method, the capillary saturation method is used here, which takes about 3 days. After the sample is saturated, weigh the sample mass m b The saturated sample was scanned by nuclear magnetic resonance to obtain its T2 spectrum.

[0069] 4) Continuous compaction of the fault core and NMR structural analysis

[0070] The scanned samples are dried at low temperature. When the sample weight is reduced to m a When the sample moisture content returns to the initial state, the upper cover of the sample storage tube is removed, and the lower cover of the sample storage tube is replaced with a drainage lower cover with fine holes. The compaction device is composed of a hydraulic system, a displacement sensor 10, and a hydraulic push rod 11 with a size scale. Figure 6The sample was compacted with a compaction rod. During the compaction process, the mass of the discharged water and soil particles was measured for every 10% compaction (i.e., 10 mm advancement). The moisture content and dry density of the fault core after compaction were calculated. The aforementioned steps of saturation with water, nuclear magnetic resonance scanning, and low-temperature drying were then repeated until the compaction depth reached 50 mm. Figure 7 shown.

[0071] 5) NMR structural analysis of fault cores in different orientations

[0072] The above 1) to 4) tests were carried out on fault core samples sampled at different orientations in areas B, C, and D to explore the relationship between the differences in the nuclear magnetic resonance structural evolution of fault cores at different locations and orientations during the compaction process and their composition, particle size, water content, etc.

[0073] 6) Analysis of the nuclear magnetic resonance T2 spectrum of the tomographic nucleus

[0074] The analysis result in step 3) is subtracted from the analysis result of the sample tube in step 2), and the T2 spectrum of the fault core under different compaction degrees is obtained. The distribution law of the pore size can be inverted by using the relationship between the T2 spectrum and the pore size.

[0075]

[0076] Where ρ2 is the rock transverse surface relaxation strength (μm / ms), T 2表面 - lateral duration of the surface, r is the pore radius (mm), F s is the geometric factor, spherical pore F s =3, columnar pores F s =2.

[0077] 7) Quantitative comprehensive evaluation of fault core structure evolution

[0078] like Figure 8 As shown, in this embodiment, the nuclear magnetic resonance instrument 12 is used to obtain the T2 spectrum of the nuclear magnetic relaxation time based on the CPMG (Carr-Purcell-Meiboom-Gill) sequence of low-field nuclear magnetic resonance, and the T2 spectra of the fault cores under different compaction degrees are superimposed on a graph to compare and analyze the change law of the T2 spectrum during the compaction process, as shown in FIG. Fig. 9 As shown. The minimum and maximum relaxation times reflect the range of the pore structure of the fault core; the relaxation time corresponding to the spectrum peak reflects the most concentrated pore size in the fault core; the ratio of the signal intensity corresponding to each relaxation time to the total signal intensity reflects the component proportion of porosity in the fault core. By studying the above data information in the T2 spectrum, the changes in the pore size and distribution of the fault core during the compaction process can be obtained, and the pore size and distribution can be further verified by combining high-pressure mercury injection, as well as the changes in nuclear magnetic resonance imaging, so as to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects.

[0079] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0080] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance, characterized in that: include: Sampling the fault zone containing the fault core and putting it into a sample storage tube to obtain the target fault core and the rock physical parameters of the target fault core; the sampling tool is an electric soil sampler consisting of a detachable spiral blade and a sample storage tube; after the sampling is completed, the fault core sample is removed from the electric soil sampler together with the sample storage tube, and the complete fault core sample after being taken out is sealed and stored with a mold lower cover and a mold upper cover, and some broken samples are taken to carry out the determination of rock physical parameters such as water content, composition, and particle grading; Perform nuclear magnetic resonance scanning on the sample storage cylinder to obtain T 2 spectrum; Measuring the mass of each component of the sample storage cylinder, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters; The target fault core is subjected to saturated water treatment and nuclear magnetic resonance scanning to obtain the target fault core. T 2 spectrum; According to the mass of soil particles and water in the target fault core, the target fault core treated with saturated water is dried at low temperature, and the upper cover of the sample storage cylinder is removed, and the lower cover of the sample storage cylinder is replaced with a perforated lower cover with drainage holes, and then different degrees of compaction treatment are performed until the compaction depth is greater than 50 mm; According to the sample cartridge T 2 Spectra and target tomographic core T 2 spectrum to determine the target fault core under different compaction degrees T 2 spectrum; The target fault core under different compaction degrees T 2 spectra are superimposed on one picture to compare and analyze the compaction process T 2. The changes in the spectrum, by studying the analysis results, determine the changes in the pore size and distribution of the target fault core during the compaction process, combine high-pressure mercury injection to further verify the pore size and distribution, and the changes in nuclear magnetic resonance imaging, so as to quantitatively evaluate the structural evolution law of the fault core under complex physical and chemical effects; Sampling the fault zone containing the fault core to obtain the target fault core and the rock physical parameters of the target fault core, including: Determine the fault strike containing the fault core on site and determine multiple fault core sampling points at different locations along the fault strike; At each of the fault core sampling points, three target fault core samples are taken at several different orientations using an electric soil sampler.

2. The experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance according to claim 1, characterized in that: Measuring the mass of each component of the sample storage cylinder, and calculating the mass of soil particles and water in the target fault core according to the mass of each component and the rock physical parameters, including: Weigh the mass of the sample storage tube respectively m 2. Quality of the cover of the sample storage tube m 3. Quality of the lower cover of the sample storage tube m 4. The quality of the bottom cover with holes of the sample storage tube m 5. Initial quality of target fault core, sample tube and upper and lower covers m a ; According to the formula m 1= m a - m 2- m 3- m 4 Calculate the mass of the target fault core m 1; The mass of the soil particles in the target fault core is calculated based on the moisture content of the target fault core. m 1土 , the quality of the water m 1水 .

3. The experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance according to claim 1, characterized in that: The target fault core is subjected to saturated water treatment and nuclear magnetic resonance scanning to obtain the target fault core. T 2 spectra, including: Based on the capillary saturation method, samples of the target fault core at each of the fault core sampling points are taken for saturated water treatment; When the sample of the target fault core is saturated, weigh the sample mass m b ; The saturated sample is scanned by nuclear magnetic resonance to obtain the target tomographic core. T 2 scores.

4. The experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance according to claim 2, characterized in that: The target fault core after saturated water treatment is dried at low temperature according to the mass of soil particles and water in the target fault core, and the upper cover of the sample storage cylinder is removed, and the lower cover of the sample storage cylinder is replaced with a perforated lower cover with drainage holes, and then different degrees of compaction treatment are performed until the compaction depth is greater than 50 mm, including: The scanned target tomographic core is dried at low temperature. m a When , it is determined that the water content of the target fault core returns to the initial state; The target fault core is compacted with a compaction rod. During the compaction process, the mass of the discharged water and soil particles is measured every 10% of the compaction, and the moisture content and dry density of the target fault core after compaction are calculated; The steps of saturated water treatment, nuclear magnetic resonance scanning and low-temperature drying are repeated until the compaction depth reaches 50 mm.

5. The experimental method for quantitatively evaluating the evolution law of fault core structure using nuclear magnetic resonance according to claim 1, characterized in that: According to the sample cartridge T 2 Spectra and target tomographic core T 2 spectrum to determine the target fault core under different compaction degrees T 2 spectra, including: The target fault core T 2 spectrum minus the sample cartridge T 2 spectrum analysis results, the target fault core under different compaction degrees is obtained T 2 spectrum; Using the target fault core T The relationship between the 2 spectrum and the aperture inverts the distribution law of the aperture; the distribution law is ; In the formula is the transverse surface relaxation strength of rock, T 2表面 is the lateral duration of the surface, is the pore radius, is the geometric factor, the spherical pore , columnar pores .

6. The experimental method for quantitatively evaluating the evolution law of fault core structure by using nuclear magnetic resonance according to claim 1, characterized in that: The target fault core under different compaction degrees T 2 spectra are superimposed on one picture to compare and analyze the compaction process T 2 spectrum changes, including: Using low-field NMR sequences to obtain NMR relaxation times T 2 spectrum, the fault core under different compaction degrees T 2 spectra are superimposed on one picture to compare and analyze the compaction process T 2 spectrum changes to obtain analysis results; the analysis results include: minimum and maximum relaxation times, relaxation times corresponding to spectrum peaks, and the proportion of signal intensity corresponding to each relaxation time to the total signal intensity; the minimum and maximum relaxation times reflect the range of the pore structure of the fault core; the relaxation time corresponding to the spectrum peak reflects the most concentrated pore size in the fault core; the proportion of the signal intensity corresponding to each relaxation time to the total signal intensity reflects the proportion of the porosity component in the fault core.

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