CN112834542B - Method for simultaneously measuring layering moisture content and pore size distribution of rock core - Google Patents
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- 239000011148 porous material Substances 0.000 title claims abstract description 66
- 239000011435 rock Substances 0.000 title claims abstract description 52
- 238000009826 distribution Methods 0.000 title claims abstract description 47
- 238000000034 method Methods 0.000 title claims abstract description 46
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 118
- 238000004364 calculation method Methods 0.000 claims abstract description 15
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 claims abstract description 14
- 239000003208 petroleum Substances 0.000 claims abstract description 5
- 229920006395 saturated elastomer Polymers 0.000 claims description 13
- 238000001228 spectrum Methods 0.000 claims description 11
- 238000005303 weighing Methods 0.000 claims description 4
- 238000012360 testing method Methods 0.000 abstract description 28
- 238000004458 analytical method Methods 0.000 abstract description 3
- 238000001514 detection method Methods 0.000 abstract description 3
- 238000011160 research Methods 0.000 abstract description 3
- 238000010998 test method Methods 0.000 abstract description 3
- 239000010410 layer Substances 0.000 description 82
- 238000000685 Carr-Purcell-Meiboom-Gill pulse sequence Methods 0.000 description 13
- 238000005481 NMR spectroscopy Methods 0.000 description 10
- 239000003921 oil Substances 0.000 description 9
- 230000008569 process Effects 0.000 description 7
- 239000007789 gas Substances 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 239000001257 hydrogen Substances 0.000 description 4
- 229910052739 hydrogen Inorganic materials 0.000 description 4
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 238000004587 chromatography analysis Methods 0.000 description 2
- 239000012792 core layer Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004821 distillation Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 239000008398 formation water Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003129 oil well Substances 0.000 description 2
- 238000009738 saturating Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
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- 230000005012 migration Effects 0.000 description 1
- 238000009659 non-destructive testing Methods 0.000 description 1
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- 230000002335 preservative effect Effects 0.000 description 1
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- 239000007787 solid Substances 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
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- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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Abstract
The invention relates to the technical field of petroleum exploration, in particular to a method for simultaneously measuring water content and pore size distribution of a rock core. The invention discloses a pulse sequence application method for detecting the water content and aperture distribution of a rock core, which is characterized in that frequency coding gradients are applied between radio frequency pulses to ensure that the resonance frequencies of water in different layers in a calibration rock sample are different, so that the rock core to be detected is subjected to layered detection, a calibration rock sample signal curve with uniform water content is obtained by utilizing the application test of the pulse sequence, and a calculation model for calibrating the water content of each layer is established; obtaining the water content of the core to be measured in full water on different layers by using the calculation model, and obtaining the pore size distribution of the core to be measured; compared with the conventional test method, the method has the advantages of simple test flow and short test time, and can realize nondestructive test of the sample; the water content and pore size distribution test of any layer number of the rock core can be simultaneously realized, and the method has great significance for research and analysis of exploration.
Description
Technical Field
The invention relates to the technical field of logging evaluation of oil and gas reservoirs in petroleum exploration, in particular to a method for simultaneously measuring layering water content and pore size distribution of a rock core.
Background
In the oil and gas exploration and development process, the water content of the core and the pore size distribution are an important index for evaluating the economic development of oil fields. In the secondary oil recovery process of an oil field, the recovery rate of the oil well is improved by injecting water into a production well, i.e., the oil well. However, as shown in FIG. 1, the process of injecting water to push crude oil in the formation into the production well is not a piston type pushing process, but a finger type pushing process with a certain angle, and the water content is different in different positions in the formation. Therefore, how to accurately measure the water content and the pore size distribution of the core has important significance for the efficient development of oil and gas fields.
The conventional method for measuring the water content of the rock core mainly comprises a distillation extraction method, a chromatographic method, a microwave method, an ethanol closed heating extraction-chromatographic method measurement, a vacuum carbonization method and a drying method; the conventional core pore size distribution measuring method mainly adopts a mercury intrusion method. The toluene in the distillation extraction method and the mercury in the mercury-pressing method pollute the environment; the conventional water content method only tests the water content of the whole rock core, but cannot test the water content of different positions of the rock core, and is not beneficial to research and analysis. The core water content and pore size distribution testing method is long in testing time and high in cost, and is not suitable for testing conventional physical parameters of the core.
The prior Chinese patent document CN105401937 discloses a saturation index prediction method based on a pore system structure, which comprises the steps of selecting a core sample with a representative target layer, saturating the core sample with a saline solution with a certain concentration, measuring nuclear magnetic resonance T2 spectrums of cores in a saturated state and nuclear magnetic resonance T2 spectrums of the cores in different centrifugal states, and obtaining a core void structure index and a core saturation index by calculating geometrical mean of the nuclear magnetic resonance T2 spectrums of the cores in different centrifugal states and core water saturation so as to determine the target layer index. However, the method is complex in flow and long in test time, and the water content and pore size distribution test of any layer number of the core cannot be simultaneously realized.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is that the water content and pore size distribution test of any layer number of the core cannot be simultaneously realized in the prior art. The invention provides a method for simultaneously measuring layered water content and pore size distribution in a saturated rock core by utilizing nuclear magnetic resonance technology, which quantitatively characterizes the water content and pore size distribution of each position of the rock core and can test the water content and pore size distribution of multiple layers of the rock core. The testing method is simple to operate and high in testing speed, and can realize nondestructive testing of water content and pore size distribution of each position of the core.
The invention discloses a pulse sequence application method for detecting core water content and pore size distribution, which sequentially comprises the following operations:
applying a 90 DEG RF pulse with a pulse width P1 on the RF pulse application channel;
applying a gradient pulse with amplitude G on the gradient pulse applying channel a0 Is a frequency encoding compensation gradient of (2);
applying N180-degree radio frequency pulses with the pulse width of P2 on a radio frequency pulse application channel; and between every two 180 DEG radio frequency pulses, applying a gradient pulse with an amplitude G on the gradient pulse applying channel a1 Is a frequency encoding gradient of (c).
Optionally, the frequency of the radio frequency pulse is 50kHz-5000kHz, and the frequency of the G a0 The value range is 0-0.05T/m, the G a1 The value range of N is 0-0.05T/m, and the value range of N is 1000-12000.
Optionally, the corresponding time of the peak of the 90 ° rf pulse and the corresponding time interval of the peak of the first 180 ° rf pulse are TE/2, and the peak time interval of each two 180 ° rf pulses is TE.
Optionally, the TE is 0.2ms-1ms.
Optionally, the value range of the P1 is 8us-12us, and the value range of the P2 is 18us-22us.
The invention also discloses a method for measuring the water content and the pore size distribution of the core, which comprises the following steps,
s1, selecting a core calibration sample with uniform water content, and obtaining the water content of the core to be measured when saturated with water;
s2, applying the pulse sequence application method to the target sample rock, stopping the time Tw, performing n times of cycles for one cycle, and collecting echo peak signals; connecting echo peaks of each layer of the scaled sample rock at different times to obtain a transverse relaxation time T2 attenuation spectrum of the corresponding layer; according to the transverse relaxation time T2 attenuation spectra of different layers of the calibration sample rock, the pore diameters of the different layers, namely the pore diameter distribution of the rock to be measured, are obtained, and the following formula is utilized:
where T2 is the transverse relaxation time of each layer of the core, fs is the pore shape factor, when the pores are spherical pores, fs=3; when the pores are columnar pores, fs=2;
r c is the aperture;
s3, establishing a core layering water content calculation model according to the nuclear magnetic signal quantity corresponding to the water content of each layer of the calibration sample rock;
and S4, applying the same pulse sequence to the rock core to be tested as that applied to the sample, and performing m times of circulation to obtain a nuclear magnetic signal quantity corresponding to the water content of each layer of the rock to be tested, and obtaining the water content and the aperture of each layer of the rock to be tested according to the rock core layering water content calculation model.
Optionally, n and m are powers of 2, and the range interval is 2-1024.
Optionally, the value range of Tw is 1000ms-10000ms.
Optionally, in step S1, the core to be measured is dried and weighed, and the weight M of the dried core is recorded 0 The method comprises the steps of carrying out a first treatment on the surface of the Vacuumizing the dry core, adding stratum water, vacuumizing until the core is completely saturated with water, and weighing to obtain weight M 1 Obtaining the total water content M of the core to be measured when the core is saturated with water 1 -M 0 。
Optionally, the core layering water content calculation model is a linear relation between each layer of core magnetic signal quantity and each layer of water content of the core, and the following formula is shown:
wherein x represents the water content of each layer;
y represents the nuclear magnetic signal quantity corresponding to the water content of each layer;
a is the slope and b is the intercept.
The invention also discloses an application method of the pulse sequence for detecting the water content and the pore size distribution of the rock core, or an application of the measurement method of the water content and the pore size distribution of the rock core in the field of petroleum exploration.
The technical scheme of the invention has the following advantages:
1. the invention discloses a pulse sequence application method for detecting the water content and the pore size distribution of a rock core, which is characterized in that a frequency coding gradient is applied between radio frequency pulses, and a gradient field is applied along the direction of a magnetic field, so that the resonance frequencies of water at different positions in a calibrated rock sample are different, layered detection of the rock core to be detected is realized, the water content of the rock core of each layer can be obtained, the pore sizes of the rock core of different layers can be obtained, the pore size distribution of the rock core to be detected can be obtained, the water content distribution and the pore size distribution of the rock core can be detected simultaneously, and the pulse sequence implementation method is simple and has good practicability.
2. The invention discloses a method for measuring core water content and pore size distribution, which utilizes a pulse sequence application method to obtain a signal curve of a calibration sample rock with uniform water content, and establishes a calculation model of the water content of each layer of the calibration sample; since nuclear magnetic resonance inside the rock only measures the signal of hydrogen in water, the substances without hydrogen have no signal; therefore, the signal quantity of each layer is in a linear relation with the water content, the water content on different layers of the core to be measured with full water is obtained by using the calculation model, and the pore diameters of all layers are measured simultaneously, so that the pore diameter distribution of the core to be measured is obtained; compared with the conventional test method, the method has the advantages of simple test flow and short test time, and can realize nondestructive test of the sample; the water content and pore size distribution test of any layer number of the rock core can be simultaneously realized, and the method has great significance for research and analysis of exploration.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of well flooding in accordance with the background of the invention;
FIG. 2 is a sequence diagram of a GR-CPMG pulse sequence used in an embodiment of the invention;
FIG. 3 is a graph of GR-CPMG echo signal acquisition of the present invention;
FIG. 4 is a graph of GR-CPMG acquisition of a scaled sample according to the invention;
FIG. 5 is a linear fit curve of the scaled sample rock portion horizon of the present invention;
FIG. 6 is a graph of GR-CPMG acquisition of a core to be measured saturated with water according to an embodiment of the present invention;
fig. 7 pore size distribution of core to be measured.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The specific experimental procedures or conditions are not noted in the examples and may be followed by the operations or conditions of conventional experimental procedures described in the literature in this field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge.
Example 1
Step 1, preparing a calibration sample and a core to be measured:
selecting five groups of core calibration samples with uniform water content, wherein the water content is respectively 0.1g,0.5g,1g,2g and 3g, and the water content is respectively 1%,5%,10%,20% and 30% in sequence;
preparing a core to be measured with the diameter of 25mm and the length of 25mm, which is standard sandstone, placing the core to be measured in a 105 ℃ oven for drying for 24 hours, and weighing the dry weight of the core to be measured as 46.6448g; placing the core to be measured in a vacuumizing water saturation device, adding formation water, vacuumizing and saturating for 48 hours to enable pores of the core to be measured to be completely saturated with formation water, weighing 45.8968g of the core to be measured in full water, and obtaining the core with the water content of 0.748g;
step 2, applying pulse sequences
Placing a rock of a calibration sample into a sample bin of a nuclear magnetic resonance instrument, applying a GR-CPMG pulse sequence shown in fig. 2, firstly applying 90-degree radio frequency pulses with the pulse width of 10us and the frequency of 200Hz to the calibration sample in a radio frequency pulse application channel (RF channel, X direction), then applying a frequency coding compensation gradient with the amplitude of 0.05T/m in a gradient pulse application channel, namely a GR channel, Y direction, and then applying 7000 radio frequency pulses with the pulse width of 20us 180 DEG to the calibration sample in the RF channel, wherein the time interval between the peak of the 90-degree radio frequency pulse and the peak of the first 180-degree radio frequency pulse is 0.5ms; the time interval between every two 180 DEG RF pulse peaks is 1ms, and a frequency coding gradient with the amplitude of 0.05T/m is applied between every two 180 DEG pulses, echo signals are acquired in the gradient application process, and the signal signals in FIG. 2 are shown; as shown in fig. 3, the 90 ° pulse application time is zero, the corresponding time at the echo peak is t, the value is equal to 1ms, the time interval between every two 180 ° radio frequency pulse peaks is the same, the echo peak points of different layers of the sample at the time t are obtained, and then the echo peaks of different times on each layer are connected to obtain the transverse relaxation time attenuation spectra of different layers;
in order to obtain a proper signal-to-noise ratio, after the GR-CPMG sequence is applied, waiting for 5000ms, and repeating the cycle of applying the GR-CPMG sequence for 1024 times as one cycle;
in other embodiments of the invention, the 90℃RF pulses and the 180℃RF pulses employ a frequency in the range of 50-5000kHz, and the frequency and amplitude employed by the frequency encoding compensation gradient and the frequency encoding gradient in the same GR-CPMG sequence are in the range of 0-0.05T/m, and in other embodiments are in the range of 0.04T/m,0.03T/m,0.02T/m, or 0.01T/m, without limitation.
In other embodiments of the present invention, the time interval between every two 180 ° rf pulse peaks may be, but is not limited to, 0.2ms,0.3ms,0.4ms,0.5ms,0.6ms,0.7ms,0.8ms, or 0.9 ms.
In other embodiments of the present invention, the number N of 180 ° rf pulses applied on the rf pulse application channel is 1000-12000, the number may be 1000,2000,3000,4000, 5000,6000,8000,9000,1000,11000 or 12000, and is not limited thereto, wherein the waiting time between each application of the pulse sequence is 1000ms-10000ms, 1000ms,2000ms,3000ms,4000ms, 700 ms,800 ms,9000ms, or 10000ms, the number of cycles is power of 2, and the value range is 2-1024, and is not limited thereto.
In other embodiments of the invention, the pulse width of the radio frequency pulse is adjusted according to different instrument and sample choices, and the pulse width of the 90 ° radio frequency pulse can be adjusted to 8us,9us,11us or 12us; the pulse width of the 180 ° rf pulse may be adjusted to 18us,19us,21us or 22us, and is not limited thereto.
In this embodiment, as shown in fig. 2, a frequency coding compensation gradient of 0.05T/m is applied to the GR channel to make the phases of all voxels consistent, a frequency coding gradient of 0.05T/m is applied between every two 180 ° radio frequency pulses to perform positioning in one dimension, and the application of the frequency coding positioning will cause the phase of all voxels in the selected layer to be out of phase, which is caused by the action of the frequency coding gradient, so that the intensity of the signal is reduced; different frequencies correspond to different positions;
storing the acquired sample signal data to obtain a T2 attenuation spectrum; wherein the most basic formula of T2 relaxation is shown in the following formula 1, wherein S is the specific surface area and the unit is m 2 V is the volume of the test sample, and the unit is m 3 ρ is the lateral surface relaxation strength of the rock, which is the ability of the hydrogen nuclei in the fluid to undergo surface relaxation by collisions with the solid surface inside the reservoir pores, in m/ms:
(1)
The formula of T2 relaxation and pore size distribution is shown in formula 2 below, assuming that the pores consist of ideal spheres, where Fs is the pore shape factor, spherical pores, fs=3; columnar pores, fs=2; rc is the aperture, and the aperture of different core layers is obtained, namely, the different aperture distribution of the core to be measured.
(2)
Step 3, establishing a core layering water content calculation model
Testing five groups of calibration stone samples with uniform water content according to the GR-CPMG pulse sequence in the step 2 to obtain a calibration sample rock GR-CPMG acquisition curve, as shown in figure 4;
according to the sample rock GR-CPMG acquisition curve shown in fig. 4, the nuclear magnetic signal quantity corresponding to the water content of each layer in the five groups of calibration samples with uniform water content is then determined, as shown in table 1, and a fitting relation curve is obtained, so as to obtain a core water content calculation model of each layer, as shown in table 2, x represents the water content corresponding to each layer, and y represents the nuclear magnetic signal quantity corresponding to the water content of each layer. As can be seen from the linear relation fitting curve of the scaled sample rock partial horizons shown in FIG. 5, the fitting curve of the selected partial horizons has good linear correlation;
table 1 nuclear magnetic semaphores corresponding to core delamination moisture content
Table 2 core layering moisture content calculation model
| Layer number | Fitting a relation curve | Layer number | Fitting a relation curve |
| Layer 1 | y=9503.4x+25.768 | Layer 21 | y=9434.8x+47.218 |
| Layer 2 | y=10009x+21.238 | Layer 22 | y=9539.9x+30.387 |
| Layer 3 | y=10109x+16.795 | Layer 23 | y=9557.5x+34.865 |
| Layer 4 | y=9965.2x+15.263 | Layer 24 | y=9611.3x+45.096 |
| Layer 5 | y=9823x+19.99 | Layer 25 | y=9661.4x+34.792 |
| Layer 6 | y=9743.5x+19.987 | Layer 26 | y=9633.9x+32.175 |
| Layer 7 | y=9663.6x+33.898 | Layer 27 | y=9650.5x+25.203 |
| Layer 8 | y=9659.9x+28.22 | Layer 28 | y=9662.7x+36.711 |
| Layer 9 | y=9595.3x+25.783 | Layer 29 | y=9786x+35.198 |
| Layer 10 | y=9458.4x+31.814 | Layer 30 | y=9849.9x+36.143 |
| Layer 11 | y=9456.3x+27.391 | Layer 31 | y=9809.4x+33.908 |
| Layer 12 | y=9507.6x+26.036 | Layer 32 | y=9782.2x+28.911 |
| Layer 13 | y=9481.8x+38.494 | Layer 33 | y=9807.1x+29.416 |
| Layer 14 | y=9493.9x+35.61 | Layer 34 | y=10021x+25.512 |
| Layer 15 | y=9444.2x+34.319 | Layer 35 | y=10085x+30.284 |
| Layer 16 | y=9425.9x+31.698 | Layer 36 | y=10103x+31.219 |
| Layer 17 | y=9471.4x+31.018 | Layer 37 | y=10051x+23.023 |
| Layer 18 | y=9475.6x+40.334 | Layer 38 | y=10047x+23.085 |
| Layer 19 | y=9530.6x+40.937 | Layer 39 | y=10187x+26.331 |
| Layer 20 | y=9518.3x+37.228 | Layer 40 | y=10436x+26.824 |
Since the resonance frequencies of all hydrogen protons are the same under the action of the magnetic field, the resonance frequencies of water at different positions in the calibration sample are different by applying a gradient field along the direction of the magnetic field, and the thickness of each layer is calculated by the following formula (formula 3):
(3)
Wherein, the FOV is the field of view, the unit is mm, and the FOV is determined according to the size of the sample (FOV is more than or equal to 2 times the length of the sample); TD represents the number of points, and the number is twice the number of cycles;
nuclear magnetic resonance only measures the signal of H in water, and substances without hydrogen have no signal; thus, the signal quantity per layer is linear with the moisture content.
Step 4, simultaneously testing nuclear magnetic resonance signals and pore diameters (r) on different layers of the core to be tested under full water c ) A distribution curve;
wrapping the core to be tested which is saturated with water by using a preservative film to prevent water loss;
testing the saturated water core sample to be tested by utilizing the GR-CPMG pulse sequence to obtain a GR-CPMG acquisition curve of the saturated water core to be tested, as shown in fig. 6; according to the measured curve, determining nuclear magnetic resonance semaphores and nuclear magnetic resonance T2 spectrums on each layer of the core to be measured under full water by using a BRD inversion algorithm;
calculating the water content of each layer of the core according to the T2 spectrum curve of each layer by using the layered water content calculation model in the table 1 to obtain the water content components of different pore layers; as shown in table 3;
according to formula 2, the pore size distribution of the core to be measured is calculated, and as shown in fig. 7, as can be seen from fig. 7, the pore size distribution of each layer of the core is approximately in a three-peak state. The first peak represents the water content of bound water in the core, and the water is not mined in the oil and gas development process; the second peak represents the water content of the movable water in the core, which is carried out during the migration of the oil and gas; the third peak represents the water content of the free water in the core, which affects the recovery of oil and gas.
Table 3 core average 40 layers each of the water content calculation results
Test case
The core to be tested was repeatedly tested 6 times according to the test method described in example 1, and the water content was shown in table 4.
Table 4 results of repeated testing of cores to be tested
Test conclusion: the detection method disclosed by the application can simply and effectively measure the water content and the pore size distribution of different core layers simultaneously, has good repeatability of the test result and good stability, and can be used in the petroleum exploration process.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (10)
1. A method for measuring the water content and pore size distribution of a rock core is characterized by comprising the following steps,
s1, selecting a core calibration sample with uniform water content, and obtaining the water content of the core to be measured when saturated with water;
s2, applying a pulse sequence application method to the rock of the calibration sample, stopping the time Tw, performing n times of cycles for one cycle, and collecting echo peak signals; connecting echo peaks of each layer of the scaled sample rock at different times to obtain a transverse relaxation time T2 attenuation spectrum of the corresponding layer; according to the transverse relaxation time T2 attenuation spectra of different layers of the calibration sample rock, the pore diameters of the different layers, namely the pore diameter distribution of the rock to be measured, are obtained, and the following formula is utilized:
where T2 is the transverse relaxation time of each layer of the core, fs is the pore shape factor, when the pores are spherical pores, fs=3; when the pores are columnar pores, fs=2;
r c is the aperture;
s3, establishing a core layering water content calculation model according to the nuclear magnetic signal quantity corresponding to the water content of each layer of the calibration sample rock;
s4, applying the same pulse sequence to the rock core to be tested as that applied to the sample, and performing m times of circulation to obtain nuclear magnetic signal quantity corresponding to the water content of each layer of the rock to be tested, and obtaining the water content and the aperture of each layer of the rock to be tested according to the rock core layering water content calculation model;
the pulse sequence application method sequentially comprises the following operations:
applying a 90 DEG RF pulse with a pulse width P1 on the RF pulse application channel;
applying a frequency encoding compensation gradient with an amplitude of Ga0 on the gradient pulse application channel;
applying N180-degree radio frequency pulses with the pulse width of P2 on a radio frequency pulse application channel; and between every two 180 ° radio frequency pulses, a frequency encoding gradient of amplitude Ga1 is applied on the gradient pulse application channel.
2. The method for measuring the water content and the pore size distribution of the core according to claim 1, wherein the frequency of the radio frequency pulse is 50kHz-5000kHz, the value range of Ga0 is 0-0.05T/m, the value range of Ga1 is 0-0.05T/m, and the value range of N is 1000-12000.
3. The method for measuring core water content and pore size distribution according to claim 1, wherein the corresponding time of the peak of the 90 ° rf pulse and the corresponding time interval of the peak of the first 180 ° rf pulse are TE/2, and the peak time interval of each two 180 ° rf pulses is TE.
4. The method for measuring core moisture content and pore size distribution according to claim 3, wherein TE is 0.2ms-1ms.
5. The method for measuring core water content and pore size distribution according to any one of claims 1 to 4, wherein the value of P1 ranges from 8us to 12us, and the value of P2 ranges from 18us to 22us.
6. The method for measuring core water content and pore size distribution according to claim 1, wherein n and m are each powers of 2 and the range interval is 2-1024.
7. The method for measuring the water content and the pore size distribution of the core according to claim 1, wherein the value range of Tw is 1000ms-10000ms.
8. The method for measuring water content and pore size distribution of a core according to claim 6, wherein in step S1, the core to be measured is dried and weighed, and the weight M of the dried core is recorded 0 The method comprises the steps of carrying out a first treatment on the surface of the Vacuumizing the dry core, adding stratum water, vacuumizing until the core is completely saturated with water, and weighing to obtain weight M 1 Obtaining the total water content M of the core to be measured when the core is saturated with water 1 -M 0 。
9. The method for measuring core water content and pore size distribution according to any one of claims 6 to 8, wherein the core layering water content calculation model is a linear relationship between core magnetic signal quantity of each layer of the core and water content of each layer of the core, and the following formula is shown as follows:
y＝ax+b
wherein x represents the water content of each layer;
y represents the nuclear magnetic signal quantity corresponding to the water content of each layer;
a is the slope and b is the intercept.
10. Use of the method for measuring the water content and the pore size distribution of the core according to any one of claims 1 to 9 in the field of petroleum exploration.
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