Porosity testing method and apparatus for irregularly shaped core

Abstract

Disclosed in the embodiments of the present invention are a porosity testing method and apparatus for an irregularly shaped core. The apparatus comprises: a magnet unit, a radio frequency unit, a spectrometer unit, a calculation unit, and a sample tube. The magnet unit comprises a magnet, wherein the magnet is used for providing a magnetic field for a volume calibration standard, a hydrogen-containing liquid and a sample to be tested, and the magnetic field strength of the magnet is 0.1-0.2 T. The radio frequency unit is used for detecting nuclear magnetic resonance signals from the volume calibration standard, the hydrogen-containing liquid and the sample to be tested, and the radio frequency unit comprises a radio frequency coil, the radio frequency coil having a nuclear magnetic resonance signal linear region, a nuclear magnetic resonance signal nonlinear region and a maximum nuclear magnetic resonance signal region. The spectrometer unit is used for controlling the radio frequency unit to collect the nuclear magnetic resonance signals from the volume calibration standard, the hydrogen-containing liquid and the sample to be tested. The calculation unit is used for calculating the porosity of the sample to be tested. The embodiments of the present invention can realize rapid and high-precision on-site testing of the porosity of irregularly shaped cores such as sidewall cores and drilling cuttings in drilling fluid.

Description

Method and device for testing porosity of irregularly shaped core TECHNICAL FIELD

[0001] The present application relates to the field of rapid detection of geological samples in oil field exploration sites, and particularly relates to a method and device for testing porosity of irregularly shaped core. BACKGROUND

[0002] Borehole sidewall core and drilling cuttings are rock samples taken from target strata during oil and gas exploration, reflecting the stratum conditions. Geologists can clearly analyze the stratum evolution traces by studying and analyzing the samples, and can study important information such as the geological environment, sedimentation and structural features, resource storage conditions of the stratum, and the like, which are related to the effect of oil and gas development. The porosity, permeability and oil saturation of the borehole sidewall core and drilling cuttings are core indicators for evaluating oil and gas reserves and productivity, and the porosity is the primary indicator for reflecting the reservoir storage space. Therefore, rapid measurement of the porosity of the borehole sidewall core and drilling cuttings on site is an important part of the logging service on the drilling site of the oil field.

[0003] The borehole sidewall core and drilling cuttings are irregularly shaped cores, and the earliest method for testing the porosity thereof is the drying method. The specific process for testing the porosity thereof by using the drying method is as follows: after the surface fluid of the fresh sample is wiped (the pores are 100% saturated with fluid, and the pore fluid is not lost for a long time), the wet weight m1 is first measured, the fresh sample is baked in an oven at high temperature until the mass is constant, the dry weight m2 is measured, and the porosity of the sample to be measured is:

[0004] In the formula, φ is the porosity of the sample to be measured, m1 is the wet weight of the sample, in grams; m2 is the dry weight of the sample, in grams; ρ G is the skeleton density of the sample, in grams per cubic centimeter. 3

[0005] The problems of the drying method are as follows: (1) the difference in the densities of oil and water in the pores is ignored, and the density of water is used to approximate the density of the pore fluid; (2) the skeleton density of the complex lithology is not easy to obtain, and the use of an empirical value instead will introduce errors; (3) if there is oil with medium or high viscosity in the pore fluid, the sample cannot be completely dried by the drying method, resulting in an overestimated dry weight and measurement errors; (4) the sample needs to be baked for a long time, the testing efficiency is low, and the baking of the hydrocarbon components in the sample will cause environmental pollution (the drilling site usually does not have the condition to build a fume hood), which is harmful to the testers.

[0006] With the popularization of the nuclear magnetic resonance (NMR) core measurement method and instrument in the logging industry laboratory, the NMR method is applied to the detection of the porosity of the borehole sidewall core and drilling cuttings on the drilling site. In the prior art, the specific steps for testing the porosity of the borehole sidewall core and drilling cuttings by using the NMR method are as follows: ​

[0007] First step: fresh borehole sidewall coring core or drilling cuttings, the surface fluid is wiped with wet filter paper, and then loaded into the nuclear magnetic resonance test sample tube. Set reasonable measurement parameters and collect nuclear magnetic resonance signals. The pore volume V of the sample to be measured is calculated by using the nuclear magnetic resonance signal-volume scale value por .

[0008] Second step: use the density balance to test the skeleton volume V of the sample to be measured T .

[0009] The porosity of the sample to be measured is:

[0010] In the formula, φ is the porosity, unit %; V por is the pore volume of the sample to be measured, unit cm 3 ; V T is the skeleton volume of the sample to be measured, unit cm 3 .

[0011] Compared with the traditional drying method, the nuclear magnetic resonance-density balance method solves the problem of hydrocarbon drying pollution, and the accuracy of the density balance in measuring the skeleton volume (i.e. the total volume of the sample, equal to the pore volume + the skeleton volume) of the sample to be measured also meets the requirements. However, the nuclear magnetic resonance-density balance method also has obvious shortcomings. First, the operation of testing the skeleton volume of the sample by the density balance method is complicated, and the two times of sample transfer will also cause low test efficiency. If the sample is poorly cemented or has cracks, etc., resulting in block or particle loss during transfer, it will cause large measurement error of the skeleton volume. Second, for the rock sample which is small particles itself, the practicability of the density balance method is very poor, and the human error is relatively large. Therefore, although the nuclear magnetic resonance-density balance method solves the problem of accurate measurement of the pore volume of part of the sample to be measured, its test process is complicated, the test efficiency is low, and there are also typical problems of not suitable for rock samples and easily broken block samples. Because of the high cost of borehole sidewall coring, it is generally only cored at key layers. Rock cuttings are a large amount of geological samples produced during drilling construction, and are also the geological samples that are most expected to be accurately tested by drilling site rock cuttings logging.

[0012] In order to solve the problems of complicated sample transfer operation and large human error in the nuclear magnetic resonance-density balance method, in 2017, Dick et al. [1]A method for simultaneously measuring pore volume and matrix volume by NMR method is proposed ([1] Dick M J, Green D, Kenney T, et al. Quick and simple porosity measurement at the well site [C] / / International Symposium of the Society of Core Analysts. Vienna, Austria. 2017: 1-10.), which includes the following steps:

[0013] 1) Preparation stage: Identify a fixed liquid level line in the linear range of the NMR signal of the sample tube, measure the water volume V1 when adding water to the liquid level line by weighing method, and measure the NMR signal S1 at this time, and then obtain the calibration coefficient K of water volume and NMR signal: H = V1 / S1, where K H is the calibration coefficient of water volume and NMR signal, with unit cm 3 ; V1 is the water volume in the sample tube when adding liquid to the identified fixed liquid level line, with unit cm 3 ; S1 is the NMR signal corresponding to the liquid amount, with unit dimensionless.

[0014] 2) Test step 1 of the sample to be tested: After wiping the fluid on the surface of fresh cuttings or core with wet filter paper, put it into the sample tube (and the sample loading height is lower than the liquid level line identified in the preparation stage), test the NMR signal S2, and the pore volume of the sample to be tested can be obtained, and the calculation formula is: por = K H *S2, where V por is the pore volume of the sample to be tested, with unit cm 3 ; S2 is the NMR signal measured for the sample to be tested, with unit dimensionless.

[0015] 3) Test step 2 of the sample to be tested: On the basis of step 1, without transferring the sample to be tested, directly add water to the liquid level line identified in the preparation stage in the sample tube, as much as possible to coincide with the liquid level line, and measure the NMR signal S3. S3<S1, the signal difference between the two is the sample matrix which does not contribute to the NMR signal of H nucleus, so the calculation formula of the sample matrix volume is: G = K H *(S1-S3), where V G is the matrix volume of the sample to be tested, with unit cm 3 ; S3 is the NMR signal measured after adding water to the sample tube, with unit dimensionless.

[0016] The apparent volume of the sample to be tested = the skeleton volume + the pore volume. Therefore, the formula for calculating the porosity of the sample to be tested is:

[0017] As can be seen from the above formula, if the liquid level is kept the same during the preparation stage and the test of the sample, and the sample loading height is lower than the liquid level, the porosity calculation of the sample is directly a combination calculation of the nuclear magnetic resonance signal in the three states, without the need for the water volume and the calibration coefficient of the nuclear magnetic resonance signal to participate in the calculation. Therefore, the NMR-H probe rock cuttings porosity measurement method has the advantages of simple method, simple operation, and no need to transfer the sample in the intermediate test process. However, this method still has two shortcomings: (1) the human error of the concave liquid surface when adding liquid to the sample tube leads to the limitation of the accuracy of the skeleton volume measurement; (2) during the pore volume test step, due to the surface tension, there will be residual fluid when wiping and cleaning the surface of the fresh sample, which will lead to the pore volume measurement value being too large, and thus the porosity measurement value being too large.

[0018] To address the challenges of maintaining a fixed liquid level in NMR-H probe-based rock cuttings porosity measurement, including human error and the influence of residual fluid on particle surfaces, Fellah and Mitchell of Schlumberger... [2-3] In 2018 and 2019, they proposed a method for measuring the porosity of rock cuttings using NMR-H and F probes ([2] Fellah K, Utsuzawa S, Song YQ, et al. Porosity of drill-cuttings using multinuclear 19F and 1H NMR measurements[J]. Energy & fuels, 2018, 32(7): 7467-7470. [3] Mitchell J, Valori A, Fordham E JA robust nuclear magnetic resonance workflow for quantitative determination of petrophysical properties from drill cuttings[J]. Journal of Petroleum Science and Engineering, 2019, 174: 351-361.). This measurement method includes the following steps:

[0019] 1) Preparation Stage, Step 1: For the H probe, within the linear region of the nuclear magnetic resonance signal in the sample tube, measure the volume V of the added water by weighing. H1 And measure the nuclear magnetic resonance signal S at this time. H1 This leads to the calibration coefficients for the water volume and NMR signal: KH =V H1 / S H1 In the formula, K H The scale factor for water volume and NMR signal is in cm. 3 V H1 The volume of water added to the sample tube, in cm³. 3 S H1 The NMR signal of water corresponds to the amount of liquid added, and the unit is dimensionless.

[0020] 2) Preparation Stage, Step 2: For the F probe, within the linear region of the NMR signal in the sample tube, measure the volume V of the fluorinated liquid FC-40 by weighing. F1 And measure the NMR signal S of element F at this time. F1 This leads to the calibration coefficients for the volume of fluorinated liquid FC-40 and the nuclear magnetic resonance signal: K F =V F1 / S F1 In the formula, K F This is a calibration coefficient for the volume of fluorinated liquid FC-40 and its nuclear magnetic resonance signal, in cm. 3 V F1 The volume of fluorinated solution FC-40 in the sample tube is expressed in cm³. 3 S F1 The NMR signal of fluorinated liquid FC-40 is given at the corresponding liquid addition volume, and the units are dimensionless.

[0021] 3) Preparation Stage, Step 3: For the F probe, continuously add fluorinating solution FC-40 to the sample tube until the NMR signal no longer increases, obtaining the maximum NMR signal S when only fluorinating solution FC-40 is added to the sample tube. Fmax And mark the liquid level line where the maximum value of the F signal is located.

[0022] 4) Step 1 of the sample test: After cleaning the sample slightly with wet filter paper, place it into the sample tube (the sample packing height should be below the upper limit of the linear region of the NMR signal). Then, add fluorinated solution FC-40 to the sample tube, ensuring the liquid level is above the liquid level line where the F signal is at its maximum value. After adding the liquid, screw the sealing cap on the sample tube and place it in a centrifuge. Select an appropriate speed and time to centrifuge the sample. Utilize the density of FC-40 (1.85 g / cm³) to determine the sample density. 3 > Water (1g / cm³) 3 The physical characteristics of the sample are utilized to remove residual fluid from the surface of the sample using centrifugal force, reducing the influence of the water film on the pore volume measurement. After centrifugation, the sample tube is placed into the nuclear magnetic resonance instrument, and the nuclear magnetic resonance signal S is measured using the H probe. H2 The pore volume of the sample to be tested is obtained as: V por =K H *SH2 , wherein V por is the pore volume of the sample under test, in cm 3 ; S H2 is the NMR signal of the sample under test measured in the H probe, dimensionless; K H is the calibration factor of water volume to NMR signal, in cm 3 .

[0023] 5) Sample under test test step 2: The sample after step 1 is put into the F probe of the NMR measuring instrument without any treatment, and the NMR signal S F2 of the F element is measured. F2 < S Fmax , and the signal difference between the two is the sample skeleton and pore volume that does not contribute to the NMR signal of the F element, so the apparent volume (i.e., the total volume) of the sample under test can be calculated: V T = K F *(S Fmax -S F2 ), wherein V T is the total volume of the sample under test, in cm 3 ; S Fmax is the maximum F signal amount when the sample tube is only filled with fluorinated liquid FC-40, dimensionless; S F2 is the NMR signal amount of the F element after the sample under test is loaded and the fluorinated liquid FC-40 is added, dimensionless.

[0024] The pore volume and the total volume of the sample under test are obtained through the 2-step measurement (using the H and F element probes in sequence), and the porosity of the sample under test is:

[0025] Compared with the NMR-H probe porosity measurement method, the NMR-H, F probe porosity measurement method has the advantage of solving the error caused by the incomplete removal of the surface fluid of the sample under test by the wiping method through the difference in fluid density. The feature of the NMR probe that there is a maximum signal amount is ingeniously used to solve the error caused by the concave liquid surface existing in the fixed liquid addition amount. However, the introduction of the F probe also leads to more complex NMR equipment, and the additional centrifugation step of the sample tube also reduces the test efficiency. Whether the centrifugal force is appropriate also affects the measurement result. If the centrifugal force is too large, the pore fluid of the sample under test will also be thrown out, resulting in a smaller pore volume measurement value; if the centrifugal force is too small, the surface fluid of the sample under test cannot be stripped; and the viscosity difference of the residual drilling mud liquid on the surface of the sample under test makes it more difficult to ensure the effect of the centrifugation operation.

[0026] In summary, the NMR-densitometer method has low speed, complicated operation, is not suitable for granular cuttings samples, and is not recognized by the industry. Although the NMR-H probe cuttings porosity measurement method and the NMR-H, F probe cuttings porosity measurement method developed in recent years have made great breakthroughs, there are still many deficiencies.

[0027] Therefore, there is an urgent need to provide a new testing method and device for irregularly shaped cores to solve the above problems. SUMMARY

[0028] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a porosity testing method and device for irregularly shaped cores, which can quickly and accurately test the porosity of irregularly shaped cores such as drilling fluid field core and drilling cuttings, and the testing method is simple and easy to operate.

[0029] In a first aspect, the present application provides a porosity testing method for irregularly shaped cores, the testing method comprising:

[0030] placing a volumetric calibration standard into the sample tube and not exceeding the first mark line of the sample tube, and testing to obtain the NMR signal S of the volumetric calibration standard H1 , calculating the calibration coefficient K of the volumetric calibration standard H , K H = V H / S H1 , V H is the volume of the hydrogen-containing liquid of the volumetric calibration standard, and the area between the first mark line of the sample tube and the bottom of the sample tube corresponds to the linear region of the NMR signal;

[0031] removing the volumetric calibration standard, adding the hydrogen-containing liquid in the sample tube until the liquid level is between the second mark line and the third mark line of the sample tube, and testing to obtain the NMR signal S of the hydrogen-containing liquid Hmax , the area between the first mark line and the second mark line corresponds to the nonlinear region of the NMR signal, and the area between the second mark line and the third mark line corresponds to the highest NMR signal region;

[0032] pretreating the sample to be tested, placing the pretreated sample to be tested in the sample tube and not exceeding the first mark line of the sample tube, and testing to obtain the NMR signal S of the sample to be tested H2 , calculating the pore volume V of the sample to be tested por , V por = K H × S H2 ;

[0033] adding the hydrogen-containing liquid into the sample tube with the sample to be tested until the liquid level is between the second mark line and the third mark line of the sample tube, and testing to obtain the nuclear magnetic resonance signal S of the sample to be tested and the hydrogen-containing liquid H3 calculating the skeleton volume V of the sample to be tested G V G = K H ×(S Hmax -S H3 );

[0034] calculating the porosity φ of the sample to be tested,

[0035] Further, the method for obtaining the second mark line comprises:

[0036] taking out the volume calibration sample, continuously adding the hydrogen-containing liquid into the sample tube until the nuclear magnetic resonance signal of the hydrogen-containing liquid is maximum, and the liquid level surface corresponding to the maximum nuclear magnetic resonance signal of the hydrogen-containing liquid is the second mark line.

[0037] Further, the pretreatment of the sample to be tested comprises removing the fluid on the surface of the sample to be tested.

[0038] Preferably, the pretreatment of the sample to be tested comprises wiping the fluid on the surface of the sample to be tested with a wet filter paper.

[0039] Further, the nuclear magnetic resonance signal is collected by using a CPMG sequence.

[0040] Further, the hydrogen-containing liquid is a copper sulfate solution with a mass concentration of 1000-1500 ppm.

[0041] Further, the adding of the hydrogen-containing liquid into the sample tube with the sample to be tested until the liquid level is between the second mark line and the third mark line of the sample tube comprises:

[0042] removing the bubbles adsorbed on the surface of the sample to be tested.

[0043] Preferably, the adding of the hydrogen-containing liquid into the sample tube with the sample to be tested until the liquid level is between the second mark line and the third mark line of the sample tube comprises:

[0044] gripping the sample tube and swinging it in one direction to slightly shake the sample to be tested at the bottom of the sample tube, so as to remove the bubbles adsorbed on the surface of the sample to be tested.

[0045] In a second aspect, the application further provides a device for the porosity testing method of the irregularly shaped core, the device comprising: a magnet unit, an RF unit, a spectrometer unit, a calculation unit and a sample tube;

[0046] The magnet unit comprises a magnet for providing a magnetic field for a volumetric calibration sample, a hydrogen-containing liquid and a sample to be tested, the magnetic field strength of the magnet being 0.1-0.2T.

[0047] The RF unit is used to detect the NMR signals of the volumetric calibration sample, the hydrogen-containing liquid and the sample to be tested, the RF unit comprising an RF coil, the RF coil being a low filling sensitivity H RF coil, the RF coil having a linear NMR signal region, a nonlinear NMR signal region and a highest NMR signal region, when the liquid level of the hydrogen-containing liquid is in the linear NMR signal region, the NMR signal of the hydrogen-containing liquid is proportional to the volume of the hydrogen-containing liquid, when the liquid level of the hydrogen-containing liquid is in the nonlinear NMR signal region, the NMR signal of the hydrogen-containing liquid is nonlinearly and monotonously increasing with the volume of the hydrogen-containing liquid, when the liquid level of the hydrogen-containing liquid is in the highest NMR signal region, the NMR signal of the hydrogen-containing liquid reaches a maximum value, and the NMR signal deviation of the hydrogen-containing liquid in the highest NMR signal region is ≤±1%.

[0048] The spectrometer unit is used to control the RF unit to collect the NMR signals of the volumetric calibration sample, the hydrogen-containing liquid and the sample to be tested.

[0049] The calculation unit is used to calculate the porosity of the sample to be tested.

[0050] The sample tube is used to place the volumetric calibration sample, the hydrogen-containing liquid and the sample to be tested in the RF coil, the surface of the sample tube being provided with a first mark line, a second mark line and a third mark line, the area between the first mark line of the sample tube and the bottom of the sample tube corresponding to the linear NMR signal region, the area between the first mark line and the second mark line corresponding to the nonlinear NMR signal region, and the area between the second mark line and the third mark line corresponding to the highest NMR signal region.

[0051] Further, the inductance of the RF coil ranges from 0.1μH to 0.5μH.

[0052] Further, the sample tube comprises a main body and a sealing cover, the main body is a barrel structure with one end open, the main body and the sealing cover form a containing space for placing the volume scale sample, the hydrogen-containing liquid and the sample to be measured, the open end of the main body is provided with an internal thread, and the sealing cover is provided with an external thread matched with the internal thread, and the sealing cover can be moved along a preset direction through the internal thread to seal the main body.

[0053] Further, the surface of the sealing cover is provided with knurling, and the end of the main body away from the opening is arc-shaped.

[0054] The above one or more embodiments of the present application have at least one or more of the following beneficial effects:

[0055] The present application provides a porosity testing method and device for irregularly shaped cores, which first tests the pore volume of the sample to be measured, then adds hydrogen-containing liquid into the sample tube containing the sample to be measured to the highest nuclear magnetic resonance signal area, tests the nuclear magnetic resonance signal of the sample to be measured and the hydrogen-containing liquid, calculates the skeleton volume of the sample to be measured by using the scale curve, and finally obtains the porosity of the sample to be measured by using the pore volume and the skeleton volume. The method provided by the present application does not need to transfer the sample when testing the skeleton volume of the sample to be measured, thereby improving the testing efficiency and avoiding the problem of large testing error of the skeleton volume caused by the existence of dropped blocks or dropped particles of the sample during the transfer process. In addition, the present application uses the nuclear magnetic resonance method to test the skeleton volume of the sample to be measured, which can improve the testing accuracy of the skeleton volume of the small particle detritus sample, and further improve the testing precision of the porosity.

[0056] Further, the radio frequency coil provided by the present application is a low filling sensitivity H radio frequency coil, which has a nuclear magnetic resonance signal linear region, a nuclear magnetic resonance signal nonlinear region and a highest nuclear magnetic resonance signal region. When the liquid level of the hydrogen-containing liquid is in the nuclear magnetic resonance signal linear region, the nuclear magnetic resonance signal of the hydrogen-containing liquid is proportional to the volume of the hydrogen-containing liquid. When the liquid level of the hydrogen-containing liquid is in the nuclear magnetic resonance signal nonlinear region, the nuclear magnetic resonance signal of the hydrogen-containing liquid is monotonously increased in a nonlinear manner with the volume of the hydrogen-containing liquid. When the liquid level of the hydrogen-containing liquid is in the highest nuclear magnetic resonance signal region, the nuclear magnetic resonance signal of the hydrogen-containing liquid reaches a maximum value, and the deviation of the nuclear magnetic resonance signal of the hydrogen-containing liquid in the highest nuclear magnetic resonance signal region is less than or equal to ±1%. Due to the above characteristics of the H radio frequency coil, when the volume of the sample skeleton is tested, the hydrogen-containing liquid only needs to be added to the highest nuclear magnetic resonance signal region, thereby avoiding the constraint that the hydrogen-containing liquid must be added to a fixed liquid level when the volume of the sample skeleton is tested. Therefore, the method and device provided by the present application can improve the accuracy of porosity testing while reducing the operation difficulty. In addition, the porosity of the sample to be tested can be accurately and quickly tested by using only the H radio frequency coil, so that the price of the nuclear magnetic resonance instrument is reduced, which is conducive to the popularization and application of the testing method and device provided by the present application.

[0057] Additional aspects and advantages of the present application will be set forth in part in the following description, will become apparent from the following description, or will be learned through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0058] The present application will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration and are not intended to limit the present application. It is readily understood that these drawings are for purposes of illustration only and are not intended to limit the scope of the present application. Like reference numerals are used to refer to like elements throughout.

[0059] FIG. 1 is a flow chart of a porosity testing method for an irregularly shaped core provided by the present application;

[0060] FIG. 2 is a schematic diagram of a porosity testing method for an irregularly shaped core provided by the present application;

[0061] FIG. 3 is a block diagram of a device for a porosity testing method for an irregularly shaped core provided by the present application;

[0062] FIG. 4 is a schematic diagram of the relationship between the volume of the hydrogen-containing liquid added to the sample tube of the porosity testing device for an irregularly shaped core provided by the present application and the nuclear magnetic resonance signal;

[0063] FIG. 5 is a schematic diagram of the relationship between the volume of the hydrogen-containing liquid added to the sample tube of the porosity testing device of the prior art and the nuclear magnetic resonance signal;

[0064] FIG. 6 is a physical diagram of a sample tube provided by the present application. Detailed Implementation

[0065] Some embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0066] As shown in the background section, the drying method for testing the porosity of irregularly shaped core samples such as wellbore cores and drilling cuttings suffers from drawbacks such as poor accuracy, low efficiency, and environmental pollution caused by the drying of hydrocarbon components in the samples, which is harmful to the health of testing personnel. While the nuclear magnetic resonance-density balance method solves the problem of hydrocarbon drying pollution, it also brings problems such as cumbersome operation, poor accuracy, and low efficiency. Although the NMR-H probe method for measuring the porosity of cuttings does not require sample transfer during the intermediate testing process, the human error of the concave meniscus when adding liquid to the sample tube limits the accuracy of the skeleton volume measurement. While the NMR-H and F probe method for measuring the porosity of cuttings can solve the concave meniscus error caused by a fixed liquid addition volume, the introduction of the F probe makes the nuclear magnetic resonance equipment more expensive and complex.

[0067] To address this issue, this invention creatively proposes a method and apparatus for testing the porosity of irregularly shaped rock cores. When testing the skeleton volume of the sample, there is no need to transfer the sample, thus improving testing efficiency and avoiding the problem of large testing errors in skeleton volume due to fragments or particles falling off during sample transfer. Furthermore, this application uses nuclear magnetic resonance (NMR) to test the skeleton volume of the sample. For small-particle rock fragments, this improves the accuracy of skeleton volume testing, thereby enhancing the precision of porosity testing. The H-radio frequency coil provided in this application is a low-fill-sensitivity H-radio frequency coil. When testing the skeleton volume of the sample, only the hydrogen-containing liquid needs to be added to the region of highest NMR signal, thus avoiding the constraint that the liquid level must be reached to a fixed level for testing the skeleton volume of the sample using hydrogen-containing liquid. In addition, this application can test the porosity of the sample using only an H-radio frequency coil, thus reducing the price of NMR instruments and facilitating the widespread adoption of the testing method and apparatus provided in this application.

[0068] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. The technical objectives and beneficial effects of this application can be better achieved through the following optional technical solutions.

[0069] Firstly, this application provides a method for testing the porosity of irregularly shaped rock cores, as shown in Figure 1. The testing method includes:

[0070] S1: Place the volumetric calibration standard into the sample tube, ensuring it does not exceed the first mark line of the sample tube, and measure the nuclear magnetic resonance signal S of the volumetric calibration standard. H1 The scale coefficient K of the volume scale standard is calculated. H K H =V H / S H1 V H The volume of the hydrogen-containing liquid in the volume scale standard is defined as the region between the first marking line of the sample tube and the bottom of the sample tube, which corresponds to the linear region of the nuclear magnetic resonance signal.

[0071] It is important to note that preparations should be made at least 3-4 hours in advance before the drilling fluid field test. First, deploy the NMR instrument, connect the power, and turn on the magnet temperature control, waiting for the magnet temperature to reach the set value and stabilize. Next, after the magnet temperature stabilizes, turn on the power to the instrument's electronic cabinet and the data acquisition computer, and use the FID sequence to preheat the entire system for half an hour. Finally, after the instrument has fully preheated, calibrate it, finding the magnet center frequency, RF excitation parameters, etc. Once the instrument is stable, use the CPMG sequence to acquire NMR signals. Specifically, fix the instrument gain parameters, and set the CPMG sequence acquisition parameters: waiting time TW, echo interval TE, number of echoes NECH, and accumulation count NS. Use the volume calibration standard provided with the instrument to test the NMR signal, obtaining the calibration coefficient K between the hydrogen-containing liquid volume and the NMR signal. H .

[0072] Specifically, as shown in Figure 2(a), firstly, the volume scale standard 200 is placed in the sample tube, not exceeding the first mark line 110 of the sample tube. Then, the sample tube is placed in the detection area of ​​the radio frequency coil, and the nuclear magnetic resonance signal S of the volume scale standard 200 is measured. H1 The scale factor K of volume scale standard 200 was calculated. H K H =V H / S H1 V H This represents the volume of hydrogen-containing liquid in volume calibration standard 200. The region between the first marking line 110 and the bottom of the sample tube corresponds to the linear region 10 of the nuclear magnetic resonance (NMR) signal. The linear region 10 refers to the area where, when the liquid level of the hydrogen-containing liquid is within this region, the NMR signal is directly proportional to the volume of the hydrogen-containing liquid; that is, as the volume of the hydrogen-containing liquid increases, its NMR signal exhibits a linear and monotonically increasing trend.

[0073] In the present application, the volumetric calibration sample 200 is a sample with a known volume of hydrogen-containing liquid. As a preferred embodiment, a known volume of hydrogen-containing liquid is sealed in a container to form the volumetric calibration sample 200, so that the evaporation of the hydrogen-containing liquid in the volumetric calibration sample 200 during use is avoided, and the scale factor K H deviation occurs.

[0074] In a specific embodiment, the hydrogen-containing liquid in the volumetric calibration sample 200 is a copper sulfate solution with a mass concentration of 1000-1500 ppm, and preferably, the hydrogen-containing liquid in the volumetric calibration sample 200 is a copper sulfate solution with a mass concentration of 1000 ppm, and the T2 relaxation time of the hydrogen-containing liquid in the nuclear magnetic resonance instrument under the corresponding magnetic field intensity is about 100 ms. The reason for using the copper sulfate solution is that the T2 relaxation time of pure water is about 2-3 seconds, and the required nuclear magnetic resonance acquisition time is too long, which will affect the test efficiency, therefore, the T2 relaxation time can be shortened by using the copper sulfate solution, and the sampling time is also shortened.

[0075] S2: taking out the volumetric calibration sample, adding the hydrogen-containing liquid in the sample tube until the liquid level is between the second mark line and the third mark line of the sample tube, and testing to obtain the nuclear magnetic resonance signal S of the hydrogen-containing liquid Hmax The area between the first mark line and the second mark line corresponds to the non-linear region of the nuclear magnetic resonance signal, and the area between the second mark line and the third mark line corresponds to the highest nuclear magnetic resonance signal region.

[0076] The non-linear region of the nuclear magnetic resonance signal refers to that when the hydrogen-containing liquid 300 is added in the sample tube until the liquid level is in the non-linear region of the nuclear magnetic resonance signal, the nuclear magnetic resonance signal of the hydrogen-containing liquid 300 and the volume of the hydrogen-containing liquid 300 are in a non-linear monotonic increasing rule. The highest nuclear magnetic resonance signal region refers to that when the hydrogen-containing liquid 300 is added in the sample tube until the liquid level is in the highest nuclear magnetic resonance signal region, the nuclear magnetic resonance signal of the hydrogen-containing liquid 300 reaches the maximum value, and the deviation of the nuclear magnetic resonance signal of the hydrogen-containing liquid 300 in the highest nuclear magnetic resonance signal region is ≤±1%. In the present application, the area between the first mark line 110 and the second mark line 120 corresponds to the non-linear region of the nuclear magnetic resonance signal 20, and the area between the second mark line 120 and the third mark line 130 corresponds to the highest nuclear magnetic resonance signal region 30.

[0077] Further, the method for obtaining the second mark line includes: as shown in FIG. 2(b), taking out the volumetric calibration sample 200, and continuously adding the hydrogen-containing liquid 300 in the sample tube until the nuclear magnetic resonance signal of the hydrogen-containing liquid 300 is maximum, and the liquid level corresponding to the maximum nuclear magnetic resonance signal of the hydrogen-containing liquid 300 is the second mark line 120.

[0078] It should be noted that steps S1 and S2 only need to be performed once before testing a batch of samples. Steps S1 and S2 are for volume calibration of the nuclear magnetic resonance signal and detection of the maximum signal amount.

[0079] S3: Pre-treat the sample to be tested by placing the pre-treated sample into the sample tube, ensuring it does not exceed the first marking line of the sample tube, and then measuring the nuclear magnetic resonance signal S of the sample to be tested. H2 The pore volume V of the sample to be tested is calculated. por V por =K H ×S H2 .

[0080] To ensure testing accuracy, the NMR instrument's operational status must be checked before testing the sample to ensure it is functioning correctly. A polytetrafluoroethylene (PTFE) block (a regular cylinder, its volume V calculated by measuring with a ruler) with a known volume provided with the instrument is used. PTFE1 Place the sample tube in a dry container, then add the hydrogen-containing liquid prepared in step S2 (the liquid level of the hydrogen-containing liquid should exceed the nonlinear region of the NMR signal). After adding the liquid, place the sample tube in the detection area of ​​the radio frequency coil and measure the NMR signal S using the same NMR acquisition parameters as in step S2. PTFE The volume V is calculated using the method proposed in this invention. PTFE2 =K H *(S Hmax -S PTFE If V PTFE2 With V PTFE1 A relative error of ≤3% indicates that the instrument is functioning normally and can be used for on-site testing of the sample to be tested.

[0081] Furthermore, the pretreatment of the sample to be tested includes removing fluid from the surface of the sample. As a preferred embodiment, the surface of the sample is wiped with wet filter paper to avoid the influence of fluid on the test results. Additionally, for wellbore core samples and cuttings, since drilling mud residue is generally present on the surface, they need to be rinsed with clean water before measurement to avoid the mud affecting the test results.

[0082] Furthermore, as shown in Figure 2(c), the pretreated sample 400 is placed in the sample tube, ensuring it does not exceed the first mark line 110 of the sample tube, and the nuclear magnetic resonance signal S of the sample is obtained. H2 The pore volume V of the sample to be tested was calculated. por V por =K H ×S H2 .

[0083] S4: adding the hydrogen-containing liquid into the sample tube with the sample to be tested until the liquid level is between the second mark line and the third mark line of the sample tube, and testing to obtain the nuclear magnetic resonance signal S of the sample to be tested and the hydrogen-containing liquid H3 , calculating the skeleton volume V of the sample to be tested G , V G = K H × (S Hmax -S H3 ).

[0084] Specifically, as shown in FIG. 2(d), the hydrogen-containing liquid 300 configured in step S2 is added into the sample tube with the sample to be tested 400 until the liquid level is between the second mark line 120 and the third mark line 130 of the sample tube, and then the sample tube with the sample to be tested 400 is placed into the radio frequency coil detection area, and the nuclear magnetic resonance signal S of the sample to be tested 400 and the hydrogen-containing liquid 300 is tested, and the skeleton volume V of the sample to be tested is calculated H3 , V G , V G = K H × (S Hmax -S H3 ).

[0085] During the process of adding the hydrogen-containing liquid into the sample tube, bubbles are usually adhered to the surface of the sample due to surface tension. If the bubbles adsorbed on the surface of the sample are not removed, the volume occupied by the bubbles will cause the skeleton volume to be larger, and thus the porosity measurement value to be lower. In order to solve this problem, the process of adding the hydrogen-containing liquid 300 into the sample tube with the sample to be tested 400 until the liquid level is between the second mark line 120 and the third mark line 130 of the sample tube includes: removing the fluid on the surface of the sample to be tested 400. Specifically, the sample tube is held and swung in one direction to slightly vibrate the sample to be tested 400 at the bottom of the sample tube, and the bubbles adsorbed on the surface of the sample to be tested 400 are removed. Through such an operation, the bubbles adsorbed on the surface of the sample can be removed in time, so that the skeleton volume test of the sample is more accurate, and thus the test precision of the porosity can be improved.

[0086] It should be noted that the sampling parameters of the nuclear magnetic resonance signal are kept consistent during the whole test process, and in particular, the cumulative number (NS) and the echo time (TE) need to be kept consistent. If a sample with a long T2 relaxation time is encountered, only the waiting time (TW) and the number of echoes (NECH) need to be adjusted so that the fluid signal in the sample can be fully relaxed. Since the sample to be tested 400 generally has micro-nano pores, the echo interval TE needs to adopt the minimum value of the nuclear magnetic resonance instrument to ensure the measurement accuracy.

[0087] In addition, in step S2, because the radio frequency coil is required to detect the state of the hydrogen-containing liquid filling the detection area in the test, the amount of nuclear magnetic resonance signal is the largest at this time. In order to avoid signal saturation of the instrument, the gain parameter of the instrument needs to be reasonably set. On the premise of ensuring that the nuclear magnetic resonance signal is not saturated, as large a gain parameter as possible is used to ensure the data signal-to-noise ratio when the nuclear magnetic resonance signal of a sample with a lower signal amount is collected. It is suggested that the gain parameter of the instrument be fixed during the test. If the gain parameter is not fixed (for example, a small gain is used to avoid signal saturation when the hydrogen-containing liquid is tested, and a large gain is used to ensure a high signal-to-noise ratio when the sample to be tested is tested), the gain of the nuclear magnetic resonance signal needs to be corrected when the porosity is calculated.

[0088] S5: calculating the porosity φ of the sample to be tested,

[0089] After all the samples to be tested 400 are tested, the hydrogen-containing liquid 300 is sent to a waste chemical recovery tank or a recovery pool at a drilling site and cannot be poured at will; data is processed and a test report is arranged, the power supply of the nuclear magnetic resonance instrument is turned off, and the sample tube, power supply line, notebook computer and the like are stored.

[0090] The hydrogen-containing liquid appears in the above steps. In the embodiments of the present application, the hydrogen-containing liquid newly added to the sample tube in different steps is the same kind but not the same liquid.

[0091] In a second aspect, the present application also provides a device for testing the porosity of the irregularly shaped core as described above, as shown in FIG. 3, the device comprises: a magnet unit, a radio frequency unit, a spectrometer unit 3000, a calculation unit 4000 and a sample tube 5000.

[0092] The radio frequency unit is used for detecting the nuclear magnetic resonance signals of the volume calibration sample, the hydrogen-containing liquid and the sample to be measured. Specifically, the radio frequency unit comprises a radio frequency coil 2100, a radio frequency power amplifier 2200, a energy dissipation module 2300, a TR switch 2400, a coupler 2500, a preamplifier 2600 and a double-channel radio frequency switch 2700. The radio frequency coil 2100 is used for transmitting radio frequency pulses, exciting H nuclei in the sample to generate nuclear magnetic resonance signals, and receiving the nuclear magnetic resonance signals of the H nuclei in the sample, and is also the position of loading the sample tube 5000; the radio frequency power amplifier 2200 is used for amplifying the radio frequency excitation signal power of the spectrometer unit 3000 to generate radio frequency excitation pulses with sufficient power; the energy dissipation module 2300 is used for quickly dissipating the radio frequency energy after excitation is finished, reducing the “acquisition preparation time” of the radio frequency unit, and realizing the function of short echo interval sampling; the TR switch 2400 is a key device for quickly switching the excitation and reception modes of the radio frequency coil 2100; the coupler 2500 and the double-channel radio frequency switch 2700 are used for realizing the functions of nuclear magnetic signal transmission and reception and radio frequency coil 2100 resonance characteristic checking; and the preamplifier 2600 is an analog signal amplifier for amplifying weak nuclear magnetic signals of the sample, and is a key device for improving the signal-to-noise ratio of the sampling data.

[0093] Unlike the nuclear magnetic resonance instrument in the prior art, the radio frequency coil 2100 in the present application has low sensitivity characteristics to reduce the amount of change in the resonance frequency of the radio frequency coil 2100 when the hydrogen-containing liquid is continuously added when testing the volume of the skeleton. Specifically, the radio frequency coil 2100 has a nuclear magnetic resonance signal linear region, a nuclear magnetic resonance signal nonlinear region and a highest nuclear magnetic resonance signal region. When the liquid level of the hydrogen-containing liquid is in the nuclear magnetic resonance signal linear region, the nuclear magnetic resonance signal of the hydrogen-containing liquid is proportional to the volume of the hydrogen-containing liquid, when the liquid level of the hydrogen-containing liquid is in the nuclear magnetic resonance signal nonlinear region, the nuclear magnetic resonance signal of the hydrogen-containing liquid is monotonically increasing in a nonlinear manner, and when the liquid level of the hydrogen-containing liquid is in the highest nuclear magnetic resonance signal region, the nuclear magnetic resonance signal of the hydrogen-containing liquid reaches a maximum value, and the deviation of the nuclear magnetic resonance signal of the hydrogen-containing liquid in the highest nuclear magnetic resonance signal region is ≤±1%.

[0094] In the present application, the sample tube 5000 containing hydrogen-containing liquid is placed in the radio frequency coil 2100, and the relationship between the nuclear magnetic resonance signal and the volume of the hydrogen-containing liquid is shown in Figure 4. When the liquid level of the hydrogen-containing liquid is in the linear region 10 of the nuclear magnetic resonance signal, the nuclear magnetic resonance signal of the hydrogen-containing liquid is proportional to the volume of the hydrogen-containing liquid; when the liquid level of the hydrogen-containing liquid is in the nonlinear region 20 of the nuclear magnetic resonance signal, the nuclear magnetic resonance signal of the hydrogen-containing liquid and the volume of the hydrogen-containing liquid show a nonlinear monotonic increasing rule, and when the liquid level of the hydrogen-containing liquid is in the highest nuclear magnetic resonance signal region 30, the nuclear magnetic resonance signal of the hydrogen-containing liquid reaches the maximum value, and the deviation of the nuclear magnetic resonance signal of the hydrogen-containing liquid in the highest nuclear magnetic resonance signal region is ≤±1%. Only when the amount of nuclear magnetic resonance signal and the volume of the hydrogen-containing liquid show the characteristics shown in Figure 4, it is not necessary to align the specific liquid level when testing the volume of the sample skeleton of the sample to be tested with the hydrogen-containing liquid, and it is only necessary to align the liquid level of the hydrogen-containing liquid in the highest nuclear magnetic resonance signal region, so as to achieve the design goals of convenient operation and small human error. Therefore, the method and device provided by the present application can improve the accuracy of porosity test while reducing the operation difficulty.

[0095] The design goal of the radio frequency coil of the nuclear magnetic resonance instrument in the prior art is only to use the first region 40 in Figure 5 (the first region 40 corresponds to the linear region of the nuclear magnetic resonance signal, and in this region, the nuclear magnetic resonance signal is proportional to the volume of the hydrogen-containing liquid), so as to achieve the purpose of quantitative calculation, and therefore the sample loading height during the test of the nuclear magnetic resonance instrument in the prior art will not exceed the first region 40. If the radio frequency coil of such a nuclear magnetic resonance instrument is directly used for measurement without improvement design, the phenomenon shown in Figure 5 will usually be encountered. As can be known from the working principle of the present application, the response characteristics of the nuclear magnetic resonance signal and the liquid volume in Figure 5 cannot be used for the method proposed in the present application. The fundamental reason for the phenomenon shown in Figure 5 is that the filling sensitivity of the radio frequency coil changes the resonance characteristics of the radio frequency coil when the liquid volume exceeds a certain range, the radio frequency coil is in a polarization state, and then the amount of the nuclear magnetic resonance signal is smaller than the normal value.

[0096] In order to achieve the response characteristics of the radio frequency coil shown in Figure 4, the radio frequency coil needs to be improved, for example, by increasing the distributed capacitance during winding of the radio frequency coil and appropriately reducing the Q value to reduce the filling sensitivity of the radio frequency coil. In the present application, the radio frequency coil is a low filling sensitivity H radio frequency coil, and the inductance range of the radio frequency coil is preferably 0.1 μH-0.5 μH. Since the present application only uses the H radio frequency coil to accurately and quickly test the porosity of the sample to be tested, the price of the nuclear magnetic resonance instrument is also reduced, which is conducive to the popularization and promotion of the test method and device provided by the present application.

[0097] The magnet unit comprises a magnet 1100 and a temperature controller 1200, which is used to control the temperature of the magnet 1100 to stabilize in a certain range. The magnet 1100 is used to provide a magnetic field for the volume calibration sample, the hydrogen-containing liquid and the sample to be measured. The magnetic field strength of the magnet 1100 also has an impact on the filling sensitivity of the radio frequency coil 2100. The lower the magnetic field strength of the magnet 1100, the smaller the filling sensitivity of the radio frequency coil 2100. However, the reduction of the magnetic field strength of the magnet 1100 will also reduce the signal-to-noise ratio of the nuclear magnetic data. In order to balance the low sensitivity of the radio frequency coil 2100 and improve the signal-to-noise ratio of the nuclear magnetic data, it has been verified that the magnetic field strength of the magnet 1100 in the application is 0.1-0.2T, preferably, the magnetic field strength of the magnet 1100 in the application is 0.14T (corresponding to the H nuclear resonance frequency of 6MHz).

[0098] Further, the spectrometer unit 3000 is used to control the radio frequency unit to collect the nuclear magnetic resonance signals of the volume calibration sample, the hydrogen-containing liquid and the sample to be measured. The calculation unit 4000 is used to calculate the porosity of the sample to be measured. Specifically, the calculation unit 4000 is composed of a collection computer and corresponding software.

[0099] The sample tube 5000 is used to place the volume calibration sample, the hydrogen-containing liquid and the sample to be measured in the radio frequency coil 2100. In order to improve the test efficiency, the sample tube provided in the application is shown in Figure 6. The surface of the sample tube is marked with a first marking line 110, a second marking line 120 and a third marking line 130 according to the test results of the radio frequency coil. The area between the first marking line 110 of the sample tube and the bottom of the sample tube corresponds to the linear region of the nuclear magnetic resonance signal. The area between the first marking line 110 and the second marking line 120 corresponds to the nonlinear region of the nuclear magnetic resonance signal. The area between the second marking line 120 and the third marking line 130 corresponds to the highest nuclear magnetic resonance signal region. The grooves facilitate the observation and control of the liquid level position when the hydrogen-containing liquid is added. The first marking line 110 is the upper limit of the sample loading height of the sample to be measured. The second marking line 120 is the lowest liquid level when the hydrogen-containing liquid is added. The third marking line 130 is the highest liquid level when the hydrogen-containing liquid is added. The third marking line 130 is designed to avoid adding too much hydrogen-containing liquid, which exposes the waveguide tube of the radio frequency coil and introduces external electromagnetic interference.

[0100] Furthermore, the sample tube includes a main body 100 and a sealing cap 200. The main body 100 is a cylindrical structure with one open end. The main body 100 and the sealing cap 200 form a receiving space for holding a volume scale standard, hydrogen-containing liquid, and the sample to be tested. The opening of the main body has an internal thread, and the sealing cap has an external thread that engages with the internal thread. The sealing cap 200 can move along a preset direction via the internal thread to seal the main body 100. This sealing cap 200 can both delay the evaporation effect of the sample upon contact with air and prevent the hydrogen-containing liquid from splashing out and contaminating the RF coil during testing after the sample tube is filled with hydrogen-containing liquid. Additionally, the surface of the sealing cap 200 is knurled for easy removal of the sample tube from the RF coil. To improve testing efficiency, the end of the main body 100 away from the opening is arc-shaped, i.e., the bottom of the sample tube is arc-shaped similar to the bottom of a thermos, facilitating quick drying of the sample tube and any residual hydrogen-containing liquid after pouring out the tested sample, before testing the next sample. To avoid introducing nuclear magnetic resonance signals, the sample tubes in this application are made of polytetrafluoroethylene, which is not easily broken, not easily deformed, and does not have nuclear magnetic resonance signals.

[0101] To further improve testing efficiency, sample tubes are manufactured using precision machining to control internal dimensional accuracy. After molding, the measurement preparation process described in this invention is used to screen out K samples. H S Hmax Three to five sample tubes with a relative numerical difference of ≤1% are grouped together and used with one nuclear magnetic resonance instrument to facilitate the loading of subsequent samples during the measurement waiting time in the field.

[0102] In addition, to facilitate transportation to and from the drilling site, the device provided in this application adopts a portable structural design.

[0103] The embodiments of the present invention will be described in more detail below through examples. However, the embodiments of the present invention are not limited to these examples.

[0104] The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0105] Example 1

[0106] To verify the accuracy of the method proposed in this invention, a verification experiment was designed: Cylindrical polytetrafluoroethylene sheets of uniform size were processed, each sheet having a volume of 4.13 cm³. 3In the sample tube, different amounts of polytetrafluoroethylene cylindrical sheet are added. Since polytetrafluoroethylene does not contain a nuclear magnetic resonance signal, the volume of the polytetrafluoroethylene cylindrical sheet added to the sample tube is measured by using the method provided in the present application, and the test results are compared with those of the measuring method, and the test results are shown in Table 1. The relative error of the volume of the polytetrafluoroethylene cylindrical sheet measured by the method provided in the present application and the volume of the polytetrafluoroethylene cylindrical sheet measured by the measuring method is ≤2%, verifying the feasibility of the method provided in the present application.

[0107] Table 1 Volume test results of cylindrical polytetrafluoroethylene sheet

[0108] Example 2

[0109] In the X well of the domestic drilling site, the porosity of the block-shaped well wall coring core sample is tested by using the method provided in the present application, and the porosity of the sample is tested by using the nuclear magnetic resonance-density balance method, and the test results are shown in Table 2.

[0110] Because it is a block sample, the total volume measured by the density balance method has high accuracy. Referring to the porosity tested by the nuclear magnetic resonance-density balance method, the absolute error and the relative error of the porosity measured by the method provided in the present application are calculated, and the results are shown in Table 2. For the block-shaped well wall coring core sample, the relative error of the porosity tested by the method provided in the present application is ≤5%, and the test accuracy meets the industry application test requirements.

[0111] Table 2 Test results of porosity of well wall coring core sample

[0112] Example 3

[0113] In the XX well of the domestic drilling site, the pore volume and the skeleton volume of the drilling cuttings sample are tested by using the method provided in the present application, and the porosity is calculated. At the same time, the porosity of the sample is tested by using the traditional drying method, and the porosity tested by the method provided in the present application is compared, and the test results are shown in Table 3.

[0114] By comparing the porosity of the traditional drying method and the porosity tested by the method provided in the present application, it is found that the porosity of the method provided in the present application is larger than that of the traditional drying method. By referring to the reservoir fluid geochemical measurement results of the drilling site, it is found that the test sample layer is an oil-bearing reservoir, and it is a medium viscosity crude oil. The 120°C drying used in the field cannot dry out the crude oil in the pore fluid of the cuttings, resulting in a larger dry weight of the drying method, and further resulting in a smaller porosity than the actual value. The effect of the larger porosity value of the cuttings measured by the present application conforms to the physical properties of the measured sample, and also verifies the effectiveness and accuracy of the method provided in the present application.

[0115] Table 3 Test results of porosity of drilling cuttings sample

[0116] In the description of the application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the description of the application, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0117] In addition, the terms "first", "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0118] Although the embodiments of the application have been shown and described above, it is understood that the above-described embodiments are exemplary and cannot be construed as limiting the application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the application.

Claims

1. A method for testing the porosity of irregularly shaped rock cores, characterized in that, The testing method includes: placing a volume scale standard sample into a sample tube, ensuring it does not exceed the first mark line of the sample tube, and then testing to obtain the nuclear magnetic resonance signal S of the volume scale standard sample. H1 The scale coefficient K of the volume scale standard is calculated. H K H =V H / S H1 V H The volume of the hydrogen-containing liquid in the volume calibration standard is given, and the area between the first marking line of the sample tube and the bottom of the sample tube corresponds to the linear region of the nuclear magnetic resonance signal. Remove the volume scale standard sample, add the hydrogen-containing liquid to the sample tube until the liquid level is between the second and third mark lines of the sample tube, and measure the nuclear magnetic resonance signal S of the hydrogen-containing liquid. Hmax The region between the first and second marker lines corresponds to the nonlinear region of the nuclear magnetic resonance signal, and the region between the second and third marker lines corresponds to the region with the highest nuclear magnetic resonance signal. The sample to be tested is pretreated by placing it into the sample tube, ensuring it does not exceed the first mark line of the sample tube, and then the nuclear magnetic resonance signal S of the sample is obtained. H2 The pore volume V of the sample to be tested is calculated. por V por =K H ×S H2 ; The hydrogen-containing liquid is added to the sample tube containing the sample to be tested until the liquid level is between the second and third mark lines in the sample tube. The nuclear magnetic resonance signals S of the sample and the hydrogen-containing liquid are then measured. H3 The skeleton volume V of the sample to be tested was calculated. G V G =K H ×(S Hmax -S H3 ); The porosity φ of the sample to be tested was calculated.

2. The porosity testing method for irregularly shaped rock cores according to claim 1, characterized in that, The method for obtaining the second marker line includes: Take out the volume scale standard sample, and continuously add the hydrogen-containing liquid to the sample tube until the nuclear magnetic resonance signal of the hydrogen-containing liquid is the maximum. The liquid level corresponding to the maximum nuclear magnetic resonance signal of the hydrogen-containing liquid is the second mark line.

3. The porosity testing method for irregularly shaped rock cores according to claim 1, characterized in that, The pretreatment of the sample to be tested includes: removing fluid from the surface of the sample to be tested.

4. The porosity testing method for irregularly shaped rock cores according to claim 1, characterized in that, The nuclear magnetic resonance signal was acquired using the CPMG sequence.

5. The porosity testing method for irregularly shaped rock cores according to claim 1, characterized in that, The hydrogen-containing liquid is a copper sulfate solution with a mass concentration of 1000-1500 ppm.

6. The porosity testing method for irregularly shaped rock cores according to any one of claims 1 to 5, characterized in that, The step of adding the hydrogen-containing liquid to the sample tube containing the sample to be tested until the liquid level is between the second and third mark lines of the sample tube includes: Remove air bubbles adsorbed on the surface of the sample to be tested.

7. An apparatus for testing the porosity of irregularly shaped rock cores according to any one of claims 1 to 6, characterized in that, The device includes: a magnet unit, a radio frequency unit, a spectrometer unit, a computing unit, and a sample tube; The magnet unit includes a magnet used to provide a magnetic field for the volume calibration standard, the hydrogen-containing liquid, and the sample to be tested, and the magnetic field strength of the magnet is 0.1-0.2T; The radio frequency (RF) unit is used to detect the nuclear magnetic resonance (NMR) signals of the volume calibration standard, the hydrogen-containing liquid, and the sample to be tested. The RF unit includes an RF coil, which is a low-fill-sensitivity H RF coil. The RF coil has a linear region, a nonlinear region, and a maximum NMR signal region. When the liquid level of the hydrogen-containing liquid is in the linear region, the NMR signal of the hydrogen-containing liquid is proportional to the volume of the hydrogen-containing liquid. When the liquid level of the hydrogen-containing liquid is in the nonlinear region, the NMR signal of the hydrogen-containing liquid and the volume of the hydrogen-containing liquid exhibit a nonlinear monotonically increasing law. When the liquid level of the hydrogen-containing liquid is in the maximum NMR signal region, the NMR signal of the hydrogen-containing liquid reaches its maximum value, and the deviation of the NMR signal of the hydrogen-containing liquid in the maximum NMR signal region is ≤±1%. The spectrometer unit is used to control the radio frequency unit to acquire the nuclear magnetic resonance signals of the volume calibration standard, the hydrogen-containing liquid, and the sample to be tested; The calculation unit is used to calculate the porosity of the sample to be tested; The sample tube is used to place the volume calibration standard, the hydrogen-containing liquid, and the sample to be tested in the radio frequency coil. The surface of the sample tube is provided with a first marking line, a second marking line, and a third marking line. The area between the first marking line and the bottom of the sample tube corresponds to the linear region of the nuclear magnetic resonance signal, the area between the first marking line and the second marking line corresponds to the nonlinear region of the nuclear magnetic resonance signal, and the area between the second marking line and the third marking line corresponds to the region of the highest nuclear magnetic resonance signal.

8. The apparatus for testing the porosity of irregularly shaped rock cores according to claim 7, characterized in that, The inductance range of the radio frequency coil is 0.1μH-0.5μH.

9. The apparatus for testing the porosity of irregularly shaped rock cores according to claim 7, characterized in that, The sample tube includes a body and a sealing cap. The body is a cylindrical structure with one end open. The body and the sealing cap form a receiving space for placing the volume scale standard, the hydrogen-containing liquid, and the sample to be tested. The opening of the body is provided with an internal thread, and the sealing cap is provided with an external thread that cooperates with the internal thread. The sealing cap can move along a preset direction through the internal thread to seal the body.

10. The apparatus for testing the porosity of irregularly shaped rock cores according to claim 9, characterized in that, The surface of the sealing cap is knurled, and the end of the main body away from the opening is arc-shaped.

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