CN104075974A - Method for accurately measuring shale porosity by adopting low-field nuclear magnetic resonance - Google Patents
Method for accurately measuring shale porosity by adopting low-field nuclear magnetic resonance Download PDFInfo
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Abstract
The invention discloses a method for accurately measuring shale porosity by adopting the low-field nuclear magnetic resonance. The method comprises the following steps: as for a saturated water column-shaped shale sample, conducting nuclear magnetic porosity measurement in different echo time and waiting time; conducting helium porosity measurement; comprehensively comparing and analyzing the porosity results of the two methods; optimizing the optimal echo time and waiting time for testing to facilitate the accurate testing of follow-up samples. The method solves the problems of how to set reasonable parameters to measure the shale porosity by adopting the low-field nuclear magnetic resonance, and solves the problem that in the actual testing, the nuclear magnetic porosity obtained in different echo time and waiting time is in great disparity, and the comparability of the nuclear magnetic porosity and the helium porosity is relatively poor; compared with the prior art, by adopting the method, the shale porosity can be quickly and nondestructively measured, the accuracy and precision of the shale porosity measurement can be improved, and the operation is convenient.
Description
Technical field
The present invention relates to a kind of measuring method of surveying the rock stratum physical property in exploitation field, relate in particular to a kind of method of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity.
Background technology
Factor of porosity has reflected the ability that medium hole can containing fluid, and shale factor of porosity is one of important parameter of shale reservoir properties research, is the basic physical properties parameter that Oil/Gas Reservoir Assessment, reserves calculate.Along with shale oil gas is the developing rapidly of global energy field, accurately measure shale factor of porosity, significant to the exploratory development of shale oil gas.Yet the test of conventional factor of porosity adopts helium porosimeter mostly, although with a high credibility, test process is loaded down with trivial details etc., and shortcoming is difficult to realize in the on-the-spot application of exploration.Utilize the method for low-field nuclear magnetic resonance commercial measurement core porosity to have advantages of quick, harmless, become gradually the hot fields of experimental exploring.
Utilize the method for low-field nuclear magnetic resonance commercial measurement core porosity to have advantages of quick, harmless, become gradually the hot fields of experimental exploring.This technology is directly utilized nuclear magnetic signal amount computing rock factor of porosity, overcome that conventional helium factor of porosity test speed is slow, efficiency is low, the shortcoming of infringement sample, at well logging scene, be expected to utilize portable low-field nuclear magnetic resonance apparatus to obtain in time the physical parameter of shale reservoir.The choose reasonable of low-field nuclear magnetic resonance apparatus parameter is the inevitable prerequisite that result is correct, and lithology is different, and the experiment parameter of Nuclear Magnetic Resonance Measurement is different.The measurement parameter of shale low-field nuclear magnetic resonance factor of porosity mainly comprises echo time (TE) and stand-by period (TW).Echo time is to be redirected the interval time of pulse twice, larger on the impact of shale porosity measurement result accuracy, in general, the excessive echo time can make the dropout of the short-and-medium relaxation fluid of saturation water shale rock core, causes measuring factor of porosity Lower result; Stand-by period refers to that hydrogen ion recovers the time of polarizing before upper once pulse signal carries out, and in general, the stand-by period is longer, and proton polarization is more complete, and the factor of porosity of measurement is more accurate.
Yet, currently utilize the echo time that low-field nuclear magnetic resonance commercial measurement shale factor of porosity adopts not seek unity of standard with the stand-by period, most measurement results are still based on conventional reservoir measurement parameter, be echo time 0.6ms, stand-by period 5s, this is not shale factor of porosity actual value with regard to the factor of porosity that causes utilizing conventional nuclear magnetic resonance parameter to obtain, in actual test, not only difference is larger for the shale nuclear-magnetism factor of porosity measuring under different echo times and stand-by period condition, and also poor with the contrast of helium factor of porosity.Therefore, determine the test condition of instrument, it is accurately to measure the matter of utmost importance that shale factor of porosity need to solve that Reasonable Parameters is set, and is also the present invention to be carried out to the innovation key of shale reservoir properties analysis determining method.
Summary of the invention
Technical matters to be solved by this invention is to provide a kind of method of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity, and the method has solved the measurement parameter how low-field nuclear magnetic resonance apparatus is rationally set, and can accurately measure shale factor of porosity.
The present invention is based on following principle:
To saturation water sample, first carry out the nuclear-magnetism porosity measurement under different echo times and stand-by period, then carry out helium porosity measurement, Comprehensive Comparison two cover factor of porosity results, optimize best echo time and the stand-by period of sample test, facilitate the accurate test of subsequent sample.
Technical matters to be solved by this invention is achieved through the following technical solutions:
A method of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity, comprises the following steps:
Under different echo times and stand-by period, survey the H atomic nucleus of water in sample by low-field nuclear magnetic resonance instrument, the Carr-Purcell-Meiboom-Gill spin echo string of water nuclear magnetic signal in collected specimens, is called for short CPMG spin echo string;
By adopting the method for multi-exponential Inversion to obtain initialize signal amplitude to nmr spin echo string, recycle initialize signal amplitude and the relation that the content of water in sample is directly proportional, try to achieve the volume of voids of sample; Get the ratio of described volume of voids and sample volume, be the nuclear-magnetism factor of porosity of sample;
Carry out helium porosity measurement;
The factor of porosity result that Comprehensive Comparison nuclear magnetic resonance and helium assay method record, optimizes best echo time and stand-by period that sample is accurately tested.
Described step further comprises:
1) make standard specimen, set up graticule equation: make standard specimen, set up graticule equation: by the addition of C uSO
45H
2o is fully dissolved in appropriate distilled water, makes CuSO
4solution T2 (T
2) between 10～100ms, above-mentioned a small amount of CuSO
45H
2dosage between O and appropriate distilled water is to guarantee CuSO
4solution relaxation time (T
2) between 10～100ms; Get the CuSO at certain mass interval
4solution is to standard model bottle; Standard model is placed in the nuclear magnetic resonance apparatus sample cell under different echo times of many groups and stand-by period to the transverse relaxation spectrum (T of measurement standard sample
2spectrum); The volume of water and standard model T in matching standard model
2spectral integral area, obtains graticule equation;
2) preparation of saturation water shale sample: drill through the column shale sample of a plurality of setting diameters, measure the size of column shale sample; By described shale sample dry tap 1.5-2.5 hour under the pressure of vacuum tightness≤-0.095MPa, preferably 2 hours; Then be soaked in 40-55 hour in distilled water, preferably 48 hours, made shale sample saturation water;
3) shale sample is measured: many groups echo time and stand-by period that standard model to be measured is set, saturation water shale sample is removed after surface moisture, be placed in the sample cell of same nuclear magnetic resonance testing tool, saturation water shale is carried out to low-field nuclear magnetic resonance measurement, obtain the T of saturation water shale
2spectrum, calculates T
2the integral area of spectrum;
4) shale sample porosity calculation: by the T of described saturation water shale
2the above-mentioned graticule equation of spectral integral area substitution, is converted into the volume of water in shale sample hole; Again the volume of water in described shale sample hole is amassed divided by shale population of samples, obtain the factor of porosity of shale;
5) helium porosity measurement: adopt conventional core analysis method, above-mentioned sample is dried in the drying box of 80 ℃, put into exsiccator and be cooled to room temperature, utilize hole to ooze automatic analyzer, at 15-25 ℃, under 20 ℃ of room temperatures, according to conventional method, shale sample is carried out to the test of helium factor of porosity;
6) measurement parameter is preferred: take helium factor of porosity as standard, contrast successively the nuclear-magnetism factor of porosity under different test conditions, carry out error and analysis of the accuracy, optimize best echo time and the stand-by period of sample test.
Described step also further comprises:
7) test of other samples: under above-mentioned best echo time and stand-by period test condition, other samples are directly carried out to NMR porosity measurement, utilize the graticule equation calculation sample nuclear-magnetism porosity value under top condition.
Described step 1) in, adopt the linear regression method matching graticule equation in statistics, expression formula is: y=kx+b (1)
Wherein, x is sample T
2spectral integral area; Y is the volume of standard specimen water, g; K is the slope of graticule equation; B is the vertical axis intercept of graticule equation.
Described step 4) the factor of porosity expression formula of described shale is
Wherein, φ is nuclear-magnetism factor of porosity, %; Y is the volume of water in shale sample hole, cm
3; V is the cumulative volume of sample, cm
3.
The demarcation principle of described nuclear magnetic resonance apparatus measurement parameter is: first determine the echo time, next mates the stand-by period;
Described measurement parameter preferably, comprise the nuclear-magnetism factor of porosity under identical echo time, different stand-by period is averaged, obtain the average nuclear-magnetism porosity value under this echo time, also be included under preferred echo time condition, contrast the identical echo time, porosity value under the different stand-by period, the coupling stand-by period.
8) nuclear-magnetism porosity value.
The condition of described shale sample low-field nuclear magnetic resonance test is: the echo time is no more than 1.0ms; The stand-by period of described mensuration factor of porosity is no less than 1s.
The optimum condition of described shale sample low-field nuclear magnetic resonance test is: the echo time is no more than 0.6ms; The stand-by period of described mensuration factor of porosity is no less than 5s.
The top condition of described shale sample low-field nuclear magnetic resonance test is: echo time 0.3ms, the stand-by period is 9s.
The present invention adopts technique scheme to have following beneficial effect:
Solved based in reality test, exist the nuclear-magnetism factor of porosity difference measuring under different echo times and stand-by period larger, and contrast the poor problem of property with helium factor of porosity, for saturation water sample, first carry out the nuclear-magnetism porosity measurement under different echo times and stand-by period, then carry out helium porosity measurement, Comprehensive Comparison two cover factor of porosity results, optimize best echo time and the stand-by period of test, facilitate the accurate test of subsequent sample.The method has solved how Reasonable Parameters is set, utilize the problem of low-field nuclear magnetic resonance Measurement accuracy shale factor of porosity, compared with prior art, application the present invention not only can fast, nondestructively measure shale factor of porosity, more can improve accuracy and the precision of shale porosity measurement, and simple operation.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the invention will be further described.
Fig. 1 is the process flow diagram that utilizes low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity
Fig. 2 is echo time 0.3ms, the typical curve of stand-by period 9s
Fig. 3 is echo time 0.3ms, the standard model T of stand-by period 9s
2spectral curve
Fig. 4 is stand-by period 9s, the T of sample 7 under the different echo times
2spectral distribution curve
Fig. 5 is echo time 0.3ms, the T of sample 7 under the different stand-by period
2spectral distribution curve
Fig. 6 is helium factor of porosity and average nuclear-magnetism factor of porosity comparing result under the different echo times, and wherein dotted line is factor of porosity baseline
Fig. 7 is helium factor of porosity and nuclear-magnetism factor of porosity comparing result under the different stand-by period, and wherein dotted line is factor of porosity baseline
Fig. 8 is that sample 7 is got T under 6s measurement parameter in demarcation and conventional stand-by period
2spectral distribution curve
Fig. 9 is the T of sample 8 under calibration measurements Parameter Conditions
2spectral distribution curve
Embodiment
A kind of method of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity as described in Fig. 1-Fig. 9, comprise by low-field nuclear magnetic resonance commercial measurement shale factor of porosity, and calibrate by helium factor of porosity, thereby the Reasonable Parameters of acquisition Nuclear Magnetic Resonance Measurement shale factor of porosity is carried out Accurate Measurement.
Fig. 1 is the flow process of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity, and step is:
1) make standard specimen, set up graticule equation: by a small amount of CuSO
45H
2o is fully dissolved in appropriate distilled water, makes CuSO
4solution T2 (T
2) between 10～100ms; With digital titration instrument, get the CuSO at certain mass interval
4solution is to standard model bottle; Standard model is placed in to different echo times of many groups and stand-by period, according to instrument range in the nuclear magnetic resonance apparatus sample cell under definite time interval, the transverse relaxation of measurement standard sample spectrum (T
2spectrum); The volume of water and standard model T in matching standard model
2spectral integral area, the volume of water, by the density of water, is got 1.0g/cm conventionally
3convert, obtain graticule equation, adopt the linear regression method matching graticule equation in statistics, expression formula is
y＝kx+b (1)
Wherein, x is sample T
2spectral integral area; Y is the volume of standard specimen water, g; K is the slope of graticule equation; B is the vertical axis intercept of graticule equation;
2) preparation of saturation water shale sample: drilling through successively a plurality of diameters is the column shale sample of 25mm, size record with vernier caliper measurement column shale sample, again by shale sample dry tap 2 hours under the pressure of vacuum tightness≤-0.095MPa, then be soaked in distilled water approximately 48 hours, made shale sample saturation water;
3) shale sample is measured: set gradually many group echo time and the stand-by period consistent with standard model, saturation water shale sample is removed after surface moisture, be placed in the sample cell of same nuclear magnetic resonance testing tool, saturation water shale is carried out to low-field nuclear magnetic resonance measurement, obtain the T of saturation water shale
2spectrum, calculates T
2the integral area of spectrum;
The condition of the sample of shale described in embodiment of the present invention low-field nuclear magnetic resonance test can be respectively: choose echo time 1.0ms, measure the stand-by period 1s of factor of porosity.Or, echo time 0.6ms, the stand-by period of measuring factor of porosity is no less than 5s.Or, echo time 0.3ms, the stand-by period is under 9s condition, to carry out the mensuration under different condition, all can reach effect of the present invention.
4) shale sample porosity calculation: by the T of saturation water shale
2spectral integral area is brought graticule equation into, is converted into the volume of water in shale sample hole, then it is long-pending divided by shale population of samples, can try to achieve respectively the factor of porosity of shale, and expression formula is
Wherein, φ is nuclear-magnetism factor of porosity, %; Y is the volume of water in shale sample hole, cm
3; V is the cumulative volume of sample, cm
3.
5) helium porosity measurement: because Nuclear Magnetic Resonance Measurement is to sample nondestructive, so, adopt conventional core analysis method, sample is dried in the drying box of 80 ℃, put into again exsiccator and be cooled to room temperature, then utilize hole to ooze automatic analyzer, under 20 ℃ of room temperatures, according to petroleum industry standard, shale sample is carried out to the test of helium factor of porosity;
6) measurement parameter is preferred: take helium factor of porosity as standard, contrast successively the nuclear-magnetism factor of porosity under different test conditions, carry out error and analysis of the accuracy, thereby optimize best echo time and the stand-by period of sample test;
7) test of other samples: under above-mentioned best test condition, other samples are directly carried out to NMR porosity measurement, utilize the graticule equation calculation sample nuclear-magnetism porosity value under top condition.
To face emerging regional shale sample, further the present invention is elaborated as an example:
Experiment material: shale, distilled water, CuSO
45H
2o powder.Test apparatus: full-hole core Magnetic resonance imaging analytic system, model MiniMR60, resonant frequency 23.1MHz, magnet strength 0.53T, probe coil 60mm, magnet is stable is controlled at 31.99～32.00 ℃; Automatic analyzer is oozed in hole, model AP608.
Preparation standard sample: contain the distilled water get 1L with measuring cup, to the CuSO that adds 4.0910g in distilled water
45H
2o powder, fully dissolves it, until above-mentioned CuSO
4the T2 T of solution
2between 10-100ms, the T2 T that this standard model peak maximum is corresponding
2be about 50ms.This standard model bottle amasss as 2.5ml, can hold CuSO
4the about 2.53g of solution, so be that the solution of choosing 6 different qualities within the scope of 0.3～0.7g is placed in standard model bottle and makes standard model at quality interval, carries out the test of standard model, and standard model quality is as shown in table 1.
Table 1 standard model quality
Preparation experiment sample: drill through successively the column core sample that 8 diameters are 25mm, numbering 1,2,3,4,5,6,7,8, measure and record length and the diameter of sample, as shown in table 2, then by shale sample dry tap 2 hours under the pressure of vacuum tightness≤-0.095MPa, be soaked in again in distilled water approximately 48 hours, made shale sample saturation water.For absolutely proving measuring process, sample 1～7 is preferred for measurement parameter, and sample 8 directly carries out porosity measurement under the Parameter Conditions that utilizes sample 1～7 to obtain.
Table 2 sample size measurement result
The main process of sample measurement and analysis, as follows:
1) consider the range of MiniMR60 nuclear magnetic resonance analyser, setting gradually the echo time is 0.2ms, 0.3ms, 0.6ms, 1.0ms, and the stand-by period is 1s, 3s, 6s, 9s, totally ten six groups of experiments.Under different test conditions, 6 matter standard models are carried out to low-field nuclear magnetic resonance measurement.Utilize the T of statistical linear regression method matching standard model
2linear relationship between spectral integral area and the water volume of standard model, obtains graticule system of equations (table 3), echo time 0.3ms wherein, the graticule equation of stand-by period 9s as shown in Figure 2, corresponding T
2spectrum as shown in Figure 3.
Graticule equation under different echo times of table 3 and stand-by period
2) saturation water shale is removed to surface moisture, it is 0.2ms, 0.3ms, 0.6ms, 1.0ms that the echo time is set equally, and the stand-by period is 1s, 3s, 6s, 9s, and saturation water shale sample 1～7 is carried out to low-field nuclear magnetic resonance measurement, obtains the T of saturation water shale
2spectrum, the T of calculating saturation water shale
2the integral area of spectrum, utilizes graticule equation (seeing formula 1 herein) and porosity calculation equation (seeing formula 2 herein), converts and obtains the sample nuclear-magnetism factor of porosity under different test conditions, as shown in table 4
Nuclear-magnetism porosity measurement result under different echo times of table 4 and stand-by period
3) more above-mentioned 7 samples are carried out to the test of helium factor of porosity, obtain the helium factor of porosity of sample, result is as shown in table 5
Table 5 sample 1～7 helium factor of porosity result
4) measurement parameter preferably and contrast
1. measurement parameter optimum principle
As can be seen from Table 3, shale nuclear-magnetism factor of porosity under same echo time, different stand-by period changes little, and shale nuclear-magnetism factor of porosity under same stand-by period, different echo time alters a great deal, the echo time is larger on the impact of shale porosity measurement result accuracy compared with the stand-by period.As sample 7, when the stand-by period is 1s, 4 groups of different echo time nextpage petrosal foramen nuclear-magnetism gap degree variation ranges are 0.660～1.208%, extreme difference is 0.548%, and the echo time is while being 1.0ms, 4 groups of different stand-by period nextpage rocky core magnetic factor of porosity variation ranges are 0.445～0.660%, and extreme difference is 0.215%.
T from sample
2on spectrogram, can see above-mentioned rule equally: take sample 7 as example, when the stand-by period is 9s, along with the echo time increases 1.0ms by 0.2ms, main peak peak value reduces gradually, T
2the spectrum total area reduces gradually, and corresponding factor of porosity is also reduced to 0.660% by 1.208%, but sample T
2the crest number of spectrum is increased to four, the T that main peak is corresponding by three
2time increases (as shown in Figure 4) gradually.This is due to the excessive echo time, to make partly to reflect in rich saturation water shale rock core argillaceous the irreducible water T of micro hole
2relaxation time reduces, this segment fluid flow nuclear magnetic signal end that substantially decays within the reaction time of nuclear-magnetism instrument impulse ejection and acceptance, cause and complete clay-bound water signal cannot be detected, cannot detect part micro hole relaxation information, and then causing nuclear magnetic signal amount to reduce, nuclear-magnetism factor of porosity is on the low side.
T from sample 7 when the echo time is 0.3ms
2compose (as shown in Figure 5) and also can see, under the different stand-by period, sample T
2spectrum all has three crests, and main peak overlaps substantially, and only peak value is slightly variant, and the size at the second peak, the 3rd peak and corresponding T
2time difference is larger.On the whole, along with the increase of stand-by period, proton polarization is more complete, and the crest total area, increasing, reflects that more macroporous nuclear magnetic signal amount is larger, and the nuclear-magnetism factor of porosity obtaining is also increasing gradually, but increase amplitude is less.
Therefore, the demarcation principle of apparatus measures parameter is: first determine the echo time, next mates the stand-by period.
2. measurement parameter is preferred
Nuclear-magnetism factor of porosity under identical echo time, different stand-by period is averaged, obtain the average nuclear-magnetism porosity value under this echo time.Table 6 shows, if adopt the 0.6ms of conventional nuclear-magnetism factor of porosity test as the echo time, relative error is minimum is 36.6%, is up to 45.9%, if the echo time is 1.0ms, sample average nuclear-magnetism factor of porosity relative error is up to 59.9%; And echo time while being no more than 0.3ms, except sample 2,6,7, other sample nuclear-magnetism factor of porosity relative errors are all lower than 20%, more approaching with helium factor of porosity.This further illustrates, and determines that the echo time is the key of shale low-field nuclear magnetic resonance parameter calibration, and conventional nuclear-magnetism porosity measurement parameter is not also suitable for shale; Measurement accuracy sample nuclear-magnetism factor of porosity, requires the echo time to be no more than 0.3ms (as shown in Figure 6).
Table 6 helium factor of porosity and average nuclear-magnetism factor of porosity comparing result under the different echo times
Note: the data in bracket are relative error, %.
Table 7 shows, when the echo time is 0.2ms, 7 sample nuclear-magnetism factor of porosity and immediate stand-by period of helium factor of porosity are followed successively by 3s, 9s, 9s, 3s, 3s, 9s, 9s, relative error is followed successively by 1.45%, 8.12%, 10.7%, 7.03%, 6.76%, 12.3%, 15.0%, and average 8.77%; And when the echo time is 0.3ms, two cover immediate stand-by period of factor of porosity were 9s, relative error is followed successively by 12.4%, 0.26%, 3.87%, 4.58%, 2.00%, 5.45%, 4.95%, average 4.08%, stand-by period is during lower than 9s, if the stand-by period is 3s, the nuclear-magnetism factor of porosity relative error of sample is all more than 10%.As can be seen here, the stand-by period is extremely important for the further accuracy of nuclear-magnetism factor of porosity.
More than comprehensive, analyze and show, the echo time is 0.3ms, and the stand-by period, while being 9s, nuclear-magnetism factor of porosity and helium factor of porosity were the most close, and average relative error was less than for 5% (as shown in Figure 7), can be used as the top condition of this shale sample low-field nuclear magnetic resonance test.
Table 7 helium factor of porosity and nuclear-magnetism factor of porosity comparing result under the different stand-by period
Note: the data in bracket are relative error, %.
3. with conventional nuclear-magnetism factor of porosity contrast
Because low-field nuclear magnetic resonance porosity measurement result is subject to the double influence of echo time and stand-by period simultaneously, only consider the very difficult Obtaining Accurate porosity value of single factors.Contrast conventional nuclear-magnetism porosity measurement parameter, echo time 0.6ms, stand-by period 6s, echo time 0.3ms, stand-by period 9s that this example is definite are all different with it.Yet above-mentioned analysis shows, the little echo time can fully be reflected average pore size and the content of shale micro hole, and the large stand-by period more can be reflected more macroporous distribution characteristics.Because shale is that a kind of average pore size only has nanoscale, the compacted rock that micro hole content is very abundant, so the definite parameter of this example more can characterize the actual porosity distribution of shale compared with routine measurement parameter, the factor of porosity obtaining is more accurate.Take sample 7 as example, under calibration measurements condition, nuclear-magnetism factor of porosity is 1.102%, relative error is 4.95%, nuclear-magnetism factor of porosity under conventionally test condition is 0.722%, relative error is 31.2%, visible conventional nuclear-magnetism factor of porosity is significantly less than demarcates nuclear-magnetism factor of porosity, demarcates nuclear-magnetism factor of porosity and more approaches true factor of porosity (as shown in Figure 8).
5) application of optimized parameter: under above-mentioned definite test condition, directly record the nuclear-magnetism factor of porosity of sample 8, its T
2as shown in Figure 9, porosity value is 1.16% to spectrogram.
The above; be only preferably embodiment of the present invention, but protection scope of the present invention is not limited to this, any people who is familiar with this technology is in the disclosed technical scope of the present invention; the variation that can expect easily or replacement, within all should being encompassed in protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.
Claims (10)
1. a method of utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity, comprises the following steps: for saturation water column shale sample, carry out the nuclear-magnetism porosity measurement under different echo times and stand-by period; Carry out helium porosity measurement; Two kinds of method factor of porosity results described in Comprehensive Comparison, optimize best echo time and the stand-by period of test.
2. the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity according to claim 1, described step further comprises: under different echo times and stand-by period, by low-field nuclear magnetic resonance instrument, survey the H atomic nucleus of water in sample, the CPMG spin echo string of water nuclear magnetic signal in collected specimens;
By adopting the method for multi-exponential Inversion to obtain initialize signal amplitude to nmr spin echo string, recycle initialize signal amplitude and the relation that the content of water in sample is directly proportional, try to achieve the volume of voids of sample; Get the ratio of described volume of voids and sample volume, be the nuclear-magnetism factor of porosity of sample;
Carry out helium porosity measurement;
The factor of porosity result that Comprehensive Comparison nuclear magnetic resonance and helium assay method record, optimizes best echo time and stand-by period that sample is accurately tested.
3. the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity according to claim 2, described step further comprises:
1) make standard specimen, set up graticule equation: by the addition of C uSO
45H
2o is fully dissolved in appropriate distilled water and guarantees CuSO
4solution T2 (T
2) between 10～100ms; Get the CuSO at certain mass interval
4solution is to standard model bottle; Standard model is placed in the nuclear magnetic resonance apparatus sample cell under different echo times of many groups and stand-by period to the transverse relaxation spectrum (T of measurement standard sample
2spectrum); The volume of water and standard model T in matching standard model
2spectral integral area, obtains graticule equation;
2) preparation of saturation water shale sample: drill through the column shale sample of a plurality of setting diameters, measure the size of column shale sample; By described shale sample dry tap 1.5-2.5 hour under the pressure of vacuum tightness≤-0.095MPa; Then be soaked in 40-55 hour in distilled water, made shale sample saturation water;
3) shale sample is measured: many groups echo time and stand-by period that standard model to be measured is set, saturation water shale sample is removed after surface moisture, be placed in the sample cell of same nuclear magnetic resonance testing tool, saturation water shale is carried out to low-field nuclear magnetic resonance measurement, obtain the T of saturation water shale
2spectrum, calculates T
2the integral area of spectrum;
4) shale sample porosity calculation: by the T of described saturation water shale
2the above-mentioned graticule equation of spectral integral area substitution, is converted into the volume of water in shale sample hole; Again the volume of water in described shale sample hole is amassed divided by shale population of samples, obtain the factor of porosity of shale;
5) helium porosity measurement: adopt conventional core analysis method, above-mentioned sample is dried in the drying box of 70-90 ℃, put into exsiccator and be cooled to room temperature, utilize hole to ooze automatic analyzer, at room temperature, according to conventional method, shale sample is carried out to the test of helium factor of porosity;
6) measurement parameter is preferred: take helium factor of porosity as standard, contrast successively the nuclear-magnetism factor of porosity under different test conditions, carry out error and analysis of the accuracy, optimize best echo time and the stand-by period of sample test.
4. according to the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity described in claim 2 or 3, described step also further comprises:
7) test of other samples: under above-mentioned best echo time and stand-by period test condition, other samples are directly carried out to NMR porosity measurement, utilize the graticule equation calculation sample nuclear-magnetism porosity value under top condition.
5. the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity according to claim 1, the condition of described shale sample low-field nuclear magnetic resonance test is: the echo time is no more than 1.0ms; The stand-by period of described mensuration factor of porosity is no less than 1s.
6. utilize according to claim 1 or 5 the method for low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity, the condition of described shale sample low-field nuclear magnetic resonance test is: the echo time is no more than 0.6ms; The stand-by period of described mensuration factor of porosity is no less than 5s.
7. according to the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity described in claim 1 or 6, the condition of described shale sample low-field nuclear magnetic resonance test is: echo time 0.3ms, the stand-by period is 9s.
8. according to the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity described in claim 1,5,6 or 7, the demarcation principle of described nuclear magnetic resonance apparatus measurement parameter is: first determine the echo time, next mates the stand-by period; Described measurement parameter preferably, comprise the nuclear-magnetism factor of porosity under identical echo time, different stand-by period is averaged, obtain the average nuclear-magnetism porosity value under this echo time, the preferred echo time, also be included under preferred echo time condition, contrast the identical echo time, the porosity value under the different stand-by period, coupling stand-by period.
9. according to the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity described in claim 2 or 3, described step 1) in, adopting the linear regression method matching graticule equation in statistics, expression formula is: y=kx+b (1)
Wherein, x is sample T
2spectral integral area; Y is the volume of standard specimen water, g; K is the slope of graticule equation; B is the vertical axis intercept of graticule equation.
10. according to the method for utilizing low-field nuclear magnetic resonance Accurate Measurement shale factor of porosity described in claim 2 or 3, described step 4) the factor of porosity expression formula of described shale is
Wherein, φ is nuclear-magnetism factor of porosity, %; Y is the volume of water in shale sample hole, cm
3; V is the cumulative volume of sample, cm
3.
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