CN104990854B - Determine the method and device of irreducible water saturation - Google Patents

Abstract

The present invention provides a kind of method and device for determining irreducible water saturation, including：The nuclear magnetic relaxation echo data of simultaneously inverting rock core is measured, nuclear magnetic resonance T2 T is obtained₂Spectrum；Measure the irreducible water saturation data of rock core；According to T₂Spectrum, the T2 T for selecting different invertings to layout₂As T_2ct, calculate different T_2ctUnder optimization spectral coefficient；According to different T_2ctUnder optimization spectral coefficient, calculate different T_2ctUnder rock core nuclear-magnetism irreducible water saturation；The irreducible water saturation and different T of rock core are calculated respectively_2ctUnder rock core nuclear-magnetism irreducible water saturation error, when error obtains minimum, corresponding optimization spectral coefficient is optimal spectral coefficient, and corresponding nuclear-magnetism irreducible water saturation is optimal nuclear-magnetism irreducible water saturation.The present invention obtains optimal spectral coefficient by magnetic nuclear resonance method, and irreducible water saturation is calculated according to optimal spectral coefficient, significantly improves the computational accuracy of irreducible water saturation.

Description

Determine the method and device of irreducible water saturation

Technical field

The present invention relates to rock seepage flow characteristics studying technological domain, more particularly to a kind of method for determining irreducible water saturation And device.

Background technology

Irreducible water saturation is to characterize one of most important parameter of reservoir properties, and key is played in sand mud reservoir evaluation Effect.As reservoir shale content is higher, permeability variation is bigger, and pore structure is more complicated, and its effect is more aobvious important, it is determined that difficult Degree is bigger.Pedigree counting method is a kind of method for calculating rock irreducible water saturation, for the seepage flow characteristics of study of rocks.It is existing Pedigree counting method, simply the simple method using data fitting, obtains spectral coefficient, then, rock is calculated according to spectral coefficient Irreducible water saturation.The problem of this method is can not to obtain the spectral coefficient with preferable precision, i.e., cannot ensure to obtain most Excellent spectral coefficient improves the computational accuracy of irreducible water saturation.

The content of the invention

A kind of method for determining irreducible water saturation is the embodiment of the invention provides, optimal pedigree is obtained by optimization method Number, so as to obtain optimal nuclear-magnetism irreducible water saturation, improves the computational accuracy of nuclear-magnetism irreducible water saturation.The method includes：

The nuclear magnetic relaxation echo data of inverting rock core, obtains nuclear magnetic resonance T2 T₂Spectrum；

Obtain the irreducible water saturation data of rock core；

According to T₂Spectrum, the T2 T for selecting different invertings to layout₂As T2 T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient；

According to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cutoff T_2ctUnder rock core nuclear-magnetism irreducible water Saturation degree；

The irreducible water saturation and different cutoff T of rock core are calculated respectively_2ctUnder rock core nuclear-magnetism irreducible water saturation Error, the corresponding optimization spectral coefficient of the minimal error that will calculate is defined as optimal spectral coefficient, and optimal spectral coefficient is corresponding Nuclear-magnetism irreducible water saturation is defined as optimal nuclear-magnetism irreducible water saturation.

In one embodiment, it is described according to T₂Spectrum, the T2 T for selecting different invertings to layout₂As transverse direction Relaxation time T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient, calculated according to equation below：

Wherein, C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

T_2jIt is the T2 that j-th inverting is layouted, ms；

T_2ctIt is T2 T₂Cutoff, ms；

A, b are fitting coefficients.

In one embodiment, the fitting coefficient a, b are obtained as follows：

The nuclear magnetic relaxation echo data of inverting polylith rock core, obtains the nuclear magnetic resonance T2 T of polylith rock core₂ Spectrum；

According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

Obtain the irreducible water saturation data of polylith rock core；

By the T2 T of the polylith rock core of gained₂Geometrical mean and polylith rock core irreducible water saturation Data are fitted, and obtain fitting coefficient a, b.

In one embodiment, the T2 T of the polylith rock core by gained₂Geometrical mean and polylith The irreducible water saturation data of rock core are fitted, and are calculated according to equation below：

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.

In one embodiment, it is described according to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cutoff T_2ct Under rock core nuclear-magnetism irreducible water saturation, according to equation below calculate；

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

The embodiment of the present invention additionally provides a kind of device for determining irreducible water saturation, and optimal spectrum is obtained by optimization method Coefficient, so as to obtain optimal nuclear-magnetism irreducible water saturation, improves the computational accuracy of nuclear-magnetism irreducible water saturation.The device bag Include：

T₂Spectrum acquiring unit, for the nuclear magnetic relaxation echo data of inverting rock core, obtains nuclear magnetic resonance T2 T₂ Spectrum；

Irreducible water saturation acquiring unit, the irreducible water saturation data for obtaining rock core；

Optimization spectral coefficient acquiring unit, for according to T₂Spectrum, the T2 T for selecting different invertings to layout₂As T2 T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient；

Nuclear-magnetism irreducible water saturation acquiring unit, for according to different cutoff T_2ctUnder optimization spectral coefficient, calculate different Cutoff T_2ctUnder rock core nuclear-magnetism irreducible water saturation；

Optimal nuclear-magnetism irreducible water saturation determining unit, for the irreducible water saturation for calculating rock core respectively and different cut-offs Value T_2ctUnder rock core nuclear-magnetism irreducible water saturation error, the corresponding optimization spectral coefficient of the minimal error that will calculate is true It is set to optimal spectral coefficient, the corresponding nuclear-magnetism irreducible water saturation of optimal spectral coefficient is defined as optimal nuclear-magnetism constraint water saturation Degree.

In one embodiment, the optimization spectral coefficient acquiring unit is specifically for being calculated as follows different cutoffs T_2ctUnder optimization spectral coefficient：

Wherein, C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

T_2jIt is the T2 that j-th inverting is layouted, ms；

T_2ctIt is T2 T₂Cutoff, ms；

A, b are fitting coefficients.

In one embodiment, the optimization spectral coefficient acquiring unit specifically for obtaining the fitting system as follows Number a, b：

The nuclear magnetic relaxation echo data of inverting polylith rock core, obtains the nuclear magnetic resonance T2 T of polylith rock core₂ Spectrum；

According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

Obtain the irreducible water saturation data of polylith rock core；

By the T2 T of the polylith rock core of gained₂Geometrical mean and polylith rock core irreducible water saturation Data are fitted, and obtain fitting coefficient a, b.

In one embodiment, the optimization spectral coefficient acquiring unit is specifically for as follows by the polylith rock of gained The T2 T of the heart₂Geometrical mean and the irreducible water saturation data of polylith rock core be fitted：

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.

In one embodiment, the nuclear-magnetism irreducible water saturation acquiring unit is specifically for being calculated as follows difference Cutoff T_2ctUnder rock core nuclear-magnetism irreducible water saturation：

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

In embodiments of the present invention, according to T₂Spectrum, the T2 T for selecting different invertings to layout₂As cutoff T_2ct, spectral coefficient is optimized, obtain different T_2ctUnder optimization spectral coefficient, according to optimization spectral coefficient be calculated nuclear-magnetism beam Water saturation is tied up, the irreducible water saturation data of rock core and the error of nuclear-magnetism irreducible water saturation, the minimum that will be calculated is calculated The corresponding optimization spectral coefficient of error is defined as optimal spectral coefficient, and the corresponding nuclear-magnetism irreducible water saturation of optimal spectral coefficient is true It is set to optimal nuclear-magnetism irreducible water saturation, spectral coefficient is obtained with being fitted by simple data in the prior art, further according to pedigree The method that number calculates the irreducible water saturation of rock is compared, and the pedigree with preferable precision can be obtained using the inventive method Number, so as to improve the computational accuracy of irreducible water saturation.

Brief description of the drawings

Accompanying drawing described herein is used for providing a further understanding of the present invention, constitutes the part of the application, not Constitute limitation of the invention.In the accompanying drawings：

Fig. 1 is a kind of method flow diagram for determining irreducible water saturation provided in an embodiment of the present invention；

Fig. 2 is a kind of nuclear magnetic resonance T2 T provided in an embodiment of the present invention₂Spectrum；

Fig. 3 is a kind of selection T provided in an embodiment of the present invention_2ctTransform the method schematic diagram of original spectral coefficient；

Fig. 4 is a kind of structure drawing of device for determining irreducible water saturation provided in an embodiment of the present invention；

Fig. 5 is that a kind of irreducible water saturation calculated using original spectral coefficient provided in an embodiment of the present invention and experiment are measured Irreducible water saturation between dependency diagram；

Fig. 6 is that a kind of irreducible water saturation calculated using improvement spectral coefficient provided in an embodiment of the present invention and experiment are measured Irreducible water comparative result figure；

Fig. 7 is a kind of blind spot inspection intersection for improving spectral coefficient calculating irreducible water saturation provided in an embodiment of the present invention Figure.

Specific embodiment

It is right with reference to implementation method and accompanying drawing to make the object, technical solutions and advantages of the present invention become more apparent The present invention is described in further details.Here, exemplary embodiment of the invention and its illustrating for explaining the present invention, but simultaneously It is not as a limitation of the invention.

In the algorithm for calculating irreducible water saturation according to nuclear-magnetism experimental data, it is important to obtain rational spectral coefficient, And the existing simply simple method using data fitting obtains spectral coefficient, this method can not obtain the pedigree of preferable precision Number, the precision also according to the irreducible water saturation obtained by spectral coefficient calculating is also not high.If a kind of method can be proposed, Optimal spectral coefficient is obtained by being optimized to spectral coefficient, nuclear-magnetism irreducible water saturation is calculated according to optimal spectral coefficient, just The computational accuracy of irreducible water saturation can be improved.Based on this, the present invention proposes a kind of method for determining irreducible water saturation.

Fig. 1 is a kind of method flow diagram for determining irreducible water saturation provided in an embodiment of the present invention；As shown in figure 1, should Method includes：

Step 101：Experiment measurement and the nuclear magnetic relaxation echo data of inverting rock core, obtain nuclear magnetic resonance T2 T₂Spectrum；

Step 102：The irreducible water saturation data of experiment measurement rock core；

Step 103：According to T₂Spectrum, the T2 T for selecting different invertings to layout₂As cutoff T_2ct, calculate Different T_2ctUnder optimization spectral coefficient；

Step 104：According to different T_2ctUnder optimization spectral coefficient, calculate different T_2ctUnder rock core nuclear-magnetism constraint water saturation Degree；

Step 105：The irreducible water saturation and different T of rock core are calculated respectively_2ctUnder rock core nuclear-magnetism irreducible water saturation Error, when error obtains minimum, corresponding optimization spectral coefficient is optimal spectral coefficient, and corresponding nuclear-magnetism irreducible water is satisfied It is optimal nuclear-magnetism irreducible water saturation with degree.

During specific implementation, before the nuclear magnetic relaxation echo data of inverting rock core, first have to acquisition rock core and be full of salt solution Nuclear magnetic relaxation echo data, and the method for obtaining described data is specific as follows：

Step 1011：Experiment rock core is pre-processed, including washing oil, the desalinization of soil by flooding or leaching, drying, vacuumize.

Step 1012：Salt solution of the configuration with certain salinity, the salinity of salt solution is configurable to 80000ppm (ppm Be volumetric concentration, i.e., the volume number of contained pollutant in the air of 1,000,000 volumes).

Step 1013：Salt solution saturated core, measurement rock core is used to be full of the nuclear magnetic relaxation echo data of salt solution, and inverting nuclear-magnetism Relaxation echo data obtains T₂Spectrum.As shown in Fig. 2 wherein T₂The inverting stationing scope of spectrum is set as between 0.01-10000ms, selects 128 cloth point datas are taken, stationing mode is logarithmic.

Specifically, the laboratory apparatus for obtaining the nuclear magnetic relaxation echo data that rock core is full of salt solution uses Oxford Instruments MARAN Ultra nuclear-magnetism experiment instruments.While the precision in order to ensure experimental data, in nuclear-magnetism experiment, it is proposed that use and repeatedly sweep Cumulative mode is retouched, the signal to noise ratio of data is improved, the signal to noise ratio of experimental data is at least greater than 25.Due to different inversion algorithms Also the significant inverting T of comparison in difference can be obtained₂Spectrum, this method is proposed with the algorithm based on singular value decomposition (SVD).Unless bright Really explanation, nuclear magnetic resonance measuring method and data inversion method below is similar.

Additionally, the embodiment of the present invention also needs to obtain the irreducible water saturation data of rock core, the data are by above-mentioned The rock core for being full of salt solution is centrifuged, and obtains the T of apocarpy as shown in Figure 2₂Spectrum, then makes rock core be in constraint water saturation State, the irreducible water saturation data of rock core are obtained by measuring.

Because the existing precision according to original spectral coefficient calculating irreducible water saturation is not high, it is therefore desirable to original pedigree Number is optimized, and specific optimization method is：Obtaining nuclear magnetic resonance T2 T₂After spectrum, according to T₂Spectrum, selection is not The T2 T that same inverting is layouted₂As T2 T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder Optimization spectral coefficient, it is specific as shown in Figure 3.Wherein, SBVI models refer to the model for calculating original spectral coefficient；New model refers to calculate Optimize the model of spectral coefficient；T2cutoff models refer to calculate T2 T₂Cutoff model, C_BVIRepresent pedigree Number.

Original spectral coefficient is calculated according to equation below：

Wherein, C_bvi-ojIt is the corresponding original spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

T_2jIt is the T2 that j-th inverting is layouted, ms；

A, b are fitting coefficients.

Original spectral coefficient is optimized according to equation below：

Wherein, C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

T_2ctIt is T2 T₂Cutoff, ms.

Wherein, the fitting coefficient a, b in the fitting coefficient a, b and formula (2) in formula (1) are identical.Fitting coefficient a, b are It is unknown, it is necessary to be prepared by the following：

The first step：Experiment measurement and the nuclear magnetic relaxation of inverting polylith (present invention uses 15 pieces) rock core (salt solution saturated core) Echo data, obtains the nuclear magnetic resonance T2 T of polylith rock core₂Spectrum；

Second step：According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

3rd step：Experiment (using centrifugal method) measures the irreducible water saturation data of polylith rock core；

4th step：By the T2 T of the polylith rock core of gained₂Geometrical mean and polylith rock core irreducible water Saturation data carries out data fitting, obtains fitting coefficient a, b.

Data fitting formula is as follows：

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.

Specific experimental data (irreducible water saturation data and T₂Geometrical mean) as shown in table 1.

Table 1

During specific implementation, after the coefficient that got optimized spectrum to the optimization of original spectral coefficient, beam is calculated according to optimization spectral coefficient Water saturation is tied up, i.e., according to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cutoff T_2ctUnder rock core nuclear-magnetism Irreducible water saturation.Specifically calculated according to equation below：

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

During specific implementation, after the nuclear-magnetism irreducible water saturation for obtaining multiple rock cores, it is thus necessary to determine that precision highest Nuclear-magnetism irreducible water saturation, specific determination method is：The irreducible water saturation and different cutoff T of rock core are calculated respectively_2ctUnder Rock core nuclear-magnetism irreducible water saturation error, will calculate error for minimal error when, its corresponding optimization spectral coefficient It is defined as optimal spectral coefficient, the corresponding nuclear-magnetism irreducible water saturation of optimal spectral coefficient is defined as optimal nuclear-magnetism constraint water saturation Degree.

Based on same inventive concept, a kind of device for determining irreducible water saturation is additionally provided in the embodiment of the present invention, such as Described in the following examples.Due to determining the principle and determination irreducible water saturation of the device solve problem of irreducible water saturation Method is similar, it is thus determined that the implementation of the device of irreducible water saturation may refer to the reality of the method for determining irreducible water saturation Apply, repeat part and repeat no more.Used below, term " unit " or " module " can realize the software of predetermined function And/or the combination of hardware.Although the device described by following examples is preferably realized with software, hardware, or soft The realization of the combination of part and hardware is also that may and be contemplated.

Fig. 4 is a kind of apparatus structure block diagram of determination irreducible water saturation of the embodiment of the present invention, as shown in figure 4, the dress Put including：

T₂Spectrum acquiring unit 401, for the nuclear magnetic relaxation echo data of inverting rock core, when obtaining nuclear magnetic resonance transverse relaxation Between T₂Spectrum；

Irreducible water saturation acquiring unit 402, the irreducible water saturation data for obtaining rock core；

Optimization spectral coefficient acquiring unit 403, for according to T₂Spectrum, the T2 T for selecting different invertings to layout₂ As T2 T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient；

Nuclear-magnetism irreducible water saturation acquiring unit 404, for according to different cutoff T_2ctUnder optimization spectral coefficient, calculate Different cutoff T_2ctUnder rock core nuclear-magnetism irreducible water saturation；

Optimal nuclear-magnetism irreducible water saturation determining unit 405, for calculate respectively the irreducible water saturation of rock core from it is different Cutoff T_2ctUnder rock core nuclear-magnetism irreducible water saturation error, the corresponding optimization pedigree of the minimal error that will calculate Number is defined as optimal spectral coefficient, and the corresponding nuclear-magnetism irreducible water saturation of optimal spectral coefficient is defined as into optimal nuclear-magnetism irreducible water satisfies And degree.

During specific implementation, optimization spectral coefficient acquiring unit 403 by above-mentioned formula (2) specifically for calculating different cutoffs T_2ctUnder optimization spectral coefficient, i.e.,：

Wherein, C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

T_2ctIt is T2 T₂Cutoff, ms.

Wherein, the fitting coefficient a, b in formula are unknown, it is necessary to be asked for by certain method, and this is also optimization spectrum The work to be done of coefficient acquiring unit 403.Specifically, optimization spectral coefficient acquiring unit 403 is specifically additionally operable to as follows Obtain fitting coefficient a, b：

The nuclear magnetic relaxation echo data of inverting polylith rock core, obtains the nuclear magnetic resonance T2 T of polylith rock core₂ Spectrum；

According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

Obtain the irreducible water saturation data of polylith rock core；

By the T2 T of the polylith rock core of gained₂Geometrical mean and polylith rock core irreducible water saturation Data are fitted, and obtain fitting coefficient a, b.

Fit correlation formula is above-mentioned formula (3), i.e.,：

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.

Optimization spectral coefficient is obtained after by optimizing to original spectral coefficient, then nuclear-magnetism constraint has been calculated by optimizing spectral coefficient Water saturation, this is the nuclear-magnetism work to be done of irreducible water saturation acquiring unit.Specifically, nuclear-magnetism irreducible water saturation is obtained Unit 404 calculates nuclear-magnetism irreducible water saturation according to above-mentioned formula (4), i.e.,：

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

That be calculated according to formula (4) is different cutoff T_2ctUnder rock core nuclear-magnetism irreducible water saturation, i.e., it is many Individual nuclear-magnetism irreducible water saturation, then needs optimal nuclear-magnetism irreducible water saturation determining unit 405 to determine optimal nuclear-magnetism constraint Water saturation, this optimal nuclear-magnetism irreducible water saturation is final required.

Below by comparative illustration the inventive method and the superiority of device.Fig. 5 is to calculate gained using original spectral coefficient The irreducible water saturation that irreducible water saturation is measured with experiment is compared, and gained constraint water saturation is calculated using original spectral coefficient It is 0.661 (r represents correlation) to spend the irreducible water saturation measured with experiment correlation between the two.Fig. 6 is to use optimization Spectral coefficient calculates the comparative result figure of the irreducible water saturation that gained irreducible water saturation is measured with experiment, uses optimization spectral coefficient The irreducible water saturation that irreducible water saturation obtained by calculating is measured with experiment correlation between the two is 0.912.It follows that Relative to traditional pedigree number calculating method, the computational accuracy that spectral coefficient calculates irreducible water saturation is optimized using the inventive method Improve 25% or so.

The inventive method, also referred to as blind-spot detection are verified below with 7 blocks of rock cores.As shown in table 2, wherein, secondary series For the irreducible water saturation BVI-NMR that other nuclear-magnetism methods are obtained, the 3rd is classified as the irreducible water saturation number of experiment measurement rock core According to BVI-Core (S_bvi)；4th is classified as the nuclear-magnetism irreducible water saturation NS obtained using the inventive method_bvi；5th is classified as experiment Measure the irreducible water saturation data BVI-Core (S of rock core_bvi) and use the nuclear-magnetism irreducible water saturation of the inventive method acquisition NS_bviBetween error.Fig. 7 is to calculate the constraint that gained irreducible water saturation is measured with experiment using present invention optimization spectral coefficient Water saturation is compared, it is known that, nuclear-magnetism calculates the phase relation between irreducible water saturation and experiment test irreducible water saturation Number is 0.895, and average relative error is 12.45%,.Relative to the calculating of original spectral coefficient, nuclear-magnetism constraint is greatly improved The computational accuracy of water saturation.

The blind-spot detection result of this invention, the inventive method has preferable applicability for rock nmr analysis data With preferable computational accuracy.

Table 2

Sample	BVI-NMR	BVI-Core(Sbvi)	NSbvi	Err
					B284-71	0.4076	0.4309	0.423	0.054073
B284-72	0.2856	0.3294	0.285	0.132969
					B284-73	0.7474	0.7776	0.639	0.038837
B284-74	0.3308	0.3782	0.335	0.125331
					B284-75	0.2606	0.3063	0.289	0.1492
B284-76	0.4073	0.4831	0.393	0.156903
					B284-77	0.3597	0.4578	0.545	0.214286

Obviously, those skilled in the art should be understood that each module or each step of the above-mentioned embodiment of the present invention can be with Realized with general computing device, they can be concentrated on single computing device, or be distributed in multiple computing devices On the network for being constituted, alternatively, the program code that they can be can perform with computing device be realized, it is thus possible to by it Store and performed by computing device in the storage device, and in some cases, can be held with different from order herein The shown or described step of row, or they are fabricated to each integrated circuit modules respectively, or by the multiple in them Module or step are fabricated to single integrated circuit module to realize.So, the embodiment of the present invention is not restricted to any specific hard Part and software are combined.

The preferred embodiments of the present invention are the foregoing is only, is not intended to limit the invention, for the skill of this area For art personnel, the embodiment of the present invention can have various modifications and variations.It is all within the spirit and principles in the present invention, made Any modification, equivalent substitution and improvements etc., should be included within the scope of the present invention.

Claims (8)

1. it is a kind of determine irreducible water saturation method, it is characterised in that including：

The nuclear magnetic relaxation echo data of inverting rock core, obtains nuclear magnetic resonance T2 T₂Spectrum；

Obtain the irreducible water saturation data of rock core；

According to T₂Spectrum, the T2 T for selecting different invertings to layout₂As T2 T₂Cutoff T_2ct, Calculate different cutoff T_2ctUnder optimization spectral coefficient；

According to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cutoff T_2ctUnder rock core nuclear-magnetism constraint water saturation Degree；

The irreducible water saturation and different cutoff T of rock core are calculated respectively_2ctUnder rock core nuclear-magnetism irreducible water saturation mistake Differ from, the corresponding optimization spectral coefficient of the minimal error that will be calculated is defined as optimal spectral coefficient, the corresponding core of optimal spectral coefficient Magnetic irreducible water saturation is defined as optimal nuclear-magnetism irreducible water saturation；

It is described according to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cutoff T_2ctUnder rock core nuclear-magnetism irreducible water Saturation degree, calculates according to equation below；

${\mathrm{NS}}_{bvi}=\frac{\underset{j=1}{\overset{128}{\Σ}}{C}_{bvi-nj}{A}_j}{\underset{j=1}{\overset{128}{\Σ}}{A}_j};$

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

2. the method for claim 1, it is characterised in that described according to T₂Spectrum, selects the horizontal relaxation that different invertings are layouted Henan time T₂As T2 T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient, according to as follows Formula is calculated：

$C_{bvi-nj}=\left\{\begin{array}{cc}1,& T_{2j}\≤T_{2ct}\\ \frac{1}{a\×T_{2j}+b},& T_{2j}>T_{2ct}\end{array}\right.;$

Wherein, T_2jIt is the T2 that j-th inverting is layouted, ms；

T_2ctIt is T2 T₂Cutoff, ms；

A, b are fitting coefficients.

3. method as claimed in claim 2, it is characterised in that the fitting coefficient a, b are obtained as follows：

The nuclear magnetic relaxation echo data of inverting polylith rock core, obtains the nuclear magnetic resonance T2 T of polylith rock core₂Spectrum；

According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

Obtain the irreducible water saturation data of polylith rock core；

By the T2 T of the polylith rock core of gained₂Geometrical mean and the irreducible water saturation data of polylith rock core enter Row fitting, obtains fitting coefficient a, b.

4. method as claimed in claim 3, it is characterised in that the T2 T of the polylith rock core by gained₂'s The irreducible water saturation data of geometrical mean and polylith rock core are fitted, and are calculated according to equation below：

$\frac{1}{S_{bvi}}=a\×T_{2lm}+b;$

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.

5. it is a kind of determine irreducible water saturation device, it is characterised in that including：

T₂Spectrum acquiring unit, for the nuclear magnetic relaxation echo data of inverting rock core, obtains nuclear magnetic resonance T2 T₂Spectrum；

Irreducible water saturation acquiring unit, the irreducible water saturation data for obtaining rock core；

Optimization spectral coefficient acquiring unit, for according to T₂Spectrum, the T2 T for selecting different invertings to layout₂As transverse direction Relaxation time T₂Cutoff T_2ct, calculate different cutoff T_2ctUnder optimization spectral coefficient；

Nuclear-magnetism irreducible water saturation acquiring unit, for according to different cutoff T_2ctUnder optimization spectral coefficient, calculate different cut-offs Value T_2ctUnder rock core nuclear-magnetism irreducible water saturation；

Optimal nuclear-magnetism irreducible water saturation determining unit, irreducible water saturation and different cutoffs for calculating rock core respectively T_2ctUnder rock core nuclear-magnetism irreducible water saturation error, the corresponding optimization spectral coefficient of the minimal error that will calculate determines It is optimal spectral coefficient, the corresponding nuclear-magnetism irreducible water saturation of optimal spectral coefficient is defined as optimal nuclear-magnetism irreducible water saturation；

The nuclear-magnetism irreducible water saturation acquiring unit is specifically for being calculated as follows different cutoff T_2ctUnder rock core Nuclear-magnetism irreducible water saturation：

${\mathrm{NS}}_{bvi}=\frac{\underset{j=1}{\overset{128}{\Σ}}{C}_{bvi-nj}{A}_j}{\underset{j=1}{\overset{128}{\Σ}}{A}_j};$

Wherein, NS_bviIt is nuclear-magnetism irreducible water saturation；

C_bvi-njIt is the corresponding optimization spectral coefficient of T2 that j-th inverting is layouted, dimensionless；

A_jFor j-th inverting is layouted the range value of corresponding porosity.

6. device as claimed in claim 5, it is characterised in that the optimization spectral coefficient acquiring unit is specifically for by following public affairs Formula calculates different cutoff T_2ctUnder optimization spectral coefficient：

$C_{bvi-nj}=\left\{\begin{array}{cc}1,& T_{2j}\≤T_{2ct}\\ \frac{1}{a\×T_{2j}+b},& T_{2j}>T_{2ct}\end{array}\right.;$

Wherein, T_2jIt is the T2 that j-th inverting is layouted, ms；

T_2ctIt is T2 T₂Cutoff, ms；

A, b are fitting coefficients.

7. device as claimed in claim 6, it is characterised in that the optimization spectral coefficient acquiring unit is specifically for by such as lower section Formula obtains the fitting coefficient a, b：

The nuclear magnetic relaxation echo data of inverting polylith rock core, obtains the nuclear magnetic resonance T2 T of polylith rock core₂Spectrum；

According to T₂Spectrum, calculates the T2 T of polylith rock core₂Geometrical mean；

Obtain the irreducible water saturation data of polylith rock core；

By the T2 T of the polylith rock core of gained₂Geometrical mean and the irreducible water saturation data of polylith rock core enter Row fitting, obtains fitting coefficient a, b.

8. device as claimed in claim 7, it is characterised in that the optimization spectral coefficient acquiring unit is specifically for by following public affairs Formula is by the T2 T of the polylith rock core of gained₂Geometrical mean and the irreducible water saturation data of polylith rock core enter Row fitting：

$\frac{1}{S_{bvi}}=a\×T_{2lm}+b;$

Wherein, S_bviIt is the irreducible water saturation of rock core；

T_2lmIt is the T2 T of rock core₂Geometrical mean, ms.