CN1869733A - Method for determining nuclear magnetic resonance logging T2 spectral T2 end value - Google Patents

Abstract

The invention relates to a method for determining T2cutoff value by nuclear magnetic resonance logging (NMRL) T2 spectra, comprising the steps of: 1. classifying NMRL T2 spectra by shape characteristics; 2. fitting and obtaining centrifugal spectrum according to different types of logging T2 spectra; 3. making area integration on the centrifugal spectrum and obtaining area of centrifugal spectrum; 4. calculating areas of logging T2 spectra; 5. accumulating the areas of logging T2 spectra, and as the accumulated area is equal to or closest to the area of centrifugal spectrum, the corresponding T2 value is a T2cutoff value. Thus, the invention determines T2cutoff value of each depth point by directly using NMRL T2 spectra.

Description

Definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value

Technical field

The present invention relates to a kind of definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value, especially a kind of nuclear magnetism log T2 is composed adopts morphological feature classification and pointwise to determine the method for the T2 cutoff that well logging T2 composes on each sampled point.

Technical background

The raw data of nuclear magnetic resonance log is the spin-echo string of decaying in time, and spin-echo string has comprised very abundant information such as reservoir properties, porosity type, pore size, fluid type and distribution thereof.Spin-echo string can be expressed as the superposition of a plurality of damped expoentials:

$\mathrm{Echo}\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\φ}}_i\exp (-t/T_{2i})---\left(1\right)$

In the formula: the echo amplitude that the t in time that Echo (t)----nuclear magnetism log measures changes;

T2 _i--the T2 an of-Di i component, i=1 ..., N;

Ф _i---corresponding to T2 _iThe NMR porosity of component, i=1 ..., N;

Carry out the multi index option match by spin-echo string (being formula (1)) that the nuclear magnetism log instrument is measured, can obtain the T2 of each measurement point _i--Ф ₁Distribution curve, promptly so-called nuclear magnetic resonance log T2 distribution profile.The horizontal ordinate of this T2 distribution profile is the T2 value, and ordinate is the signal relative amplitude, and total signal amplitude is relevant with rock porosity.Under the monophasic fluid condition, the T2 qualitative reflection pore size distribution that distributes.Be the bigger T2 value of large aperture hole correspondence, the T2 value that the small-bore hole is corresponding less.

Nuclear magnetic resonance log is the unique a kind of logging method that can distinguish fluid occurrence status in the hole at present, therefore has the unique technique advantage.By nuclear magnetism log T2 spectrum is handled, can obtain the blowhole size and distribute, thereby more directly determine the irreducible water saturation of reservoir and permeability etc.Yet (MDT, FMI etc.) compare with other new Logging Technology, all also there is very big gap in the nuclear magnetism log technology from the geological effect of the degree of depth used and performance, one of them important factor is exactly that definite method of existing T2 cutoff also exists difficulty in the application, and definite technology of nuclear magnetism log T2 cutoff exists defective and limitation.

The T2 cutoff is the important underlying parameter that Nuclear Magnetic Resonance Logging analysis and data are used, and it is the key parameter that calculates reservoir movable fluid or constraint fluid content, also is the underlying parameter of quantitative evaluation RESERVOIR PORE STRUCTURE, permeability etc.So-called T2 cutoff is meant to have the value of fixing limit on the T2 spectrum, is referred to as free fluid greater than the fluid in the pairing hole of this numerical value, can flow under reservoir conditions.Pore fluid less than this numerical value correspondence is referred to as (hollow billet) constraint fluid, can not flow.Promptly

$\mathrm{BVI}=\underset{T_2\≤T_{2\mathrm{cutoff}}}{\mathrm{\Σ}}{\mathrm{\φ}}_i---\left(2\right)$

$\mathrm{FFI}=\underset{T_2>T_{2\mathrm{cutoff}}}{\mathrm{\Σ}}{\mathrm{\φ}}_i---\left(3\right)$

In the formula,

T _2cutoff---the T2 cutoff;

BVI---hollow billet constraint water voids volume;

FFI---free fluid volume of voids (or claiming free fluid index).

The T2 cutoff is as a underlying parameter of fluid behaviour in the characterize reservoir capillary pore, and the chamber is measured and determined by experiment.External researchist is by a large amount of rock cores (mainly from north America region) experiment measuring, think that the T2 cutoff of clastic reservoir rock rock is 33ms, the carbonate reservoir rock is 92ms (Morriss etc., 1993), and promptly the T2 cutoff is a constant numerical value basically under the situation of known lithology.In fact, also adopt these two cutoffs that Nuclear Magnetic Resonance Logging is handled and used at present both at home and abroad basically.

Since the mid-90 in last century nuclear magnetism log technology was incorporated into China, the T2 cutoff of but not supporting external colleague generally to admit about the nuclear magnetic resonance experiment chamber measurement result of rock core T2 cutoff was the conclusion of certain constant numerical value.Particularly in clastic reservoir rock, the variation range of T2 cutoff is quite big, is not a definite value.The T2 cutoff is different and widely different with area or reservoir.Fig. 1 gathers according to the T2 cutoff data that the rock core nuclear magnetic resonance experiment obtains for China's part oil field sandstone reservoir, can find out obviously that from Fig. 1 the T2 cutoff is not a fixing value, do not see that data have the sign that trends towards 33ms (petroclastic rock stratum) yet, the external 33ms (petroclastic rock stratum) that is suitable for is become inapplicable in the actual formation of China.

At present at home, everybody has approved that basically the T2 cutoff of sandstone clastic reservoir rock is not the objective fact of the such definite value of 33ms, but about the T2 cutoff of sandstone reservoir why so big variation can take place, the Changing Pattern of the T2 cutoff of the sandstone reservoir that is what controlling factors still do not have clear and definite understanding.Therefore the difficult problem that has caused that Nuclear Magnetic Resonance Logging handles and use and difficult situation: although have realized that the T2 cutoff of sandstone reservoir is not a definite value, but owing to can't find the usability methods of a definite T2 cutoff, when the Data Processing of nuclear magnetism log, still helplessly continue to use external way, promptly still use 33ms as the unified T2 cutoff of sandstone reservoir.A serious consequence of doing like this is exactly that the technician holds the suspicious attitude to the nuclear magnetism log result relevant with the T2 cutoff, has therefore restricted the nuclear magnetism log The Application of Technology.

The relevant method of asking for the T2 cutoff has following several in the document of having delivered at present:

1.. core experiment chamber nuclear magnetic resonance experiment method (area under spectrum method).As shown in Figure 2, the rock core to saturation water carries out Nuclear Magnetic Resonance Measurement earlier, obtains the saturated T2 distribution profile of T2; The rock core of saturation water thrown away free water wherein then under certain pressure condition on hydro-extractor, behind the only remaining irreducible water, again rock core is carried out Nuclear Magnetic Resonance Measurement and obtain T2 distribution profile after centrifugal, both compare.Begin to carry out area integral S1 from low side (little T2 value) in well logging T2 spectrum, when integral area S1=S2 (the centrifugal spectrum total area), corresponding T2 value was the T2 cutoff and (is designated as T during well logging T2 composed _2cutoff).This method is determined according to the definition of T2 cutoff, also is the method for determining the T2 cutoff accurately.The centrifugal spectrum area is irreducible water saturation (Swi represents with symbol) with the ratio of well logging T2 area under spectrum.

2.. the capillary pressure curve scale method.At first measure the factor of porosity and the capillary pressure curve of rock core, determine to be similar to the irreducible water saturation Swir of oil reservoir by capillary pressure curve, and the constraint fluid volume of rock core is φ Swir, presses the method scale T2 cutoff of Fig. 3 then.By iteration graphic Method Optimization T2 cutoff shown in Figure 4.Among Fig. 4, horizontal ordinate is an oil reservoir depth-logger scope rock core scale T2 cutoff, and ordinate is the T2 spectrum of same reservoir depth scope and analyzes cumulative errors between the BVI that definite T2 cutoff asked with conventional core NMR.The pairing T2 cutoff of minimum cumulative errors is the best T2 cutoff in stratum.When carrying out the rock sample scale, should collect regional representative coring data, and coring data be carried out degree of depth playback handle.Because of may there be error in coring data on the degree of depth, so should carefully contrast with well-log information through overcorrect.

3.. the permeability cross-plot.Running into the difficulty of coring, coring and the core analysis time is long and when being difficult for obtaining representational core sample, can utilize the permeability crossplot technique to determine the T2 cutoff on stratum.Obtain a series of T2 cutoffs by the logging trace in the NMR depth-logger scope.By changing the T2 cutoff and calculating its corresponding Timur-Coates permeability value (K _NMR), the permeability value (K that draws with same depth range MDT (modular formation tester) drop measurement then _MDT) draw X plot, the best corresponding T2 cutoff of NMR well logging permeability of linear dependence is best T2 cutoff on the selection X plot.

4.. other mathematical statistics methods.Referring in February, 2004 " geophysical prospecting for oil " magazine, Gao Chuqiao, the article of " relation of nuclear magnetic resonance T2 cutoff and capillary pressure " of works such as He Zongbin has wherein been put down in writing between T2 cutoff and the capillary pressure Pc and has been had exponential relationship, draws T2 _c=A/Pc ^BReferring in September, 2004 " Advances in Geophysics " magazine, Wang Zhonghao, Zhang Chengguang, T2 cutoff and petrophysical parameter wherein put down in writing in the article of " the low permeability reservoir T2 cutoff experimental study " of works such as Xiao Chengwen Between have certain relation, draw

$T_{2c}=a\×{\left(\sqrt{\frac{k}{\mathrm{\φ}}}\right)}^2+b\×\left(\sqrt{\frac{k}{\mathrm{\φ}}}\right)+c.$

Definite T2 cutoff the whole bag of tricks that last branch is discussed has benefit and limitation separately.The advantage of preceding two kinds of methods is to obtain T2 cutoff accurately.But it use to go up to such an extent that limitation is to need core sample, all needs the core experiment analysis maybe will use other auxiliary logging method, and cost height, cycle are long.Because the restriction of interval, when there is not good rule (as a collection of experimental data Changing Pattern very complicated or do not have what Changing Pattern to seek) in limited core experiment data at all, even obtained the continuous processing that these experimental datas also can't be applied to well-log information.Method 3 and method 4 all are based on the experimental formula that regionalism draws, and are difficult to be applied to other areas, and the parameter in the formula neither be unique, and it is different and change to look strata condition.In a word, a tangible limitation of existing definite T2 cutoff the whole bag of tricks is exactly to need the information in core experiment or other sources to demarcate.No matter moreover many times can not find the statistical law of experiment of certain well or certain reservoir T2 cutoff or calibration result at all, promptly enable to accomplish this point, also be regional rule and often have very mistake, can't generally promote and use, and its degree of reliability and precision also can not get guaranteeing.

In order to solve the practical challenges that the T2 cutoff is accurately determined in the nuclear magnetism log application, should adopt brand-new research thinking and method, promptly avoid conventional thought and method that core experiment or other information are demarcated, the T2 cutoff of each measurement point is directly determined in research according to the morphological feature of nuclear magnetic resonance log T2 spectrum (saturated T2 spectrum).A kind of reliable method and the technology of determining nuclear magnetic resonance log T2 cutoff are provided, overcome the technical limitation of current methods.Promote the nuclear magnetism log The Application of Technology, bring into play its technical advantage to a greater degree, this technology is played an important role in the oil field prospecting exploitation.By research, we think to have only under the situation of nuclear magnetism log T2 spectrum, are the T2 cutoffs that can determine each depth point according to the form of well logging T2 spectrum.

Summary of the invention

The T2 that the objective of the invention is directly to utilize nuclear magnetic resonance log to obtain composes and the T2 cutoff of definite each depth point.

For achieving the above object, the invention provides a kind of definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value, may further comprise the steps:

Step 1, nuclear magnetic resonance log T2 spectrum is classified by morphological feature;

Step 2, match draws its centrifugal spectrum according to dissimilar well logging T2 spectrum;

Step 3, centrifugal spectrum is carried out area integral, draw the area of centrifugal spectrum;

The area of step 4, calculating well logging T2 spectrum;

The area of step 5, the T2 that will log well spectrum adds up, and when cumulative area equaled or be the most close with the centrifugal spectrum area, this moment, corresponding T2 value was the T2 cutoff.

Also have step 6 after the described step 5, with the area of centrifugal spectrum area divided by well logging T2 spectrum, be the value of irreducible water saturation.Described nuclear magnetic resonance well T2 spectrum is divided into bimodal pattern, single peak type and three peak types.Described bimodal pattern is divided into bimodal pinhole type, bimodal macroporous type, and single peak type is divided into unimodal pinhole type, unimodal macroporous type.The computing method of unimodal macroporous type logging T 2 spectral T 2 end value are carried out match for utilizing mathematical function to the macropore section in the described step 2, and its mathematical form is:

$f\left(x\right)=A\×4\×(1-e^{\frac{x-B}{C}})\×e^{\frac{x-B}{C}}$

Wherein:

Amplitude maximum value in the A-------match T2 spectrum, the A value is got the amplitude maximum value in the T2 distribution profile;

Certain T2 time value of B-------, B value are got range value and are reduced to certain T2 value when minimum;

Certain parameter undetermined of C-------;

The T2 time value of x-----each component is identical with the T2 time value of well logging T2 spectrum;

The range value that f (x)-----match obtains;

The computing method of unimodal pinhole type logging T 2 spectral T 2 end value are in the described step 2, suppose that the fluid in the hole all is the constraint fluid, give a fixing T2 cutoff with hole.Described fixing T2 cutoff is 33ms.

The computing method of bimodal pattern logging T 2 spectral T 2 end value are in the described step 2, utilize normal function to simulate a centrifugal spectrum on well logging T2 spectrum, and its mathematical form is:

$f\left(x\right)=A\×e^{-\frac{{(x-\mathrm{\μ})}^2}{2{\mathrm{\σ}}^2}}$

Wherein:

A is a match T2 spectral amplitude value, and the A value is got the amplitude at first peak in the T2 distribution profile, even the functional digraph of match has identical amplitude with the T2 distribution profile;

μ is the expectation value of match T2 spectrum, and the μ value is got the pairing T2 time value of first peak value; σ is the variance of match T2 spectrum;

X is that the T2 time value of each component is identical with the T2 time value of well logging spectrum;

The range value that f (x) obtains for match;

The computing method of three peak type logging T 2 spectral T 2 end values simulate a centrifugal spectrum for utilizing normal function in the described step 2 on well logging T2 spectrum, and its mathematical form is:

$f\left(x\right)=A\×e^{-\frac{{(x-\mathrm{\μ})}^2}{2{\mathrm{\σ}}^2}}$

Wherein:

A is a match T2 spectral amplitude value, and the A value is got the amplitude at first peak in the T2 distribution profile, even intend

The functional digraph that closes has identical amplitude with the T2 distribution profile;

μ is the expectation value of match T2 spectrum, and the μ value is got the pairing T2 time value of first peak value;

σ is the variance of match T2 spectrum;

X is that the T2 time value of each component is identical with the T2 time value of well logging spectrum;

The range value that f (x) obtains for match;

The computing method of described area are carried out area integral for spectrum Romber integral method.

The computing method of T2 cutoff add up for the area of the T2 spectrum of will logging well in the described step 5, and when cumulative area equaled or be the most close with the centrifugal spectrum area, this moment, corresponding T2 value was the T2 cutoff.Above-mentioned all kinds all adopt this kind method to calculate the T2 cutoff.

Therefore, the present invention has realized that the T2 that directly utilizes nuclear magnetic resonance log to obtain composes and the T2 cutoff of definite each depth point.

Below in conjunction with drawings and Examples, technical scheme of the present invention is described in further detail.

Description of drawings

Fig. 1 is the T2 cutoff statistical graph of the core experiment of Xinjiang, North China and northwestward region-by-region.

Fig. 2 determines T2 cutoff synoptic diagram for centrifuge method.

Fig. 3 determines T2 cutoff synoptic diagram for the capillary pressure curve scale method.

Fig. 4 is BVI cumulative errors and T2 cutoff graph of relation.

Fig. 5 is the bimodal pinhole type rock core of the definite method Nuclear Magnetic Resonance Measurement result schematic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Fig. 6 is the actual nuclear magnetism log instrument of the bimodal pinhole type of the definite method measurement result synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Fig. 7 is the bimodal macroporous type rock core of the definite method Nuclear Magnetic Resonance Measurement result schematic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Fig. 8 is the actual nuclear magnetism log instrument of the bimodal macroporous type of the definite method measurement result synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Fig. 9 is the unimodal macroporous type rock core of the definite method Nuclear Magnetic Resonance Measurement result schematic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 10 is the actual nuclear magnetism log instrument of the unimodal macroporous type of the definite method measurement result synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 11 is the unimodal pinhole type rock core of the definite method Nuclear Magnetic Resonance Measurement result schematic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 12 is the actual nuclear magnetism log instrument of the unimodal pinhole type of the definite method measurement result synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 13 is definite method three peak type rock core Nuclear Magnetic Resonance Measurement result schematic diagrams of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 14 is the actual nuclear magnetism log instrument of the definite method three peak types measurement result synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 15 is definite method embodiment bimodal pattern synoptic diagram 1 of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 16 is definite method embodiment bimodal pattern synoptic diagram 2 of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 17 is definite method embodiment single peak type synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 18 is definite method embodiment three peak type synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 19 is the design sketch of definite method Xinjiang Oilfield well actual treatment of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 20 is the design sketch of definite method the Northwest well actual treatment of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

The T2 cutoff that Figure 21 calculates for four areas such as definite method Xinjiang of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention and the T2 cutoff of core analysis be comparison diagram as a result.

The irreducible water saturation that Figure 22 calculates for four areas such as definite method Xinjiang of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention and the irreducible water saturation result's of core analysis comparison diagram.

Figure 23 is definite method COMPUTER CALCULATION schematic flow sheet of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Figure 24 is definite method flow synoptic diagram of nuclear magnetic resonance logging T 2 spectral T 2 end value of the present invention.

Embodiment

By our years of researches, on the basis of a large amount of experimental datas and field data, proposed a kind ofly to determine the method for T2 cutoff, abbreviation form method based on nuclear magnetism log T2 spectrum morphological feature.The schematic flow sheet that the form method is determined the T2 cutoff is as shown in figure 24:

The first step is classified by morphological feature to the T2 spectrum of nuclear magnetic resonance log.

Because the saturated spectrum of rock core and the centrifugal spectrum feature difference of different pore structures are bigger, through comparative analysis, the saturated spectrum of T2 is divided into following three major types five groups, be respectively: a. bimodal pattern (being divided into bimodal macroporous type and bimodal pinhole type again); B. single peak type (being divided into unimodal macroporous type and unimodal pinhole type again); C. three peak types.Corresponding different pore texture types, the method for calculating the T2 cutoff also has difference.For the low porosity and low permeability reservoir core, T2 distribution profile form is mainly unimodal pinhole type, bimodal pinhole type, bimodal macroporous type, for high hole, in-Gao oozes reservoir rock T2 distribution profile then usually based on unimodal macroporous type.

The feature and the form of all kinds of spectrums are described below:

A. bimodal pattern (subclass: bimodal pinhole type, bimodal macroporous type)

Bimodal pinhole type: as shown in Figure 5 and Figure 6, be bimodal pinhole type rock core Nuclear Magnetic Resonance Measurement synoptic diagram and actual nuclear magnetism log instrument instrumentation plan.The T2 distribution profile is bimodal distribution, two amplitude maximum value are arranged on whole T2 distribution profile, and the amplitude at first peak is greater than the amplitude at second peak, because the pairing T2 time of fine porosity (the T2 value of first peak point) is less than the macroporous T2 time (the T2 value of second peak point), so the type is called as bimodal pinhole type.

Bimodal macroporous type: as shown in Figure 7 and Figure 8, be bimodal macroporous type rock core Nuclear Magnetic Resonance Measurement synoptic diagram and actual nuclear magnetism log instrument instrumentation plan.The T2 distribution profile is bimodal distribution, two amplitude maximum value are arranged on whole T2 distribution profile, and the amplitude at first peak is less than the amplitude at second peak, because the pairing T2 time of fine porosity (the T2 value of first peak point) is less than the macroporous T2 time (the T2 value of second peak point), so the type is called as bimodal macroporous type.

B. single peak type (subclass: unimodal macroporous type, unimodal pinhole type)

Unimodal macroporous type:, be unimodal macroporous type rock core Nuclear Magnetic Resonance Measurement synoptic diagram and actual nuclear magnetism log instrument instrumentation plan as Fig. 9 and shown in Figure 10.The T2 distribution profile is unimodal distribution, has only an amplitude maximum value on whole T2 distribution profile, and the pairing T2 time ratio of this maximum value is by back (generally greater than 100ms), and just certain the T2 value in the macropore section reaches greatly, so be called unimodal macroporous type.

Unimodal pinhole type: shown in Figure 12 as Figure 11, be unimodal pinhole type rock core Nuclear Magnetic Resonance Measurement synoptic diagram and actual nuclear magnetism log instrument instrumentation plan.The T2 distribution profile is unimodal distribution, has only an amplitude maximum value on whole T2 distribution profile, and the pairing T2 time of this maximum value earlier (generally greater than 100ms), and just certain the T2 value in the fine porosity section reaches greatly, so be called unimodal pinhole type.

C. three peak types such as Figure 13 and shown in Figure 14 are three peak type rock core Nuclear Magnetic Resonance Measurement synoptic diagram and actual nuclear magnetism log instrument instrumentation plan.

The T2 distribution profile is three peaks and distributes, and three amplitude maximum value are arranged on whole T2 distribution profile, and largest peaks is indefinite, may be first peak, may be second peak, also may be the 3rd peak.

Second step, at all kinds of T2 distribution profiles, adopt diverse ways to determine its T2 cutoff, determine that specifically method is as follows:

A. definite method of the T2 cutoff of bimodal pattern:

Utilize normal function to simulate a centrifugal spectrum on well logging T2 spectrum, its mathematical form is:

$f\left(x\right)=A\×e^{-\frac{{(x-\mathrm{\μ})}^2}{2{\mathrm{\σ}}^2}}$

In the formula: A-----match T2 spectral amplitude value; The expectation value of μ-----match T2 spectrum; The variance of σ-----match T2 spectrum; The T2 time value of x-----each component (identical) with the T2 time value of well logging T2 spectrum; The range value that f (x)-----match obtains.

For will accurately determining the T2 cutoff, then above-mentioned A, μ, three parameters of σ definite most important, our definite method is as follows:

The A value is got the amplitude at first peak in the T2 distribution profile, even the functional digraph of match has identical amplitude with the T2 distribution profile; The μ value is got the pairing T2 time value of first peak value; σ value and certain correlativity is arranged with the width of two T2 values on half pairing T2 distribution profile of first peak value.

B. definite method of the T2 cutoff of unimodal macroporous type:

Utilize mathematical function that the macropore section is carried out match, its mathematical form is:

$f\left(x\right)=A\×4\×(1-e^{\frac{x-B}{C}})\×e^{\frac{x-B}{C}}$

In the formula: the amplitude maximum value in the A-------match T2 spectrum; Certain T2 time value of B-------; Certain parameter undetermined of C-------; The T2 time value of x-----each component (identical) with the T2 time value of well logging T2 spectrum; The range value that f (x)-----match obtains.

As previously mentioned, above-mentioned A, B, three parameters of C determines determining that the T2 cutoff also is most important.Discover that the A value is got the amplitude maximum value in the T2 distribution profile, the B value is got range value and is reduced to certain T2 value when minimum, and the C value also and with the width of two T2 values on half pairing T2 distribution profile of first peak value has certain correlativity.

C. definite method of the T2 cutoff of unimodal pinhole type:

The pairing pore texture of unimodal pinhole type mostly is microcapillary interstice or mutual disconnected stagnant pore, fluid is completely enclosed within wherein, can not flow, the fluid in such pore texture be can not by extraction or produced quantity very limited, in actual production, do not have commercial value yet.Therefore, we give for example 33ms of a fixing T2 cutoff can for this class hole, think that the fluid in this hole all is the constraint fluid.

D. definite method of the T2 cutoff of three peak types

Definite employing normal function identical with bimodal pattern of the T2 cutoff of three peak types asked for the acquiring method of its method such as bimodal pattern.

After above each classification algorithms has been arranged, calculate T2 cutoff and irreducible water saturation with the area integral method:

1.. match draws centrifugal spectrum as stated above;

2.. centrifugal spectrum is carried out area integral by Long Beige (Romberg) method of quadrature, and the value that draws is equivalent to the area of centrifugal spectrum;

3.. with the area of same algorithm computation well logging T2 spectrum;

4.. the area of the T2 that will log well spectrum adds up, and when cumulative area equaled or be the most close with the centrifugal spectrum area, this moment, corresponding T2 value was the T2 cutoff;

5.. with the area that the area of centrifugal spectrum is composed divided by well logging T2, the value that obtains is irreducible water saturation.

According to above thinking, we have realized automatic processing with the program that Visual Fortran has write this method.Process flow diagram as shown in figure 23.

We calculate the part rock core in areas such as Xinjiang to utilize the form method, and fitting result chart of each classification is as follows:

Bimodal pattern: shown in Figure 15 and 16, to the direct match of aperture section, integration is obtained the area that its area is the constraint fluid, and what utilize that this area obtains divided by total area under spectrum is irreducible water saturation; Score is begun to do area integral from little T2 value, and when cumulative area was equal with constraint fluid area, the T2 value of this moment was the T2 cutoff.

Single peak type: as shown in figure 17, after the match of macropore section, integration is obtained its area, and in score area deducts macropore section area then, the area that is the constraint fluid that obtains, and what utilize that this area obtains divided by total area under spectrum is irreducible water saturation; Score is begun to do area integral from little T2 value, and when cumulative area was equal with constraint fluid area, the T2 value of this moment was the T2 cutoff.

Three peak types: as shown in figure 18, to the direct match of aperture section, integration is obtained the area that its area is the constraint fluid, and what utilize that this area obtains divided by total area under spectrum is irreducible water saturation; Score is begun to do area integral from little T2 value, and when cumulative area was equal with constraint fluid area, the T2 value of this moment was the T2 cutoff.

Utilize the form method to determine the software package of nuclear magnetic resonance log T2 cutoff method and independent development automatically, we handle Xinjiang Oilfield well and the Northwest's well, be depicted as the design sketch of Xinjiang Oilfield well actual treatment and the design sketch of the Northwest's well actual treatment as Figure 19 and 20, the design sketch of processing is as follows:

First road is CALI (CAL) and GR (gamma ray curve) among the figure; Second road is the degree of depth; SWICAL is the irreducible water saturation curve that utilizes the form method to calculate in the 3rd road, the irreducible water saturation curve of SWI33 for calculating during as the T2 cutoff with 33ms, and CSWI is the irreducible water saturation that core analysis obtains; T2_AMP is the T2 spectrum that nuclear magnetic resonance log obtains in the 4th road, T2CUTCAL is the T2 cutoff curve that utilizes the form method to calculate, the T2 cutoff curve of T2CUT33 for calculating during as the T2 cutoff with 33ms, T2CUT_CORE is the T2 cutoff that core analysis obtains.From the figure as can be seen, the irreducible water saturation of utilizing the T2 cutoff that the form method calculates and utilizing cutoff to calculate is better than the result as the T2 cutoff with fixed value 33ms, form method result calculated is followed the result near core analysis, this explanation, can be under the situation of not coring, directly utilize the form method to determine the T2 cutoff and need not rely on core experiment.

Compare with the method for existing definite T2 cutoff, the form method can pointwise calculates the T2 cutoff on each depth point of logging interval, and classic method is owing to be that rock core is done experiment, so can only be the T2 cutoff of determining a place that cores.Utilize the software package of above-mentioned form method and independent development, we just can determine its T2 cutoff to the spectrum of the well logging T2 on each depth point of nuclear magnetic resonance log data, so just obtain a continuous T2 cutoff curve that is complementary with logging interval, and then utilized this curve can calculate irreducible water saturation on each depth point and permeability etc.Utilize the form method, we calculate the rock core in four areas such as Xinjiang, two boundary lines among Figure 21 be respectively with ± 10ms is the separatrix of error, two boundary lines among Figure 22 are respectively ± 5% being the separatrix of error, utilize on Figure 21 and Figure 22 the result of form method can well replace the result of core analysis as can be seen.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is had been described in detail with reference to preferred embodiment, those of ordinary skill in the art is to be understood that, can make amendment or be equal to replacement technical scheme of the present invention, and not breaking away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (12)

1, a kind of definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value is characterized in that may further comprise the steps:

Step 1, nuclear magnetic resonance log T2 spectrum is classified by morphological feature;

Step 2, match draws its centrifugal spectrum according to dissimilar well logging T2 spectrum;

Step 3, centrifugal spectrum is carried out area integral, draw the area of centrifugal spectrum;

The area of step 4, calculating well logging T2 spectrum;

The area of step 5, the T2 that will log well spectrum adds up, and when cumulative area equaled or be the most close with the centrifugal spectrum area, this moment, corresponding T2 value was the T2 cutoff.

2, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 1 is characterized in that: also have step 6 after the described step 5, with the area of the centrifugal spectrum area divided by well logging T2 spectrum, be the value of irreducible water saturation.

3, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 1 is characterized in that: described nuclear magnetic resonance log T2 spectrum is divided into bimodal pattern, single peak type and three peak types.

4, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 3 is characterized in that: described bimodal pattern is divided into bimodal pinhole type, bimodal macroporous type, and single peak type is divided into unimodal pinhole type, unimodal macroporous type.

5, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 4, it is characterized in that: the computing method of unimodal macroporous type logging T 2 spectral T 2 end value are carried out match for utilizing mathematical function to the macropore section in the described step 2, and its mathematical form is:

$f\left(x\right)=A\×4\×(1-e^{\frac{x-B}{C}})\×e^{\frac{x-B}{C}}$

Wherein:

Amplitude maximum value in the A-------match T2 spectrum, the A value is got the amplitude maximum value in the T2 distribution profile;

Certain T2 time value of B-------, B value are got range value and are reduced to certain T2 value when minimum;

Certain parameter undetermined of C-------;

The T2 time value of x-----each component is identical with the T2 time value of well logging T2 spectrum;

The range value that f (x)-----match obtains.

6, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 5, it is characterized in that: the computing method of unimodal macroporous type logging T 2 spectral T 2 end value are in the described step 2, the area of well logging T2 spectrum is deducted the match area under spectrum be the centrifugal spectrum area.

7, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 4, it is characterized in that: the computing method of unimodal pinhole type logging T 2 spectral T 2 end value are in the described step 2, suppose that the fluid in the hole all is the constraint fluid, give a fixing T2 cutoff hole.

8, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 7 is characterized in that: described fixing T2 cutoff is 33ms.

9, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 4, it is characterized in that: the computing method of bimodal pattern logging T 2 spectral T 2 end value are in the described step 2, utilize normal function to simulate a centrifugal spectrum on well logging T2 spectrum, its mathematical form is:

$f\left(x\right)=A\×e^{-\frac{{(x-\mathrm{\μ})}^2}{2{\mathrm{\σ}}^2}}$

Wherein:

A is a match T2 spectral amplitude value, and the A value is got the amplitude at first peak in the T2 distribution profile, even the functional digraph of match has identical amplitude with the T2 distribution profile;

μ is the expectation value of match T2 spectrum, and the μ value is got the pairing T2 time value of first peak value;

σ is the variance of match T2 spectrum;

X is that the T2 time value of each component is identical with the T2 time value of well logging T2 spectrum;

The range value that f (x) obtains for match.

10, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 4, it is characterized in that: the computing method of three peak type logging T 2 spectral T 2 end values simulate a centrifugal spectrum for utilizing normal function in the described step 2 on well logging T2 spectrum, and its mathematical form is:

$f\left(x\right)=A\×e^{-\frac{{(x-\mathrm{\μ})}^2}{2{\mathrm{\σ}}^2}}$

Wherein:

A is a match T2 spectral amplitude value, and the A value is got the amplitude at first peak in the T2 distribution profile, even the functional digraph of match has identical amplitude with the T2 distribution profile;

μ is the expectation value of match T2 spectrum, and the μ value is got the pairing T2 time value of first peak value;

σ is the variance of match T2 spectrum;

X is that the T2 time value of each component is identical with the T2 time value of well logging T2 spectrum;

The range value that f (x) obtains for match.

11, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 1, it is characterized in that: the computing method of the T2 cutoff in the described step 5 are, the area of well logging T2 spectrum is added up, when cumulative area equaled or be the most close with the centrifugal spectrum area, this moment, corresponding T2 value was the T2 cutoff.

12, definite method of nuclear magnetic resonance logging T 2 spectral T 2 end value according to claim 1 is characterized in that: the computing method of described area are carried out area integral for the Romber integral method.

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