CN104278989B - Method for obtaining saturability index of low porosity and low permeability reservoir - Google Patents
Method for obtaining saturability index of low porosity and low permeability reservoir Download PDFInfo
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Abstract
The invention discloses a method for obtaining the saturability index of a low porosity and low permeability reservoir and belongs to the field of reservoir assessment. According to the method, the rock core nuclear magnetic resonance T2 spectrum, T2 geometric mean value, T2 cutoff value, rock core water saturation and rock core resistivity index are obtained through the nuclear magnetic resonance experiment and rock core resistivity experiment conducted on a rock core sample, and the computation model of the saturation index n of the low porosity and low permeability reservoir is established. By means of the establishment of the computation formula of the saturation index n of the low porosity and low permeability reservoir, the variable saturability index n, changing along with the pore structure, of the low porosity and low permeability reservoir can be obtained continuously and accurately.
Description
Technical field
The present invention relates to evaluating reservoir field, particularly to a kind of method obtaining low porosity and low permeability reservoir saturation exponent.
Background technology
Water saturation refers in oil reservoir, the ratio of the pore volume shared by water and rock pore volume.Water saturation
It is one of evaluating reservoir, reserves calculating very important parameter.At present, reservoir water saturation the most effectively obtains
Method is to utilize Archie formula, to calculate water saturation in conjunction with conventional logging porosity and resistivity.Public based on A Erqi
The water saturation computing formula of formula is as follows：
In formula,
Rw----formation water resistivity, Ω .m；
Rt----oil-bearing rock resistivity, Ω .m；
----rock porosity, decimal；
M---- cementation factor；
Sw----water saturation, decimal；
N---- saturation exponent；
A the and b---- coefficient relevant with lithology, its value is often 1.0.
At present, in low porosity and low permeability reservoir, affected by Complicated Pore Structures, the value leading to saturation exponent is not
Fixed value, but be in dependency relation and pore structure between, i.e. the better rock of pore structure, the value of saturation exponent is lower,
Conversely, the poorer rock of pore structure, the value of saturation exponent is higher.Therefore, in order to accurately calculate low porosity and low permeability complexity hole
The water saturation of structure reservoir is it is thus necessary to determine that variable saturation exponent with pore structure change.Relevant special according to stratum
Levy calculate variable saturation exponent method have following several：
（1）According to Reservoir Flow Unit difference, core sample is divided into three major types, for the rock core of different flow units
Sample, does water saturation-resistivity index cross plot, then adopts the method that power function returns, respectively obtains each rocks
Saturation exponent value.Then, in actual formation evaluation, adopt and core sample identical flow unit criteria for classification, will
Reservoir division is three classes, and the reservoir for each type is respectively adopted different saturation exponents to calculate water saturation.
（2）In the case of water according to same sample saturation difference salinity, the measurement result of saturation exponent value, summarizes
Go out the rule that n value changes with saturation water salinity：Under the conditions of low mineralization, rock saturation exponent is with the increasing of porosity
Big and increase, and under conditions of the salinity working as water used by saturated core is more than 200000mg/L, saturation exponent and porosity
Relation less, and trends towards a stationary value.Based on this rule, draw respectively in known a certain saturation water salinity condition
Under n value calculate another under the conditions of n value and in the case of just knowing that formation porosity and formation water salinity calculating saturation degree refer to
The method of number n.
（3）By the geologic(al) factor of analyzing influence compact clastic rock n value, including porosity size, cement type and its
On the basis of content and particle mean size, according to porosity, granularity and cement cubage saturation exponent.
During realizing the present invention, inventor finds that prior art at least has problems with：
Although existing method is variable according to the saturation exponent of stratum feature calculation, it is not as earth bore
The consecutive variations of gap structure and continuous, the change of pointwise, for the stratum with Complicated Pore Structures, its pore structure meeting
There are consecutive variations, saturation exponent can occur consecutive variations with the consecutive variations of pore structure.Therefore, for having
The low porosity and low permeability reservoir of Complicated Pore Structures, existing method does not enable the calculating to continually varying reservoir saturation exponent.
Content of the invention
It is not carried out asking according to the variable saturation exponent of pore structure characteristic node-by-node algorithm in order to solve prior art
Topic, embodiments provides a kind of method obtaining low porosity and low permeability reservoir saturation exponent.Described technical scheme is as follows：
A kind of method obtaining low porosity and low permeability reservoir saturation exponent, methods described is carried out in accordance with the following steps：
1）Choose core sample, nuclear magnetic resonance experiment is carried out to described core sample, obtains T2Geometrical mean T2lm；
2）Obtain irreducible water saturation S of core samplewi；
3）Using described T2Geometrical mean T2lmWith described irreducible water saturation Swi, calculate low porosity and low permeability reservoir saturation degree
Index n, is specifically calculated according to such as drag,
In formula：N---- reservoir saturation exponent；
Swi----irreducible water saturation；
----rock core macrovoid component and the ratio of fine pore component, characterize RESERVOIR PORE STRUCTURE;
T2lm----T2Geometrical mean；
C---- model parameter；
A---- model parameter；
B---- model parameter.
Specifically, described irreducible water saturation S obtaining core samplewiIt is specially：First obtain multiple described core samples
Unified T2Cutoff T2cutoff, recycle unified T2Cutoff T2cutoffObtain irreducible water saturation S of core samplewi.
Specifically, the described unified T obtaining multiple described core samples2Cutoff T2cutoffIt is specially：Obtain rock core first
The T of sample2Cutoff, the then T to multiple core samples2Cutoff, according to sequentially being counted from small to large, is chosen and frequency
Rate highest T2Cutoff is as the unified T of multiple described core samples2Cutoff T2cutoff.
Specifically, the described T obtaining core sample2Cutoff is specially：Nuclear magnetic resonance T is obtained by nuclear magnetic resonance experiment2
Spectrum, in described nuclear magnetic resonance T2The T of described core sample is obtained on spectrum2Cutoff.
Specifically, described utilization unification T2Cutoff T2cutoffObtain irreducible water saturation S of core samplewiIt is specially：
Using unified T2Cutoff T2cutoff, rock core 100% is full of the T under water state2Spectrum is divided into two parts, T2Relaxation time is less than institute
State unified T2Cutoff T2cutoffT2Spectrum area encompassed and T2Relaxation time is more than described unified T2Cutoff T2cutoff's
T2Spectrum area encompassed, calculates T2Relaxation time is less than described unified T2Cutoff T2cutoffT2The face of spectrum area encompassed
Amass and T2Compose the ratio of the surrounded area of overall area, as irreducible water saturation Swi.
Specifically, described nuclear magnetic resonance experiment is full of the nuclear magnetic resonance experiment under water state for core sample 100%.
Specifically, described step 1）Described in obtain described T2Geometrical mean T2lmIt is specially：By nuclear magnetic resonance experiment
Obtain nuclear magnetic resonance T2Spectrum, in described nuclear magnetic resonance T2Described T is obtained on spectrum2Geometrical mean T2lm.
Specifically, described obtain nuclear magnetic resonance T2That composes is specially：Rock core is obtained by described rock core nuclear magnetic resonance experiment
Nmr spin echo string, and inversion procedure is carried out to described spin echo string, obtain described nuclear magnetic resonance T2Spectrum.
Further, described step 1）Also include afterwards：Carry out rock core resistivity experiment, obtain containing of every piece of core sample
Water saturation and resistivity index.
Specifically, described step 3）Described model parameter C, a and the value of b obtained using the method matching of multivariate statistical regression
Arrive, specially：First pass through the water saturation making described every piece of core sample and resistivity index cross plot, and adopt power letter
Number return methods, obtain every piece of core sample saturation exponent, then by the saturation exponent of all core samples, with
And irreducible water saturation S of corresponding core samplewiAnd T2Geometrical mean, substitutes into the calculating mould of described reservoir saturation exponent
TypeIn, the method matching using multivariate statistical regression obtains.
The beneficial effect that technical scheme provided in an embodiment of the present invention is brought is：
By using NMR logging data set up low porosity and low permeability reservoir saturation exponent computing formula it is achieved that
Obtain the purpose of the saturation exponent of low porosity and low permeability reservoir continuous variable.
Brief description
For the technical scheme being illustrated more clearly that in the embodiment of the present invention, will make to required in embodiment description below
Accompanying drawing be briefly described it should be apparent that, drawings in the following description are only some embodiments of the present invention, for
For those of ordinary skill in the art, on the premise of not paying creative work, other can also be obtained according to these accompanying drawings
Accompanying drawing.
Fig. 1 is a kind of method flow diagram obtaining low porosity and low permeability reservoir saturation exponent provided in an embodiment of the present invention；
Fig. 2 is that 4, the gas field in domestic southwest provided in an embodiment of the present invention low porosity and low permeability core sample contains water saturation
Degree-resistivity index cross plot；
Fig. 3 is full of for 4, the gas field in domestic southwest provided in an embodiment of the present invention low porosity and low permeability core sample 100%
Nuclear magnetic resonance T under water state2Spectrum；
Fig. 4 is that mercury hollow billet pressed by 4, domestic southwest provided in an embodiment of the present invention gas field low porosity and low permeability core sample
Pressure curve；
Fig. 5 is that the body of casting of No. 1 low porosity and low permeability core sample in domestic southwest provided in an embodiment of the present invention gas field is thin
Piece schematic diagram；
Fig. 6 is that the body of casting of No. 3 low porosity and low permeability core samples in domestic southwest provided in an embodiment of the present invention gas field is thin
Piece schematic diagram；
Fig. 7 is 20 pieces of domestic the Northwest provided in an embodiment of the present invention oil field low porosity and low permeability core sample nuclear magnetic resonance
T2Cutoff statistic histogram；
Fig. 8 is the reservoir saturation exponent using technology of the present invention calculating provided in an embodiment of the present invention and rock core
The comparison diagram of sample saturation exponent；
Fig. 9 is the variable reservoir saturation exponent using technical limit spacing of the present invention provided in an embodiment of the present invention
Calculate the design sketch of reservoir water saturation.
Specific embodiment
For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing to embodiment party of the present invention
Formula is described in further detail.
The principle of the present invention：
The present invention is real in substantial amounts of low porosity and low permeability reservoir core resistivity, nuclear magnetic resonance, pressure mercury and casting body flake translocation
Launch on the basis of testing.
Wherein, described rock core nuclear magnetic resonance experiment according to《Rock sample nuclear magnetic resonance parameter laboratory measurement specification SY/T6490-
2007》The regulation of standard is carried out；The experiment of described rock core resistivity according to《Rock resistivity Experiment Parameter room methods of measurement and calculation
SY/T5385-2007》The regulation of standard is carried out；Described pressure mercury experiment according to《Mensure SY/T5346- of rock capillary pressure curve
2005》The regulation of standard is carried out；The experiment of described casting body flake according to《Rock flaking method SY/T5913-2004》The regulation of standard
Carry out.
Below with the resistivity of the 4 pieces of low porosity and low permeability representative core samples in Southwestern China certain gas field of area, nuclear magnetic resonance, pressure
Illustrate as a example mercury and casting body flake translocation experiment.Experimental result is as shown in figures 2-6.Fig. 2 is domestic southwest gas field 4
Water saturation-resistivity index the cross plot of block low porosity and low permeability representative core sample, wherein, X-axis is water saturation, can
Decimally to represent, Y-axis is resistivity index；Fig. 3 is that the nuclear magnetic resonance that corresponding 4 pieces of core samples 100% are full of under water state is surveyed
Well T2Spectrum, wherein, X-axis is T2In the relaxation time, unit can be ms, and Y-axis is T2Amplitude, unit can be v/v；Fig. 4 is corresponding 4
The pressure mercury capillary pressure curve of block core sample, wherein, X-axis is into mercury saturation degree, %；Y-axis is into mercury pressure, MPa；Fig. 5 is 1
The schematic diagram of the casting body flake of number sample, Fig. 6 is the schematic diagram of the casting body flake of No. 3 samples.
Referring to Fig. 2,4 core sample saturation exponents are significantly different, and its excursion changes to from 1.6628
2.8656.
No. 1 sample that saturation exponent is equal to 1.6628（Referring to Fig. 2）, nuclear-magnetism T2The wider distribution of spectrum, maximum T2Relaxation
Time reaches 2000ms, and based on bimodal macrovoid, the position at movable peak concentrates between 350-400ms（Referring to Fig. 3）；No. 1
The rock core of sample presses mercury capillary pressure curve position on the lower, based on big pore throat（Referring to Fig. 4）；No. 1 sample casting body flake experiment
The ligancy of display is 1.22, illustrates that pore communication is preferable（Referring to Fig. 5）；
No. 2 samples that saturation exponent is equal to 2.0358（Referring to Fig. 2）, 100% is full of the nuclear magnetic resonance survey under water state
Well T2Spectrum is based on bimodal macrovoid, but maximum T2Relaxation time is less than No. 1 sample, and the distribution at movable peak is between 100-
Between 150ms（Referring to Fig. 3）, press the position of mercury capillary pressure curve top relative to No. 1 sample（Referring to Fig. 4）, show No. 2 samples
Pore structure compared with No. 1 sample difference.
No. 3 samples that saturation exponent is equal to 2.5703（Referring to Fig. 2）, 100% is full of the nuclear magnetic resonance survey under water state
Well T2Compose based on bimodal fine pore, maximum T2Relaxation time is less than No. 1 and No. 2 samples, and the distribution at movable peak is between 75-
Between 140ms（Referring to Fig. 3）, relative to No. 1 and No. 2 samples are top for the position of pressure mercury capillary pressure curve（Referring to Fig. 4）.The body of casting is thin
The ligancy of piece experiment No. 3 samples of display is equal to 0.88, and pore communication is compared with No. 1 sample difference（Referring to Fig. 6）.
No. 4 samples that saturation exponent is equal to 2.8656（Referring to Fig. 2）, 100% is full of the nuclear magnetic resonance survey under water state
Well T2Spectrum shows as unimodal, and the relaxation time is shorter, exists almost without movable peak（Referring to Fig. 3）, press mercury capillary pressure curve position
The top in Fig. 4, the pore structure of reflection rock is worst（Referring to Fig. 4）.
By carry out the resistivity of substantial amounts of similar above-mentioned low porosity and low permeability reservoir core sample, nuclear magnetic resonance, pressure mercury and
Casting body flake translocation is tested, and inventor finds that the saturation exponent of low porosity and low permeability reservoir rock does not trend towards some and fixes
Value, but the amount changing between some scope.Close phase between the change of saturation exponent and corresponding rock pore structure
Close.The better rock of pore structure, 100% is full of nuclear magnetic resonance log T under water state2The wider distribution of spectrum, T2Spectrum is with bimodal big
Based on hole, and T2Movable T corresponding to peak position in spectrum2Relaxation time is longer, and rock pressure mercury capillary pressure curve position is relatively
On the lower, based on big pore throat, rock ligancy（Characterize pore communication）Higher, the corresponding rock saturation that resistivity experiment obtains
Index n is less for degree.Conversely, the poorer rock of pore structure, 100% is full of nuclear magnetic resonance log T under water state2The distribution of spectrum is relatively
Narrow, T2Spectrum is based on unimodal fine pore, and T2Movable T corresponding to peak position in spectrum2Relaxation time is shorter or even no movable peak,
Rock pressure mercury capillary pressure curve position is relatively top, based on little pore throat, rock ligancy（Characterize pore communication）It is relatively low,
The corresponding rock saturation exponent that resistivity experiment obtains is larger.
The present invention on the basis of above-mentioned experiment, the proposition shared proportion in total pore space of reservoir rock fine pore component
To reflect pore structure.Proportion shared by the component of rock fine pore is bigger, and the proportion shared by macrovoid component is then less, reflects rock
The pore structure of stone is poorer, and the corresponding rock saturation exponent that resistivity experiment obtains is also bigger.Conversely, rock fine pore group
Point proportion is less, and the proportion shared by corresponding macrovoid component is then bigger, and the pore structure of rock is better, and resistivity is tested
The corresponding rock saturation exponent obtaining is also less.
In order to visual rationing characterizes reservoir rock fine pore component proportion in total pore space, inventor is proposed for institute
Some rock core nuclear magnetic resonance experiment samples, using unified T2Cutoff, from nuclear magnetic resonance log T2Calculate irreducible water in spectrum to satisfy
With degree Swi, and the ratio using macrovoid component and rock total pore space proportion shared by the component of fine poreTo characterize rock
Pore structure.The better rock of pore structure, the proportion shared by macrovoid component is bigger, using unified T2Cutoff calculates
Irreducible water saturation SwiCan be lower, thenBigger.Conversely, the poorer rock of pore structure, the ratio shared by the component of fine pore
Again bigger, using unified T2Cutoff calculates irreducible water saturation SwiCan be higher, thenLess.Meanwhile, nuclear magnetic resonance
Well logging T2Geometrical mean T2lmIt is T2The macroscopic view reflection of spectrum, T2Spectral structure is wider, and more keep right in the position at movable peak, then T2lmAlso get over
Greatly, on the contrary then T2lmAlso less.
On the basis of above-mentioned a large amount of theory analysises and core experiment result it is determined that low porosity and low permeability of the present invention complexity hole
The computation model of structure reservoir saturation exponent, that is,：
In formula：N---- reservoir saturation exponent；
Swi----irreducible water saturation；
--- the ratio of-rock core macrovoid component and fine pore component;
T2lm----T2Geometrical mean；
C---- model parameter；
A---- model parameter；
B---- model parameter.
In above formula, the determination method of parameter C, a and b is as follows：
The determination of C, a and b relies on core sample experiment to carry out scale and completes, include the resistivity experiment of identical core sample with
Nuclear magnetic resonance experiment.By the resistivity experiment of core sample, obtain every piece of core sample water saturation and resistivity index,
By doing every piece of core sample water saturation and resistivity index cross plot, using the method for power function recurrence, obtain every piece
The saturation exponent of core sample；Meanwhile, identical core sample is carried out with nuclear magnetic resonance experiment, obtains rock core nuclear magnetic resonance certainly
Cycle wave train, and spin echo string is carried out after inversion procedure, obtain rock core nuclear magnetic resonance T2Spectrum, to the nuclear magnetic resonance being obtained
T2Spectrum carries out process and obtains corresponding nuclear-magnetism T2Geometrical mean T2lmAnd T2Cutoff, the method using statistics with histogram obtains rock
The unified T of heart sample2Cutoff simultaneously calculates irreducible water saturation Swi, finally by the saturation exponent of all core samples and
Corresponding nuclear-magnetism T2Geometrical mean T2lmWith irreducible water saturation SwiSubstitute in the computation model of above-mentioned reservoir saturation exponent,
Method matching using multivariate statistical regression obtains the value of C, a and b.
Specific embodiment：
Referring to Fig. 1, a kind of method of acquisition low porosity and low permeability reservoir saturation exponent, carry out in accordance with the following steps：
Step one：Choose low porosity and low permeability core sample, carry out resistivity experimental study, obtain core sample water saturation
And resistivity index, by doing every piece of core sample water saturation and resistivity index cross plot, returned using power function
Method, obtains the saturation exponent of every piece of core sample.
In the embodiment of the present invention, choose 20 pieces of domestic the Northwest oil field low porosity and low permeability core sample and carry out resistivity in fact
Test, as shown in figure 8, in figure, X-axis is passed through electric for core sample for every piece of core sample water saturation and resistivity index cross plot
The saturation exponent that the experiment of resistance rate obtains.
Step 2：Core sample is carried out with nuclear magnetic resonance experiment, obtains the nmr spin echo string of core sample, and
Spin echo string is carried out obtaining after inverting with the nuclear magnetic resonance T of core sample2Spectrum, to the nuclear magnetic resonance T being obtained2At spectrum
Reason obtains corresponding nuclear magnetic resonance T2Geometrical mean T2lmAnd T2Cutoff.
In the embodiment of the present invention, nuclear magnetic resonance experiment is carried out to 20 pieces of core samples of identical of above-mentioned selection, obtain every piece
The T of core sample2Geometrical mean T2lmAnd T2Cutoff.Result is as shown in table 1.
The nuclear magnetic resonance experiment data of 1 20 pieces of core samples of table
Step 3：The T of 20 pieces of core samples that step 2 is obtained2Cutoff, counts according to order from small to large
Histogram, chooses frequency of occurrences highest T2Cutoff is the unified T of all core samples2Cutoff T2cutoff.
T to the 20 pieces of core samples obtaining in the embodiment of the present invention2Cutoff obtains 20 blocks of rock cores according to the method described above
The unified T of sample2Cutoff T2cutoff, result is as shown in Figure 7.Wherein, X-axis is T2Cutoff, unit is ms；Y-axis is divided for frequency
Implantation.It can be seen from figure 7 that the corresponding T of frequency distribution peak2Cutoff between 15.0ms to 20.0ms, averagely
It is worth for 18.05ms.Therefore, select 18.05ms as the unified T of 20 pieces of core samples2Cutoff T2cutoff.
Step 4：Unified T is obtained using step 32Cutoff T2cutoffCalculate irreducible water saturation Swi, and calculate table
Levy the parameter of RESERVOIR PORE STRUCTURE
In the embodiment of the present invention, using 18.05ms as unified T2Cutoff T2cutoffCalculate the constraint of 20 pieces of core samples
Water saturation Swi, and calculate the parameter characterizing RESERVOIR PORE STRUCTUREResult is as shown in table 1.
Step 5：The T of the core sample that core sample saturation exponent that step one is obtained, step 2 are obtained2
Geometrical mean T2lmIrreducible water saturation S with the core sample acquired in step 4wi, substitute into the meter of reservoir saturation exponent
Calculate in model, the method matching using multivariate statistical regression obtains model parameter C, a and b.The meter of described reservoir saturation exponent
Calculate model to be specially：
In formula：N---- reservoir saturation exponent；
Swi----irreducible water saturation, decimal；
----rock core macrovoid component and the ratio of fine pore component, characterize RESERVOIR PORE STRUCTURE;
T2lm----nuclear magnetic resonance T2Geometrical mean, ms；
C---- model parameter；
A---- model parameter；
B---- model parameter.
In the embodiment of the present invention, all 20 pieces of core sample saturation exponents, step 2 that step one is obtained are obtained
The T of all 20 pieces of core samples obtaining2Geometrical mean T2lmIrreducible water with all 20 pieces of core samples acquired in step 4
Saturation degree Swi, substitute in the computation model of reservoir saturation exponent, model ginseng obtained using the method matching of multivariate statistical regression
Number C, a and b, can be respectively by the value being calculated C, a and b：C=2.361, a=-0.0605, b=-0.111.
Step 6：Model parameter C, a and b are substituted into the computation model of described reservoir saturation exponent, be obtained by nuclear-magnetism
Resonance well-log information calculates the computation model of low porosity and low permeability saturation exponent.
In the embodiment of the present invention, the value of C, a and b can be specially：C=2.361, a=-0.0605, b=-0.111, obtain
The computation model calculating low porosity and low permeability saturation exponent can be specially：
Using the acquisition methods of above-mentioned reservoir saturation exponent, calculate the saturation exponent of reservoir different depth, and
The saturation exponent being obtained with the core sample resistivity experiment of corresponding depth is contrasted, and result is as shown in figure 8, X-axis is rock
The saturation exponent that the experiment of heart sample resistivity obtains, Y-axis is the reservoir saturation exponent being calculated using technology of the present invention
N, as can be seen from Figure 8, the reservoir saturation exponent being obtained by computation model provided in an embodiment of the present invention with by reality
The saturation exponent testing the core sample of acquisition is substantially identical, more than 90% reservoir saturation exponent fall ± 0.3 error
Within the scope of, the reservoir saturation exponent being obtained by computation model and the saturation by testing the core sample obtaining are described
The degree of agreement of degree index n is high.
Using the method obtaining low porosity and low permeability reservoir saturation exponent provided in an embodiment of the present invention, obtain saturation exponent
N, and it is updated to Archie formula, specially：
In formula,
Rw----formation water resistivity, Ω .m；
Rt----oil-bearing rock resistivity, Ω .m；
----rock porosity, decimal；
M---- cementation factor；
Sw----water saturation, decimal；
N---- saturation exponent；
A the and b---- coefficient relevant with lithology, its value is often 1.0.
Calculate water saturation S of low porosity and low permeability reservoirw, the value of wherein each parameter is Rw：0.075Ω.m；Rt：Referring to
Numerical value shown in Fig. 9 the 3rd channel array induction motor curve；：Referring to numerical value shown in Fig. 9 the 6th road core analysis porosity；m：
1.45；a：1.0；b：1.0.
The saturation exponent and aqueous that will be obtained using the computing formula of saturation exponent provided in an embodiment of the present invention
Saturation degree SwWith experiment obtain the saturation exponent of core sample and water saturation contrasted, its effect such as Fig. 9 institute
Show.Design sketch shown in Fig. 9 is divided into eight roads, and in figure includes gamma ray curve first（GR）, spontaneous potential curve（SP）
And CAL（CAL）, it is mainly used in identifying effective sandstone reservoir；Second is depth track, unit m；3rd road is array sense
Answer resistivity curve；4th road includes density log（RHOB）Curve, neutron well logging（NPHI）Curve and acoustic travel time logging
（DT）Curve, is mainly used in calculating the porosity of reservoir；5th road includes the nuclear magnetic resonance log T of actual measurement2Spectrum T2_
Distribution, nuclear magnetic resonance log T2Geometrical mean T2lm, unified T2Cutoff T2cutoff, its value is 18.05ms；6th
Road includes nuclear-magnetism total porosity PHIT, core analysis porosity Core_Por.From in figure nuclear-magnetism porosity and core analysis hole
The contrast of degree can be seen, the porosity obtaining from NMR logging data is accurate, can represent the true of stratum
Porosity, which ensure that aftermentioned water saturation will not be because insecure formation porosity be to the meter of water saturation in calculating
Calculation brings extra error；7th road Calc_n is to calculate, using method provided in an embodiment of the present invention, the reservoir saturation degree obtaining to refer to
Number n；8th road Sw is to calculate degree of the becoming saturated index n obtaining to calculate containing of acquisition using method provided in an embodiment of the present invention
Water saturation, the water saturation that Core_Sw obtains for sealing core data.It can be seen that using variable reservoir
The water saturation that saturation exponent calculates is close to core experiment result.This explanation, using utilization provided in an embodiment of the present invention
The method that NMR logging data calculates low porosity and low permeability reservoir saturation exponent, can accurately obtain reflection reservoir pore space knot
Degree of the becoming saturated index n of structure change, accurately to calculate reservoir water saturation.
The foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention, all spirit in the present invention and
Within principle, any modification, equivalent substitution and improvement made etc., should be included within the scope of the present invention.
Claims (8)
1. a kind of method obtaining low porosity and low permeability reservoir saturation exponent is it is characterised in that methods described is entered in accordance with the following steps
OK：
1) choose core sample, carry out rock core resistivity experiment, obtain the water saturation of every piece of core sample and resistivity refers to
Number；Nuclear magnetic resonance experiment is carried out to described core sample, obtains T2Geometrical mean T2lm；
2) obtain irreducible water saturation S of core samplewi；
3) utilize described T2Geometrical mean T2lmWith described irreducible water saturation Swi, calculate low porosity and low permeability reservoir saturation exponent
N, is specifically calculated according to such as drag,
In formula：N---- reservoir saturation exponent；
Swi----irreducible water saturation；
----rock core macrovoid component and the ratio of fine pore component, characterize RESERVOIR PORE STRUCTURE；
T2lm----T2Geometrical mean；
C---- model parameter；
A---- model parameter；
B---- model parameter；
The value of described model parameter C, a and b is obtained using the method matching of multivariate statistical regression, specially：First pass through and do institute
State water saturation and the resistivity index cross plot of every piece of core sample, and the method returning using power function, obtain every piece
The saturation exponent of core sample, then by the constraint of the saturation exponent of all core samples and corresponding core sample
Water saturation SwiAnd T2Geometrical mean, substitutes into the computation model of described reservoir saturation exponent
In, the method matching using multivariate statistical regression obtains.
2. the method for claim 1 is it is characterised in that irreducible water saturation S of described acquisition core samplewiSpecifically
For：First obtain the unified T of multiple described core samples2Cutoff T2cutoff, recycle unified T2Cutoff T2cutoffObtain rock core
Irreducible water saturation S of samplewi.
3. method as claimed in claim 2 is it is characterised in that the unified T of the multiple described core sample of described acquisition2Cutoff
T2cutoffIt is specially：Obtain the T of core sample first2Cutoff, the then T to multiple core samples2Cutoff according to from little to
Sequentially counted greatly, chosen frequency of occurrences highest T2Cutoff is as the unified T of multiple described core samples2Cutoff
T2cutoff.
4. method as claimed in claim 3 is it is characterised in that the described T obtaining core sample2Cutoff is specially：By core
Magnetic resonance experiments obtain nuclear magnetic resonance T2Spectrum, in described nuclear magnetic resonance T2The T of described core sample is obtained on spectrum2Cutoff.
5. method as claimed in claim 2 is it is characterised in that described utilize unified T2Cutoff T2cutoffObtain core sample
Irreducible water saturation SwiIt is specially：Using unified T2Cutoff T2cutoff, rock core 100% is full of the T under water state2Spectrum point
For two parts, T2Relaxation time is less than described unified T2Cutoff T2cutoffT2Spectrum area encompassed and T2Relaxation time is more than
Described unified T2Cutoff T2cutoffT2Spectrum area encompassed, calculates T2Relaxation time is less than described unified T2Cutoff
T2cutoffT2The area of spectrum area encompassed and T2Compose the ratio of the surrounded area of overall area, as fetter water saturation
Degree Swi.
6. the method for claim 1 is it is characterised in that described nuclear magnetic resonance experiment is full of water for core sample 100%
Nuclear magnetic resonance experiment under state.
7. the method for claim 1 is it is characterised in that described step 1) described in obtain described T2Geometrical mean T2lm
It is specially：Nuclear magnetic resonance T is obtained by nuclear magnetic resonance experiment2Spectrum, in described nuclear magnetic resonance T2Described T is obtained on spectrum2Geometric average
Value T2lm.
8. the method as described in claim 4 or 7 is it is characterised in that described obtain nuclear magnetic resonance T2Spectrum, specially：By rock core
Nuclear magnetic resonance experiment obtains rock core nmr spin echo string, and carries out inversion procedure to described spin echo string, obtains institute
State nuclear magnetic resonance T2Spectrum.
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