CN104278989A - 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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- CN104278989A CN104278989A CN201310274726.XA CN201310274726A CN104278989A CN 104278989 A CN104278989 A CN 104278989A CN 201310274726 A CN201310274726 A CN 201310274726A CN 104278989 A CN104278989 A CN 104278989A
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
- G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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- G—PHYSICS
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- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
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 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 voids volume shared by water and rock pore volume.Water saturation is a very important parameter in evaluating reservoir, reserves calculating.At present, reservoir water saturation the most effective acquisition methods utilizes Archie formula, calculates water saturation in conjunction with conventional logging degree of porosity and resistivity.Water saturation design formulas based on Archie formula is as follows:
In formula,
R
w----formation water resistivity, Ω .m;
R
t----oil-bearing rock resistivity, Ω .m;
----rock porosity, decimal;
M----cementation factor;
S
w----water saturation, decimal;
N----saturation exponent;
The coefficient that a with b----is relevant with lithology, its value is often 1.0.
At present, in low porosity and low permeability reservoir, by the impact of Complicated Pore Structures, the value of saturation exponent is caused not to be fixed value, but and in dependency relation between pore structure, the rock that namely pore structure is better, the value of saturation exponent is lower, otherwise the rock that pore structure is poorer, the value of saturation exponent is higher.Therefore, in order to accurately calculate the water saturation of low porosity and low permeability Complicated Pore Structures reservoir, need to determine the variable saturation exponent with pore structure change.About having following several according to the method for the variable saturation exponent of stratum feature calculation:
(1) according to Reservoir Flow Unit difference, core sample is divided into three major types, for the core sample of various flows moving cell, does water saturation-resistivity index cross plot, then the method adopting power function to return, obtains the saturation exponent value of each rocks respectively.Then, in actual formation is evaluated, adopt the flow unit criteria for classification identical with core sample, be three classes by reservoir division, the reservoir for each type adopts different saturation exponents to calculate water saturation respectively.
(2) measurement result of saturation exponent value when water according to the saturated different salinity of same sample, sum up the rule that n value changes with saturation water salinity: under low mineralization condition, rock saturation exponent increases along with the increase of degree of porosity, and under the salinity of saturated core water used is greater than the condition of 200000mg/L, saturation exponent and degree of porosity relation not quite, and trend towards a stationary value.Based on this rule, show that n value under known a certain saturation water salinity condition calculates the n value under another condition and calculates the method for saturation exponent under only knowing formation porosity and formation water salinity situation respectively.
(3) by the geologic(al) factor of analyzing influence compact clastic rock n value, comprise on the basis of degree of porosity size, cement type and content and particle mean size, according to degree of porosity, granularity and cement cubage saturation exponent.
Realizing in process of the present invention, inventor finds that prior art at least exists following problem:
Although existing method is variable according to the saturation exponent of stratum feature calculation, but not the change of continuous print, pointwise along with the consecutive variations of formation pore structure, for the stratum with Complicated Pore Structures, can there is consecutive variations in its pore structure, saturation exponent along with the consecutive variations of pore structure, consecutive variations can occur.Therefore, for the low porosity and low permeability reservoir with Complicated Pore Structures, existing method can not realize the calculating to continually varying reservoir saturation exponent.
Summary of the invention
In order to solve the problem that prior art does not realize according to the variable saturation exponent of pore structure characteristic node-by-node algorithm, embodiments provide a kind of method obtaining low porosity and low permeability reservoir saturation exponent.Described technical scheme is as follows:
Obtain a method for low porosity and low permeability reservoir saturation exponent, described method 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 T
2geometrical mean T
2lm;
2) the irreducible water saturation S of core sample is obtained
wi;
3) described T is utilized
2geometrical mean T
2lmwith described irreducible water saturation S
wi, calculate low porosity and low permeability reservoir saturation exponent, specifically calculate according to such as drag,
In formula: n----reservoir saturation exponent;
S
wi----irreducible water saturation;
---the ratio of-rock core macrovoid component and fine pore component, characterizes RESERVOIR PORE STRUCTURE;
T
2lm----T
2geometrical mean;
C----model parameter;
A----model parameter;
B----model parameter.
Concrete, the irreducible water saturation S of described acquisition core sample
wibe specially: the unified T first obtaining multiple described core sample
2cutoff T
2cutoff, the unified T of recycling
2cutoff T
2cutoffobtain the irreducible water saturation S of core sample
wi.
Concrete, the unified T of the multiple described core sample of described acquisition
2cutoff T
2cutoffbe specially: the T first obtaining core sample
2cutoff, then to the T of multiple core sample
2cutoff, according to sequentially adding up from small to large, chooses the T that the frequency of occurrences is the highest
2cutoff is as the unified T of multiple described core sample
2cutoff T
2cutoff.
Concrete, described in obtain the T of core sample
2cutoff is specially: obtain nuclear magnetic resonance T by nuclear magnetic resonance experiment
2spectrum, at described nuclear magnetic resonance T
2spectrum obtains the T of described core sample
2cutoff.
Concrete, the unified T of described utilization
2cutoff T
2cutoffobtain the irreducible water saturation S of core sample
wibe specially: utilize unified T
2cutoff T
2cutoff, rock core 100% is full of the T under water state
2spectrum is divided into two parts, T
2relaxation time is less than described unified T
2cutoff T
2cutofft
2compose the region and T that surround
2relaxation time is greater than described unified T
2cutoff T
2cutofft
2compose the region surrounded, calculate T
2relaxation time is less than described unified T
2cutoff T
2cutofft
2compose area and the T in the region surrounded
2compose the ratio of the area of the overall area surrounded, be irreducible water saturation S
wi.
Concrete, described nuclear magnetic resonance experiment is the nuclear magnetic resonance experiment under core sample 100% is full of water state.
Concrete, obtain described T described in described step 1)
2geometrical mean T
2lmbe specially: obtain nuclear magnetic resonance T by nuclear magnetic resonance experiment
2spectrum, at described nuclear magnetic resonance T
2spectrum obtains described T
2geometrical mean T
2lm.
Concrete, described in obtain nuclear magnetic resonance T
2being specially of spectrum: obtain rock core nmr spin echo string by described rock core nuclear magnetic resonance experiment, and inversion procedure is carried out to described spin echo string, obtain described nuclear magnetic resonance T
2spectrum.
Further, also comprise after described step 1): carry out the experiment of rock core resistivity, obtain water saturation and the resistivity index of every block core sample.
Concrete, the described model parameter C of described step 3), the value of a and b adopt the method matching of multivariate statistical regression to obtain, be specially: first by doing water saturation and the resistivity index cross plot of described every block core sample, and the method adopting power function to return, obtain the saturation exponent of every block core sample, then by the irreducible water saturation S of the saturation exponent of all core samples and corresponding core sample
wiand T
2geometrical mean, substitutes into the computation model of described reservoir saturation exponent
in, adopt the method matching of multivariate statistical regression to obtain.
The beneficial effect that the technical scheme that the embodiment of the present invention provides is brought is:
By the design formulas utilizing NMR logging data to set up low porosity and low permeability reservoir saturation exponent, achieve the object of the saturation exponent obtaining low porosity and low permeability reservoir continuous variable.
Accompanying drawing explanation
In order to be illustrated more clearly in the technical scheme in the embodiment of the present invention, below the accompanying drawing used required in describing embodiment is briefly described, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.
Fig. 1 is a kind of method flow diagram obtaining low porosity and low permeability reservoir saturation exponent that the embodiment of the present invention provides;
4, gas field, domestic southwest low porosity and low permeability core sample water saturation-resistivity index cross plot that Fig. 2 provides for the embodiment of the present invention;
Fig. 3 is full of the nuclear magnetic resonance T under water state for 4, gas field, domestic southwest low porosity and low permeability core sample 100% that the embodiment of the present invention provides
2spectrum;
4, gas field, the domestic southwest low porosity and low permeability core sample pressure mercury capillary pressure curve that Fig. 4 provides for the embodiment of the present invention;
The casting body flake schematic diagram of No. 1 low porosity and low permeability core sample in gas field, domestic southwest that Fig. 5 provides for the embodiment of the present invention;
The casting body flake schematic diagram of No. 3 low porosity and low permeability core samples in gas field, domestic southwest that Fig. 6 provides for the embodiment of the present invention;
20 pieces, oil field, the domestic the Northwest low porosity and low permeability core sample nuclear magnetic resonance T that Fig. 7 provides for the embodiment of the present invention
2cutoff statistic histogram;
What Fig. 8 provided for the embodiment of the present invention utilizes the reservoir saturation exponent of technique computes of the present invention and the comparison diagram of core sample saturation exponent;
The variable reservoir saturation exponent of technical limit spacing of the present invention that utilizes that Fig. 9 provides for the embodiment of the present invention calculates the design sketch of reservoir water saturation.
Detailed description of the invention
For making the object, technical solutions and advantages of the present invention clearly, below in conjunction with accompanying drawing, embodiment of the present invention is described further in detail.
Principle of the present invention:
The present invention launches on the basis that a large amount of low porosity and low permeability reservoir core resistivity, nuclear magnetic resonance, pressure mercury and casting body flake translocation are tested.
Wherein, described rock core nuclear magnetic resonance experiment carries out according to the regulation of " rock sample nuclear magnetic resonance parameter laboratory measurement specification SY/T6490-2007 " standard; Described rock core resistivity experiment is carried out according to the regulation of " rock resistivity Experiment Parameter room methods of measurement and calculation SY/T5385-2007 " standard; Described pressure mercury experiment is carried out according to the regulation of " the mensuration SY/T5346-2005 of rock capillary pressure curve " standard; Described casting body flake experiment is carried out according to the regulation of " rock flaking method SY/T5913-2004 " standard.
Be described for the resistivity of the 4 pieces of low porosity and low permeability representative core samples in Southwestern China certain gas field, area, nuclear magnetic resonance, pressure mercury and casting body flake translocation experiment below.Experimental result as shown in figures 2-6.Fig. 2 is the water saturation-resistivity index cross plot of the 4 pieces of low porosity and low permeability representative core samples in gas field, domestic southwest, and wherein, X-axis is water saturation, can represent decimally, and Y-axis is resistivity index; Fig. 3 is the nuclear magnetic resonance log T under corresponding 4 pieces of core samples 100% are full of water state
2spectrum, wherein, X-axis is T
2in the relaxation time, unit can be ms, and Y-axis is T
2amplitude, unit can be v/v; Fig. 4 is the pressure mercury capillary pressure curve of corresponding 4 pieces of core samples, wherein, X-axis for entering mercury saturation, %; Y-axis for entering mercury pressure, MPa; Fig. 5 is the schematic diagram of the casting body flake of No. 1 sample, and Fig. 6 is the schematic diagram of the casting body flake of No. 3 samples.
See Fig. 2,4 core sample saturation exponents are obviously different, and its excursion changes to 2.8656 from 1.6628.
No. 1 sample (see Fig. 2) that saturation exponent equals 1.6628, nuclear-magnetism T
2the wider distribution of spectrum, maximum T
2relaxation time reaches 2000ms, and based on bimodal macrovoid, the position at movable peak concentrates on (see Fig. 3) between 350-400ms; The rock core of No. 1 sample presses mercury capillary pressure curve position on the lower, based on large pore throat (see Fig. 4); The ligancy of No. 1 sample casting body flake experiment display is 1.22, illustrates that pore communication better (see Fig. 5);
No. 2 samples (see Fig. 2) that saturation exponent equals 2.0358,100% is full of the nuclear magnetic resonance log T under water state
2spectrum is based on bimodal macrovoid, but the maximum T2 relaxation time is less than No. 1 sample, the distribution between 100-150ms (see Fig. 3) at movable peak, the position of pressure mercury capillary pressure curve, relative to No. 1 sample top (see Fig. 4), shows the pore structure comparatively No. 1 sample difference of No. 2 samples.
No. 3 samples (see Fig. 2) that saturation exponent equals 2.5703,100% is full of the nuclear magnetic resonance log T under water state
2compose based on bimodal fine pore, maximum T
2relaxation time is less than No. 1 and No. 2 samples, the distribution between 75-140ms (see Fig. 3) at movable peak, presses the position of mercury capillary pressure curve relative to No. 1 and No. 2 samples top (see Fig. 4).The ligancy of casting body flake experiment display No. 3 samples equals 0.88, and pore communication is No. 1 sample difference (see Fig. 6) comparatively.
No. 4 samples (see Fig. 2) that saturation exponent equals 2.8656,100% is full of the nuclear magnetic resonance log T under water state
2spectrum shows as unimodal, and the relaxation time is shorter, almost there is (see Fig. 3) without movable peak, and pressure mercury capillary pressure curve is arranged in the top of Fig. 4, the pore structure the poorest (see Fig. 4) of reflection rock.
By carrying out the resistivity of a large amount of similar above-mentioned low porosity and low permeability reservoir core samples, nuclear magnetic resonance, pressure mercury and casting body flake translocation experiment, inventor finds that the saturation exponent of low porosity and low permeability reservoir rock does not trend towards some fixed values, but the amount changed between some scopes.Closely related between the change of saturation exponent and corresponding rock pore structure.The rock that pore structure is better, 100% is full of nuclear magnetic resonance log T under water state
2the wider distribution of spectrum, T
2spectrum is based on bimodal macrovoid, and T
2movable T corresponding to peak position in spectrum
2relaxation time is longer, and relatively on the lower, based on large pore throat, rock ligancy (sign pore communication) is higher in rock pressure mercury capillary pressure curve position, and the corresponding rock saturation exponent that resistivity experiment obtains is less.Otherwise the rock that pore structure is poorer, 100% is full of nuclear magnetic resonance log T under water state
2the narrow distribution of spectrum, T
2spectrum is based on unimodal fine pore, and T
2movable T corresponding to peak position in spectrum
2relaxation time is shorter even without movable peak, and rock pressure mercury capillary pressure curve position is relatively top, and based on little pore throat, rock ligancy (sign pore communication) is lower, and the corresponding rock saturation exponent that resistivity experiment obtains is larger.
The present invention is on the basis of above-mentioned experiment, and the proportion of proposition reservoir rock fine pore component shared by total pore space reflects pore structure.Proportion shared by the component of rock fine pore is larger, and the proportion shared by macrovoid component is then less, and the pore structure of reflection rock is poorer, and the corresponding rock saturation exponent that resistivity experiment obtains is also larger.Otherwise rock fine pore component proportion is less, the proportion shared by corresponding macrovoid component is then larger, and the pore structure of rock is better, and the corresponding rock saturation exponent that resistivity experiment obtains is also less.
In order to visual rationing characterizes reservoir rock fine pore component proportion in total pore space, inventor proposes for all rock core nuclear magnetic resonance experiment samples, adopts unified T
2cutoff, from nuclear magnetic resonance log T
2irreducible water saturation S is calculated in spectrum
wi, and utilize the ratio of rock total pore space proportion shared by macrovoid component and fine pore component
characterize the pore structure of rock.The rock that pore structure is better, the proportion shared by macrovoid component is larger, adopts unified T
2the irreducible water saturation S that cutoff calculates
wican be lower, then
larger.Otherwise the rock that pore structure is poorer, the proportion shared by the component of fine pore is larger, adopts unified T
2cutoff calculates irreducible water saturation S
wican be higher, then
less.Meanwhile, nuclear magnetic resonance log T
2geometrical mean T
2lmt
2the macroscopic view reflection of spectrum, T
2spectral structure is wider, and more keep right in the position at movable peak, then T
2lmalso larger, on the contrary then T
2lmalso less.
On the basis of above-mentioned a large amount of theory analysis and core experiment result, determine the computation model of low porosity and low permeability Complicated Pore Structures reservoir saturation exponent of the present invention, that is:
In formula: n----reservoir saturation exponent;
S
wi----irreducible water saturation;
---the ratio of-rock core macrovoid component and fine pore component;
T
2lm----T
2geometrical mean;
C----model parameter;
A----model parameter;
B----model parameter.
In above formula, the defining 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, and comprises resistivity experiment and the nuclear magnetic resonance experiment of identical core sample.Tested by the resistivity of core sample, obtain every block core sample water saturation and resistivity index, by doing every block core sample water saturation and resistivity index cross plot, the method adopting power function to return, obtains the saturation exponent of every block core sample; Meanwhile, nuclear magnetic resonance experiment is carried out to identical core sample, obtain rock core nmr spin echo string, and after inversion procedure is carried out to spin echo string, obtain rock core nuclear magnetic resonance T
2spectrum, to obtained nuclear magnetic resonance T
2spectrum is carried out process and is obtained corresponding nuclear-magnetism T
2geometrical mean T
2lmand T
2cutoff, adopts the method for statistics with histogram to obtain the unified T of core sample
2cutoff also calculates irreducible water saturation S
wi, finally by the nuclear-magnetism T of the saturation exponent of all core samples and correspondence
2geometrical mean T
2lmwith irreducible water saturation S
wisubstitute in the computation model of above-mentioned reservoir saturation exponent, adopt the method matching of multivariate statistical regression to obtain the value of C, a and b.
Specific embodiment:
See Fig. 1, a kind of method obtaining 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 block core sample water saturation and resistivity index cross plot, the method adopting power function to return, obtains the saturation exponent of every block core sample.
In the embodiment of the present invention, choose 20 pieces, oil field, domestic the Northwest low porosity and low permeability core sample and carry out resistivity experiment, as shown in Figure 8, in figure, X-axis is the saturation exponent that core sample is obtained by resistivity experiment for every block core sample water saturation and resistivity index cross plot.
Step 2: carry out nuclear magnetic resonance experiment to core sample, obtains the nmr spin echo string of core sample, and after carrying out inverting to spin echo string, obtains the nuclear magnetic resonance T of core sample
2spectrum, to obtained nuclear magnetic resonance T
2spectrum is carried out process and is obtained corresponding nuclear magnetic resonance T
2geometrical mean T
2lmand T
2cutoff.
In the embodiment of the present invention, nuclear magnetic resonance experiment is carried out to the above-mentioned 20 pieces of identical core samples chosen, obtain the T of every block core sample
2geometrical mean T
2lmand T
2cutoff.Result is as shown in table 1.
The nuclear magnetic resonance experiment data of table 120 piece core sample
Step 3: to the T of 20 pieces of core samples that step 2 obtains
2cutoff, does statistic histogram according to order from small to large, chooses the T that the frequency of occurrences is the highest
2cutoff is the unified T of all core samples
2cutoff T
2cutoff.
In the embodiment of the present invention, the T2 cutoff of the 20 pieces of core samples obtained is obtained according to the method described above to the unified T of 20 pieces of core samples
2cutoff T
2cutoff, result as shown in Figure 7.Wherein, X-axis is T
2cutoff, unit is ms; Y-axis is frequency distribution value.As can be seen from Figure 7, the T that frequency distribution peak is corresponding
2cutoff is between 15.0ms to 20.0ms, and average is 18.05ms.Therefore, select 18.05ms as the unified T of 20 pieces of core samples
2cutoff T
2cutoff.
Step 4: adopt step 3 to obtain unified T
2cutoff T
2cutoffcalculate irreducible water saturation S
wi, and calculate the parameter characterizing RESERVOIR PORE STRUCTURE
In the embodiment of the present invention, adopt 18.05ms as unified T
2cutoff T
2cutoffcalculate the irreducible water saturation S of 20 pieces of core samples
wi, and calculate the parameter characterizing RESERVOIR PORE STRUCTURE
result is as shown in table 1.
Step 5: the T of the core sample that core sample saturation exponent step one obtained, step 2 obtain
2geometrical mean T
2lmwith the irreducible water saturation S of the core sample that step 4 obtains
wi, substitute in the computation model of reservoir saturation exponent, adopt the method matching of multivariate statistical regression to obtain model parameter C, a and b.The computation model of described reservoir saturation exponent is specially:
In formula: n----reservoir saturation exponent;
S
wi----irreducible water saturation, decimal;
---the ratio of-rock core macrovoid component and fine pore component, characterizes RESERVOIR PORE STRUCTURE;
T
2lm----nuclear magnetic resonance T
2geometrical mean, ms;
C----model parameter;
A----model parameter;
B----model parameter.
In the embodiment of the present invention, the T of all 20 pieces of core samples that all 20 pieces of core sample saturation exponents, the step 2 that step one are obtained obtain
2geometrical mean T
2lmwith the irreducible water saturation S of all 20 pieces of core samples that step 4 obtains
wi, substitute in the computation model of reservoir saturation exponent, adopt the method matching of multivariate statistical regression to obtain model parameter C, a and b, can be respectively by the value calculating C, a and b: C=2.361, a=-0.0605, b=-0.111.
Step 6: computation model model parameter C, a and b being substituted into described reservoir saturation exponent, obtains utilizing NMR logging data to calculate 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, and the computation model of the calculating low porosity and low permeability saturation exponent obtained can be specially:
Utilize the acquisition methods of above-mentioned reservoir saturation exponent, calculate the saturation exponent of reservoir different depth, and test with the core sample resistivity of the corresponding degree of depth saturation exponent obtained and contrast, result as shown in Figure 8, X-axis is the saturation exponent that the experiment of core sample resistivity obtains, Y-axis is the reservoir saturation exponent utilizing technique computes of the present invention, as can be seen from Figure 8, the reservoir saturation exponent obtained by computation model that the embodiment of the present invention provides is substantially identical with the saturation exponent of the core sample obtained by experiment, the reservoir saturation exponent of more than 90% drops on ± error range of 0.3 within, illustrate that the reservoir saturation exponent obtained by computation model is high with the degree of agreement of the saturation exponent of the core sample obtained by experiment.
The method of the acquisition low porosity and low permeability reservoir saturation exponent utilizing the embodiment of the present invention to provide, obtains saturation exponent, and is updated to Archie formula, be specially:
In formula,
R
w----formation water resistivity, Ω .m;
R
t----oil-bearing rock resistivity, Ω .m;
----rock porosity, decimal;
M----cementation factor;
S
w----water saturation, decimal;
N----saturation exponent;
The coefficient that a with b----is relevant with lithology, its value is often 1.0.
Calculate the water saturation S of low porosity and low permeability reservoir
w, wherein the value of each parameter is R
w: 0.075 Ω .m; R
t: see Fig. 9 the 3rd channel array induction motor Curves registration value;
: see numerical value shown in Fig. 9 the 6th road core analysis porosity; M:1.45; A:1.0; B:1.0.
The saturation exponent of the design formulas acquisition of the saturation exponent provided utilizing the embodiment of the present invention and water saturation S
wwith experiment obtain the saturation exponent of core sample and water saturation contrast, its effect is as shown in Figure 9.Design sketch shown in Fig. 9 is divided into eight roads, and in figure, first comprises gamma ray curve (GR), spontaneous potential curve (SP) and CAL (CAL), is mainly used in identifying effective sandstone reservoir; Second is depth track, unit m; 3rd road is array induction resistivity curve; 4th road comprises density log (RHOB) curve, neutron well logging (NPHI) curve and acoustic travel time logging (DT) curve, is mainly used in the degree of porosity calculating reservoir; 5th road comprises the nuclear magnetic resonance log T of actual measurement
2spectrum T2_Distribution, nuclear magnetic resonance log T
2geometrical mean T
2lm, unified T
2cutoff T
2cutoff, its value is 18.05ms; 6th road comprises nuclear-magnetism total porosity PHIT, core analysis porosity Core_Por.Can see from the contrast of figure center bore porosity and core analysis porosity, the degree of porosity obtained from NMR logging data is accurately, the true hole porosity on stratum can be represented, which ensure that aftermentioned water saturation can not bring extra error due to insecure formation porosity to the calculating of water saturation in calculating; The reservoir saturation exponent that 7th road Calc_n obtains for the method calculating utilizing the embodiment of the present invention to provide; 8th road Sw calculates for the method utilizing the embodiment of the present invention to provide calculates degree of the becoming saturated index n obtained the water saturation obtained, and Core_Sw is the water saturation that sealing core data obtains.As can be seen from the figure, the water saturation utilizing variable reservoir saturation exponent to calculate is close to core experiment result.This explanation, the NMR logging data that utilizes utilizing the embodiment of the present invention to provide calculates the method for low porosity and low permeability reservoir saturation exponent, degree of the becoming saturated index n of reflection RESERVOIR PORE STRUCTURE change can be obtained accurately, to calculate reservoir water saturation accurately.
The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (10)
1. obtain a method for low porosity and low permeability reservoir saturation exponent, it is characterized in that, described method 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 T
2geometrical mean T
2lm;
2) the irreducible water saturation S of core sample is obtained
wi;
3) described T is utilized
2geometrical mean T
2lmwith described irreducible water saturation S
wi, calculate low porosity and low permeability reservoir saturation exponent, specifically calculate according to such as drag,
In formula: n----reservoir saturation exponent;
S
wi----irreducible water saturation;
---the ratio of-rock core macrovoid component and fine pore component, characterizes RESERVOIR PORE STRUCTURE;
T
2lm----T
2geometrical mean;
C----model parameter;
A----model parameter;
B----model parameter.
2. the method for claim 1, is characterized in that, the irreducible water saturation S of described acquisition core sample
wibe specially: the unified T first obtaining multiple described core sample
2cutoff T
2cutoff, the unified T of recycling
2cutoff T
2cutoffobtain the irreducible water saturation S of core sample
wi.
3. method as claimed in claim 2, is characterized in that, the unified T of the multiple described core sample of described acquisition
2cutoff T
2cutoffbe specially: the T first obtaining core sample
2cutoff, then to the T of multiple core sample
2cutoff, according to sequentially adding up from small to large, chooses the T that the frequency of occurrences is the highest
2cutoff is as the unified T of multiple described core sample
2cutoff T
2cutoff.
4. method as claimed in claim 3, is characterized in that, described in obtain the T of core sample
2cutoff is specially: obtain nuclear magnetic resonance T by nuclear magnetic resonance experiment
2spectrum, at described nuclear magnetic resonance T
2spectrum obtains the T of described core sample
2cutoff.
5. method as claimed in claim 2, is characterized in that, the unified T of described utilization
2cutoff T
2cutoffobtain the irreducible water saturation S of core sample
wibe specially: utilize unified T
2cutoff T
2cutoff, rock core 100% is full of the T under water state
2spectrum is divided into two parts, T
2relaxation time is less than described unified T
2cutoff T
2cutofft
2compose the region and T that surround
2relaxation time is greater than described unified T
2cutoff T
2cutofft
2compose the region surrounded, calculate T
2relaxation time is less than described unified T
2cutoff T
2cutofft
2compose area and the T in the region surrounded
2compose the ratio of the area of the overall area surrounded, be irreducible water saturation S
wi.
6. the method for claim 1, is characterized in that, described nuclear magnetic resonance experiment is the nuclear magnetic resonance experiment under core sample 100% is full of water state.
7. the method for claim 1, is characterized in that, obtains described T described in described step 1)
2geometrical mean T
2lmbe specially: obtain nuclear magnetic resonance T by nuclear magnetic resonance experiment
2spectrum, at described nuclear magnetic resonance T
2spectrum obtains described T
2geometrical mean T
2lm.
8. the method as described in claim 4 or 7, is characterized in that, described in obtain nuclear magnetic resonance T
2spectrum, is specially: obtain rock core nmr spin echo string by described rock core nuclear magnetic resonance experiment, and carry out inversion procedure to described spin echo string, obtain described nuclear magnetic resonance T
2spectrum.
9. the method for claim 1, is characterized in that, also comprises after described step 1): carry out the experiment of rock core resistivity, obtains water saturation and the resistivity index of every block core sample.
10. method as claimed in claim 9, it is characterized in that, the value of described model parameter C, a and b adopts the method matching of multivariate statistical regression to obtain, be specially: first by doing water saturation and the resistivity index cross plot of described every block core sample, and the method adopting power function to return, obtain the saturation exponent of every block core sample, then by the irreducible water saturation S of the saturation exponent of all core samples and corresponding core sample
wiand T
2geometrical mean, substitutes into the computation model of described reservoir saturation exponent
in, adopt the method matching of multivariate statistical regression to obtain.
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