CN112859180A - Rock wettability recognition method and device based on rock electrical experiment data - Google Patents
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Abstract
According to the rock wettability identification method and device based on the rock electrical experimental data, the wettability characteristics of the rock are extracted through the conductive characteristics contained in the rock electrical data, a saturation calculation equation considering the rock wettability is formed, and the calculation accuracy of the oil saturation is improved. According to the rock electric experiment data, a practical method for judging the rock wettability is formed. The method generates corresponding characteristics for the rock conductivity according to the wettability, performs characteristic extraction through data processing to obtain rock wettability information, and forms a saturation calculation equation considering the rock wettability through the step 2. A straight line is a special form of a curve, i.e. an approximation; in addition, as for a physical mechanism, the influence of the wettability on the conductivity of the rock cannot be considered by a classical Archie formula, the influence of the wettability of the rock on the conductivity is considered by the method, the oil saturation is calculated according to the saturation equation, and the calculation accuracy of the oil saturation of the reservoir can be expected to be improved.
Description
Technical Field
The invention relates to the field of petroleum logging interpretation, in particular to a rock wettability identification method and device based on rock electric experimental data.
Background
The interaction between the molecules of the rock solid and the molecules of the fluid in the pores has different forms and ranges, resulting in different contact patterns between the rock solid and the fluid, which is the wettability of the rock. Therefore, the wettability of the rock is a physical characteristic of the rock itself, which is related to the interaction force between solid particle molecules and fluid molecules in the rock, and the wettability influences the conductive path of the rock to form different conductive characteristics. The wettability of rock is divided into three types, water-wet, mixed-wet and oil-wet.
The rock sample rock electricity experiment is basic data of conventional rock core analysis and can be used for determining the relation between the conductivity of rock and the rock sample saturation. However, almost all researchers have simply performed linear fitting to obtain the parameters of Archie's formula for the measured petroelectric analysis data, including Archie itself. Under simple reservoir conditions, although a simple linear fit may also reflect the essential characteristics of the reservoir. However, more and more researches prove that simple linear fitting only extracts limited information in rock-electricity experimental data, and with increasing complexity of oil and gas reservoir characteristics, the influence of factors such as the wettability of rock, the shale content of rock and the like on the conductivity of the rock becomes more and more important, different wettability characteristics of the rock may influence the conductivity of the rock, cause calculation errors of oil saturation of rock samples and even directly cause difficulty in identifying a production layer and a non-production layer.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a rock wettability recognition method and device based on rock electrical experimental data.
The invention is realized by the following technical scheme:
a rock wettability identification method based on rock electrical experiment data comprises the following steps,
step 2, increasing the resistance coefficient I and the corresponding rock sample water saturation S in each group of rock electricity datawRespectively taking logarithm, and performing linear fitting and 3-degree polynomial fitting on the data after taking the logarithm to obtain a linear fitting equation and a 3-degree polynomial fitting equation of the resistance increasing coefficient;
step 3, respectively drawing the rock electricity experimental data, the linear fitting equation and the 3 rd-order polynomial fitting equation to I-SWTaking logarithmic coordinate system, wherein the ordinate is dimensionless resistance increasing coefficient I, and dimensionless, and the abscissa is dimensionless water saturation Sw; extending towards the low saturation direction according to the lowest experimental saturation value to obtain an extension region outside the low saturation; respectively calculating resistance increasing coefficients in an epitaxial region except for low saturation according to a linear fitting equation and a 3-power fitting equation;
step 4, calculating a resistance increase coefficient difference value obtained by two equations in the saturation low value epitaxial region; if the difference is larger than zero, the core sample corresponds to water-wet rock, if the difference is equal to zero, the core sample corresponds to mixed wet rock, and if the difference is smaller than zero, the core sample corresponds to oil-wet rock.
Preferably, the specific steps of step 1 are as follows,
according to the rock electricity experimental data of the rock core sample, obtaining the resistivity R of the fully saturated saline water of the rock sampleoResistivity R of rock sample at specified oil saturationtAnd corresponding rock sample water saturation SwThe resistance increase coefficient I is obtained by the following formula,
increasing the resistance coefficient I and the corresponding rock sample water saturation SwA set of petroelectrical data is formed.
Further, in the step 1, the rock sample is vacuumized, pressurized and saturated by using a rock electricity experimental analysis method to obtain the resistivity R of the fully saturated saline water of the rock sampleo。
Further, in the step 1, displacing the saline water in the rock core point by using experimental simulation oil to a water-binding state, recording the volume of the displaced saline water under each displacement point, and calculating the water saturation S of the rock core under each displacement pointwAnd measuring the resistivity of the rock core under each displacement point, namely the resistivity R of the rock sample under the corresponding specified oil saturationt(ii) a The viscosity of the experimental simulation oil is the same as that of reservoir oil corresponding to the rock sample.
Preferably, in step 2, the linear fitting equation and the 3 rd order polynomial fitting equation for obtaining the resistance increase coefficient are as follows,
wherein, I, SwRespectively the resistivity increase coefficient and the water saturation in the same group of rock electricity data; a is0，a1，a2，a3Respectively, are fitting coefficients.
Preferably, in step 4, when the difference is equal to zero within a range of plus or minus 0.05, the core sample corresponds to a mixed wet rock.
A rock wettability recognition device based on rock electricity experimental data comprises:
the data processing device obtains the resistance increase coefficient I and the corresponding rock sample water saturation S according to the rock electricity experimental data of the rock core samplewAnd shaping itForming a set of rock electricity data;
fitting device for resistance increase coefficient I and corresponding rock sample water saturation S in each group of rock electricity datawRespectively taking logarithm, and performing linear fitting and 3-degree polynomial fitting on the data after taking the logarithm to obtain a linear fitting equation and a 3-degree polynomial fitting equation of the resistance increasing coefficient;
drawing a calculating device, and respectively drawing the rock electricity experimental data, the linear fitting equation and the 3 rd-order polynomial fitting equation to I-SWTaking logarithmic coordinate system, wherein the ordinate is dimensionless resistance increasing coefficient I, and dimensionless, and the abscissa is dimensionless water saturation Sw; extending towards the low saturation direction according to the lowest experimental saturation value to obtain an extension region outside the low saturation; respectively calculating resistance increasing coefficients in an epitaxial region except for low saturation according to a linear fitting equation and a 3-power fitting equation;
a difference value judging device for calculating the difference value of the resistance increase coefficients obtained by the two equations in the saturation low value epitaxial region; if the difference is larger than zero, the core sample corresponds to water-wet rock, if the difference is equal to zero, the core sample corresponds to mixed wet rock, and if the difference is smaller than zero, the core sample corresponds to oil-wet rock.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the rock electric experiment data, a practical method for judging the rock wettability is formed. The method does not need to increase the experiment time and cost, and realizes the full mining of the information of the rock-electricity experiment data. According to the method, the rock conductivity can generate corresponding characteristics according to the wettability, the characteristics are extracted through data processing, the rock wettability information is obtained, and a saturation calculation equation considering the rock wettability is formed through the step 2. A straight line is a special form of a curve, i.e. an approximation; in addition, as for a physical mechanism, the influence of the wettability on the conductivity of the rock cannot be considered by a classical Archie formula, the influence of the wettability of the rock on the conductivity is considered by the method, the oil saturation is calculated according to the saturation equation, and the calculation accuracy of the oil saturation of the reservoir can be expected to be improved.
Drawings
FIG. 1 is a schematic view of a low saturation epitaxial region of the method of the present invention.
FIG. 2 is an oil-wet rock judged by the difference in resistivity of increase according to the method of the example of the invention.
FIG. 3 is a water-wet rock judged by the difference in resistivity of increase according to the method of the example of the invention.
FIG. 4 is a block flow diagram of a method according to an embodiment of the invention.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The invention provides a rock wettability identification method based on rock electricity experimental data, and a saturation calculation formula considering rock wettability is formed. Through deep analysis of the rock electricity experimental data, the wettability information of the rock is extracted. And calculating an equation considering the saturation of rock wettability. The experimental analysis cost is not increased, and the calculation precision of the rock sample saturation is improved. In the evaluation of the logging reservoir, the accuracy of the oil saturation degree in logging calculation can be expected to be improved. The complete content of the method comprises two parts of rock electricity experimental test and data processing analysis.
The contents of the rock electricity experiment test comprise that the resistivity of a rock sample under the conditions of completely saturated saline water and different oil saturation degrees is respectively measured and researched, the resistance increasing coefficient and the saturation degree data of the rock are obtained, and logarithm is taken for the resistance increasing coefficient and the oil saturation degree.
The data processing and analyzing content comprises that linear fitting and 3-degree polynomial fitting are respectively carried out on the resistivity increasing coefficient and the saturation data after logarithm taking is finished, and a linear calculation equation and a 3-degree polynomial calculation equation of the resistivity increasing coefficient are obtained. And in a low-value extension area except the lowest test saturation, calculating the resistance increase coefficient of the rock sample by using a linear equation and a 3 rd-order polynomial equation respectively, and calculating the difference between the two resistance increase coefficients. If the difference is larger than zero, wetting by water; the difference is near zero value, the difference of resistance increasing coefficient is in the range of [ -0.05,0.05], and the mixture is wet; the difference is less than zero and the oil is wet. Then, comparing the discrimination result of the rock electrical data with the actually measured rock sample wettability index, and determining the reliability of the method for discriminating the rock wettability; the reliability of the rock wettability method is judged according to the difference value and the sign of the difference value between the resistance increase coefficients calculated according to a simple Archie formula (linear relation) and a polynomial rock electrical relation.
The invention aims to improve the wettability information of a rock sample extracted according to rock electrical experiment data. The key content of which comprises 3 points.
1. Performing linear fitting and cubic polynomial fitting on the same batch of rock-electricity experimental data;
2. determining a low value extension area of water saturation according to the lowest water saturation measurement value;
3. and calculating resistance increasing coefficients of a linear fitting equation and a 3 rd-order polynomial fitting equation in a low-value extension area of water saturation, and judging the wettability of the rock according to the difference value of the resistance increasing coefficients under the same saturation.
Fig. 4 is a flow chart of the implementation of the present invention, which mainly includes the following steps:
Step 2, displacing the brine by using the oil sample, and recording the resistivity R of the rock with different oil saturation degreestAnd corresponding water saturation Sw；
Step 3, according to the equation (1), calculating the resistance increase coefficient I of the rock, and calculating the resistance increase coefficient I and the water saturation SwTaking logarithm respectively;
wherein, I, the resistance increase coefficient is dimensionless;
Rtspecifying the resistivity of the rock under oil saturation; omega.m;
Roresistivity of rock fully saturated brine, Ω · m.
SwIs the water saturation, decimal fraction, of the rock sample.
And 4, respectively performing linear fitting and 3-degree polynomial fitting on the resistance increase coefficient and the water saturation after logarithm taking to obtain a linear fitting equation and a 3-degree polynomial fitting equation for calculating the resistance increase coefficient.
logI＝a0+a1logSw
logI＝a0+a1logSw+a2log2Sw+a3log3Sw (2)
Wherein, I and Sw are respectively the resistance increase coefficient and the water saturation; dimensionless; a is0，a1，a2，a3Respectively, are fitting coefficients.
And step 5, adding the rock electricity experimental data, the linear fitting equation and the 3 rd-order polynomial fitting equation into a coordinate system with logarithms of I-SW respectively, as shown in figure 1. And according to the lowest experimental saturation value, extending towards the low saturation direction to obtain an extension region except the low saturation. And calculating the resistance increase coefficient of the linear fitting equation and the 3 rd order polynomial fitting equation in the low value extension interval of the lowest water saturation. The difference between these two resistivity increases is calculated as shown in equation (6), with the difference being greater than zero (>0.05), near zero ([ -0.05,0.05]), and less than zero (< 0.05), corresponding to water-wet, mixed-wet, and oil-wet rocks, respectively.
Il-ItGreater than 0, water wetting
Il-I t0, mixed wetting
Il-It< 0, oil wet (3)
Il，ItThe resistance increase coefficients calculated by the linear fitting equation and the 3 rd order polynomial fitting equation, respectively.
Finally, in order to verify the reliability and the effectiveness of the method, the wettability of the rock sample determined according to the resistance increase coefficient difference can be compared with the actually measured wettability index of the rock sample, and the application effect of the method is determined.
Table 1 below shows the practical data of the embodiment of the present invention, and the equation parameters in step 4 can be determined by using these data; the details are as follows.
TABLE 2 core numbering and saturation data
The implementation case of the invention adopts a rock electricity measurement technology, and the experimental instrument adopts an SCMS-YD type plunger sample rock core experimental system of a metropolis completion rock electricity experimental technology center company to carry out rock electricity experiments of rock core oil water-driving, and the test standard is as follows: SY/T5385-2007 rock resistivity parameter laboratory measurement and calculation method; the 'oil reservoir rock wettability measuring device' measures the wettability of a rock core by a self-absorption method, and has the following test standards: SY/T5153-2007 method for measuring wettability of reservoir rock. Data analysis data fitting was performed using a conventional least squares method.
According to the implementation case of the invention, the rock electricity experimental data of 10 rock cores are obtained, and after linear fitting and 3-degree polynomial fitting are carried out on the data, a linear equation and a 3-degree polynomial equation of the resistance increasing coefficient are obtained. And calculating the resistance increase coefficient according to the linear equation of the resistance increase coefficient and the 3 rd-order polynomial equation, and judging the wettability of the rock according to the difference of the resistance increase coefficients.
The implementation process of the case is as follows:
in the step 1, the wettability of the rock core is measured by a self-priming method described in SY/T5153-2007 oil reservoir rock wettability measurement method.
And step 2, after the wettability measurement is completed, pretreating the rock core: comprises oil washing, salt washing, drying and the like.
And 3, measuring the porosity and permeability of the rock core.
And 4, preparing brine of the saturated rock core, wherein the salinity concentration of the brine of the saturated rock core is 80000 mg/L.
And 5, vacuumizing, pressurizing and saturating the rock core.
Step 6, measuring the resistivity R of the saturated state of the rock core0。
7, using an experiment simulation oil consistent with the viscosity of the reservoir oil to displace the saline water in the rock core point by point to a bound water state, recording the displaced saline water volume under each displacement point, calculating the water saturation of the rock core under each displacement point, and measuring the resistivity R of the rock core under each displacement pointt。
Step 8, calculating the resistance increase coefficient I of the rock core under different water saturation degrees and the corresponding water saturation degree S by using the equation (1)wA set of petroelectrical data is formed.
Step 9, increasing the resistance coefficient I and the water saturation SwAnd taking a logarithm. And respectively carrying out linear fitting and 3-degree polynomial fitting on the data after logarithm taking to obtain a linear calculation equation of the resistance increasing coefficient and a 3-degree polynomial calculation equation (2).
logI＝a0+a1logSw
logI＝a0+a1logSw+a2log2Sw+a3log3Sw (2)
And 7, in a low value extension interval of the lowest water saturation, as shown in fig. 2 and fig. 3, respectively calculating resistance increasing coefficients of a linear fitting equation and a 3 rd-order polynomial fitting equation by using an equation of the interval, and calculating a difference value of the two resistance increasing coefficients. The difference is greater than zero (>0.05), located near zero ([ -0.05,0.05]) and less than zero (< -0.05), corresponding to water-wet rock, mixed-wet rock and oil-wet rock (3), respectively.
Il-ItGreater than 0, water wetting
Il-I t0, mixed wetting
Il-It< 0, oil wet (8)
As shown in Table 2, the wettability of the rock sample determined by the difference of the resistance increase coefficients is compared with the actually measured wettability index of the rock sample to determine the application effect of the method.
TABLE 2 rock electric data judgment wettability comparison table
In the present invention, 15 real cores from a field were selected (table 2, section). The results of the calculations performed by the technique of the present invention show that, as shown in table 2, fig. 2 and fig. 3, it is possible to distinguish the change in conductivity from the wettability factor or the fluid factor of the pore space, taking into account the wettability of the rock. The core basis for improving the calculation accuracy of the saturation is to identify the influence of pore fluid on the resistivity and eliminate non-fluid factors (for example, the influence of rock wettability on the rock resistivity). Firstly, a rock electrical equation in a curve form is used, and the change of the resistivity of the rock caused by non-fluid factors is considered, so that the calculation precision of the fluid saturation can be improved; and secondly, information contained in rock electricity experimental data is fully excavated, and a qualitative judgment method for rock wettability is provided. In the absence of experimental data on rock wettability, the method can provide reference information on rock wettability.
The invention also provides a rock wettability recognition device based on the rock electricity experimental data, which comprises the following components:
the data processing device obtains the resistance increase coefficient I and the corresponding rock sample water saturation S according to the rock electricity experimental data of the rock core samplewAnd forming a set of rock electricity data;
fitting device for resistance increase coefficient I and corresponding rock sample water saturation S in each group of rock electricity datawRespectively taking logarithm, and performing linear fitting and 3-degree polynomial fitting on the data after taking the logarithm to obtain a linear fitting equation and a 3-degree polynomial fitting equation of the resistance increasing coefficient;
drawing a computing device, and carrying out rock-electricity experimentData, linear fitting equation and 3 rd order polynomial fitting equation are respectively plotted to I-SWTaking logarithmic coordinate system, wherein the ordinate is dimensionless resistance increasing coefficient I, and dimensionless, and the abscissa is dimensionless water saturation Sw; extending towards the low saturation direction according to the lowest experimental saturation value to obtain an extension region outside the low saturation; respectively calculating resistance increasing coefficients in an epitaxial region except for low saturation according to a linear fitting equation and a 3-power fitting equation;
a difference value judging device for calculating the difference value of the resistance increase coefficients obtained by the two equations in the saturation low value epitaxial region; if the difference is larger than zero, the core sample corresponds to water-wet rock, if the difference is equal to zero, the core sample corresponds to mixed wet rock, and if the difference is smaller than zero, the core sample corresponds to oil-wet rock.
Claims (7)
1. A rock wettability recognition method based on rock electrical experiment data is characterized by comprising the following steps,
step 1, obtaining a resistance increase coefficient I and corresponding rock sample water saturation S according to rock electricity experimental data of a rock core samplewAnd forming a set of rock electricity data;
step 2, increasing the resistance coefficient I and the corresponding rock sample water saturation S in each group of rock electricity datawRespectively taking logarithm, and performing linear fitting and 3-degree polynomial fitting on the data after taking the logarithm to obtain a linear fitting equation and a 3-degree polynomial fitting equation of the resistance increasing coefficient;
step 3, respectively drawing the rock electricity experimental data, the linear fitting equation and the 3 rd-order polynomial fitting equation to I-SWTaking logarithmic coordinate system, wherein the ordinate is dimensionless resistance increasing coefficient I, and dimensionless, and the abscissa is dimensionless water saturation Sw; extending towards the low saturation direction according to the lowest experimental saturation value to obtain an extension region outside the low saturation; respectively calculating resistance increasing coefficients in an epitaxial region except for low saturation according to a linear fitting equation and a 3-power fitting equation;
step 4, calculating a resistance increase coefficient difference value obtained by two equations in the saturation low value epitaxial region; if the difference is larger than zero, the core sample corresponds to water-wet rock, if the difference is equal to zero, the core sample corresponds to mixed wet rock, and if the difference is smaller than zero, the core sample corresponds to oil-wet rock.
2. The method of claim 1, wherein in step 1, the set of petroelectrical data is formed by,
according to the rock electricity experimental data of the rock core sample, obtaining the resistivity R of the fully saturated saline water of the rock sampleoResistivity R of rock sample at specified oil saturationtAnd corresponding rock sample water saturation Sw；
The resistance increase coefficient I is obtained by the following formula,
increasing the resistance coefficient I and the corresponding rock sample water saturation SwA set of petroelectrical data is formed.
3. The method as claimed in claim 2, wherein the rock sample is subjected to vacuum pumping and pressurized saturation by using a rock electrical experiment analysis method according to rock electrical experiment data of the rock core sample to obtain the resistivity R of the rock sample fully saturated saline watero。
4. The method as claimed in claim 2, wherein the experimental simulation oil is used to displace the brine in the core point by point to a irreducible water state, the displaced brine volume at each displacement point is recorded, and the water saturation S of the core at each displacement point is calculatedwAnd measuring the resistivity of the rock core under each displacement point, namely the resistivity R of the rock sample under the corresponding specified oil saturationt(ii) a The viscosity of the experimental simulation oil is the same as that of reservoir oil corresponding to the rock sample.
5. The method of claim 1, wherein in step 2, the linear fitting equation of the resistance increasing coefficient and the 3 rd order polynomial fitting equation are as follows,
wherein, I, SwRespectively the resistivity increase coefficient and the water saturation in the same group of rock electricity data; a is0，a1，a2，a3Respectively, are fitting coefficients.
6. The method of claim 1, wherein in step 4, when the difference is equal to zero within a range of plus or minus 0.05, the core sample corresponds to a mixed wet rock.
7. A rock wettability recognition device based on rock electricity experimental data is characterized by comprising:
the data processing device obtains the resistance increase coefficient I and the corresponding rock sample water saturation S according to the rock electricity experimental data of the rock core samplewAnd forming a set of rock electricity data;
fitting device for resistance increase coefficient I and corresponding rock sample water saturation S in each group of rock electricity datawRespectively taking logarithm, and performing linear fitting and 3-degree polynomial fitting on the data after taking the logarithm to obtain a linear fitting equation and a 3-degree polynomial fitting equation of the resistance increasing coefficient;
drawing a calculating device, and respectively drawing the rock electricity experimental data, the linear fitting equation and the 3 rd-order polynomial fitting equation to I-SWTaking logarithmic coordinate system, wherein the ordinate is dimensionless resistance increasing coefficient I, and dimensionless, and the abscissa is dimensionless water saturation Sw; extending towards the low saturation direction according to the lowest experimental saturation value to obtain an extension region outside the low saturation; respectively calculating resistance increasing coefficients in an epitaxial region except for low saturation according to a linear fitting equation and a 3-power fitting equation;
a difference value judging device for calculating the difference value of the resistance increase coefficients obtained by the two equations in the saturation low value epitaxial region; if the difference is larger than zero, the core sample corresponds to water-wet rock, if the difference is equal to zero, the core sample corresponds to mixed wet rock, and if the difference is smaller than zero, the core sample corresponds to oil-wet rock.
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