CN112324421A - Method for calculating saturation before and after flooding of low-resistivity heavy oil reservoir - Google Patents

Method for calculating saturation before and after flooding of low-resistivity heavy oil reservoir Download PDF

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CN112324421A
CN112324421A CN202010540198.8A CN202010540198A CN112324421A CN 112324421 A CN112324421 A CN 112324421A CN 202010540198 A CN202010540198 A CN 202010540198A CN 112324421 A CN112324421 A CN 112324421A
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时新磊
崔云江
张建升
陈红兵
朱猛
关叶钦
杨洪伟
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China National Offshore Oil Corp CNOOC
CNOOC China Ltd Tianjin Branch
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Abstract

The invention discloses a method for calculating the saturation degree of a low-resistivity heavy oil layer before and after flooding, which comprises the following four steps: step 1: determining a cutoff value of low-resistivity heavy oil nuclear magnetic resonance logging T2; step 2: calculating the original water saturation of the low-resistivity heavy oil by nuclear magnetic resonance logging; and step 3: determining the resistivity of the mixed water after the oil layer is flooded and calculating the water saturation; and 4, step 4: and calculating the oil displacement efficiency of the water flooded layer and dividing the water flooded level. The method can improve the calculation precision of the oil displacement efficiency, further improve the dividing precision of the low-resistivity oil layer water flooded level, has good technical effect and simple use, can be widely applied to quantitative evaluation of the low-resistivity heavy oil reservoir water flooded layer of the Bohai sea oil field, and has important guiding significance for improving the recovery ratio in the oil field development process.

Description

Method for calculating saturation before and after flooding of low-resistivity heavy oil reservoir
Technical Field
The invention belongs to the technical field of reservoir parameter evaluation and petrophysical research, and particularly relates to a method for calculating saturation before and after flooding of a low-resistivity heavy oil reservoir.
Background
Because the resistivity of the low-resistivity oil layer is very close to that of the water layer and even lower than that of the water layer in the same system, with the continuous deepening of the water injection development of the oil field, the quantitative evaluation of the flooding of the low-resistivity oil layer brings huge challenges to logging personnel, and the dividing result of the flooding level of the low-resistivity oil layer directly relates to the perforation decision of the oil reservoir personnel. The difficulty of low-resistivity oil layer flooding evaluation mainly lies in how to accurately calculate the water saturation before and after the oil layer flooding, and the calculation accuracy of the water saturation is directly related to the calculation accuracy of the oil displacement efficiency, so as to determine the classification of the flooding layer level. At present, the original water saturation of a water flooded layer is mainly determined by utilizing the resistivity inversion of an adjacent well or performing nuclear magnetic resonance well logging, and the calculation precision of the water saturation after the water flooding depends on the resistivity of mixed water (injected water and formation water) in a stratum after water injection development. Due to the fact that the change of reservoir and fluid properties on a plane is large, a large error exists in the traditional resistivity inversion method for calculating the original water saturation, meanwhile, the nuclear magnetic resonance logging for obtaining the accurate original water saturation mainly depends on the accurate determination of a T2 cut-off value, for a low-resistivity heavy oil reservoir, the determination of the T2 cut-off value caused by the superposition of free fluid T2 spectrum forward movement and capillary bound water has a large difficulty, and for a argillaceous sandstone, the original water saturation calculated by using the traditional T2 cut-off value of 33ms is obviously high, and the error is large. At present, the resistivity of the mixed water is mainly obtained by three methods, namely laboratory water analysis data, natural potential curve calculation, an iteration method and the like. The offshore oil field well logging series mainly use well logging while drilling as a main part, no natural potential well logging exists, and laboratory water analysis data are limited, so that the resistivity of mixed water is determined by an iteration method. The current iteration method commonly uses the following equations:
Figure BDA0002538610150000011
in the formula:
Swethe water saturation after the oil layer is flooded, f;
Swirthe original water saturation of the oil layer, f;
Rwzresistivity of formation mixed water, Ω · m;
Rwiis the connate water resistivity, Ω · m;
Rwjresistivity for injected water, Ω · m;
Rdis the formation depth resistivity, Ω · m;
m is a cementation index;
n is a saturation index;
φeeffective porosity, f;
a is lithology coefficient;
Vshis the argillaceous content, f;
Rshis mudstone resistivity, Ω · m.
The above equation set has only two formulas, but has Swe、SwirAnd RwzThree unknowns are underdetermined equation sets, the traditional iteration method has multiple resolvability, and the iteration result has larger error.
In addition, for a argillaceous sandstone formation, the lithoelectric parameters can change along with the change of the mineralization degree of the mixed water. The conventional iteration method only considers the change of the resistivity of the mixed water, neglects the influence of the change of the rock electrical parameters on the calculation of the current water saturation, further reduces the accuracy of the iteration result, and the calculation result cannot meet the saturation evaluation after the low-resistivity oil reservoir is flooded. Therefore, the interpretation precision of the saturation before and after flooding is very important for the logging evaluation of the flooding layer.
Disclosure of Invention
The invention aims to provide a method for calculating the saturation degree of a low-resistivity heavy oil layer before and after flooding so as to solve the problem of the background technology.
In order to realize the aim, the specific technical scheme of the method for calculating the saturation before and after the low-resistivity heavy oil reservoir is flooded is as follows: a method for calculating saturation before and after flooding of a low-resistivity heavy oil reservoir comprises the following steps:
step 1: determining a cutoff value of low-resistivity heavy oil nuclear magnetic resonance logging T2;
step 2: calculating the original water saturation of the low-resistivity heavy oil by nuclear magnetic resonance logging;
and step 3: determining the resistivity of the mixed water after the oil layer is flooded and calculating the water saturation;
and 4, step 4: and calculating the oil displacement efficiency of the water flooded layer and dividing the water flooded level.
Preferably, in step 1, a method for determining a T2 cut-off value of the equal-area compensation of a T2 spectrum of the thickened oil capillary bound water and the free fluid is established; and (3) setting a T2 cut-off value range by establishing a target function based on the water saturation of the core analysis, and solving to obtain a T2 cut-off value of the heavy oil reservoir.
Preferably, when the shadow area S1 of the part of the free fluid T2 spectrum superposed on the capillary bound water is equal to the shadow area S2 of the part of the capillary bound water T2 spectrum, the limit value is the cut-off value of the thick oil T2;
Figure BDA0002538610150000031
in the formula:
f is an objective function, and the minimum value is taken and is dimensionless;
CSwi _ SCAL is the water saturation of the rock core, f;
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt measured for NMR logging instrument2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
Preferably, the original water saturation of the water flooded layer is calculated in the development well based on the T2 cut-off value obtained in the step 1, namely the step 2 method;
Figure BDA0002538610150000032
in the formula:
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt measured for NMR logging instrument2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
Preferably, the method for determining the resistivity of the mixed water and calculating the water saturation after the oil layer is flooded in the step 3 comprises the following steps:
the mineralization degree equation of the mixed water is obtained on the basis of a substance balance theory on the assumption that the injected water and the primary formation water are subjected to sufficient ion exchange and are in a complete dynamic balance mixed state.
Figure BDA0002538610150000041
In the formula:
Cwthe mineralization degree of the mixed water is mg/L;
k is the multiple of injected water, and the specific value depends on the current flooding degree of the oil field;
Swethe water saturation after the oil layer is flooded, f;
Swirthe original water saturation of the oil layer, f;
Cwithe mineralization degree of the capillary water is mg/L;
Cwjthe degree of mineralization of the injected water is mg/L.
Secondly, establishing a correlation between the mineralization degree of the mixed water and the rock electrical parameter based on the experimental analysis of the rock resistivity under different mineralization degrees. In the argillaceous sandstone stratum, the lithoelectric parameters can change along with the change of the mineralization degree of the mixed water, and the two have obvious exponential relationship;
Figure BDA0002538610150000042
Figure BDA0002538610150000043
in the formula:
m is a cementation index;
n is a saturation index;
Cwthe mineralization degree of the mixed water is mg/L;
C1、C2、C3、C4the fitting coefficient is obtained by rock resistivity experiments.
And thirdly, the resistivity of the mixed water is controlled by the mineralization degree and the temperature of the mixed water, and the resistivity of the mixed water can be accurately calculated by utilizing the mineralization degree and the temperature.
Figure BDA0002538610150000051
In the formula:
Rwzresistivity of formation mixed water, Ω · m;
t is the temperature in centigrade, DEG C;
substituting the electrical parameter expression of the rock in the step II into a saturation formula (Simandoux), and combining the electrical parameter expression with the formula in the step I and the step III to obtain the following simultaneous equation set:
Figure BDA0002538610150000052
in the formula:
a is lithology coefficient;
Rdis the formation depth resistivity, Ω · m;
φeeffective porosity, f;
Vshis the argillaceous content, f;
Rshis mudstone resistivity, omega m
Substituting the original water saturation Swir NMR calculated in step 1 into the simultaneous equation set for SwirThe system of equations has three unknowns, Swe, Rwz and Cw. And (4) carrying out iterative solution on the mixed water resistivity Rwz and the water saturation Swe under the current flooding state.
Preferably, in step 4, the oil displacement efficiency is calculated by utilizing the original saturation calculated by nuclear magnetic resonance logging and the stratum mixed water saturation calculated by utilizing the mixed water resistivity, and the flooding level is divided by combining a chart of the relation between the core oil displacement efficiency and the water content.
Figure BDA0002538610150000061
In the formula:
eta is the oil displacement efficiency, f;
swe is the water saturation after the oil layer is flooded, f;
swir NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a method for calculating the water saturation before and after flooding of a low-resistivity heavy oil reservoir, wherein the method for calculating the water saturation before flooding is based on nuclear magnetic resonance well logging information, and a method for determining a T2 cut-off value of equal-area compensation of low-resistivity heavy oil capillary bound water and a free fluid T2 spectrum is established, so that the accurate calculation of the original water saturation of the flooding layer is realized; the method for calculating the water saturation after the water logging is based on conventional well logging information, and a mixed water resistivity iterative calculation method based on nuclear magnetic original water saturation constraint is established, so that the accurate calculation of the current water saturation of the water logging layer is realized. The accurate calculation of the water saturation before and after the water flooding of the low-resistivity heavy oil reservoir improves the calculation accuracy of quantitative evaluation parameters of the oil displacement efficiency of the water flooding layer, and realizes the grading division of the water flooding layer of the low-resistivity heavy oil reservoir.
Drawings
FIG. 1 is a flow chart of a method for calculating saturation before and after flooding of a low-resistivity heavy oil reservoir according to an embodiment of the present invention;
fig. 2a and 2b are schematic diagrams of a new method for determining a cut-off value of nuclear magnetic resonance logging T2 of heavy oil according to an embodiment of the present invention;
FIG. 3 is a graph comparing the nuclear magnetic original water saturation and the core water saturation of a W-well low resistivity heavy oil reservoir provided by an embodiment of the invention;
4a, 4b and 4c are graphs of the fitting relationship between the mineralization degree of the mixed water and the lithoelectric parameters (m and n values) provided by the embodiment of the invention;
FIG. 5 is a diagram illustrating the effect of water saturation calculation before and after flooding of a low resistivity section of an X-well according to an embodiment of the present invention;
FIG. 6 is a diagram of the oil displacement efficiency calculation and water flooding level division results of the low resistivity section of the X well according to the embodiment of the invention;
FIG. 7 is a chart of the relationship between oil displacement efficiency and water content of a low-resistivity section of a P oil field according to an embodiment of the invention;
FIG. 8 is a graph of X-well production provided by an embodiment of the present invention.
Detailed Description
For a better understanding of the objects, structure and function of the invention, reference should be made to the drawings, FIGS. 1-8, which illustrate the invention.
The invention provides a method for determining a cut-off value of low-resistivity heavy oil nuclear magnetic resonance logging T2 by combining conventional core analysis, rock electricity experiments under different mineralization degrees, water flooding experiments and nuclear magnetic resonance experiment results, and further calculates the original water saturation of an oil layer by using the cut-off value of T2.
The change rule of the rock electrical parameters under different mineralization degrees is analyzed, a determining formula of the rock electrical parameters is obtained, a mixed water resistivity iterative equation set of a simultaneous mixed water mineralization degree equation, a mixed water resistivity calculation formula and a saturation formula (Simandoux) is provided, and the calculation of the water saturation after the oil layer is flooded is realized. The accurate calculation of the water saturation before and after the oil reservoir is flooded improves the calculation accuracy of the oil displacement efficiency, and further improves the dividing accuracy of the low-resistivity oil reservoir flooding level.
As shown in a flow chart of figure 1, the invention provides a method for calculating the saturation before and after a low-resistivity heavy oil reservoir is flooded, which is operated according to the following steps and mainly comprises four major steps.
Step 1: determination of cut-off value of nuclear magnetic resonance logging T2 of low-resistivity heavy oil
For a low-resistivity thick oil layer, due to high fluid viscosity and fine lithology, partial free fluid T2 spectrum forward movement and partial overlapping of capillary bound water are difficult to distinguish. For the problem that the cutoff value of thick oil T2 is difficult to determine, a method for determining the cutoff value of T2 for area compensation of thick oil capillary bound water and free fluid T2 spectrums and the like is established, as shown in FIG. 2, a shaded area S1 in the graph is a part of the free fluid T2 spectrums superposed on the thick oil capillary bound water, an area S2 in the graph is a part of the thick oil capillary bound water T2 spectrums, and when the shaded area S1 is equal to S2, the boundary value at the moment is the cutoff value of thick oil T2. And setting a T2 cut-off value range by establishing an objective function based on the water saturation of the core analysis, and traversing to obtain a T2 cut-off value of the heavy oil reservoir.
Figure BDA0002538610150000071
In the formula:
f is an objective function, and the minimum value is taken and is dimensionless;
CSwi _ SCAL is the water saturation of the rock core, f;
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt observed for NMR logging instruments2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
Calculated by the formula (1), when the viscosity of the crude oil in the low-resistivity oil layer section is about 50mPa · s, the cut-off value of T2 ranges from 15ms to 18ms, and when the viscosity of the crude oil in the low-resistivity oil layer section is 147-182 mPa · s, the cut-off value of T2 ranges from 13 ms to 15 ms.
Step 2, calculating the original water saturation of the low-resistivity heavy oil nuclear magnetic resonance logging
And (3) based on the T2 cut-off value determined in the step (1), popularizing and applying the T2 cut-off value to the development well to calculate the original water saturation of the water flooded layer.
Figure BDA0002538610150000081
In the formula:
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt observed for NMR logging instruments2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
As shown in FIG. 3, the original nuclear magnetic resonance water saturation Swir _ NMR determined by the cut-off value of T2 in the 7 th curve is better matched with the core analysis water saturation Csaw _ SCAL, which indicates that the method determines that the cut-off value of T2 has higher reliability.
Step 3, determining mixed water resistivity after oil layer flooding and calculating water saturation
The mineralization degree equation of the mixed water is obtained on the basis of a substance balance theory on the assumption that the injected water and the primary formation water are subjected to sufficient ion exchange and are in a complete dynamic balance mixed state.
Figure BDA0002538610150000091
In the formula:
Cwthe mineralization degree of the mixed water is mg/L;
k is the multiple of injected water, and the specific value depends on the current flooding degree of the oil field;
Swethe water saturation after the oil layer is flooded, f;
Swirthe original water saturation of the oil layer, f;
Cwithe mineralization degree of the capillary water is mg/L;
Cwjthe degree of mineralization of the injected water is mg/L.
Secondly, establishing a correlation between the mineralization degree of the mixed water and the rock electrical parameter based on the experimental analysis of the rock resistivity under different mineralization degrees. As shown in fig. 4, in a argillaceous sandstone formation, the bioelectric parameter changes with the change of the mineralization degree of mixed water, and the two have a clear exponential relationship.
Figure BDA0002538610150000092
Figure BDA0002538610150000093
In the formula:
m is a cementation index;
n is a saturation index;
Cwthe mineralization degree of the mixed water is mg/L;
C1、C2、C3、C4the fitting coefficient is obtained by rock resistivity experiments.
And thirdly, the resistivity of the mixed water is controlled by the mineralization degree and the temperature of the mixed water, and the resistivity of the mixed water can be accurately calculated by utilizing the mineralization degree and the temperature.
Figure BDA0002538610150000094
In the formula:
Rwzresistivity of formation mixed water, Ω · m;
t is the temperature in centigrade, DEG C;
substituting the electrical parameter expression of the rock in the step II into a saturation formula (Simandoux), and combining the electrical parameter expression with the formula in the step I and the step III to obtain the following simultaneous equation set:
Figure BDA0002538610150000101
in the formula:
a is lithology coefficient;
Rdis the formation depth resistivity, Ω · m;
φeeffective porosity, f;
Vshis the argillaceous content, f;
Rshis mudstone resistivity, Ω · m.
Substituting the original nuclear magnetic resonance logging water saturation Swir _ NMR calculated in the step (1) into a simultaneous equation set to replace SwirThe equation set comprises three unknowns of Swe, Rwz and Cw, and iterative solution is carried out on the unknowns, so that the mixed water resistivity Rwz and the water saturation Swe under the current flooding state can be obtained. As shown in fig. 5, Cw in the 6 th curve is the mixed water mineralization calculated iteratively; r in the 7 th curvewzThe mixed water resistivity is calculated by utilizing the mineralization degree Cw of the mixed water; m in the 8 th curve is the calculated bond index; n in the 9 th curve is the calculated saturation index; swe in the 10 th curve is the water saturation of the oil layer after the oil layer is flooded according to the mixed water resistivity calculation; swir NMR is the reservoir original water saturation calculated using the T2 cutoff determined in step (1).
Step 4, calculating the oil displacement efficiency of the water flooded layer and dividing the water flooded level
And calculating the oil displacement efficiency by utilizing the original saturation calculated by nuclear magnetic resonance logging and the stratum mixed water saturation calculated by mixed water resistivity, and dividing the flooding level by combining a chart of the relation between the core oil displacement efficiency and the water content.
Figure BDA0002538610150000111
In the formula:
eta is the oil displacement efficiency, f;
swe is the water saturation after the oil layer is flooded, f;
swir NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f.
As shown in fig. 6, QUYOU in the 7 th curve is the calculated displacement efficiency. And combining a chart of relation between oil displacement efficiency and water content of a rock core experiment.
As shown in fig. 7, the low resistivity section of the X-well is divided into flood grades, and the 8 th curve in fig. 6 is the result of the division of the flood grades, where water _ flood is 2 to represent weak flooding, water _ flood is 3 to represent medium flooding, and water _ flood is 4 to represent strong flooding. See table 1 for well logging interpretation results.
In the development stage, the low resistivity section of the X well is subjected to perforation production according to the interpretation result of the table 1, namely weak flooding and medium flooding, and the stable water content of the well is about 50% after production, as shown in a production curve diagram of the X well in FIG. 8, and the water content is identical with the dividing result of the flooding grade. The method can improve the calculation precision of the oil displacement efficiency, further improve the dividing precision of the low-resistivity oil layer water flooding level, and has a good application effect in the implementation of the comprehensive adjustment while drilling of the oil field.
TABLE 1 well low resistivity section water flooded layer well logging interpretation achievement table
Figure BDA0002538610150000112
The technology is simple to use, can be widely applied to quantitative evaluation of the low-resistivity heavy oil reservoir water flooded layer of the Bohai oilfield, has important guiding significance for improving the recovery ratio in the oilfield development process, and provides technical support for continuous stable production of 3000 thousands of the Bohai oilfield.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (7)

1. A method for calculating saturation before and after flooding of a low-resistivity heavy oil reservoir is characterized by comprising the following steps:
step 1: determining a cutoff value of low-resistivity heavy oil nuclear magnetic resonance logging T2;
step 2: calculating the original water saturation of the low-resistivity heavy oil by nuclear magnetic resonance logging;
and step 3: and determining the resistivity of the mixed water after the oil layer is flooded and calculating the water saturation.
2. The method for calculating the saturation before and after flooding of the low-resistivity thick oil layer according to claim 1, wherein after the calculation in the step 3, the flooding efficiency of the flooding layer and the classification of the flooding level are performed.
3. The method for calculating the saturation before and after the low-resistivity thick oil reservoir is flooded with water according to claim 1, wherein in the step 1, a method for determining a T2 cut-off value of equal-area compensation of thick oil capillary bound water and a free fluid T2 spectrum is established;
and (3) setting a T2 cut-off value range by establishing a target function based on the water saturation of the core analysis, and solving to obtain a T2 cut-off value of the heavy oil reservoir.
4. The method for calculating the saturation before and after flooding of the low-resistivity thick oil reservoir as claimed in claim 3, wherein when the shadow area S1 of the part of the free fluid T2 spectrum superimposed on the capillary bound water is equal to the shadow area S2 of the part of the capillary bound water T2 spectrum, the limit value is the cut-off value of the thick oil T2;
Figure FDA0002538610140000011
in the formula:
f is an objective function, and the minimum value is taken and is dimensionless;
CSwi _ SCAL is the water saturation of the rock core, f;
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt measured for NMR logging instrument2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
5. The method for calculating the saturation degree of the low resistivity thick oil reservoir before and after the water logging is carried out on the low resistivity thick oil reservoir according to the method 1, wherein the method is used for calculating the original water saturation degree of the water logging layer in a development well based on the T2 cut-off value obtained in the step 1, namely the method in the step 2;
Figure FDA0002538610140000021
in the formula:
swir _ NMR is the original water saturation calculated by nuclear magnetic resonance of the low-resistivity heavy oil, f;
S1measuring partial free fluid signal T2 spectral area, f for NMR logging;
s is total area of T2 spectrum measured by nuclear magnetic resonance logging, f;
S3measuring partial capillary bound water signal T2 spectral area f for nuclear magnetic resonance logging;
T2time for nuclear magnetic resonance measurement, ms;
T2maxt measured for NMR logging instrument2Maximum, ms;
T2cutofffor restraining water T for capillary2Cutoff value, ms.
6. The method for calculating the saturation before and after flooding of the low-resistivity thick oil reservoir as claimed in claim 1, wherein the method for determining the resistivity of the mixed water after flooding of the oil reservoir and calculating the water saturation in step 3 comprises the following steps:
firstly, supposing that injected water and primary formation water are subjected to sufficient ion exchange and are in a completely mixed state of dynamic balance, and obtaining a mineralization degree equation of mixed water based on a substance balance theory;
Figure FDA0002538610140000022
in the formula:
Cwthe mineralization degree of the mixed water is mg/L;
k is the multiple of injected water, and the specific value depends on the current flooding degree of the oil field;
Swethe water saturation after the oil layer is flooded, f;
Swirthe original water saturation of the oil layer, f;
Cwithe mineralization degree of the capillary water is mg/L;
Cwjthe degree of mineralization of injected water is mg/L;
secondly, establishing a correlation between the mineralization degree of the mixed water and the rock electrical parameter based on the experimental analysis of the rock resistivity under different mineralization degrees; in the argillaceous sandstone stratum, the lithoelectric parameters can change along with the change of the mineralization degree of the mixed water, and the two have obvious exponential relationship;
Figure FDA0002538610140000031
Figure FDA0002538610140000032
in the formula:
m is a cementation index;
n is a saturation index;
Cwthe mineralization degree of the mixed water is mg/L;
C1、C2、C3、C4the fitting coefficient is obtained by rock resistivity experiment;
controlling the resistivity of the mixed water by the mineralization degree and the temperature of the mixed water, and accurately calculating the resistivity of the mixed water by utilizing the mineralization degree and the temperature;
Figure FDA0002538610140000033
in the formula:
Rwzresistivity of formation mixed water, Ω · m;
t is the temperature in centigrade, DEG C;
substituting the electrical parameter expression of the rock in the step II into a saturation formula (Simandoux), and combining the electrical parameter expression with the formula in the step I and the step III to obtain the following simultaneous equation set:
Figure FDA0002538610140000041
in the formula:
a is lithology coefficient;
Rdis the formation depth resistivity, Ω · m;
φeeffective porosity, f;
Vshis the argillaceous content, f;
Rshis mudstone resistivity, omega m
Substituting the original water saturation Swir NMR calculated in step 1 into the simultaneous equation set for SwirThe equation set has three unknowns of Swe, Rwz and Cw; and carrying out iterative solution on the mixed water resistivity Rwz and the water saturation Swe under the current flooding state.
7. The method for calculating the saturation before and after the low-resistivity thick oil reservoir is flooded according to claim 2, wherein the oil displacement efficiency is calculated by utilizing the original saturation calculated by nuclear magnetic resonance logging and the stratum mixed water saturation calculated by the mixed water resistivity, and the flooding level is divided by combining a chart of the relation between the core oil displacement efficiency and the water content
Figure FDA0002538610140000042
In the formula:
eta is the oil displacement efficiency, f;
swe is the water saturation after the oil layer is flooded, f;
swir NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f.
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CN103225500A (en) * 2013-05-02 2013-07-31 中国石油大学(华东) Novel water flooding layer logging evaluation method applying three parameters self-consistent iterative algorithm
CN104500055A (en) * 2014-12-16 2015-04-08 中国石油天然气股份有限公司 Calculation method for water saturation of water flooded layer of ultralow permeability reservoir
CN104806231A (en) * 2014-01-27 2015-07-29 中国石油化工股份有限公司 Quantitative evaluation method of heavy oil steam stimulation water flooded layer

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101004134A (en) * 2007-01-10 2007-07-25 辽河石油勘探局 Method for explaining thick oil reservoir bed by using T2 relaxation spectrum
CN103225500A (en) * 2013-05-02 2013-07-31 中国石油大学(华东) Novel water flooding layer logging evaluation method applying three parameters self-consistent iterative algorithm
CN104806231A (en) * 2014-01-27 2015-07-29 中国石油化工股份有限公司 Quantitative evaluation method of heavy oil steam stimulation water flooded layer
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