CN112324421B - Method for calculating saturation of low-resistivity thick oil layer before and after flooding - Google Patents
Method for calculating saturation of low-resistivity thick oil layer before and after flooding Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
- G01V3/32—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with electron or nuclear magnetic resonance
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- G—PHYSICS
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A10/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE at coastal zones; at river basins
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- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention discloses a method for calculating saturation of a low-resistivity thick oil layer before and after flooding, which comprises the following four steps: step 1: determining a T2 cut-off value of the low-resistivity thick oil nuclear magnetic resonance logging; step 2: calculating the original water saturation of the low-resistivity thick oil nuclear magnetic resonance logging; step 3: after the oil layer is flooded, determining the resistivity of the mixed water and calculating the water saturation; step 4: and (5) calculating the flooding efficiency of the flooding layer and dividing the flooding level. The method can improve the calculation accuracy of the oil displacement efficiency, further improves the division accuracy of the flooding level of the low-resistivity oil layer, has good technical effect and simple use, can be widely applied to quantitative evaluation of the flooding level of the low-resistivity heavy oil reservoir of the Bohai sea oil field, and has important guiding significance for improving the recovery ratio in the oil field development process.
Description
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 of a low-resistivity thick oil layer before and after flooding.
Background
Because the resistivity of the low-resistivity oil layer is very close to or even lower than that of the water layer in the same system, along with the continuous deep development of the water injection of the oil field, quantitative evaluation of flooding of the low-resistivity oil layer brings great challenges to logging staff, and the division result of the flooding level of the low-resistivity oil layer is directly related to perforation decisions of the oil reservoir staff. The difficulty in evaluating the flooding of the low-resistivity oil layer is mainly how to accurately calculate the water saturation of the oil layer before and after flooding, wherein the water saturation calculation accuracy directly relates to the calculation accuracy of the oil displacement efficiency, and further the division of the flooding layer level is determined. At present, the original water saturation of a water flooded layer is mainly determined by using resistivity inversion of an adjacent well or nuclear magnetic resonance logging, and the calculation accuracy of the water saturation after flooding depends on the resistivity of mixed water (injected water and formation water) in the stratum after water flooding development. Because the reservoir and fluid properties on the plane change greatly, the original water saturation calculated by the traditional resistivity inversion method has larger error, and meanwhile, the accurate original water saturation obtained by nuclear magnetic resonance logging mainly depends on the accurate determination of the T2 cut-off value, but for a low-resistivity heavy oil reservoir, the determination of the T2 cut-off value is difficult due to the superposition of free fluid T2 spectrum advancing and capillary constraint water, and for argillaceous sandstone, the original water saturation calculated by using the traditional T2 cut-off value of 33ms is obviously higher, and the error is larger. At present, the resistivity of the mixed water is mainly obtained by three methods of laboratory water analysis data, natural potential curve calculation and an iteration method. The offshore oil field logging series mainly comprises logging while drilling, does not have natural potential logging, and has limited laboratory water analysis data, so that an iteration method is commonly used for determining the resistivity of mixed water. The current iteration method is generally shown in the following equation:
wherein:
S we f, the water saturation after the oil layer is flooded;
S wir f, the original water saturation of an oil layer;
R wz mixing water resistivity for the stratum, omega-m;
R wi is the resistivity of the connate water, omega.m;
R wj for injection of water powerResistivity, Ω·m;
R d is the deep resistivity of stratum, omega.m;
m is the cementation index;
n is a saturation index;
φ e is the effective porosity, f;
a is lithology coefficient;
V sh is the clay content, f;
R sh is mudstone resistivity, Ω·m.
The above equation set has only two formulas, but S we 、S wir And R is wz Three unknowns are underdetermined equation sets, the traditional iteration method has multiple solutions, and the iteration result has larger errors.
In addition, for muddy sandstone formations, the rock electrical parameters will change as the degree of mineralization of the mixed water changes. The conventional iteration method only considers the change of the mixed water resistivity, but ignores the influence of the rock electrical parameter change on solving the current water saturation, further reduces the accuracy of an iteration result, and the calculation result cannot meet the saturation evaluation after the low-resistivity oil layer is flooded. Therefore, the interpretation accuracy of the saturation before and after flooding is critical to logging evaluation of the flooding layer.
Disclosure of Invention
The invention aims to provide a method for calculating the saturation of a low-resistivity thick oil layer before and after flooding, so as to solve the problem of the background technology.
In order to achieve the purpose, the specific technical scheme of the method for calculating the saturation of the low-resistivity thick oil layer before and after flooding is as follows: a method for calculating saturation of a low-resistivity thick oil layer before and after flooding comprises the following steps:
step 1: determining a T2 cut-off value of the low-resistivity thick oil nuclear magnetic resonance logging;
step 2: calculating the original water saturation of the low-resistivity thick oil nuclear magnetic resonance logging;
step 3: after the oil layer is flooded, determining the resistivity of the mixed water and calculating the water saturation;
step 4: and (5) calculating the flooding efficiency of the flooding layer and dividing the flooding level.
Preferably, in the step 1, a T2 cut-off value determining method of area compensation such as thick oil capillary bound water and free fluid T2 spectrum is established; and (3) based on the water saturation of core analysis, setting a T2 cut-off value range by establishing an objective function, and solving and obtaining a T2 cut-off value of the thick oil layer.
Preferably, when the shadow area S1 of the portion of the free fluid T2 spectrum superimposed on the capillary bound water is equal to the shadow area S2 of the portion of the capillary bound water T2 spectrum, the limit value at this time is the heavy oil T2 cut-off value;
wherein:
f is an objective function, takes the minimum value and has no dimension;
cswi_scal is the water saturation of the core, f;
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max t measured for nuclear magnetic resonance logging instrument 2 Maximum value, ms;
T 2cutoff binding water T for capillary 2 Cut-off value, ms.
Preferably, based on the T2 cut-off value obtained in the step 1, calculating the original water saturation of the water flooded layer in the development well, namely, the step 2 method;
wherein:
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max t measured for nuclear magnetic resonance logging instrument 2 Maximum value, ms;
T 2cutoff binding water T for capillary 2 Cut-off value, ms.
Preferably, in the step 3, the method for determining the resistivity of the mixed water after flooding the oil layer and calculating the water saturation comprises the following steps:
(1) assuming that the injected water and the primary stratum water are fully ion exchanged and are in a dynamic balance and complete mixing state, and obtaining a mineralization degree equation of the mixed water based on a material balance theory.
Wherein:
C w is the mineralization degree of the mixed water, mg/L;
k is the multiple of the injected water, and the specific value depends on the current flooding degree of the oil field;
S we f, the water saturation after the oil layer is flooded;
S wir f, the original water saturation of an oil layer;
C wi is the mineralization degree of capillary water, mg/L;
C wj mg/L for mineralization of injected water.
(2) Based on rock resistivity experimental analysis under different mineralization degrees, a correlation relation between the mineralization degree of the mixed water and the rock electric parameters is established. In a argillaceous sandstone stratum, the rock electric parameters can change along with the change of the mineralization degree of the mixed water, and the two have obvious exponential relationship;
wherein:
m is the cementation index;
n is a saturation index;
C w is the mineralization degree of the mixed water, mg/L;
C 1 、C 2 、C 3 、C 4 the fitting coefficients were obtained from rock resistivity experiments.
(3) 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.
Wherein:
R wz mixing water resistivity for the stratum, omega-m;
t is the temperature in centigrade, DEG C;
(4) bringing the petroelectric parameter expression in step (2) into a saturation formula (Simandoux) and combining the formulas in step (1) and step (3) can obtain the following simultaneous equations:
wherein:
a is lithology coefficient;
R d is the deep resistivity of stratum, omega.m;
φ e in order for the porosity to be effective,f；
V sh is the clay content, f;
R sh is mudstone resistivity, omega.m
Substituting S by substituting the raw water saturation Swir_NMR calculated in step 1 into a simultaneous equation set wir The equation set has three unknowns, swe, rwz, and Cw. And (3) carrying out iterative solution to obtain the mixed water resistivity Rwz and the water saturation Swe in the current flooding state.
Preferably, in step 4, the oil displacement efficiency is calculated by using the original saturation calculated by nuclear magnetic resonance logging and the stratum mixed water saturation calculated by mixed water resistivity, and the flooding grade is divided by combining the core oil displacement efficiency and the water content relation chart.
Wherein:
η is oil displacement efficiency, f;
swe is the water saturation of the oil layer after flooding, and 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 water saturation of a low-resistivity thick oil layer before and after flooding, which establishes a method for determining a T2 cut-off value of area compensation such as low-resistivity thick oil capillary tie-down water and free fluid T2 spectrum based on nuclear magnetic resonance logging data, and realizes accurate calculation of original water saturation of a flooding layer; the method for calculating the water saturation after flooding is based on conventional logging data, 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 flooding layer is realized. The accurate calculation of the water saturation of the low-resistivity heavy oil reservoir before and after flooding improves the calculation precision of the quantitative evaluation parameter oil displacement efficiency of the flooding layer, realizes the level division of the flooding layer of the low-resistivity heavy oil reservoir, has better matching of the result of the method and the actual production data of the oil well after production, and has important guiding significance for the development and the recovery ratio improvement of the oil field.
Drawings
FIG. 1 is a flow chart of a method for calculating saturation of a low-resistivity thick oil reservoir before and after flooding, which is provided by an embodiment of the invention;
fig. 2a and 2b are schematic diagrams of a new method for determining a T2 cut-off value of a thick oil nmr well logging according to an embodiment of the present invention;
FIG. 3 is a graph showing the comparison between the original water saturation of the core magnetic core and the water saturation of the core of the W-well low-resistivity heavy oil layer according to the embodiment of the invention;
fig. 4a, 4b and 4c are graphs showing the fitting relation between the mineralization degree of the mixed water and the rock electric parameters (m and n values) provided by the embodiment of the invention;
FIG. 5 is a graph showing the effect of calculating water saturation before and after flooding of the low resistivity section of the X well according to the embodiment of the present invention;
FIG. 6 is a graph of the flooding efficiency calculation and flooding level division results for the low resistivity section of the X well according to the embodiment of the invention;
FIG. 7 is a graph of displacement efficiency versus water content for a low resistivity section of a P-field according to an embodiment of the present 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, structures and functions of the present invention, the present invention will be understood with reference to fig. 1-8.
The invention provides a method for determining a T2 cut-off value of a low-resistivity thick oil nuclear magnetic resonance logging by combining the results of conventional core analysis, rock electric experiments under different mineralization degrees, water flooding experiments and nuclear magnetic resonance experiments, and further calculates the original water saturation of an oil layer by using the T2 cut-off value.
The change rule of the rock electric parameters under different mineralization degrees is analyzed, a determination formula of the rock electric parameters is obtained, a simultaneous mixed water mineralization degree equation, a mixed water resistivity calculation formula and a mixed water resistivity iteration equation set of a saturation formula (Simandoux) are provided, and the calculation of the water saturation of the oil layer after flooding is realized. The accurate calculation of the water saturation before and after the flooding of the oil layer improves the calculation accuracy of the oil displacement efficiency, and further improves the division accuracy of the flooding level of the low-resistivity oil layer.
As shown in the flow chart of FIG. 1, the invention provides a method for calculating the saturation of a low-resistivity thick oil layer before and after flooding, which is operated according to the following steps, and mainly comprises four steps.
Step 1: determination of T2 cut-off value of low-resistivity thick oil nuclear magnetic resonance logging
For a low-resistivity thick oil layer, the partial free fluid T2 spectrum forward movement is difficult to distinguish by the partial superposition of capillary bound water due to high fluid viscosity and finer lithology. For the problem of difficult determination of the thick oil T2 cut-off value, a T2 cut-off value determination method of area compensation such as thick oil capillary bound water and free fluid T2 spectrum is established, as shown in fig. 2, a shadow area S1 is a part of the free fluid T2 spectrum superimposed on the capillary bound water, a shadow area S2 is a part of the capillary bound water T2 spectrum, and when the shadow area S1=S2, the limit value at the moment is the thick oil T2 cut-off value. And (3) analyzing the water saturation based on the core, setting a T2 cut-off value range by establishing an objective function, and traversing to obtain a thick oil layer T2 cut-off value.
Wherein:
f is an objective function, takes the minimum value and has no dimension;
cswi_scal is the water saturation of the core, f;
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max t observed for nuclear magnetic resonance logging instrument 2 Maximum value, ms;
T 2cutoff binding water T for capillary 2 Cut-off value, ms.
And (3) calculating according to a formula (1), wherein when the viscosity of the crude oil in the low-resistivity oil layer section is about 50 mPas, the value range of the T2 cut-off value is 15-18 ms, and when the viscosity of the crude oil in the low-resistivity oil layer section is 147-182 mPas, the value range of the T2 cut-off value is 13-15 ms.
And (3) based on the T2 cut-off value determined in the step (1), popularizing and applying the cut-off value to a development well to calculate the original water saturation of the flooding layer.
Wherein:
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max t observed for nuclear magnetic resonance logging instrument 2 Maximum value, ms;
T 2cutoff binding water T for capillary 2 Cut-off value, ms.
As shown in FIG. 3, the nuclear magnetic resonance original water saturation Swir_NMR determined by the T2 cut-off value in the 7 th curve has better coincidence relation with the core analysis water saturation Cdwi_SCAL, which indicates that the reliability of the method for determining the T2 cut-off value is higher.
Step 3, determining the resistivity of the mixed water after the oil layer is flooded and calculating the water saturation
(1) Assuming that the injected water and the primary stratum water are fully ion exchanged and are in a dynamic balance and complete mixing state, and obtaining a mineralization degree equation of the mixed water based on a material balance theory.
Wherein:
C w is the mineralization degree of the mixed water, mg/L;
k is the multiple of the injected water, and the specific value depends on the current flooding degree of the oil field;
S we f, the water saturation after the oil layer is flooded;
S wir f, the original water saturation of an oil layer;
C wi is the mineralization degree of capillary water, mg/L;
C wj mg/L for mineralization of injected water.
(2) Based on rock resistivity experimental analysis under different mineralization degrees, a correlation relation between the mineralization degree of the mixed water and the rock electric parameters is established. As shown in fig. 4, in the argillaceous sandstone stratum, the rock electric parameters can change along with the change of the mineralization degree of the mixed water, and the rock electric parameters and the mineralization degree of the mixed water have obvious exponential relationship.
Wherein:
m is the cementation index;
n is a saturation index;
C w is the mineralization degree of the mixed water, mg/L;
C 1 、C 2 、C 3 、C 4 the fitting coefficients were obtained from rock resistivity experiments.
(3) 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.
Wherein:
R wz mixing water resistivity for the stratum, omega-m;
t is the temperature in centigrade, DEG C;
(4) bringing the petroelectric parameter expression in step (2) into a saturation formula (Simandoux) and combining the formulas in step (1) and step (3) can obtain the following simultaneous equations:
wherein:
a is lithology coefficient;
R d is the deep resistivity of stratum, omega.m;
φ e is the effective porosity, f;
V sh is the clay content, f;
R sh is mudstone resistivity, Ω·m.
Substituting S by substituting the raw water saturation Swir_NMR of the nuclear magnetic resonance log calculated in step (1) into a simultaneous equation set wir The equation set has three unknown quantities of Swe, rwz and Cw, and the mixed water resistivity Rwz and the water saturation Swe in the current flooding state can be obtained by carrying out iterative solution on the three unknown quantities. As shown in fig. 5, cw in the 6 th curve is the degree of mineralization of the mixed water calculated iteratively; r in curve 7 wz The mixed water resistivity calculated for the mineralization degree Cw of the mixed water; m in lane 8 is the calculated bond index; n in trace 9 is the calculated saturation index; swe in curve 10 is the mixed water resistivityThe calculated water saturation of the oil layer after flooding; swir_NMR is the original water saturation of the oil layer calculated using the T2 cut-off value determined in step (1).
Step 4, calculating the flooding efficiency of the flooding layer and dividing flooding levels
And calculating the oil displacement efficiency by using the original saturation calculated by nuclear magnetic resonance logging and the stratum mixed water saturation calculated by the mixed water resistivity, and dividing the flooding level by combining the core oil displacement efficiency and the water content relation chart.
Wherein:
η is oil displacement efficiency, f;
swe is the water saturation of the oil layer after flooding, and 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 curve 7 is the calculated displacement efficiency. And combining the relation plate of the oil displacement efficiency and the water content of the core experiment.
As shown in fig. 7, the low-resistivity section of the X-well is classified into flooding grades, and the 8 th curve in fig. 6 is the result of the classification of flooding grades, wherein water_flood=2 in the figure represents weak flooding, water_flood=3 represents flooding, and water_flood=4 represents strong flooding. Details of the log interpretation are shown in Table 1.
In the development stage, the low-resistivity section of the X well is used for explaining the result of weak flooding and medium flooding perforation production according to the table 1, the stable water content of the well after production is about 50%, and as shown in a production graph of the well in fig. 8 and X, the water content is identical with the classification result of the flooding level. The method can improve the calculation accuracy of the oil displacement efficiency, further improve the division accuracy of the flooding level of the low-resistivity oil layer, and has a good application effect in the implementation of oil field comprehensive adjustment while drilling.
Table 1X well logging interpretation results table for low resistivity section flooding layer
The technique is simple to use, can be widely applied to quantitative evaluation of the water flooded layer of the low-resistivity heavy oil reservoir of the Bohai sea oil field, has important guiding significance for improving the recovery ratio in the oil field development process, and provides technical support for 3000 thousands of continuous stable production of the Bohai sea oil field.
It will be understood that the invention has been described in terms of several embodiments, and that various changes and equivalents may be made to these features and embodiments 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 (3)
1. The method for calculating the saturation of the low-resistivity thick oil layer before and after flooding is characterized by comprising the following steps of:
step 1: a low resistivity thick oil nmr log T2cutoff determination comprising:
establishing a T2 cut-off value determining method of area compensation such as thick oil capillary bound water and free fluid T2 spectrum;
analyzing the water saturation based on the core, setting a T2 cut-off value range by establishing an objective function, and solving to obtain a T2 cut-off value of the thick oil layer;
when the shadow area S1 of the free fluid T2 spectrum superimposed on the capillary bound water is equal to the shadow area S2 of the partial capillary bound water T2 spectrum, the limit value at the moment is the cut-off value of the thick oil T2;
wherein:
f is an objective function, takes the minimum value and has no dimension;
cswi_scal is the water saturation of the core, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max a maximum value of T2 measured by a nuclear magnetic resonance logging instrument, ms;
t2cutoff is the capillary bound water T2cutoff value, ms;
step 2: the original water saturation calculation of the low-resistivity thick oil nuclear magnetic resonance logging comprises the following steps:
based on the T2 cut-off value obtained in the step 1, calculating the original water saturation of the water flooded layer in the development well, namely, a step 2 method;
wherein:
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f;
S 1 measuring a partial free fluid signal T2 spectral area, f, for nuclear magnetic resonance logging;
s is the total area of a nuclear magnetic resonance logging measurement T2 spectrum, and f;
S 3 measuring the T2 spectrum area and f of a partial capillary bound water signal for nuclear magnetic resonance logging;
T 2 for nuclear magnetic resonance measurement time, ms;
T 2max t measured for nuclear magnetic resonance logging instrument 2 Maximum value, ms;
T 2cutoff binding water T for capillary 2 Cut-off value, ms;
step 3: and determining the resistivity of the mixed water after flooding the oil layer and calculating the water saturation, wherein the method comprises the following steps of: (1) assuming that the injected water and the primary stratum water are fully ion-exchanged and are in a dynamic balance complete mixing state, and obtaining a mineralization degree equation of the mixed water based on a material balance theory;
wherein:
C w is the mineralization degree of the mixed water, mg/L;
k is the multiple of the injected water, and the specific value depends on the current flooding degree of the oil field;
S we f, the water saturation after the oil layer is flooded;
S wir f, the original water saturation of an oil layer;
C wi is the mineralization degree of capillary water, mg/L;
C wj mg/L for mineralization of injected water;
(2) based on rock resistivity experimental analysis under different mineralization degrees, establishing a correlation relation between the mineralization degree of mixed water and rock electric parameters; in a argillaceous sandstone stratum, the rock electric parameters can change along with the change of the mineralization degree of the mixed water, and the two have obvious exponential relationship;
wherein:
m is the cementation index;
n is a saturation index;
C w is the mineralization degree of the mixed water, mg/L;
C 1 、C 2 、C 3 、C 4 the fitting coefficient is obtained by rock resistivity experiments;
(3) 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;
wherein:
R wz mixing water resistivity for the stratum, omega-m;
t is the temperature in centigrade, DEG C;
(4) bringing the petroelectric parameter expression in step (2) into a saturation formula (Simandoux) and combining the formulas in step (1) and step (3) can obtain the following simultaneous equations:
wherein:
a is lithology coefficient;
R d is the deep resistivity of stratum, omega.m;
φ e is the effective porosity, f;
V sh is the clay content, f;
R sh is mudstone resistivity, omega.m
Substituting S by substituting the raw water saturation Swir_NMR calculated in step 2 into a simultaneous equation set wir The equation set has three unknowns of Swe, rwz and Cw; and (3) carrying out iterative solution to obtain the mixed water resistivity Rwz and the water saturation Swe in the current flooding state.
2. The method for calculating the saturation of a low-resistivity thick oil reservoir before and after flooding according to claim 1, wherein after the calculation in the step 3, reservoir displacement efficiency calculation and flooding grade division are performed.
3. The method for calculating the saturation of a low-resistivity thick oil reservoir before and after flooding according to claim 2, wherein the oil displacement efficiency is calculated by using the original saturation calculated by nuclear magnetic resonance logging and the formation mixed water saturation calculated by mixed water resistivity, and the flooding level is divided by combining a core oil displacement efficiency and water content relation chart
Wherein:
η is oil displacement efficiency, f;
swe is the water saturation of the oil layer after flooding, and f;
Swir_NMR is the original water saturation calculated by nuclear magnetic resonance of the low resistivity heavy oil, f.
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| 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 |
| 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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| Publication number | Priority date | Publication date | Assignee | Title |
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| 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 |
| 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 |
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