CN116084929A - Oil-water interface determining method - Google Patents

Oil-water interface determining method Download PDF

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CN116084929A
CN116084929A CN202310373782.2A CN202310373782A CN116084929A CN 116084929 A CN116084929 A CN 116084929A CN 202310373782 A CN202310373782 A CN 202310373782A CN 116084929 A CN116084929 A CN 116084929A
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oil
depth
water
formula
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CN116084929B (en
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陈义国
封从军
王超
樊笑微
贺永红
郝世彦
郭顺
陈治军
周伟
左龙
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Northwest University
Changan University
Shaanxi Yanchang Petroleum Group Co Ltd
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Changan University
Shaanxi Yanchang Petroleum Group Co Ltd
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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
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. analysis, for interpretation, for correction
    • G01V1/30—Analysis
    • G01V1/306—Analysis for determining physical properties of the subsurface, e.g. impedance, porosity or attenuation profiles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V11/00—Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01V3/38—Processing data, e.g. for analysis, for interpretation, for correction
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    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/62—Physical property of subsurface
    • G01V2210/622—Velocity, density or impedance
    • G01V2210/6226—Impedance
    • G—PHYSICS
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    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/62—Physical property of subsurface
    • G01V2210/624—Reservoir parameters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/62—Physical property of subsurface
    • G01V2210/624—Reservoir parameters
    • G01V2210/6244—Porosity
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    • Y02A90/30—Assessment of water resources

Abstract

An oil-water interface determining method belongs to the field of oil-gas field development, and comprises the following steps: step one: comprehensively judging the type of the reservoir according to the longitudinal acoustic time difference and the resistivity logging curve response characteristics of the reservoir and by combining geological logging data; step two: determining a reference water interval, a reference depth, a reference resistivity and a logging apparent resistivity at depth N; step three: calculating the substrate resistivity above the reference depth, the substrate resistivity ratio and the reference porosity; step four: calculating the ratio of the reconstructed resistivity to the reconstructed resistivity above the reference depth; step five: and determining whether an oil-water interface and a position depth exist according to a determination formula. On the basis of the traditional apparent resistivity ratio method, the method analyzes the differential influence of the matrix and the fluid on the resistivity, further determines the oil-water interface position, realizes accurate judgment and calculation of the oil-water interface position of the full-class reservoir, and has important popularization and application prospects.

Description

Oil-water interface determining method
Technical Field
The invention belongs to the field of oil-gas field development, and particularly relates to an oil-water interface determining method.
Background
The deposition basin in China develops a large amount of bottom water, such as an Erdos basin triad Yanan oil layer and an extension group top oil layer, a Songliao basin Qing mountain mouth oil layer and a Yaojia oil layer, a Bohai Bay basin east ying sunk sand river street oil layer, a Tarim basin Tahe oil field triad oil layer, a quasi-Song basin clear water river top oil layer and the like, and meanwhile, the oil reservoirs are an important resource type for guaranteeing the safety of the petroleum energy strategy in China because of active bottom water, sufficient stratum energy, higher oil yield and longer stable production period.
In the standard "working specification for exploration and oil testing," reservoir "refers to a formation that has industrial oil flow production capacity and is primarily producing oil. From this, the oil saturation at the "oil-water interface" is approximately equal to 50%; the oil-water interface is mainly the industrial oil flow, and the saturation of oil is more than 50%; under the "oil-water interface" the water production is the main, and the oil saturation is less than 50% (log data processing and comprehensive interpretation page 135, yong Shi and 2004). The accurate calculation of the oil-water interface position is not only related to petroleum geological reserve estimation, well drilling and completion technology, fracturing measure selection, development effect dynamic evaluation and the like, but also directly affects the oil field productivity construction, and is one of the core and difficulty of oil reservoir research. At present, the industry judging method of the oil-water interface mainly comprises a dynamic data testing method and a static data identification method, is limited by factors such as oil well type, data acquisition rate and timeliness, and has defects of different degrees in the existing two technical methods.
(1) Dynamic data testing method: and determining the position of the oil-water interface through dynamic data analysis such as wellbore pressure test, working fluid level measurement, core mercury pressing and the like. The method is biased to the determination of the oil-water interface position in the oil well production process and is limited by factors such as the number of test wells, cost, time efficiency and the like, is mainly used in a horizontal well and a shut-in well, is mainly used for improving the oil extraction efficiency of the oil well and treating the shut-in well, and is difficult to determine the original stratum oil-water interface position, so that the method has limitation in application.
(2) Static data identification method: and the oil-water interface position of the original stratum is determined by interpretation processing of static data such as logging, earthquake and the like. In contrast, "seismic data" also has the limitations of sporadic measurement and local acquisition. The oil field well in China carries out general logging of logging data, and the oil-water interface identification method is researched by applying the logging data, so that the method has extremely important significance. Logging data entry for existing applicationsThe oil-water interface identification method mainly comprises an oil saturation evaluation method and a apparent resistivity ratio method. (1) The oil saturation evaluation method is to calculate the oil saturation based on a classical Archie model or saturation models in other transformation forms, and determine the oil-water interface position by taking the oil saturation of more than or equal to 50 percent as a judgment condition. Based on classical Archie model, students put forward tens of saturation evaluation improvement models (Sun Jianmeng, development and analysis of logging saturation interpretation models, petroleum exploration and development, 2008), but various model process parameters are numerous and difficult to accurately determine, such as classical Archie model parameters including porosity index m, lithology coefficient a, saturation index n, saturation coefficient b and formation water resistivity R w 5, wherein the porosity index, the lithology coefficient, the saturation index and the saturation coefficient are determined through a rock electric experiment, but the core with general representativeness is difficult to select or is freshly existing; the formation water resistivity parameter is usually obtained by carrying out test statistics on water samples of a limited sampling well or by calculating a natural potential curve, but the water samples with general representativeness are also difficult to select, the influence factors of the natural potential curve are more than ten kinds, and the calculation accuracy is also difficult to guarantee. (2) The visual resistivity ratio method is used for judging the position of an oil-water interface according to the longitudinal resistivity ratio of a reservoir, and determining the position of the oil-water interface by taking the resistivity ratio of more than or equal to 3-5 as a judging condition (page 133, harmony and sum, 2004, and 170 pages 170 and 184 of log theory and comprehensive interpretation, and is dense in flood, 2005, han Qianfeng, and application of visual resistivity increase rate in oil-gas-water research of the Nanyang oil-gas field, and logging technology, 2006), and the method is used for fully attributing the visual resistivity change to the change of fluid properties, ignoring the influence of the rock matrix variability on the visual resistivity, and not giving a standard water layer quantification determination scheme, and meanwhile, the ratio of more than or equal to 3-5 is too wide and lacks a certain theoretical basis, so that the error of calculating the position of the oil-water interface is increased.
In summary, the oil saturation evaluation method focuses on the establishment of a new oil saturation evaluation formula based on different stratum simplified models through core experiments, the stratum simplified models established by the experiments are different from actual stratum greatly, and the formula calculation parameters are obtained based on limited quantity of core actual measurement, so that the oil saturation evaluation method is difficult to obtain widely representativeness, and therefore various oil saturation evaluation models have good application effects in the experiments and have uneven application effects in field practice of oil fields. The apparent resistivity ratio method pays attention to the judging speed of the oil-water interface, neglects the identification accuracy and precision to a certain extent, is suitable for determining the oil-water interface of a high-saturation oil layer for early exploration and development of oil fields, and has the disadvantages of lower oil layer quality, lower oil-containing saturation and increased water flooding layer proportion as most oil fields in China gradually enter the later exploration and development stage.
The method is used for judging that the oil-water interface position error is larger, and particularly for the bottom water development oil reservoir, a large number of oil wells often have higher water content, insufficient oil layer utilization, petroleum resource waste and the like.
Disclosure of Invention
The invention aims to provide an oil-water interface determining method, which is used for determining the position of an oil-water interface by analyzing the differential influence of matrix and fluid on resistivity on the basis of a traditional apparent resistivity ratio method, so that the accurate judgment and calculation of the position of the oil-water interface of a full-scale reservoir are realized, and the method has important popularization and application prospects.
The technical scheme adopted by the invention is as follows:
an oil-water interface determining method comprises the following steps:
step one: comprehensively judging the type of the reservoir according to the longitudinal acoustic time difference and the apparent resistivity logging curve response characteristics of the reservoir and by combining geological logging data;
step two: determining a reference water interval, a reference depth and a reference resistivity R B Logging apparent resistivity R at depth N N ；
R B And R is N Obtained directly by deep induction or deep lateral resistivity logging methods.
Step three: calculating the substrate resistivity R above the reference depth NJ Matrix resistivity ratio I NJ And a reference porosity phi B ；
SubstrateResistivity R NJ The physical meaning of (2) is the resistivity at depth N at which the reservoir matrix pores are saturated with water, i.e., assuming that the fluids are all water, where the resistivity is equal to the baseline resistivity R B Only the differences in matrix are caused by changes in Ω·m; matrix resistivity ratio I NJ The ratio of the matrix resistivity to the reference resistivity at depth N is dimensionless.
The equation (2) can be obtained for the Archie equation (1):
Figure SMS_1
（1）
Figure SMS_2
（2）
regression modeling is carried out according to the acoustic time difference logging value and the core porosity data to obtain a porosity calculation formula (3); according to the rock electricity experimental data, a cementing index calculation formula (4) is obtained:
Figure SMS_3
（3）
Figure SMS_4
（4）
in the formulas (1) - (4), S w Is water saturation, dimensionless; phi is porosity, dimensionless; r is R w Is the formation water resistivity, Ω·m; r is total resistivity, omega.m; a is lithology coefficient, dimensionless; b is a saturation coefficient, dimensionless; n is a saturation index, is dimensionless, and takes a theoretical value of 2; m is a cementation index, dimensionless; AC is the difference in logging acoustic wave, mu s/m; c. d, e and f are undetermined coefficients;
the reference resistivity R is determined according to equation (2) B Represented by the form of formula (5):
Figure SMS_5
（5）
since a and b are unknown quantities and are difficult to accurately calculate, the expression (5) is modified, and these two parameter values are calculated by other parameters as a whole.
Formula (6) is obtained from formula (5):
Figure SMS_6
（6）
reference porosity phi B The porosity at each depth point in the reference water layer section is obtained from formula (3) as the average value of the porosity of the reference water layer section, and in addition, the porosity Φ at the depth N N Also from formula (3);
equation (2) is a general equation, for a reference water interval, the porosity and water saturation are both actual values for the interval, for a depth N, the porosity is the actual value for the interval, and the water saturation is assumed to be water-only and oil-free, so as to obtain a matrix resistivity value for the depth N;
Obtaining the substrate resistivity R from the formula (2) and the formula (6) NJ Further, the matrix resistivity ratio I is obtained NJ See formula (7) and formula (8), respectively:
Figure SMS_7
（7）
Figure SMS_8
（8）
in the formulas (5) and (7), m B Is the cementation index at the reference depth, and has no dimension; m is m N Is the cementation index at depth N, dimensionless; s is S Bw Taking a theoretical value of 1 of a bottom water oil layer as the water saturation at the reference depth and the dimensionless; phi B 、Φ N The porosity at the reference porosity and the depth N are respectively dimensionless;
R NJ and R is R B The difference is the resistivity difference between the matrix at depth N and the matrix at the reference depth.
Step four: calculating a reconstructed resistivity R above a reference depth NR Ratio of resistivity to reconstruction I NR ；
Reconstructing resistivity R NR The physical meaning of (2) is that the apparent resistivity at depth N is the resistivity after the change in resistivity due to the change in matrix is eliminated. Reconstruction resistivity ratio I NR Is the ratio of the reconstructed resistivity at depth N to the reference resistivity.
The apparent resistivity at depth N is different from the reference resistivity (R N -R B ) Is the difference in resistivity (R) resulting from the difference in matrix at depth N from the reference depth matrix NJ -R B ) And the difference in resistivity (R) between the fluid at depth N (i.e. the resistivity of the fluid itself containing the oil phase to be determined) and the reference depth fluid NR -R B ) The following relation (9) is given for the common constitution:
Figure SMS_9
（9）
equation (10) is obtained from equation (9), and equation (11) is obtained:
Figure SMS_10
（10）
Figure SMS_11
（11）
in the formulae (9) and (11), R NR Is the reconstructed resistivity at depth N, Ω·m; i NR Is the reconstructed resistivity ratio at depth N, dimensionless; i NS The apparent resistivity ratio at depth N is the apparent resistivity R at depth N N And reference resistivity R B Is a ratio of (2);
R N and R is R B The difference of (2) is composed of the matrix resistivity difference and the fluid resistivity difference at two depths, and represents the matrix difference and the oil-water fluid difference.
The reconstructed resistivity is expressed as equation (12), and by combining equation (6), equations (13) and (14) are obtained, respectively:
Figure SMS_12
（12）
Figure SMS_13
（13）
Figure SMS_14
（14）
in the formula (12), S Nw For the actual water saturation at depth N (whereas in equation (7), for the matrix resistivity, all water is assumed), dimensionless;
step five: at the oil-water interface and above,
Figure SMS_15
then there is a decision equation (15):
Figure SMS_16
（15）
judgment of I NR ≥4*I NJ If so, taking the lowest depth as an oil-water interface when the oil-water interface is established; when not established, no oil-water interface exists.
Further, in the first step, the reservoir is divided into 3 types 9 according to the longitudinal acoustic time difference and the apparent resistivity logging curve response characteristics of the reservoir,
The type I reservoir is thinned from bottom to top in lithology, and the pores become smaller, wherein the type I reservoir comprises type I-1 bell-shaped sonic time difference and apparent resistivity in bell shape; type I-2 bell-shaped acoustic time difference, wherein the apparent resistivity is funnel-shaped; i-3 type bell-shaped sound wave time difference, wherein the apparent resistivity is straight;
the lithology of the II type reservoir layer is thickened from bottom to top, the pores are enlarged, the II type reservoir layer comprises II-1 type funnel-shaped acoustic wave time difference, and the apparent resistivity is bell-shaped; the II-2 type funnel-shaped acoustic wave time difference and apparent resistivity are funnel-shaped; type II-3 funnel-shaped acoustic wave time difference, and apparent resistivity is straight;
the III type reservoir is stable in lithology from bottom to top and small in pore change, comprises III-1 type straight acoustic wave time difference and has bell-shaped apparent resistivity; III-2 straight sound wave time difference, and apparent resistivity is funnel-shaped; III-3 type straight shape acoustic wave time difference, and apparent resistivity is straight.
Further, in the second step, in a depth section with the oil saturation less than 0.1 calculated by an oil saturation evaluation method, the upper third and the lower third are removed, and the middle third is used as a reference water interval (effectively reducing the interference of upper and lower surrounding rocks on logging response, and overcoming the problem of low accuracy of pure water interval determined empirically in the existing method); taking the average value of the depth of the reference water layer segment as the reference depth and taking the average value of the apparent resistivity of the reference water layer segment as the reference resistivity R B 。
The invention has the beneficial effects that:
the method comprehensively considers the dual influence of the matrix and the fluid on the resistivity, overcomes the defects that the conventional oil saturation evaluation method has more parameters and is difficult to accurately determine, and the apparent resistivity ratio method ignores the influence of matrix change on the resistivity, and effectively improves the reliability of the calculation of the oil-water interface position of the full-type bottom water oil layer under the original stratum condition.
The resistivity reconstruction-parameter reduction method is based on the physical response principle of the logging rock, and introduces the matrix deoiling resistivity (abbreviated as matrix resistivity) and the reconstruction resistivity, comprehensively considers the influence of double factors of the matrix and the fluid on the logging apparent resistivity, and carries out oil-water interface judgment and calculation according to the relation of the reconstruction resistivity ratio and the matrix resistivity ratio according to the classical Arhcie formula conversion form, thereby reducing the number of parameters. The method has the advantages of rapidness, intuitiveness and quantification of a visual resistivity ratio method and an oil saturation evaluation method, and overcomes the defects that the random error of the selection of a standard water layer of the visual resistivity ratio method is large, the influence of matrix diversity on the visual resistivity is ignored, the judging condition is too wide and the strict theoretical basis is lacking; at the same time make up for the evaluation of oil saturation degree to a certain extent Valence method, limitation of more calculation parameters and difficult accurate determination, and lithology coefficient a, saturation coefficient b and formation water resistivity R w The 3 difficult-to-determine parameters are irrelevant, and error transfer is reduced.
The resistivity reconstruction-parameter reduction method has the advantages that the accuracy and the calculation accuracy of the oil-water interface position judgment of the I-1, II-2 and II-3 type reservoirs are obviously improved compared with those of the conventional method, particularly, the oil-water interface position of the II-2 and II-3 type reservoirs which are not judged by the conventional method is accurately judged and calculated, and the calculation result of the oil-water interface position of the III-1 type reservoirs is relatively similar to that of the conventional method, so that the conventional method is mainly suitable for the oil-water interface calculation of reservoirs with relatively stable matrixes. All three methods judge that the oil-water interface does not exist in the reservoirs I-2, I-3, III-2 and III-3. The resistivity reconstruction-parameter reduction method realizes accurate judgment and calculation of the oil-water interface position of the full-class reservoir, and has important popularization and application prospects.
Drawings
FIG. 1 is a flow chart of resistivity reconstruction-parameter reduction process procedures;
FIG. 2 is a log of nine reservoir types;
FIG. 3 is a graph of acoustic time difference versus porosity;
FIG. 4 is a graph of porosity versus cementation index;
FIG. 5 is a graph of the results of the YJ-15 well oil-water interface calculation;
FIG. 6 is a graph of the results of YJ006 well oil-water interface determinations;
FIG. 7 is a graph of D152 well oil-water interface determination results;
FIG. 8 is a graph of the results of calculation of the ZH255 well oil-water interface;
FIG. 9 is a graph of the calculation result of the oil-water interface of the S712 well;
FIG. 10 is a graph of the calculation result of the oil-water interface of the Z253 well;
FIG. 11 is a graph of the calculation result of the oil-water interface of the N039 well;
FIG. 12 is a graph of the results of the calculation of the oil-water interface of the Y148 well;
FIG. 13 is a graph of the results of the calculation of the oil-water interface of the Y046 well;
fig. 14 is a diagram of the calculation result of the oil-water interface of the S827 well.
Detailed Description
The method mainly comprises the following steps: because the reservoir below the reference depth is mainly saturated with water, an oil-water interface does not exist, well logging response at the bottom of the reservoir is easily interfered by surrounding rock, and in order to improve the calculation speed and the calculation accuracy, only matrix resistivity, matrix resistivity ratio, reconstruction resistivity and reconstruction resistivity ratio above the reference depth are calculated to judge whether the oil-water interface exists or not and calculate the depth position.
An oil-water interface determining method comprises the following steps (see fig. 1):
step one: according to the response characteristics of the longitudinal acoustic time difference and the apparent resistivity logging curve of the reservoir, and by combining with geological logging data, the reservoir type is comprehensively judged, and the specific process is as follows:
the reservoirs were divided into types 3 and 9 (see fig. 2) based on their longitudinal sonic time difference and apparent resistivity log response characteristics, wherein,
The type I reservoir is thinned from bottom to top in lithology, and the pores become smaller, wherein the type I reservoir comprises type I-1 bell-shaped sonic time difference and apparent resistivity in bell shape; type I-2 bell-shaped acoustic time difference, wherein the apparent resistivity is funnel-shaped; i-3 type bell-shaped sound wave time difference, wherein the apparent resistivity is straight;
the lithology of the II type reservoir layer is thickened from bottom to top, the pores are enlarged, the II type reservoir layer comprises II-1 type funnel-shaped acoustic wave time difference, and the apparent resistivity is bell-shaped; the II-2 type funnel-shaped acoustic wave time difference and apparent resistivity are funnel-shaped; type II-3 funnel-shaped acoustic wave time difference, and apparent resistivity is straight;
the III type reservoir is stable in lithology from bottom to top and small in pore change, comprises III-1 type straight acoustic wave time difference and has bell-shaped apparent resistivity; III-2 straight sound wave time difference, and apparent resistivity is funnel-shaped; III-3 type straight shape acoustic wave time difference, and apparent resistivity is straight.
Step two: determining a reference water interval, a reference depth and a reference resistivity R B Logging apparent resistivity R at depth N N ；
The process of determining the reference water layer section is as follows: in the depth section with the oil saturation less than 0.1 calculated by the oil saturation evaluation method, the upper third and the lower third are removed, the middle third is used as a reference water layer section (effectively reducing the interference of upper and lower surrounding rocks on logging response, and overcoming the problem that the pure water layer section is not clear by using experience in the existing method), and the average value of the depth of the reference water layer section is used as the reference depth.
R B And R is N Obtained directly by deep induction or deep lateral resistivity logging methods.
Step three: calculating the substrate resistivity R above the reference depth NJ Matrix resistivity ratio I NJ And a reference porosity phi B ；
Matrix resistivity R NJ The physical meaning of (2) is the resistivity at depth N at which the reservoir matrix pores are saturated with water, i.e., assuming that the fluids are all water, where the resistivity is equal to the baseline resistivity R B Only the differences in matrix are caused by changes in Ω·m; matrix resistivity ratio I NJ The ratio of the matrix resistivity to the reference resistivity at depth N is dimensionless.
The equation (2) can be obtained for the Archie equation (1):
Figure SMS_17
（1）
Figure SMS_18
（2）
regression modeling is carried out according to the acoustic time difference logging value and the core porosity data (figure 3), so as to obtain a porosity calculation formula (3); obtaining a cementing index calculation formula (4) according to the rock electricity experimental data (figure 4);
Figure SMS_19
（3）
Figure SMS_20
（4）
in the formulas (1) - (4), S w Is water saturation, dimensionless; Φ is the porosity (representation in the general formula),dimensionless; r is R w Is the formation water resistivity, Ω·m; r is general total resistivity, omega.m; a is lithology coefficient, dimensionless; b is a saturation coefficient, dimensionless; n is a saturation index, is dimensionless, and takes a theoretical value of 2; m is a cementation index, dimensionless; AC is the difference in logging acoustic wave, mu s/m; c. d, e and f are undetermined coefficients;
The reference resistivity R can be determined according to equation (2) B Represented by the form of formula (5):
Figure SMS_21
（5）
since a and b are unknown quantities and are difficult to accurately calculate, the expression (5) is modified, and these two parameter values are calculated by other parameters as a whole.
Formula (6) is obtained from formula (5):
Figure SMS_22
（6）
reference porosity phi B The porosity at each depth point in the reference water layer section is obtained from formula (3) as the average value of the porosity of the reference water layer section, and in addition, the porosity Φ at the depth N N Also from formula (3);
equation (2) is a general equation, for a reference water interval, the porosity and water saturation are both actual values for the interval, for a depth N, the porosity is the actual value for the interval, and the water saturation is assumed to be water-only and oil-free, so as to obtain a matrix resistivity value for the depth N;
obtaining the substrate resistivity R from the formula (2) and the formula (6) NJ Further, the matrix resistivity ratio I is obtained NJ See formula (7) and formula (8), respectively:
Figure SMS_23
（7）
Figure SMS_24
（8）
in the formulas (5) and (7), m B Is the cementation index at the reference depth, and has no dimension; m is m N Is the cementation index at depth N, dimensionless; s is S Bw Taking a theoretical value of 1 of a bottom water oil layer as the water saturation at the reference depth and the dimensionless; phi B 、Φ N The porosity at the reference porosity and the depth N are respectively dimensionless;
R NJ And R is R B The difference is the resistivity difference between the matrix at depth N and the matrix at the reference depth.
Step four: calculating a reconstructed resistivity R above a reference depth NR Ratio of resistivity to reconstruction I NR ；
Reconstructing resistivity R NR The physical meaning of (2) is that the apparent resistivity at depth N is the resistivity after the change in resistivity due to the change in matrix is eliminated. Reconstruction resistivity ratio I NR Is the ratio of the reconstructed resistivity at depth N to the reference resistivity.
The apparent resistivity at depth N is different from the reference resistivity (R N -R B ) Is the difference in resistivity (R) resulting from the difference in matrix at depth N from the reference depth matrix NJ -R B ) And the difference in resistivity (R) between the fluid at depth N (i.e. the resistivity of the fluid itself containing the oil phase to be determined) and the reference depth fluid NR -R B ) The following relation (9) is given for the common constitution:
Figure SMS_25
（9）
equation (10) is obtained from equation (9), and equation (11) is obtained:
Figure SMS_26
（10）
Figure SMS_27
（11）
in the formulae (9) and (11), R NR Is the reconstructed resistivity at depth N, Ω·m; i NR Is the reconstructed resistivity ratio at depth N, dimensionless; i NS The apparent resistivity ratio at depth N is the apparent resistivity R at depth N N And reference resistivity R B Is a ratio of (2);
R N and R is R B The difference of (2) is composed of the matrix resistivity difference and the fluid resistivity difference at two depths, and represents the matrix difference and the oil-water fluid difference.
The reconstructed resistivity is expressed as equation (12), and by combining equation (6), equations (13) and (14) are obtained, respectively:
Figure SMS_28
（12）
Figure SMS_29
（13）/>
Figure SMS_30
（14）
in the formula (12), S Nw For the actual water saturation at depth N (whereas in equation (7), for the matrix resistivity, all water is assumed), dimensionless;
step five: at the oil-water interface and above,
Figure SMS_31
then there is a decision equation (15):
Figure SMS_32
（15）
judgment of I NR ≥4*I NJ If so, taking the lowest depth as an oil-water interface when the oil-water interface is established; when not established, no oil-water interface exists.
Application example:
three methods were used for each reservoir type (see table 1) to evaluate the accuracy of each method. Before determining the position of the oil-water interface, determining the undetermined coefficients of the formulas (3) and (4) through regression modeling and rock electric experiments to obtain four undetermined coefficients c, d, e, f with values of 0.0023, -0.4201, 0.4225 and 2.9685 (fig. 3 and 4).
1. Determining I-1 type oil-water interface in I type reservoir
1. Take YJ-15 well as an example (see FIG. 5).
Logging and logging data display 1263.00-1240.125 m for sandstone reservoir, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses R N ≥4*R B As a judgment condition (median value of the apparent resistivity ratio judgment condition is not less than 3 to 5).
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (1261.125-1259.375 m) of the depth section (1263.0-1257.5 m) of 'So < 0.1' is used as a reference water layer section, and 'So is more than or equal to 0.5' is used as a judging condition, and the depth of an oil-water interface is calculated to be 1245.375m.
(2) Apparent resistivity ratio method: taking the average value (7.342 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B The oil-water interface depth was calculated to be 1246.0m.
The depth of the oil-water interface determined by the two conventional methods is relatively close, and the average depth value is 1245.688m. And the fracturing oil test is carried out on 1245.688-1240.125 m, the oil production rate is 0.6 square/day, the water production rate is 7.4 square/day, the water content is up to 92.50%, and the implementation effect is poor. The reasons for poor implementation effect of the conventional method mainly comprise: (1) the oil saturation evaluation method has the advantages that the calculation parameters are more, the spatial variation of each parameter is large, the accuracy is poor, and the theoretical value of the parameter is selected for calculation, so that the real situation of a reservoir is difficult to reflect; (2) the lithology of the reservoir matrix is thinned and the pores are reduced from bottom to top, so that the apparent resistivity is increased, and the apparent resistivity is increased by the 'apparent resistivity ratio method' totally due to the change of oil saturation, so that the conventional method has error in judging whether an oil-water interface exists or not.
(3) Resistivity reconstruction-parameter reduction method: taking the average value (1260.25 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (7.342 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (17.672%) of the section porosity as a reference porosity phi B The method comprises the steps of calculating the matrix resistivity in a formula (7), calculating the matrix resistivity ratio in a formula (8), calculating the reconstruction resistivity in a formula (10), calculating the reconstruction resistivity ratio in a formula (11), determining that an oil-water interface does not exist in the well by taking a formula (15) as a judging condition, and closing the well.
2. Take the YJ006 well as an example (FIG. 6).
Logging and logging data display 1177.0-1154.375 are sandstone reservoirs, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses R N ≥4*R B As a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (1174.25-1171.5 m) of the depth section (1177.0-1168.75 m) of ' So < 0.1 ' is used as a reference water layer section, so is more than or equal to 0.5 ' as a judging condition, and the depth of an oil-water interface is calculated to be 1161.625m.
(2) Apparent resistivity ratio method: taking the average value of apparent resistivity of the reference water layer section (6.514 Ω -m) as the reference resistivity R B The oil-water interface depth was calculated to be 1162.0m.
The depth of the oil-water interface determined by the two conventional methods is relatively close, and the average depth value is 1162.688m. And (3) carrying out fracturing oil test on 1162.688-1154.375 m, wherein the oil yield is 2.6 square/day, the water yield is 9.3 square/day, the water content is as high as 78.15%, and the ideal effect is not obtained. The reason for the poor implementation effect of the conventional method is mainly as follows: from bottom to top, reservoir matrix lithology becomes thin, pores are reduced, R NJ ＞R B The conventional method is to fully attribute the apparent resistivity increase to the change of oil saturation, and simultaneously calculate the parameter to take theoretical valueThe determined oil-water interface position is lower, and the water content after fracturing is higher.
(3) Resistivity reconstruction-parameter reduction method: taking the average value (1172.875 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (6.514 Ω -m) of the resistivity of the section as the reference resistivity R B Taking the average value (18.944%) of the section porosity as a reference porosity phi B The matrix resistivity is calculated in the formula (7), the matrix resistivity ratio is calculated in the formula (8), the reconstruction resistivity is calculated in the formula (10), the reconstruction resistivity ratio is calculated in the formula (11), and the oil-water interface depth is calculated to be 1160.0m by taking the formula (15) as a judgment condition. Compared with the average value of the depth of the oil-water interface calculated by two conventional methods, which is 2.688m higher, the 2.688m water layer is considered to be fractured to cause higher water content, the original perforation section is plugged, the stratum 1160.0-1154.375 m is subjected to secondary production, the oil production is 5.2 square/day, the water production is 4.3 square/day, the water content is reduced to 45.26%, the water control and oil increase are realized, and a better application effect is obtained.
2. Determining I-2 type oil-water interface in I type reservoir
Take the example of a D152 well (fig. 7).
Logging and logging data show 1750.375-1721.25 m for sandstone reservoirs, wherein the values of parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses R N ≥4*R B As a judgment condition (median value of the apparent resistivity ratio judgment condition is not less than 3 to 5).
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the oil saturation is calculated to be lower than 0.1 as a whole, an oil-water interface is judged to be absent, and the middle third (1740.625-1731.0 m) of the depth section (1750.375-1721.25 m) is taken as a reference water layer section.
(2) Apparent resistivity ratio method: taking the average value (25.498 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B Judging that an oil-water interface does not exist.
(3) Resistivity reconstruction-parameter reduction method: taking a reference water layer section depth average value (1135.813 m) as a reference depth, and taking a section resistivity average value (25.498 Ω.m) as a reference depthReference resistivity R B Taking the average value (9.637%) of the section porosity as a reference porosity phi B The formula (7) calculates the substrate resistivity, the formula (8) calculates the substrate resistivity ratio, the formula (10) calculates the reconstruction resistivity, the formula (11) calculates the reconstruction resistivity ratio, and the formula (15) is used as a judgment condition to judge that an oil-water interface does not exist.
The three methods show that the reservoir is mainly saturated with water, and the absence of an oil-water interface of the type I-2 reservoir is comprehensively determined.
3. Determining I-3 type oil-water interface in I type reservoir
Take the ZH255 well as an example (fig. 8).
Logging and logging data show 2142.0-2116.875 m for sandstone reservoirs, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses R N ≥4*R B As a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the oil saturation is calculated to be lower than 0.1 as a whole, an oil-water interface is judged to be absent, and the middle third (2133.625-2125.25 m) of the depth section (2142.0-2116.875 m) is taken as a reference water layer section.
(2) Apparent resistivity ratio method: taking the average value (20.206 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B Judging that an oil-water interface does not exist.
(3) Resistivity reconstruction-parameter reduction method: taking the average value (2129.5 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (20.206 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value of the section of porosity (9.798%) as a reference porosity phi B The formula (7) calculates the substrate resistivity, the formula (8) calculates the substrate resistivity ratio, the formula (10) calculates the reconstruction resistivity, the formula (11) calculates the reconstruction resistivity ratio, and the formula (15) is used as a judgment condition to judge that an oil-water interface does not exist.
The three methods show that the reservoir is mainly saturated with water, and the oil-water interface of the type I-3 reservoir is comprehensively determined.
4. Determining II-1 type oil-water interface in II type reservoir
Taking the S712 well as an example (fig. 9).
Logging and logging data show that 883.125-822.375 is a sandstone reservoir, wherein the parameter values of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in table 2, and the apparent resistivity ratio method takes RN not less than 4 x RB as a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (872.5-861.875) of the depth section (883.125-851.25 m) of the 'So < 0.1' is used as a reference water layer section, the 'So is more than or equal to 0.5' is used as a judging condition, and the depth of an oil-water interface is calculated to be 835.25m.
(2) Apparent resistivity ratio method: taking the average value (6.343 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B The oil-water interface depth was calculated to be 842.375m.
The depth difference of the oil-water interface determined by the two conventional methods is up to 7.125m.
(3) Resistivity reconstruction-parameter reduction method (fig. 9): taking the average value (867.188 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (6.343 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (15.24%) of the section porosity as a reference porosity phi B The matrix resistivity is calculated in the formula (7), the matrix resistivity ratio is calculated in the formula (8), the reconstruction resistivity is calculated in the formula (10), the reconstruction resistivity ratio is calculated in the formula (11), and the oil-water interface depth is calculated as 838.625m by taking the formula (15) as a judgment condition. The fracturing test oil for 838.625-822.37m stratum has the advantages of 15.6 square/day of oil production, 10.9 square/day of water production and 41.13% of water content, and has obvious implementation effect.
5. Determining II-2 type oil-water interface in II type reservoir
Take the example of the Z253 well (fig. 10).
Logging and logging data show that 1221.75-1024.5 m is a sandstone reservoir, wherein the parameter values of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in table 2, and the apparent resistivity ratio method takes RN not less than 4 x RB as a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (1184.125-1146.625 m) of the depth section (1221.75-1109.0 m) of 'So < 0.1' is used as a reference water layer section, and 'So is more than or equal to 0.5' is used as a judging condition, and the absence of an oil-water interface is calculated.
(2) Apparent resistivity ratio method: taking the average value of apparent resistivity of the reference water layer section (8.209 Ω.m) as the reference resistivity R B The oil-water interface is calculated to be absent.
(3) Resistivity reconstruction-parameter reduction method: taking a reference water layer section depth average value (1165.375 m) as a reference depth, and taking a section resistivity average value (8.209 Ω & m) as a reference resistivity R B Taking the average value (10.773%) of the section porosity as a reference porosity phi B The matrix resistivity is calculated in the formula (7), the matrix resistivity ratio is calculated in the formula (8), the reconstruction resistivity is calculated in the formula (10), the reconstruction resistivity ratio is calculated in the formula (11), and the oil-water interface depth is calculated to be 1038.5m by taking the formula (15) as a judgment condition. And (3) carrying out fracturing oil test on 1038.5-1024.5 m stratum, wherein the oil yield is 13.7 square/day, the water yield is 11.5 square/day, the water content is 45.63%, the omission of an oil layer is avoided, and a good application effect is obtained.
6. Determining II-3 type oil-water interface in II type reservoir
Take an N039 well as an example (fig. 11).
Logging and logging data show 1366.875-1216.375 as sandstone reservoir, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses RN not less than 4×RB as a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (1353.75-1340.75 m) of the depth section (1366.875-1323.0 m) of the 'So < 0.1' is taken as a reference water layer section, and the 'So is more than or equal to 0.5' is taken as a judging condition, so that the oil-water interface is calculated to be absent.
(2) Apparent resistivity ratio method: taking the average value (18.043 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B The oil-water interface is calculated to be absent.
(3) ResistorThe rate reconstruction-parameter reduction method comprises the following steps: taking the average value (1347.25 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (18.043 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (10.236%) of the section porosity as a reference porosity phi B The matrix resistivity is calculated in the formula (7), the matrix resistivity ratio is calculated in the formula (8), the reconstruction resistivity is calculated in the formula (10), the reconstruction resistivity ratio is calculated in the formula (11), and the oil-water interface depth is calculated as 1230.875m by taking the formula (15) as a judgment condition. The oil is tested by fracturing the 1230.875-1216.375 stratum, the oil production is 16.5 square/day, the water production is 15.8 square/day, the water content is 48.92%, the omission of an oil layer is avoided, and a good application effect is obtained.
7. Determining III-1 type oil-water interface in III type reservoir
Take the example of a Y148 well (FIG. 12).
Logging and logging data show that 869.0-859.25 m is a sandstone reservoir, wherein the parameter values of an oil saturation evaluation method and a resistivity reconstruction-parameter reduction method are shown in table 2, and the apparent resistivity ratio method takes RN not less than 4 x RB as a judgment condition.
(1) Oil saturation evaluation method: the water saturation is obtained through the formula (1), then the oil saturation is calculated through so=1-Sw, the middle third (867.375-866.0 m) of the depth section (869.0-864.37m) of ' So < 0.1 ' is used as a reference water layer section, so is more than or equal to 0.5 ' as a judging condition, and the depth of an oil-water interface is calculated to be 861.375m.
(2) Apparent resistivity ratio method: taking the average value (7.868 omega.m) of apparent resistivity of the reference water layer section as the reference resistivity R B The oil-water interface depth was calculated to be 861.625m.
The depth of the oil-water interface calculated by the two conventional methods is only 0.25m different, and the average value of the depth is 861.5m.
(3) Resistivity reconstruction-parameter reduction method: taking the average value (866.688 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (7.868 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (14.961%) of the section porosity as a reference porosity phi B Calculating the substrate resistivity in the formula (7), calculating the substrate resistivity ratio in the formula (8), calculating the reconstruction resistivity in the formula (10), and calculating the reconstruction resistivity in the formula (11)And calculating the reconstruction resistivity ratio, and taking the formula (15) as a judgment condition, wherein the depth of the oil-water interface is 861.625m, and the difference between the depth average value and the oil-water interface depth average value calculated by the conventional method is only 0.125m. The conventional method is mainly suitable for oil-water interface calculation of matrix lithology and pore stable reservoirs. The fracturing test oil for the stratum of 861.625-859.25 m produces 2.8 square/day of oil and 2.6 square/day of water, and the water content is 48.15 percent, thereby meeting the expected effect.
8. Determining III-2 type oil-water interface in III type reservoir
Take the example of a Y046 well (FIG. 13).
Logging and logging data show 1192.2-1144.0 is sandstone reservoir, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in table 2, and the apparent resistivity ratio method uses RN not less than 4 x RB as a judgment condition.
(1) Oil saturation evaluation method: obtaining water saturation through a formula (1), calculating oil saturation through so=1-Sw, wherein the oil saturation is lower than 0.1 as a whole, judging that an oil-water interface does not exist, and taking the middle third (1176.0-1160.0 m) of a reservoir depth section (1192.125-1143.875) as a reference water layer section;
(2) Apparent resistivity ratio method: taking the average value (11.522 omega.m) of the resistivity of the reference water layer segment as the reference resistivity R B Judging that an oil-water interface does not exist;
(3) Resistivity reconstruction-parameter reduction method: taking the average value (1168.0 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (11.522 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (15.865%) of the section porosity as a reference porosity phi B The formula (7) calculates the substrate resistivity, the formula (8) calculates the substrate resistivity ratio, the formula (10) calculates the reconstruction resistivity, the formula (11) calculates the reconstruction resistivity ratio, and the formula (15) is used as a judgment condition to judge that an oil-water interface does not exist.
The three methods show that the reservoir is mainly saturated with water, and the oil-water interface of the III-2 reservoir is comprehensively determined.
9. Determining III-3 type oil-water interface in III type reservoir
Take the S827 well as an example (fig. 14).
Logging and logging data show 938.5-872.5 m as sandstone reservoir, wherein the parameters of the oil saturation evaluation method and the resistivity reconstruction-parameter reduction method are shown in Table 2, and the apparent resistivity ratio method uses RN not less than 4 x RB as a judgment condition.
(1) Oil saturation evaluation method: obtaining water saturation through a formula (1), calculating oil saturation through so=1-Sw, wherein the oil saturation is lower than 0.1 as a whole, judging that an oil-water interface does not exist, and taking the middle third (916.375-894.75 m) of a reservoir depth section (938.25-872.875) as a reference water layer section;
(2) Apparent resistivity ratio method: taking the average value (9.371 omega.m) of the resistivity of the reference water layer segment as the reference resistivity R B Judging that an oil-water interface does not exist;
(3) Resistivity reconstruction-parameter reduction method: taking the average value (905.625 m) of the depth of the section of the reference water layer as the reference depth, and taking the average value (9.371 Ω.m) of the resistivity of the section as the reference resistivity R B Taking the average value (15.481%) of the section porosity as a reference porosity phi B The formula (7) calculates the substrate resistivity, the formula (8) calculates the substrate resistivity ratio, the formula (10) calculates the reconstruction resistivity, the formula (11) calculates the reconstruction resistivity ratio, and the formula (15) is used as a judgment condition to judge that an oil-water interface does not exist.
The three methods show that the reservoir is mainly saturated with water, and the oil-water interface of the III-3 reservoir is comprehensively determined.
Table 1 three methods criteria
Figure SMS_33
Table 2 parameter value table
Figure SMS_34
The influence factors of the apparent resistivity of the rock logging can be mainly summarized into 2 aspects, namely the influence of the rock, including clastic minerals, gap fillers, reservoir space characteristics and the like; and secondly, oil-water characteristics, distribution state and the like in a storage space. Based on the physical response principle of the logging rock, the difference between apparent resistivity at the depth N and the resistivity of the bottom reference water layer is formed by the difference between resistivity generated by the difference between the matrix at the depth N and the matrix of the bottom reference water layer and the difference between resistivity generated by the difference between pore fluid at the depth N and pore fluid of the bottom reference water layer. The "substrate degreasing resistivity" (substrate resistivity for short) is introduced to reflect the "resistivity due to the difference between the substrate at depth N and the bottom reference aqueous layer substrate", the effect due to the change of the substrate is eliminated in apparent resistivity, and the "reconstruction resistivity" is introduced to reflect the "resistivity due to the difference between the pore fluid at depth N and the bottom reference aqueous layer pore fluid". According to the classical Arhcie formula conversion form, oil-water interface judgment and calculation are carried out according to the relation of the 'reconstruction resistivity ratio' and the 'matrix resistivity ratio', so that the number of parameters is reduced, and the accuracy is improved.
The resistivity reconstruction-parameter reduction oil-water interface determination method has the advantages of rapidness, intuitiveness and quantification of a visual resistivity ratio method and an oil saturation evaluation method, and overcomes the defects that the random error of the selection of a standard water layer of the visual resistivity ratio method is large, the influence of matrix diversity on the visual resistivity is neglected, the judgment condition is too wide and the strict theoretical basis is lacking; meanwhile, the method does not need lithology coefficient a, saturation coefficient b and formation water resistivity R w And 3 parameters which are difficult to determine are equal, so that the limitation that the calculated parameters of the oil saturation evaluation method are more and difficult to determine accurately is overcome to a certain extent, and error transmission is reduced.
The accuracy of judging whether the oil-water interface of the I-1, II-2 and II-3 type reservoirs exists or not and the depth position calculating accuracy is obviously improved compared with that of the conventional method, particularly, the oil-water interface position of the II-2 and II-3 type reservoirs which are omitted by judging according to the conventional method is accurately judged and calculated, the oil-water interface position calculating result of the III-1 type reservoirs is relatively similar to that of the conventional method, and the conventional method is mainly suitable for oil-water interface calculation of reservoirs with relatively stable matrixes. The resistivity reconstruction-parameter reduction method realizes accurate judgment and calculation of the oil-water interface position of the full-class reservoir, and has important popularization and application prospects.

Claims (3)

1. The oil-water interface determining method is characterized by comprising the following steps of:
step one: comprehensively judging the type of the reservoir according to the longitudinal acoustic time difference and the apparent resistivity logging curve response characteristics of the reservoir and by combining geological logging data;
step two: determining a reference water interval, a reference depth and a reference resistivity R B Logging apparent resistivity R at depth N N ；
Step three: calculating the substrate resistivity R above the reference depth NJ Matrix resistivity ratio I NJ And a reference porosity phi B ；
The equation (2) can be obtained for the Archie equation (1):
Figure QLYQS_1
（1）
Figure QLYQS_2
（2）
regression modeling is carried out according to the acoustic time difference logging value and the core porosity data to obtain a porosity calculation formula (3); according to the rock electricity experimental data, a cementing index calculation formula (4) is obtained:
Figure QLYQS_3
（3）
Figure QLYQS_4
（4）
in the formulas (1) - (4), S w Is water saturation, dimensionless; phi is porosity, dimensionless; r is R w Is the formation water resistivity, Ω·m; r is total resistivity, omega.m; a is lithology coefficient, dimensionless; b is a saturation coefficient, dimensionless; n is a saturation index, is dimensionless, and takes a theoretical value of 2; m is glueJunction index, dimensionless; AC is the difference in logging acoustic wave, mu s/m; c. d, e and f are undetermined coefficients;
the reference resistivity R is determined according to equation (2) B Represented by the form of formula (5):
Figure QLYQS_5
（5）
formula (6) is obtained from formula (5):
Figure QLYQS_6
（6）
reference porosity phi B The porosity of each depth point in the reference water layer section is obtained by the formula (3) as the average value of the porosity of the reference water layer section; porosity Φ at depth N N Also from formula (3);
obtaining the substrate resistivity R from the formula (2) and the formula (6) NJ Further, the matrix resistivity ratio I is obtained NJ See formula (7) and formula (8), respectively:
Figure QLYQS_7
（7）
Figure QLYQS_8
（8）
in the formulas (5) and (7), m B Is the cementation index at the reference depth, and has no dimension; m is m N Is the cementation index at depth N, dimensionless; s is S Bw Taking a theoretical value of 1 of a bottom water oil layer as the water saturation at the reference depth and the dimensionless; phi B 、Φ N The porosity at the reference porosity and the depth N are respectively dimensionless;
step four: calculating a reconstructed resistivity R above a reference depth NR Ratio of resistivity to reconstruction I NR ；
The apparent resistivity at depth N is different from the reference resistivity (R N -R B ) Is formed by depth NThe difference in resistivity (R NJ -R B ) And the difference in resistivity (R) between the fluid at depth N and the reference depth fluid NR -R B ) The following relation (9) is given for the common constitution:
Figure QLYQS_9
（9）
equation (10) is obtained from equation (9), and equation (11) is obtained:
Figure QLYQS_10
（10）
Figure QLYQS_11
（11）
In the formulae (9) and (11), R NR Is the reconstructed resistivity at depth N, Ω·m; i NR Is the reconstructed resistivity ratio at depth N, dimensionless; i NS The apparent resistivity ratio at depth N is the apparent resistivity R at depth N N And reference resistivity R B Is a ratio of (2);
the reconstructed resistivity is expressed as equation (12), and by combining equation (6), equations (13) and (14) are obtained, respectively:
Figure QLYQS_12
（12）
Figure QLYQS_13
（13）
Figure QLYQS_14
（14）
in the formula (12), S Nw The actual water saturation at depth N is dimensionless;
step five: at the oil-water interface and above,
Figure QLYQS_15
then there is a decision equation (15):
Figure QLYQS_16
（15）
judgment of I NR ≥4*I NJ If so, taking the lowest depth as an oil-water interface when the oil-water interface is established; when not established, no oil-water interface exists.
2. The method for determining an oil-water interface according to claim 1, wherein in the first step, the reservoir is divided into 3 types 9 according to the longitudinal acoustic time difference and the apparent resistivity logging response characteristic of the reservoir,
the type I reservoir is thinned from bottom to top in lithology, and the pores become smaller, wherein the type I reservoir comprises type I-1 bell-shaped sonic time difference and apparent resistivity in bell shape; type I-2 bell-shaped acoustic time difference, wherein the apparent resistivity is funnel-shaped; i-3 type bell-shaped sound wave time difference, wherein the apparent resistivity is straight;
the lithology of the II type reservoir layer is thickened from bottom to top, the pores are enlarged, the II type reservoir layer comprises II-1 type funnel-shaped acoustic wave time difference, and the apparent resistivity is bell-shaped; the II-2 type funnel-shaped acoustic wave time difference and apparent resistivity are funnel-shaped; type II-3 funnel-shaped acoustic wave time difference, and apparent resistivity is straight;
The III type reservoir is stable in lithology from bottom to top and small in pore change, comprises III-1 type straight acoustic wave time difference and has bell-shaped apparent resistivity; III-2 straight sound wave time difference, and apparent resistivity is funnel-shaped; III-3 type straight shape acoustic wave time difference, and apparent resistivity is straight.
3. The method for determining an oil-water interface according to claim 1, wherein the method for determining the reference water interval in the second step comprises the following steps: in a depth section with the oil saturation less than 0.1 calculated by an oil saturation evaluation method, removing an upper third and a lower third, and taking a middle third as a reference water layer section;
taking the average value of the depth of the reference water layer segment as the reference depth and taking the average value of the apparent resistivity of the reference water layer segment as the reference resistivity R B 。
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