CN106948811B - Quantitative characterization method for capping performance of dense carbonate rock cover layer of superimposed basin - Google Patents
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Abstract
The invention provides a quantitative characterization method for the capping performance of a dense carbonate rock cover layer of a superposed basin. The method comprises the following steps: identifying specific layer sections and thicknesses of compact carbonate rocks in a single well in a stratum layer of the development of the compact carbonate rock cover layer of the oil-gas reservoir in a research area; analyzing and testing the breakthrough pressure and the porosity of a rock core of a well for collecting a typical developing carbonate rock cover; fitting a linear formula between breakthrough pressure and reciprocal porosity of the compact carbonate rock cover layer of the oil and gas reservoir in the research area; obtaining breakthrough pressure values of other wells in the depth of the untested well section and the research area; and (4) bringing the breakthrough pressure value, the thickness value obtained by well logging, the shale content and the corresponding lower limit value into a comprehensive evaluation index to finish the quantitative characterization of the capping performance of the compact carbonate rock cover layer of the superposed basin. The method of the invention simply, conveniently and scientifically characterizes the capping performance of the cover layer, and comprehensively evaluates the sealing performance of the compact carbonate rock cover layer under the combination of the specific geological characteristics of the superposed basin.
Description
Technical Field
The invention relates to a characterization method, in particular to a quantitative characterization method for the capping performance of a compact carbonate rock cover layer of a superimposed basin, and belongs to the technical field of oil exploitation.
Background
The overlapped basins are also called overlapped basins, and are basins with complex structures, which are longitudinally overlapped by a plurality of different basins (different structural layers). The oil and gas distribution in the marine facies carbonate reservoir of the superposed basin has the characteristics of longitudinal stratification and transverse blocking, so that the direct cover layer and the interlayer of the longitudinal stratification of the compact carbonate are compact carbonate, and the compact carbonate can be used as an effective cover layer of a large oil and gas field (the cover layer is a protective layer which is positioned above the reservoir and can seal the reservoir to prevent the oil and gas in the reservoir from upwards escaping).
Under the new situation that the laminated basin marine carbonate rock gradually becomes an important field of oil and gas exploration in China, recognization of the tight carbonate rock cover layer sealing mechanism and establishment of a cover layer sealing quantitative evaluation method are particularly necessary.
Previous people have made more researches on the shale cover layer and proposed some evaluation methods, but the compact carbonate rock is different from mudstone and gypsum rock, and due to the characteristics of brittle, easy and non-homogeneous properties, the blocking property of the cover layer is not only related to the breakthrough pressure, the porosity, the thickness and the like, but also has a larger relation with the shale content.
Therefore, it is an urgent problem in the art to provide a method for evaluating the capping performance of a cap rock, which is suitable for tight carbonate rocks, simply and quantitatively.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a simple, convenient and scientific quantitative characterization method for the capping performance of the dense carbonate rock cover layer of the superposed basin. The quantitative characterization method can more conveniently and scientifically characterize the sealing performance of the compact carbonate rock cover layer on the oil and gas reservoir, thereby effectively guiding the exploration of the oil and gas reservoir under the cover layer sealing cover and providing a favorable direction for the exploration of the carbonate rock oil and gas reservoir.
In order to achieve the technical purpose, the invention provides a quantitative characterization method for the capping performance of a compact carbonate rock cover layer of a laminated basin, which comprises the following steps: a quantitative characterization method for the capping performance of dense carbonate rock cover layers in an overlapped basin comprises the following steps:
the method comprises the following steps: determining a layer position of oil-gas reservoir compact carbonate rock cover layer development in a research area, identifying specific layer sections and thicknesses of compact carbonate rock in a single well in the layer position, and determining a typical well for developing the carbonate rock cover layer;
step two: collecting a rock core of a well with a typical developing carbonate rock cover layer, and carrying out analysis tests on the breakthrough pressure and the porosity of the rock core;
step three: fitting a linear formula between breakthrough pressure and reciprocal porosity of the compact carbonate rock cover layer of the oil and gas reservoir in the research area by using the data analyzed and tested in the second step;
step four: obtaining breakthrough pressure values of other wells in the depth of the untested well section and the research area according to the linear formula between the breakthrough pressure of the compact carbonate rock cover layer of the oil-gas reservoir in the research area and the reciprocal of the porosity, which is fitted in the third step;
step five: determining a lower limit value of breakthrough pressure, a lower limit value of thickness plugging and a lower limit value of natural gamma of a compact carbonate rock cover layer of an oil and gas reservoir in a research area by combining geological analysis, and obtaining a lower limit value of shale content according to the lower limit value of the natural gamma;
step six: obtaining a quantitative characterization result of the capping performance of the compact carbonate rock cover layer of the laminated basin according to the comprehensive evaluation index lambda, wherein according to a lambda contour map, the higher the lambda value is, the better the capping performance is, the favorable capping area in the compact carbonate rock cover layer is indicated, and the quantitative characterization of the capping performance of the compact carbonate rock cover layer of the laminated basin is completed;
wherein, the calculation formula of the comprehensive evaluation index lambda is as follows:
wherein H is the thickness of compact carbonate rock cover layer of the oil and gas reservoir in the research area, and the unit is m;
ho is the lower limit thickness of the cover of the compact carbonate rock cover layer of the oil and gas reservoir in the research area, and the unit is m; max (P is Ao/phi-Bo) is the maximum value of the breakthrough pressure calculated by using the porosity phi in a certain single-well compact carbonate rock interval, and the unit is MPa;
po is the lower limit value of the dense carbonate rock cover, and the unit is MPa;
GRb is the most (larger) natural gamma value in the tight carbonate interval, in API;
GRa is the smallest (smaller) natural gamma value in the tight carbonate interval, in API;
vsho is the lower limit of the argillaceous content;
GR is the natural gamma value of a certain point in the compact carbonate rock interval, and the unit is API;
GRmin is the natural gamma value of the pure mud rock stratum, and the unit is API;
GRmax is the natural gamma value of a pure carbonate rock formation in API;
GCUR is an empirical parameter related to the formation, new formation (old and after its deposition) GCUR 3.7, old formation (before old deposition) GCUR 2.0;
ao and BoIs a coefficient fitted according to a linear relationship between the breakthrough pressure P and the reciprocal 1/phi of the pore.
According to the specific embodiment of the invention, in the sixth step, the breakthrough pressure (taking the maximum value), the average value of the shale content (the total amount of the shale content in the interval is obtained in an integral form, and the difference of the maximum value and the minimum value of the natural gamma in the interval is used as the average value of the shale content), and the product of the thickness and the ratio of the corresponding lower limit value is used as the comprehensive evaluation index λ.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin, preferably, in the third step, linear fitting is performed by utilizing the relation between the reciprocal 1/phi of the porosity obtained by analysis and test and the breakthrough pressure P, and according to the breakthrough pressure formula: p is A/phi-B to give Ao，BoCalculating the P value in the P ═ Ao/phi-Bo by using the porosity obtained by logging;
ao and BoIs a coefficient fitted according to a linear relationship between the breakthrough pressure P and the reciprocal 1/Φ of the pore;
p is a breakthrough pressure value and is in MPa;
Φ is the porosity, expressed in percentage units, without units.
The above formula P ═ a/Φ -B was proposed by luyan defense, et al (luyan defense, octogming, wanlonggui. use of acoustic moveout to calculate cap rejection pressure. oil exploration and development, 1994,21(2): 43-47).
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superposed basin, the breakthrough pressure and the porosity in the step two are obtained by performing experiments on coring samples at a certain depth point in a compact carbonate rock development interval in the well. Because the sampling points are limited, it is impossible to sample at each depth point for experiments, and the fit breakthrough pressure calculation formula is to obtain the relationship between the porosity and the breakthrough pressure. Porosity can be obtained from well logs. Because the logging curves are continuously distributed and are a curve which changes along with the depth, the obtained breakthrough pressure is a curve which also changes along with the depth and is not limited by the sample points of the experiment.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superposed basin, in the second step, the typical well for developing the carbonate rock cover layer refers to that the well in the research area takes the compact carbonate rock as the cover layer in the layer section where the compact carbonate rock cover layer develops, and oil or natural gas can be directly sealed under the cover layer.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the overlapped basin, preferably, the porosity parameter obtained through a single well logging curve in the fourth step is obtained.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin, the porosity parameter is preferably introduced into a breakthrough pressure formula P ═ Ao/Φ–BoAnd obtaining the untested depth of the interval in the research area and the breakthrough pressure values of corresponding intervals of other wells in the research area.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin, preferably, in the step five, the lower limit value of the breakthrough pressure of the cover layer is determined according to the following steps:
according to the relation between the daily oil and gas yield and the gas-oil ratio of each oil-gas-containing well in a research area and the breakthrough pressure of the compact carbonate cover layer of the corresponding oil-gas reservoir (the breakthrough pressure refers to the maximum breakthrough pressure obtained in the compact carbonate cover layer section of a single well), the minimum breakthrough pressure capable of sealing the oil and gas is used as the lower limit of the cover layer thickness plugging; or the like, or, alternatively,
and determining by combining a breakthrough pressure contour line (the breakthrough pressure refers to the maximum breakthrough pressure obtained in the single-well compact carbonate rock cover layer interval) and an oil-gas-containing surface integral distribution diagram, and taking a numerical value corresponding to the contour line of the minimum plugging oil gas as the lower limit value of the cover layer breakthrough pressure plugging.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin, preferably, in the fifth step, the lower limit value of the thickness plugging of the cover layer is determined according to the following steps:
according to the relation between the daily oil-gas yield and the gas-oil ratio of each oil-gas well in a research area and the thickness of the compact carbonate rock cover layer of the corresponding oil-gas reservoir, taking the minimum cover layer thickness capable of sealing oil and gas as the lower limit value of cover layer thickness plugging; or the like, or, alternatively,
and determining by combining the cover layer thickness contour line and the oil-gas-containing surface integral distribution map, and taking the value corresponding to the contour line of the minimum blocking oil gas as the lower limit value of the cover layer thickness blocking.
In the quantitative characterization method for the capping performance of the dense carbonate rock cover layer in the superposed basin, preferably, in the step five, the lower limit value of natural gamma is determined according to the following steps:
according to the fact that the thickness of the compact carbonate rock cover layer in the research area is about a thickness lower limit value or within a certain thickness range, namely the thickness is not a factor mainly influencing sealing performance, in the compact carbonate rock cover layer section with the sealing capacity, the minimum value of the mean value of natural gamma in different wells serves as the lower sealing limit value or the oil-gas-containing area distribution is superposed with a natural gamma isoline, and the minimum natural gamma value capable of sealing oil gas serves as the lower limit value.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the overlapped basin, preferably, in the fifth step, the shale content is obtained according to the following formula:
wherein
GR in the formula is a natural gamma value of a certain point, and the unit is API;
GRmin is the natural gamma value of the pure mud rock stratum, and the unit is API;
GRmax is the natural gamma value of a pure carbonate rock formation in API;
GCUR is an empirical parameter related to the formation, with 3.7 for the new formation (the old formation and the formation after its deposition) and 2.0 for the old formation (the formation before its deposition).
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superposed basin, preferably, the lower limit value of the argillaceous content is obtained according to the lower limit value of the natural gamma in the step five. Specifically, according to the lower limit value GRo of the natural gamma in the step five, the GRo is substituted into a calculation formula of Vsh ' to obtain Vsho ', and then the Vsho ' is substituted into the calculation formula of Vsh to obtain the lower limit value Vsho of the sludge content.
In the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin, in the sixth step, the comprehensive evaluation index lambda is a lambda contour map, and the lambda contour map is mainly drawn according to the distribution of sedimentary facies and the thickness of the stratum by combining the lambda-values counted by a plurality of single wells as much as possible in a research area.
The specific steps for drawing the lambda contour map are as follows: the lambda value of a single well in the research area can be obtained according to a calculation formula of the lambda value, and the lambda value of each well is projected onto a plan of the research area according to the well position coordinates, so that the lambda values corresponding to a series of wells on the plane can be obtained. Determining a lambda value high value area and approximate distribution by combining sedimentary backgrounds such as sedimentary facies, stratum thickness and the like, and then refining according to an interpolation method to make a lambda contour map.
The quantitative characterization method for the capping performance of the dense carbonate rock cover layer of the superposed basin mainly aims at the dense carbonate cover layers of marlite, marlite-containing and the like. The method is based on the characteristics that dense carbonate rock is strong in heterogeneity, the sealing performance is influenced by the shale content and the like, and by using the evaluation thought and method of the mudstone cover layer, the sealing performance of the cover layer is comprehensively and quantitatively evaluated by using the parameters of the cover layer thickness, the porosity, the breakthrough pressure, the natural gamma (the shale content) and the like on the basis of analyzing the main influence factors of the sealing performance of the dense carbonate rock cover layer. The breakthrough pressure is a key parameter for evaluating the cover layer, and a fitting equation of the breakthrough pressure is obtained by adopting a linear regression fitting calculation formula between the breakthrough pressure and the reciprocal of the porosity on the basis of analysis and test, so that the breakthrough pressure values of other wells in the depth of the untested well section and the research area are calculated. Meanwhile, considering the geological condition of a research area, determining the lower limit values of the breakthrough pressure, the cover layer cover sealing thickness and the natural gamma (argillaceous content) of the research area, bringing the lower limit values into a comprehensive evaluation index lambda (related to the breakthrough pressure, the cover layer thickness, the natural gamma and the argillaceous content), and making a lambda contour map of the research area, wherein the larger the lambda value is, the better the cover layer sealing performance is, and therefore the size of the cover layer sealing performance of the compact carbonate rock is quantitatively evaluated. Meanwhile, a quantitative characterization method more suitable for researching the performance of the capping cap is provided, and a favorable direction is indicated for the exploration of the oil and gas reservoir of the overlapping basin compact carbonate rock capping cap on the basis.
According to the quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superimposed basin, the higher the comprehensive evaluation index value lambda is, the better the capping performance is, and further the favorable capping area of the compact carbonate rock is indicated, so that the exploration of an oil-gas reservoir is guided.
The quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superposed basin is based on the characteristics that the heterogeneity of the compact carbonate rock is strong, the capping performance is influenced by the argillaceous content and the like, and the capping sealing performance is comprehensively and quantitatively evaluated by using the parameters of the cover layer thickness, the breakthrough pressure, the natural gamma (argillaceous content) and the like on the basis of analyzing the main influence factors of the capping sealing performance of the compact carbonate rock cover layer by using the evaluation thought and method of the argillaceous rock cover layer.
According to the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the overlapped basin, on the basis of analyzing the relation between the daily output of oil gas, the gas-oil ratio and the like and the thickness of the compact carbonate rock and the breakthrough pressure, and analyzing the contour line of the thickness of the cover layer and the breakthrough pressure and the oil-gas containing area, the lower limit value of the breakthrough pressure and the cover layer thickness capping is determined, and then according to geological analysis, namely about the lower limit value of the thickness capping, the minimum value of the natural gamma mean value of the cover layer with the capping performance in a single well is used as the lower limit value of the natural gamma, so that the lower limit value of the shale content is obtained. The parameters are brought into a comprehensive evaluation index lambda (related to breakthrough pressure, cover layer thickness and natural gamma), so that the cover layer sealing performance can be evaluated quantitatively, and meanwhile, a quantitative characterization method more suitable for the compact carbonate rock cover layer sealing oil and gas reservoir is provided, and a favorable direction is indicated for the exploration of the oil and gas reservoir on the basis.
The quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the superimposed basin can be used for calculating the breakthrough pressure values of other wells in the depth of an untested well section and a research area by fitting a linear equation of the breakthrough pressure and the reciprocal of the porosity through the tested porosity and the breakthrough pressure values on the basis of describing the compact carbonate rock cover layer in detail, and quantitatively calculating the capping performance of the compact carbonate rock cover layer of the research layer section by utilizing the thickness, the breakthrough pressure, the natural gamma and corresponding critical values of the compact carbonate rock cover layer, so that the capping performance of the compact carbonate rock cover layer on the oil-gas reservoir is more simply and scientifically characterized, and the exploration of the oil-gas reservoir under the cover layer is more effectively guided.
Compared with the prior art, the quantitative characterization method for the capping performance of the compact carbonate rock cover layer in the superposed basin takes various factors influencing the capping performance of the compact carbonate rock cover layer into consideration, so that the capping performance of the carbonate rock cover layer is more simply, conveniently and scientifically characterized, and the capping performance of the compact carbonate rock cover layer is comprehensively evaluated under the combination of specific geological characteristics of the superposed basin.
Drawings
FIG. 1 is a flow chart of a quantitative characterization method of the capping performance of the dense carbonate rock cover in the superimposed basin of example 1.
FIG. 2 is a scatter diagram showing the relationship between the thickness of the marl section and the daily oil-gas yield and gas-oil ratio of the eagle mountain group of the lower Ordoodle system in example 1.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
Example 1
The embodiment provides a quantitative characterization method for the sealing performance of a fine-cell dense mudstone-containing cover layer of a fine-cell tower in a Tarim basin tower, the process flow is shown in FIG. 1, and the method comprises the following specific steps:
the good-lining tower lattice group in the middle area of the tower is divided into 5 sections from bottom to top: and the good 5 section, the good 4 section, the good 3 section, the good 2 section and the good 1 section, wherein the good 3-good 5 section marl is a direct covering layer of a Tarim basin, oil gas of a lower eagle mountain group is covered, and lithology is mainly marl, marl-containing and then sillimanite.
(1) Critical thickness Po of cap seal: by counting the thickness of the direct cover layer of the dense limestone at the 3-5 sections of the industrial oil well of 30 wells on the north slope in the tower, the area of oil and gas on the plane is distributed in the range that the thickness of the dense limestone exceeds 80m in the whole view, and the thickness of the cover layer for producing the oil and gas is at least 80m in the view (figure 2) of the relation between the thickness of the cover layer and the gas-oil ratio and the yield, so that 80m is taken as the lower limit value for blocking the oil and gas by the cover layer.
(2) Determination of breakthrough pressure lower limit Po: a3-good-5 section sample of a good area in a tower is selected to carry out a breakthrough pressure (P) and porosity (phi) experiment to obtain two columns of data, and an empirical formula between the breakthrough pressure and the porosity provided by Llingfang et al (1994) is utilized:
P＝A/φ–B ①
substituting the measured porosity and the corresponding breakthrough pressure value into formula (1), solving coefficients A and B, and fitting formula ②:
P＝0.06/φ+4 ②
the method comprises the steps of obtaining porosity phi values of different continuous depths of wells by utilizing the porosity of the well logging, substituting the porosity phi values into a formula ② to calculate breakthrough pressure values of 3-5 sections of other wells on the north slope in the tower, making a breakthrough pressure contour map on a plane through the calculated breakthrough pressure values of the wells (the calculated breakthrough pressure value of a single well on the plane is the maximum value of the compact carbonate rock cover layer of each well), and overlapping the calculated breakthrough pressure values with the area containing oil gas, wherein the oil gas is mainly distributed in the range of the breakthrough pressure being more than 14Mpa, so that the lower limit value of the breakthrough pressure of the cover layer plugging is determined to be 14 Mpa.
(3) Determination of the lower limit of the argillaceous content Vsho (natural gamma GRo):
the argillaceous content Vsh may be derived from the natural gamma GR:
the calculation formula of the argillaceous content Vsh is as follows:
Therefore, the higher the GR value, the higher the argillaceous content.
From figure 2 it can be seen that mudstone thickness is not the main covering factor when the thickness is 80-200m, and is analytically considered to be the mudstone content. When greater than 200m, the primary blocking element is the cap layer thickness.
The West well area of the Zhonggu A well and the West well area of the Zhonggu B well similarly lack 4-5 good sections, only 3 good sections of strata are used as direct cover layers of the eagle mountain group, the thickness of the cover layers is between 80m and 200m, oil gas of the Zhonggu A well area is distributed in the eagle mountain group, namely 3 good sections of compact limestone on the upper part of the eagle mountain group plays a good sealing role, the oil gas of the Zhonggu B West well area is basically on the top of the 3 good sections, the eagle mountain group does not have oil gas, so that the oil gas from the deep part is likely to pass through the 3 good sections and is gathered on the top of the 3 good sections. And (3) counting the shale content (natural gamma) of the dense limestone of 3-5 sections of the good areas in the tower, wherein the analysis shows that the shale content of the West well areas in the Zhonggu B is lower, the natural gamma log value mean value of each single well is less than 20API, and the natural gamma mean value of each single well in the Zhonggu A well areas is more than 20 API. In addition, the superposition of the oil-gas containing area and the natural gamma contour can also show that the oil gas is basically distributed in the range of the natural gamma contour line being more than 20API, therefore, the lower limit value of the natural gamma is defined as 20API, and the corresponding argillaceous content is 6%.
(4) Calculation of comprehensive sealing capacity λ:
in addition, the porosity obtained by logging of 3-5 marl sections of single-well marl in the north slope of the tower is subjected to statistical analysis, so that a simple standard for sealing oil and gas by a compact carbonate cover layer is preliminarily formulated.
TABLE 1 characteristic parameter criteria for achieving cap-sealing ability of tight carbonate rock cap in the middle tower region
Table 1 shows the control effect of each parameter on the sealing property of the good 3-5 segment cap layer alone, and establishes a comprehensive sealing property evaluation index λ of the good 3-5 segment cap layer for comprehensively evaluating the sealing property of the entire good 3-5 segment direct cap layer:
it can reflect the magnitude of the comprehensive sealing capacity of the good 3-5 segment cover layer at a certain point on the plane. The composite evaluation index is related to and proportional to the thickness of the cap rock, the shale content and the breakthrough pressure, which is consistent with the actual geological conditions. The comprehensive evaluation index of good 3-5 sections of 50 wells was calculated using the above method and a planar lambda contour plot was made. If the comprehensive evaluation index is less than 1, the good 3-5 sections can not be used as effective covering layers; if the comprehensive evaluation index is more than 1, the minimum standard of the good 3-5 section capping capacity is achieved, and the capping material is considered to be an effective capping layer.
(5) And (3) verification: the superposed graphs of the gas-oil ratio and the lambda contour lines of different oil-gas-containing wells in the research area show that the oil-gas-containing wells are distributed in a range of lambda >1, the larger the lambda value is, the larger the corresponding gas-oil ratio in the closed well is, and the lambda value contour line graph can better evaluate the capability of a cover layer for closing oil and gas.
The above embodiments illustrate that the quantitative characterization method for the capping performance of the dense carbonate rock cover layer in the superimposed basin can more simply, conveniently and scientifically characterize the capping performance of the carbonate rock cover layer, so that the capping performance of the dense carbonate rock cover layer can be comprehensively evaluated under the combination of specific geological characteristics of the superimposed basin.
Claims (8)
1. The quantitative characterization method for the capping performance of the compact carbonate rock cover layer of the overlapped basin is characterized by comprising the following steps of:
the method comprises the following steps: determining a layer position of oil-gas reservoir compact carbonate rock cover layer development in a research area, identifying a specific depth section and thickness of the compact carbonate rock in a single well in the layer position, and determining a typical well for developing the carbonate rock cover layer;
step two: collecting a rock core of a well with a typical developing carbonate rock cover layer, and carrying out analysis tests on the breakthrough pressure and the porosity of the rock core;
step three: fitting a linear formula between breakthrough pressure and reciprocal porosity of the compact carbonate rock cover layer of the oil and gas reservoir in the research area by using the data analyzed and tested in the second step;
step four: obtaining breakthrough pressure values of other wells in the depth of the untested well section and the research area according to the linear formula between the breakthrough pressure of the compact carbonate rock cover layer of the oil-gas reservoir in the research area and the reciprocal of the porosity, which is fitted in the third step;
step five: determining a lower limit value of breakthrough pressure, a lower limit value of thickness plugging and a lower limit value of natural gamma of a compact carbonate rock cover layer of an oil and gas reservoir in a research area by combining geological analysis, and obtaining a lower limit value of the shale content according to the lower limit value of the natural gamma; the lower limit value of the breakthrough pressure of the cap layer is determined according to the following steps: according to the relation between the daily oil-gas yield and the gas-oil ratio of each oil-gas well in a research area and the breakthrough pressure of the compact carbonate rock cover of the corresponding oil-gas reservoir, the minimum breakthrough pressure capable of sealing oil gas is used as the lower limit value of the cover thickness plugging; or the like, or, alternatively,
determining by combining a breakthrough pressure contour line and an oil-gas-containing surface integral distribution map, and taking a numerical value corresponding to the contour line of the minimum blocking oil gas as a cover layer breakthrough pressure blocking lower limit value;
step six: obtaining quantitative characterization of the capping performance of the compact carbonate rock cover layer of the laminated basin according to the comprehensive evaluation index lambda, wherein the higher the lambda value is, the better the capping performance is, indicating a favorable capping area in the compact carbonate rock cover layer, and completing the quantitative characterization of the capping performance of the compact carbonate rock cover layer of the laminated basin; obtaining the lambda value of a single well in a research area according to a calculation formula of the lambda value, casting the lambda value of each well on a plan view of the research area according to well position coordinates to obtain the corresponding lambda values of a series of wells on the plan, determining a high-value area and approximate distribution of the lambda values by combining sedimentary facies and stratum thickness sedimentary backgrounds, and then refining according to an interpolation method to make a lambda contour map;
wherein, the calculation formula of the comprehensive evaluation index lambda is as follows:
wherein H is the thickness value of the compact carbonate rock cover layer of the oil and gas reservoir in the research area, and the unit is m;
ho is the lower limit thickness value of the cover of the compact carbonate rock cover layer of the oil and gas reservoir in the research area, and the unit is m;
max (P is Ao/phi-Bo) is the maximum value of the breakthrough pressure calculated by using the porosity phi in a certain single-well compact carbonate rock interval, and the unit is MPa;
po is the lower limit value of the dense carbonate rock cover, and the unit is MPa;
GRb is the maximum natural gamma value in the tight carbonate rock interval, with the unit being API;
GRa is the minimum natural gamma value in API in the tight carbonate interval;
vsho is the lower limit of the argillaceous content;
GR is the natural gamma value of a certain point in the compact carbonate rock interval, and the unit is API;
GRmin is the natural gamma value of the pure mud rock stratum, and the unit is API;
GRmax is the natural gamma value of a pure carbonate rock formation in API;
the GCUR of the new stratum is 3.7, and the GCUR of the old stratum is 2.0;
ao and Bo are coefficients fitted using a linear relationship between the inverse of the measured porosity and the breakthrough pressure.
2. The quantitative characterization method of compact carbonate rock cover capping performance in superimposed basin according to claim 1, characterized in that in step three, linear fitting is performed by using the relation between the reciprocal 1/Φ of porosity obtained by analytical tests and breakthrough pressure P, according to the breakthrough pressure formula: p is A/phi-B to give Ao，BoThe value is then calculated using the porosity obtained from the log P ═ ao/Φ–BoP value of (1);
ao and BoIs a coefficient fitted according to a linear relationship between the breakthrough pressure P and the reciprocal 1/Φ of the pore;
p is a breakthrough pressure value and is in MPa;
Φ is porosity.
3. The method for quantitatively characterizing the capping performance of tight carbonate rock covers in superimposed basins according to claim 1, characterized in that the porosity parameters to be obtained by single well logging are in step four.
4. The method for quantitatively characterizing the capping performance of compact carbonate rock cover in superimposed basin according to claim 1 or 3, characterized in that porosity parameters are introduced into the breakthrough pressure formula P ═ Ao/Φ–BoAnd obtaining the untested depth of the interval in the research area and the breakthrough pressure values of corresponding intervals of other wells in the research area.
5. The method for quantitatively characterizing the capping performance of compact carbonate rock cover in an overlapped basin according to claim 1, wherein in the step five, the lower limit value of the thickness plugging of the cover is determined according to the following steps:
according to the relation between the daily oil-gas yield and the gas-oil ratio of each oil-gas well in a research area and the thickness of the compact carbonate rock cover layer of the corresponding oil-gas reservoir, taking the minimum cover layer thickness capable of sealing oil and gas as the lower limit value of cover layer thickness plugging; or the like, or, alternatively,
and determining by combining the cover layer thickness contour line and the oil-gas-containing surface integral distribution map, and taking the value corresponding to the contour line of the minimum blocking oil gas as the lower limit value of the cover layer thickness blocking.
6. The method for quantitatively characterizing the capping performance of compact carbonate rock cover in superimposed basins according to claim 1, wherein in the fifth step, the lower limit value of natural gamma is determined according to the following steps:
when the thickness is not a factor mainly influencing the sealing performance, in an interval with the sealing capacity, the minimum value of the mean value of natural gamma rays in different wells is used as the lower sealing limit or the area distribution of oil and gas is superposed with a natural gamma ray isoline, so that the minimum natural gamma value capable of sealing oil and gas is used as the lower limit value.
7. The quantitative characterization method of the capping performance of the compact carbonate rock cover of the overlapped basin according to claim 1, wherein in the step five, the shale content is obtained according to the following formula:
wherein
GR in the formula is a natural gamma value of a certain point, and the unit is API;
GRmin is the natural gamma value of the pure mud rock stratum, and the unit is API;
GRmax is the natural gamma value of a pure carbonate rock formation in API;
the new stratum GCUR is 3.7 and the old stratum GCUR is 2.0.
8. The quantitative characterization method of the capping performance of the compact carbonate rock cover of the overlapped basin according to claim 1, wherein the lower limit value of the argillaceous content is obtained according to the lower limit value of the natural gamma in the fifth step.
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