Method for quantitative characterization of carbonate reservoir pore cause type

Abstract

The invention discloses a quantitative characterization method for carbonate reservoir pore formation types. The method provided by the invention comprises the following steps: collecting a carbonate rock sample, and preparing a casting body sheet; carrying out petrology observation on the casting body sheet, determining the cause type of the pore and shooting a microscopic image; performing image analysis processing on the microscopic image, quantitatively identifying pores of various cause types, and calculating pore type proportions of various pores; drawing a pore classification three-end-member graph according to the pore type proportion, and determining a pore phase type; drawing a longitudinal distribution diagram of the pore phase on the basis of a stratigraphic framework, and summarizing a longitudinal evolution path of the pore phase; and integrating the pore facies type and the longitudinal evolution path, and analyzing the formation mechanism of the reservoir pores. According to the method, the pore phase of the carbonate reservoir can be quantitatively represented, and the pore formation cause of the carbonate reservoir is analyzed by analyzing the longitudinal change characteristics of the pore phase.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geological exploration, and in particular to a method for quantitatively characterizing the pore genesis type of a carbonate reservoir. Background Art

[0002] The pores in carbonate reservoirs are an important characteristic sign for studying the genesis of the reservoirs. Characterization and classification of the pores can reveal the genesis of the reservoirs by clarifying the genesis of carbonate pores through the close connection between rock properties and pore characteristics. Therefore, quantitative characterization of the genesis of carbonate reservoir pores is crucial for the development and distribution of large-scale high-quality carbonate reservoirs.

[0003] The origin of pores in carbonate reservoirs is relatively complex, and reservoir pores are often formed under the superposition of multiple factors rather than a single cause. At present, the research on the origin of pores in carbonate reservoirs mainly uses geochemical methods to analyze the source of fluids through elemental analysis or isotope detection, thereby indirectly studying the origin of pores in carbonate reservoirs; in addition, some scholars have made petrological observations of carbonate rocks and used image analysis technology to qualitatively describe the pores in carbonate reservoirs, as well as quantitatively characterize the residual pores, but have failed to quantitatively characterize pores of different origins separately, especially for the superposition of pores of multiple genesis types, it is impossible to quantitatively determine the proportion of pores of different origins separately, which is easy to exaggerate the influence of a certain geological action on the pore genesis, which has certain limitations in reflecting the complex pore genesis of carbonate reservoirs and affects the analysis of the main controlling factors of pore genesis.

[0004] Tavakoli et al. proposed a classification of pore three-end members, which mainly divides pores into three types: sedimentary pores, fabric-selective pores and non-fabric-selective pores; among them, sedimentary pores are mainly intergranular pores, window pane pores and (primary) intragranular pores; fabric-selective pores are mainly mold pores, intragranular solution pores and fabric-selective dolomite intercrystalline pores; non-fabric-selective pores include fabric-destructive dolomite intercrystalline pores, non-fabric-selective solution pores, cracks and sutures. This classification obtains the proportion of various pores through quantitative identification and characterization of pores, and can analyze the contribution of various geological processes to the pore genesis of carbonate reservoirs. Although foreign scholars have used this method to analyze the influence of carbonate diagenesis, the process of pore phase quantification has not been specifically explained, especially the quantitative method of composite pores, nor has the vertical variation characteristics of pore phase been analyzed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for characterizing the formation pore genesis type, which can quantitatively characterize the pore phase of a carbonate reservoir and analyze the pore genesis type of a carbonate reservoir by analyzing the longitudinal variation characteristics of the pore phase.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The method for quantitatively characterizing the pore genesis type of carbonate reservoir provided by the present invention comprises the following steps: S1: Collect samples and make casting thin sections; S2: determining the genesis type of the pores on the surface of the casting thin slice and taking a microscopic image; S3: quantitatively identifying pores of various genetic types according to the microscopic image, and calculating the proportion of pores of various genetic types; S4: according to the proportion data, a pore classification three-end member diagram is drawn to determine the type of pore phase; S5: according to the type of the pore phase, draw a longitudinal distribution diagram and summarize the longitudinal evolution path of the pore phase; S6: Analyze the genesis mechanism of reservoir pores based on the type of pore phase and the longitudinal evolution path.

[0007] In the present invention, in step S1, the sample is a single well carbonate rock core sample.

[0008] In the present invention, in step S2, a polarizing microscope is used to perform petrological observation on the pores on the surface of the casting thin slice to determine the genetic type of the pores.

[0009] In the present invention, in step S3, the quantitative identification of pores of various genesis types is performed according to the following operations: through image analysis processing, different color blocks are used to mark pores of various genesis types, and then the pixel values ​​of the color blocks are used to quantitatively identify pores of various genesis types.

[0010] Specifically, the identification of the pores of various genetic types is performed according to the following operations: If the pores are primary intergranular pores, they are identified as sedimentary pores; If the pore is a single-origin pore, it is identified as a fabric-selective pore; If the pores are composite pores with multiple origins, they are identified as sedimentary pores or a combination of fabric-selective pores and non-fabric-selective pores. The area of ​​the non-fabric-selective pores is the area of ​​the composite pores minus the area of ​​the primary sedimentary pores and the area of ​​the fabric-selective pores; the sedimentary pore content in the composite pores can use the data of the sedimentary pores that are better preserved in the thin section.

[0011] In the present invention, in step S3, the proportion of pores of various genetic types is calculated according to the following formula: The calculation formula for the proportion of pores of various genesis types is: R=P X / P T ; in: R is the proportion of pores of various genetic types; P X is the pixel value of a certain pore type extracted from the microscopic image; P T is the total pore pixel value extracted from the microscopic image.

[0012] In the present invention, in step S4, the type of the porous phase is determined according to the following operation: sedimentary pores, fabric-selective pores and non-fabric-selective pores are taken as three-end members, a three-end member diagram is drawn, and whether the proportion reaches 70% is used as a division condition to divide the three-end member diagram into six regions PF1-PF6; then, the sample points are projected in the three-end member diagram according to the proportion data to obtain the quantitative results of the type of the porous phase.

[0013] In the present invention, in step S5, the summary of the longitudinal evolution path of the porous phase is carried out according to the following operations: a single well stratigraphic framework is established, and high-frequency sedimentary cycles are divided. On this basis, a longitudinal distribution map of the porous phase is drawn according to the depth position corresponding to the casting thin section and the type of porous phase; based on the longitudinal distribution map, the longitudinal evolution law of the porous phase is analyzed in combination with high-frequency sedimentary cycles, and the longitudinal evolution path of the porous phase is summarized.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Based on the three-end-member classification of pores, the present invention proposes the quantitative identification and characterization of pores of different genetic types in carbonate rock cast thin sections, specifically explains the quantitative method of pore types, especially the quantitative method of composite pores, and combines high-frequency stratigraphic analysis to analyze the vertical evolution path of pore phases in order to study the development and distribution characteristics of high-quality carbonate reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic flow chart of a method for quantitatively characterizing pore genesis types in carbonate reservoirs provided by the present invention.

[0016] Figure 2 Schematic diagram of the analysis and processing of cast thin section images in an embodiment of the present invention.

[0017] Figure 3 It is a classified three-end member diagram for quantitative characterization of the pore phase obtained by the image analysis method in an embodiment of the present invention.

[0018] Figure 4 This is a vertical distribution diagram of the pore phase of the target reservoir section of a single well in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0020] Example Methods for quantitative characterization of pore genesis types in carbonate reservoirs, such as Figure 1 As shown, the specific operations are as follows: S1. First, a single well core carbonate rock sample was collected and 123 casting thin sections were prepared; S2. Perform petrological observation on the casting thin section under a polarizing microscope to determine the type of pore genesis, and then take 4-6 microscopic images of each casting thin section.

[0021] S3. Through image analysis and processing methods (implemented with the help of Photoshop software), each pore type is marked with a color block of different colors, and the pixel value of the color block is used to quantitatively identify pores of various genetic types in the casting thin section micrograph.

[0022] The specific steps for identifying pore types are as follows: pores of a single origin, such as primary intergranular pores or mold pores, can be directly identified as sedimentary pores or fabric-selective pores according to the pore classification; some complex composite pores with multiple origins are usually a combination of sedimentary pores / fabric-selective pores and non-fabric-selective pores. The size of non-fabric-selective pores is the size of the composite pores minus the primary sedimentary pores and fabric-selective pores. The sedimentary pore content in the composite pores can be determined using the data of sedimentary pores that are well preserved in the thin section. The results are shown in Figure 2. Figure 2 At the same time, the quantitative data of pores are collected, and the proportion of pore types is obtained according to the formula: pore type proportion = pixel value of a certain type of pores / total pore pixel value.

[0023] The pore quantitative data of one thin slice is used as an example, and the results are shown in Table 1.

[0024] Table 1 Porosity quantitative data of reservoir

[0025] S4. Sedimentary pores, fabric-selective pores and non-fabric-selective pores are used as three end members to draw a three-end member diagram. The three-end member diagram is divided into six regions, PF1-PF6, based on whether the proportion of various pore types reaches 70%. Each region can represent a pore phase type. Among them, the pore types related to sedimentary origin account for more than 70% in PF1; sedimentary pores and fabric-selective pores account for 30%-70% in PF2; sedimentary pores and non-fabric-selective pores account for 30%-70% in PF3; fabric-selective pore types account for more than 70% in PF4; fabric-selective pores and non-fabric-selective pores account for 30%-70% in PF5; non-fabric-selective pore types account for more than 70% in PF6; Then, according to the quantitative proportion data of various pores, the casting thin section samples are projected in the three-end member diagram, and the pore phase type is determined according to the distribution of sample points. The pore phase quantitative results are as follows: Figure 3 shown.

[0026] S5. Establish a single well stratigraphic framework and divide high-frequency sedimentary cycles. On this basis, draw a vertical distribution map of the pore phase according to the depth position and pore phase type corresponding to the casting thin section. The results are as follows: Figure 4 Each pore phase can represent a major pore genesis type. Therefore, by analyzing the longitudinal evolution law of the pore phase in combination with high-frequency sedimentary cycles, it is concluded that there are mainly three longitudinal evolution paths of the pore phase.

[0027] S6. The formation mechanism of reservoir pores is analyzed based on the pore phase types described in the three-end member diagram and the pore phase longitudinal evolution path shown in the pore phase longitudinal distribution diagram.

[0028] The analysis shows that in evolutionary path ①, during the shallowing cycle, the rock was likely to be exposed to atmospheric fresh water due to short-term exposure, resulting in the formation of a large number of selective pores; in evolutionary path ②, due to the weak atmospheric fresh water effect, dolomitization had a greater impact on the transformation of reservoir pores and the porosity increased relatively; in evolutionary path ③, the reservoir rock may have its pores transformed during dolomitization, and non-fabric selective pores such as non-fabric selective solution pores and intercrystalline pores may develop, playing a constructive role, or may develop microcracks under the influence of tectonic action.

[0029] The above embodiments illustrate that the quantitative evaluation method of the present invention can achieve quantitative characterization of the pore genesis type of carbonate reservoirs.

[0030] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A quantitative characterization method for the pore genesis type of carbonate reservoirs, comprising the following steps: S1: Collect samples and make casting thin sections; S2: determining the genesis type of the pores on the surface of the casting thin slice and taking a microscopic image; S3: quantitatively identifying pores of various genetic types according to the microscopic image, and calculating the proportion of pores of various genetic types; S4: according to the proportion data, a pore classification three-end member diagram is drawn to determine the type of pore phase; S5: according to the type of the pore phase, draw a longitudinal distribution diagram and summarize the longitudinal evolution path of the pore phase; S6: Analyze the genesis mechanism of reservoir pores based on the type of pore phase and the longitudinal evolution path.

2. The method according to claim 1, characterized in that In step S1, the sample is a single well carbonate rock core sample.

3. The method according to claim 1 or 2, characterized in that: In step S2, a polarizing microscope is used to perform petrological observation on the pores on the surface of the casting thin slice to determine the genesis type of the pores.

4. The method according to any one of claims 1 to 3, characterized in that In step S3, the quantitative identification of pores of various genesis types is performed according to the following operations: through image analysis processing, different color blocks are used to mark pores of various genesis types, and then the pixel values ​​of the color blocks are used to quantitatively identify pores of various genesis types.

5. The method according to claim 4, characterized in that The identification of the various genetic types of pores is carried out as follows: If the pores are primary intergranular pores, they are identified as sedimentary pores; If the pore is a single-origin pore, it is identified as a fabric-selective pore; If the pores are composite pores with multiple origins, they are identified as sedimentary pores or a combination of fabric-selective pores and non-fabric-selective pores.

6. The method according to any one of claims 1 to 5, characterized in that In step S3, the proportion of pores of various genetic types is calculated according to the following formula: The calculation formula for the proportion of pores of various genesis types is: R=P X / P T ; in: R is the proportion of pores of various genetic types; P X is the pixel value of a certain pore type extracted from the microscopic image; P T is the total pore pixel value extracted from the microscopic image.

7. The method according to any one of claims 1 to 6, characterized in that In step S4, the type of the porous phase is determined according to the following operation: sedimentary pores, fabric-selective pores and non-fabric-selective pores are used as three-end members to draw a three-end member diagram, and the three-end member diagram is divided into PF1-PF6 regions based on whether the proportion reaches 70%; then the sample points are projected in the three-end member diagram according to the proportion data to obtain the quantitative results of the type of the porous phase.

8. The method according to any one of claims 1 to 7, characterized in that In step S5, the vertical evolution path of the porous phase is summarized according to the following operations: a single well stratigraphic framework is established, and high-frequency sedimentary cycles are divided. On this basis, a vertical distribution map of the porous phase is drawn according to the depth position corresponding to the casting thin section and the type of porous phase; based on the vertical distribution map and in combination with high-frequency sedimentary cycles, the vertical evolution law of the porous phase is analyzed to summarize the vertical evolution path of the porous phase.

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