Microscopic identification method for hydrothermal cause calcite

Abstract

The invention provides a microscopic identification method for hydrothermal cause calcite, and the method comprises the steps: judging the calcite according to the optical characteristics of the calcite, and judging the hydrothermal cause calcite according to the characteristics of triangular cleavage, triangular holes and triangular crystals; and carrying out identification and elemental analysis on the identified cathodoluminescence characteristics of the hydrothermal cause calcite, and further identifying the hydrothermal cause calcite. According to the method, the bright crystal calcite existing in the carbonate reservoir is directly subjected to crystal optical judgment, whether the calcite is a hydrothermal cause or not is quickly and conveniently judged through the unique cleavage and optical characteristics of the hydrothermal calcite under a polarizing microscope, and the hydrothermal transformation effect of the reservoir rock is judged.

Description

Technical Field

[0001] The invention belongs to the field of reservoir analysis and relates to a microscopic identification method of hydrothermal calcite. Background Art

[0002] Hydrothermal transformation is a common but very important diagenesis in the development of carbonate reservoirs. During the transformation process, hydrothermal fluids interact with carbonate minerals such as calcite and dolomite, and mineral crystals undergo diagenetic phenomena such as dissolution, replacement, precipitation and recrystallization, thus affecting the quality of the reservoir. Therefore, it is crucial to determine whether a reservoir has been hydrothermally transformed for reservoir research.

[0003] There are two main conventional identification methods: one is to infer that the reservoir rock may have been subjected to hydrothermal transformation in the geological history through the presence of hydrothermal minerals in the reservoir rock, such as pyrite, sphalerite, galena, gypsum, dolomite and other special minerals; the other is to obtain the chemical composition characteristics of the reservoir rock minerals such as trace elements, rare earth elements, isotopes, etc. through petrological and geochemical analysis to determine whether the reservoir rock has undergone hydrothermal transformation. For example, compared with primary minerals, hydrothermally modified dolomite and calcite often have higher Sr and Mg isotope ratios, higher Fe, Mn, and Pb element contents, lower Na content and abnormal rare earth element distribution patterns. However, these two types of identification methods have three shortcomings: (1) Minerals such as pyrite existing in reservoir rocks are not necessarily hydrothermal minerals. For example, pyrite can be generated in anoxic and reducing deep water, swamps and other environments, and may be of sedimentary origin; gypsum can also be primary precipitated in evaporated seawater, and the judgment based on this will produce deviations. (2) Geochemical analysis requires cumbersome chemical processes, which is time-consuming and labor-intensive, and often selects a tiny area in the mineral crystal for analysis, which is not representative enough. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the present invention provides a microscopic identification method for hydrothermal calcite. The method directly performs crystal optical judgment on the spar calcite existing in the carbonate reservoir, and through the unique cleavage and optical characteristics of hydrothermal calcite under a polarizing microscope, it is possible to quickly and conveniently judge whether the calcite is of hydrothermal origin and judge the hydrothermal transformation effect of the reservoir rock.

[0005] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0006] The present invention provides a microscopic identification method of hydrothermal calcite, the identification method comprising:

[0007] Identify calcite based on its optical characteristics, and identify hydrothermal calcite based on its triangular cleavage, triangular pores, and triangular crystals;

[0008] The cathodoluminescence characteristics of the identified hydrothermal calcite are identified and elemental analysis is performed to further identify the hydrothermal calcite.

[0009] After the high-temperature hydrothermal fluid dissolves carbonate crystal minerals such as calcite and dolomite, it is saturated with Ca 2+ , CO 3 2- On the one hand, when the Ca in the fluid 2+ When the content reaches saturation, it will crystallize and precipitate to form bright calcite crystals. On the other hand, the continuous high temperature will affect the crystal morphology and physical properties of bright calcite, thus forming the unique "triangular" cleavage, triangular pores and triangular crystals of hydrothermal calcite (such as Figure 1a ), which is obviously different from the two sets of cleavage of calcite formed by conventional primary sedimentation or undergoing low-temperature diagenesis (such as Figure 1b , 1c ).

[0010] In the present invention, rock samples containing spar calcite are first selected based on petrological observations, and cathode luminescence films are made on a portion of the samples to identify optical characteristics and cathode luminescence characteristics to find the target calcite. Then, the hydrothermal origin is determined based on triangular cleavage and triangular crystals. Elemental analysis is performed on the other portion of the samples to assist in determining the origin of the calcite.

[0011] As a preferred technical solution of the present invention, a polarizing microscope is used to identify calcite based on optical characteristics.

[0012] As a preferred technical solution of the present invention, the optical characteristics include colorless transparency, sparkling protrusions and high-grade white interference color.

[0013] As a preferred technical solution of the present invention, when the optical characteristics are not sufficient to identify calcite, the sample is dyed before identification.

[0014] As a preferred technical solution of the present invention, the dyeing treatment is Alizarin Red dyeing.

[0015] As a preferred technical solution of the present invention, a cathode luminescence instrument is used to identify the cathode luminescence characteristics of the identified hydrothermal calcite.

[0016] As a preferred technical solution of the present invention, the cathode luminescence characteristics of the hydrothermal calcite include any one of bright red, orange-red or bright dark red.

[0017] As a preferred technical solution of the present invention, the element analysis includes laser micro-area carbon and oxygen isotope analysis and laser micro-area trace element and rare earth element analysis.

[0018] As a preferred technical solution of the present invention, the characteristics of hydrothermal calcite in the elemental analysis include Sr, Mg isotope ratios, Fe, Mn and Pb element contents, Na element content and rare earth element distribution pattern.

[0019] As a preferred technical solution of the present invention, the microscopic identification method of hydrothermal calcite includes:

[0020] Using a polarizing microscope to identify calcite based on its optical characteristics, including colorless transparency, flash protrusions, and high-grade white interference color; when the optical characteristics are insufficient to identify calcite, the sample is subjected to alizarin red dyeing for identification; hydrothermal calcite is identified based on the characteristics of triangular cleavage, triangular pores, and triangular crystals;

[0021] A cathodoluminescence instrument is used to identify the cathode luminescence characteristics of the identified hydrothermal calcite, wherein the cathode luminescence characteristics of the hydrothermal calcite include any one of bright red, orange-red or bright dark red; carbon and oxygen isotope analysis as well as laser micro-area trace element and rare earth element analysis are performed on the identified hydrothermal calcite to further identify the hydrothermal calcite.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The present invention provides a microscopic identification method for hydrothermal calcite. The method directly performs crystal optical judgment on spar calcite existing in carbonate reservoirs, and through the unique cleavage and optical characteristics of hydrothermal calcite under a polarizing microscope, it is quickly and conveniently judged whether the calcite is of hydrothermal origin, and the hydrothermal transformation effect of the reservoir rock is judged. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a This is the cleavage diagram of hydrothermal calcite (unique "triangular" cleavage, triangular pores and triangular crystals);

[0025] Figure 1b This is the cleavage diagram of sedimentary calcite;

[0026] Figure 1c This is the cleavage diagram of calcite in marble;

[0027] Figure 2 A schematic flow chart of a method for microscopic identification of hydrothermal calcite provided in a specific embodiment of the present invention;

[0028] Figure 3 This is a sample diagram of the calcite from the Yingshan Formation of the Ordovician System in the Qigu 5 well in Example 1 of the present invention;

[0029] Figure 4aThis is a polarizing microscope image of the brightly coarse-grained calcite filled in the crystalline dolomite bedrock sample in Example 1 of the present invention;

[0030] Figure 4b This is a polarizing microscope image of the rock sample after being stained with alizarin red in Example 1 of the present invention;

[0031] Figure 4c This is a polarizing microscope image of a rock sample with triangular cleavage in Example 1 of the present invention;

[0032] Figure 4d This is a cathode luminescence image of a rock sample with triangular cleavage in Example 1 of the present invention;

[0033] Figure 5 This is a laser carbon and oxygen isotope test diagram of the rock sample in Example 1 of the present invention;

[0034] Figure 6 This is a rare earth distribution pattern diagram of different components in Qigu 5 Well in Example 1 of the present invention (f5-calcite is the rock sample in Example 1);

[0035] Figure 7 This is the distribution diagram of the sodium and silicon content of different components in the Qigu 5 well in Example 1 of the present invention (f5 is the rock sample in Example 1).

[0036] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0038] A specific embodiment of the present invention provides a microscopic identification method of hydrothermal calcite, the identification method comprising:

[0039] Identify calcite based on its optical characteristics, and identify hydrothermal calcite based on its triangular cleavage, triangular pores, and triangular crystals;

[0040] The cathodoluminescence characteristics of the identified hydrothermal calcite are identified and elemental analysis is performed to further identify the hydrothermal calcite.

[0041] In a specific embodiment of the present invention, before microscopic identification, the rock containing spar calcite is sampled. The sample is divided into three parts, and rock thin sections, cathode luminescence sections and geochemical samples are prepared respectively. Among them, the rock sample preparation method is SY / T 5913-2004, and two parts are prepared for geochemical sample analysis.

[0042] In a specific embodiment of the present invention, different transparent mineral crystals have different cleavage and optical characteristics. The cleavage and optical characteristics of the same mineral may also be different due to different causes of origin. The cleavage, protrusions, crystal shape, color, interference color, extinction, etc. of the mineral are identified by single polarized light and orthogonal polarized light of a polarizing microscope, and supplemented by cathode luminescence, trace elements, rare earth elements and isotopes, etc., to identify the mineral type and determine the mineral origin.

[0043] In a specific embodiment of the present invention, under a polarizing microscope, the optical properties and cleavage characteristics of calcite are generally: colorless and transparent, with flashes and protrusions, mostly rhombohedral crystals, interference color high-grade white, and generally having two groups of completely parallel cleavages and rhombohedral crystals. When the cleavage is based on two groups of complete cleavages, a third group of cleavages develops along the obtuse angle, so that the overall cleavage characteristics are manifested as three groups of cleavages, the missing part of the cleavage forms a triangular hole, and the remaining crystal shape is a triangle, such as Figure 1a This form is a special form of hydrothermal calcite.

[0044] In one embodiment of the present invention, the laser micro-area δ 13 C‰, δ 13 When 18‰ is 1.38 and -11.59 respectively, it can be judged to be consistent with the characteristics of hydrothermal calcite genesis.

[0045] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0046] Example 1

[0047] This embodiment provides a microscopic identification method of hydrothermal calcite, the process of which is as follows: Figure 2 As shown, the identification method includes:

[0048] Using a polarizing microscope to identify calcite based on its optical characteristics, including colorless transparency, flash protrusions, and high-grade white interference color; when the optical characteristics are insufficient to identify calcite, the sample is subjected to alizarin red dyeing for identification; hydrothermal calcite is identified based on the characteristics of triangular cleavage, triangular pores, and triangular crystals;

[0049] A cathodoluminescence instrument is used to identify the cathode luminescence characteristics of the identified hydrothermal calcite, wherein the cathode luminescence characteristics of the hydrothermal calcite include any one of bright red, orange-red or bright dark red; carbon and oxygen isotope analysis as well as laser micro-area trace element and rare earth element analysis are performed on the identified hydrothermal calcite to further identify the hydrothermal calcite.

[0050] Specifically, the source of the rock samples is the sparry and coarse-grained calcite in the crystalline dolomite of the Yingshan Formation of the Ordovician System in the Qigu 5 well in the Tabei uplift of the Tarim Basin.

[0051] Well Qigu 5 is located on the western slope of the Lunnan Low Uplift, south of the Luntai Fault. The Ordovician strata encountered Yijianfang Formation, Yingshan Formation, and Penglaiba Formation from top to bottom, among which the Penglaiba Formation contains basalt. The samples were taken from the Yingshan Formation, and the cracks in the samples were well-developed, and the cracks were filled with bright coarse-grained calcite (such as Figure 3 ).

[0052] First, the cleavage and optical characteristics of the sample were observed using a polarizing microscope, as shown in Figure 4. The figure shows that the crystalline dolomite bedrock sample is filled with bright coarse crystalline calcite (such as Figure 4a ), Alizarin red staining is red (such as Figure 4b ) There are three groups of cleavage in calcite (such as Figure 4c ), showing triangular holes and triangular crystals, which are mainly bright red under cathode luminescence (such as Figure 4d ).

[0053] Corresponding selection Figure 3 The spar calcite in the sample has a temperature of 114.6℃ according to the Δ47 test result, which has high temperature characteristics (such as Figure 3 ). Laser carbon and oxygen isotope analysis (such as Figure 5 ), showing that the carbon and oxygen isotope values ​​are obviously negative, which may be formed by hydrothermal precipitation after thermodynamic fractionation. The results of the rare earth distribution pattern of the laser micro-area show (such as Figure 6 ), developed bright coarse-grained calcite with "triangular cleavage, triangular pores and triangular crystals", the total amount of rare earths was significantly higher than that of the matrix, and showed a similar pattern to that of siliceous; while the Sr-Na cross-plot of trace elements (such as Figure 7 ) The sparry coarse-grained calcite in the f5 fracture has high Sr and low Na, both of which confirm that the sparry coarse-grained calcite in the sample is of late hydrothermal origin.

[0054] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0055] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for microscopic identification of hydrothermal calcite, characterized in that: The identification method comprises: Identify calcite based on its optical characteristics, and identify hydrothermal calcite based on its triangular cleavage, triangular pores, and triangular crystals; The cathodoluminescence characteristics of the identified hydrothermal calcite are identified and elemental analysis is performed to further identify the hydrothermal calcite.

2. The method according to claim 1, characterized in that Calcite was identified based on its optical characteristics using a polarizing microscope.

3. The method according to claim 1, characterized in that The optical characteristics include colorless transparency, sparkling protrusions and high-grade white interference color.

4. The method according to claim 3, characterized in that When the optical characteristics are not sufficient to identify calcite, the sample is dyed before identification.

5. The method according to claim 4, characterized in that The staining treatment is Alizarin Red staining.

6. The method according to claim 1, characterized in that A cathodoluminescence instrument is used to identify the cathodoluminescence characteristics of the identified hydrothermal calcite.

7. The method according to claim 1, characterized in that The cathode luminescence characteristics of the hydrothermal calcite include any one of bright red, orange-red or bright dark red.

8. The method according to claim 1, characterized in that The element analysis includes laser micro-area carbon and oxygen isotope analysis and laser micro-area trace element and rare earth element analysis.

9. The method according to claim 8, characterized in that The characteristics of hydrothermal calcite in the elemental analysis include Sr, Mg isotope ratios, Fe, Mn and Pb element contents, Na element content and rare earth element distribution pattern.

10. The method according to any one of claims 1 to 9, characterized in that: The identification method comprises: Using a polarizing microscope to identify calcite based on its optical characteristics, including colorless transparency, flash protrusions, and high-grade white interference color; when the optical characteristics are insufficient to identify calcite, the sample is subjected to alizarin red dyeing for identification; hydrothermal calcite is identified based on the characteristics of triangular cleavage, triangular pores, and triangular crystals; A cathodoluminescence instrument is used to identify the cathode luminescence characteristics of the identified hydrothermal calcite, wherein the cathode luminescence characteristics of the hydrothermal calcite include any one of bright red, orange-red or bright dark red; carbon and oxygen isotope analysis as well as laser micro-area trace element and rare earth element analysis are performed on the identified hydrothermal calcite to further identify the hydrothermal calcite.

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