A method for tracing the source of metamorphic rock debris composition in clastic rocks

Abstract

The present invention provides a method for tracing the source of metamorphic rock cuttings in clastic rocks, belonging to the technical field of oil and gas field exploration and development. The method comprises the following steps: determining a research basin or well and a potential provenance area, conducting data research and selecting rock samples for each of the research basin or well and the potential provenance area; preparing and identifying cast thin sections of the selected rock samples, and classifying and summarizing the identification results of rock thin sections from the same horizon; statistically analyzing the metamorphic rock cutting content and metamorphic rock type in the samples; and inferring the provenance direction of the research basin or well based on the metamorphic rock type, absolute content, relative content, and combination characteristics of the research basin or well and the potential provenance area. The method can effectively identify the provenance of the research basin or well (area) without requiring sampling and preparing rock thin sections, effectively saving labor and economic costs. It also reduces the number of steps in rock thin section preparation and greatly improves work efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field exploration and development, and in particular relates to a source tracing method for a metamorphic rock cuttings composition in clastic rock. Background Art

[0002] Early on, the "source-sink system" approach aimed to analyze geological evolution from the perspective of geomorphic evolution and comprehensively decipher the geological developmental information contained in the stratigraphic sedimentary record. In recent years, the development of the "source-sink system" approach has been closely linked to a series of scientific drilling programs established in Europe and the United States. These programs emphasize the transport processes, transport pathways, and spatiotemporal evolution of sedimentary fluxes from source to sink within a sedimentary system, as well as the mechanisms controlling sedimentation. Research on the "source-sink system" has also garnered widespread attention in China. The approach not only explores the sedimentary responses and configuration relationships among the elements that comprise the "source-sink system," as well as the tectonic responses and sand-control mechanisms that influence it, but also systematically expounds on the basic concepts, research methods, and practical implications of the source-sink system.

[0003] A provenance refers to the source or parent area of ​​clastic material in a basin. Provenance analysis uses the final products of sedimentation to infer the petrological characteristics of the parent rock in the provenance area, as well as the tectonic setting and climatic conditions at the time of sedimentation. Provenance analysis is crucial for determining the provenance location and properties of sediments, their transport pathways, and even the sedimentation and tectonic evolution of the entire basin. Currently, the most commonly used provenance analysis methods include thin sections, grain size analysis, heavy mineral assemblages, rare earth elements, and zircon U-Pb dating. Previous studies of the composition of clastics in sandstone thin sections have only allowed for general inferences of parent rock type and sandstone composition, or for determining provenance distance based on the abundance of rock fragments and feldspar, without being able to determine provenance direction. Summary of the Invention

[0004] In view of this, the present invention aims to propose a method for basin or well (area) provenance tracing using the distribution characteristics of medium- and high-grade regional metamorphic rock fragments and dynamic metamorphic rock fragments in sandstone, conglomerate, and conglomerate rocks. The method innovatively uses existing rock thin section samples to perform quantitative statistical analysis on the content and type of metamorphic rock fragments, eliminating the need to take samples to prepare rock thin sections, saving labor and economic costs, while reducing the steps in rock thin section preparation and greatly improving work efficiency. This method can effectively carry out research on basin or well (area) provenance identification and provide scientific and effective technical guidance for oil and gas field exploration.

[0005] To achieve the above object, the technical solution of the present invention is implemented as follows: A method for tracing the source of a metamorphic rock debris composition in a clastic rock comprises the following steps:

[0006] Step 1: Determine the research basin or well and potential provenance area, conduct data survey and rock sample selection for the research basin or well and potential provenance area respectively;

[0007] Step 2: Prepare and identify cast thin sections of the rock samples selected in step 1, and classify and summarize the identification results of rock thin sections at the same level;

[0008] Step 3: After classifying and summarizing the data from step 2, the content of metamorphic rock debris and the type of metamorphic rock in the sample are counted;

[0009] Step 4: Infer the provenance direction of the study basin or well based on the metamorphic rock type, absolute content, relative content and combination regularity characteristics of the study basin or well and potential provenance area.

[0010] Furthermore, in step 1, when selecting rock samples, it is necessary to first determine the structural background of the research basin or well, the specific research layer, the rock type, and the potential provenance direction.

[0011] Furthermore, when determining the research basin or well, that is, selecting the research target area, it is necessary to ensure the feasibility of selecting rock samples in the research target area or whether there are sufficient rock thin section data in the research target area.

[0012] Furthermore, it is necessary to select more than 100 rock samples or more than 100 rock thin section data from the research target area to conduct a thorough investigation of the geological structural background, water system, rock types and major events in the geological history period around the research target area.

[0013] Furthermore, in step 2, the rock thin section identification standard is based on "Q / HXJ1030-93 Sandstone Thin Section Identification Method" or SY / T5368-2016 Rock Thin Section Identification", and the dynamic metamorphic rocks and regional metamorphic rocks in the clastic rock fragments are classified according to the common metamorphic rock classification method.

[0014] Furthermore, when conducting rock thin section identification, the rock cuttings are sub-categorized and quantified according to area percentage.

[0015] Furthermore, in step 3, the metamorphic rock debris content includes the absolute content and relative content of medium and high-grade regional metamorphic rock debris and dynamic metamorphic rock debris; the metamorphic rock types include regional metamorphic rocks and dynamic metamorphic rocks, wherein regional metamorphic rocks include slate, phyllite, metamorphosed conglomerate, schist and gneiss; dynamic metamorphic rocks include crushed rock, mylonite and phyllite.

[0016] Furthermore, when conducting metamorphic rock debris identification and quantitative statistics, two types of metamorphic rocks are mainly counted. One type is medium and high-grade regional metamorphic rocks with dense crystalline structure; the other type is rigid rocks that are squeezed and broken. In severe cases, the rocks become mylonitic, and their fine fragments often recrystallize or silicify into quartzized metamorphic rocks. The metamorphic rock minerals used are all relatively stable in physical and chemical properties. When they become fragments and are transported over long distances or buried underground and during the diagenesis period, they are not easily dissolved and can retain the characteristics of the parent rock.

[0017] Furthermore, in step 4, the absolute and relative contents of metamorphic rocks, dynamic metamorphic rocks, and regional metamorphic rocks are statistically analyzed. At the same time, detailed statistics are performed on specific sub-type rock types. The rock types of potential provenance areas are compared based on the multi-index statistical results to determine the potential provenance area of ​​the research basin or well.

[0018] Furthermore, if the debris particles of the rock samples in the study basin or well contain a large amount of dynamic metamorphic rocks, no regional metamorphic rocks are found, and the content and type of dynamic metamorphic rocks are similar to those in potential provenance area A and completely opposite to those in potential provenance area B, then it is inferred that the provenance direction of the study basin or well is potential provenance area A.

[0019] The regional metamorphic rocks used in the present invention do not include slightly metamorphosed mudstones, and mainly use medium and high-grade regional metamorphic rocks with dense crystalline structures, whose internal mineral types are mainly quartz, feldspar, mica and hornblende. Another type of dynamic metamorphic rock used is mainly rigid rocks that are squeezed and crushed, and in severe cases, the rocks are mylonized, and their fine fragments often recrystallize or silicify into quartzization. The metamorphic rock minerals used are all relatively stable in physical and chemical properties. When they become fragmentary particles and are transported over long distances or buried underground and during the diagenesis period, they are not easily dissolved, and the characteristics of the parent rock can be retained. The above-mentioned metamorphic rocks are distributed in rocks before the Mesozoic. Therefore, this method can be used to trace the provenance of basins in both pre-Mesozoic sedimentary basins and Cenozoic sedimentary basins. This method uses the same slice as ordinary rock thin section identification, pore imaging, and diagenetic identification, and there is no need to sample and make rock thin sections. Therefore, in addition to the exploration significance of provenance tracing, it is almost economically cost-effective.

[0020] Compared with the prior art, the source tracing method of metamorphic rock cuttings composition in clastic rock of the present invention has the following advantages:

[0021] (1) The method of the present invention only requires microscopic identification and quantitative statistical analysis of the content and type of metamorphic rock fragments in existing rock thin section samples, without the need to re-prepare rock samples, effectively saving labor costs and economic costs, while reducing the number of steps in rock thin section preparation and greatly improving work efficiency;

[0022] (2) The regional metamorphic rocks and dynamic metamorphic rocks used in the method of the present invention can be observed visually under a microscope, reflecting the most original and true appearance of the strata, and the data are reliable;

[0023] (3) The present invention uses relatively stable intermediate and advanced regional metamorphic rocks and metamorphic rocks with relatively stable physical and chemical properties. They are not easily dissolved when they are transported over long distances or buried underground during the diagenesis period, and they can retain the characteristics of the parent rock, so they are highly reliable. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0025] The present invention will be further described below with reference to the following examples, but the present invention is not limited to these examples.

[0026] The present invention provides a method for tracing the source of a metamorphic rock cuttings composition in clastic rock, comprising the following steps:

[0027] Step 1: Determine the research basin or well (area) and potential provenance area, and conduct data surveys and rock sample selection for the research basin or well (area) and potential provenance area respectively; when selecting rock samples, it is necessary to first determine the structural background of the research basin or well (area), specific research layer, rock type and potential provenance direction.

[0028] When determining the research basin or well (area), that is, selecting the research target area, it is necessary to ensure the feasibility of rock sample selection in the target area or whether sufficient rock thin section data are available. It is necessary to select more than 100 rock samples (cores or wall cores) or more than 100 rock thin section data from the target area, and conduct a thorough investigation of the geological tectonic setting, water systems, rock types, and major events in the geological history of the surrounding area (east, west, south, and north). Select more than 50 rock samples from outcrops of the water systems related to the potential provenance area, or thoroughly investigate and collect rock types and metamorphic rock content around the water systems related to the potential provenance area.

[0029] Two aspects require attention in this step. First, ensure that the selected research target area has sufficient rock thin section samples, preferably core and wall core samples, to represent the most realistic information of the stratum. If the number of existing rock thin section samples is less than 100, ensure that the total number of re-sampled rock thin sections plus existing thin section samples is greater than 100 to ensure the representativeness of statistical data and research results. Second, the potential provenance area surrounding the selected research target area must have sufficient research data, including water system distribution, outcrop lithology, parent rock type, and geomorphic background. At the same time, the surrounding potential provenance area must meet the conditions for conducting on-site geological surveys, outcrop observations, and sampling and analysis.

[0030] Step 2: Prepare and identify cast thin sections of the rock samples selected in step 1, and classify and summarize the identification results of rock thin sections in the same layer; the rock thin section identification standards are based on "Q / HXJ1030-93 Sandstone Thin Section Identification Method" or SY / T5368-2016 Rock Thin Section Identification", and the dynamic metamorphic rocks and regional metamorphic rocks in the clastic rock fragments are classified according to the common metamorphic rock classification method.

[0031] If resampling is required, cast thin sections should be prepared and identified from the rock samples selected in step 1. Dynamic metamorphic rocks and regional metamorphic rocks in the cuttings should be classified according to the rock thin section identification standard "Q / HXJ1030-93 Sandstone Thin Section Identification Method" or SY / T5368-2016 "Rock Thin Section Identification" using common metamorphic rock classification methods. If existing core (wellbore) cast thin section data are used, further observation and statistics of different types and subtypes of metamorphic rocks should be conducted according to the rock thin section identification standard "Q / HXJ1030-93 Sandstone Thin Section Identification Method" or SY / T5368-2016 "Rock Thin Section Identification". Metamorphic rock types and subtypes in the potential provenance area should be classified using statistical methods for the target area. Importantly, during the rock thin section identification, the cuttings should be counted by subtype and quantified by area percentage.

[0032] Step 3: Statistically analyze the metamorphic rock content and types in the target area and potential provenance area. Metamorphic rock debris content includes the absolute and relative content of intermediate and advanced regional metamorphic rock debris and dynamic metamorphic rock debris. Metamorphic rock types include regional metamorphic rocks and dynamic metamorphic rocks. Specifically, regional metamorphic rocks include slate, phyllite, metamorphosed conglomerate, schist, and gneiss; dynamic metamorphic rocks include crushed rock, mylonite, and mylonite. When identifying and quantitatively analyzing metamorphic rock debris, slightly metamorphosed mudstone is excluded. Two main types of metamorphic rocks are analyzed: intermediate and advanced regional metamorphic rocks with dense crystalline structures; and metamorphic rocks in which rigid rocks are squeezed and crushed, and in severe cases, mylonitized, with their fine fragments often recrystallizing or silicifying to quartz. The metamorphic minerals used are all relatively stable in physical and chemical properties. They are not easily dissolved when they are transported long distances as fragments or when buried underground or during diagenesis, thus preserving the characteristics of the parent rock.

[0033] Step 4: Infer the provenance direction of the study basin or well (area) based on the metamorphic rock types, absolute content, relative content, and combination characteristics of the study basin or well (area) and potential provenance areas. Statistics are collected for the absolute and relative content of metamorphic rocks, dynamic metamorphic rocks, and regional metamorphic rocks. At the same time, detailed statistics are performed for specific sub-type rock types. Based on the multi-index statistical results, the rock types of the potential provenance areas are compared to determine the potential provenance area of ​​the study basin or well (area). For example, if the debris particles of the rock samples in the study basin or well (area) contain a large amount of dynamic metamorphic rocks, no regional metamorphic rocks are found, and the content and type of dynamic metamorphic rocks are similar to those of potential provenance area A and completely opposite to those of potential provenance area B, then the provenance direction of the study basin or well (area) is inferred to be potential provenance area A.

[0034] Application Case: Rock samples from the MS Formation in the northern QX Basin are depleted in metamorphic rock fragments, with an average absolute content of less than 5%, and exhibit a combination of low-regional metamorphic rocks and high-dynamic metamorphic rocks. In contrast, rock samples from the MS Formation in the southern QX Basin are rich in metamorphic rock fragments, with an average absolute content of over 65%, and exhibit high-regional metamorphic rocks and low-dynamic metamorphic rocks. This indicates that the MS Formation in the northern and southern QX Basin derived its material from two different provenances.

[0035] At the same time, the metamorphic rock content and assemblage characteristics of potential provenance area A are consistent with those of the MS Formation in the northern QX Basin, and the metamorphic rock content and assemblage characteristics of potential provenance area B are consistent with those of the MS Formation in the southern QX Basin, indicating that the northern provenance comes from potential provenance area A and the southern provenance comes from potential provenance area B.

[0036] The regional metamorphic rocks used in the present invention do not include slightly metamorphosed mudstones, and mainly use medium and high-grade regional metamorphic rocks with dense crystalline structures, whose internal mineral types are mainly quartz, feldspar, mica and amphibole. Another type of dynamic metamorphic rock used is mainly rigid rocks that are squeezed and crushed, and in severe cases, the rocks are mylonized, and their fine fragments often recrystallize or silicify into quartzization. The metamorphic rock minerals used are all relatively stable in physical and chemical properties. When they become fragmentary particles and are transported over long distances or buried underground and during the diagenesis period, they are not easily dissolved and can retain the characteristics of the parent rock. The above-mentioned metamorphic rocks are distributed in rocks before the Mesozoic. Therefore, this method can be used to trace the provenance of basins in both pre-Mesozoic sedimentary basins and Cenozoic sedimentary basins. This method uses the same slice as ordinary rock thin section identification, pore imaging, and diagenetic identification, and there is no need to sample and make rock thin sections. Therefore, in addition to the exploration significance of provenance tracing, it is economically zero cost.

[0037] The beneficial effects of the present invention are as follows: the method of the present invention is economically cost-free and only requires microscopic identification and quantitative statistical analysis of the content and type of metamorphic rock fragments in existing rock thin section samples (existing rock thin section samples refer to samples that have been prepared before the use of the present invention, which have always existed but have not been used to carry out the research of the present invention), without the need to re-prepare rock samples. The regional metamorphic rocks and dynamic metamorphic rocks used in the method of the present invention can be observed intuitively under a microscope, can reflect the most original and true appearance of the strata, and the data are reliable. The present invention uses relatively stable medium and high-level regional metamorphic rocks and metamorphic rocks with relatively stable physical and chemical properties. When they become fragments and are transported over long distances or buried underground during the diagenesis period, they are not easily dissolved and can retain the characteristics of the parent rock, so they have high credibility.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for tracing the source of metamorphic rock debris compositions in clastic rocks, characterized in that: The method utilizes the distribution characteristics of medium- and high-grade regional metamorphic rock fragments and dynamic metamorphic rock fragments in sandstone, conglomerate, and conglomerate rocks to trace the provenance of a basin or well, and utilizes existing rock thin section samples to perform quantitative statistical analysis on the content and type of metamorphic rock fragments, including the following steps: Step 1: Determine the research basin or well and potential provenance area, conduct data survey and rock sample selection for the research basin or well and potential provenance area respectively; Step 2: Prepare and identify cast thin sections of the rock samples selected in step 1, and classify and summarize the identification results of rock thin sections at the same level; Step 3: After classifying and summarizing the data from step 2, the content of metamorphic rock debris and the type of metamorphic rock in the sample are counted; Step 4: Infer the provenance direction of the research basin or well based on the metamorphic rock types, absolute content, relative content, and combination characteristics of the research basin or well and potential provenance area; In step 3, the metamorphic rock debris content includes the absolute content and relative content of medium- and high-grade regional metamorphic rock debris and dynamic metamorphic rock debris; the metamorphic rock types include regional metamorphic rocks and dynamic metamorphic rocks, wherein the regional metamorphic rocks include slate, phyllite, metamorphosed conglomerate, schist, and gneiss; the dynamic metamorphic rocks include crushed rock, mylonite, and mylonite; When conducting identification and quantitative statistics of metamorphic rock debris, two types of metamorphic rocks are mainly counted. One type is medium and high-grade regional metamorphic rocks with dense crystalline structure; the other type is metamorphic rocks in which rigid rocks are squeezed and broken, and in severe cases, the rocks become mylonitic, and their fine fragments often undergo recrystallization or silicification to become quartzized metamorphic rocks; the metamorphic rock minerals used are all relatively stable in physical and chemical properties. When they become fragments and are transported over long distances or buried underground and during the diagenesis period, they are not easily dissolved and can retain the characteristics of the parent rock.

2. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 1, characterized in that: In step 1, when selecting rock samples, the first thing to do is to determine the tectonic background of the study basin or well, the specific study horizon, the rock type, and the potential provenance direction.

3. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 2, characterized in that: When determining the research basin or well, that is, selecting the research target area, it is necessary to ensure the feasibility of selecting rock samples in the research target area or whether there are sufficient rock thin section data in the research target area.

4. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 3, characterized in that: It is necessary to select more than 100 rock samples or more than 100 rock thin section data from the research target area, and conduct a thorough investigation of the geological structural background, water system, rock types and major events in the geological history period around the research target area.

5. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 1, characterized in that: In step 2, the rock thin section identification standard is based on "Q / HXJ 1030-93 Sandstone Thin Section Identification Method" or SY / T 5368-2016 Rock Thin Section Identification", and the dynamic metamorphic rocks and regional metamorphic rocks in the clastic rock fragments are classified according to the common metamorphic rock classification method.

6. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 5, characterized in that: When conducting rock thin section identification, the rock cuttings are sub-categorized and quantified according to area percentage.

7. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 1, characterized in that: In step 4, the absolute and relative contents of metamorphic rocks, dynamic metamorphic rocks, and regional metamorphic rocks are statistically analyzed. At the same time, detailed statistics are performed on specific sub-type rock types. The rock types of potential provenance areas are compared based on the multi-index statistical results to determine the potential provenance area of ​​the study basin or well.

8. The method for tracing the source of a metamorphic rock debris composition in clastic rock according to claim 1, characterized in that: If the debris particles of the rock samples in the study basin or well contain a large amount of dynamic metamorphic rocks, no regional metamorphic rocks are found, and the content and type of dynamic metamorphic rocks are similar to those in potential provenance area A and completely opposite to those in potential provenance area B, then it is inferred that the provenance direction of the study basin or well is potential provenance area A.