Basin Bottom Flow Velocity Reconstruction Method

Abstract

This invention provides a method for reconstructing basin bottom flow velocity, relating to the field of flow velocity reconstruction technology. The method includes the following steps: S1, selecting a shale sample formed under turbulent conditions in the basin's sedimentary strata, and taking bedding rock samples along the horizontal layers from the depositional period; performing non-destructive particle dispersion on the shale sample; S2, distinguishing between terrigenous quartz particles and authigenic quartz particles, and obtaining their respective percentage content data. This invention only requires collecting shale rock samples formed by bottom flow in the basin to reconstruct the basin's bottom flow velocity during geological history. If systematic sampling of shale from the same depositional period in the basin can be performed, the bottom flow characteristics of the entire basin's deep-water area can be obtained. The basin hydrodynamic data derived from the bottom flow velocity is one of the most important characteristics of the basin's shale depositional environment and an important basis for further classifying shale sedimentary facies.

Description

Technical Field

[0001] This invention relates to the field of velocity reconstruction technology, specifically a method for reconstructing the velocity of basin bottom flow. Background Technology

[0002] Bottom-flow sediments hold significant exploration value for unconventional oil and gas reservoirs, which are becoming a hotspot in global oil and gas exploration. Bottom-flow sediments are found almost everywhere in deep-sea environments worldwide and are one of the important oil and gas reservoirs in marine basins. As the primary target for unconventional oil and gas exploration, deep-water sedimentary systems are not only source rocks but also reservoirs. Currently, various types of unconventional oil and gas reservoirs, including tight oil, tight gas, shale oil, and shale gas, have been discovered in deep-water sedimentary systems, forming a "source-reservoir integrated" system. The exploration focus in China's continental basins has gradually shifted and expanded from simple structural traps to lithological stratigraphic traps, from shallow targets to deep exploration targets, and from conventional to unconventional areas. The discovery of bottom-flow sediments in continental basins is of great significance for expanding the exploration scope of unconventional oil and gas reservoirs in my country's continental basins, mainly in two aspects: ① Thick layers of bottom-flow sediments in deep-water areas can form tight oil and gas reservoirs; ② The widespread distribution of bottom-flow sediments increases the content of brittle minerals in shale and mudstone, and the distribution areas are also sweet spots for shale and mudstone oil and gas reservoir exploration. Taking the bottom-flow sediment distribution area in the Songliao Basin as an example, the quartz content in shale and mudstone can reach over 45%, and the brittle mineral index can reach over 60. The distribution areas or strata of bottom-flow sediments are realistic targets for unconventional exploration that are both "brittle and sweet." Currently, some exploration wells in basins have obtained industrial oil and gas flows through fracturing in bottom-flow distribution areas.

[0003] In deep-sea environments, bottom currents are mainly categorized into four types: differential temperature and salinity bottom currents, wind-driven bottom currents, tidal-driven bottom currents, and internal wave tidal bottom currents. Due to the relatively small area and shallow water of terrestrial lacustrine basins, there is no significant water body differentiation or temperature and salinity difference, thus the likelihood of differential temperature and salinity bottom currents, tidal-driven bottom currents, and internal wave tidal bottom currents forming is relatively low. However, since land and ocean both belong to the Earth's surface system, major climate events such as global climate anomalies and atmospheric circulation not only affect and control ocean bottom current deposition, but terrestrial lakes should also exhibit "response" characteristics of wind-driven bottom currents. Chinese sedimentologists have discovered various surface lake currents in modern lakes and Miocene basins, including bay currents, circulations, eddies, storm currents, slope currents, downstream currents, onshore waves, and offshore waves. These lake currents play a crucial role in controlling the formation and distribution of lacustrine sand bodies. The driving force of surface lake currents is mainly wind, and their flow direction is mainly affected by wind direction, the landforms around the lake and the landforms inside the lake. Large-scale surface lake currents can be completely transformed into bottom lake currents.

[0004] McCave et al. elaborated on the basis of the "sortable silt" velocity proxy, arguing that the average grain size of sortable silt (10-63 μm) is linearly correlated with bottom current velocity. They obtained modern seafloor bottom current velocities by in-situ inserting current meters and then established a correlation function between the velocity and the average grain size of sortable silt in the region based on modern sediment grain size data. Using this function and the average grain size data of sortable silt in the strata, they reconstructed the bottom current velocities during the deposition of different strata in the region.

[0005] However, McCave et al.'s method of reconstructing underflow velocity using the average particle size of sortable silt has the following drawbacks:

[0006] 1) Grain size data of the whole sample at the time of deposition is required, which is not applicable to rock samples that have already undergone diagenesis, making it difficult to study consolidated rock formations;

[0007] 2) In-situ current meters must be installed on the seabed to obtain the functional relationship between local modern current velocity and the average particle size of sortable silt. This method is technically difficult, costly, and has limited applicability. As a result, this method is currently only used in modern marine research in some areas, and the upper limit of the age of the reconstructed current-strata generally does not exceed the Quaternary period. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a method for reconstructing basin bottom flow velocity, which solves the defects and deficiencies in existing technologies.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the present invention provides the following technical solution: a method for reconstructing basin bottom flow velocity, the method comprising the following steps:

[0012] S1. Select a shale sample formed under turbulent conditions in the sedimentary strata of the basin, and take bedding rock samples along the horizontal layer during deposition; perform non-destructive particle dispersion on the shale sample; extract quartz particles, and record the percentage data of clay mineral content during the extraction process;

[0013] S2. Distinguish between terrigenous quartz particles and authigenic quartz particles, and obtain their respective content percentage data;

[0014] S3. Perform particle size analysis on the identified terrigenous quartz particles;

[0015] S4. Prepare sample A. Based on the particle size distribution data of quartz particles from the root source, prepare quartz sample B with a similar particle size.

[0016] S5. Obtain the ratio data of clay minerals and terrigenous quartz, and mix sample A and sample B thoroughly according to the ratio to prepare sample C. Sample C is the sample for the water tank simulation experiment.

[0017] S6. Based on the water physicochemical information reflected in the basin geological data, configure a water tank to simulate fluid medium D;

[0018] S7. Conduct a water tank simulation experiment in a traction flow circulating water tank. Add fluid medium D and sample C to the water tank. Adjust the flow velocity v in the straight channel deposition zone. Starting from 40 cm / s, the flow velocity is gradually reduced in stages, with each stage lasting 10 minutes, until the fluid becomes clear. Record the flow velocity v1 at this time. v1 is the flow velocity when the shale sample is deposited.

[0019] Preferably, the shale sample in step 1 has a thickness of 0.2 to 0.5 cm and an upper and lower surface area of ​​not less than 4 square centimeters.

[0020] Preferably, the method for extracting quartz particles in step 1 uses the potassium pyrosulfate method.

[0021] Preferably, in step 2, cathodoluminescence analysis is performed on the extracted quartz particles to distinguish between terrigenous quartz particles and authigenic quartz particles.

[0022] Preferably, in step 4, kaolinite with a particle size of less than 10 micrometers is used to prepare sample A.

[0023] Preferably, the clay mineral and terrigenous quartz ratio data obtained in step 5 are obtained based on the clay mineral content percentage data and the terrigenous quartz content percentage data.

[0024] (III) Beneficial Effects

[0025] This invention provides a method for reconstructing basin bottom flow velocity. It has the following beneficial effects:

[0026] 1. This invention only requires collecting shale rock samples formed by bottom flow in the basin to reconstruct the bottom flow velocity of the basin during geological history. If systematic sampling of shale from the same depositional period in the basin can be performed, the bottom flow characteristics of the entire deep-water area of ​​the basin can be obtained. The basin hydrodynamic data derived from the bottom flow velocity is one of the most important characteristics of the basin shale depositional environment and an important basis for further classifying shale depositional facies.

[0027] 2. In this invention, the research material is basin shale that has already formed diagenesis. By analyzing the terrigenous quartz grains in the shale and using methods such as flume simulation, the ancient shale is linked to flow velocity. This allows the study of bottom flow velocity reconstruction to be extended to ancient basins in geological history, thus expanding the scope of related research to the fields of deep-time geological research and oil and gas exploration. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example:

[0031] like Figure 1 As shown, this embodiment of the invention provides a method for reconstructing basin bottom flow velocity, the method comprising the following steps:

[0032] S1. Select a shale sample formed under turbulent conditions in the sedimentary strata of the basin. Take a bedding rock sample along the horizontal layer at the time of deposition, with a thickness of 0.2-0.5 cm and an upper and lower surface area of ​​not less than 4 square centimeters. Disperse the shale sample non-destructively. Extract quartz particles using the potassium pyrosulfate method. Record the percentage data of clay mineral content during the extraction process.

[0033] S2. Perform cathodoluminescence analysis on the extracted quartz particles to distinguish between terrigenous quartz particles and authigenic quartz particles, and obtain their respective content percentage data.

[0034] S3. Perform particle size analysis on the identified terrigenous quartz particles;

[0035] S4. Use kaolinite with a particle size of less than 10 micrometers to prepare sample A, and prepare quartz sample B with a similar particle size according to the particle size distribution data of terrestrial quartz particles.

[0036] S5. Based on the percentage data of clay mineral content and the percentage data of terrigenous quartz content, obtain the ratio data of clay mineral and terrigenous quartz. Mix sample A and sample B thoroughly according to the ratio to prepare sample C. Sample C is the sample for the water tank simulation experiment.

[0037] S6. Based on the water physicochemical information reflected in the basin geological data, configure a water tank to simulate fluid medium D;

[0038] S7. Conduct a water tank simulation experiment in a traction flow circulating water tank. Add fluid medium D and sample C to the water tank. Adjust the flow velocity v in the straight channel deposition zone. Starting from 40 cm / s, the flow velocity is gradually reduced in stages, with each stage lasting 10 minutes, until the fluid becomes clear. Record the flow velocity v1 at this time. v1 is the flow velocity when the shale sample is deposited.

[0039] This invention presents a method for reconstructing paleobasin bottom flow velocities using shale rock samples, overcoming the limitations of existing methods by McCave et al., which can only be used with unformed samples and require modern bottom flow data. Our method can be applied to the reconstruction of paleobasin bottom flow velocities during geological history. Terrigenous quartz, separated from shale rock samples after non-destructive dispersion, is a key carrier of hydrodynamic information during deposition. The ratio of terrigenous quartz to clay minerals is an important step in reconstructing flow velocity through flume simulation. By collecting the gradation information of terrigenous quartz and the terrigenous quartz-to-clay mineral ratio data, and combining it with paleobasin fluid data, the flow velocity information at that time can be directly simulated in a circulating flume. This method has fewer limitations on sample sources and the conclusions are reliable.

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for reconstructing basin bottom flow velocity, characterized in that: The method includes the following steps: S1. Select a shale sample formed under turbulent conditions in the sedimentary strata of the basin, and take bedding rock samples along the horizontal layer during deposition; perform non-destructive particle dispersion on the shale sample; extract quartz particles, and record the percentage data of clay mineral content during the extraction process; S2. Distinguish between terrigenous quartz particles and authigenic quartz particles, and obtain their respective content percentage data; S3. Perform particle size analysis on the identified terrigenous quartz particles; S4. Prepare sample A. Based on the particle size distribution data of quartz particles from the root source, prepare quartz sample B with a similar particle size. S5. Obtain the ratio data of clay minerals and terrigenous quartz, and mix sample A and sample B thoroughly according to the ratio to prepare sample C. Sample C is the sample for the water tank simulation experiment. S6. Based on the water physicochemical information reflected in the basin geological data, configure a water tank to simulate fluid medium D; S7. Conduct a water tank simulation experiment in a traction flow circulating water tank. Add fluid medium D and sample C to the water tank. Adjust the flow velocity v in the straight channel deposition zone. Starting from 40 cm / s, the flow velocity is gradually reduced in stages, with each stage lasting 10 minutes, until the fluid becomes clear. Record the flow velocity v1 at this time. v1 is the flow velocity when the shale sample is deposited.

2. The basin bottom flow velocity reconstruction method according to claim 1, characterized in that: In step 1, the shale sample has a thickness of 0.2–0.5 cm and an upper and lower surface area of ​​not less than 4 square centimeters.

3. The basin bottom flow velocity reconstruction method according to claim 1, characterized in that: The method for extracting quartz particles in step 1 uses the potassium pyrosulfate method.

4. The basin bottom flow velocity reconstruction method according to claim 1, characterized in that: In step 2, cathodoluminescence analysis is performed on the extracted quartz particles to distinguish between terrestrial quartz particles and authigenic quartz particles.

5. The basin bottom flow velocity reconstruction method according to claim 1, characterized in that: In step 4, sample A is prepared using kaolinite with a particle size of less than 10 micrometers.

6. The basin bottom flow velocity reconstruction method according to claim 1, characterized in that: The data on the ratio of clay minerals and terrigenous quartz in step 5 are obtained based on the percentage data of clay mineral content and the percentage data of terrigenous quartz content.

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