Basin underflow velocity reconstruction method

Abstract

The invention provides a basin underflow velocity reconstruction method, and relates to the technical field of velocity reconstruction. The basin underflow velocity reconstruction method comprises the following steps: S1, selecting a shale sample formed in a basin sedimentary stratum under a turbulent flow condition, and taking a bedding rock sample along a horizontal layer during deposition; carrying out particle lossless dispersion on the shale sample; and S2, distinguishing terrestrial quartz particles from authigenic quartz particles, and obtaining respective content percentage data. According to the invention, the flow velocity of the basin underflow in the geological history period can be reconstructed only by collecting the shale rock sample formed by the underflow effect in the basin. If the shale in the same deposition period in the basin can be systematically sampled, the underflow characteristics of the deepwater area of the whole basin can be obtained, and the basin hydrodynamic data obtained according to the underflow velocity is one of the most important characteristics of the basin shale deposition environment and is also an important basis for further dividing the shale sedimentary facies.

Description

Technical Field

[0001] The invention relates to the technical field of flow velocity reconstruction, and in particular to a method for basin bottom flow velocity reconstruction. Background Art

[0002] Bottom-current sediments have important exploration value for unconventional oil and gas reservoirs, which are becoming a hot area for global oil and gas exploration. Bottom-current sediments are found almost everywhere in the deep-sea environment around the world and are one of the important oil and gas reservoirs in marine basins. As the most important object of unconventional oil and gas exploration, deep-water sedimentary systems are not only source rock layers but also reservoirs. Currently, many types of unconventional oil and gas reservoirs, such as tight oil, tight gas, shale oil and shale gas, have been discovered in deep-water sedimentary systems. The exploration focus of China's continental basins has gradually shifted and expanded from simple structural traps to lithologic stratigraphic traps, from shallow targets to deep exploration targets, and from conventional fields to unconventional fields. The discovery of bottom flow sediments in continental basins is of great significance for expanding the exploration field of unconventional oil and gas reservoirs in my country's continental basins, mainly in two aspects: ① Thick 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 mud shale, and its distribution area is also a sweet spot for mud shale oil and gas reservoir exploration. Taking the bottom flow sediment distribution area of ​​Songliao Basin as an example, the quartz content in mud shale can reach more than 45%, and the brittle mineral index can reach more than 60. The distribution area or distribution layer of bottom flow sediments is a realistic target of "brittle and sweet" unconventional exploration. At present, some exploration wells in some basins have obtained industrial oil and gas flows through fracturing in the bottom flow distribution area.

[0003] In the deep sea environment, the causes of bottom currents mainly include four types: temperature-salinity difference bottom currents, wind-driven bottom currents, tidal-driven bottom currents, and internal wave-intertidal bottom currents. Since the continental lake basins are relatively small in area and shallow in water, there is no significant water body differentiation and temperature-salinity difference, so the possibility of forming temperature-salinity difference bottom currents, tidal-driven bottom currents, and internal wave-intertidal bottom currents is relatively small. However, the land and the ocean belong to the same earth surface system. Major climate events such as global climate anomalies and atmospheric circulation not only affect and control the sedimentation of ocean bottom currents, but also continental lakes should have the "response" characteristics of wind-driven bottom currents. Chinese sedimentologists have discovered a variety of surface lake currents such as bay currents, circulations, eddies, storm currents, slope currents, downslope currents, onshore waves, and offshore waves in modern lakes and Miocene basins. These lake currents play an important role in controlling the formation and distribution of lake sand bodies. The driving force of surface lake currents is mainly wind-driven, and their direction is mainly affected by wind direction, the topography of the lake's periphery and the topography of the lake's interior. Large-scale surface lake currents can be completely transformed into lake bottom currents.

[0004] McCave et al. elaborated on the basis of the velocity proxy of "sortable silt", and believed that the average particle size of 10-63μm sortable silt is linearly related to the bottom current velocity. The modern bottom current velocity was obtained by inserting a velocity meter in situ on the seabed, and then a correlation function between the flow velocity and the average particle size of the sortable silt in the area was established based on the modern sediment particle size data. The function and the average particle size data of the sortable silt in the stratum were used to reconstruct the bottom current velocity during the deposition of different strata in this area.

[0005] However, the method proposed by McCave et al. to reconstruct the underflow velocity using the average particle size of the sortable silt has the following disadvantages:

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

[0007] 2) It is necessary to install an in-situ flow meter on the bottom of the water to obtain the functional relationship between the local modern flow velocity and the average particle size of the sortable silt. This is technically difficult, costly, and has a limited applicable area. As a result, this method is currently only used in modern marine research in some areas, and the upper limit of the stratigraphic age for reconstructing the flow velocity generally does not exceed the Quaternary. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] In view of the deficiencies in the prior art, the present invention provides a method for reconstructing basin bottom flow velocity, which solves the defects and deficiencies in the prior art.

[0010] (II) Technical solution

[0011] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method for reconstructing the flow velocity of a basin bottom flow, 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 a sample of the rock block along the horizontal layer during deposition; perform non-destructive dispersion of particles of the shale sample; extract quartz particles, and record the percentage data of clay mineral content during the extraction process;

[0013] S2. Distinguish terrigenous quartz grains from authigenic quartz grains and obtain their respective content percentage data;

[0014] S3, performing particle size analysis on the identified terrigenous quartz particles;

[0015] S4, prepare sample A, and prepare quartz sample B of similar particle size according to the particle size distribution data of terrigenous quartz particles;

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

[0017] S6. According to the physical and chemical information of water bodies reflected by the geological data of the basin, a water tank is configured to simulate the fluid medium D;

[0018] S7. Carry out a water tank simulation experiment in a traction flow circulating water tank, add fluid medium D and sample C into the water tank; adjust the flow velocity v in the straight tank deposition area, and slowly reduce the flow velocity in stages from 40 cm / s, with each stage lasting 10 minutes, until the fluid becomes clear, and record the flow velocity v1 at this time, which is the flow velocity when the shale sample is deposited.

[0019] Preferably, the thickness of the shale sample in step 1 is 0.2-0.5 cm, and the upper and lower surface areas are not less than 4 square centimeters.

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

[0021] Preferably, in step 2, cathode luminescence 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 microns is used to prepare sample A.

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

[0024] (III) Beneficial effects

[0025] The present invention provides a method for reconstructing the flow velocity of basin bottom flow, which has the following beneficial effects:

[0026] 1. The present invention only needs to collect shale rock samples formed by bottom flow in the basin to reconstruct the bottom flow velocity of the basin in the geological history period. If the shale in the same deposition period in the basin can be systematically sampled, the bottom flow characteristics of the deep water area of ​​the entire basin can be obtained. The basin hydrodynamic data obtained based on the bottom flow velocity is one of the most important characteristics of the basin shale deposition environment and is also an important basis for further classification of shale deposition phases.

[0027] 2. The present invention uses basin shale that has already been formed as research material. By analyzing the terrigenous quartz particles in the shale and trough simulation and other methods, the ancient shale is linked to the flow velocity. The bottom flow velocity reconstruction research can be extended to the ancient basins in the geological history period, so that the relevant research scope can be expanded to the field of deep geological research and oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example:

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

[0032] S1. Select a shale sample formed under turbulent conditions in the sedimentary strata of the basin, and take a layered rock block sample along the horizontal layer during deposition, with a thickness of 0.2 to 0.5 cm and an upper and lower surface area of ​​not less than 4 square centimeters; perform non-destructive dispersion of particles of the shale sample; use the potassium pyrosulfate method to extract quartz particles, and record the percentage data of clay mineral content during the extraction process;

[0033] S2. Conduct cathode luminescence analysis on the extracted quartz particles to distinguish between terrigenous quartz particles and authigenic quartz particles and obtain the percentage data of their respective contents;

[0034] S3, performing particle size analysis on the identified terrigenous quartz particles;

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

[0036] S5. According to the clay mineral content percentage data and the terrigenous quartz content percentage data, obtain the clay mineral and terrigenous quartz ratio data, and fully mix sample A and sample B according to the ratio to prepare sample C, where sample C is the water tank simulation experiment sample;

[0037] S6. According to the physical and chemical information of water bodies reflected by the geological data of the basin, a water tank is configured to simulate the fluid medium D;

[0038] S7. Carry out a water tank simulation experiment in a traction flow circulating water tank, add fluid medium D and sample C into the water tank; adjust the flow velocity v in the straight tank deposition area, and slowly reduce the flow velocity in stages from 40 cm / s, with each stage lasting 10 minutes, until the fluid becomes clear, and record the flow velocity v1 at this time, which is the flow velocity when the shale sample is deposited.

[0039] The present invention, this method uses shale rock samples to reconstruct the bottom flow velocity of the ancient basin, getting rid of the many limitations of the existing method of McCave et al. that it can only be used for undiagenetic samples and requires modern bottom flow data. Our method can be applied to the reconstruction of the bottom flow velocity of the ancient basin during the geological history period. The terrigenous quartz separated after the lossless dispersion of the shale rock sample is the key carrier of fluid dynamic information during deposition, and the ratio of terrigenous quartz to clay minerals is an important step in reconstructing the flow velocity through water tank simulation. After collecting the grading information of terrigenous quartz and the ratio of terrigenous quartz to clay minerals, combined with the ancient basin fluid data, the flow velocity information at that time is directly simulated in the circulating water tank, with fewer restrictions on the source of the sample and reliable conclusions.

[0040] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprising a reference structure" do not exclude the existence of other identical elements in the process, method, article or device including the elements.

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

Claims

1. A method for reconstructing the velocity of bottom flow in a basin, characterized by: The method comprises the following steps: S1. Select a shale sample formed under turbulent conditions in the sedimentary strata of the basin, and take a sample of the rock block along the horizontal layer during deposition; perform non-destructive dispersion of particles of the shale sample; extract quartz particles, and record the percentage data of clay mineral content during the extraction process; S2. Distinguish terrigenous quartz grains from authigenic quartz grains and obtain their respective content percentage data; S3, performing particle size analysis on the identified terrigenous quartz particles; S4, prepare sample A, and prepare quartz sample B of similar particle size according to the particle size distribution data of terrigenous quartz particles; S5. Obtain the ratio data of clay minerals and terrigenous quartz, and fully mix sample A and sample B according to the ratio to prepare sample C, where sample C is the water tank simulation experiment sample; S6. According to the physical and chemical information of water bodies reflected by the geological data of the basin, a water tank is configured to simulate the fluid medium D; S7. Carry out a water tank simulation experiment in a traction flow circulating water tank, add fluid medium D and sample C into the water tank; adjust the flow velocity v in the straight tank deposition area, and slowly reduce the flow velocity in stages from 40 cm / s, with each stage lasting 10 minutes, until the fluid becomes clear, and record the flow velocity v1 at this time, which is the flow velocity when the shale sample is deposited.

2. The method for reconstructing basin bottom flow velocity according to claim 1, characterized in that: The thickness of the shale sample in step 1 is 0.2-0.5 cm, and the upper and lower surface areas are not less than 4 square centimeters.

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

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

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

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

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