Quantitative method for rheological dynamics of plume in deep-sea mining field

Abstract

The present application belongs to the technical field of deep-sea mining, and discloses a method for quantifying the rheological dynamics characteristics of plumes in deep-sea mining areas. The method comprises the following steps: preparing samples of a target study area and testing the physical properties of the samples; then, testing the rheology of the samples to obtain the variation law of shear strength and dynamic viscosity within a certain shear rate range; finally, fitting the rheological test data according to different rheological models to determine the rheological parameters of the plumes of sediments with different physical properties, and then quantifying the influence of the change of the physical properties of the plumes on the rheological characteristics based on the data fitting method, establishing a plume rheological model considering the change of the physical properties, and quantifying the influence of the change of the physical properties on the plumes of sediments in low-density polymetallic mining areas. The method has important guiding significance for optimizing deep-sea mining operations, reducing environmental impact, and formulating scientific ocean management strategies.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of deep-sea mining, and particularly relates to a method for quantifying the rheological dynamics characteristics of a plume in a deep-sea mining area. BACKGROUND

[0002] The deep-sea mining sediment plume is mainly composed of tiny particulate matter caused by excavation, cutting, drilling, and mining equipment movement and mining loss during the mining process. The spatial distribution characteristics of the deep-sea mining sediment plume are an important basis for predicting its diffusion range. In the prior art, in order to obtain the property changes of the sediment plume during the propagation process, a deep-sea mining simulation in-situ experiment of a certain scale is usually carried out to provide important data reference for subsequent indoor experiments and numerical simulation work.

[0003] However, the existing researches mostly simplify the sediment plume as a low-concentration Newtonian fluid for analysis (Jankowski et al., 1996; Gillard et al., 2019), ignoring the complex rheological characteristics of the deep-sea sediment. According to a large number of engineering geological investigation results, the deep-sea surface sediment in the mining area is usually high-viscosity sediment, which has super-high water content and thixotropy, and the static and dynamic characteristics are relatively complex. When the sediment is disturbed by the mining equipment, a transition from solid state to flow state occurs, resulting in a dramatic change in the physical and mechanical properties thereof. In addition, the generated sediment plume also involves the evolution process of non-Newtonian fluid and Newtonian fluid, which further increases the difficulty of quantitatively describing the rheological characteristics thereof. More importantly, the factors affecting the rheological behavior of the deep-sea mining sediment plume are complex and diverse, including the plume sediment concentration, the particle size distribution and the mineral composition of the sediment, and the pH, temperature, and salinity of seawater, etc., resulting in the complex nonlinear and time-dependent rheological characteristics of the plume diffusion.

[0004] Although the in-situ monitoring means can obtain the physical and mechanical properties of the deep-sea mining sediment plume, it is difficult to quantify the transition of the rheological characteristics during the propagation process. In the current existing technology, although some technologies have quantified the influence of the change of physical parameters on the rheological properties of the homogeneous sediment plume with large density (1.5 g / cm 3 However, the method for the evolution rule of the rheological characteristics of the low-density and non-homogeneous deep-sea mining area sediment plume still needs to be further explored.

[0005] Therefore, in order to accurately characterize the rheological characteristics of the deep-sea mining sediment plume, a more refined rheological model that is suitable for the characteristics of the deep-sea environment needs to be established, thereby providing a scientific basis for the environmental impact assessment of deep-sea mining. SUMMARY

[0006] The technical scheme of the present application can overcome the above technical defects, provide a quantitative method for the rheological dynamics characteristics of the plume in a deep-sea mining area, solve the problem of inaccurate testing of the rheological parameters of the low-density sediment plume under low shear rate conditions, and innovatively consider the change of density in the construction of the rheological model, so as to realize the quantification of the rheological characteristics of the low-density sediment plume under low shear rate conditions

[0007] To achieve the above object, the present application is realized by the following technical scheme: a quantitative method for the rheological dynamics characteristics of the plume in a deep-sea mining area,

[0008] Step A, engineering requirement analysis:

[0009] According to the project requirements, the target deep-sea mining area and the geological conditions of the deep-sea mining area are determined, the relevant environmental specifications for deep-sea mineral development are investigated, and the collection system, transportation system and detection system for deep-sea mineral development are investigated;

[0010] According to the above information, the plume type, formation mechanism and plume distribution are further analyzed;

[0011] Through the above analysis, the density dependence of the sediment plume rheological parameters is further analyzed;

[0012] Step B, engineering geological survey:

[0013] The environmental parameters of the target deep-sea mining area are investigated, and the test samples of the target deep-sea mining area are obtained;

[0014] Step C, sample indoor test:

[0015] Based on the rheometer, the shear effect is applied to the test sample to obtain the change rule of the shear strength and dynamic viscosity of the test sample within a certain shear rate range; the concentration of the test sample is determined according to the physical properties of the sediment sample, and specifically as follows:

[0016] (1) The density, natural moisture content and liquid limit and plastic limit of the sediment sample are determined;

[0017] (2) The state of the sediment in the natural state is preliminarily judged by comparing the natural moisture content with the liquid limit;

[0018] (3) According to the liquid limit, the mass ratio of the solid phase to the liquid phase in the sediment is converted, and the mass concentration of the sediment dry sample-water mixture under the moisture content condition is estimated, so as to determine the configuration concentration of the sediment plume, and the maximum concentration is required to be not more than the sediment concentration under the condition that the moisture content is the liquid limit;

[0019] Step D, rheological model construction:

[0020] Viscosity data of low shear rate and low density sediment plume is acquired, rheological test data is fitted according to different rheological models, rheological parameters of sediment plume with different physical properties are determined, and a plume rheological model is established:

[0021] (1) The change rule of shear strength with shear rate is quantified according to the power-law model through the method of data fitting, so that the rheological parameters of the plume under different density conditions are determined;

[0022] (2) The relationship between the rheological parameters of the plume and its density is constructed;

[0023] ;

[0024]

[0025] Wherein, K(ρ) is the consistency coefficient, n(ρ) is the flow index, is a fitting constant, which reflects the trend of the consistency coefficient and the flow index of the sediment plume changing with the density, and quantifies the influence of the plume density on the rheological parameters k and n; 、 are b k , b n power of the plume density respectively;

[0026] (3) The plume rheological model considering the change of physical properties is established:

[0027] ;

[0028] Wherein, is the shear strength, is the shear rate.

[0029] The present application solves the lack of research on the rheological properties of low-density, heterogeneous deep-sea mining area sediment plume in the prior art, and proposes a quantitative method for the rheological dynamics of low-density deep-sea mining area plume under low shear rate conditions. Through analyzing the engineering requirements to determine the target research area, obtaining the environmental parameters of the research area, and collecting the required sediment samples and seawater samples. Using the method of indoor test, first, the basic soil test is carried out on the sediment sample, and the plume sample is prepared according to the physical properties of the sediment sample, and then the rheological properties of the plume sample are tested. By comparing the applicability of different classical rheological models, the rheological parameters of the sediment plume with different densities are determined. Coupling, a plume rheological model considering the change of physical properties is established, and the influence of the change of physical properties on the low-density polymetallic mining area sediment plume under low shear rate conditions is quantified.

[0030] In the present application, low shear rate (0 ~ 25 s -1 ) and low density (1.035 ~ 1.2343 g / cm3 ) Rheological test of sediment plume, rheological parameters of different density sediment plume under low shear rate condition are determined based on power law model. The mathematical relationship between density and rheological parameters (a and n) is determined, and then the mathematical relationship is brought into the power law model, so that the rheological model of deep-sea mining sediment plume considering density change can be constructed.

[0031] Compared with the prior art, the advantages and positive effects of the present application are:

[0032] The present scheme is mainly aimed at the rheological dynamics characteristics of low-density, non-homogeneous deep-sea mining sediment plume under low shear rate condition, and the indoor test method is adopted to perform plume rheological test on the test sample, and then the rheological test data are fitted according to different rheological models to determine the rheological parameters of sediment plume with different physical properties; the influence of the change of physical properties on the rheological characteristics of the plume is quantified based on the data fitting method, and the plume rheological model considering the change of physical properties is established; the influence of the change of physical properties on the low-density polymetallic mining sediment plume is quantified, which has important guiding significance for optimizing deep-sea mining operation, reducing environmental impact and formulating scientific marine management strategy. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The deep-sea mining plume rheological dynamics quantification method flowchart described in the embodiments of the present application is shown in the figure;

[0034] Figure 2 The rheological property test results of West Pacific sediment plume in the embodiments of the present application are shown in the figure,

[0035] (a) Shear strength changes with shear rate;

[0036] (b) Dynamic viscosity changes with shear rate;

[0037] Figure 3 The rheological test data fitting curve of West Pacific sediment plume in the embodiments of the present application is shown in the figure;

[0038] Figure 4 The rheological parameter change rule of West Pacific sediment plume with density in the embodiments of the present application is shown in the figure,

[0039] (a) Relationship between consistency coefficient and density,

[0040] (b) Relationship between flow index and density. DETAILED DESCRIPTION

[0041] For the purpose of more clearly understanding the above-mentioned objects, features and advantages of the present application, the present application will be further described below in conjunction with the accompanying drawings and embodiments. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, and therefore, the present application is not limited to the specific embodiments disclosed below.

[0042] The embodiment proposes a quantification method for the rheological dynamics characteristics of the plume in a deep-sea mining area, based on the rheological theory, combined with the actual environment of deep-sea mining, systematically studies the rheological characteristics of the sediment plume and the influence of the physical parameters of the plume on the rheological characteristics, such as Figure 1 The method comprises the following steps:

[0043] Step A, engineering requirement analysis:

[0044] According to the project requirements, the target deep-sea mining area and the geological conditions of the deep-sea mining area are determined, the relevant environmental specifications for deep-sea mineral development are investigated, and the collection system, the conveying system and the detection system for deep-sea mineral development are investigated;

[0045] According to the above information, the plume type, the formation mechanism and the plume distribution are further analyzed;

[0046] Through the above analysis, the density dependence of the rheological parameters of the sediment plume is further analyzed;

[0047] Step B, engineering geological survey:

[0048] The environmental parameters of the target deep-sea mining area are investigated, and the test samples of the target deep-sea mining area are obtained;

[0049] Step C, sample indoor test:

[0050] Based on the rheometer, the test sample is subjected to shearing action to obtain the change rule of the shearing strength and dynamic viscosity of the test sample within a certain shearing rate range; the concentration of the test sample is determined according to the physical properties of the sediment sample, and specifically as follows:

[0051] (1) The density, the natural water content, the liquid limit and the plastic limit of the sediment sample are measured;

[0052] (2) The state of the sediment in the natural state is preliminarily judged by comparing the natural water content with the liquid limit;

[0053] (3) According to the liquid limit, the mass ratio of the solid phase to the liquid phase in the sediment is converted, and the mass concentration of the sediment dry sample-water mixture under the water content condition is estimated, so as to determine the configuration concentration of the sediment plume, and the maximum concentration is required to be not more than the sediment concentration when the water content is the liquid limit;

[0054] Step D, rheological model construction:

[0055] Obtain the viscosity data of low shear rate and low density sediment plume, fit the rheological test data according to different rheological models, determine the rheological parameters of sediment plume with different physical properties, and establish the rheological model of the plume:

[0056] (1) According to the power law model, the change rule of shear strength with shear rate is quantified by data fitting method, so as to determine the rheological parameters of the plume under different density conditions;

[0057] (2) The relationship between the rheological parameters of the plume and its density is constructed;

[0058] ;

[0059] ;

[0060] Wherein, K(ρ) is the consistency coefficient, n(ρ) is the flow index, is a fitting constant, which reflects the trend of the consistency coefficient and the flow index of the sediment plume changing with the density, and quantifies the influence of the density of the plume on the rheological parameters and n; 、 are the b k , b n power of the density of the plume;

[0061] (3) Establish the rheological model of the plume considering the change of physical properties:

[0062] ;

[0063] Wherein, is the shear strength, is the shear rate.

[0064] In order to more clearly understand the scheme of the present application, the present embodiment takes the northwest Pacific polymetallic nodule mining area as an example for illustration, and specifically:

[0065] Step A, engineering requirement analysis:

[0066] According to the engineering demand analysis, the deep sea mining activity environmental protection and preservation guide (T / CAOE 41-2021) is taken as a reference standard, and the mining mode of hydraulic lifting is selected. Specifically, the mining mode of hydraulic lifting is firstly relied on the water surface mother ship, and the water surface mother ship is connected with the seabed ore collecting vehicle through the connecting conveying pipeline. Then, the mining vehicle transports the collected deep sea mineral to the water surface mother ship again through the conveying pipeline. The plume caused by the above deep sea mining mode comes from two aspects: on the one hand, the plume of the mining vehicle is formed during the seabed operation and advancement of the seabed ore collecting vehicle. The formation of the mining vehicle plume has three sources, including the disturbance of the sediment during the collection of the nodule, the resuspension of the sediment caused by the advancement of the mining vehicle, and the seabed sediment collected together with the nodule being directly discharged on the seabed after being preliminarily screened by the seabed ore collecting vehicle. On the other hand, after the water surface ore dressing work is completed, the tailings are discharged in the middle layer of the sea through the pipeline, forming a tailings plume composed of water, ore debris and seabed sediment.

[0067] For the plume of the mining vehicle, some seabed in-situ monitoring data show that the advancement of the seabed mining vehicle in the normal working state can cause about 50% of the disturbed surface sediment to resuspend. Although the currently monitored plume density is lower than 1010 kg / m³, the change of the clay content can significantly change the rheological parameters (such as yield strength and viscosity) thereof. Experiments show that when the volume content of the sediment is greater than or equal to 13% (density is approximately 1240 kg / m³) and the proportion of viscous sediment is 50%, the plume will exhibit non-Newtonian fluid characteristics; if the volume content is greater than or equal to 4% (density is approximately 1060 kg / m³), the viscous sediment flow will begin to change to a non-Newtonian fluid. Therefore, when the disturbance is severe, the high-concentration plume of the mining vehicle may also exhibit non-Newtonian fluid behavior during the release stage. For the tailings plume, its propagation will experience the process from being sprayed out of the pipeline to being mixed with the environment water, and the rheological characteristics of the tailings plume in the initial stage depend on the rheological characteristics of the sediment flow in the pipeline. With the propagation of the tailings plume in the sea, the physical properties (such as water content and density) of the tailings plume will change obviously, thereby causing the change of the rheological properties (such as yield strength and viscosity) thereof. It can be seen that the tailings plume sprayed out of the pipeline will inevitably experience the change from a non-Newtonian fluid to a Newtonian fluid during the propagation process in the environment water. Therefore, the rheological characteristics of the plume of the mining vehicle and the tailings plume will change significantly during the propagation process, and the density dependence is obvious.

[0068] The deep sea mining area plume rheological dynamics quantification method provided by the present application will be applied to quantifying the density dependence of the rheological parameters of the sediment plume in the deep sea mining area. The northwest Pacific Magellan Seamount area is selected as the target research area, which is a polymetallic nodule enrichment area and is also located in the rare earth metallogenic belt.

[0069] Rheological tests were carried out using a TA Instrument HR10 flat-plate rotational rheometer, the core component of which is a flat-plate measuring system, which can accurately obtain the viscosity data of the low-density sediment plume, solving the problem of inaccurate rheological parameter testing of low-density sediment plume under low shear rate conditions.

[0070] The test principle of the TA Instrument HR10 flat-plate rotational rheometer used in the application is as follows:

[0071] (1)

[0072] (2)

[0073] (3)

[0074] In the formula, is the shear strength, is the torque, is the flat plate radius, is the shear rate, is the angular velocity, is the gap height between the two flat plates, is the apparent viscosity.

[0075] The physical definition of shear rate is as follows:

[0076] wherein is the fluid flow rate (m·s -1 ), is the shear layer thickness (m), the shear rate describes the change of fluid velocity within a certain distance, and for fluids with viscosity, the shear layer thickness is generally not more than 0.01 m. The deep-sea mining plume has a large initial velocity when it is ejected from the pipe, and as it propagates and diffuses in the marine environment, the flow rate tends to be consistent with the environment. According to the engineering geological survey, the maximum velocity of the deep-sea mining plume ejected from the pipe is 2.85 m·s -1 , and the flow rate of the environment is 0.1 ~ 0.3 m / s (related to depth).

[0077] In the present application, we focus on the rheological properties of low-concentration plumes under low flow rate conditions, so we consider that the plume flow rate is similar to that of the environment, taking 0.25 m·s -1 , and the shear layer thickness is 0.01 m, so the shear rate is 25 s -1 .

[0078] Step B, engineering geological survey:

[0079] First, the environmental parameters of the study area are investigated, including the environmental flow rate, water temperature, salinity and turbidity information. Then the sample acquisition work in the study area is carried out, specifically using a box sampler to obtain deep-sea surface sediment samples and using a CTD water sampler to obtain bottom seawater samples. The sampling depth is 5459.8 m, and the sampling location is 19.00 °N, 149.99 °E.

[0080] Step C, sample room test:

[0081] The concentration of the test sample is determined according to the physical properties of the sediment sample, specifically the density, natural moisture content, and liquid limit and plastic limit of the sediment sample. By comparing the natural moisture content with the liquid limit, the state of the sediment in the natural state is preliminarily judged. Then according to the liquid limit, the mass ratio of solid phase and liquid phase in the sediment is converted, and the mass concentration of the sediment dry sample-water mixture under the condition of this moisture content is estimated, so as to determine the configuration concentration of the sediment plume, and the maximum concentration is required to be not more than the sediment concentration under the condition of the moisture content being the liquid limit. According to the physical properties of the sediment, the sediment plume sample is prepared using the mine sediment sample and the bottom seawater sample, and the specific operation is as follows:

[0082] Specifically, the drying method shows that the moisture content of the sediment in the West Pacific is high, which is 131.96%; the cutting ring method shows that the density of the sediment in the West Pacific is 1247.18 kg / m 3 ; the liquid-plastic limit combined determination method shows that the liquid limit of the sediment in the West Pacific is 132.1%, the plastic limit is 43.6%, the liquidity index is 1.11, and it belongs to high liquid limit clay, which is in a liquid state in the natural state. According to the liquid limit, when the plume moisture content is the liquid limit, the mass ratio of water and sediment in it is about 100:75, i.e. 1000 g of water (density is 1000 kg / m 3) is 750 g, which is considered to be 750 g / L. Therefore, when preparing the sediment plume sample, its concentration should be lower than 750 g / L. In this patent, in order to ensure that the differences in the rheological properties of the plume can be clearly compared within a certain range of plume concentration changes, and to test the rheological properties of low-concentration sediment plumes as much as possible, the maximum concentration of the sediment plume sample is taken as 400 g / L, and the minimum concentration is taken as 25 g / L. The particle size of kaolin and Xitai sediment after removing large impurities by screening is determined by using a Beckman laser particle size analyzer (LS13320), and the particle size distribution range is between 0.3~70.0 µm, D50 is about 6.0 µm, D90 is about 40.0 µm, the peak particle size is about 4 µm, and the overall shows the characteristics of multi-peak distribution. The mineral composition and content of Xitai sediment are determined by X-ray diffraction method, and the test results show that the mineral composition of Xitai sediment is mainly non-clay minerals, accounting for 74.9% of the total, including feldspar, mica, hornblende and quartz. And contains a small amount of clay minerals, accounting for 25.1% of the total, such as illite, chlorite, montmorillonite and kaolin. The shear strength of the undisturbed sample of Xitai surface sediment is low, which is 493.76 Pa. After being subjected to shear, the internal structure is destroyed, causing a large decrease in shear strength. The residual strength after shear damage is 4.26 Pa, which is two orders of magnitude lower than the original strength. These test results show that Xitai sediment has special physical and mechanical properties-high water content, high liquid limit, low shear strength and contains more clay minerals.

[0083] The preparation of the plume sample needs to refer to the water content, liquid limit and density data of Xitai sediment. The minimum water content of the plume sample should be higher than the natural water content, and the maximum concentration should be lower than the natural density. Different concentrations of Xitai sediment plume are prepared in this way. Then, the density of the plume sample is determined by using Mettler Toledo ME204E density tester, as shown in Table 1:

[0084] Table 1 Physical properties of plume sample

[0085] .

[0086] The test sample in this example comes from the polymetallic nodule mining area in the northwest Pacific Ocean, which is a typical non-homogeneous deep-sea clay. When using this sediment to prepare low-density sediment plume, the following problems may exist: (1) It is difficult for the conventional vane rheometer to obtain the low-density (<1.2 g / cm 3) rheological parameters of the plume; (2) the sediment plume has a common settlement problem during the test process, resulting in inaccurate rheological test data. The Discovery HR10 rheometer produced by TA Instruments Company is used to realize the quantification of the rheological parameters of the low-density (<1.2 g / cm 3 ) sediment plume.

[0087] During the test process, the temperature is kept stable at 20°C. According to the environmental flow rate investigation, the strain control mode is adopted to test 50 seconds at a shear rate increment of 0.5 s⁻¹ per second, and the test data of the three sediment plumes in the shear rate range of 0 to 25 s⁻¹ are obtained. Compared with the traditional paddle rheometer, the device can obtain the rheological parameters of the extremely low-density (<1.05 g / cm 3 ) sediment plume. In addition, the flat plate rotor of the device avoids the settlement of sediment ions in the plume sample during the test process, and the test results are as shown in Figure 2 .

[0088] Step D, rheological model construction:

[0089] In this embodiment, a method for quantifying low-density West Pacific sediment is proposed, which is as follows:

[0090] (1) The power-law model (see formula 4) is not suitable for describing plastic fluids with significant yield stress, i.e., high-concentration deep-sea mining plumes. However, for the low-density deep-sea mining plume described in the present application, the power-law model can well describe the shear thinning characteristics, and only two parameters are more suitable for the establishment of a mathematical model. In addition, the present application applies three typical non-Newtonian fluid rheological models, namely the power-law model, the Bingham model and the Herschel-Bulkley model, to fit the rheological test results. The results show that the fitting degree of the power-law model is the highest, which can accurately represent the evolution characteristics of the rheological test data of the plume. Therefore, finally, the variation law of the shear strength with the shear rate is quantified according to the power-law model through data fitting, so as to determine the rheological parameters of the low-density West Pacific sediment plume under the condition of low shear rate, and the fitting results are as shown in Table 2, and the fitting curve is as shown in Figure 3 .

[0091] (4)

[0092] wherein, is the shear strength, Pa; is the consistency coefficient, Pa·s n , which is a parameter representing viscosity, increases with the increase of viscosity; is the shear rate, s -1n is a flow index, dimensionless, reflecting the change of fluid viscosity with the increase of shear rate, when n<1, the fluid is shear thinning fluid, when n>1, the fluid is shear thickening fluid, when n=1, the fluid viscosity does not change with the increase of shear rate.

[0093] The fitting result shows that the power law model can accurately describe the rheological characteristics of the West Pacific sediment plume under the condition of the determined density.

[0094] Table 2 Fitting results of rheological test data of the West Pacific sediment plume

[0095] .

[0096] (2) Then, the fitting results of the rheological test data of the West Pacific sediment plume are further analyzed, and the evolution law of the rheological properties of the deep-sea mining sediment plume during the seabed propagation process is quantified by coupling the physical parameters and rheological parameters of the plume sample. Due to the dilution of the environmental water and the diffusion of the plume itself and the flocculation and sedimentation of the sediment therein, the physical parameters of the deep-sea mining sediment plume will change during the propagation process. In order to quantitatively characterize the propagation process of the sediment plume, the present application selects the density as the key parameter, and by establishing the mathematical relationship between the density and the rheological parameters of the plume, the quantitative description of the rheological kinetic characteristics during the propagation process of the plume is realized.

[0097] In the present application, the data fitting method is used to construct the relationship between the rheological parameters (consistency coefficient and flow index) of the West Pacific sediment plume and its density Figure 4 ). Based on a large amount of fitting work, the fitting effects of polynomial function, power function and exponential function are compared, and the comparison result shows that the power function is most suitable for describing the quantitative relationship between the two. Specifically, the rheological parameters (consistency coefficient and flow index) of the West Pacific sediment plume and the density have a power function relationship as follows:

[0098] (5)

[0099] (6)

[0100] Wherein, =0.01545, Pa·s n ·m 3 ·kg -1 ; =5.10211, dimensionless; =0.28035, m 3 ·kg -1 ; =3.94343, dimensionless.

[0101] and is a scale factor that determines the overall magnitude of the rheological parameters k and n in the fitted density range, and b k and b n jointly constrain the position of the fitted curve in the coordinate space.

[0102] and is a density sensitivity index, b>0 then the rheological parameters and increase with power law (increasing density strengthens the rheological behavior); b<0 then the rheological parameters and decrease with power law (increasing density weakens the rheological behavior).

[0103] This mathematical relationship indicates that the consistency coefficient and flow index of the West Pacific sediment plume both increase with the density of the plume in a power function, revealing the significant influence of density on the rheological behavior of the plume. Specifically, the increase in the consistency coefficient reflects the phenomenon that the viscosity of the plume increases significantly with the density, which is mainly due to the increase in the concentration of solid particles in the plume and the enhancement of the interaction between sediment particles under high-density conditions. The increase in the flow index indicates that the West Pacific sediment plume still exhibits shear thinning characteristics, but its shear thinning characteristics are weakened as the density of the plume increases.

[0104] (3) Based on the above mathematical relationship between the rheological parameters of the West Pacific sediment plume and the density, a rheological model of the West Pacific sediment plume considering the change in physical properties is established:

[0105] (7)

[0106] This model not only accurately describes the rheological characteristics of the West Pacific sediment plume under different density conditions, but also provides an important theoretical basis for predicting the diffusion and flow behavior of deep-sea mining plumes. By incorporating density as a key variable into the rheological model, the dynamics of the plume in the deep-sea environment, including its diffusion range, settling rate, and impact on the marine ecosystem, can be more accurately simulated. This has important guiding significance for optimizing deep-sea mining operations, reducing environmental impact, and developing scientific ocean management strategies.

[0107] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiments shall still fall within the protection scope of the present application.

Claims

1. A method for quantifying the rheological dynamics of plumes in deep-sea mining areas, characterized in that: The following steps are involved: Step A: Project requirements analysis: Determine the target deep-sea mining area and its geological conditions based on project requirements, investigate relevant environmental regulations for deep-sea mineral development, and the collection, transportation, and detection systems for deep-sea mineral development; Further analyze the plume type, formation mechanism, and plume distribution; Through the above analysis, the density dependence of the sediment plume rheological parameters is further analyzed; Step B: Engineering geological survey: Investigate the environmental parameters of the target deep-sea mining area and obtain test samples from the target deep-sea mining area; Step C: Sample indoor test: Based on the rheometer, shearing is applied to the test sample to obtain the variation pattern of shear strength and dynamic viscosity of the test sample within a certain shear rate range. The concentration of the test sample is determined based on the physical properties of the sediment sample, as follows: (1) Determine the density, natural water content, liquid limit and plastic limit of sediment samples; (2) Preliminary judgment of the state of sediments in their natural state by comparing the natural water content with the liquid limit; (3) Based on the liquid limit, convert the mass ratio of the solid phase to the liquid phase in the sediment and estimate the mass concentration of the sediment-water mixture under this water content condition. In this way, the configuration concentration of the sediment plume is determined, and the maximum concentration is required not to exceed the sediment concentration under the liquid limit condition; Step D: Rheological model construction: Obtain viscosity data of low-shear-rate, low-density sediment plumes, fit the rheological test data according to different rheological models, determine the rheological parameters of sediment plumes with different physical properties, and establish a plume rheological model: (1) Based on the power law model, the variation of shear strength with shear rate is quantified by data fitting, thereby determining the rheological parameters of the plume under different density conditions; (2) Constructing the relationship between the rheological parameters of the plume and its density; ； ；‘ Among them, K(ρ) is the consistency coefficient, n(ρ) is the flow index, a k 、b k 、a n 、b n is the fitting constant, reflecting the trend of sediment plume consistency coefficient and flow index with density, and quantifying the effect of plume density on rheological parameters K and n; 、 are the plume density and b k 、b n power; (3) Establish a plume rheological model that takes into account changes in physical properties: ； Where τ is the shear strength, is the shear rate; In step D, when acquiring viscosity data, the rheological test loading conditions, i.e., the shear rate variation range, are set based on the geological survey results. The test principle is as follows: ; ; ; Where τ is the shear strength, M is the torque, and R is the plate radius. is the shear rate, ω is the angular velocity, h is the gap height between the two plates, μ app is the apparent viscosity; Shear rate describes the change in fluid velocity over a certain distance and its physical definition is as follows: ; Where v is the fluid velocity, is the shear layer thickness.

2. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 1, characterized in that: The test samples in step B include surface sediments and bottom seawater.

3. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 2, characterized in that: The step B is specifically implemented in the following manner: (1) Dry and fully grind the surface sediments, and remove large particles of shells and gravel through a sieve; then add the obtained bottom seawater to prepare the test sample of the target concentration; (2) Use a density tester to measure the density of the plume sample.

4. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 3, characterized in that: The target concentration of the test samples was 25-400 g / l.

5. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 1, characterized in that: In the step C, the shear rate is between 0 and 25 s -1 Within the range of 0.5s per second -1 Shear rate increment test data.

6. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 5, characterized in that: In the step C, during the test, the temperature is kept stable at 20° C., and the sediment plume test data is obtained using a strain control mode or a stress control mode.

7. The method for quantifying the rheological dynamics of deep-sea mining plumes according to claim 1, characterized in that: In step D, the low shear rate is 0 ~ 25s -1 , low density is 1.035 ~ 1.2343 g / cm 3 .

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