A Method for Measuring Cohesive Force and Micromechanical Parameters of Wax Crystal Flocs Based on Microfluidic-CFD-DEM

Abstract

This invention relates to a method for measuring the cohesion and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM. It combines microfluidic experimental observation with CFD-DEM numerical simulation to quantitatively characterize the formation-fracture dynamics of wax crystal flocs. Microfluidic experimental observation is conducted through a dynamic behavior observation platform for wax crystal flocs, enabling visual observation of the formation process and the floc fragmentation process under fluid shear. A mathematical model consistent with the microfluidic experimental conditions is constructed in the CFD-DEM, and the dynamic fragmentation process of the flocs in a shear flow field is simulated through two-way fluid-structure interaction calculations. The simulated fragmentation results are then compared with the microfluidic experimental observation data. When the relative error between the two is less than a certain value, accurate measurement of the cohesion and micromechanical parameters of the wax crystal flocs is achieved. This invention realizes the accurate measurement of the cohesion and micromechanical parameters of wax crystal flocs through the inversion of experimental phenomena.

Description

Technical fields:

[0001] This invention relates to the field of flow assurance and storage and transportation technology for waxy crude oil, specifically a method for measuring the cohesive force and micromechanical parameters of wax crystal flocs based on microfluidic experiments and coupled simulation of computational fluid dynamics-discrete element method (CFD-DEM). Background technology:

[0002] In 2024, my country's total oil and gas production exceeded 400 million tons of oil equivalent for the first time, with crude oil production reaching 213 million tons. Driven by the "dual-carbon" strategic goal, the petroleum industry urgently needs to develop green and efficient flow assurance technologies to reduce energy consumption and carbon emissions during the storage and transportation of high-wax crude oil. my country's crude oil resources are mainly characterized by "three-high" crude oil: high wax content, high pour point, and high viscosity. This type of crude oil faces severe flow safety challenges during low-temperature gathering and transportation. When the temperature is below the wax precipitation point, wax crystals continuously precipitate and form a three-dimensional flocculated network structure, leading to a sharp increase in the apparent viscosity of the crude oil and increased pipeline resistance, which can even cause pipeline blockage accidents due to wax deposition. According to statistics, the annual pipeline maintenance cost caused by wax deposition in my country's onshore oil fields exceeds 1 billion yuan, and traditional thermal deblocking methods are energy-intensive, which contradicts the goal of low-carbon development.

[0003] Currently, the academic community has conducted multifaceted research on wax crystal flocs of waxy crude oil: in terms of formation mechanism, microscopic observations have revealed the regulatory laws of temperature field and shear field on wax crystal growth rate and morphology; in terms of macroscopic rheological properties, a correlation model of temperature-shear rate-floc structure has been established. However, existing research still faces two major technical bottlenecks: (1) lack of microscopic mechanical parameters: key forces such as van der Waals force and adhesion force between wax crystals are difficult to measure directly, resulting in a lack of theoretical basis for quantifying floc strength; (2) insufficient multi-scale correlation: traditional methods cannot simultaneously correlate microscopic wax crystal forces and macroscopic rheological behavior, which restricts the accuracy of pour point depressant molecular design.

[0004] During the storage, pipeline transportation, and gathering of waxy crude oil, as the temperature decreases, wax crystals precipitate and aggregate to form a three-dimensional flocculated network structure, leading to increased apparent viscosity, deteriorated fluidity, and even pipeline condensation accidents. Traditional methods are insufficient to directly measure the microscopic forces between wax crystals and the macroscopic mechanical properties of the flocs, thus hindering the development of pour point depressants and the precise optimization of flow improvement measures. Summary of the Invention:

[0005] The purpose of this invention is to provide a method for measuring the cohesive force and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM. This method for measuring the cohesive force and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM is used to solve the problem that traditional methods are difficult to directly measure the micro-forces between wax crystals and the macro-mechanical properties of flocs.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: This method for measuring the cohesion and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM combines microfluidic experimental observation with CFD-DEM numerical simulation to quantitatively characterize the formation-fracture dynamics of wax crystal flocs; the microfluidic experimental observation is carried out through a wax crystal floc dynamic behavior observation platform, which is a platform integrating a multi-channel microfluidic chip system and a high-resolution microscopic imaging system. By selecting different microfluidic channel types and setting the temperature and flow rate, the formation process of wax crystal flocs and the fracture process under fluid shear can be visualized and observed.

[0007] A mathematical model consistent with microfluidic experimental conditions is constructed in CFD-DEM, and initial cohesion and micromechanical parameters between wax crystals are randomly set. The dynamic fragmentation process of flocs in a shear flow field is simulated through two-way fluid-structure interaction calculations. The simulated fragmentation results are then compared with microfluidic experimental observation data. When the relative error between the two is less than a certain value, the preset mechanical parameters match the actual parameters, thus achieving the measurement of cohesion and micromechanical parameters of wax crystal flocs. Otherwise, the basic mechanical parameters are intelligently adjusted and iteratively optimized until the floc fragmentation characteristics meet the error range, ultimately achieving the measurement of cohesion and micromechanical parameters of wax crystal flocs in the microfluidic chip. The experimental conditions include microfluidic channel size, initial floc morphology, and flow field parameters. The fragmentation results include fragmentation critical time, fragmented particle position, fragmented particle number distribution, particle size after fragmentation, and velocity.

[0008] The above-mentioned dynamic behavior observation platform for wax crystal flocs includes a power module, a delivery module, a temperature control module, and an imaging module. The power module includes a constant flow pump, which provides kinetic energy to the delivery medium, ensuring it is uniformly filled into the microfluidic chip after being acted upon by the temperature control module. The delivery module includes a micro-sampler, a delivery hose, and a waste liquid recovery hose. Under the action of the power module, the oil flows through the delivery hose to the imaging module and finally to the waste liquid recovery hose. The temperature control module includes a microscopic hot stage and a water bath device, ensuring that the temperature of the microfluidic chip and the delivery hose is maintained at the experimental set temperature. The imaging module includes a polarizing microscope and a microfluidic chip. The polarizing microscope is used to capture and record the wax crystal formation process and the shearing process of the scouring medium on the wax crystal flocs. The microfluidic chip is the floc formation area, forming wax crystal flocs, enabling visual observation of the wax crystal floc formation process and the breakup process under fluid shearing.

[0009] The microfluidic chip in the above scheme includes a chip inlet, a microfluidic channel, and a chip outlet. There are four types of microfluidic channels: multi-field coupling control type pillar structure, groove type channel structure, multi-level gradient sieving structure, and micro-region gradient temperature control structure. By selecting microfluidic chips with different microfluidic channels, wax crystal flocs of different shapes and sizes can be formed.

[0010] The multi-field coupled control type column structure consists of several columns arranged in an array within the cavity of a microfluidic channel. This array of columns creates a multi-physics coupled environment, enabling the structure to simultaneously generate three key control effects: fluid dynamics control, interface effect control, and confined space control. In terms of fluid dynamics, the column structure forms a characteristic flow field distribution through boundary layer separation. Regarding interface effects, it achieves selective adsorption of wax crystals. In terms of spatial constraints, it controls the growth orientation and density of flocs through geometric restrictions. By utilizing the boundary layer effect and flow separation phenomena in fluid mechanics, the formation and fragmentation processes of wax crystal flocs can be controllably regulated.

[0011] The grooved channel structure consists of several parallel grooves within the cavity of a microfluidic channel. These grooves are strip-shaped. When waxy crude oil flows into the cavity, the grooves promote the orderly growth of wax crystals, increasing the collision frequency and adhesion probability between wax crystal particles. A characteristic velocity gradient distribution forms inside the grooves, and the stratified flow pattern allows the wax crystals to obtain optimal growth conditions at the bottom of the grooves. By adjusting the depth-to-width ratio and arrangement density of the grooves, quantitative control over the morphology and mechanical properties of the flocs can be achieved. During the scouring stage, the shear failure behavior of wax crystal flocs with different bonding strengths is studied.

[0012] The multi-level gradient sieving structure integrates multi-level gradient pore size filters within the cavity of the microfluidic channel. Through a graded sieving mechanism, it achieves precise sorting and mechanical property analysis of wax crystal flocs. The filter array with decreasing pore size is arranged sequentially along the fluid flow direction to form a progressive spatial sieving structure, realizing graded capture of floc groups. At the same time, it constructs a physical environment with progressively changing flow field intensity, and the flow field intensity exhibits a gradient enhancement.

[0013] The micro-region gradient temperature control structure integrates a micro temperature control unit array within the cavity of the microfluidic channel. Micron-level temperature control microfilaments penetrate the flow channel vertically and maintain the same height as the microfluidic channel, forming a stable temperature gradient distribution within the microfluidic flow channel.

[0014] In the above scheme, the flushing medium is selected from mineral oil, silicone oil, and methylene blue solution. The flushing methods include steady-flow impact, oscillating impact, pulse impact, and impact with different fluid properties, including viscosity and density. Steady-flow impact simulates the continuous shearing action under stable pipeline transport conditions; oscillating impact simulates the periodic shear fluctuations caused by pump and valve start-up and shutdown, flow regulation, or slug flow; and pulse impact simulates the instantaneous high shear stress generated by the passage of pigs, water hammer, or sudden operations. Impact with different fluid properties examines the effect of changes in crude oil properties or the injection of different chemical agents on the smooth shear characteristics and... The influence of scouring effect is explored through a media-dynamic coupling simulation strategy that combines the scouring medium system and the impact method. This strategy enhances the simulation similarity to the variable and complex flow environment in oilfields, quantitatively revealing key mechanical responses and fragmentation mechanisms. By combining scouring methods, the critical shear stress, fragmentation rate, and structural stability parameters of wax crystal flocs under different media environments and dynamic conditions are accurately measured. The influence of scouring medium properties and impact methods on the cohesion, structural stability, and fragmentation mode of wax crystal flocs is quantitatively analyzed, revealing the intrinsic mechanism of dynamic fragmentation and redeposition of wax deposits under complex field conditions.

[0015] The method for intelligently adjusting and iteratively optimizing the basic mechanical parameters in the above scheme is as follows: by initially setting the basic mechanical parameters, including the van der Waals force, adhesion force, and elastic modulus between wax crystals, and combining the geometric characteristic parameters of the wax crystal floc particles, the basic mechanical parameters are continuously iteratively optimized using an intelligent optimization algorithm, so that the numerical simulation accurately reproduces the floc fragmentation characteristics observed in the microfluidic experiment. The floc fragmentation characteristics include the fragmentation sequence, fragment morphology, and motion trajectory. When the simulation results are consistent with the experimental results within the allowable error range, it means that the preset mechanical parameters are consistent with the actual parameters, thus achieving accurate measurement of the cohesive force and micromechanical parameters of the wax crystal flocs.

[0016] The above scheme utilizes a microfluidic-CFD-DEM-based method for measuring the cohesion and micromechanical parameters of wax crystal flocs. This method employs a high-resolution microscopic imaging system to observe the formation process of wax crystal flocs in the microfluidic channel and their fragmentation behavior under fluid impact in real time. Simultaneously, a consistent CFD-DEM coupled numerical model is established to simulate the dynamic evolution of the flocs, constructing a complete closed loop of experimental observation, numerical simulation, and phenomenon inversion. First, based on the actual geometric dimensions of the microfluidic channel, the initial morphological characteristics of the flocs, and the flow field boundary conditions, the CFD-DEM coupled model is established. The Monte Carlo method is used to randomly set micromechanical parameters, including inter-crystal van der Waals forces, adhesion forces, elastic modulus, and Poisson's ratio, and the internal... Cohesion is precisely simulated through two-way fluid-structure interaction calculations to simulate the dynamic response process of flocs in a shear flow field. Subsequently, key parameters obtained from the numerical simulation, including critical breakage time, spatial distribution characteristics of breakage, particle number distribution, particle size evolution law, and velocity, are quantitatively compared with dynamic breakage process data obtained from microfluidic experiments. When the simulation results and experimental data show consistency in breakage mode and dynamic evolution trend, and the relative error of key parameters is less than α, the value of α is set according to the accuracy requirements. This confirms that the currently preset cohesion and micromechanical parameters are consistent with the mechanical properties of wax crystals in the microfluidic experiment, realizing the accurate measurement of cohesion and micromechanical parameters of wax crystal flocs through experimental phenomena.

[0017] The specific method for measuring the cohesive force and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM in the above scheme is as follows:

[0018] Step 1: Based on the key parameters of the target wax crystal flocs, including target size distribution, structural strength, and environmental sensitivity, dynamically select and combine matching microfluidic chip structures, scouring media, and impact methods from a pre-set parameter module library:

[0019] Step Two: In-situ Dynamic Observation of Wax Crystal Flocs: A constant flow pump is started, and the pretreated waxy crude oil sample is delivered to the microfluidic chip in the imaging module at a constant flow rate via a micro-sampler. During delivery, a three-stage temperature control strategy—pre-cooling / pre-heating with a water bath, precise temperature control on a microscopic hot stage, and real-time monitoring and feedback of the flow channel temperature—ensures that the waxy crude oil is injected into the microfluidic channel at a uniform and constant temperature. Once the microfluidic channel is completely filled, the power unit is stopped, allowing the waxy crude oil to reach a static equilibrium state within the microfluidic chip. Subsequently, the waxy crude oil within the microfluidic chip undergoes gradient cooling. During the cooling process, the nucleation, growth, and aggregation of wax crystal flocs are captured in real-time using a polarizing microscope, and the morphological characteristics at key temperature points are recorded.

[0020] Step 3: In-situ quantitative observation of the shear breakage dynamics of wax crystal flocs: After the temperature is gradually reduced to form a stable wax crystal floc network structure, cooling is stopped and the microfluidic chip is left to stand at a constant temperature for 30-60 minutes to ensure the full stability of the floc structure. Subsequently, the flushing program is started, and a flushing medium with the same temperature as the microfluidic chip is injected in a stepwise manner through a constant flow pump. A small amount of tracer particles has been injected into the flushing medium in advance, and temperature control ensures temperature consistency. During the flushing process, the deformation and breakage process of the wax crystal flocs under the fluid shear action are captured in real time using a polarizing microscope, and the morphological characteristics of the flocs at the critical breakage moment are recorded. Based on the motion trajectory of the tracer particles, combined with the digital image correlation (DIC) algorithm, the local velocity field distribution and shear stress field at the moment of floc breakage are calculated. At the same time, the captured wax crystal floc breakage phenomenon is analyzed from multiple angles, including the quantitative extraction of parameters such as floc size distribution, shape factor, flow channel geometry, and flow field velocity distribution.

[0021] Step 4: CFD-DEM coupled simulation of wax crystal flocculent particle breakage:

[0022] (1) Constructing a CFD model: Based on the geometric features of the microfluidic channel, a fluid domain computational model is established to characterize the dynamic flow characteristics of fluid in the microchannel;

[0023] (2) Constructing the DEM model: Based on the observed morphological parameters of wax crystal flocs, including particle size distribution, shape factor and initial state, a multi-scale particle cluster model is constructed using the discrete element method, and the initial cohesion and micromechanical parameters of the particles are randomly set.

[0024] (3) The two-way dynamic coupling algorithm is used for coupling calculation: First, CFD iterative calculation is performed until the flow field converges to obtain complete flow field information including velocity field, pressure field and vorticity field; then the flow field data is mapped to the DEM calculation domain as the boundary condition for particle stress calculation. The DEM calculates the interaction between particles and feeds the updated particle position and velocity information back to the CFD model for flow field boundary reconstruction. This coupling process realizes dynamic data exchange. When the stress on the particle exceeds its critical crushing strength, the particle model triggers the crushing phenomenon.

[0025] Step 5: Calculation and Analysis of Cohesion and Micromechanical Parameters: Five key parameters—critical crushing time, crushed particle location, particle number distribution, crushed particle size, and particle velocity—were selected to establish consistency analysis criteria between experimental and simulation results.

[0026]

[0027] Where: σ is the error; P1 is the critical crushing time; P2 is the spatial distribution of crushed particles; P3 is the number distribution of crushed particles; P4 is the particle size distribution after crushing; P5 is the particle velocity; P i sim For simulated parameter values; P i exp These are experimental parameter values;

[0028] When the error σ < α, the simulated cohesive force and micromechanical parameters of the wax crystal flocs meet the requirements; otherwise, the cohesive force and micromechanical parameters are adjusted by intelligent optimization algorithm, and a genetic algorithm is used to screen within the initially set parameter range to select a subset of parameters with an error < α. The genetic algorithm optimization screening formula is as follows:

[0029]

[0030] In the formula: θ represents the cohesive force and micromechanical parameters;

[0031] When σ = 0, a perfect match occurs, and F(θ) = 1, the fitness reaches its maximum value.

[0032] When σ = 1 and the total error is 100%, F(θ) = 0, and the fitness is zero.

[0033] If σ>1, the error exceeds the limit, then F(θ)<0, and the algorithm automatically eliminates the individual.

[0034] When the optimal fitness value F is in the parameter range best ≥β, where β is set according to accuracy requirements and is generally 1-α; the process terminates when the composite error is ≤α, and the output parameter subset θ is output. sub ={θ∣F(θ)≥β}, and finally output the cohesive force and micromechanical parameters that meet the requirements.

[0035] Step one of the above scheme is as follows:

[0036] (1) Determine the characteristics of the target flocs: Clarify the core parameters of the wax crystal flocs to be studied in the experiment and select the microfluidic chip structure;

[0037] Pore ​​size gradient sieving function: The microfluidic chip precisely integrates a micropore array layer with a continuous or discrete gradient pore size, which gradually changes from 10μm to 80μm. During the transverse scouring stage, the fluid flows parallel to the pore array layer. This pore size gradient structure is like a dynamic screen, which efficiently filters and enriches flocs of different sizes into pore size regions that match their size according to the physical size of the flocs.

[0038] (2) Selection of scouring medium: Based on the chemical composition, strength and experimental purpose of the target flocs, a scouring medium with specific physical property parameters is selected, including viscosity, density and surface tension.

[0039] (3) Impact mode selection: Based on the on-site fluid dynamics conditions to be simulated and the research objectives, select the impact mode and its specific parameters. Fluid dynamics conditions include steady flow, turbulent flow, and pressure pulse generated by the passing of the pig. Research objectives include measuring the critical shear stress of peeling and observing the structural failure mode. Specific parameters include flow velocity amplitude, frequency, duration, and impact angle.

[0040] (4) Scheme generation: The selected chip structure, scouring medium and impact method are dynamically combined to form an experimental scheme that accurately reproduces the target working condition, realizing the modular decomposition and on-demand reconstruction of the complex wax deposition environment on site.

[0041] Beneficial effects:

[0042] 1. This invention overcomes the limitations of experimental techniques in directly measuring microscopic forces and avoids the assumption-dependent nature of pure numerical simulation, providing a new research paradigm that integrates experimentation and simulation for studying the mechanical properties of wax crystal flocs. It can not only measure the cohesive force of wax crystal flocs but also simultaneously deduce the van der Waals forces, adhesive forces, and other interaction forces between wax crystals, as well as microscopic mechanical parameters such as the elastic modulus and Poisson's ratio of the wax crystals. This provides important theoretical basis and technical support for optimizing the flow assurance technology for waxy crude oil.

[0043] 2. This invention is a microfluidic chip-based device and method for rapid screening and intelligent formulation optimization of pour point depressants, integrating multi-parameter detection. Firstly, it demonstrates an experimental device for observing wax crystal growth under the influence of pour point depressants and cooling based on microfluidics and microscopic systems, as well as the specific structure of the microfluidic chip. Secondly, it demonstrates a statistical method based on the morphological, kinematic, and kinetic parameters of wax crystals and voxel characteristics, which serves as relevant data for a pour point depressant effect evaluation model constructed using a long short-term memory network and the PPO algorithm, achieving the purpose of screening and optimizing pour point depressants with different contents.

[0044] 3. This invention breaks through the limitations of existing technologies by proposing a collaborative research system of "microfluidic experiment-CFD-DEM inversion": It achieves visualized observation of the dynamic formation and fragmentation process of wax crystal flocs through microfluidic chips, and combines this with coupled numerical simulation to invert microscopic mechanical parameters. For the first time, it establishes a full-chain quantitative analysis method from intermolecular forces (nanoscale) to floc strength (micrometer scale) and then to crude oil rheology (macroscale). This not only provides a new paradigm for revealing the microscopic mechanical nature of the deterioration of waxy crude oil fluidity, but also guides the development of novel pour point depressants that target and weaken wax crystal cohesion and microscopic mechanical parameters, promoting the low-carbon transformation of active flow control in oilfields, reducing pipeline transportation energy consumption, and contributing to the achievement of the "dual-carbon" goals of the oil and gas industry.

[0045] 4. This invention can provide a theoretical basis and technical support for the molecular design of pour point depressants, wax crystal modification technology and low-temperature flow safety regulation of waxy crude oil, which is of great significance for ensuring the safety of oil and gas storage and transportation and energy conservation and consumption reduction.

[0046] 5. Reliability: This invention uses microfluidic experimental observation data as the physical benchmark and overcomes the high randomness and inefficiency of traditional trial-and-error methods through parameter optimization of intelligent algorithms.

[0047] 6. Multi-objective constraints: This invention simultaneously matches multiple objective functions such as the critical condition for fragmentation, fragment morphological characteristics, and kinematic parameters to ensure the generalization ability of the cohesive force and micromechanical parameter models.

[0048] 7. Adaptability: When experimental results deviate from simulation results, this invention can accurately locate the source of the difference and scientifically and rationally adjust the simulation parameters. Attached Figure Description

[0049] Figure 1 This is the technical roadmap of the present invention.

[0050] Figure 2 This is a schematic diagram of the multi-field coupling control type column structure in this invention.

[0051] Figure 3 This is a schematic diagram of the groove-shaped channel structure in this invention.

[0052] Figure 4 This is a schematic diagram of the multi-stage gradient sieving structure in this invention.

[0053] Figure 5 This is a schematic diagram of the micro-region gradient temperature control structure in this invention.

[0054] In the diagram: 1. Chip inlet, 2. Post, 3. Chip outlet, 4. Medium inlet, 5. Medium outlet, 6. Groove, 7. Filter screen, 8. Flushing inlet, 10. Temperature control microwire. Detailed implementation method:

[0055] The present invention will be further described below with reference to the accompanying drawings:

[0056] See Figures 1-5This method for measuring the cohesion and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM combines microfluidic experimental observation with CFD-DEM numerical simulation to quantitatively characterize the formation-fracture dynamics of wax crystal flocs. The microfluidic experimental observation is conducted through a wax crystal floc dynamic behavior observation platform, which integrates a multi-channel microfluidic chip system and a high-resolution microscopic imaging system. By selecting different microfluidic channel types and setting temperature and flow rate, the platform enables visual observation of the wax crystal floc formation process and its fragmentation process under fluid shear. Furthermore, by designing different microfluidic channel types and setting multiple experimental conditions such as temperature and flow rate, the platform enables visual observation of the wax crystal floc formation process and its fragmentation process under fluid shear. Figure 1 The microfluidic-CFD-DEM joint inversion measurement device for measuring the cohesion and micromechanical parameters of wax crystal flocs is a dynamic behavior observation platform for wax crystal flocs, and the microfluidic-CFD-DEM joint inversion measurement method for measuring the cohesion and micromechanical parameters of wax crystal flocs is a measurement method based on microfluidic-CFD-DEM for measuring the cohesion and micromechanical parameters of wax crystal flocs.

[0057] A mathematical model consistent with microfluidic experimental conditions is constructed using CFD-DEM. Basic mechanical parameters such as van der Waals forces, adhesion forces, and elastic moduli between wax crystals are initially set. The dynamic fragmentation process of the flocs in a shear flow field is simulated through two-way fluid-structure interaction calculations. Combining the geometric characteristic parameters of the wax crystal floc particles, the simulated fragmentation results are compared with microfluidic experimental observation data. When the relative error between the two is less than a certain value, the preset mechanical parameters match the actual parameters, thus achieving the measurement of the cohesive force and micromechanical parameters within the wax crystal flocs. Otherwise, the basic mechanical parameters are intelligently adjusted. The simulation is continuously iterated and optimized using intelligent optimization algorithms to accurately reproduce the observed floc fragmentation characteristics (including fragmentation timing, fragment morphology, and motion trajectory) in numerical simulations until the floc fragmentation characteristics meet the error range. Ultimately, this enables the measurement of the cohesive force and micromechanical parameters of wax crystal flocs in a microfluidic chip. The experimental conditions include the microfluidic channel size, initial floc morphology, and flow field parameters. The fragmentation results include the critical fragmentation time, fragmented particle location, fragmented particle number distribution, fragmented particle size, and motion velocity.

[0058] Based on the formation and fragmentation of wax crystal flocs in waxy crude oil observed by microfluidic experiments, this study achieved precise determination of the cohesion and micromechanical parameters within the wax crystal flocs through a coupled microfluidic experiment-CFD-DEM numerical simulation and inversion measurement. The cohesion and micromechanical parameters within the wax crystal flocs, as key microscopic parameters characterizing their structural strength, are in dynamic equilibrium with the flow field forces leading to floc fragmentation. Based on this, by systematically controlling experimental temperature, oil type, and microfluidic chip structure, and combining key parameters such as oil density, viscosity, scouring velocity, and floc size, a complete research closed loop of "experimental observation-numerical simulation-phenomenon inversion" was established. Through multi-scale, multi-physics cross-validation, a quantitative correlation between macroscopic fragmentation phenomena and micromechanical parameters was successfully constructed. Specifically, firstly, a mathematical model with geometric conditions consistent with the experiment (such as microfluidic channel dimensions, initial morphology of flocs, and flow field parameters) is constructed in CFD-DEM, and initial cohesion and micromechanical parameters between wax crystals are randomly set. The dynamic fragmentation process of flocs in a shear flow field is simulated through two-way fluid-structure interaction calculations. Subsequently, the simulated fragmentation results (such as critical fragmentation time, fragmented particle location, fragmented particle number distribution, post-fracture particle size, and velocity) are compared with microfluidic experimental observation data. When the relative error of the key parameters is less than a certain value, the preset mechanical parameters are considered to match the actual parameters, thus enabling the measurement of cohesion and micromechanical parameters within the wax crystal flocs. Otherwise, the basic mechanical parameters need to be adjusted using an intelligent optimization algorithm and recalculated iteratively. The comparison yields floc fragmentation characteristics within the error range that match the experimental results, ultimately achieving the measurement of cohesion and micromechanical parameters within the wax crystal flocs in the microfluidic chip.

[0059] A device for measuring the cohesive force and micromechanical parameters of wax crystal flocs based on microfluidic technology and computational fluid dynamics-discrete element (CFD-DEM) coupled simulation (i.e., a dynamic behavior observation platform for wax crystal flocs) includes a power module, a transport module, a temperature control module, and an imaging module. The power module, comprising a constant flow pump and a mechanical transmission device, provides a stable and controllable fluid driving force for the entire experimental system. The constant flow pump provides kinetic energy to the transport medium, ensuring it is uniformly filled into the microfluidic chip after being controlled by the temperature control module. The transport module includes a micro-sampler, a transport hose, and a waste liquid recovery hose, forming a complete sample transport loop. The sample, under the action of the power module, travels through the transport hose to the imaging module and finally flows to the waste liquid recovery hose. The temperature control module includes a microscopic hot stage and a water bath device, employing a three-stage temperature control strategy to ensure uniform and stable temperature throughout the experiment, aiming to maintain the temperature of the microfluidic chip and the transport hose at the experimental set temperature. The imaging module includes a polarizing microscope and a microfluidic chip, enabling high-definition recording and quantitative analysis of the dynamic behavior of wax crystal flocs. The polarizing microscope is used to capture and record the wax crystal formation process and the shearing process of the scouring medium on the wax crystal flocs. The microfluidic chip is the floc formation region; by changing the internal structure of different microfluidic chips, wax crystal flocs of different shapes and sizes can be achieved.

[0060] The dynamic behavior observation platform for wax crystal flocs is based on the formation and fragmentation of wax crystal flocs in waxy crude oil under microscopic imaging in microfluidic experiments. When the system temperature is above the wax precipitation point, the crude oil maintains a single-phase flow state with no wax crystal precipitation. When the temperature drops below the wax precipitation point at a specific rate, wax crystals begin to precipitate in an orderly manner and gradually form a three-dimensional network structure as the temperature decreases. By precisely controlling key parameters such as experimental temperature, shear rate, and wax content, a quantitative research system for the fragmentation of wax crystal flocs in waxy crude oil is established.

[0061] This invention relates to a microfluidic chip comprising a chip inlet 1, a microfluidic channel, and a chip outlet 3. Four types of microfluidic channels are available: a multi-field coupled control type pillar structure, a grooved channel structure, a multi-level gradient sieving structure, and a micro-region gradient temperature control structure. By selecting microfluidic chips with different microfluidic channels, wax crystal flocs of different shapes and sizes can be formed. Through the design of diverse microfluidic channel configurations, the structural characteristics of wax crystals formed under different field environmental conditions can be simulated. Combining scour experiments and numerical simulation inversion, key parameters such as wax crystal cohesion can be obtained, providing direct guidance for understanding the fragmentation mechanism of wax crystal flocs during field operation. This achieves effective integration from microscale (microfluidic channel) to macroscale (field pipeline) research.

[0062] A multi-field coupled control type column structure is proposed, using a column structure as the core control unit. Several columns arranged in an array are placed within the cavity of the microfluidic channel, and a multi-physics coupling environment is constructed within the microfluidic channel through a precisely designed geometric configuration. The column structure can simultaneously generate three key control effects: fluid dynamics control, interface effect control, and confined space control. In terms of fluid dynamics, the column structure forms a characteristic flow field distribution through boundary layer separation effect; in terms of interface effect, selective adsorption of wax crystals is achieved through special surface treatment; and in terms of spatial constraint, the growth orientation and density of flocs are controlled through geometric constraints. Specifically, by precisely setting cylindrical columns with specific geometric structures within the microfluidic chip channel, the boundary layer effect and flow separation phenomenon in fluid mechanics are utilized to achieve controllable regulation of the formation and fragmentation process of wax crystal flocs. Specifically, the optimized column structure generates a characteristic non-uniform flow field distribution, forming a stagnant zone with significantly reduced flow velocity at the front of the structure, providing an ideal environment for wax crystal aggregation. Simultaneously, a high-shear zone with a significantly increased velocity gradient is generated in the sidewall region, promoting the directional breakup of flocs. Furthermore, by systematically screening materials with special surface properties (such as low-surface-energy polymers and functionalized coatings) to fabricate key structural components, the wettability between wax crystals and material surfaces can be precisely controlled, achieving selective aggregation and separation of wax crystal flocs in specific regions. This design method can generate floc samples with different compositional characteristics, structural density, and mechanical properties by adjusting the combination of flow channel geometry parameters and surface properties, providing an ideal experimental system for systematically studying the nucleation and growth mechanism, network construction process, and mechanical property evolution of wax crystal flocs. The multi-field coupled controllable column structure, deeply integrated with CFD-DEM numerical simulation, establishes a multi-scale coupled model that accurately correlates microstructural features with macroscopic mechanical properties. This provides reliable technical support for the quantitative measurement of cohesion and micromechanical parameters within wax crystal flocs. Featuring modular design and parametric control, it allows for flexible adjustment of key parameters such as flow channel configuration, surface properties, and flow conditions according to different research needs, playing a crucial role in the study of the structure and mechanical properties of wax crystal flocs. The specific structure is as follows... Figure 2 As shown.

[0063] The grooved channel structure consists of several parallel grooves 6 within the cavity of the microfluidic channel, employing a multi-level strip-shaped groove configuration. Each groove unit has an independent medium inlet / outlet control system (i.e., one end of each groove 6 is the medium inlet 4, and the other end is the medium outlet 5). When waxy crude oil flows into the cavity region from the main channel, the groove structure promotes the orderly growth of wax crystals through the following mechanisms: First, the three-dimensional space of the grooves provides an ideal confined environment for wax crystal growth, and its geometric constraint effect significantly enhances the collision frequency and adhesion probability between wax crystal particles. Second, based on the principles of fluid dynamics, a characteristic velocity gradient distribution forms inside the grooves, specifically manifested as an exponential decrease in flow velocity with increasing depth, forming a quasi-static fluid environment near the bottom. This stratified flow state allows the wax crystals to obtain optimal growth conditions at the bottom of the grooves. During the dynamic growth process, the wax crystal particles undergo three stages: nucleation, growth, and aggregation, ultimately forming a strip-shaped flocculent structure with directional arrangement characteristics. By precisely controlling the depth-to-width ratio and arrangement density of the grooves, quantitative control of the morphology and mechanical properties of the flocculents can be achieved. During the scouring stage, the medium is injected from the inlet of the groove at a controlled flow rate. The shearing effect is mainly concentrated in the upper region of the groove, while the flocs generated in the lower part remain relatively stable. This selective scouring mechanism allows for the study of the shear failure behavior of wax crystal flocs with different bonding strengths. Combining the groove-type channel structure with CFD-DEM coupled simulation allows for the establishment of a quantitative correlation model between velocity gradient, flocculation intensity, and mechanical properties by analyzing the correspondence between the flow field distribution within the groove and the stress response of the flocs. Specific structural and flow characteristics are as follows: Figure 3 As shown.

[0064] The multi-stage gradient sieving structure integrates multi-stage gradient pore size filters within the cavity of a microfluidic channel, forming a multi-stage gradient pore size filtration system within the microfluidic channel. This system achieves precise sorting and mechanical property analysis of wax crystal flocs through a graded sieving mechanism. A filter array with decreasing pore sizes is arranged sequentially along the fluid flow direction, forming a progressive spatial sieving structure. For example, the filter pore sizes decrease from large to small as follows: 80μm, 70μm, 60μm, 50μm, 400μm, 300μm, 200μm, and 100μm. Each stage of the filter has a flushing inlet and a flushing outlet. When waxy oil flows through this structure, filters with different pore sizes selectively trap wax crystal flocs of varying characteristic sizes based on size effects. This achieves graded capture of the floc population, effectively distinguishing floc types with different structural stability. Larger flocs typically exhibit stronger cohesive properties, while smaller flocs are more prone to breakage under fluid action. Simultaneously, a physical environment with progressively varying flow field intensity is created. The initial large-pore region maintains relatively mild flow conditions, while the flow field intensity gradually increases towards the end of the channel, achieving not only physical sieving of the flocs but also simultaneously creating experimental conditions for studying the response behavior of flocs under different flow field intensities. By analyzing the distribution characteristics of flocs trapped on each level of the filter, the correlation between floc size and its cohesive properties can be established, providing important evidence for understanding the structure-property relationship of wax crystal flocs. The combination of a multi-stage gradient sieving structure and CFD-DEM coupled simulation allows for in-depth analysis of the influence mechanism of floc size on the mechanical response of flocs by simulating the motion trajectory and stress distribution of flocs of different sizes in a gradient flow field. This multi-stage sieving structure complements the aforementioned strategies, together forming a complete technical system for studying the multi-scale mechanical properties of wax crystal flocs. Specific structural and flow characteristics are as follows: Figure 4 As shown.

[0065] The micro-region gradient temperature control structure incorporates temperature-controlled microfilaments 10 within the cavity of a microfluidic channel. A micro-temperature control unit array is integrated into the microfluidic chip. By constructing a precisely controllable temperature gradient field, the crystallization behavior of wax crystals is regulated. Micrometer-scale temperature-controlled pillars serve as the core component. These pillars vertically penetrate the flow channel and maintain the same height as the channel, achieving localized cooling of the surrounding oil through heat conduction. The working principle of the temperature-controlled pillars is as follows: as localized cooling points, their thermal influence is mainly concentrated in the adjacent area, with limited impact on the oil temperature in most areas far from the pillars, thus forming a stable temperature gradient distribution within the flow channel. Specifically, under continuous operation, a stable low-temperature zone forms around the temperature-controlled pillars, while areas far away maintain a temperature close to the initial oil temperature. This stable temperature field distribution provides ideal conditions for the controllable formation of localized wax crystal flocs. This chip structure has the following technical advantages:

[0066] ① Achieving precise local temperature control allows for the formation of wax crystal flocs within a confined space, facilitating the study of microscopic mechanical behavior;

[0067] ② Effectively disperses wax crystal deposits and flocculation, avoiding flow channel blockage caused by localized overcooling;

[0068] ③ The micron-level size design minimizes interference with the flow field and ensures the reliability of experimental data.

[0069] By adjusting key parameters such as the temperature parameters and array spacing of the temperature-controlled columns, the formation process of wax crystal flocs under different temperature gradients can be precisely controlled, providing an important experimental method for studying the structural properties and mechanical characteristics of flocs. Specific structural and temperature field distribution characteristics are as follows: Figure 5 As shown.

[0070] This invention employs a dual design combining a flushing medium system and impact methods. The flushing medium utilizes media with representative physicochemical properties, including but not limited to mineral oil simulating the light components of crude oil, silicone oil representing the environment of silicon-containing flow modifiers, and methylene blue solution for flow field visualization and tracing studies. The impact methods implement diverse fluid dynamic impacts, specifically including stable velocity impacts, oscillating impacts, pulsed impacts, and impacts introducing different fluid properties (such as viscosity and density). The selection of differentiated media accurately reproduces the key characteristics of actual fluids in pipelines (such as the influence of oil components and chemical additives). The diversified impact methods directly correspond to the various rheological dynamic states present in the field pipelines. For example, stable flow velocity impacts simulate continuous shearing under stable pipeline transport conditions; oscillating impacts simulate periodic shear fluctuations caused by pump and valve start-up and shutdown, flow regulation, or slug flow; pulsating impacts simulate instantaneous high shear stress generated by pig passage, water hammer, or sudden operations; and impacts with different fluid properties examine the effects of changes in crude oil properties or the injection of different chemical agents on smooth shear characteristics and scouring effects. This media-dynamic coupling simulation strategy significantly improves the simulation similarity of laboratory experiments to the variable and complex flow environment of oilfields. It quantitatively reveals key mechanical responses and fragmentation mechanisms. By implementing the corresponding combined scouring methods, it can accurately measure key parameters such as critical stripping shear stress, fragmentation rate, and structural stability of wax crystal flocs under different media environments and dynamic conditions. It quantitatively analyzes the influence of scouring media properties and impact methods on the cohesion, structural stability, and fragmentation mode of wax crystal flocs, deeply revealing the intrinsic mechanism of dynamic fragmentation and redeposition of wax deposits under complex field conditions. This provides crucial experimental evidence and more targeted guidance for optimizing on-site cleaning strategies, screening and evaluating the efficacy of chemical inhibitors, and predicting the removability of wax deposits under different operating conditions.

[0071] The cohesive force and micromechanical parameters of wax crystal flocs are regulated by multiple factors, and their structural stability mainly depends on intrinsic parameters such as crude oil composition, temperature, and pressure. When fluid scouring is applied to the formed flocs, the physical properties of the scouring medium (such as viscosity, temperature, and density) and the impact mode (such as flow velocity and frequency) serve as key external regulating factors, exerting complex and diverse mechanical effects on the wax crystal flocs. Different scouring medium properties directly affect the type and intensity of the force, while differences in the impact mode may lead to different responses in the flocs, such as breakage, deformation, or reorganization.

[0072] (1) The main scouring media for the wax crystal flocs of the present invention are mineral oil, silicone oil and methylene blue solution.

[0073] ① Mineral oil has the following advantages: First, it has the advantage of oil phase displacement: Mineral oil can efficiently strip the liquid oil phase in the initial blend system, fully exposing the wax crystal flocs and promoting the transformation of the system from an oil-wax blend to a pure wax crystal phase, reducing the interference of the oil phase on the cohesive force and micromechanical parameters of the wax crystal flocs. Second, it has the advantage of structural visualization: Mineral oil has a suitable refractive index, combining light transmittance and reflectivity during microscopic observation, clearly revealing the polygonal contours, angular structures, and surface topology of the wax crystal flocs, significantly improving observation accuracy. ② Silicone oil has the following advantages: First, it has a wide viscosity range: It can simulate flow field conditions with different shear intensities. Second, it is chemically inert: It does not easily react with wax crystals, making it suitable for long-term stability experiments. ③ Methylene blue solution has the advantage of auxiliary observation for flow tracing: Due to the significant color difference between methylene blue solution and wax crystal flocs, it is easy to observe the flow field distribution and scouring path, providing a unique visualization advantage for experimental observation.

[0074] (2) The impact modes of wax crystal flocs in this invention are mainly as follows: stable flow velocity impact, oscillation impact, pulse impact, and impact of different fluid properties.

[0075] For wax crystal flocs formed within the chip, they are subjected to different types of shear forces from the fluid in the flow field, which have a crucial impact on the floc fragmentation process. Steady-velocity impact, by applying a constant shear rate, replicates the quasi-static conditions of pipeline flow within the microfluidic chip, causing progressive lamellar delamination of the floc surface. The measured cohesion and micromechanical parameters essentially characterize the critical stress threshold of the wax crystal network's resistance to sustained shear failure. It is characterized by relatively low measured cohesion and micromechanical parameter values, but best reflects the long-term deposition behavior in actual pipeline flow. Oscillating impact induces structural damage to the wax crystal flocs through alternating stress, with moderate measured cohesion and micromechanical parameter values. It can efficiently simulate complex load conditions such as fluid disturbances and valve opening and closing in actual pipelines. Pulsed impact utilizes transient high-energy impacts to induce large-area fracture of the wax crystal flocs, exhibiting the highest measured values ​​of cohesion and micromechanical parameters, reflecting the ultimate cohesion and micromechanical parameters of the wax crystal flocs. Impacts with different fluid properties modulate the interfacial forces between wax crystals by altering the viscosity of the medium. This method features the lowest measured values ​​of cohesive forces and micromechanical parameters, yet the widest controllable range. Furthermore, considering the different chemical compositions of waxy crude oils and the structural characteristics of the flocs they form, the optimal impact method or combination can be selected based on their differences in mechanical properties: for example, for high-colloidal crude oils, an oscillation-different fluid property combination impact is used to overcome interfacial film resistance; for high-wax crude oils, a pulse-steady-state combination is used to overcome the crystal network strength; and for different pipeline sections, pulse impact is the primary method at the inlet section, while steady-state impact is used in the middle section (stabilized flow).

[0076] Method 1: Stable flow velocity impact

[0077] Under stable flow velocity impact conditions, the fluid exerts a continuous and stable shear force on the wax crystal flocs, and its mechanical response exhibits the following characteristics: Structural evolution mechanism: ① Surface peeling effect: The wax crystals on the floc surface exhibit progressive layered peeling; ② Overall displacement characteristics: The flocs undergo slow displacement while maintaining structural integrity; ③ Low-damage breakage mode: Avoiding severe structural damage caused by instantaneous high shear. Applicability characteristics: This flow field condition is particularly suitable for: ① flocculation systems with low cohesion and micromechanical parameters; ② experimental scenarios requiring the maintenance of the basic structure of the flocs; ③ studies of oil-wax two-phase interface behavior. Oil phase regulation effect: Through continuous and stable shear stress: ① effectively promotes the peeling of the liquid oil phase; ② reduces the shielding effect of the oil phase on the interaction forces between wax crystals.

[0078] Method 2: Oscillating Impact

[0079] Applying two oppositely oriented fluids to the same wax crystal flocculent provides a multi-angle stress that is more conducive to flocculent breakage than a single-directional impact. Limitations of unidirectional shear: ① Stress distribution characteristics: The flocculent only experiences a single shear stress along the direction of fluid movement; ② Limited breakage efficiency: Leads to significant non-uniformity in stress distribution, manifested as localized stress concentration causing partial structural failure, while other areas lack sufficient stress to maintain the structure; ③ Overall impact: Only localized wax crystal connections are broken, making it difficult to achieve efficient breakage. Advantages of bidirectional oscillating impact: When using periodic shearing with opposite phases: ① Mechanical characteristics: Multi-directional stress loading: Achieves uniform stress distribution in space; ② Improved breakage mechanism: Promotes uniform stress distribution within the flocculent; eliminates the stress blind zone of unidirectional impact.

[0080] Method 3: Pulse Impact

[0081] The velocity suddenly increases from 0 and then decreases to 0. This impact method is suitable for wax crystal flocs with large cohesion and micromechanical parameters, a robust structure, and adhesion to the wall. When the first pulse arrives, the fluid velocity suddenly increases from 0, reaching a high velocity in a very short time. This process causes the fluid to carry enormous kinetic energy. When the high-speed fluid impacts the wax crystal flocs, it carries a strong force that instantly shears the flocs. Due to the robust structure, large cohesion, and high micromechanical parameters of the wax crystal flocs, ordinary steady-flow impacts cannot provide enough energy to break their internal connections. However, the instantaneous high kinetic energy characteristic of pulsed impacts can effectively generate a powerful impact force on the wax crystal flocs, causing them to break apart. During the interval when the fluid velocity decreases to 0, due to the deformation and shearing forces generated during the impact phase, the wax crystal flocs undergo a series of changes, such as displacement between wax crystals, breakage, and the formation of new wax crystal flocs. With the continuous arrival of subsequent pulses, each impact further amplifies the effects of the previous impact. The cumulative effect of multiple pulses intensifies the shear force within the wax crystal flocs, gradually breaking down the bonds between the wax crystals and ultimately causing them to break into smaller fragments. ① Changing the pulse frequency: Traditional pulse impact frequencies are often fixed, while variable frequency pulse impacts can produce different impacts on the wax crystal flocs by changing the pulse frequency. Higher pulse frequencies allow the wax crystal flocs to withstand multiple impacts in a short time, helping to break down the weak bonds between the wax crystals and are suitable for initial loosening. Lower pulse frequencies give the wax crystal flocs more mutual adsorption, causing them to re-aggregate into larger flocs. ② Changing the pulse intensity: Adjusting the intensity of each pulse controls the instantaneous energy of the fluid during each impact. High-intensity pulses can release enormous impact force instantaneously, causing severe damage to the wax crystal flocs and directly breaking large flocs into multiple small fragments. Low-intensity pulses are suitable for situations where the degree of fragmentation is not critical, generally used for localized impact fragmentation of the wax crystal flocs without damaging the overall structure.

[0082] Method 4: Impact of different fluid properties

[0083] Different viscosities of mineral oil were used in scouring experiments. During the impact on the wax crystal flocs, different viscosities of mineral oil were used. First, low-viscosity mineral oil was used to scour the wax crystal flocs; its lower shear force effectively removed free liquid oil and loose wax crystal particles adhering to the floc surface while maintaining the integrity of the main floc structure. Then, high-viscosity mineral oil was used. Under the same flow rate conditions, the higher viscosity mineral oil, due to its greater flow resistance, resulted in higher shear stress, thus enhancing the destructive effect on the wax crystal floc structure. By comparing the impact experiments with different viscosities of mineral oil, the independent influence of viscosity on floc fragmentation can be analyzed.

[0084] This invention presents a method for measuring the cohesion and micromechanical parameters of wax crystal flocs based on microfluidics-CFD-DEM. It utilizes a high-resolution microscopic imaging system to observe the formation process of wax crystal flocs in microfluidic channels and their breakup behavior under fluid impact in real time. Simultaneously, a consistent CFD-DEM coupled numerical model is established to simulate the dynamic evolution of the flocs, constructing a complete research loop of "experimental observation - numerical simulation - phenomenon inversion." In the specific implementation, a highly consistent CFD-DEM coupled model is first established based on the actual geometric dimensions of the microfluidic channel, the initial morphological characteristics of the flocs, and the flow field boundary conditions. The Monte Carlo method is used to randomly set micromechanical parameters and cohesion, including inter-crystal van der Waals forces, adhesion forces, elastic modulus, and Poisson's ratio. Two-way fluid-structure interaction calculations are then used to accurately simulate the dynamic response process of the flocs in a shear flow field. Subsequently, key parameters obtained from the numerical simulation, such as the critical breakup time, spatial distribution characteristics of breakup, particle number distribution, particle size evolution law, and velocity, are quantitatively compared with the dynamic breakup process data obtained from the microscopic observation experiment in multiple dimensions. When the simulation results and experimental data show good consistency in terms of fragmentation mode and dynamic evolution trend, and the relative error of key parameters is less than α (the value of α is set according to accuracy requirements), it can be confirmed that the currently preset cohesion and micromechanical parameters are consistent with the mechanical properties of wax crystals in the microfluidic experiment. This achieves accurate measurement of the cohesion and micromechanical parameters of wax crystal flocculation through experimental inversion. Specifically, the following steps are included:

[0085] Step 1: Parameterized Construction and Module Selection of the Experimental System: Based on the key parameters of the target wax crystal flocs (target size distribution, structural strength, environmental sensitivity), matching microfluidic chip structures, scouring media, and impact methods are dynamically selected and combined from a pre-set parameter module library to construct a high-fidelity, customizable experimental system. The specific implementation process is as follows:

[0086] (1) Determine the characteristics of the target floc: Identify the core parameters of the wax crystal flocs to be studied in the experiment, such as the cohesive force of wax crystal flocs with a size range of 10-80 μm under pulse shear. Modular selection and combination: Select the microfluidic chip structure based on the characteristics of the target floc and choose a core structure with corresponding functions from the chip library. When the experimental objective involves separating wax crystal flocs of a specific size range and studying their fragmentation behavior under pulse shear, a multi-stage gradient sieving structure chip design is preferred. The core advantage of this chip lies in its integrated pore size sieving and temperature control stabilization functions.

[0087] Pore ​​size gradient sieving function: The chip internally integrates a microporous array layer with continuously or discretely gradient pore sizes (e.g., pore sizes gradually changing from 10μm to 80μm). This structural design is key to selective separation based on target floc size. During the lateral flushing stage (when the fluid flows parallel to the pore array layer), this pore size gradient structure acts like a dynamic sieve, efficiently screening and enriching flocs of different sizes into pore size regions that match their physical dimensions.

[0088] (2) Selection of scouring medium: Based on the chemical composition and strength of the target flocs and the experimental purpose (such as simulating real oil products or testing stripping efficiency), a scouring medium with specific physical properties (such as viscosity, density, and surface tension) is selected. For example, for the medium-strength flocs mentioned above, a medium that simulates the viscosity of crude oil in the field can be selected to study its actual scouring behavior.

[0089] (3) Impact mode selection: Based on the on-site fluid dynamics conditions to be simulated (such as steady flow, turbulent flow, pressure pulses generated by the passing of the pig) and the research objectives (such as determining the critical shear stress for stripping, observing the structural breakage mode), select the impact mode (such as constant velocity, pulsed flow, oscillating flow) and its specific parameters (such as velocity amplitude, frequency, duration, and impact angle). For the target flocs in the above examples, a controllable pulsed shear force can be applied to study the deposition stability and stripping threshold of flocs of this specific size under dynamic disturbance.

[0090] (4) Scheme Generation: The selected chip structure, scouring medium, and impact method are dynamically combined to form an experimental scheme that can accurately reproduce the target working condition (the scouring behavior of a specific flocculant under a specific environment). Through this parameterized construction method, modular decomposition and on-demand reconstruction of complex wax deposition environments in the field are realized.

[0091] Step Two: In-situ Dynamic Observation of Wax Crystal Flocs: After assembling and integrating the experimental apparatus with its various functional modules and checking the system's airtightness, the high-precision constant flow pump in the power unit is started. The pretreated waxy crude oil sample is then delivered at a constant flow rate to the microfluidic chip in the imaging module via a micro-sampler. During delivery, the temperature control system operates continuously, employing a three-stage temperature control strategy—water bath precooling / preheating, precise temperature control on the hot stage, and real-time monitoring and feedback of the flow channel temperature—to ensure that the waxy crude oil is injected into the chip's flow channel at a uniform and constant temperature. Once the sample has completely filled the chip's flow channel, the power unit is stopped, allowing the waxy crude oil to reach a static equilibrium state within the chip. Subsequently, the waxy crude oil within the chip undergoes gradient cooling according to a preset cooling program (typically 0.5-5℃ / min). During the cooling process, the nucleation, growth, and aggregation of wax crystal flocs are captured in real-time using a polarizing microscope, recording the morphological characteristics at key temperature points.

[0092] Step 3: In-situ quantitative observation of the shear breakage dynamics of wax crystal flocs: After the system temperature is gradually reduced to a stable wax crystal floc network structure formed in the microscopic field (usually 10-15℃ below the wax precipitation point), the cooling process is stopped, and the microfluidic chip is left to stand at a constant temperature for a certain period of time (usually 30-60 minutes) to ensure sufficient stability of the floc structure. Subsequently, the flushing process is started, and a flushing medium with the same temperature as the system is injected in a stepwise manner through a high-precision constant flow pump, and temperature consistency is ensured by a multi-stage temperature control unit. During the flushing process, the deformation and breakage process of the wax crystal flocs under fluid shearing are captured in real time using a microscopic imaging system, with a focus on recording the morphological characteristics of the flocs at the critical moment of breakage. Without affecting the system flow and without interacting with crude oil and wax crystals, a small amount of tracer particles are injected into the flushing medium in advance. Based on the motion trajectory of the tracer particles and combined with the digital image correlation (DIC) algorithm, the local velocity field distribution and shear stress field at the moment of floc breakage are calculated, providing key parameters for subsequent calculation of cohesion and micromechanical parameters. Meanwhile, the fragmentation phenomenon of the captured wax crystal flocs was analyzed from multiple perspectives, including the quantitative extraction of parameters such as floc size distribution, shape factor, flow channel geometry, and flow field velocity distribution.

[0093] Step 4: CFD-DEM Coupled Simulation of Wax Crystal Flocculent Particle Breakage: The implementation of CFD-DEM coupled simulation of particle breakage mainly includes the following key steps: (1) Model Construction Stage: ① CFD Model Construction: Based on the geometric features of the microfluidic channel, a fluid domain calculation model is established to characterize the dynamic flow characteristics of the fluid in the microchannel; ② DEM Model Construction: Based on the experimentally observed morphological parameters of wax crystal flocculents (including particle size distribution, shape factor and initial state), a multi-scale particle cluster model is constructed using the discrete element method, and the initial cohesion and micromechanical parameters of the particles are randomly set. (2) Coupled Calculation Process: The calculation process adopts a two-way dynamic coupling algorithm: First, CFD iterative calculation is performed until the flow field converges to obtain complete flow field information including velocity field, pressure field and vorticity field; then, the flow field data is mapped to the DEM calculation domain as the boundary condition for particle force calculation. The DEM calculates the interaction between particles and feeds back the updated particle position, velocity and other information to the CFD model for flow field boundary reconstruction. This coupling process enables dynamic data exchange. When the stress on a particle exceeds its critical crushing strength, the particle model triggers a crushing phenomenon.

[0094] Step 5: Calculation and analysis of cohesion and micromechanical parameters: Five key parameters, namely critical crushing time, crushed particle location, particle number distribution, crushed particle size, and particle velocity, are selected to establish a consistency analysis criterion between experimental and simulation results.

[0095]

[0096] In the formula:

[0097] σ—Error; P1—Critical crushing time (s); P2—Spatial distribution of crushed particles (spatial coordinate set); P3—Number distribution of crushed particles (%); P4—Particle size distribution after crushing (μm); P5—Particle velocity (m / s); P i sim and P i exp —Simulation and experimental parameter values.

[0098] When the error σ < α, the cohesive force and micromechanical parameters of the wax crystal flocs obtained by simulation are considered to meet the requirements; otherwise, the cohesive force and micromechanical parameters need to be adjusted by intelligent optimization algorithm, and the genetic algorithm is used to screen within the initially set parameter range to select the parameter subset with error < α.

[0099] For example, the following formula establishes a genetic algorithm optimization and screening formula using cohesion (micromechanical parameters can also be selected as required):

[0100]

[0101] In the formula: θ represents the cohesive force and micromechanical parameters;

[0102] When σ = 0 (perfect match), F(θ) = 1, and the fitness reaches its maximum value;

[0103] When σ = 1 (total error 100%), F(θ) = 0, and the fitness is zero.

[0104] If σ>1 (error exceeds limit), then F(θ)<0, and the algorithm automatically eliminates the individual.

[0105] High-fitness individuals are randomly selected from the parameter range for competition, and elite individuals with high fitness are retained. The optimal fitness value F within the parameter range is then determined. best The process terminates when the error is ≥β (β is set according to accuracy requirements and is generally 1-α; corresponding to a composite error ≤α), and the output parameter subset θ is reached. sub ={θ∣F(θ)≥β}, and finally output the cohesive force and micromechanical parameters that meet the requirements.

Claims

1. A microfluidic-CFD-DEM-based method for measuring the flocculation cohesion of wax crystals and micro-mechanical parameters in vivo, characterized by: The wax crystal flocculation body cohesion force and micro-mechanical parameter measurement method based on microfluidic-CFD-DEM combines microfluidic experimental observation with CFD-DEM numerical simulation to quantitatively characterize the formation and breaking dynamics of wax crystal flocculation bodies; The microfluidic experimental observation is performed on a wax crystal flocculation body dynamic behavior observation platform, which is a platform integrating a multi-channel microfluidic chip system and a high-resolution microscopic imaging system. By selecting different microfluidic channel types and setting the temperature and flow rate, the formation process of wax crystal flocculation bodies and the breaking process under fluid shear can be visualized and observed. A mathematical model consistent with the microfluidic experimental conditions is constructed in CFD-DEM, and the initial cohesion force and micro-mechanical parameters between the wax crystals are randomly set. The dynamic breaking process of the flocculation body in the shear flow field is simulated through two-way fluid-structure coupling calculation. The simulated breaking results are compared with the microfluidic experimental observation data. When the relative error is less than a certain value, the preset mechanical parameters are consistent with the actual parameters, and the measurement of the cohesion force and micro-mechanical parameters of the wax crystal flocculation body is realized. Otherwise, the basic mechanical parameters are intelligently adjusted and iteratively optimized until the flocculation body breaking characteristics meet the error range, and finally the measurement of the cohesion force and micro-mechanical parameters of the wax crystal flocculation body in the microfluidic chip is realized. The experimental conditions include microfluidic channel size, initial morphology of the flocculation body, and flow field parameters. The breaking results include, for example, breaking critical time, breaking particle position, breaking particle number distribution, particle size after breaking, and particle velocity. The wax crystal flocculation body cohesion force and micro-mechanical parameter measurement method based on microfluidic-CFD-DEM includes the following steps: Step one: According to the key parameters of the target wax crystal flocculation body, including target size distribution, structural strength, and environmental sensitivity, dynamically select and combine matching microfluidic chip structures, flushing media, and impact methods from a preset parameter module library: Step two: In-situ dynamic observation of wax crystal flocculation bodies: Start the constant flow pump and use a micro-sampler to deliver the pretreated wax-containing crude oil sample into the microfluidic chip in the imaging module at a constant flow rate. During the delivery process, use a three-stage temperature control strategy of pre-cooling / pre-heating by a water bath device, precise temperature control by a microscopic hot stage, and real-time monitoring and feedback of flow channel temperature to ensure that the wax-containing crude oil is injected into the microfluidic channel at a uniform and constant temperature. After the microfluidic channel is completely filled, pause the power device to allow the wax-containing crude oil to reach a static equilibrium state in the microfluidic chip. Subsequently, the wax-containing crude oil in the microfluidic chip is subjected to gradient cooling treatment. During the cooling process, the nucleation, growth, and aggregation process of the wax crystal flocculation body is captured in real time by a polarizing microscope, and the morphology characteristics at key temperature points are recorded. Step three: In-situ quantitative observation of the shear-induced breakup kinetics of wax crystal flocculates: After the temperature is gradually reduced to form a stable network structure of wax crystal flocculates, stop the temperature reduction and place the microfluidic chip at a constant temperature for 30-60 minutes to ensure the full stability of the flocculate structure; then, start the flushing program, inject the flushing medium consistent with the temperature of the microfluidic chip in a stepwise increasing manner by a constant flow pump, and a small amount of tracer particles have been injected in advance in the flushing medium, and the temperature is ensured to be consistent; during the flushing process, the deformation and breakup process of the wax crystal flocculates under the action of fluid shear are captured in real time by a polarizing microscope, and the morphological characteristics at the moment of critical breakup of the flocculates are recorded; based on the motion trajectory of the tracer particles, combined with the digital image correlation DIC algorithm, the local velocity field distribution and shear stress field of the flocculates at the moment of breakup are calculated, and the breakup phenomenon of the captured wax crystal flocculates is analyzed from multiple angles, including the quantitative extraction of parameters such as flocculate size distribution, shape factor, flow channel geometric characteristics, and flow velocity distribution; Step four: CFD-DEM coupled simulation of wax crystal flocculate particle breakup: (1) Construct a CFD model: based on the geometric characteristics of the microfluidic channel, establish a fluid domain calculation model to represent the dynamic flow characteristics of the fluid in the microchannel; (2) Construct a DEM model: based on the observed morphological parameters of the wax crystal flocculates, including particle size distribution, shape factor, and initial state, a multi-scale particle cluster model is constructed using the discrete element method, and the initial cohesion and micro-mechanical parameters of the particles are randomly set; (3) Coupling calculation using a bidirectional dynamic coupling algorithm: first, perform CFD iterative calculation until the flow field converges to obtain complete flow field information including velocity field, pressure field, and vorticity field; then map the flow field data to the DEM calculation domain as the boundary conditions for particle force calculation, and the DEM calculates the interaction between particles and feeds back the updated particle position and velocity information to the CFD model for flow field boundary reconstruction, and the coupling process realizes dynamic data exchange, when the stress on the particles exceeds the critical breakup strength, the particle model triggers the breakup phenomenon; Step five: Cohesion and micro-mechanical parameter calculation and analysis: five key parameters, including critical breakup time, breakup particle position, particle number distribution, breakup particle size, and particle velocity, are selected to establish the consistency analysis criteria between experimental and simulation results: ； where: σ error; P 1 breakage critical time; P 2 breakage particle spatial distribution; P 3 breakage particle number distribution; P 4 breakage size spectrum; P 5 particle velocity; P i sim simulated parameter value; P i exp experimental parameter value; When the error σ < α, the simulation of the wax crystal flocculation body cohesion and micro-mechanical parameters meets the requirements; otherwise, the cohesion and micro-mechanical parameters are adjusted through an intelligent optimization algorithm, a genetic algorithm is used to screen within the initially set parameter range, a parameter subset with an error < α is screened out, and the genetic algorithm optimization screening formula is as follows: α σ < α. ； In the formula: θ are cohesion and micromechanical parameters; When σ = 0, perfect match, F(θ) = 1, fitness reaches maximum value; When σ = 1, total error 100%, F(θ) = 0, fitness zeroed; If σ >1, error is out of limit, then F(θ)< 0, at this time the algorithm automatically eliminates the individual; When the best fitness value in the parameter range F best ≥β , β Set according to the accuracy requirement, and generally 1- α ; the corresponding composite error is less than or equal to α , the parameter subset is output θ sub ={ θ | F(θ) ≥ β} and finally the cohesive force and micro mechanical parameters meeting the requirements are output.

2. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 1, characterized in that: The wax crystal flocculation body dynamic behavior observation platform comprises a power module, a conveying module, a temperature control module and an imaging module, the power module comprises a constant flow pump, which provides kinetic energy for the conveying medium so that the conveying medium is uniformly affected by the temperature control module and then fills in the microfluidic chip; the conveying module comprises a micro sample feeder, a conveying hose and a waste liquid recovery hose, oil liquid reaches the imaging module through the conveying hose under the action of the power module, and finally flows to the waste liquid recovery hose; the temperature control module comprises a microscopic hot table and a water bath device, which ensures that the temperature of the microfluidic chip and the conveying hose is maintained at the experimental set temperature; the imaging module comprises a polarized microscope and a microfluidic chip, the polarized microscope is used to capture and record the formation process of wax crystals and the shearing process of the flushing medium on the wax crystal flocculation body; the microfluidic chip is a formation area of the flocculation body, which forms the wax crystal flocculation body and realizes the visual observation of the formation process of the wax crystal flocculation body and the breaking process under the action of fluid shearing.

3. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 2, characterized in that: The microfluidic chip comprises a chip inlet, a microfluidic channel and a chip outlet, the microfluidic channel has four types, namely a multi-field coupling regulation type column structure, a groove type channel structure, a multi-stage gradient screening structure and a micro zone gradient temperature control structure, different shapes and sizes of wax crystal flocculation bodies are formed by selecting microfluidic chips with different microfluidic channels; The multi-field coupling regulation type column structure is provided with a plurality of arrayed columns in the cavity of the microfluidic channel, a multi-physical field coupling environment is constructed by the arrayed columns, and the column structure can simultaneously generate three key regulation effects: fluid dynamics regulation, interface effect regulation and limited space regulation; In terms of fluid dynamics, the column structure forms a characteristic flow field distribution through boundary layer separation effect; in terms of interface effect, selective adsorption of wax crystals is realized; in terms of space constraint, the growth orientation and density of the flocculation body are regulated through geometric limitation; the boundary layer effect and flow separation phenomenon in fluid mechanics are utilized to realize controllable regulation of the formation and breaking process of the wax crystal flocculation body.

4. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 3, characterized in that: The groove type channel structure is provided with a plurality of parallel grooves in the cavity of the microfluidic channel, the grooves are strip grooves, when the wax-containing crude oil flows into the cavity, the grooves promote the ordered growth of wax crystals and enhance the collision frequency and adhesion probability between wax crystal particles; a characteristic velocity gradient distribution is formed in the grooves, the layered flow state enables the wax crystals to obtain optimal growth conditions at the bottom of the grooves, and the depth-width ratio and arrangement density of the grooves are adjusted to realize quantitative control of the morphology and mechanical properties of the flocculation body; in the flushing stage, the shear failure behavior of wax crystal flocculation bodies with different bonding strengths is studied.

5. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 4, characterized in that: The multi-stage gradient screening structure is integrated with multi-stage gradient pore size filter screens in the cavity of the microfluidic channel, precise sorting and mechanical property analysis of the wax crystal flocculation body are realized through the grading screening mechanism, the filter screen array with decreasing pore sizes is arranged in sequence along the fluid flow direction, forming a progressive space screening structure, and realizing the grading capture of the flocculation body group; meanwhile, a physical environment with gradually changing flow field intensity is constructed, and the flow field intensity presents a gradient type enhancement; The micro-zone gradient temperature control structure is a micro temperature control unit array integrated in the cavity of the micro-fluidic channel, and the micron-level temperature control micro wires vertically penetrate the flow channel and are kept at the same height with the micro-fluidic channel, thereby forming a stable temperature gradient distribution in the micro-fluidic channel.

6. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 5, characterized in that: The flushing medium is selected from mineral oil, silicone oil and methylene blue solution, and the flushing mode of the flushing medium includes stable flow rate impact, oscillation impact, pulse impact and impact of different fluid properties, and the different fluid properties include viscosity and density; the stable flow rate impact simulates the continuous shearing effect under the stable conveying condition of the pipeline, the oscillation impact simulates the periodic shearing fluctuation caused by the start-stop of the pump valve, flow regulation or slug flow, the pulse impact simulates the instantaneous high shearing stress generated by the passage of the pig, water hammer or sudden operation; the different fluid property impact investigates the influence of the change of the crude oil property or the injection of different chemical agents on the smooth shearing characteristics and flushing effect, the medium-dynamics coupling simulation strategy of the double combination of the flushing medium system and the impact mode improves the simulation similarity of the variable and responsible flow environment in the oilfield site, quantitatively reveals the key mechanical response and breaking mechanism, accurately measures the critical peeling shearing stress, breaking rate structure stability parameters of the wax crystal flocculation body under different medium environments and dynamic conditions by combining the flushing modes, quantitatively analyzes the influence law of the flushing medium property and the impact method on the cohesion, structure stability and breaking mode of the wax crystal flocculation body, and deeply reveals the internal mechanism of the dynamic breaking and re-deposition of the wax deposit under the complex working condition in the field.

7. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 6, characterized in that: The method for intelligently adjusting and iteratively optimizing the basic mechanical parameters is as follows: the basic mechanical parameters including the van der Waals force, adhesion force and elastic modulus between the wax crystals are initially set, the geometric characteristic parameters of the wax crystal flocculation body particles are combined, and the basic mechanical parameters are iteratively optimized by using an intelligent optimization algorithm, so that the numerical simulation accurately reproduces the flocculation body breaking characteristics observed in the micro-fluidic experiment, the flocculation body breaking characteristics include the breaking timing, fragment morphology and motion trajectory, when the simulation results are consistent with the experimental results within the allowable error range, the preset mechanical parameters are consistent with the actual parameters, and the cohesion of the wax crystal flocculation body and the micro mechanical parameters are accurately measured.

8. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 7, characterized in that: The wax crystal flocculation body cohesion force and micro-mechanical parameter measurement method based on microfluidic-CFD-DEM, through a high-resolution microscopic imaging system, real-time observes the formation process of the wax crystal flocculation body in the microfluidic channel and the breaking behavior of the wax crystal flocculation body under fluid impact, synchronously establishes a consistent CFD-DEM coupled numerical model to simulate the dynamic evolution process of the flocculation body, and constructs a complete closed loop of experimental observation-numerical simulation-phenomenon inversion; first, based on the actual geometric size of the microfluidic channel, the initial morphological characteristics of the flocculation body and the flow field boundary conditions, the CFD-DEM coupled model is established, the Monte Carlo method is used to randomly set the micro-mechanical parameters and cohesion force including the van der Waals force between wax crystals, adhesion, elastic modulus and Poisson's ratio, and the dynamic response process of the flocculation body in the shear flow field is accurately simulated through two-way fluid-structure coupling calculation; then, the key parameters obtained by numerical simulation, including the breaking critical time, the breaking spatial distribution characteristics, the particle number distribution, the particle size evolution law and the movement velocity, are compared with the dynamic breaking process data obtained by microfluidic experimental observation in multiple dimensions; when the simulation results and the experimental data are consistent in the breaking mode and the dynamic evolution trend, and the relative error of the key parameters is less than α , α The value is set according to the accuracy requirement, that is, it can be confirmed that the current preset cohesion force and micro-mechanical parameters are consistent with the wax crystal mechanical characteristics in the microfluidic experiment, and the accurate measurement of the cohesion force and micro-mechanical parameters of the wax crystal flocculation body through experimental phenomenon inversion is realized.

9. The microfluidic-CFD-DEM based wax crystal floe cohesive force and micro-mechanical parameter measurement method according to claim 8, characterized in that: The step one is specifically as follows: (1) determining the target flocculation body characteristics: determining the core parameters of the wax crystal flocculation body to be studied in the experiment, and selecting a micro-fluidic chip structure; The pore size gradient screening function: the micro-fluidic chip precisely integrates a micro-pore array layer with continuously or discretely gradient changing pore sizes, the pore sizes gradually change from 10 μm to 80 μm, in the transverse flushing stage, the fluid flows parallel to the pore array layer, the pore size gradient structure is like a dynamic screen, different sizes of flocculation bodies are efficiently screened and enriched in the pore size area matched with their sizes according to the physical size of the flocculation body; (2) selecting a flushing medium: according to the chemical composition, strength and experimental purpose of the target flocculation body, a flushing medium with specific property parameters is selected, and the specific property parameters include viscosity, density and surface tension. (3) Impact mode selection: According to the simulated field fluid mechanics conditions and research targets, the impact mode and its specific parameters are selected, the fluid mechanics conditions include steady flow, turbulent flow, and pressure pulse generated by pig passing, the research targets include determining the critical shear stress of stripping and observing the structure fracture mode, and the specific parameters include flow rate amplitude, frequency, duration, and impact angle; (4) Scheme generation: The selected chip structure, flushing medium, and impact mode are dynamically combined to form an experimental scheme that accurately reproduces the target working condition, realizing the modular decomposition and on-demand reconstruction of the complex wax deposition environment in the field.

Images