Fluid Density Research Articles

Dependencies between effective parameters in coarse-grained models for phase separation of DNA-based fluids.

DNA is now firmly established as a versatile and robust platform for achieving synthetic nanostructures. While the folding of single molecules into complex structures is routinely achieved through engineering basepair sequences, very little is known about the emergence of structure on larger scales in DNA fluids. The fact that polymeric DNA fluids can undergo phase separation into dense fluid and dilute gas opens avenues to design hierachical and multifarious assemblies. Here, we investigate to which extent the phase behavior of single-stranded DNA fluids can be captured by a minimal model of semiflexible charged homopolymers while neglecting specific hybridization interactions. We first characterize the single-polymer behavior and then perform direct coexistence simulations to test the model against experimental data. While low-resolution models show great promise to bridge the gap to relevant length and time scales, obtaining consistent and transferable parameters is challenging. In particular, we conclude that counterions not only determine the effective range of direct electrostatic interactions but also contribute to the effective attractions.

Investigation of the Effect of Casing-to-Wellbore Clearance on Equivalent Circulating Density During Casing Running

As drilling depth increases, the demand for a multi-layer wellbore structure grows. However, with the upper wellbore diameter fixed, reducing the casing-to-wellbore clearance becomes necessary to increase the number of casing strings. This poses a significant challenge to maintaining adequate casing-to-wellbore clearance. However, in actual drilling operations, the casing-to-wellbore clearance cannot be continuously reduced. Equivalent circulating density (ECD) during running casing becomes a critical factor to consider. When the casing-to-wellbore clearance is too small, excessive surge pressures can occur, increasing the risk of lost circulation. In this study, a surge pressure calculation model was developed for the casing running process to analyze the variation in ECD under 10,000 m well conditions in China. Focusing on key formations with narrow density windows, the effects of different casing-to-wellbore clearances on ECD were evaluated. The analysis determined that under the constraints of fracture pressure, the minimum allowable casing-to-wellbore clearance for this casing string is 27 mm. Subsequently, using response surface methodology, a fitting formula was derived to describe the relationship between the selected variables—drilling fluid density, casing running speed, and casing-to-wellbore clearance—and the ECD during casing operations. This provides a theoretical basis for the optimal matching of casing-to-wellbore clearance.

Nonlinear pressure evolution in wellbore during the tubing conveyed perforation process

Abstract With increasing wellbore depth, the environmental conditions become progressively more severe, characterized by elevated temperatures and pressures. Consequently, the pressure variations within the well induced by Tubing Conveyed Perforation (TCP) operations exhibit a more pronounced intensity. These nonlinear pressure fluctuations generate significant impact loads at the bottom of the perforating gun, which can cause failure of the perforating tubing. A transient nonlinear pressure field model of perforation explosion was established based on hydraulic-mechanical coupling to effectively control the risk of accidents. The model considers the effects of several hundred perforation charges and their precise placement in relation to blind holes, thus taking into account the impact of shot density. As a result, the model more accurately reflects actual field conditions. The study investigated the evolution of nonlinear pressure fields at different positions of the entire tubing under perforation explosion and analyzed the influence of different factors on nonlinear pressure fluctuations at the bottom of the perforating gun. The results showed that the peak pressure of the perforation section was much higher than that of the tubing section and the rathole section, maintaining at approximately 200 MPa. The pressure wave attenuated to the initial wellbore pressure of about 80 MPa only seven meters away from the perforation section center. The peak pressure at the bottom of the perforating gun was positively correlated with the initial wellbore pressure, perforating fluid density, shot density, and quantity of explosive. These results provided guidance for the prediction of TCP wellbore nonlinear pressure fluctuation.

Physics-based numerical evaluation of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) in the Upper Jurassic reservoir of the German Molasse Basin

Abstract. Concepts of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) (> 50 °C) are investigated in this study for system application in the Upper Jurassic reservoir (Malm aquifer) of the German Molasse Basin (North Alpine Foreland Basin). The karstified and fractured carbonate rocks exhibit favourable conditions for conventional geothermal exploitation of the hydrothermal resource. Here, we perform a physics-based numerical analysis to further assess the sustainability of HT-ATES development in the Upper Jurassic reservoir. With an estimated heating capacity of approx. 19.5 MW over half a year, our approach aims at determining numerically the efficiency of heat storage under the in situ Upper Jurassic reservoir conditions and projected operation parameters. In addition, the hydraulic performance of the HT-ATES system is further evaluated in terms of productivity and injectivity index. The numerical models build upon datasets from three operating geothermal sites at depths of approx. 2000–3000 m TVD, located in a subset of the reservoir dominated by karst-controlled fluid fluxes. Commonly considered as a single homogeneous unit, the 500 m thick reservoir is subdivided into three discrete layers based on field tests and borehole logs from the three considered sites. The introduced vertical heterogeneity with associated layer-specific enhanced permeabilities allows to examine potentially arising favourable heat transfer, and in combination with the facilitated high operation flow rates (100 kg s−1) to evaluate thermal recoveries in the multilayered reservoir. All simulations account for fluid density and viscosity variation based on thermodynamically consistent equations of state (EOS). Computation results reveal that the reservoir layering induces preferential fluid and heat migration primarily into the high-permeability zone, while thermal front propagation into the lower permeable rock matrix is inhibited. The simulations further display a gradual temperature increase in the warm wellbore and its surrounding host rock, and a consequent progressive improvement in the heat recovery efficiency. Despite the elevated permeability that may trigger advective heat losses, heat recovery factor values range from approx. 0.7 over the first year of operation to over 0.85 after 10 years of operation. An additional scenario is examined with fluid injection solely in the high permeable zone, in order to quantify potential enhancement in the recovery efficiency by omitting fluid injection in the lower-permeability layers where heat propagation is diminished. This is due to the geometrical shape of the thermally perturbed rock volume as heat losses occur during thermal equilibration between injected fluid and reservoir rock, as well as at the contact-surface area between propagating thermal front and adjacent rock matrix. Results suggest that under the stratified reservoir configuration, additionally constrained by the selected spatial distribution of rock properties, heat storage performed only into the upper high-permeability zone corresponds to an improved thermal performance. Simulation results further indicate that density-induced buoyant fluxes, which would considerably decrease thermal efficiencies are inhibited in the system, and the prevailing heat transport mechanism is forced convection.

Flow field computation and sealing performance analysis of high-speed micro-grooved pumping seal for new energy vehicles

A micro-grooved pumping seal for electric vehicles was investigated. In this regard, the real gas effect and viscosity were described using the virial and Lucas equations, respectively, and the oil–air ratio was used to determine the equivalent density and viscosity of the two-phase fluid formed in the mixture of the lubricant and air in the seal. The compressible steady-state Reynolds equation was solved using the finite difference method. The pumping mechanisms of the seal and the effects of operating parameters (rotational velocity, oil–air ratio, inlet pressure, and temperature) on the steady-state sealing performance were analysed. The seal produces a significant hydrodynamic effect on the sealing face. The opening force of the seal increases with rotational velocity, oil–air ratio, and inlet pressure. However, the force decreases as temperature increases. The oil–air ratio has the most significant effect on the opening force. The pumping rate first increases and then decreases as the rotational velocity increases. It increases with the oil–air ratio and temperature but decreases as the inlet pressure increases. In particular, the pumping rate reaches a maximum when the rotational velocity or temperature increases to a certain value. This phenomenon requires special attention during seal design. Our results provide input for the design of micro-grooved pumping seals for new energy vehicles.

Freely rising or falling of a sphere in a square tube at intermediate Reynolds numbers

The motion of a sphere freely rising or falling in a 5d (d is the diameter of the sphere) square tube was numerically studied for the sphere-to-fluid density ratio ranging from 0.1 to 2.3 (0.1 ≤ ρs/ρ ≤ 2.3, ρs is the density of spheres and ρ the fluid density) and Galileo number from 140 to 230 (140 ≤ Ga ≤ 230). We report that Hopf bifurcation occurs at Gacrit ≈ 157, where both the heavy and light spheres lose stability. The helical motion is widely seen for all spheres at Ga > 160 resulting from a double-threaded vortex interacting with the tube walls, which becomes irregular at Ga ≥ 190 where heavy spheres act differently from their counterparts; that is, heavy spheres change their helical directions alternately while light spheres exhibit helical trajectories with jaggedness in connection with the shedding of the double-threaded vortices. This is because of the difference in inertia between the heavy and light spheres. We also checked the oscillation periods for the helical motion of the spheres. They show opposite variations with ρs/ρ for the two types of spheres. Light spheres (ρs/ρ ≤ 0.7) reach a zigzagging regime at Ga ≥ 200 where a vortex loop (hairpin-like vortical structure) is formed which may develop into a vortex ring downstream at small ρs/ρ. This might be the first time a transition from the helical motion to the zigzagging motion for heavy spheres (ρs/ρ ≥ 1.8) has been reported. Finally, we examined the dependence of both the terminal Reynolds number and the drag coefficient of the spheres on the Galileo number.

Alternative Solvents for Life: Framework for Evaluation, Current Status, and Future Research.

Life is a complex, dynamic chemical system that requires a dense fluid solvent in which to take place. A common assumption is that the most likely solvent for life is liquid water, and some researchers argue that water is the only plausible solvent. However, a persistent theme in astrobiological research postulates that other liquids might be cosmically common and could be solvents for the chemistry of life. In this article, we present a new framework for the analysis of candidate solvents for life, and we deploy this framework to review substances that have been suggested as solvent candidates. We categorize each solvent candidate through the following four criteria: occurrence, solvation, solute stability, and solvent chemical functionality. Our semiquantitative approach addresses all the requirements for a solvent not only from the point of view of its chemical properties but also from the standpoint of its biochemical function. Only the protonating solvents fulfill all the chemical requirements to be a solvent for life, and of those only water and concentrated sulfuric acid are also likely to be abundant in a rocky planetary context. Among the nonprotonating solvents, liquid CO2 stands out as a planetary solvent, and its potential as a solvent for life should be explored. We conclude with a discussion of whether it is possible for a biochemistry to change solvents as an adaptation to radical changes in a planet's environment. Our analysis provides the basis for prioritizing future experimental work to explore potential complex chemistry on other planets. Key Words: Habitability-Alternative solvents for life-Alternative biochemistry. Astrobiology xx, xxx-xxx.

A new semi-empirical correlation for the evaluation of the dynamic viscosity of nanofluids

Thanks to their excellent heat transfer coefficient, nanofluids can be considered as ideal heat transfer fluids for a large number of relevant engineering and scientific applications. Precise assessments of their thermophysical properties are thus essential for reliable calculations. In this work, a new semi-empirical scaled correlation based on 8 parameters (volume fraction, temperature, base fluid critical temperature, base fluid density, base fluid critical density, nanoparticle diameter, base fluid molar mass, nanoparticle density) is introduced to evaluate the dynamic viscosity of nanofluids. The correlation is regressed and evaluated using a dynamic viscosity dataset for 32 nanofluids, including a total of 737 experimental points: 10 nanofluids have water as base fluid (Ag, Al2O3, Al2O3/CuO, C, CuO, diamond, Fe/Si, MWCNT, ND-Ni, TiO2), 6 nanofluids have ethylene glycol (Ag, Al2O3, CeO2, Co3O4, SiC, TiO2/CuO), 11 nanofluids comprise different mixtures of water and ethylene glycol (Al2O3, MWCNT/WO3, CB, fGnP, G/Dp, G/Dr, nD87, nD97, TiO2), 1 nanofluid has propylene glycol (SiC) and 4 nanofluids comprise different mixtures of water and propylene glycol (TiB2, TiB2/B4C, fGnP). The dynamic viscosity dataset was derived from experimental measurements documented in the scientific literature and conducted with samples that were prepared using consistent and reliable methods. The study evaluates the dynamic viscosity of nanofluids using 14 literature equations to verify their accuracy against the proposed correlation. Results show that the correlation has an average absolute relative deviation of 8.16%, which is significantly lower than that of the literature equations. A 4-fold cross-validation also shows that the correlation is resilient and accurate with different regression datasets.

Transport of Au–Ag Nanoparticles in Dense Carbon Dioxide Fluid of the Middle Crust

Individual fluid inclusions with dense carbon dioxide hosted in quartz from the gold-bearing interval penetrated by the SD-3 Kola Superdeep Borehole were studied using modern techniques. The composition and density of the carbon dioxide fluid were determined by Raman spectroscopy and microthermometry. The density of the fluid is 0.37–1.14 g/cm3 and contains minor admixtures of nitrogen (0.3–1.8 mol %) and water (0.1–0.4 mol %). LA-ICP-MS data indicate that the carbon dioxide fluid inclusions contain high concentrations of Au (1–2611 ppm) and Ag (1–4389 ppm), and high-precision optical data indicate that the high-density CO2 fluid of the inclusions contains Au–Ag nanoparticles. Evidently, gold and silver were transported from the Earth’s mantle to the crust by high-density carbon dioxide fluid in the form of nanoparticles.

Instability evolution on a shock-accelerated cylindrical fluid layer with arbitrary Atwood numbers

Developing a model to describe the shock-accelerated cylindrical fluid layer with arbitrary Atwood numbers is essential for uncovering the effect of Atwood numbers on the perturbation growth. The recent model (J. Fluid Mech., vol. 969, 2023, p. A6) reveals several contributions to the instability evolution of a shock-accelerated cylindrical fluid layer but its applicability is limited to cases with an absolute value of Atwood numbers close to $1$ , due to the employment of the thin-shell correction and interface coupling effect of the fluid layer in vacuum. By employing the linear stability analysis on a cylindrical fluid layer in which two interfaces separate three arbitrary-density fluids, the present work generalizes the thin-shell correction and interface coupling effect, and thus, extends the recent model to cases with arbitrary Atwood numbers. The accuracy of this extended model in describing the instability evolution of the shock-accelerated fluid layer before reshock is confirmed via direct numerical simulations. In the verification simulations, three fluid-layer configurations are considered, where the outer and intermediate fluids remain fixed and the density of the inner fluid is reduced. Moreover, the mechanisms underlying the effect of the Atwood number at the inner interface on the perturbation growth are mainly elucidated by employing the model to analyse each contribution. As the Atwood number decreases, the dominant contribution of the Richtmyer–Meshkov instability is enhanced due to the stronger waves reverberated inside the layer, leading to weakened perturbation growth at initial in-phase interfaces and enhanced perturbation growth at initial anti-phase interfaces.

Molecular anatomy of the pressure anisotropy in the interface of one and two component fluids: Local thermodynamic description of the interfacial tension.

Through the decomposition of the pressure into the kinetic and the intermolecular contributions, we show that the pressure anisotropy in the fluid interface, which is the source of the interfacial tension, comes solely from the latter contribution. The pressure anisotropy due to the intermolecular force between the fluid particles in the same or the different fluid components is approximately proportional to the multiplication of the corresponding fluid density gradients, and from the molecular dynamics simulation of the liquid-vapor and liquid-liquid interfaces, we demonstrate that the density gradient theory by van der Waals gives the leading order approximation of the free energy density in inhomogeneous systems, neglecting the Tolman length.

Modeling saline-fluid flow through subglacial channels

Abstract. Subglacial hydrological systems impact ice dynamics, biological environments, and sediment transport. Previous numerical models of channelized subglacial flow have focused on freshwater in temperate ice without considering variable fluid chemistry and properties. Saline fluids can exist in cold glacier systems where freshwater cannot, making the routing of these fluids critical for understanding their influence on geochemical and physical processes in relevant glacial environments. This study advances previous efforts by modeling saline fluid in cold glacier systems, where variable fluid chemistry significantly influences melt rates and drainage processes. We model the drainage of a hypersaline subglacial lake through an ice-walled channel, highlighting the impact of salinity on channel evolution. The model results show that, in subglacial systems at salinity-dependent melting points, channel walls grow more slowly when fluids have higher salt concentrations, leading to significantly lower discharge rates. At higher salinities, more energy is required to warm the fluid to the new melting point as the brine is diluted, which reduces the energy available for melting the channel walls. We also highlight the impact of increased fluid density on subglacial drainage and the importance of accounting for accurate suspended sediment concentrations when modeling outburst floods. This model provides a framework to assess the impact of fluid chemistry and properties on the spatial and temporal variations of fluid flux.

Models of Hydration Dependent Lymphatic Opening, Interstitial Fluid Flows and Ambipolar Diffusion.

A theoretical understanding of fluid exchange and the role of initial lymph formation in tissues through mathematical/physical modeling is lacking. Here, we present three models for tissues rich in negative fixed charges due to glycosaminoglycans interacting with the extracellular matrix. We first model a lymphatic opening mechanism at relevant hydrations of the interstitium. At each hydration affecting tissue strain, two equations coupled in time are developed and solved with the new lymphatic opening and particle draining mechanism. The lymphatic opening mechanism is then included in a new model of interstitial fluid and macromolecular flow where the influence of different exclusion and available volumes for charged and neutral particles are quantified. For therapeutic interactions with cells, essential differences are found between electrically charged and neutral therapeutic substances. The interstitial fluid hydrostatic pressure gradient and flow are expressed through an extended Darcy equation, derived using similar methods as in kinetic theory of dense gases and fluid flows. Finally, a model for ambipolar diffusion of electrically charged macromolecules in tissue is developed. Our study will inform transport of charged and neutral macromolecules between the vasculature, interstitium, and the lymphatic system, thus having implications for tissue uptake of therapeutic agents.

Sacrificing Surfactants to Improve Oil Recovery: A Fluid Density Functional Theory Study.

In the chemically enhanced oil recovery (CEOR) processes, heavy components in crude oil, such as asphaltenes, adhere to reservoir rocks, significantly impeding crude oil extraction. Surfactants are frequently utilized to improve oil recovery due to their ability to reduce interfacial tension (IFT) and modify surface wettability. Nevertheless, indiscriminate surfactant usage may result in resource wastage and hinder the attainment of optimal recovery outcomes. Therefore, it is urgent to accurately and efficiently screen out optimal surfactants suitable for different oil fields. This work employs fluid density functional theory (FDFT) to investigate the competitive adsorption mechanism of surfactants and asphaltenes on rock interfaces. We examined the impact of surfactants on asphaltene adsorption and determined the optimal surfactant concentration and chain length for differing reservoir electrical properties and asphaltene compositions. Furthermore, a comprehensive assessment of surfactants was conducted, considering both performance and economic factors. The findings contribute to a deeper comprehension of the displacement effect of surfactants on asphaltenes and offer scientific screening solutions for surfactants in oil recovery processes.

Medium-Range Structural Order as the Driver of Activated Dynamics and Complexity Reduction in Glass-Forming Liquids.

We analyze in depth the Elastically Collective Nonlinear Langevin Equation theory of activated dynamics in metastable liquids to establish that the predicted inter-relationships between the alpha relaxation time, local cage and collective elastic barriers, dynamic localization length, and shear modulus are causally related within the theory to the medium range order (MRO) static correlation length. The latter grows exponentially with density for metastable hard sphere fluids and as a nonuniversal inverse power law with temperature for supercooled liquids under isobaric conditions. The physical origin of predicted connections between the alpha time and other metrics of cage order and the thermodynamic inverse dimensionless compressibility is fully established. It is discovered that although kinetic constraints from the real space first coordination shell are important for the alpha time, they are of secondary importance compared to the consequences of the more universal MRO correlations in both the modestly and deeply metastable regimes. This understanding sheds new light on the theoretical basis for, and prior successes of, the predictive mapping of chemically complex thermal liquids to effective hard sphere fluids based on matching their dimensionless compressibilities, a scheme we call "complexity reduction". In essence, the latter is equivalent to the physical requirement that the thermal liquid MRO correlation equals that of its effective hard sphere analog. The mapping alone is shown to provide a remarkable level of quantitative predictive power for the glass transition temperature Tg of 21 molecular and polymer liquids. Predictions for the chemically specific absolute magnitude and growth with cooling of the MRO correlation length are obtained and lie in the window of 2-6 nm at Tg. Dynamic heterogeneity, elastic facilitation, and beyond pair structure issues are briefly discussed. Future opportunities to theoretically analyze the equilibrated deep glass regime are outlined.

Radio-pathomic estimates of cellular growth kinetics predict survival in recurrent glioblastoma.

Aim: A radio-pathomic machine learning (ML) model has been developed to estimate tumor cell density, cytoplasm density (Cyt) and extracellular fluid density (ECF) from multimodal MR images and autopsy pathology. In this multicenter study, we implemented this model to test its ability to predict survival in patients with recurrent glioblastoma (rGBM) treated with chemotherapy.Methods: Pre- and post-contrast T1-weighted, FLAIR and ADC images were used to generate radio-pathomic maps for 51 patients with longitudinal pre- and post-treatment scans. Univariate and multivariate Cox regression analyses were used to test the influence of contrast-enhancing tumor volume, total cellularity, mean Cyt and mean ECF at baseline, immediately post-treatment and the pre- and post-treatment rate of change in volume and cellularity on overall survival (OS).Results: Smaller Cyt and larger ECF after treatment were significant predictors of OS, independent of tumor volume and other clinical prognostic factors (HR=3.23×10-6, p<0.001 and HR=2.39×105, p<0.001, respectively). Both post-treatment volumetric growth rate and the rate of change in cellularity were significantly correlated with OS (HR=1.17, p=0.003 and HR=1.14, p=0.01, respectively).Conclusion: Changes in histological characteristics estimated from a radio-pathomic ML model are a promising tool for evaluating treatment response and predicting outcome in rGBM.

Innovative machine learning for drilling fluid density prediction: a novel central force search-adaptive XGBoost in HPHT environments

Oil and gas industries are facing a special dilemma when it comes to high-pressure, high-temperature (HPHT) drilling as the accurate forecasting of the drilling fluid density (DFD) is a vital factor for safe and efficient operations. Complicated relationships and inconsistencies in HPHT situations are rarely mapped by current forecasting models, while their buggy performance and safety risks during drilling can be underestimated. In this research, we propose a novel machine learning (ML) approach to enhance the accuracy of DFD anticipation under HPHT conditions: central force search-adaptive extreme gradient boosting (CFS-XGB). This paper uses a dataset that has drilling variables together with the DFD for HPHT situations to examine the accuracy of the CFS-XGB model. Excluding the abnormalities of data or mistakes, the reliability of the original data is maintained by applying min–max normalization. After that, finding the important features with the help of the boosted principal component analysis (BPCA) approach to the normalized data will ensure a major improvement in the CFS-XGB methodology’s prediction efficacy. This research is experimented in the Python platform, and the performance of the proposed CFS-XGB method is analyzed in terms of MSE, R2, and AAPRE metrics. The suggested approach performs better than the current methods in forecasting the drilling fluid concentration in HPHT settings, according to the experimental data. This development in predictive modeling helps increase the productivity and safety of drilling operations, which will eventually help the oil and gas sector manage the challenges posed by HPHT drilling settings.

Gauss–Bonnet AdS planar and spherical black hole thermodynamics and holography

Abstract In this work, we extend the study in Bilic and Fabris (2022 J. High Energy Phys. JHEP11(2022)013) incorporating the AdS/CFT duality to establish a relationship between the local temperatures (Tolman temperatures) of a large (AdS) spherical and a (AdS) planar Schwarzschild black hole near the AdS boundary considering Gauss–Bonnet (GB) curvature correction in the gravitational action. We have shown that the higher curvature corrections appear in the local temperature relationship due to the inclusion of GB term in the bulk. By transforming the metric into Fefferman–Graham form, we have calculated the energy density of the conformal fluid at the boundary. The obtained result contains finite coupling corrections which are holographically induced by the GB curvature correction in the bulk theory. Following the well known approach of fluid/gravity duality, the energy density of the conformal fluid at the boundary is then compared with the black body radiation energy density. This comparison shows that the energy density is proportional to the temperature of the conformal fluid. The temperature of the conformal fluid is then shown to be related to the Tolman temperature of the black hole which then eventually helps us to establish both the Hawking temperature and Tolman temperature relationship between large spherically symmetric and planar Schwarzschild black holes in GB gravity near the AdS boundary.

Numerical Simulation on the Influence of the Distribution Characteristics of Cracks and Solution Cavities on the Wellbore Stability in Carbonate Formation

The development of cracks and solution cavities in carbonate reservoirs can notably reduce the rock’s mechanical properties, leading to a severe wellbore collapse problem during drilling operations. To clarify the influence of the characteristics of cracks and solution cavities on the wellbore stability in the Dengying Formation carbonate reservoir in the Gaoshiti–Moxi area of Sichuan, the mechanical properties of carbonate rock were analyzed. Then, the influences of the attitude and width of cracks, the size and quantity of solution cavities, and their connectivity on wellbore stability were studied using FLAC3D 6.00 numerical simulation software. Our results show the following: (1) The cracks and solution cavities in the Dengying Formation carbonate rock cause significant differences in the rock’s mechanical properties. (2) The equivalent drilling fluid density of collapse pressure (ρc) considering the effects of cracks and solution cavities is 6.4% higher than without these effects, which is in good accordance with engineering practice. Additionally, cracks play a more significant role than solution cavities in affecting the wellbore stability. (3) When the orientation of a crack is closer to the direction of maximum horizontal stress, and the dip angle and width of the crack increase, the stress and deformation at the intersection of the crack and wellbore gradually increase, and correspondingly, ρc also increases. (4) The stress and displacement of various points around the solution cavities gradually increase with the increases in diameter and quantity of solution cavities, and ρc also increases. (5) Compared with the situation where cracks and solution cavities are not interconnected, the stress disturbance area around the wellbore is larger, and ρc is greater when cracks and solution cavities are interconnected.

Effects of fluid properties on coarse particles transport in vertical pipe

The mineral resources in deep-seabed are attracting extensive attention. A numerical simulation of particle transport in a vertical pipe for a deep-sea mining system is conducted using the CFD-DEM method. The effects of fluid density, fluid viscosity and rheological parameters of non-Newtonian fluids on the liquid-solid flow behavior in a vertical pipe are investigated. For Newtonian fluids, increasing the density or viscosity enhances the particles' performance in following the fluid and reduces the slip velocity, but also increases the pressure drop. The efficient lifting of particles can be facilitated by adjusting fluid density and viscosity, while considering factors such as energy consumption. For non-Newtonian fluids, an increase in either the flow behavior index n or the consistency coefficient k results in an increase in the fluid's apparent viscosity. This leads to an increase in the particle suspension capacity and local particle velocity, along with a decrease in local particle concentration.