A New Model for Predicting the Maximum Gas Entrapment Concentration in a Yield Stress Fluid

Summary Gas entrapment is a typical phenomenon in gas-yield stress fluid two-phase flow, and most of the related research focuses on the entrapped condition of the single bubble. However, the amount of entrapped gas, which is more meaningful for engineering, is rarely involved. In this paper, a theoretical model for calculating the maximum gas entrapment concentration (MGEC) is established for the first time. The critical distance between horizontal and vertical entrapped bubbles was determined by the yielded region caused by the buoyancy and the coupled stress field around the multiple bubbles. The MGEC is the ratio of a single bubble volume to its domain volume, which is calculated from the distance between the vertical and the horizontal bubbles. By comparing with the experimental results, the average error of MGEC calculated by this model is 4.42%, and the maximum error is 7.32%. According to the prediction results of the model, an empirical equation that can be conveniently used for predicting MGEC is proposed.

Flow onset for a single bubble in a yield-stress fluid

We use computational methods to determine the minimal yield stress required in order to hold static a buoyant bubble in a yield-stress liquid. The static limit is governed by the bubble shape, the dimensionless surface tension ( $\gamma$ ) and the ratio of the yield stress to the buoyancy stress ( $Y$ ). For a given geometry, bubbles are static for $Y > Y_c$ , which we determine for a range of shapes. Given that surface tension is negligible, long prolate bubbles require larger yield stress to hold static compared with oblate bubbles. Non-zero $\gamma$ increases $Y_c$ and for large $\gamma$ the yield-capillary number ( $Y/\gamma$ ) determines the static boundary. In this limit, although bubble shape is important, bubble orientation is not. Two-dimensional planar and axisymmetric bubbles are studied.

SONOLUMINESCENCE SPECTROSCOPY OF COLLOIDAL SUSPENSIONS: MOLECULAR, IONIC AND ATOMIC LUMINESCENCE DURING SONOCHEMICAL DECOMPOSITION OF SILICON DIOXIDE NANOPARTICLES CONTAINING RUTHENIUM AND COPPER COMPOUNDS

The article is devoted to an example of the sonoluminescence spectroscopy use, which was previously known as a method for analyzing substances from the characteristic spectra of their sonoluminescence only in true solutions, for carrying out a similar analysis of substances contained in insoluble nanoparticles in colloidal suspensions. The solutions sonolysis, that is, their irradiation with ultrasound, is accompanied by the formation of cavitation bubbles that vibrate radially at the frequency of the ultrasonic field. Volatile components of the solution enter the bubbles, evaporating from the liquid-gas interface; nonvolatile components can penetrate into the bubble as a result of the injection of solution nanodroplets into the gas phase, which occurs during intense bubble movements accompanied by their deformation. In a nonequilibrium plasma periodically forming in cavitation bubbles, destruction occurs, as well as collisional excitation of these components, followed by luminescence. It has been shown that this mechanism of sonoluminescence also operates in colloidal suspensions, where substances are present in the form of nanoparticles with sizes less than 50 nm. Such nanoparticles penetrate into moving cavitation bubbles, without destroying them, as part of nanodroplets, and then undergo decomposition in bubble plasma with the excited particles generation as emitters of characteristic sonoluminescence. In this work, we synthesized colloidal suspensions in dodecane of porous SiO2 nanoparticles containing adsorbed Ru(bpy)3Cl2 and CuSO4 salts. During moving single-bubble sonolysis for these suspensions, characteristic emission spectra of Ru and Cu atoms, SiO molecules, and Ru(bpy)3 ions suitable for sonoluminescence spectroscopic analysis were recorded. By comparing the experimental and calculated (at different temperatures) luminescence spectra of Ru atoms, we estimated the electron temperature attained upon acoustic compression of single bubble in colloidal suspension in dodecane: Te = 7000 K.

ACTIVATION OF SINGLE-BUBBLE SONOLUMINESCENCE AND RADIOLUMINESCENCE OF GD3+ AND DY3+ IONS BY ELECTRON ACCEPTORS IN AQUEOUS SOLUTIONS AS CONSEQUENCE OF THE HYDRATED ELECTRON GENERATION DURING WATER SONOLYSIS AND RADIOLYSIS

Discovered the activation of moving single-bubble sonoluminescence and radioluminescence for Gd3+ and Dy3+ ions in aqueous solutions of GdCl3 and DyCl3 by the acceptor of a hydrated electron (eaq-): H+, Cd2+, etc. This activation is similar to the previously found activation by acceptors of eaq- radioluminescence and single-bubble sonoluminescence for the Tb3+ ion. Electron acceptors do not affect the quantum yield of the said lantha-nide ions photoluminescence. They also do not affect the yield of their multibubble sonoluminescence in aqueous solutions, since eaqdoes not appear in significant amounts during multibubble sonolysis. The found luminescence activation effects of lanthanide ions are interpreted as a consequence of the suppression of the quenching (reduction) reactions of these electronically excited ions eaq: *Ln3+ + eaq- → Ln2+ by acceptors. The feasibility of these reactions was predicted for all Ln3+ ions based on a theoretical estimate of their free energy. The discovery of the described effects of activation of the luminescence of Ln3+ ions is a consequence and serves as confirmation of not only the known generation of eaq- during radiolysis, but also its previously unknown generation during moving single-bubble sonolysis of water.

Automated Workflow Based on Transient, Multiphase Technology Improves Well Control Planning Efficiency and Reduces Risk

The use of automated workflows for engineering calculations is significantly improving the efficiency of modern well planning systems. Current automated well control solutions are at large limited to single bubble considerations. Transient, multiphase technology has proven to be more accurate and reliable for well control planning, but it has been too complex to automate and integrate into automated engineering systems. The objective of this work is to improve well control planning efficiency by using an automated workflow that enables integration of transient multiphase technology into modern well-planning systems. The workflow is based around an advanced multiphase engine that covers all relevant physical processes in the wellbore including transient temperature and acceleration. The model has an accurate equations-of-state- (EOS) based pressure-volume-temperature (PVT) model with compositional tracking that, in combination with the transient temperature, can accurately predict the transition from dissolved to free gas - a key parameter in the development of a kick. The workflow is based on Driller's method and has been automated with a controller network that moves the simulation through the distinct phases of the driller's first circulation without any interaction from the user. High-performance cloud computing ensures the workflow performance. The drilling industry has focused on risk reductions after the Deepwater Horizon (BSSE 2010) accident. But the well-control risk is still high. In Norway, the reported incidents indicate a flat or increasing trend. Geological uncertainties and inaccurate mud density (static and circulating) have been identified as root causes for the majority of the reported incidents. Transient multiphase models are reducing well-control risk by accurately modeling downhole variations in fluid pressure as a function of operational mode, fluids, influx type, geometry, water depth, and pressure and temperature conditions. Such models have been regarded as expert tools because of the complexity and numerically demanding simulations. The automated workflow enables a well control engineer to run accurate multiphase simulations with the same user effort as single bubble kick tolerance tools. In special cases where more sensitivities are required, it is easy to transfer the project to the expert mode - where the automated simulation can be finetuned.