Free Gas Bubbles Research Articles

New cold seep sites on the continental slope southwest to Svalbard

We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs.

Spontaneous cecal perforation in a cat diagnosed with ultrasonography.

An 8-year-old cat was presented for an acute history of anorexia, marked abdominal pain, and hyperthermia. Ultrasonography showed a cecal perforation with focal steatitis and adjacent free gas bubbles, consistent with focal peritonitis. Surgery confirmed the imaging findings. An enterectomy was performed with the removal of the cecum and ileocolic valve, and anastomosis between the ileum and colon was performed. Histology revealed transmural enteritis and chronic severe pyogranulomatous peritonitis with intralesional plant fragments.

Outcomes of initially nonoperative management of diverticulitis with abscess formation in immunosuppressed patients. DIPLICAB study COLLABORATIVE group.

Management of diverticulitis with abscess formation in immunosuppressed patients (IMS) remains unclear. The main objective of the study was to assess short- and long-term outcomes between IMS and immunocompetent patients (IC). The secondary aim was to identify risk factors for emergency surgery. A nationwide retrospective cohort study was performed at 29 Spanish referral centres between 2015-2019 including consecutive patients with first episode of diverticulitis classified as modified Hinchey Ib or II. IMS included immunosuppressive therapy, biologic therapy, malignant neoplasm with active chemotherapy and chronic steroid therapy. A multivariate analysis was performed to identify independent risk factors to emergency surgery in IMS. A total of 1395 patients were included; 118 IMS and 1277 IC. There were no significant differences in emergency surgery between IMS and IC (19.5% and 13.5%, p = 0.075) but IMS was associated with higher mortality (15.1% vs. 0.6%, p < 0.001). Similar recurrent episodes were found between IMS and IC (28% vs. 28.2%, p = 0.963). Following multivariate analysis, immunosuppressive treatment, p = 0.002; OR: 3.35 (1.57-7.15), free gas bubbles, p < 0.001; OR: 2.91 (2.01-4.21), Hinchey II, p = 0.002; OR: 1.88 (1.26-2.83), use of morphine, p < 0.001; OR: 3.08 (1.98-4.80), abscess size ≥5 cm, p = 0.001; OR: 1.97 (1.33-2.93) and leucocytosis at third day, p < 0.001; OR: 1.001 (1.001-1.002) were independently associated with emergency surgery in IMS. Nonoperative management in IMS has been shown to be safe with similar treatment failure than IC. IMS presented higher mortality in emergency surgery and similar rate of recurrent diverticulitis than IC. Identifying risk factors to emergency surgery may anticipate emergency surgery.

Sound scattering and radiation suppression by pressurized spherical shells.

Thin-shell models offer important insights into the complex process of sound-structure interaction but are found to be inconsistent with the rigorous thick-shell theory for fluid-loaded spherical shells. Here, linearized equations of motion of fluid-loaded, thin, spherical shells are re-derived from the first principles. The shell may be prestressed due to the difference in the static pressures in the internal and external fluids. Differences in the fluid-loading terms from previously proposed ad hoc models are identified and their significance is analyzed. Analytic solutions are derived of the problems of spherical sound wave scattering by a fluid-filled, prestressed spherical shell and resonant vibrations of the shell. The results reduce to a number of known exact and asymptotic solutions in appropriate limiting cases. The mathematical model of the shell vibrations is applied to characterize the influence of the shell's material properties and the prestress on passive suppression of low-frequency underwater sound radiation due to diffraction on an acoustically compliant sphere, such as an encapsulated gas bubble. Using soft rubber as the encapsulating membrane is found to preserve the sound suppression qualities of the free gas bubble.

Совершенствование проточной части газосепараторов с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

The paper analyzes features of the flowing formation fluid that contains free gas bubbles in the flow part of a vortex-type separator with the movable screw. Expressions are derived for a dimensionless multiphase coefficient of the discrete particles relative separation rate and the multiphase similarity criterion, which are making it possible to evaluate the gas separator efficiency, design and develop new devices based on the previously created highly efficient models. The derived equations allow determining the main geometric dimensions of the gas separator flow part based on the given radial dimensions, nominal flow rate and permissible content of free gas at the inlet. For the obtained geometric dimensions of the gas separator flow part, it becomes possible to construct dependences of the separation coefficient and the permissible amount of free gas at the inlet on the rotor rotation speed, flow rate and physical properties of the multiphase mixture.

Linking Sediment Gas Storage to the Methane Dynamics in a Shallow Freshwater Reservoir

AbstractFreshwater reservoirs are globally relevant sources of the greenhouse gas methane. Organic matter rich sediments are hot spots of methane production and can store large amounts of methane dissolved in porewater and as free gas. Yet, in situ data on the gas storage as free gas (bubbles) in freshwater sediments are scarce. Here, an acoustic approach was tested and used to map the gas content in the sediment of a shallow temperate reservoir. The sediment gas storage was linked to the methane budget obtained from almost 2 years of in situ monitoring. The emission fluxes were dominated by ebullition and degassing at the reservoir outlet, which combined accounted for 93% of the total methane emissions. 66% of the ebullition variability was explained by a combination of environmental parameters. Mappings of sediment gas content using echo sounder surveys revealed the accumulation of free gas in regions of elevated sediment deposition. Temporally, the gas storage in the sediment was related to methane emissions, in which a period of intensified emissions resulted in a reduction of sediment gas storage. The sediment could store an equivalent of 4 to 13 days of accumulated potential methane production, which could supply the mean ebullition flux for more than 2 months. We suggest that sediment gas storage plays an important role in buffering and modulating methane emissions in aquatic systems and need to be accounted for in process‐based models.

Совершенствование проточной части мультифазных ступеней с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

Equations are derived to design and develop the multiphase stages flow path in a diagonal form using the dimensionless multiphase coefficient of the discrete particles relative speed. An analysis was made of the formation fluid flow containing free gas bubbles in the serial multiphase stages flow path of axial and axis-diagonal types in comparison with the developed diagonal-type stages and with inclined-cylindrical and helical blades. It is shown that, compared to the axial and axis-diagonal type stages, multiphase stages of the diagonal type with the inclined-cylindrical and helical blades have higher pressure when operating on the gas-liquid mixtures, especially in the multi-stage design. When operating on water without free gas, pressure and efficiency of the multiphase stages exceed characteristics of the best analogues, which makes it possible to manufacture the full-size pumps operating efficiently on liquid without gas and on the gas-liquid mixture.

Совершенствование проточной части десендеров циклонного типа с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

In the oil producing wells with high content of mechanical impurities and free gas, efficiency of the electric centrifugal pump is increased by installing the cyclone-type desenders at its inlet. Desender protects the submersed pump from mechanical impurities entering it by separation and collecting them in a special container. At the same time, the problem of free gas bubbles enlargement is being solved to facilitate their separation into the annulus and thus reduce the free gas content at the pump inlet. Analysis was made of specifics of the formation fluid flow containing mechanical impurities and free gas in the flow path of a cyclone-type separator with the fixed screw. Expressions were derived to determine the dimensionless multiphase coefficient of the discrete particles relative separation rate and of the multiphase similarity criterion. They allow evaluating efficiency of the mechanical impurity separators and developing new highly efficient structures based on the previously created ones. Recommendations are provided for development of the new highly efficient structures.

Effective medium modeling of acoustic propagation in a seagrass meadow

Seagrasses are foundation species in many coastal ecosystems, but these environments are declining globally due to climate change and other anthropogenic impacts. Ballard et al. [J. Acoust. Soc. Am. 147, 2020] established the efficacy of acoustic remote sensing techniques for seagrass monitoring by exploiting acoustic sensitivity to gas bubbles produced by photosynthesis and gas channels within the seagrass leaves. However, the effects of seagrass on acoustic propagation are not understood with sufficient quantitative detail, and an improved model describing propagation through a mixture of seagrass leaves, free gas bubbles, and seawater is needed to aid in integrating acoustic methods into conservation efforts. This talk provides an overview of developments in the modeling of acoustic propagation through a Thalassia testudinum meadow using a homogeneous effective medium approach to represent the seagrass leaves and seawater. The model accounts for the complex microstructure of seagrass leaves including the encapsulated gas channels and the elastic properties of the seagrass tissue. The model is intended for use in geoacoustic inference algorithms for the overall goal of providing estimates of seagrass productivity and biomass. Candidate effective medium models include 2D cylindrical seagrass leaves and a micromechanical model of a seagrass leaf cross-section. [Work supported by NSF.]

High-speed imaging of degassing kinetics of CO2–water mixtures

The exsolution of gas molecules from gas–liquid mixtures plays a significant role in a wide range of applications from industrial processes such as metal casting to subsurface flow of oil or geothermal waters. This study aims to improve the understanding of the conditions under which free gas bubbles start forming in CO2–water mixtures. The bubble point pressure was determined under various different conditions like the temperature and initial pressure of the mixture along with other parameters such as the bubble growth rate. A series of depressurization experiments at high pressure and temperature (up to 100 bar and 100 °C) is performed using a pressure cell that allows for visual monitoring of the degassing process. Bubble formation during the depressurization process is recorded using a high-speed camera paired with a uniform light source along with a pressure transducer and thermocouple. Image analysis allows for the determination of the bubble point pressure and rate of bubble formation. For CO2 in its gaseous state and at moderate temperatures, decent agreement between experimental results and the theoretical bubble point pressure is found, although significant deviations are observed at elevated temperatures. More pronounced differences in bubble point are observed for mixtures starting out at high pressures where CO2 is a supercritical fluid, which lead to lower than expected bubble point pressures.

A yearlong record of acoustic propagation and ambient sound in a seagrass meadow

Seagrasses are sentinel species whose structures are sensitive to variations in environmental conditions and thus reliable indicators of long-term changes in sea level and regional climate. The biological and physical characteristics of seagrasses are known to affect acoustic propagation. Gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production result in free gas bubbles attached to the plants and in the water. The detachment of gas bubbles from the plants is also a source of ambient sound. In this work, we deployed a measurement system in a shallow (1.3 m deep) seagrass meadow that included an acoustic projector, a set of receiving hydrophones, an instrumentation pressure vessel that housed the electronics controlling the acoustic data acquisition and data storage, and a suite of environmental sensor loggers. Acoustic propagation and ambient sound were collected every ten minutes for a period of one year. Coincident measurements of water temperature, salinity, dissolved oxygen, and photosynthetically active radiation were also collected and used to interpret the acoustic data. We present preliminary results from the yearlong deployment of the acoustic system in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. [Work supported by NSF.]

Determining the influence of endoskeleton friction on the damping of pulsating antibubbles

Abstract Recent in-vivo work showed the suitability of Pickering-stabilized antibubbles in harmonic imaging and ultrasound-guided drug delivery. To date, however, theoretical considerations of antibubble core properties and their effects on antibubble dynamics have been rather sparse. The purpose of this study was to investigate the influence of skeletal friction on the damping of a pulsating antibubble and the pulsation phase of an antibubble relative to the incident sound wave. Numerical simulations were performed to compute damping terms and pulsation phases of micron-sized antibubbles with thin elastic shells and 30% endoskeleton volume fraction. The simulations showed that the damping owing to skeleton presence dominates the damping mechanism for antibubbles of radii less than 2.5 μm, whilst it is negligible for greater radii. The pulsation phase of such small antibubbles was simulated to have a phase delay of up to 1/6 π with respect to pulsating free gas bubbles. Our findings demonstrate that the presence of an endoskeleton inside a bubble influences pulsation phase and damping of small antibubbles. Antibubbles of radii less than 3 μm are of interest for the use as ultrasound contrast agents.

Long-term monitoring of a seagrass meadow using wideband acoustic measurements

Seagrasses are sentinel species whose sensitivity to changing water conditions makes them an indicator for sea level rise and climate change. The biological processes and physical characteristics associated with seagrass are known to affect acoustic propagation due to gas bodies contained within the seagrass tissue as well as photosynthesis-driven bubble production that results in free gas bubbles in the water. In this work, acoustical methods are applied to monitor seagrass biomass and gas ebullition with an autonomous field-deployed system using broadband acoustic measurements. Supporting environmental measurements including water temperature and salinity, dissolved oxygen, and photosynthetically active radiation (PAR) were also collected and used to interpret the acoustic data. A ray-based propagation model that includes losses due to the dispersion, absorption, and scattering of sound is applied to relate the measured acoustic signals to the gas bodies in the seagrass tissue and free bubbles in the water. This talk will present preliminary results from the first six months of a year-long deployment of the acoustic system in a dense seagrass meadow dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas (Gulf of Mexico). [Work supported by NSF.]

Simulation Analysis of Temperature Effects on the Shear Behavior of Gassy Sand

The gas in gassy sand is enclosed in the pores of soil skeleton mainly in the form of dissolved in water or free gas bubbles, which is considered to be a perfect equilibrium composed of soil particles, pore water, gas, temperature, and overlying pressure. If any of these elements changes, this balance will be destroyed, resulting in disturbance in its mechanical properties. It is generally assumed that the existence of closed gas bubbles will not affect the soil skeleton but increase the compressibility of pore fluid. Assuming that the closed gas bubbles follow Boyle’s law and Henry’s law, the relationship between pore pressure change and volume strain is established. On the basis of the constitutive model which can reflect the temperature characteristics of saturated sand proposed by the author previously, combined with the special characteristics of gassy sand, the effect of temperature effects on the shear behavior of gassy sand is preliminarily explored and analyzed. The results show that under the condition of drained shear, the increase of temperature will increase the shear strength of gassy sand, and the simulation results are in good agreement with the test data. Under the condition of undrained shear, the shear strength of loose gassy sand increases with the increase of temperature, while that of dense gassy sand decreases. Moreover, the larger the gas volume, the more obvious these phenomena tend to be. However, only qualitative simulation analysis is carried out for undrained shear, which needs further verification in combination with relevant tests.

Effect of Total Stress Path and Gas Volume Change on Undrained Shear Strength of Gassy Clay

Clay with free gas bubbles can be frequently encountered in the seabed. Gassy clay is an unsaturated soil, but its mechanical behavior cannot be described using conventional unsaturated soil mechanics because it has a composite internal structure with a saturated soil matrix and gas bubbles. The gas bubbles can have either a detrimental or beneficial effect on the undrained shear strength of clay. New lower and upper bounds for the undrained shear strength of gassy clay are derived by considering the effect of total stress path and plastic hardening of the saturated soil matrix. For the upper bound, it is assumed that there is only bubble flooding, and the shear strength of an unsaturated soil sample is the same as that of the saturated soil matrix. Bubble flooding makes the saturated soil matrix partially drained and increases the undrained shear strength. The amount of bubble flooding is calculated using the modified Cam-Clay model and Boyle's law for ideal gas. The lower bound is derived based on the assumption that the entire soil fails without bubble flooding and the gas cavity size evolves due to plastic hardening of the saturated soil matrix. Compared with Wheeler's upper and lower bounds that do not consider plastic hardening of the saturated soil matrix, the new theoretical results give a better prediction of the undrained shear strength of gassy clays, especially for the upper bound. Implications for constitutive modeling of gassy clay are discussed based on the new research outcomes.

Conceptual features for improving the flow part of the multiphase stages of ESP submersible plants for small and medium feeds for extracting stratal liquid with a high free gas content

AnnotationThis article analyzes the operation numerical simulation for serial and multiphase stages of various manufacturers on water and gas-liquid mixtures (GLM). Are identified the local gas separation areas in serial stages, which can lead to the formation of gas plugs and disruption of the pump supply.These factors include: the creation of a finely dispersed flow structure at the entrance of the stage, the preservation along the flow with small free gas bubbles diameters, the sustenance of the value for the allowed free gas content by circulation means of fluid part in the impeller, a defined relationship between the pressure gradient and the GLM flow rate. A mathematical model is selected, hydrodynamic calculations of structural options, optimization are carried out, a conceptual option is selected. Bench tests were carried out, confirming the high parameters of the product when working on GLM.

Tunable Nonlinear Acoustic Reporters Using Micro- and Nanosized Air Bubbles with Porous Polymeric Hard Shells.

The ability to tailor acoustic cavitation of contrast agents is pivotal for ultrasound applications in enhanced imaging, drug delivery, and cancer therapy, etc. A biopolymer-based system of microbubbles and nanobubbles was developed as acoustic reporters that consist of extremely porous hard shells. Despite the existence of an incompressible shell, these porous contrast agents exhibited strong nonlinear acoustic response under very low acoustic pressure, e.g, harmonics, characteristic of free gas bubbles. The large air/water surface area within the transmural capillaries are believed to facilitate oscillation of the inner gas core. Furthermore, the acoustic cavitation can be tailored by variation in polymer structures. This synthetically based platform offers insight for the rational design of advanced acoustic biomaterials.

Single-component multiphase lattice Boltzmann simulation of free bubble and crevice heterogeneous cavitation nucleation.

This work serves as an important extension of previous work on cavitation simulation [Sukop and Or, Phys. Rev. E 71, 046703 (2005)10.1103/PhysRevE.71.046703]. A modified Shan-Chen single-component multiphase lattice Boltzmann method is used to simulate two different heterogeneous cavitation nucleation mechanisms, the free gas bubble model and the crevice nucleation model. Improvements include the use of a real-gas equation of state, a redefined effective mass function, and the exact difference method forcing scheme. As a result, much larger density ratios, better thermodynamic consistency, and improved numerical accuracy are achieved. In addition, the crevice nucleation model is numerically investigated using the lattice Boltzmann method. The simulations show excellent qualitative and quantitative agreement with the heterogeneous nucleation theories.

Processing of multibeam water column image data for automated bubble/seep detection and repeated mapping

AbstractWater Column Imaging Multibeam Echosounder Systems (MBES) are effective and sensitive tools for investigating free gas (bubble) release and its rise through the water column. The main advantages of MBES are the detection range and lateral coverage in the water column and at the seafloor; furthermore, they are becoming increasingly available on research vessels worldwide. However, high noise levels and systematic artefacts due to side‐lobe induced signal interference degrade MBES Water Column Images (WCIs) and hampered automated bubble detection and related gas seepage investigations. We present a new technique advancing automated detection of bubble streams and moving toward a quantitative gas‐release assessment. It is shown that bubble streams can be detected reliably by their spatio‐temporal behavior even when they are discontinuous in WCI data. Using assumptions about the bubble rising trajectories, bubble release spots at the seafloor can be traced even if the source location is obscured by acoustic noise or unwanted acoustic targets. A map with acoustic response and source locations of bubbles being released can be produced and serves as a starting point for more detailed quantitative analyses. The efficiency of the method has been assessed at a methane seep site in the Dutch North Sea. Multiple survey lines are merged to a detailed acoustic map of the area. Processed results are in good agreement with manual investigations of the WCI data as well as ROV‐based video analysis.

Mechanisms of Formation of Natural Hydrogen Reservoirs in Thermal Aquifers - Impact of Bacteria and Gas Bubble Dynamics

Underground hydrogen reservoirs, whose existence has been confirmed recently by geologists all over the world, represent a new source of renewable energy. Hydrogen is formed as the product of reaction of serpentinization between ferromagnesian minerals of the Mantle and water in the offshore zones of subduction or in continental zones at considerable depth beneath hydrothermal aquifers. Initially dissolved in water, hydrogen can create free gas bubbles when the local concentration of H2 dissolved in water exceeds the equilibrium value. The bubbles raise up and create the gas cap of free hydrogen. This process is significantly influenced by methanogen bacteria inhibiting in aquifers and consuming hydrogen for their metabolism. The reactions initiated by bacteria leads to the appearance of other volatile components as methane. The dimension, the form of the gas cap and the concentration of hydrogen and methane determine the efficiency of gas production and the energy potential of the reservoir. In the present paper we develop the conceptual mathematical model of gas cap formation in hydrogen reservoir. The bacterial activity is described by the equation of population dynamics with specific kinetic functions obtained by the authors by treating experimental data. The formation of free gas is modelled in terms of the formation of oversaturated nuclei, their growth and simultaneous motion of isolated bubbles. As far as the bubbles grow, they stick together and create continuous free gas. Thus, the hydrogen motion consists of two stages: (i) the motion of isolated bubbles, controlled by the equations of ganglion dynamics; and (ii) the motion of continuous gas through water, governed by Darcy’s law. The bubble growth is ensured by the mass exchange with hydrogen dissolved in water, which involves a non-equilibrium in the average hydrogen concentrations. Such a problem of hydrogen raising is solved analytically in simplified situation without bacteria. The problem can be reduced to a system of nonlinear hyperbolic equations, which has either continuous or discontinuous solutions (shock waves) depending on the degree of the non-equilibrium. Multiples deformations of the shocks under gas raising are described. The impact of bacteria is studied numerically by using the open source Basilisk (developed by D’Alembert Institute). We have revealed non trivial scenarios of the appearance of piece-wise constant traveling waves, or auto-oscillations caused by the nonlinear population dynamics. The result obtained enables us to give estimation to the characteristic time of gas cap formation and the evolution of its composition in time.