Collapse Pressure Research Articles

Reliability-based structural design of a vertical subsea separator for deep-water applications

This paper presents an integrated framework for the reliability-based design of deep-water vertical subsea separators using a novel collapse strength model. An analytical model for collapse strength prediction of a vertical subsea separator subjected to external pressure is proposed based on numerical simulations covering different geometries and imperfections. The proposed strength model is verified against experimental collapse pressure and other analytical models. The application of the presented methodology is demonstrated in a case study where uncertainties are systematically considered and the target reliability is used as a single design constraint. The First Order Reliability Method is adopted for the reliability-based design and probabilistic safety evaluation of the subsea separator and sensitivity and partial safety factors assessment. This framework is useful for the design of subsea processing systems as technology qualification and standardization of subsea separators are not fully available.

Research on cavity collapse characteristics during high-speed water-exit of the supercavitating projectile

During high-speed water-exit of the supercavitating projectile, the cavity interacts with the free surface and collapses, with instantaneous high collapse pressure impacting on the projectile. In order to study the cavity collapse characteristics during high-speed water-exit of the supercavitating projectile, the numerical study based on the Reynolds-averaged equation and the volume of fluid multiphase flow model is conducted in this paper. The results show that the cavity near the free surface will gradually become larger with the movement of the projectile during water-exit of the supercavitating projectile. The existence of attitude angles will cause the asymmetry of cavity to collapse. The cavity on the upstream side will first collapse and generate collapse pressure, while the cavity on the downstream side will collapse later but generate higher collapse pressure. The asymmetry of the cavity collapse becomes stronger with the increasing attitude angles. The time interval of the collapse pressure on the downstream and upstream sides of the projectile becomes shorter close to the projectile tail.

Study on the energy-focusing mechanism of spatial bubble clusters

Cavitation research has important implications in fields such as mechanical drag reduction, material processing, and new medical device development. Bubble cluster formation, development, and collapse are critical steps in the cavitation process. High-precision numerical simulations have shown that the collapse of bubble clusters exhibits a characteristic energy focusing from the outside to the inside. This study proposes a focus-type model for the energy transfer in bubble clusters to analyze the formation mechanism of collapse pressure and improve the accuracy of quantitative predictions. The model comprises multiple bubbles (α) radiating energy and a bubble (β) receiving energy. Through numerical simulation, the energy transfer law during bubble interaction is studied, showing that relative energy transfer decreases as the dimensionless distance increases, which corresponds with the theoretical model. The study further analyses the relationship between energy transfer in basic and composite bubble cluster structures. Additionally, the study observed the pressure focusing effect of the bubble clusters and found a strong correlation between the focusing effect and dimensionless distance.

An equivalent time-dependent analysis for predicting horizontal wellbore instability in a reactive shale formation using the imbibition/diffusion principle

Osmotic pressure generation, ion migration, shale swelling, and strength reduction are some problems engineers face when drilling through reactive shale. Mody and Hale's model for evaluating the osmotic pressure is not explicitly time-dependent, whereas diffusion is. Moreover, it does not consider membrane destruction with time. Thus, it becomes difficult to apply the model during the analysis of time-dependent instability without needing the conventional thermo-chemo-mechanical coupling process. This process is costly, rigorous, and time-consuming and does not consider the membrane's destruction with time. To this end, the authors analyzed wellbore instability in reactive shale by exploiting Kirsch's stresses. The authors derived some equations for strength reduction, membrane destruction with time, and the time-dependent osmotic pressure based on empirical analysis. Then, they added these equations to the constitutive stresses and applied the Mogi-Coulomb criterion. The study area is located in the passive continental margin of the Tertiary Niger Delta, which has shale diapirs and many growth faults near the deep Atlantic. The results show that the wellbore instability increases with time in an open face mainly because of diffusion and strength reduction. Wellbore instability affected the fracture pressure more than the collapse pressure. In addition, the increase in the Cation Exchange Capacity (CEC) or clay content causes the mud window to reduce with time.

Doxorubicin Interaction with Lipid Monolayers Leads to Decreased Membrane Stiffness when Experiencing Compression-Expansion Dynamics.

Physical membrane models permit to study and quantify the interactions of many external molecules with monitored and simplified systems. In this work, we have constructed artificial Langmuir single-lipid monolayers with dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylserine (DPPS), or sphingomyelin to resemble the main lipid components of the mammalian cell membranes. We determined the collapse pressure, minimum area per molecule, and maximum compression modulus (Cs-1) from surface pressure measurements in a Langmuir trough. Also, from compression/expansion isotherms, we estimated the viscoelastic properties of the monolayers. With this model, we explored the membrane molecular mechanism of toxicity of the well-known anticancer drug doxorubicin, with particular emphasis in cardiotoxicity. The results showed that doxorubicin intercalates mainly between DPPS and sphingomyelin, and less between DPPE, inducing a change in the Cs-1 of up to 34% for DPPS. The isotherm experiments suggested that doxorubicin had little effect on DPPC, partially solubilized DPPS lipids toward the bulk of the subphase, and caused a slight or large expansion in the DPPE and sphingomyelin monolayers, respectively. Furthermore, the dynamic viscoelasticity of the DPPE and DPPS membranes was greatly reduced (by 43 and 23%, respectively), while the reduction amounted only to 12% for sphingomyelin and DPPC models. In conclusion, doxorubicin intercalates into the DPPS, DPPE, and sphingomyelin, but not into the DPPC, membrane lipids, inducing a structural distortion that leads to decreased membrane stiffness and reduced compressibility modulus. These alterations may constitute a novel, early step in explaining the doxorubicin mechanism of action in mammalian cancer cells or its toxicity in non-cancer cells, with relevance to explain its cardiotoxicity.

Investigation of collapse pressure in layered formations based on a continuous anisotropic rock strength criterion

Wellbore instability severely constrains the exploration and development of shale gas. In order to evaluate the impacts of anisotropy and water on wellbore instability, three different types of criteria are fitted to strength data of LMX shales with different moisture contents. A new model of transversely isotropic borehole stability considering compliance incremental tensor induced by natural fractures is proposed, then a more preferred drilling direction is performed by the new model. Results indicated that, Pariseau’s model is more attractive in predicting shale strength, including the difference of strength between vertical bedding and parallel bedding. Based on Pariseau’s model, the prediction accuracy of shale strength is improved by 33.04%. The Pariseau’ model gives a disparate collapse pressure from Jæger’s weak plane criterion, the most unstable drilling area shifts from northeast and southwest to the central area corresponding to relatively lower inclination. The collapse pressure only decreased by 0.55 MPa with considering the anisotropy of elastic parameters, but the strength criteria have a distinct influence. Compared with the results predicted by Jæger’s plane of weakness, the collapse pressure increased by 8.55 MPa using Pariseau’ model. Besides, invasion of water in bedding plane will aggravate borehole instability, especially in late drilling period, collapse pressure for the vertical wellbore increased by 6.35 MPa. Shale strength depends not only on the hydrostatic pressure and orientation angle, but also on the water content, which should be considered in mud weight design and well trajectory optimum.

Double-porosity poromechanical models for wellbore stability of inclined borehole drilled through the naturally fractured porous rocks

Fractured porous rock comprises the matrix and fracture systems with double-porosity and double-permeability. This paper treats the fracture system as a porous media due to the fracture-occupied space filled by the depositional minerals or assumes it to be fully saturated with the formation fluid. Thus, one considers the double-porosity poromechanical models and provides the semi-analytical dual-poroelastic solutions to the field variables around arbitrally inclined boreholes subjected to non-hydrostatic stresses. The plane strain assumption holds for deriving solutions to field variables. The field variables include displacements, stresses, and two pore-pressures in the matrix system and fracture system. This work conducts a quantitative study of the relation between fracture spacing related to fracture density, fracture width, and the safe pressure ratios window (SPRW). One defines that the upper limit of SPRW is related to the ratio of fracture pressure to the original formation pore pressure, and the lower limit is referred to as the ratio of collapse pressure to formation pore pressure. The main results show that the dual-porosity medium displays a higher wellbore instability potential than the single-porosity one. The fracture system that is fully saturated with formation fluid has a narrower SPRW than that of the minerals-filled one referred to as a porous medium. When the coupled hydro-mechanical model is considered, the drilling mud-pressure window narrows with increasing time. It suggests that the drilling engineer considers fracture spacing, and fracture width in the predrilling design of the time-dependent SPRW of naturally fractured porous rocks.

Numerical investigation on acoustic cavitation characteristics of an air-vapor bubble: Effect of equation of state for interior gases

The cavitation dynamics of an air-vapor mixture bubble with ultrasonic excitation can be greatly affected by the equation of state (EOS) for the interior gases. To simulate the cavitation dynamics, the Gilmore-Akulichev equation was coupled with the Peng–Robinson (PR) EOS or the Van der Waals (vdW) EOS. In this study, the thermodynamic properties of air and water vapor predicted by the PR and vdW EOS were first compared, and the results showed that the PR EOS gives a more accurate estimation of the gases within the bubble due to the less deviation from the experimental values. Moreover, the acoustic cavitation characteristics predicted by the Gilmore-PR model were compared to the Gilmore-vdW model, including the bubble collapse strength, the temperature, pressure and number of water molecules within the bubble. The results indicated that a stronger bubble collapse was predicted by the Gilmore-PR model rather than the Gilmore-vdW model, with higher temperature and pressure, as well as more water molecules within the collapsing bubble. More importantly, it was found that the differences between both models increase at higher ultrasound amplitudes or lower ultrasound frequencies while decreasing as the initial bubble radius and the liquid parameters (e.g., surface tension, viscosity and temperature of the surrounding liquid) increase. This study might offer important insights into the effects of the EOS for interior gases on the cavitation bubble dynamics and the resultant acoustic cavitation-associated effects, contributing to further optimization of its applications in sonochemistry and biomedicine.

Numerical investigation on the hydrodynamic performance with special emphasis on the cavitation intensity detection in a Venturi cavitator

Venturi is one of the structures that have been frequently adopted for the generation of hydrodynamic cavitation, which is now a promising technology and method in wastewater treatment. Despite the wide spread application, insight into the characteristics of cavity dynamics and cavitation intensity to optimize cavitation performance remains lacking. This paper presents computational investigation of the cavitation performance with emphasis on cavitation intensity prediction inside a Venturi cavitator, through a robust modeling approach. Particularly, a new physical model as the criterion to account for the evaluation of cavitation intensity was developed. The predictions gave satisfactory agreement with published data for acoustic bubble dynamics, and experimental results for typical cavitation characteristics of the Venturi. Further investigations analyzed the size oscillations, collapse pressure and collapse temperature of bubbles, as well as the cavitation intensity during its dynamic behavior of the hydrodynamic cavitation in this cavitator. The results showed that the bubbles originally generated near the wall of the Venturi had the strongest oscillations for cavity dynamics. The normalized average bubble collapse pressure was consistent with the distributions of the cavitation intensity within the whole flow domain. Besides, the rear part of the attached cavity at the stage of developing cavitation showed the strongest intensity of cavitation, while the chocking cavitation had no advantage for this issue. This research provides an available and useful criterion to effectively compare and evaluate the bubble dynamics and cavitation intensity in the multiphase flow of cavitational reactors.

Responsive polymer thin films

Responsive polymer thin films

Prediction of Casing Collapse Resistance by 3D Finite Element Modeling

Summary 3D outside diameter (OD) and wall thickness mapping of a casing joint consists of synchronized OD laser scanning and ultrasonic testing (UT) wall thickness measurement at a resolution of every 1 in. along the length and every 1° or 2° around the circumference. This full-length mapping data can then be used to construct a 3D finite element analysis (FEA) model that captures the geometric attributes, including OD, wall thickness, OD ovality, and wall eccentricity, of a casing joint. Together with the actual nonlinear material plasticity model and the measured as-manufactured residual stress, the 3D FEA model can predict the casing collapse strength with good accuracy. Also, the Klever-Tamano ultimate limit-state (KT ULS) collapse equation per API TR 5C3 (2018) together with a moving-average (MA) scheme can calculate the joint’s collapse strength. Results predicted by 3D FEA and KT ULS collapse models are compared to the actual full-scale collapse test results. A 3D FEA model generally produces more accurate results than the KT collapse equation. In addition, both 3D FEA and KT collapse models predict a collapse pressure slightly lower than the actual collapse pressure, which is therefore on the conservative side. The prediction of casing collapse strength can be beneficial to the end user in sorting and ranking the casing joints by collapse resistance, and therefore provides valuable information that can be used in the end user’s risk assessment. Furthermore, the end user may potentially select the joints with the highest predicted collapse strength for the portion of the casing string where the highest collapse resistance is desired. In addition, the OD and wall mapping data together with the actual material tensile properties (yield strength, ultimate tensile strength, and strain hardening parameters) can be used in estimating the internal yield, ductile rupture pressures, and other performance properties. This is outside the scope of this paper and can be pursued in future work. These predicted casing performance properties may then be used in sorting and ranking the joints based on a specific performance property of interest or a combination of performance properties.

Enhancing the bubble collapse energy using the electrohydrodynamic force

The energy released during the bubble collapse process is used for medical and industrial purposes. The present study investigates the effects of electrohydrodynamic force on the collapse phenomenon near the rigid wall and the enhancement of the collapse energy. A solver in the OpenFoam open-source code is developed based on the volume-of-fluid model, in which the effects of compressibility, energy transfer, and electrohydrodynamic force are included. The developed solver is validated against the available experimental data, and a good agreement is seen. The effects of an electric field on the bubble collapse for the range of the electrocapillary number (CaE) of 0–5.76 and normalized wall distance (γ) of 0.8–2.0 are investigated. The results indicate that the bubble is deformed due to the presence of an electric field, and the values obtained for the maximum velocity and pressure are 33 and 35 times the state without the electric field at γ = 2 and CaE = 5.76, respectively. Also, due to the increase in velocity, the maximum shear stress on the rigid wall is increased up to seven times in the absence of the electric field. Therefore, the jet force obtained from the bubble collapse can be enhanced by applying the electric field in the continuous phase fluid. Also, the correlations are proposed to estimate the jet velocity, pressure, and wall shear stress of bubble collapse in the presence of an electric field.

Study on Collapse Pressure Prediction of Fractured Strata

Study on Collapse Pressure Prediction of Fractured Strata

Cyanobacteria mitigation using low power ultrasound for gas vesicle collapse

AbstractThe ability of a low‐power ultrasound system to alter the physiology of cyanobacteria cells in controlled field applications was evaluated. Serratia sp., a model bacteria, and cyanobacteria collected from a bloom containing Microcystis sp. and Aphanizomenon sp., were placed in sound transparent containers and exposed to ultrasound in field studies. No observed changes in Serratia sp. and cyanobacteria gas vesicles between unexposed controls and ultrasound exposed samples were found. Cell viability and phycocyanin concentration for both model bacteria and environmental samples were not significantly affected. At the highest acoustic pressure measured (3.5 kPa), 1 m from the transducer, the acoustic pressures were over 100× lower than gas vesicle critical collapse pressures. Moreover, the ultrasound frequencies emitted are significantly lower than gas vesicle resonance frequencies. Therefore, consistent with pressure and frequency measurements, we found no evidence that gas vesicle collapse is the mechanism of ultrasound as a cyanobacteria mitigation strategy.

Study of the Wellbore Instability Mechanism of Shale in the Jidong Oilfield under the Action of Fluid

Wellbore instability is the primary technical problem that restricts the low-cost drilling of long-interval horizontal wells in the shale formation of the Jidong Oilfield. Based on the evaluation of the mineral composition, structure and physicochemical properties of shale, this paper investigates the mechanical behavior and instability characteristics of shale under fluid action by combining theoretical analysis, experimental evaluation and numerical simulation. Due to the existence of shale bedding and microcracks, the strength of shale deteriorates after soaking in drilling fluid. The conductivity of the weak surface of shale is much higher than that of the rock matrix. The penetration of drilling fluid into the formation along the weak surface directly reduces the strength of the structural surface of shale, which is prone to wellbore collapse. The collapse pressure of the shale formation in the Nanpu block of the Jidong oilfield was calculated. The well inclination angle, azimuth angle and drilling fluid soaking time were substituted in the deterioration model of rock mechanics parameters, and the safe drilling fluid density of the target layer was given. This work has important guiding significance for realizing wellbore stability and safe drilling of hard brittle shale in the Jidong Oilfield.

Effects of ring stiffeners on the underwater collapse behavior of carbon/epoxy composite tubes

An experimental study was performed to analyze the dynamic buckling behavior of stiffened composite tubes. The structures analyzed were filament-wound carbon-fiber/epoxy composite tubes with press-fitted compliant and rigid aluminum ring stiffeners. The ring thicknesses were chosen for a consistent buckling pressure for equally spaced one, two, and three compliant stiffener configurations. The composite structures were submerged inside a pressure vessel and then subjected to increasing hydrostatic pressure until buckle initiation. High-speed photography and Digital Image Correlation were used to acquire full-field displacements and velocities of the collapse event. In addition, piezoelectric transducers were used to concurrently record the local dynamic pressure histories along the length of the tube. The results show that increasing the number of stiffeners for the same collapse pressure decreases the overall energy emission from the implosion event by more than 16%. However, the energy mitigation effects are also influenced by the location of the stiffeners in relation to the buckling initiation point.

Study on mechanical properties and wellbore stability of deep sandstone rock based on variable parameter M-C criterion

With the depletion of shallow oil and gas resources and the increase in fossil energy consumption, deep oil and gas resources have become the main driving force of economic development. However, the physical and chemical properties and rock mechanics characteristics of the deep sandstone stratum are remarkable, and there is little research on the rock failure law of the deep sandstone stratum. Therefore, a batch of sandstone with similar homogeneity was selected, and several triaxial mechanical experiments with variable confining pressure were conducted for such sandstone. The mechanical constitutive model of rock samples under different confining pressures, the macroscopic failure characteristics of rock samples, and the evolution law of wave velocity and internal energy of rock samples during mechanical loading were analyzed. According to the experimental results of triaxial mechanics, a calculation model of wellbore collapse pressure in deep sandstone formation was established based on the variable parameter Mohr–Coulomb criterion. The results show that the crack propagation process of rock samples under mechanical loading can be divided into four stages. The characteristic strength, peak strain, elastic modulus, and deformation modulus of rock samples were positively correlated with confining pressure and showed obvious nonlinearity in high confining pressure areas. The failure mode of the rock sample changed from brittle failure to plastic brittle failure with the increase in confining pressure. According to the characteristics of the stress-strain curve, the variation of acoustic wave velocity during triaxial mechanical loading can be divided into three different types. The variation trend of acoustic wave amplitude of rock samples is consistent with the stress-strain curve. With the loading of axial stress, the elastic energy curve was a concave function, the curve of dissipated energy started increasing at the cracking stress of rock samples. After destroying the rock sample, the decline slope of the dissipated energy curve decreased with the increase in confining pressure. Considering the limited failure of the borehole wall, an evaluation model of borehole wall stability in deep sandstone formation based on variable parameter M–C criterion was established. The equivalent density of borehole collapse pressure predicted using the M–C strength criterion method with variable parameters was smaller than that predicted with traditional methods. The research results provide a theoretical basis for safe and efficient drilling in a deep sandstone formation.

Construction of micro/macro‐scale Janus polypeptoid‐based two‐dimensional structures at the air–water interface

AbstractJanus two‐dimensional (2D) polymeric materials present asymmetric dual surfaces that enable a variety of applications of biosensors, catalysts, drug delivery, etc. This work reports the evaporation‐induced interfacial self‐assembly of amphiphilic block copolymer poly(ethylene glycol)‐b‐poly(N‐(2‐phenylethyl) glycine) (PEG‐b‐PNPE) at the air–water interface. The PEG‐b‐PNPE was initially assembled into a monolayer with a uniform thickness of ~2.5 ± 0.1 nm, which was mechanically compressed into a bilayer structure by Langmuir–Blodgett (LB) technology as surface pressure is exceeding the critical collapse pressure. Both monolayer and bilayer nanostructure span over hundreds of microns in both dimensions. The surface contact angle of the sample was measured by dynamic/static optical contact angle/interface tensiometer, which showed asymmetric wettability on the air side and the water side. The evolution from a monolayer to a bilayer was further tracked by an atomic force microscope. By the evaporation‐induced interfacial self‐assembly at the air–water interface, we also prepared macroscopic Janus films with a diameter of ~3.5 mm. The obtained micro/macro‐scale 2D materials have potential applications in nanoscience and biomedicine.

Numerical investigation of the collapse pressure of concentric tubes with frictionless and tied interface

The understanding and study of the mechanical behavior of submarine pipes have significant relevance in ocean exploration, allowing the application of these structures in adverse conditions. In this sense, protecting the tube's internal surface is vital for the transportation of corrosive materials, threatening structural integrity. Usually, the external surface is at constant hydrostatic pressure, leading to possible structural failure if the project does not consider all failure modes. Within the framework of Metallurgically Cladded Pipes (MCP) and Mechanically Lined Pipes (MLP), Corrosion-Resistant Alloys (CRAs) are inserted in the internal surface of pipelines. However, they are not typically deemed in the structural analysis as an integrant part of the mechanical resistance for the external load. This work presents an initial analytical proposal to calculate the collapse pressure of concentric tubes incorporating the rigidity provided by the CRA. Tied or frictionless numerical models are assumed to describe the interaction between the two bodies at the interface region. These two scenarios establish the upper and lower boundaries for cases where friction is part of the problem. The methodology applies a least-square minimization function based on nonlinear finite element simulations to extract analytical expressions that estimate the collapse pressure. An effort is made to reduce the number of sensitive parameters involved in the analytical proposals and minimize the complexity of the formulation. This process allows the analyst to visualize which parameters are more relevant in various scenarios. Nevertheless, the main goal is to evaluate how the variables are coupled and develop a methodology that can be adapted to reproduce the analyst's necessities.

Analysis of Anisotropic Strength and Wellbore Unstable Zone in Shale Formation Relating to Water Content

During oil and gas exploitation, wellbore stability has always been the focus of many scholars. Instability of wellbore will lead to washouts, breakout, stuck pipe, mud loss, and so on, even the abandon of the well. Shale rock is widely distributed in nature and must be taken into account in some rock engineering applications. In order to evaluate the strength anisotropy and the influence of moisture content of the wellbore integrity, the LMX outcrops are divided into three groups to carry out triaxial strength experiment. Based on the fitting method of collaborative search, the strength parameters of different moisture contents are determined; then, the effect of strength anisotropy and the moisture content of the LMX reservoir on wellbore collapse pressure and wellbore integrity are investigated. The results show that shale strength, especially cohesion, is more sensitive to the influence of water. With the increase of water content, the inclination angle of the minimum value obtained by shale strength is deviated to the left, and the collapse pressure and instability area increase significantly. At the same time, it is necessary to adjust the direction of borehole drilling to avoid the occurrence of the zone of bedding slip instability in the direction of the minimum in situ stress, and the inversion of in situ stress should be corrected by considering the effect of bedding on the location of the maximum in situ stress. The study on the effects of bedding and water content on the instability zone can provide suggestions and guidance for the optimization of borehole trajectory, the control of bottom hole safety pressure, the inversion of in situ stress, and the drilling and completion of wells.