Rune Time - Academia.edu (original) (raw)

Papers by Rune Time

$Research paper thumbnail of Method for reconstruction of axisymmetric capillary wave surface topography using inverse ray-tracing of refracted laser sheet$

AIP Advances, Oct 1, 2022

Capillary waves can be used to measure the fundamental fluid properties such as surface tension a... more Capillary waves can be used to measure the fundamental fluid properties such as surface tension as well as, potentially, the viscosity of Newtonian fluids. This requires the measurement of various wave parameters, mainly wavelength, amplitude, and decay coefficient. However, the different scales of magnitudes make it a challenging task. Optical methods are well suited to analyze such problems due to their non-intrusive nature and high dynamic measurement resolution in both space and time. These methods are further categorized as point methods for a single probe measurement and space-time methods for transient measurement of the complete surface. Dynamic space-time methods are preferred despite the associated complex post-processing since they enable reconstruction of the wave surface. Some existing methods are discussed, and an improved method is then proposed to actually solve the associated inverse optics problem. In the method, an axisymmetric wave surface is reconstructed by analyzing the refracted laser sheet. The assumptions, simplifications, and constraints are taken to be compatible with experimental aspects for future validation. It is derived using the fundamental concepts in physics and the only major assumption of the axisymmetric nature of wave surface. The method exploits the underlying symmetry in the topography, making it more versatile, and suited for linear and non-linear capillary waves and waves with planar wavefront. The impact of parameters on the final result is determined through numerical simulations. Very low error (average and maximum) values are observed between reference and reconstructed topography for damped and undamped wave surfaces with a wide range of curvatures. Optimum values of critical parameters and associated reasoning are presented.

WIT transactions on engineering sciences, Aug 13, 2019

The effect of vertically imposed, low frequency oscillations on the rheology of shear-thinning no... more The effect of vertically imposed, low frequency oscillations on the rheology of shear-thinning non-Newtonian fluids are studied numerically by computational fluid dynamics (CFD). Both Newtonian (water) and inelastic time-independent fluids of power-law (Poly-Anionic Cellulose (PAC)) are used as test fluids. Unsteady state simulations were performed using ANSYS Fluent version 18.0 for a vertical 2-D pipe geometry (ID = 50 mm and H = 850 mm) and sinusoidal, vertical oscillations to the liquid body itself were imposed with a user-defined function (UDF). The multiphase volume of fluid (VOF) method with realizable k-ε method was used to impose the turbulence nature of the flow for the cases with water while the cases with non-Newtonian fluids were simulated under the laminar condition. Oscillations of different low frequency values (0.25-5 Hz) and different velocity amplitudes (0.1-0.3 m/s) were tested numerically. The dynamic variation of velocity and shear rate within the oscillated, bulk liquid medium is demonstrated. The flow inside the vertical pipe acts plug like at higher frequencies for both Newtonian and non-Newtonian fluids. The air-liquid interface becomes unstable with small disruptive peaks for the cases with water at higher velocity amplitudes while that is very calm for the laminar cases with non-Newtonian fluids. The achieved velocity gradients and the resultant shear rate variation are low with the increased PAC concentration due to the viscous resistance. However, the instantaneous velocity profiles display a progressively more complex structure with increased frequency and velocity amplitude, revealing the presence of alternating upward/downward motion. These alternating velocity profiles confirm the varying shear field present within a drilling pipe at different frequencies and velocity amplitudes while the variation of the shear field is more dependent on the velocity amplitude.

Flow Measurement and Instrumentation, Dec 1, 2019

Oscillatory flow in pipelines is common in many industrial applications, including oil well drill... more Oscillatory flow in pipelines is common in many industrial applications, including oil well drilling. An experimental investigation of oscillatory flow inside a vertical U-shaped circular pipe is presented in this paper to mimic the practical scenario takes place within a vertical oil well. Flow visualization was deployed to compare the velocity distributions in Newtonian (deionized water) and non-Newtonian fluid (a mixture of three waterbased polymeric liquids). The experiments were performed in a 1.2 m high, 50 mm diameter transparent test section, at room temperature (21°C) and atmospheric pressure. Particle image velocimetry (PIV) technique was used to obtain non-invasive instantaneous flow velocity profiles. Based on local velocities, the streamwise (axial) velocity component within the pipe across its diameter was determined and the cross-sectional average velocity together with the normalized axial velocity were also calculated. In addition, high-speed motion pictures were used to determine the displacement of the air-liquid interface at the top of the U-tube limb. This enabled comparison of the flow field with the overall volumetric oscillating flow. A piston was driven at harmonic motion via a gas buffer, to provide the driving force for the test fluids at four different low frequencies ranging from 0.1 to 0.75 Hz. Oscillatory Reynolds number (Re δ) based on Stokes layer thickness was used as the criteria for determining the specific flow regime. According to the literature, the critical value for the oscillating Reynolds number was considered to be 500, and with this as reference all the experimental cases were within the laminar regime. Eight different experimental cases were tested within the ranges of (4 < Re δ < 116) and Womersley number (3 < Wo < 55). At higher frequencies, the viscous effects for the Newtonian fluid are confined to the Stokes layer and the central core of the velocity profile is plug-type. At the same time, higher frequencies resulted with increased velocity amplitudes. The viscous resistance of the non-Newtonian fluid and the presence of shear layer contribute to an uneven velocity profile across the pipe cross-section. Cross-sectional average velocity provides a more complete picture of the kinematic structure of oscillating flow and its dynamic distribution across the crosssection. Non-Newtonian fluid tends to achieve higher normalized axial velocities compared to that for Newtonian fluid, which is more or less equals to unity. The study was partly motivated by challenges associated with operational procedures during drilling and maintenance of petroleum wells. Furthermore, this study is also part of a comprehensive study aimed at investigating the influence of low frequency oscillations on particle settling in non-Newtonian drilling fluids.

Flow Measurement and Instrumentation, Aug 1, 2017

Electrical Capacitance Tomography (ECT) is well established as a tool for multiphase flow studies... more Electrical Capacitance Tomography (ECT) is well established as a tool for multiphase flow studies when permittivities of the media in the flow, are not too different, e.g. for oil and gas. In this work, we investigate how ECT performs for high permittivity contrasts as for oil and water. The main objective of the study has been to perform analysis on ECT data to identify flow regimes. Different oil-water flow patterns were generated for a range of mixture velocities (0.25-1.5 m/s) and water cuts (0%-97.5%) at different pipe inclinations (-5 ,-1 , 0 , +1 , +5) The test fluids were de-ionized water and mineral oil (Exxsol D60). The tests were performed in a 15m long, inclinable stainless steel pipe with inner diameter of 56.3 mm. Flow patterns were determined by visual observation and high-speed video. Cross-sectional images of flow patterns were obtained using ECT to study how far so called "soft-field" sensing methods can reveal details of multiphase flow. Normalized data of individual inter-electrode capacitances were analyzed to obtain local volume fractions of the two phases for each representative flow pattern. Gamma densitometry was deployed along with ECT for obtaining simultaneous measurements and comparing with volume fractions estimated using interelectrode capacitance values. Even though ECT is a fast data acquiring and online flow imaging technique, the image resolution is low or biased due to several factors. Some of the limitations are due to the maximum number of independent capacitance measurements possible with the ECT module used. There are some shortcomings of the Linear Back Projection (LBP) image reconstruction algorithm, also higher permittivity contrast between oil and water contributes for deficiencies of the ECT images and there is dependence on accurate sensitivity mapping for the various electrode combinations. Off-line iterative image reconstruction improved the image quality and the accuracy of the estimation of volume fractions. ECT images were sufficient for qualitative identification of flow patterns, but it was difficult to acquire image details of the flow such as droplets and small-scale phase distributions. The local volume fractions revealed by inter-electrode capacitance measurements and gamma densitometry were in reasonable agreement. These same capacitances showed consistency with negligible standard deviation, while the standard deviation of the gamma densitometer readings were much higher. However, it is possible to determine flow patterns based on a combination of inter-electrode capacitance measurements, together with volume fraction variations.

Chemical Engineering Science, Mar 1, 2019

The interfacial wave phenomenon in oil-water flow systems is an important area of research, due t... more The interfacial wave phenomenon in oil-water flow systems is an important area of research, due to its importance in real world applications, especially in oil-water transportation in petroleum industry. The influence of interfacial wavy flow and transition of flow regimes on pressure drop, holdup and heat transfer has motivated the research on this topic to enhance the understanding, to ensure the process safety and to improve the process economy. This paper investigates the interfacial oil-water wavy flow in upwardly inclined pipes. The test fluids are mineral oil (viscosity-1.6 mPa.s, density-788 kg/m 3) and water. The scope of the study covers the upward pipe inclination angles of +3 , +5 , +6 , mixture velocities of 0.2-0.5 m/s, and input water cut (input water volume ratio) 0.1-0.9. Two different flow patterns were observed in wavy flow in upwardly inclined pipes, namely stratified wavy (SW) and stratified wavy and mixed interface (SW&MI). The flow images were recorded using a highspeed video camera through a transparent test section. The image analysis was performed using several Matlab programs to extract wave properties such as wavelength and wave amplitude, as well as the wave speed. It is observed that the interfacial instabilities increase with the increasing mixture velocity and with increasing inclinations. Increased instabilities cause interfacial waves to generate and release droplets, while the turbulent intensity in the oil phase also influence droplet formation. An approximately linear relation between wave velocity and mixture velocity was obtained for the wavy flow and a correlation is presented accordingly. Wave energy manifests itself in the combined potential and kinetic energy. The potential energy via the wave amplitude and kinetic energy via the wave speed and wavelength. The overall energy for nonlinear breaking waves is a major source for generation of interfacial droplets. When the flow velocities are increased at a constant input water cut and at a given pipe inclination, the flow regime transition from SW to SW&MI occurs. Meanwhile, the prevailing wavelength decreases and the wave amplitude increases towards the point of transition from SW to SW&MI. The wavelength and the amplitude reach a critical value and remain constant until droplets start to form and release. Once the onset of drop formation occurs at the SW&MI flow regime, the wavelength starts to increase and the wave amplitude decreases with respect to their magnitudes at the point of transition. For a given velocity range, the mean amplitude increases with increasing inclination and decreases with increasing water cut. There is an inverse relation between wavelength and wave amplitude, which means higher amplitude always results in lower wavelength and vice versa. The wave velocity was calculated independently by two different analysis techniques applied to high-speed video images. One was carried out in space domain and one in time domain from high-speed image sequences. All data points were within the 7% error margin with respect to 1:1 reference correlation line, assuring the accuracy of analysis techniques and the validity of the correlation derived for relating the wave velocity to the mixture velocity.

All Days, Sep 11, 2000

A mechanistic model is formulated to predict the flow behavior of two-phase mixtures in horizonta... more A mechanistic model is formulated to predict the flow behavior of two-phase mixtures in horizontal or slightly inclined fully eccentric annuli. The model is composed of a procedure for flow pattern prediction and a set of independent models for calculating gas fraction and pressure drop in stratified, intermittent, dispersed bubble, and annular flow. Small-scale experimental data performed in a 50 m long straight 4" (101.6 mm) ID pipe containing a 2" (50.8 mm) OD tube lying at the bottom validate the predictions of the model. Test matrix covered not only the horizontal inclination, but also -4° and +4° relative to the horizontal. A total number of 115 tests were carried out with the following mixtures:air and water were used in 61, anddiesel oil and N2 in 54 tests. The mechanistic model presents also better performance when compared to the results of some empirical models, as the Beggs and Brill1 correlation and a modified version of the Aziz, Govier, and Fogarasi2 method. Introduction Underbalanced drilling (UBD) technology is becoming a valuable instrument for minimizing the problems associated with invasive formation damage, which is notably responsible for reducing the productivity of oil and gas reservoirs. An UBD operation, when suitably planned and executed, mitigates or eradicates a multitude of effects caused by the invasion of mud filtrate as well as the migration of particulate matter. Despite the varied sort of stimulation techniques already available for overcoming impairment, they are indeed effective for treating vertical wells or shallow damage in horizontal wells. Deeper matrix damage is frequently difficult to remove in long horizontal wells. In this scenario, the combination of the underbalanced process with horizontal drilling results in a consistent way to prevent formation damage, as successfully experienced and documented3–5. However, effective damage reduction depends on the continuous maintenance of the underbalanced condition during the whole drilling period, which brings particular importance to downhole pressure prediction and control6. A poorly designed and/or executed UBD procedure can provoke deeper formation damage than that which may result from a properly planned and executed conventional overbalanced drilling operation4. Effective two-phase flow modeling is one of the essential components for the achievement of a successful UBD operation. In the planning stage, downhole pressure estimates and injection rates are required to investigate and optimize distinct design concepts. Later on, onsite support is also necessary to analyze actual operational parameters and make any required adjustments3,6. Despite this necessity of accurate prediction of pressure distribution along the well, very limited efforts have been applied in modeling the flow of liquid and gas through horizontal or near-horizontal annuli. Most studies focused on adapting empirical methods, which where originally developed for handling flow through pipes, to treat the annular geometry7,8. Even though, the search for better models to simulate two-phase flow in pipes switched long time ago, as pointed out in the literature9,10, towards the use of mechanistic or phenomenological approaches.

Journal of Petroleum Science and Engineering, 2021

An experimental study is performed to observe the effect of vertical fluid oscillations on the me... more An experimental study is performed to observe the effect of vertical fluid oscillations on the mean settling velocity of single spherical glass particles released into mixtures of water and polymeric fluids which exhibit shearthinning behavior for "non-zero" shear rates. The influence of the shear region in shear-thinning non-Newtonian fluids on the settling rate of spherical particles at different oscillatory conditions is also discussed. A transparent, U-shaped pipe with a circular cross-section of 50 mm inner diameter is used. Visualizations are captured along one of the two vertical branches of the pipe while a piston generates pressure gradient oscillations in the other branch at three different low frequencies (0.25, 0.5, and 0.75 Hz). Tests at still fluid are also carried out for comparison. Four fluids are considered: water and three mixtures of water-based polymeric solutions which provide the mixture with viscoelastic properties and shear-thinning behavior. Spherical particles of diameter d = 1 mm, 2 mm, and 3 mm are released at three different distances from the center of the cross-section: 0, 0.5 R, and 0.8 R, where R is the pipe radius. Particles are released one-by-one and their trajectory is captured from the high-speed camera. The settling velocity was found smaller if particles were released close to the pipe wall, independently on the rheology of the fluid. A significant reduction of the settling velocity was observed in the presence of an oscillatory flow when a fluid characterized by shear-thinning viscosity is used. According to the results, it was found that the liquid oscillations brought a decrement of up to 7% in the average settling velocity in Newtonian fluid and a 23% decrement of that in non-Newtonian fluids. Moreover, when the fluid oscillates, the shear-layer associated with the particle wake and the pipe wall does not result in any reduction of the settling velocity. In other words, the effect of the near-wall shear layer, which reduces the viscosity of shear-thinning fluids, dominates over the other effects that would not keep the particle longer in suspension.

In the last decades, drilling industry has been developing solutions to overcome challenges that ... more In the last decades, drilling industry has been developing solutions to overcome challenges that impede drilling of long directional wells as excessive friction, poor directional control, narrow drilling windows, etc. One of the problems that is identified, yet not solved is the drillstring vibrations. Drillstring vibrations result in low ROP, fatigue and failure of the drillstring elements and weakened wellbore integrity. They are often detected through surface symptoms, as large surface WOB fluctuations (axial vibrations), torque and RPM fluctuations (torsional vibrations), reduced ROP, pressure fluctuations, rig/top drive shaking, etc. To control vibrations, a good understanding of basic mechanisms of vibrations initiation and propagation is required. Therefore, this paper aims at the experimental investigation of the drillstring dynamics using a small-scale drilling rig constructed at the University of Stavanger. The experimental drilling rig is equipped with a WOB surface sensor, which works as a strain gauge, as well as RPM and torque encoder and other sensors. For a small-scale system, measurements of the surface sensors represent the combined responses of the whole rig structure, not just the drillstring. Therefore, more information to show drillstring dynamics (displacements and frequencies) is desired, besides surface measurement. This paper presents experiments designed to detect vibrations of the drillstring using a high-speed camera, which in this study serves as an along-the-pipe downhole sensor. The paper also provides the image-processing algorithm that was developed to extract the signal from the images, digitize and normalize it. The high-speed camera has proved to be an accurate and practically noise-free displacement sensor. As a part of this study, analysis of the captured frequencies and decaying amplitudes (damping) was performed for both the high-speed camera and the load cells data. It helped to evaluate whether the surface sensors are able to provide sufficient information about the downhole vibrations. We have seen that in the case where the drillstring interacts with the wellbore, the downhole vibrations are reflected to the surface. However, when the string hangs freely, surface and downhole sensors measure responses from different parts of the system. These conclusions are mostly valid for small-scale vertical systems, however, can also be considered for drilling shallow vertical wells/top sections.

Downhole torque measurements have become an inherent part of MWD (measurement while drilling) sys... more Downhole torque measurements have become an inherent part of MWD (measurement while drilling) systems. It allows drilling engineers to estimate the downhole friction and detect the presence of obstructions, for instance, cuttings bed caused by insufficient cuttings transport. The latter is a big concern when drilling horizontal and extended-reach wells. This paper describes a method of well friction analysis as a function of adjustable drilling parameters and parameters that describe moving cuttings dune. Experiments are performed in a pipe with an internal diameter of 0.04 m and 5° inclination from the horizon, which represents a wellbore. An inside rotating pipe with an outer diameter of 0.025 m simulates a drillpipe, with a possibility of rotating speed from 0 to 1000 RPM (revolutions per minute). Glass pellets are used to simulate and display cuttings behavior in the wellbore. An electric motor is used to provide rotation of the drillpipe, supplied with an encoder to measure the electric current associated with the torque. The measurements are used to calculate the torque loss over the studied pipe length. A high-speed camera installed outside the outer pipe allows capturing images of the height of the particle bed as well as the pipe eccentricity, which increases with distance from the origin (rotating mechanism) due to the pipe’s weight and inclination. The combined effect of these factors on the kinetic friction between the outer and inner pipes is investigated in this paper. Ultimately, the friction factor is calculated by equating measured motor torque to the theoretical torque. The main objective of the study is a development of a methodology to express the friction factor in terms of adjustable drilling parameters in an environment, complicated with the presence of moving cuttings bed and varying pipe eccentricity. This study can supplement other research that is aimed to improve understanding of the intricate phenomenon of the wellbore friction.

The downhole friction is a response to mechanical and hydraulic forces. The mechanical friction t... more The downhole friction is a response to mechanical and hydraulic forces. The mechanical friction takes place when the drillpipe is moving in the wellbore, either in translational or rotational mode. The hydraulic friction occurs due to the circulation of fluids flowing downwards in the pipe, and upwards in the annulus. The additional factors that affect the hydraulic friction are drillpipe rotation, surface roughness, wellbore geometry, etc. This paper experimentally examines hydraulic friction and studies its variations with adjustable operational parameters (flow rate and rotational speed). The experiments were performed using two pipes, where one was located inside the other. The outside pipe with an inner diameter of 0.04 m simulated the wellbore walls, and the inside one simulated the drillpipe with an outer diameter of 0.025 m. The pipes’ inclination was 5° from the horizontal axis. The drillpipe could be rotated by an electric motor with speeds up to 1000 RPM (revolutions per minute). Spherical glass beads were used to simulate the cuttings behaviour in the wellbore. The pressure gradient variations associated with fluid flow, pipe rotation as well as particles movement was measured over the test section (length of 1.52 m), using a pressure transducer. In addition, a high-speed camera, installed outside the outer pipe, was used to take images of the particles distribution and pipe dynamic oscillations. The combined effect of fluid flow rate, drillpipe rotation and presence of particles on the hydraulic friction between the outer and inner pipes is investigated in this study. The data analysis for the single-phase liquid flow showed that the pressure loss increased with RPM. It was seen that the secondary flow, created by the drillpipe rotation, was not the only reason to affect the pressure loss, but the drillpipe&amp;#39;s eccentricity variations with RPM and flow rate also had a considerable effect. A higher drillpipe eccentricity provided lower friction factor, in the case single-phase liquid flow. Finally, empirical relations to describe the drillpipe eccentricity and hydraulic friction factor as functions of RPM and flow rate were proposed. When the particles were present, the friction factor decreased with RPM. The above-mentioned conclusions and relations are valid for a Newtonian fluid in the turbulent regime.

THE INTERNATIONAL JOURNAL OF COMPUTATIONAL METHODS AND EXPERIMENTAL MEASUREMENTS, Nov 1, 2017

Flow patterns in oil-water carrying pipes vary due to the flow characteristics, fluid properties ... more Flow patterns in oil-water carrying pipes vary due to the flow characteristics, fluid properties and pipe inclination. For inclined pipes, the gravity component along the pipe influences the flow patterns. Plug flow (PF) is one special flow pattern that occurs in slightly upward inclined pipelines. Mineral oil-Exxsol D60 (viscosity = 1.6 mPa.s, density =788 kg/m 3) and water (viscosity = 1mPa.s, density = 997 kg/m 3) were used as test-fluids. A test matrix was carried out to determine the possible flow patterns that occur at upward pipe inclinations +1° , +3° , +5° and +6° for low mixture velocities (0.2-0.5 m/s), and at water-cut 0.9. The plug flow regime was found only for +5° and +6° inclinations, while no plug flow was noticed at +1° and +3° inclinations. Plug flow was found only for lower flow velocity and higher water-cuts. Plug flow patterns were identified both through visual observation and by means of high-speed video imaging. Two new flow patterns 'oil droplet clusters in continuous oil and water (OC/O&W)' and 'distinct oil droplet clusters in water (D-OC/W)' were introduced, and they occur around the plug flow regime. High-speed images were post-processed for determination of the oil-water interface and subsequently used to calculate the water holdup. The time averaged water hold up decreased with increasing mixture velocity due to the decrease of oil-water slip as a result of increased degree of dispersion. The oil plugs entrained more droplets as mixture velocity was increased, leading to high-frequency fluctuations of volume fraction of the oil plugs. Holdup increased with increasing inclination due to the onset of plug flow, which leads to increased slip. The pressure drop over the test section was measured, and the frictional pressure drops were calculated using average water holdup values. The frictional pressure drop increased with increasing mixture velocity, due to increased mixing and subsequent increase of effective viscosity. The frictional pressure drop decreased with increased inclination due to the appearing of oil plugs and the drag reduction effect associated with the plug flow.

Journal of Non-newtonian Fluid Mechanics, Mar 1, 2020

This study investigates the effect of oscillatory motion on velocity and shear rate change within... more This study investigates the effect of oscillatory motion on velocity and shear rate change within different non-Newtonian, slightly viscoelastic fluids oscillated in a vertical U-shaped circular pipe. An estimation to quantify the influence on particle settling in an oscillatory environment is also presented. Flow visualization using particle image velocimetry (PIV) technique was deployed to compare the two-dimensional velocity field in the vertical plane of the U-tube axis and the resulting shear rate change in three different non-Newtonian fluids. The experiments were performed in a 1.2 m high, 50 mm diameter transparent test section, at room temperature (21 ± 0.5 °C) and atmospheric pressure. A piston was driven at harmonic motion via a gas buffer, to provide the driving force for the test fluids at four different low frequencies ranging from 0.1-0.75 Hz and at three different piston oscillation amplitude ratios of A = a / D = 0.3, 0.4 and 0.5, where a is the displacement amplitude of the piston and D is the pipe diameter. Oscillatory Reynolds number (Re) based on Stokes layer thickness was used as the criteria for determining the specific flow regime. 36 different experimental cases were tested within the range of 2 < Re < 34, and all the experimental cases exhibited the laminar flow regime. The study reveals that the axial velocity amplitude along the pipe centerline increases with the increasing frequency and with increasing oscillation amplitude irrespective of the non-Newtonian fluid type. The thickness of the shear region decreases with the increase of frequency. The change of shear rate is maximum near the wall region of the pipe and that is achieved at the maximum position of the phase cycle, where the axial velocity also possesses its highest magnitude. The most viscous and the least elastic fluid have reported a maximum reduction of viscosity as an effect of the oscillatory motion and the viscosity reduction becomes insignificant when the non-Newtonian fluids become less viscous.

International Journal of Multiphase Flow, Feb 1, 2018

Cuttings transport under laminar and turbulent liquid flow in horizontal and deviated pipes were ... more Cuttings transport under laminar and turbulent liquid flow in horizontal and deviated pipes were investigated. Several experiments were conducted both for single-phase liquid flow and liquid-particle flow in order to study the impact of rotation of a drill string, as well as fluid rheology and particle size on dynamic feature of particle dunes. Long time series of pressure gradients and flow patterns of the liquidparticle flow were obtained for off-line analysis. Fast Fourier Transform (FFT) was the methodology used to study the time series of pressure gradient signals. The time series were recorded as long continuous experimental sequences, while the flow conditions were changed in time stamped steps. The off-line analysis could then be carried out on each sequence which was easily extracted from the original based on the time intervals. The analysis indicated an existence of dominant frequencies corresponding to liquid and particle dynamics, and to the rotational speed of the drill string. It was found that the distribution and width of the frequency spectrum can be used as an indicator of the particle concentration at given flow conditions. Particle size has a large impact on the frequency spectrum, mostly when the drill string is rotating. The results of this study could help in real time prediction of downhole conditions in petroleum geology, exploration, and drilling operations.

World Academy of Science, Engineering and Technology, International Journal of Aerospace and Mechanical Engineering, May 25, 2017

Slug flow is a prevalent and undesirable multiphase flow regime which occurs in many industrial p... more Slug flow is a prevalent and undesirable multiphase flow regime which occurs in many industrial processes, causing time varying stresses in pipes and supports and consequently causes structural fatigue damage and failure. In this study, a series of experimental tests were conducted to address the effect of the slug frequency on the stresses of structural pipes. The slug frequency was measured using non-intrusive measuring technique through utilizing Phantom 9.1 high speed camera, while the pipe wall strain was captured using bi-axial strain gauges. The effects of the superficial gas and liquid velocities on the slug frequency were investigated. Additionally, the relation between the slug frequency and the induced stresses was examined. Moreover, a Slug Frequency Stress Prediction Model (SFSPM) based on the exerted slug unit forces was developed and validated. The presented results revealed that an excellent correlation with a deviation of 0.7% between the predicted and experimental stresses was achieved.

$Research paper thumbnail of Void fraction measurements in two-phase flow using X-ray attenuation technique$

This paper describes the design and optimization of a fast, three-beam densitometer system, which... more This paper describes the design and optimization of a fast, three-beam densitometer system, which uses an X-ray tube as a source of radiation. The X-ray densitometer is developed for local void fraction measurements of water/air and oil/air two-phase mixtures. The densitometer setup consists basically of two almost horizontal measurement beams passing through a horizontal pipe. The transmitted beam intensities are measured together with a reference beam outside the tube. The beams can be displaced vertically in the plane normal to the flow direction, and it is possible to measure the local void fraction at different vertical levels. With the instrument one can determine the transversal void fraction profile in near steady horizontal two-phase flow. The measuring technique, error sources and some initial results are described and discussed in this paper.

WIT transactions on engineering sciences, Jul 10, 2018

Interfacial shape of stratified flow of two liquids in pipes may take a planar or curved shape de... more Interfacial shape of stratified flow of two liquids in pipes may take a planar or curved shape depending on the physical properties of the fluids, wall-fluid wettability, the geometrical dimensions and the fluids holdup. It is traditionally accepted that the interfacial curvature is present in capillary and small-scale systems where the surface tension effect is significant against gravity effects. However, it is possible that interfacial curvature is present in liquid-liquid systems with small density differences or in reduced gravity systems due to dominating surface phenomena. Two phase flow of oil (density = 788 kg/m 3 , viscosity = 1.6 mPa.s) and water (density = 997 kg/m 3 , viscosity = 1 mPa.s) in a horizontal pipe was investigated for stratified flows. The longitudinal view was recorded using high-speed video imaging, while the cross sectional view of the flow was captured via Electrical Capacitance Tomography (ECT). As a third method, the interfacial level at the mid-pipe was calculated by referring to a work reported in literature. In addition, the interfacial level and the curvature in stratified smooth flow (ST), were calculated using CFD simulations as well. The ECT images indicated a blurred interfacial margin where the interface was reconstructed with a considerable thickness. However, the interfacial level at the pipe wall shown by the cross sectional ECT images were comparable with that of the high-speed images and the CFD simulations. Nevertheless, a significant interfacial curvature was encountered in ECT images towards the mid-pipe, which is 4.3 times deeper than the calculated value. CFD results agreed well with the calculated interfacial level using constant curvature arc model. In ECT, the depth of the curvature at the mid pipe seemed to be far more than the reality due to the possible field distortion effects occurring when the electrical flux lines pass through the media of high permittivity contrast (oil-water). Therefore, it was found that ECT can predict the interfacial oil-water level at the walls with acceptable accuracy, while it over-predicts the interfacial curvature present in the mid-pipe region. It is important to note that the ECT electrodes have their highest sensitivity near the wall region.

Measurement Science and Technology, Apr 17, 2018

Journal of Non-newtonian Fluid Mechanics, Sep 1, 2016

Fall velocity of particles traversing through viscoelastic non-Newtonian flow in a horizontal cha... more Fall velocity of particles traversing through viscoelastic non-Newtonian flow in a horizontal channel was measured. Aqueous solutions of Poly-Anionic Cellulose (PAC) with two different concentrations 2 and 4 g/l were used as a continuous liquid phase. An experimental setup with a rectangular test section was carried out to achieve good optical conditions. Particle image velocity (PIV) and particle tracking velocity (PTV) techniques were used to measure fluid velocity, particle trajectories as well as particle fall velocities. Experiments were also performed for Newtonian fluid (water) as a reference fluid. It was found that the particle fall dynamics is closely related to the fluid rheology as well as the local fluid velocity, shear rate and particle size. The more concentrated the PAC solution the stronger is the drag coupling, and with less spread in particle trajectory. The experimental results were compared with 3D CFD simulations. The effect of parameters which influences the hole cleaning aspects on model prediction was investigated and developed a correlation to predict the settling impingement distance of the particles.

Spe Journal, Sep 1, 2002

Summary A steady-state mechanistic model is formulated to predict the mixture behavior for upward... more Summary A steady-state mechanistic model is formulated to predict the mixture behavior for upward two-phase flow in concentric annuli. It consists of a procedure for flow pattern prediction and a set of independent models for calculating gas fraction and pressure drop in bubble, dispersed bubble, slug, and annular flow. Some aspects of churn flow are also discussed. Experiments are performed in a 1278 m vertical well and in a small-scale U-tube, which comprises a descending pipe and an ascending annulus. Small-scale data available in the literature were also collected and catalogued. The model is validated against the database. The performance of the model is compared with the performances of other models from the literature. It shows that the proposed model is more accurate than the alternatives.