Nabil Kharoua

A theoretical and numerical analysis is presented on the squeezed film of an incompressible fluid between two parallel fracture walls induced by seismic waves at normal incidence. In the frame of small oscillations, a closed form of the fluid pressure changes along with the fracture, and the fluid velocity field distribution is proposed. The developed analytical solutions are valid for any relative amplitude and phase of the vibrations within the assumed small oscillations and can help in understanding the induced fluid flow in fractures near zero-offset seismic wave propagation in a fluid-saturated fractured reservoir with nearly parallel fracture walls. It is found that the fluid flow is governed by the squeezing motion due solely to the difference of the vertical fluid velocities. In the absence of experimental data, the analytical solutions are validated with numerical solutions of the full Navier-Stokes equations. The comparison confirms the accuracy of the analytical solutions, showing that average fracture pressure rises with frequency, fracture length squared, and decreasing wall separation. It is also found that the presence of a pressure gradient does not hinder the overall flow during an oscillation cycle. The high induced horizontal acceleration of the fluid can reduce surface tension and improve oil to dissolve in any injected solvents. This may help mobilize fluids in fractured reservoirs, potentially explaining the improved oil recovery observed with surface seismic wave stimulation near production wells. Optimizing flow parameters through accurate fracture characterization can further enhance oil recovery.

Turbulent swirling flow inside a short pipe interacting with a conical bluff body was simulated using the commercial CFD code Fluent. The geometry used is a simplified version of a novel liquid/gas separator used in multiphase flow metering. Three turbulence models, belonging to the Reynolds averaged Navier-Stokes (RANS) equations framework, are used. These are, RNG k-ε, SST k-ω and the full Reynolds stress model (RSM) in their steady and unsteady versions. Steady and unsteady RSM simulations show similar behavior. Compared to other turbulence models, they yield the best predictions of the mean velocity profiles though they exhibit some discrepancies in the core region. The influence of the Reynolds number on velocity profiles, swirl decay, and wall pressure on the bluff body are also presented. For Reynolds numbers generating a Rankine-like velocity profile, the width and magnitude of flow reversal zone decreases along the pipe axis disappearing downstream for lower Reynolds numbers. The tangential velocity peaks increase with increasing Reynolds number. The swirl decay rate follows an exponential form in accordance with the existing literature. These flow features would affect the performance of the real separator and, thus, the multiphase flow meter, noticeably.

Detailed laser Doppler velocimetry (LDV) measurements of profiles of mean axial and tangential velocities and their corresponding root-mean-square (RMS) components in confined turbulent swirling pipe flow with and without the presence of a conical bluff body have been conducted. The working fluid was water and the Reynolds number based on the bulk velocity inside the pipe was equal to 40,850. The main focus of the study was to document the interaction between turbulent swirling flow inside a pipe and in the presence of a conical bluff body. The flow structure was found in all cases to be composed of a forced-free vortex. The swirl decay was exponential for Reynolds numbers of 40,850 and 14,450. The effect of the presence of the bluff body on the flow is limited to a short region upstream of it; so that the effect on the flow structure and strength of swirl upstream can be considered negligible. The flow around the bluff body adopts a different structure where the mean axial and tangential velocities tend to assume uniform profiles with turbulence activity limited to the region close to the surface of the bluff body.

The present study addresses itself to the performance assessment of a novel in-line gas-liquid separator. The separator is developed by FRAMES company under the name of SwirlSep based on the interaction of a swirling flow, generated by an innovative devise called swirl cage, and a hollow conical bluff body designed to deviate the gaseous phase internally.. The separator is intended to be implemented within a multiphase flow metering system in oil field gathering stations in the Gulf region. The study represents a preliminary step among a design process including elaborate lab-scale and filed tests. The flow in the gas-liquid separator is studied using Computational Fluid Dynamics CFD. The Shear Stress Transport (SST) k-ω turbulence and Eulerian-Eulerian multiphase models, under different flow conditions, were used to simulate real flow scenarios. The scenarios were chosen to replicate flow conditions that could exist during the operation of oil wells over their lifetime with the aim to provide guidance for proper control of the separator valves. The fraction of the total flow is prescribed at each outlet, using an outflow boundary condition, to mimic the action of the control valves. At the inlet, the phase velocity and volume fraction were prescribed. The outlet streams and their phase’s content were, then, analyzed together with the distribution of the velocity and concentration fields inside the separator. Velocity and pressure drop were found to increase with the increase of the outflow in one outlet when changing the flow split. Flow control, at the outlets, caused an increase of the oil-in-gas entrainment when trying to minimize gas-in-oil entrainment which is a non-trivial task. The effects of the flow split specified appeared downstream of the conical bluff body only when the inflow conditions were kept constant whereas the flow field remained identical upstream of the cone. A recirculation zone was generated in the annular space downstream of the cone and affected the separator performance considerably. The recirculation zone was due to the effect of the higher flow rate towards the gas outlet and disappeared when the flow rate towards the oil outlet tended to be equal or higher. The phase distribution was identical upstream of the cone and depended on the flow split downstream of the cone. The cases considered served as an assessment of the separator performance under different multiphase flow conditions replicating realistic scenarios.

Swirling flows in pipes are encountered in several industrial applications for separation or mixing purposes. In this work turbulent swirling flow is generated using a new swirl generator in the form of thick-walled pipe with multi-radial holes which is lodged inside a larger cylindrical housing, called the Swirl Cage. The swirling flow exiting from the Swirl Cage feeds into a long pipe where the Reynolds number based on the pipe diameter and average velocity is equal to 40836.67. Large Eddy Simulation (LES) is used to calculate the swirling flow and explore its characteristics in conjunction with the Dynamic Kinetic Energy Subgrid-Scale model. Experiments were conducted using LDV and the results are used for validation purposes and for the discussion of the flow features. The results are discussed in relation with the mean fluid velocity and its RMS component. Profiles of the mean tangential velocity reveal a Rankine vortex swirling flow type along the whole axial distance. The core flow was slightly oscillating exhibiting a processing vortex behavior reflected by the radial velocities at the centerline. The profiles of the turbulent kinetic energy were characterized by a peak at the centerline increasing in magnitude with the axial distance. The swirl number decayed from 1.5 right at the outlet of the swirl cage to unity close to the outlet of the pipe.

Phase separation using swirling flows is a technique used in inline separators. In the present study, an existing separator device generates a swirling flow which interacts with a conical hollow bluff body to where the air phase is collect. We use the commercial CFD code Fluent to simulate and investigate the characteristics of single-phase turbulent swirling flow interaction with a solid conical bluff body on a laboratory-scale model. The simulation work employed different RANS turbulence models; namely, RNG k-ε, SST k-ω and RSM. A constant velocity was imposed at the inlet of the computational domain while a constant pressure was prescribed at the outlet. The results are validated against experimental measurements. The effect of flow rate was investigated. The resulting flow is investigated around the bluff body and within the whole outlet pipe downstream of the swirl generator because the separation depends strongly on the flow behavior in this extended region. The core flow reversal persists up to the bluff body at high flow rates. This is significant in terms of phase behavior in the separation application in addition to the loads on the bluff body. The profiles of the tangential velocity corresponded to a Rankine vortex swirling flow type along the whole axial distance. The results show that the RSM gives the best accuracy among the three RANS models compared with the experimental data. The rate of swirl decay decreases as the flow rate increases. For the lowest flow rate, the swirl decay followed an exponential trend which becomes almost linear for the highest flow rate considered. At low swirl intensities, the pressure peaks are observed on the bluff body apex while, at high swirl intensities, the reversal flow generates the lowest pressure at the centerline affecting the cone as well.