Pressure drop and holdup predictions in horizontal oil-water flows for curved and wavy interfaces

In this work a modified two-fluid model was developed based on experimental observations of the interface configuration in stratified liquid-liquid flows. The experimental data were obtained in a horizontal 14. mmID acrylic pipe, for test oil and water superficial velocities ranging from 0.02. m/s to 0.51. m/s and from 0.05. m/s to 0.62. m/s, respectively. Using conductance probes, average interface heights were obtained at the pipe centre and close to the pipe wall, which revealed a concave interface shape in all cases studied. A correlation between the two heights was developed that was used in the two-fluid model. In addition, from the time series of the probe signal at the pipe centre, the average wave amplitude was calculated to be 0.0005. m and was used as an equivalent roughness in the interfacial shear stress model. Both the interface shape and roughness were considered in the two-fluid model together with literature interfacial shear stress correlations. Results showed that the inclusion of both the interface curvature and the equivalent roughness in the two-fluid model improved its predictions of pressure drop and interface height over the range of studied superficial oil and water velocities. Compared to the two-fluid model with other interfacial shear stress correlations, the modified model performed better particularly for predicting pressure drop

Drag Reduction in Oil-water Flows

Liquid-liquid flows occur in many chemical and process industries including the petroleum industry where crude oil and its derivatives are transported over long distances often in mixtures with water. Depending on flow conditions and pipe geometry different flow patterns can appear ranging from fully separated to dispersed ones. The addition of small amounts of some polymeric materials to one of the phases has been found to change the flow patterns and their boundaries and reduce the frictional pressure drop. Understanding these changes and the underlying physical mechanisms is necessary for the design of pipelines for the transport of oil-water mixtures. In this thesis, the effects of a drag reducing polymer (Magnafloc 1011; hydrolysed copolymer of polyacrylamide and sodium acrylate, HPAM, mol. wt. = 10 x 106 g/mol) added in the water phase of an oil-water mixture were studied experimentally in a horizontal 14 mmID acrylic test section. The test fluids were a distillate oil (Exxsol D140: viscosity 5.5 mPas, density 828 kg/m3) and tap water. For some measurements two different molecular weights; 5 x 106 g/mol and 8 x 106 g/mol polyethylene oxide (PEO) polymers were also used. Flow patterns and pressure drop were investigated for a wide range of fluid velocities ranging from 0.052 m/s to 3.620 m/s for single phase water flows while oil and water superficial velocities ranged from 0.008 m/s to 0.580 m/s, and from 0.052 m/s to 0.80 m/s respectively. Both before and after the addition of polymer. Detailed studies of interface height and velocity fields were then carried out in stratified flows. Two types of conductivity probes, a wire probe and a ring probe, were used to measure interface heights in the middle and the wall of the pipe respectively. The velocity profiles and turbulence properties of the water phase were studied with particle image velocimetry (PIV) within the stratified flow regimes of the oil-water flows. The addition of 20 ppm of polymer solution to the water phase resulted in drag reduction of 80 % in single phase water flows and 52 % in oil-water flows. In addition, flow patterns were changed while the region of stratified flows was extended to higher superficial oil and water velocities. In stratified flows with the addition of polymer the in-situ average water velocity, interfacial wave celerity, and wavelength increased while the interface height, amplitude, and power spectrum were decreased. The conductivity probe measurements revealed a curved interface in stratified flows which with the addition of the polymer remained relatively unaffected. A relationship was developed between the two interface heights. The velocity profiles in the water phase became more parabolic compared to the flow without polymer. In addition, the axial component of velocity fluctuations decreased close to the interface and the wall but increased in the middle of the flow, while the Reynolds stresses and radial component of velocity fluctuations reduced throughout the water phase. From the two types of PEO tested, drag reduction was found to increase with polymer molecular weight but also depended on the mechanical degradation of the polymers at high Reynolds numbers and their ionic strength. A two-fluid model was developed that took into account the interface shape and waviness. To calculate its length, the interface was considered circular and the correlation between the two interface heights in the middle and the wall of the pipe was used. The interface waviness was included as roughness in the interfacial friction factor correlation, equal to the average wave amplitude found experimentally. Results showed when both interface curvature and waviness were included; the model predicted better the experimental pressure drop data compared to the two-fluid model with other interfacial shear stress correlations found in the literature. The friction factor correlation in the two-fluid model was also modified to account for drag reduction and it was able to predict the drag reduction in oil-water flows better than correlation available in the literature. The combination of polymer and fibers in single phase water flows resulted in a synergistic effect with drag reduction higher than when either polymer or fibers were used alone

Effect of Branched and Straight Chained Alcohols on Performance of Crude oil Demulsifiers

Unwanted crude oil emulsions occur in many stages of oil production,  transportation, and processing. The huge cost resulting from corrosion of transport system and production facilities, because of the presence of water is a major challenge to the oil industry and the global economy. However, the addition of alcohols to demulsifiers has been reported to enhance their efficiency in removing water from emulsions. There is therefore the need to identify the best type of alcohols and optimize this process of addition.  Consequently in this work, the effect of different straight and branched chain alcohols on the performance enhancement of demulsifiers was investigated using four different crude oil emulsion samples. The results showed that straight alcohols performed better when compared to branched chain alcohols under all conditions of temperature. This may be due to their slow mobility particularly in stable emulsions.Keywords: Crude Oil, Emulsion, Emulsifiers, Demulsifiers, Alcohols

Numerical study of nonlinear heat transfer from a wavy surface to a high permeability medium with pseudo-spectral and smoothed particle methods

Motivated by petro-chemical geological systems, we consider the natural convection boundary layer flow from a vertical isothermal wavy surface adjacent to a saturated non-Darcian high permeability porous medium. High permeability is considered to represent geologically sparsely packed porous media. Both Darcian drag and Forchheimer inertial drag terms are included in the velocity boundary layer equation. A high permeability medium is considered. We employ a sinusoidal relation for the wavy surface. Using a set of transformations, the momentum and heat conservation equations are converted from an (x, y) coordinate system to an (x,η) dimensionless system. The two-point boundary value problem is then solved numerically with a pseudo-spectral method based on combining the Bellman–Kalaba quasi linearization method with the Chebyschev spectral collocation technique (SQLM). The SQLM computations are demonstrated to achieve excellent correlation with smoothed particle hydrodynamic (SPH) Lagrangian solutions. We study the effect of Darcy number (Da), Forchheimer number (Fs), amplitude wavelength (A) and Prandtl number (Pr) on the velocity and temperature distributions in the regime. Local Nusselt number is also computed for selected cases. The study finds important applications in petroleum engineering and also energy systems exploiting porous media and undulating (wavy) surface geometry. The SQLM algorithm is shown to be exceptionally robust and achieves fast convergence and excellent accuracy in nonlinear heat transfer simulations

Separated oil-water flows with drag reducing polymers

The effects on velocity and turbulent properties of drag reducing polymers added in the water phase of oil-water flows were studied with Particle Image Velocimetry (PIV). The experiments were performed in separated horizontal oil-water flows in an acrylic pipe with an internal diameter of 14 mm. The test fluids were tap water (1.0 mPas, density = 1000 kg/m3 ) and a middle distillate oil (Exxsol D140; viscosity = 5.5 mPas, density = 828 kg/m3 ). Magnafloc 1011 (hydrolysed copolymer of polyacrylamide and sodium acrylate, HPAM; mol. wt. = 10 x 106 g/mol) was used as drag reducing agent in the water phase at 20 ppm concentration. Results showed that the polymer reduced frictional pressure drop at all conditions studied. The addition of polymer decreased the interface height and increased the in-situ average water velocity. The velocity profile in the water phase became more parabolic compared to the flow without polymer while the maximum velocity value increased. In addition, when polymer was added the axial stress tensor decreased close to the interface and the wall but increased in the middle of the flow, while the Reynolds and radial stress tensors reduced throughout the water phase. Two types of polyethylene oxide (PEO) polymers with different molecular weights, 5 x 106 g/mol and 8 x 106 g/mol were also tested. Drag reduction was found to increase with polymer molecular weight but depended also on the mechanical degradation of the polymers at high Reynolds numbers and on their ionic strength