Ramin Dabirian

Solid-Particles Flow Regimes in Air/Water Stratified Flow in a Horizontal Pipeline

There are a few studies covering solid-particles transport in multiphase pipelines. Solid-particles transport is complicated because it depends on several variables, including flow patterns, fluid properties, phase velocities, and pipe-geometry features such as roughness, diameter, and inclination angle. Each of these variables can have significant effects on the solid-particles-transport process. More attention has been paid recently to the importance of tracking solid-particles-transport management over reservoir life. There are three options available for managing solid-particles transport: applying a cleaning operation, installing solid-particles exclusion facilities, and operating above the critical solid-particles-deposition velocity. Cleaning operations, such as pigging, are only applicable for small amounts of solid particles, and they often result in the pig becoming stuck if the pigging frequency is not high enough. Installing solid-particles exclusion systems (e.g., gravel packs) can reduce production and create excessive pressure drops. The third option, operating above the critical solid-particles-deposition velocity, is preferred for solid-particles-production management as a prevention technique under favorable operating conditions because it has practical applications and can be beneficial commercially. To avoid solid-particles deposition, it is necessary to manage solid-particles transport above solid-particles-deposition velocities. On the other hand, operating under unnecessarily high flow rates is not only cost inefficient, but can also create facility damages; therefore, it is necessary to find the optimum velocity to maintain continuous particle movement. This velocity is called the critical solid-particles-deposition velocity.

Pressure-Minimization Method for Prediction of Two-Phase-Flow Splitting

was developed to predict the splitting phenomena under these regimes. Shoham extended his flow-splitting work to a horizontal reduced tee with a smaller-diameter branch arm (Shoham et al. 1989). Hong (1978) studied two-phase-flow splitting for a branching tee, considering the effect of side-arm angle and flow regimes on gas and liquid splitting. Hong and Griston (1995) studied flow splitting of an air/water system and concluded that, as the air split ratio increased to greater than 2:1, the experimental data points deviated from a 50:50 split. Hong and Griston (1995) also studied the effects of some devices on flow splitting. They recommended that nozzles be inserted directly downstream of an impacting tee to increase the chance of equal splitting. Azzopardi et al. (1987) considered the effects of annular flow for splitting at the tee junction. Azzopardi et al. (1988) investigated the effect of churn flow in the tee junctions. The experimental results for churn flow were the same as those for annular flow; therefore, they concluded that the inletgasand liquid-flow rates do not affect flow splitting. Peake (1992) concluded theoretically that uneven two-phase-flow splitting occurs as a result of unequal vapor-flow splitting. Tshuva et al. (1999) studied two-phase-flow splitting in horizontal and inclined parallel pipes. Taitel et al. (2003) studied the splitting of gas and liquid for four parallel pipes with a common inlet and outlet manifold capable of inclining from 0 to 15°. For the horizontal case, they observed identical splitting for each looped pipe, while for the other inclination angles, they observed a stagnant flow in at least one pipe. Pustylnik et al. (2006) investigated flow splitting in the lines on the basis of stability analysis, and proposed a model that was able to predict the number of pipes filled with stagnant liquid. One of the more-recent investigations on flow splitting was conducted by Alvarez et al. (2010). Their study investigated two-phase-flow splitting for looped lines such as parallel and looped configurations, and they developed a mechanistic model capable of predicting split ratio and pressure drop across each looped line on the basis of equal gas/liquid ratio in each branch. The purpose of our study is to discover the manner in which two phases of gas and liquid are split on the basis of the minimum pressure drop.

CFD Simulation of Turbulent Flow Structure in Stratified Gas/Liquid Flow and Validation with Experimental Data

Although two-phase stratified flow pattern commonly occurs in petroleum industry the understanding of it, in terms of structure of the wave interface and the ensuing interaction between the two phases, is limited compared to single phase flow. Also, most of the studies have not taken the velocity profile across the pipe cross-section into account, rather just focused on the average velocity of each cross section. This paper will provide a unique insight into these velocity profiles, which are critical for frictional pressure drop calculations and prediction of phenomena such as wall effects of multiphase flow, erosion, corrosion, hydrate formation, wax deposition, etc. The objective of this paper is the analysis of this gas-liquid flow pattern in a horizontal pipe utilizing Computational Fluid Dynamics (CFD) simulation and comparison of the results with experimental data. The scope also includes the investigation of turbulent flow structure beneath gas-liquid interface by calculating the stream-wise velocity profile. Experimental studies have been conducted to investigate gas-liquid stratified flow in horizontal pipe. A unique experimental facility was constructed with a 4-in ID PVC pipe and measurements were performed utilizing air-water. Liquid level at the center of the pipe is measured by ultrasonic proximity sensor at different superficial velocities of gas and liquid. Along with experimental tests, CFD simulations for the same test conditions have been performed using a commercial CFD code. For tracking the two-phase interface, Volume of Fluid (VOF) method was applied. The numerical simulation was obtained with the Realizable k-epsilon model of turbulence. Comparing the CFD simulation results and liquid hold up measured experimentally revealed a good agreement (discrepancy 15%). The experimental data also show that at constant superficial liquid velocities, the liquid level increases with decreasing superficial gas velocities. The validation of the CFD results with experimental data indicates that, CFD simulation has the potential to be used for facility design and scale-up processes in petroleum industry.