Ozan Sayman Successfully Defends Thesis

July 30, 2019

TUHWALP student Ozan Sayman successfully defended his MSE thesis, "Continuous Flow Plunger Lift." The abstract is below. Members can download the entire thesis and other deliverables in the Member Access section.


Liquid loading occurs when the gas flow rate decreases to a certain extent due to reservoir pressure decline which is experienced sooner in unconventional reservoirs. The slippage between gas and liquid phases set up liquid accumulation in wellbore which creates hydrostatic backpressure. In contrast to conventional plunger lift, continuous flow plunger lift is capable to eliminate liquid loading without stopping the production. Experimental and theoretical study of continuous flow plunger lift conducted to understand hydrodynamics behavior and the liquid removal process. A 2-in ID static and dynamic facility were used for both fall and upstroke stages with different fluids and gas-liquid injection rates. Fall motion of balls, sleeves and bypass plunger against the static liquid column and two-phase flowing conditions was experimentally investigated.

Fall characteristic defined with dimensionless parameters and corrections factors for wall effect, two-phase and inclination angle are proposed. A sensitivity analysis of the proposed model showed influential parameters that affect fall velocity of plungers. A new drag coefficient number is proposed that can simplify the plunger selection from the catalog. Additionally, a comprehensive fall model (TUFALL) developed with multiphase fluid flow simulators for better accuracy.

Theoretical study has been conducted on the upstroke stage in order to define the mechanism and liquid removal process. Force balance on plunger used to introduce drag driven model for upstroke stage. Experimental studies show that continuous flow plungers do not require pressure build-up in the casing to rise. Two-piece plungers switch into high drag mode as they merged at the bottom hole assembly. As soon as high drag mode is achieved, they started to rise if there was enough gas velocity to overcome plunger weight. Experiments have shown that continuous flow plunger does not start upstroke movement with a liquid slug, but it catches liquid along with the tubing. A new model is proposed to estimate liquid velocity and plunger velocity along the well to estimate liquid slug growth and removal. Comparison between liquid removal of the plunger and total liquid inventory of the tubing proposed as sweep ratio to gauge the efficiency of this process. Plunger assisted gas lift applications considered with various gas flow rate experiments. Operational boundaries defined and optimization strategies are discussed for continuous flow plunger lift.

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