Gas Evolution and Gas-liquid Separator Modeling
Abstract
Gas-liquid separation is a critical unit operation for oil and gas production. While there has been a large number of studies investigating the removal of liquid droplets from the gas phase, relatively little attention has been paid to the separation of gas bubbles from the liquid phase. Understanding the liquid degassing process is critical as oil and gas production is pushed towards more extreme operating conditions, particularly those involving heavy oil and high pressure environments. Current degassing guidelines rely on overly simplistic assumptions and field experience. Additionally, the entering gas and liquid phases are assumed to be in thermodynamic equilibrium with one another. Any pressure drop experienced by the multiphase stream prior to entering the separator will result in excess solution gas evolving out of solution. If the separator liquid residence time is less than the time required to re-establish equilibrium, the exiting liquid stream will then contain excess dissolved gas that will evolve out of solution further downstream. The aim of this study was twofold: construct a new experiment capable of measuring gas evolution at high pressures and develop a modeling framework for degassing within a horizontal gas-liquid separator incorporating the experimental gas evolution findings. A reference hydrocarbon system of methane and n-dodecane was used for the gas evolution experiments. Both rates of absorption and desorption were measured using the same process conditions, confirming that both mass transfer coefficients were symmetric within the experimental error. The surface renewal theory in the form of the small eddy model was found fit the data with an average error of 12.3 %. Using the separator degassing model, separation performance of entrained gas was found to be driven primarily by the liquid viscosity as well as the overall size of the initial bubble distribution. New entrained gas separation guidelines were developed using the separator model. Removing significant amounts of excess solution gas was found to be challenging using inlet conditions that also favored entrained gas separation. As more bubbles are separated from the liquid, the interfacial area available for mass transfer along with the net mass transfer rate also decrease.
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- OSU Dissertations [11222]