Modeling and Control of Three-Phase Gravity Separators in Oil & Gas

Abstract
Oil production facilities exhibit complex and challenging dynamic behavior. A dynamic mathematical modeling study was done to address the tasks of design, control and optimization of such facilities. The focus of this paper is on the three-phase separator, where each phase’s dynamics are modeled. The hydrodynamics of liquid-liquid separation are modeled based on the American Petroleum Institute design criteria. Given some simplifying assumptions, the oil and gas phases’ dynamic behaviors are modeled assuming vapor-liquid phase equilibrium at the oil surface. In order to validate the developed mathematical model, an oil production facility simulation was designed and implemented based on such models. As far as the thermodynamics aspects of the separator are concerned (i.e., the oil and gas phases), many modeling approaches have been suggested in this paper. The phase equilibrium modeling approaches have been used for 50 years and has provided satisfactory results for such equipment as flash tanks and distillation columns. The basic equations in this approach are used to describe the material balances, equilibrium relations, the composition summation equations, and the enthalpy equations.