A Predictive Methodology to Determine the Rate of Gas Evolution in Hydrocarbon Systems at Elevated Pressures

Abstract

The rate of gas evolution (volumetric mass transfer coefficient) is a critical parameter in understanding and predicting gas–liquid separation, especially in the energy industry. This work led to the development of an empirical correlation to determine the mass transfer coefficient based on the dead oil properties and energy dissipation. The approach was evaluated using published n-dodecane data. The empirical correlation was tested for model and crude oils using experimental data for the rate of gas evolution and absorption under varying levels of energy dissipation and from liquids of varying viscosities. The energy dissipated in the liquid was varied by changing the mixing speed from 25 to 500 rpm. The rate of gas evolution/absorption was measured using one model oil (Exxsol D-110) and three crude oils (crudes A, B, and C) of varying viscosities at elevated pressure (3.45 MPa) and at two different temperatures (298.15 and 348.15 K), while pure methane was used as the gas phase. The mass transfer coefficient determined for each liquid was correlated with an empirical equation based on the kinematic viscosity and energy dissipation, similar to the Lamont and Scott model. This work also evaluated the impact of inlet conditioning (multiple shear environments) on gas evolution. In gas–liquid separators, varying levels of energy dissipation are encountered. For example, high levels of energy are encountered in inlet conditioning devices, followed by lower levels of energy within the separator. Thus, the impact on the rate of gas evolution when an initial shear pulse (high energy dissipation) was applied prior to the gas evolution stage was investigated. The initial shear pulse increased the rate of gas evolution in all cases. This work provides an approach for estimating the rate of mass transfer in hydrocarbons, and it provides insight into cases where different levels of energy dissipation are experienced.