Optimum Separation Pressure for Heavy Oils Sequential Separation

Abstract

Abstract The estimation of quantity of liquid that is collected from gas/oil separation system is a very complex task because it requires the application of the flash calculations which needs to solve the cubic equation of state and to use some numerical techniques. These difficulties can be overcome by a computer model which requires a lot of experimental data, long time, and experience. This paper adopts a new technique to simplify this problem. It suggests new correlations for optimum separator pressure for separation station of heavy oils. The correlations have been achieved for two- and three- stage separation systems. The correlations have been created depending on many Iraqi oil samples. The optimum separator pressure of each individual separator was found at the maximum amount of liquid recovered with the minimum oil formation volume factor. The Optimum Separator Soave – Redlich – Kwong model (OSSRK) has been adopted to estimate the optimum separator pressure, while the objective functions, like oil formation volume factor, are predicted by Separator Flash Soave – Redlich – Kwong model (SFSRK) (Hassan 2004). The optimum separator pressures have been correlated with mole percent of hexane plus in the well stream fluid, mole percent of methane in the well stream fluid, temperature of the separator and the optimum pressure of the previous separator. Nonlinear multiple regression analysis has been applied to get the best correlation for each system. Many statistical tests are used to check the validity of the proposed correlations. The error percents of API, GOR, Bo between the optimal cases for each model and the relevant correlations show a maximum of 0.047%, 0.3% and 0.15% for two – stage systems, and 0.2%, 0.6% and 0.22% for three – stage systems. Also the cross plot method is applied to test the correlation validity. These checks are good indication to use these correlations with high degree of confidence.