Investigating the impact of dissolved natural gas on the flow characteristics of multicomponent fluid in pipelines

Abstract

The conventional equations for describing the flow characteristics of the mixtures merely consider fluid that is homogenic, if it is above the bubble point conditions but ignore that a system containing sub-micron sized gas or vapor bubbles distributed throughout the volume of the liquid, which can exhibit unexpected heterogenic and complex phase properties. In this paper, a new mathematical model for the flowing gas-liquid mixture is presented, which has been proposed considering the colloidal feature of the system above the saturation or bubble point pressure. This approach is more in line with the actual dynamic performance of the oil and gas mixture export pipeline. Experimental data, simulations and field case studies validate the new proposed mathematical model of flow characteristics in pipeline. The obtained results confirmed that the calculated data are in good agreement with the experimental data. Based on Azerbaijan oil-gas-condensate field “Guneshli” data, this new model was used for calculating the condition in which the transformation of the flow characteristics from stable into instable is occurred. It has been discovered that the flow becomes unstable at a pressure about 30% higher than Bubble Point Pressure, which causes pulsation effect in the pipeline structure. However, homogenic behavior should be observed in this hydrodynamic condition. Also, the model provides a guideline on how to optimize the flow rate by adjusting the pipeline parameters to minimize the flow resistance, liquid slugging and hydraulic hammering effects, which cause instable operation.