Simulação numérica do reinício do escoamento de petróleo parafínico gelificado em tubulações providas de aliviadores de pressão

Abstract

Pre-salt layer oil commonly presents a paraffinic composition, resulting on its gellification for low temperatures. With production stops in mind, the development of a tool to evaluate pressure and volumetric flow during flow restart of gelified oil, in tubes provided with pressure release reservoirs, was set as the paper’s objective. The pressure release reservoirs are employed in order to reduce pressure peaks, although they delay the flow estabilization. Two types of pressure release reservoirs were idealized, one provided with an embolus, that both receives and returns fluid to the tube; and another with a fixed hydraulic resistance, that only receives the oil. A mathematical model for thixotropy, available in the literature, that uses a mechanical analogy was employed. The tool was then used to simulate the flow restart with two different boundary conditions for the tube’s entrance, of fixed pressure or volumetric flow. For the fixed pressure condition, maximum increases in estabilization time, of ~5% for both types of reservoirs, were registered for two reservoirs with total volume equal to 1% of the tube’s volume were introduced. For the fixed volumetric flow case, the resistive reservoirs performed better, with 56,3% reduction for the pressure peak (24,3% for the embolus case), although presenting a 104,7% maximum rise in estabilization time (44,3% for the embolus case), when up to two reservoirs of the same total volume of 1% were employed.