Study Of Fluid Flow Assurance In Hydrocarbon Production – Investigation Wax Mechanisms

Abstract

The current work is a study of wax deposition, a phenomenon that is one of the main flow assurance problems faced by the oil industry, affecting numerous oil companies around the world. Wax deposition can result in the restriction of crude oil flow in the pipeline, creating pressure abnormalities and causing an artificial blockage that can lead to reduced or interrupted production. Wax can precipitate as a solid phase on the pipe wall when its temperature drops below the wax appearance temperature (WAT). The aim of this research is to study in a lab rig the influence of some of the factors that control and affect the wax deposition process, such as pipe wall temperature (inlet coolant temperature), flow rate, pressure drop, oil temperature, shear stress, recirculation time of crude oil and viscosity. It aims to study the chemical and mechanical methods of inhibiting wax deposition in pipelines. The work also aims to simulate the multiphase flow process in the rig for this study. A new experimental flow loop system was built in the lab to study the variation of wax deposition under single-phase transport through a pipe. A series of experiments were carried out for varying inlet coolant temperatures, flow rates and run times, while the pressure drop was monitored to evaluate the effect of chemical inhibitors and to evaluate the effect of spiral flow on wax deposition. Multiphase flow numerical simulations were undertaken using OLGA software in order to study the effect of the factors that control the wax deposition. Use of mixtures of inhibitors was evaluated, considering their effects on the rheological behaviour of the crude oil. The experimental results show that there is a direct relation between the deposition time, pressure drop and wax deposit thickness, which is also highly dependent on the temperature. The wax deposit increases as the inlet coolant temperature decreases, even if the oil temperature exceeds the WAT, resulting in a larger pressure drop. The wax inhibition percentage was the highest using a combination of spiral flow with the inhibitor polyacrylate polymer (C16-C22) due to the synergy effect of high shear stress and the effect of an inhibitor that interferes with wax crystal growth. Three different mixtures of inhibitors were prepared in this work depending to the inhibitors that provide the greatest reduction in wax deposition; the mixtures of inhibitors presented a high reduction in crude oil viscosity, even at lower temperatures, due to interfere with wax molecules and prevent the growth processes. The findings of the numerical simulation, using a simulator to reproduce the experimental results by tuning analogical properties (assumptions), show agreement with the experimental results. This study presents the spiral flow and the combination of spiral flow with the inhibitor polyacrylate polymer (C16-C22) as efficient mitigation methods to prevent or reduce wax deposition in hydrocarbon pipelines.