Effect of Temperature on Asphaltene Deposition Mechanisms in Horizontal Flow
Asphaltene deposition is a longstanding flow assurance issue that has been extensively investigated at near ambient temperatures where asphaltenes typically precipitate as glassy particles. However, at the higher temperatures sometimes encountered in deep formations, asphaltenes may come out of solution as liquid droplets. Deposition at these conditions has not been rigorously examined. The purpose of this study was to investigate deposition behavior in the liquid droplet regime and compare it with deposition in the glassy particle regime. An apparatus was designed and commissioned to investigate deposition mechanisms over a range of temperatures in horizontal laminar flow using a test fluid of bitumen diluted with n-heptane. Pre-diluted bitumen and additional n-heptane were fed through a static mixer to induce asphaltene precipitation and the subsequent mixture was then displaced through a capillary tube test section. The pressure drop across the test section was monitored for indications of deposition during the flow period, and the capillary tube was removed from the apparatus at the end of each experiment to measure the mass and location of the deposit. Asphaltene deposition was assessed considering the following variables: capillary tube lengths from 3 to 30 cm, solvent contents in the feed from 65 to 90 wt% n-heptane, fluid flow rates of 2 and 4 cm³/min, and temperatures from 50 to 130°C. In the glassy particle regime, a highly porous, orifice-like deposit with a high solvent content formed near the inlet of the test section. The fully developed wet deposit occupied 37% of the tube volume on average. The initial deposition rate increased as the solvent content in the feed increased. Cycles of deposition and erosion were observed during the flow period. The results were consistent with the literature. In the liquid droplet regime, periodically unstable stratified flow was observed. The heavy phase hold up cycled from 70 to 98% of the tube volume. The solvent content of the heavy phase was lower compared to glassy particle deposits and consistent with equilibrium heavy phase compositions reported in the literature. The heavy phase accumulated faster as the solvent content in the feed increased. In one experiment, an orifice-like deposit appeared to form at the start of the experiment indicating that, even in the liquid regime, deposition may occur near a flow disturbance. However, the effect of the orifice was overwhelmed by the accumulation of the flowing heavy phase. The results suggest that the models and treatments developed for deposition in the glassy particle regime may not apply in the liquid regime.
Asphaltene Deposition, Capillary Flow, Reservoir Temperature, Phase Behaviour, Heavy Oil, Flow Assurance, Upstream
Do, N. (2021). Effect of Temperature on Asphaltene Deposition Mechanisms in Horizontal Flow (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.