Asphaltene Precipitation Study during Natural Depletion at Reservoir Conditions

Abstract This study concerns with experimental investigations of asphaltene precipitation at reservoir conditions of a crude sample from an Iranian oil reservoir during pressure depletion. High pressure high temperature set up and filtration method was used to quantify amount of precipitated asphaltene at different pressures. In addition the effect of temperature on asphaltene precipitation during pressure depletion has also been examined. The experimental results have been used to develop the asphaltene precipitation model with the application of commercial software as well. The movement of production systems to deepwater and subsea environments in recent years has increased the importance of fluid property related flow assurance issues. Fluid property variations that commonly occur during the production of oil, such as changes in pressure, temperature and composition, can precipitate asphaltenes. Asphaltene precipitation causes severe problems in reservoir oil production which is highly costly and laborious to remediate. Optimizing production in this case requires knowing the conditions under which asphaltenes will remain in solution. Experimental measurements at reservoir conditions play an important role in understanding asphaltene behavior as well as developing and justifying asphaltene models. The results of this study confirm that asphaltene precipitation increases when temperature decreases, this can be interpreted as a result of variation in volume fraction of species when temperature changes. After the pressure onset, asphaltene precipitation increases with reduction of pressure and reaches to a maximum near the bubblepoint. Furthermore reduction in pressure leads to asphaltene redissolusion due to light gas liberation. Also it is revealed that denser asphaltene components have tendency to precipitate initially. The results of this study can be applied as criteria for designing successful production operation in order to avoid asphaltene problem and also for thermodynamic model development or modification.