Effect of the Gas Composition and Gas/Oil Ratio on Asphaltene Deposition

Arterial deposition of asphaltene is a major flow assurance issue in pipelines and wellbores. The numerous compounds constituting crude oils are mutually soluble at reservoir conditions, but precipitation can occur with changes in the pressure, temperature, or composition. As the pressure and temperature change through the wellbore, asphaltenes can precipitate and potentially deposit. Unfortunately, remediation by solvent soaks is expensive; hence, the need to forecast the potential risk of asphaltene deposition. In this paper, a previously reported simulation tool, asphaltene deposition tool (ADEPT), is used to predict the magnitude and location of asphaltene deposits in flow lines and wellbores. ADEPT is to be used to gauge the frequency and location of deposits and how often intervention will be needed. The phase behavior of asphaltene is described by the perturbed-chain statistical associating fluid theory equation of state, while the transport equations are coupled with kinetic rates of precipitation, aggregation, and deposition. The transport model is simplified, resulting in dramatic speed up of the simulator. This paper presents a field case as well as a simulation on the effect of different gases and gas/oil ratio on asphaltene deposition.