Modeling of Asphaltene Precipitation and Deposition
Al Hammadi, Ali AbdulKareem
Chapman, Walter G
Doctor of Philosophy
The tendency of Asphaltene to deposit and block tubing can potentially lead to production loss and significant cost of remediation. Unlike other deposits, the deposition behavior of Asphaltene is still not fully understood and is hindered by asphaltene complex nature. This thesis will provide insight into the mechanism of Asphaltene deposition through a better understanding of its thermodynamics and kinetics. Despite the contribution made by this thesis to better understand its behaviors, asphaltene still represents an ongoing challenge. Generally, a lengthy and time consuming characterization is required to obtain the optimum parameters before using EOS for crude oils. Therefore, an automatic characterization has been developed. In this thesis, a comparison between CPA and PC-SAFT EOSs is presented to illustrate their potential and limitations on the prediction of asphaltene phase behavior, and PVT properties over a range of pressure and temperature. With an optimized characterization, both EOSs give acceptable predictions of the asphaltene precipitation tendency. However, PC-SAFT is superior in the prediction of derivative properties especially at high pressures. As gas injection is crucial part of enhanced oil recovery, the effect of various gases on asphaltene phase behavior is presented. Nitrogen is shown to be the strongest precipitant while hydrogen sulfide stabilizes asphaltene. The addition of polystyrene to a mixture of asphaltene and toluene causes phase separation into two liquids due to depletion flocculation and is modeled using PC-SAFT EOS. The effects of temperature, pressure and polystyrene MW on the mixture phase behavior are investigated. The phase behavior was not sensitive to the range of pressures studied; however, increasing temperature or reducing polystyrene MW caused the one phase region to expand. The paper demonstrates that a solution model with rigorous physics can capture the depletion flocculation mechanism typically presented as colloidal behavior. This thesis also introduces Asphaltene Deposition Tool by incorporating both asphaltene kinetics and thermodynamics. The asphaltene phase behavior is described by PC-SAFT EOS while 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. Furthermore, this thesis presents a field case as well as the effects of different gases and GOR on asphaltene deposition.