Simulation of paraffin deposition and removal in wellbores

Abstract

The purpose of this research is to develop a numerical simulator to model paraffin deposition and removal in the production tubing, and to gain a better understanding of the following three different thermal removal processes: (1) hot oil injection, (2) downhole heater, and (3) electric heating of the tubing. This is believed to be the first such simulator. To model paraffin deposition in the production tubing, a reservoir simulator is needed to accurately feed paraffinic oil into the annulus and the production tubing. A reservoir simulator that was developed by Ring was used. This simulator was modified and linked to an overburden and a wellbore simulators by using the principle of domain decomposition. By linking these three simulators, paraffin deposition is in the tubing was modelled. The removal of deposited paraffin was studied with one of the folowing three thermal methods: (1) a downhole heater, (2) the electric heating of the tubing, or (3) hot oil injection. To model these thermal removal methods, energy is added to the wellbore simulator in different manners each of which mimics one of the removal methods. Four cases, one depositional and three removal, are documented to illustrate the results obtained from this simulator. The conclusions were made by running the four cases and by developing the simulator. The following conclusions were made by running the four cases: (1) most of the precipitated paraffin is produced with the oil, (2) hot oil injected into the annulus may flow into the formation and reduce its effective permeability, however some damage may be removed by producing undersaturated oil, (3) downhole heaters take several hours to remove deposited paraffin near the surface and (4) electric heating of the tubing is a viable thermal removal process. The following conclusion were made by developing the simulator: (1) To thermally remove paraffin in a paraffinic black oil reserboir simulator, the variable cloud point problem must be modeled, and (2) the principle of domain decomposition can be effectively used to link a wellbore simulator to a reservoir and overburden simulator.