Partial movement of asphaltene in presence of connate water in VAPEX process

Vapor extraction (VAPEX) process is solvent analogue of SAGD process in which low molecular weight solvent are used to reduce the viscosity of heavy oil and bitumen. This process may be a good candidate to be applied in problematic reservoirs in which thermal methods are not efficient due to severe heat losses. Asphaltene precipitation as a result of compositional alteration of solvent/bitumen has substantial effects on performance of VAPEX. In this process if operating pressure is very close to dew point pressure, asphaltene precipitation occurs. In-situ deasphalting of heavy oil and bitumen reduces the viscosity of the produced oil and creates the oil that is more easily refined, but the main concern is whether this advantage can outweigh reduced permeability and plugging of formation caused by adsorption and precipitation of asphaltenes. In current work experiments have been conducted in low permeability sandpacks in both dry and non-dry systems to assess the performance of Vapex process when asphaltene precipitation occurs. Experiments are carried out in a 2D visual cell using highly asphaltenic heavy oil from one of Iranian reservoirs (Kuh-e-Mond) and propane as a solvent. The results show that performance of Vapex process increases when asphaltene precipitation occurs provided that optimal pressure has been designed to prevent extensive asphaltene deposition and subsequent plugging of porous media. It has been observed that adsorption of asphaltenes has considerably decreased in non-dry systems. Movement of precipitated asphaltene and less adsorption in non-dry experiments results in a more stable and efficient Vapex process while in dry experiments higher adsorption of asphaltenes resulted in plugging of low permeability porous medium.