Reservoir Simulation Assessment for the Effect of Asphaltene Deposition on Waterflooding in B Oilfield

Asphaltene deposition has been observed in some wells within low-pressure areas in B oilfield during depletion. It is therefore concerns about asphaltene precipitation in the reservoir casued by decreasing pressure are raised. In this study, the impact of asphaltene deposition on water flooding in B oilfield was assessed by reservoir simulation. This work built a new simulation model and investigated five kinds of formation damage due to asphaltene precipitation, which are porosity loss, permeability impairment, wettability alteration, relative permeability and capillary pressure changes, and oil viscosity variation. The instantaneous porosity loss equals to the volume of compressed pore and deposited asphaltene per grid block volume. The permeability impairment is calculated considering rock compressibility, asphaltene deposition on rock surface and throat plugging by asphaltene. The wettability alteration, oil-water relative permeability and capillary pressure changes were investigated according to published laboratory experiments, Gibbs adsorption theory and the modified Corey type model. Moreover, the oil viscosity variation was calculated by using a linear function model. The simulation results show that asphaltene deposition in the reservoir would easily cause well skin and reduce the productivity index. As a result of wettability alteration caused by asphaltene surface deposition, the predicted oilfield water cut increases more quickly than that of the model without considering asphaltene deposition. Besides, the oil recovery factor reduces significantly when the reservoir pressure maintenance level is far lower than the upper onset pressure. The preferred reservoir pressure in a specific oilfield should be optimized based on sensitivity simulation cases to obtain a high oil recovery factor and slow water cut increase. B oilfield is recommended to maintain reservoir pressure around 5000 psi.