Identifying and understanding wettability alteration caused by asphaltene deposition, and its implications for field development optimization is growing in interest. In this paper, we present a field case study on the cause of an unexpected decline in reservoir productivity and simultaneous rapid increase in water production. We concluded that the decline in productivity and water cut increase were caused by asphaltene precipitation in the formation with a subsequent increase in the water relative permeability. This was caused by alteration of rock wettability from water-wet to oil-wet by asphaltene deposition.
This work's findings can improve understanding of reservoir performance and help optimize reservoir management strategies for oil reservoirs with potential asphaltene precipitation problems.
All possible parameters in the reservoir simulation model was thoroughly examined and discussed. Switching the relative permeability type from water-wet toward oil-wet at the asphaltene onset pressure (AOP) yielded an excellent history match with the observed rapid water production increase. The reservoir had been depleted following primary production; the laboratory PVT data indicated that the AOP was a little below the initial reservoir pressure and hence asphaltene precipitation had been predicted.
This work contributes to (1) providing a field case bridging asphaltene deposition and wettability alteration, (2) understanding phenomena such as rapid increase in water production associated with asphaltene deposition, and (3) optimizing reservoir management and field development for oil reservoirs with potential asphaltene precipitation problems.