Several mechanisms are proposed for Nano-EOR recovering residual oil in pore space, such as altering the wettability of rock surface to water wet. However, the conclusive mechanisms remain under investigation. Despite its uncertain mechanisms, the application of Nano-EOR for shale oil/gas reservoirs looks promising and has received a lot of attention in research. This research aims to develop a numerical simulator predicting Nano-EOR performances in shale oil/gas reservoirs.
At a first stage in this research, the simulator predicting Nano-EOR performances in conventional oil-water system reservoirs and the simulator predicting shale oil/gas reservoir performances were constructed individually. For conventional oil-water system reservoirs, the simulator employs an imbibition capillary pressure curve to estimate the residual oil saturation, which is automatically calculated taking the concentration and aggregation of nanoparticles into consideration. This function was validated by successfully matching the simulation results with the existing core flooding experimental data. On the other hand, a multi permeability, white oil type simulator was developed to simulate the performances in shale reservoirs. White oil type simulator is considered representative to model the phase behavior of gas-condensate system, while multi permeability can deal the fluid flow in any number of fractures and matrixes.
Then, the multi-permeability, white oil type reservoir simulator, which enables to predict Nano-EOR performances in shale oil/gas reservoirs, was constructed combining the Nano-EOR simulator in conventional oil-water system reservoirs and the multi permeability, white oil type simulator. Using this simulator, it was successfully simulated that the condensate blocking could be mitigated in a gas-condensate reservoir by injecting nano-fluid due to the reduction of residual (critical) oil saturation.
Finally, the effects of Nano-EOR in shale gas/oil reservoirs were investigated through the case studies assuming the application of huff’n’puff operation. In these studies, the effect of the stimulation of shale gas/oil reservoirs by huff’n’puff with nano-fluid was compared with that by formation water. The following were revealed through these studies: (a) The huff’n’puff operation with nano-fluid may not be effective if there exist only a few major fractures in a reservoir. (b) The huff’n’puff operation with nano-fluid can result in the better shale gas recovery than that with water, if small but dense fractures are created.