After years of production, most oilfields with nonmarine deposits in China have been at their mature stage with high water cut and high recovery. The remaining oil is, on one hand, highly scattered in the reservoir, but on the other hand, relatively concentrated in some locations. The identification of the exact distribution of these locations with relatively abundant remaining oil is of great importance for improving oil recovery, but is very difficult. The oilfield development, which has been complicated by all the above factors, calls for more powerful numerical reservoir simulation techniques. The large-scale sophisticated numerical simulation technique with high efficiency, high precision, and high computing speed will be the key to the study on the remaining oil distribution for oilfields at their mature stage with high water cut. As for various types of complicated reservoirs, it is essential to develop different fluid flowing models and corresponding numerical simulation techniques.