Horizontal well is an important technology to enhance oil recovery for both old oilfield and new oilfield. Horizontal well have four characteristics: large drainable area; small producing pressure drop; high fluid productivity index and long water free production period (Joshi S. D. 1991) compared with vertical well. The contact pattern between horizontal section and the layer is line contact, and the pressure drop around the horizontal section is a linear distribution. The pressure drop near the bottom of the horizontal well will be far less than that of the vertical well if the same fluid is produced. Therefore, horizontal well can inhibit bottom water coning more effectively. The critical production of horizontal well is greater than that of vertical well for bottom water reservoir(Chaperon 1986, Papatzacos P. et al. 1991). But horizontal well may form water cresting. The reserves controlled by the horizontal section and volume swept by the bottom water is far larger than that of the vertical well, so it can increase the cumulative water free production. Therefore, comparing with vertical well, horizontal well can prolong water breakthrough time and improve the ultimate recovery (Permadi P et al. 1995, Wibowo W et al. 2004), which is one of the reasons for horizontal well technology used in bottom water reservoir widely at home and abroad. But with the oilfield development, horizontal well has also exposed some questions gradually. Vertical well has a long water cut production period, but water cut of the horizontal well increase dramatically after water breakthrough, which affected horizontal well development seriously (Souza A L S. 1997).

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