Reservoir of Es3-I in JZ25-1S oilfield in Bohai bay is a fault type characterizing in big gas cap, narrow oil rim and edge water. The main development problem in gas cap reservoir with vertical wells is coning from gas cap, which causes the oil wells ring gas channeling and seriously affects well productivity. Faced with a number of negative factors and aimed at low development degree of vertical wells, researchers present development from horizontal wells and apply a pilot test and numerical simulation to demonstrate the adaptability. Compared with vertical wells, some obvious advantages of horizontal wells can be demonstrated by deliverability, individual-well controlled reserves, and final development efficiency. The orientation, vertical location, trajectory and length of horizontal wells and production speed in the study areas were also optimally designed. In this optimal design, the length of horizontal segment should be 400 meters; while the vertical distance between the WOC should be a third, and conversely, two-third between the GOC. The horizontal well technology is proved to be helpful for the economic and high efficiency development in Es3-I oilfield. It is showed by the mining practice of horizontal well technology in seven horizontal wells located in the gas cap of JZ25-1S oilfield Es3-I reservoir that the application is good and the daily oil production of the single well is high, from 150 to 300 m3/d. It is proved that there is great potential of the horizontal well in development of the reservoirs with big gas cap and narrow oil rim, which can significantly increase the economic benefits of offshore oil fields and provides a reference for the development of other similar reservoirs.
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