DUAN Jingjie;LI Pei;CHEN Fangping;WANG Min;SHI Bin;DING Lei
Yanchang Oil Field is located in the Loess Plateau, where the water resource is deficient and the ground conditions are hostile. In the oil field, waterflood had not been implemented and the well pattern was very irregular in the early development stage. In the recent years, for the efficient development of oil resources, a remedial waterflooding development mode has been implemented. The analysis on oil production, water cut, formation pressure, injection pressure, injection production ratio, and recovery is very important. The waterflood characteristics of Yanchang low permeability reservoirs are analyzed and studied in details and the waterflooding development effect and its influence factors are evaluated based on the waterflood practices of three major reservoirs in Yanchang Oil Field in order to provide the theoretical guidance for the efficient waterflooding development of Yanchang Oil Field. Different reservoir properties show different waterflooding development characteristics and need different waterflood policies. For the bottom water reservoirs of Yan'an formation. and the Chang 2 reservoirs of Yanchang formation. with weak bottom water development, the physical reservoir properties are relatively good with the permeability range of 2.0×10-3-80×10-3μm2, under the conditions of mild waterflood, the movement of reservoir fluid is mainly percolation among pores, all directions receive injected water evenly and the original irregular well pattern is basically suitable. Chang 6 reservoir of Yanchang Fm. is a fractured lithologic reservoir with poor physical properties, e.g. the permeability is of 0.3×10-3-2.0×10-3μm2, the waterflooding development is significantly impacted by the fracture directions and sand body distribution directions. The waterflood adaptability for the original irregular well pattern of the oil field is poor due to rapid increase of directional water cut and difficulties in late-stage adjustment. In addition, the strengthened waterflood mode along fractures is difficult to be implemented in the old well areas as well. It is concluded that for the irregular well pattern of Chang 6 reservoir, the measurement involving conventional water plugging and profile control would be an effective way to improve the waterflooding development effect. At the same time, a waterflooding development mode idea for increasing the amount of water injection wells and controlling the injection rate of each injection well is proposed. In addition, based on the features of Chang 6 reservoir, that is, there are many small vertically layers, the necessity for separate-zone water injection is put forward.
