Abstract
Most of oil fields in China have stepped into the middle or later stage of waterflooding life, and oil wells begin to appear above water. In conventional acid treatment, acid fluid always flows into the pore path with high water saturation firstly, and broadens the pore path filled with water. However, it can't stimulate the pore path filled with oil as well as that filled with water. To solve this problem, especially in heterogeneous formation, this paper indicates a novel selective emulsified acid system, of which viscosity will increase when meets water and decrease when meets oil in the formation. The core flooding experiment shows that the average permeability increment of cores saturated by oil reaches to 96.1% after treated by this acid system, while the average increment of cores saturated by water is only 10.1%. The novel selective emulsified acid system behaves good retarded and protective capability to the formation. This acid system has been applied on thirteen wells in Gasikule oil field in Qinghai with remarkable results achieved. After the treatment of the new selective emulsified acid, the daily average incremental oil production of single well reachedes to 8.5t, and the water cut decreased by 3.5%. Experimental study and field applications indicate the new emulsified acid system has an excellent ability to acidify the formation selectively.
