Abstract: Xin4-6 region in Daqing oilfield has undergone three infill development processes since 1967. The production performance data from these infill processes are analyzed followed by proposing a practical method for evaluation of enhanced oil recovery (EOR) from infill wells. The technical EOR from them is 40.1%, 53.0% and 57.8%, respectively. In microscopic and macroscopic aspects, the original formula of Selkachev's network density method is deduced. Using the data from five oilfields in Daqing (Xin4-6 region), Romashikino, Dumaz, Bovilin and East-Texas, a new relative empirical formula for determination of EOR of waterflooding oilfield and well-controlled area is established. The mobility and well-controlled area in Xin4-6 region are substituted into this formula, the primary infilled recovery efficiency equals to 38.7%, which is close to that given by production decline method (40.1%), showing the reliability or practicability of the relative empirical formula.

Key words: waterflooding, development, infill well, recoverable reserve, recovery efficiency, EOR