Abstract: Re fracturing is an important stimulation for low permeability reservoir. stress field induced by existed fractures and oil production in SN Oilfield is simulated in this paper, it is proven that the azimuth of new fractures created by refracturing will be different from that of existed fractures on the base of principle of minimum principal stress. Then, according to theory of orthogonal design, simulator of fractured well production performance is used to analyze such factors affecting the oil production as formation pressure, current water cut, permeability and porosity, fracturing scale and conductivity on re fracturing effect, depending on the NPV criteria, conditions of refracturing are determined, moreover, the best time of re fracturing of SN oilfield is determined, effective thickness greater than 5m, pressure coefficient greater than 0.5，permeability greater than 1.0×10^-3μm², current water cut less than 60%。Fracture length should be controlled within 90~120m and sand ratio at 30% application effect is good.

Key words: re fracturing, fracture propagation, fracturing conditions, SN Oilfield