Abstract: The replacing front generated in the process of gas injection production is a mutant interface alternating oil and gas,in mathematics,it is a discontinuous interface.The conventional Muskat fractal phase flowing model is suitable only to the reservoir with continuous media,according to the replacement phenomena in capillary while gas replacement,the gas out put through the front interface is divided into two parts,i.e.the flow rate generated by gas replacing oil and gas replacing gas,taking micro-flow element as object,the flow model with the style of variance is set up.Case study shows the saturation distribution of gas injection expected with the weighting model of fractal phase replacement is more reasonable.

Key words: gas injection production, replacement front, discontinue, flow model