Abstract: As productivity of mature oilfields lowers and the proportion of reserves in low-permeability reservoirs increases,horizontal-well theory needs to be improved to innovate horizontal well technologies. Beginning with the basic see-page flow theory,this paper reviews different seepage models of horizontal wells at home and abroad.These models are divided into 4 types,including steady state model,pseudo steady state model,unsteady state model and wellbore-reservoir coupled flow models.The applicable conditions as well as advantages and disadvantages of every model are analyzed and evaluated.The results show that the steady state model is of pioneering significance,but their assumptions are too ideal to be in accordance with the actual situations;the pseudo steady state model is simple in forms,but can only describe see-page flow in a short-period;the unsteady state model is universal,but does not take the influences of wellbore flow in near wellbore areas into consideration; the wellbore-reservoir coupled flow model is high in accuracy,but also high in complexity of computation.Based on the study above,the paper presents the trend of seepage model development.Actual parameters will be introduced based on the wellbore-reservoir coupled flow model and will be fitted according the actural conditions.Some of the parameters will be determined to simplify the calculation procedure.Moreover,methods such as tracking streamline and vector well pattern will be incorporated to enrich research tools.

Key words: steady state, unsteady state, pseudo steady state, seepage model, horizontal well, enhanced oil recovery