In this paper,we first understood the unique flow behaviors in gas shale formation with a focus on the physics of multi-transport mechanisms,and gas adsorption and desorption,gave mathematical expression of b/p in Klinkenberg apparent permeability correlation based on Knudsen number and μ/p in an isothermal shale-reservoir system,then developed fully implicit numerical simulation model using PEBI gridding,and finally conducted parametric studies to quantify the transient pressure behaviors for flow in shale.Our conclusions could be summarized as below.With effect of the gas desorption,the drawdown pressure has a seeming singular point.When the ultimate adsorption capacity(UAC)is bigger,the singular points of the pressure are more obvious,which is different from performance of the well in conventional reservoir.Our explanation is that the desorbed gas helps slow down the rate of pressure drop.The angle at the seeming singular point is determined by the UAC,and the position of the seeming singular point is mainly determined by the permeability,which can help us to interpret the UAC and intrinsic permeability.Of course,in a very short time,the interpretation is not unique.At least it provides an economic and quick way to approximately estimate the UAC and intrinsic permeability.The porosity slightly affects seeming singular point.The buildup period of shale gas wells seems shorter than that of a conventional system due to gas adsorption after the well shut-in.The adsorbed gas slows down the pressure increase.The new understanding in this work helps us understand pressure transient behaviors and develop new methods for pressure analysis in shale gas reservoirs.However,this paper just studies the transient pressure response numerically.We need to do further work to develop the interpretation method based on the field data or experimental data in the future.