Abstract: In this paper, considering the high mobility, fluid flow in cavity-fractur reservoir is assumed as pseudo-steady state flowing .Firstly, two flow models are set up separately for the reservoirs with one and two bulk, then Laplace transfer and inverse transfer are used to obtain the solutions in real space of the two models. In the log-log plot，both the pressure and pressure derivative curves of the reservoir with only one bulk show straight line segments no matter at early time or late time, which are similar to those of the single well in a homogeneous formation with a closed circle boundary. As the reservoirs with two bulks, the pressure derivative curve of two bulk system is shown as an parabolic profile with downward mouth in early period ,which is similar to that of the double porosity model. That is to say the derivative plot shows a "minimum" or a "dip" on the pressure derivative curve caused by the "inter-porosity" flow during the transition period. But the pressure derivative curve at late period shows a slanted line segment which is different from a horizontal line segment of the general double porosity model. The pressures difference plots at early period and late period are also both straight lines in the log-log coordinates. Finally, the new well-test model is used to analyze one well test data in Tahe Reservoir and the explanation of welltest keeps the same with the result of geologic model.

Key words: cavity, fracture, big size, well test explain, pseudo steady state, model