Abstract: In order to study the effects of threshold pressure gradient at low-velocity gas flow in shale matrix on well test curves, and to overcome the difficulties of coupling of flow mechanism of shale gas, a new cylindrical triple-porosity shale matrix model was proposed. Combined with the five-region flow model, a new linear seepage model characterizing flow process of multifractured horizontal wells was established. Laplace transformation and Green function were employed to solve the model, and the Stehfest numerical inversion algorithm was applied to plot dimensionless pseudo-pressure curves and conduct sensitivity analysis. The results show that pressure response curves of the new model could be divided into 7 periods and the threshold pressure gradient conspicuously affects the middle and later periods. The lager the threshold pressure gradient is, the larger seepage resistance is, and the higher pseudo-pressure and its derivative are. The smaller the matrix permeability is, the more difficult it is for transition flow from matrix to fractures, and the later the boundary control flow occurs.

Key words: shale gas, fractured horizontal well, triple-porosity shale matrix, threshold pressure gradient, pressure response