Abstract: For many reasons, there is gate pressure gradient problem in the low permeability reservoirs, i.e. only the reservoir pressure gradient is larger than the gate pressure gradient, can the fluid flow in the porous media. Because of the existence of gate pressure gradient, the flow rate will decrease at the same production pressure drop. Generally speaking, in order to increasing deliverability of low permeability reservoirs, larger scale acid or hydraulic fracture activities is needed to increase permeability near the wellbore and to overcome the influence of gate pressure gradient. Based on this realization, a new, composite flow model is developed in the present work. The model is composite in that the flow near the wellbore is treated as Darcy flow in
double porosity media while the flow farther away from the wellbore is considered as low-velocity non-Darcy flow with gate pressure gradient problem. The solution of this composite model is derived, the transient pressure behavior is analyzed,and the type curves of well test are presented.

Key words: low permeability reservoir, acidizing, fracturing, non-Darcy flow, well test interpretation, composite flow model