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An experimental investigation of existing conditions of the threshold pressure gradient (TPG) for gas flow in waterbearing tight gas reservoirs was made and discussed, using cores at different water saturations prepared from the Sichuan gas field in China. The existence of TPG was proven, and the relationship between TPG and water saturation and absolute permeability were obtained by laboratory tests. TPG increases with higher water saturation and lower absolute permeability. Consequently, a mathematical model of low-velocity non-Darcy gas flow was established on the basis of conservation of mass and momentum equations. According to the analytical solution of non-Darcy radial flow derived here, an easy and accurate calculation method of the control radius is presented, which is most popular with reservoir engineers. Factors, such as TPG and isothermal compressibility, on effective deployment were also discussed. The analysis of calculation results demonstrates that peripheral reserves of the wellbore are difficult to deploy and formation energy is used mainly near the wellbore because of the existence of TPG, unlike in Darcy flow. The quantification of effective deployment of water-bearing tight gas reservoirs provides a theoretical foundation for reservoir evaluation and development design.

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