The study and analysis of starting pressure gradient in low permeability gas reservoirs

In the gas reservoirs with low permeability, whether there is starting pressure gradient or not and the qualification of starting pressure gradient appearance in the gas seepage is always one of the debate focus among the petroleum researchers. This article presents a series of experiments to obtain the qualification of starting pressure gradient appearance in the gas reservoirs with low permeability, and concludes that when the permeability of gas reservoirs is bigger than 0.1×10^-3μm² or the irreducible water saturation is less than 20%, there isn't starting pressure gradient. This paper also presents the formula between the starting pressure gradient and irreducible water saturation.