Research on reservoir evaluation index for low-permeability water-bearing gas reservoir

The features of low-permeability water-bearing gas reservoir were analyzed by using the rate controlled mercury injection, nuclear magnetic resonance and physical simulation technologies.The three parameters of throat radius,irreducible water saturation, critical pressure gradient of low-permeability gas reservoir were regarded as the evaluation indexs for low-permeability water-bearing gas reservoir.The research results show that the pore radius is basically same,but the throat radius is different in the low permea- bility cores with different permeability.The permeability of cores has a high correlation with irreducible water saturation.The irre- ducible water saturation varies with the different proeess of gas drive.When water saturation is very low,gas permeation in low-per- meability cores follows the Darcy flow.When water saturation gets up a certain value,gas permeation in low-permeability cores shows the characteristics of nonlinear flow.The above three parameters have the important significanees to calculate recoverable gas reserves and to research porous flow in the low-permeability water-bearing gas reservoir.These parameters are also favorable to de- sign the developing scheme of gas reservoir.