Permeability Gas Reservoir Hydrodynamic Experimental Study

There is an intricate phenomenon that the content of primary water is high in sandstone gas reservoir with low-permeability, but several gas wells can produce water. Practically representative low-permeability cores are sampled to determine irreducible water saturation by centrifugal capillary pressure method and gas drive water dynamic method and Nuclear magnetic resonance (NMR) method, and then determine movable water saturation. From the principle of centrifugal capillary pressure method and gas drive water dynamic method, it can be seen that the flow of fluids in stratum is dominated by capillary pressure. Oil and water can flow as long as the pressure is bigger than such capillary pressure. Nuclear magnetic resonance (NMR) method can determine movable water saturation according to relaxation time table, T₂.From the test results of capillary pressure curve, it is shown that Shanxi Formation and Taiyuan Formation of Daniudi gas field are provided with high drainage pressure and capillary median pressure, small pore throat occupying much space, and poor structure. But Qiao-Bai gas reservoir is better than Daniudi gas filed. From nuclear magnetic resonance measurement test, it is can be seen that pore structure of Qiao-Bai gas reservoir is better, the percents of movable fluid saturation. As far as the cores in different region with different character are concerned, percents of movable fluid have not pertinences with porosity and permeability. Even if the cores are approach in porosity and permeability, there are great differences with the percents of movable fluid, which is related to pore structure. But with the increase of porosity and permeability, the trend of movable fluid saturation is to increase.With different measure condition, there is difference between irreduciblewater saturation determined by centrifugal method and that by NMR, which just showirreducible water is rate-sensitive. It is proved in Gas drive water experimentthat with the increase of airflow velocity, water saturation of cores is dropping,and gaseous relative permeability is increasing. This viewpoint indicates thatrreducible water saturation in gas layer is a physical quantity related to gaseousrelative permeability, and explains the reason why near-well-bore permeabilityin low-permeability sandstone reservoir increases, and primary water saturationis lower than conventional irreducible water saturation, but water can flow yet.ombined with log interpretation primary water saturation, it is shown that primarywater saturation is higher in Qiao-Bai gas reservoir, and irreducible water saturation is lower determined by centrifugal method and NMR, so it is likely to producing water when developed with a large pressure difference. The study results have direct guidance significance for developing other low-permeability gas reservoir.