Pore throat characteristics of extra-ultra low permeability sandstone reservoir based on constant-rate mercury penetration technique

Based on constant-rate mercury penetration technique, micro pore throat characteristics of extraultra low permeability sandstone reservoir of the Yangchang Formation in the Ordos Basin were analyzed, and the alterations of pore throat characteristic parameters were also quantitatively characterized. Pore radiuses were similar, usually 100～200 μm, and the peak values were about 140 μm. Compared to those in the extra-low permeability reservoir, distribution ranges of throat in the ultra-low permeability reservoir were narrow. Throats less than 1 μm accounted for large amount, and were more sensitive to permeability. Distribution ranges of pore throat radius ratio were wide and permeability had big influence on input mercury saturation of throat in ultra-low permeability reservoir. The differences of pore throat characteristics between extra-and ultra-low permeability sandstone reservoir mainly lay in throats. 3 variation periods were identified on overall capillary pressure curves. Each period was affected by pore or throat in different extent due to different permeability. Throats should be focused on in the ultra-low permeability reservoir during the middle and latter stages.