Issues

The Chang 7-1 sandstone members of the Triassic Yanchang Group in the Longdong region of the SW Ordos Basin are typical ultra-low-permeability reservoirs which are studied in detail in Tan et al. (2017 Petroleum Geoscience, 23, 454–465). This SEM image taken from a core sample in the Chang 7-1 section illustrates grain coating and pore-throat blockage by iron, calcite and dolomite cementation, which reduces both porosity and permeability.