Abstract: The Upper Paleozoic tight sandstone reservoirs in the Linxing area of the Ordos Basin show various rock and mineral compositions, complex pore structures, and high clay mineral contents, which directly affect the reservoir engineering and development. Based on X-ray diffraction, casting thin sections, gas porosity and permeability test, mercury intrusion porosimetry and sensitivity experiments, the reservoir sensitivity and its influencing factors were systematically investigated. The results show that the sandstones in the study area are of high contents of fragment quartz and lithic, while the feldspar content is low. The sandstones consist mainly of lithic, lithic quartz, feldspar lithic, and quartz sandstones. Clay minerals are mainly of illite, kaolinite, chlorite and illite/smectite (I/S)
mixed layer. The reservoir properties are of low porosity and permeability, with poor pore structure. The sandstones of Taiyuan Formation show the strongest velocity sensitivity, while the Shanxi Formation sandstones are of the weakest, positively correlated with illite and chlorite content, while negatively correlated with kaolinite content. As for water sensitivity, the Xiashihezi Formation sandstones are the strongest while the Taiyuan Formation sandstones are the weakest, which are positively correlated with the I/S contents. The salt sensitivity is similar to water sensitivity, showing a positive correlation with I/S contents. The acid sensitivity of the Shanxi Formation sandstones is the strongest while the Xiashihezi Formation sandstones is the weakest, which is positively correlated with the contents of chlorite and ankerite. The alkali sensitivity is strong in the Shanxi Formation sandstones and weak in Taiyuan Formation sandstones, being associated with the contents of feldspar, quartz, and kaolinite. The results are helpful in guiding well drilling, fracturing and reservoir engineering processes, and also gas drainage controls.

Key words: tight sandstone gas, sensitivity, diagenesis, clay minerals, pore structure