Tight sand oil reservoirs in China's Ordos Basin have varying qualities due to differences in how they were formed and changed over time. The size of the pores in the rock affects how easily oil can flow through it. Sandstones with larger pores and better connectivity between them are better for oil to accumulate. Certain types of sandstone structures, like parallel layers, are more likely to have good oil-holding spaces. The presence of a mineral called chlorite can help keep the pores open for oil to move through, but too much chlorite can block the pores. Sandstones close to mudstone layers tend to have less space for oil to collect. Overall, the properties of the rock play a big role in how well oil can flow and gather in these tight sand reservoirs.