The secondary porosity is the major porosity type of sandstones reservoirs in the firstmember of the Dainan Formation in the Qintong depression,northern Jiangsu. The distri-bution of the secondary porosity is closely related to oil and gas accumulation. The authorinquires,on the basis of the studies of diagenesis,into the genetic mechanism of the sec-ondary porosity and owes its origin to the dissolution of organic acids. Some speculationsupon the horizontal distribution of the secondary porosity were also made by the author inthe light of organic maturity and compaction anomaly of the mudstones caused by claymineral transformation,thus resulting in the improvement of the knowledge of the distri-bution of the secondary porosity and oil and gas accumulation in different structural zonesin the study area.
secondary porosity, genesis, distribution, first member of the Dainan Formation of the Qintong depression in northern Jiangsu