1. Key Laboratory of Compact Oil and Mudstone Oil Reservoir Formation Research in Heilongjiang Province, Daqing 163712, Heilongjiang, China;
2. Exploration and Development Research Institute of Daqing Oilfield Company Ltd., Daqing 163712, Heilongjiang, China

Nantun Formation is an important exploration target in Beizhong sub-sag, with volcanic clastic rocks developed in its reservoirs. The diagenesis characteristics and the main controlling factors of high-quality reservoirs of Nantun Formation were systematically analyzed using ordinary thin sections, cast thin sections, scanning electron microscopy, X-ray diffraction and alizarin red staining. The reservoir rock consists of tuff, sediment-tuff, tuff sandstone and sandstone. The reservoir has experienced strong diagenesis, which is defined as mid-diagenetic stage A through comprehensive analysis of organic matter maturity, clay mineral combination and autogenic mineral assemblage. Three types of diagenetic facies (compaction facies, cementation facies and dissolution facies) have been identified in Nantun Formation based on the main diagenesis and its strength, which affect the reservoir physical properties. Among which the dissolution facies is most favorable for the development of storage space. The main controlling factors of high-quality reservoirs include:��dominant sedimentary facies-the fan delta front; ��dissolution, which improves storage performance, including dissolution of feldspar, rock debris, calcite and tuff cement, of which the dissolution of tuff cement is most critical.