Genetic mechanisms of low-permeability clastic reservoirs include many controlling factors, such as low-permeability reservoir properties and a matching relationship between the reservoir compaction history and the hydrocarbon accumulation history. Currently, studies on the controlling factors of low-permeability reservoir properties have been relatively mature, while the matching relationship between the reservoir compaction history and the hydrocarbon accumulation history has been less studied. Therefore, we studied the Lower Cretaceous Qingshuihe Formation low-permeability reservoirs of the Beisantai area, Junggar Basin by means of core observation, thin section identification, image analysis, scanning electron microscopy observation, mercury penetration, petrophysical property testing and other technical methods. The result showed that the low-permeability reservoirs are characterized of being controlled by deposition, predominated by compaction, improved by dissolution and enhanced by cementation. Confined by “reservoir diagenesis evolutionary sequence and reservoir pore structure” conditions, physical properties of sandy-fine conglomerate, fine sandstone, siltstone and argillaceous siltstone reservoirs in geological history were restored, respectively, and the geological time when reservoirs with different lithology in different zones form low-permeability properties was determined based on the reservoir property evolutionary history. Genetic mechanisms of the Qingshuihe Formation low-permeability reservoirs were investigated in combination with the reservoir property evolutionary history, hydrocarbon accumulation history and distribution features of crude oils. The results showed that there exist three different genetic types of reservoirs in the Qingshuihe Formation. Type Ⅰ had medium permeability in the hydrocarbon accumulation period and remains in this permeability now. Type Ⅱ had medium permeability in the hydrocarbon accumulation period and shows low (extra- or super-low) permeability now. Type Ⅲ had low (extra- or super-low) permeability in the hydrocarbon accumulation period and remains in the permeability now. Moreover, type Ⅱ can be subdivided into two sub-types and type Ⅲ into four sub-types. Integrated with reservoir physical properties in the hydrocarbon accumulation period, oil-bearing grades of reservoirs, characteristics of crude oils and oil testing results, we analyzed the exploration potential of different genetic types of reservoirs before drilling, and optimized effective development and stimulation methods.
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