[Objective]The paleokarst reservoirs of the Sinian Dengying Formation in the central Sichuan Basin are key targets for marine natural gas exploration in China,characterized by long diagenetic history,multiple diagenetic events,and strong heterogeneity.These characteristics lead to the complexity of oil and gas accumulation results,which restricts the next large-scale exploration and development.[Methods]By diagenetic mineral sequences,U-Pb isotope dating and laser in-situ element measurement in the Dengying Formation paleokarst reservoirs,combined with physical property testing of cores and image software identification,reservoir type,diagenetic sequence,reservoir-forming and hydrocarbon accumulation effect are determined.[Results]Two-types reservoir are identified in the 2nd and 4th members of the Dengying Formation:a fracture-vug type and a pore-vug type.Nine-stages diagenesis-hydrocarbon accumulation events were identified.The diagenetic fluids were of three types:seawater,modified sea-water and hydrothermal.Multi-stage diagenetic events including three-stages seawater cementation(606±21 Ma,604±42 Ma and 590±15 Ma)and three-stages hydrothermal activity(403±30 Ma,259.4±3 Ma and 199±12 Ma)had destructive effects on reservoir physical properties.[Conclusions]Reconstructed paleoporosity for the period of diagenetic evolution indicate that the fracture-vug type of reservoirs in the 2nd member of the Dengying Formation always enabled hydrocarbon migration and accumulation during the formation stage of paleo-oil reservoirs,also during the stage of crude oil cracking into gas and during the stage of gas reservoir adjustment.Pore-vug type reservoirs allowed migration and accumulation only in the latter two stages.In the 4th member,fracture-vug reservoirs enabled migration and accumulation in all three stages of hydrocarbon accumulation.
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