Characteristics of stratigraphy and oil—gas reservoir types in Langgu—Dachang sag

As a half-graben down-faulted lake basin formed in the post plaeogene,controlled by the tectonic movement,the fracture system of Langgu-Dachang sag is complicated. The development of the lake basin played a decisive role in the deposit stratum.Shahejie Formation is the major oil con- tainer layer.Because of the structure,the lithology,the stratum and other factors,various types of oil-gas reser- voirs were formed in the study area.They are structural res- ervoirs,stratigraphic reservoirs,lithological reservoirs, palaeo-buried hill reservoirs and combination reservoirs. The structural reservoirs including the fault block reservoirs, the fault-nose reservoirs and the anticline reservoirs are the main oil-gas reservoirs of the study area.