Abstract:

The Meso Cenozoic Qaidam basin has experienced four evolution stages including the Early to Middle Jurassic chasmic stage, the Late Jurassic to Cretaceous compression stage, the Early Tertiary (Lulehe age) to Late Pliocene (Shangyoushashan age) regional compressive downwarping and local strike slipping and squeezing out stage, as well as the Late Pliocene (Shizigou age) to Quaternary compressive napping stage. The Middle and Lower Jurassic source rocks were deposited in the northern edge of Qaidam basin during the chasmic stage. The Tertiary source rocks were deposited while the massive deppression developed in western basin during the compressive downwarping stage. The Quaternary source rocks were deposited in the Quaternary depression in eastern basin along with the uplifting of western basin and the strong subsidence of eastern basin during the compressive napping stage. Fault and fold structures are well developed in Qaidam basin. Structural reservoirs are the main reservoir types, of which anticlinal and fault nose reservoirs are mainly distributed in Mangya sag in western basin, while the fault-related fault nose and fault block reservoirs are mainly distributed in the downfaulted area in the northern edge of Qaidam basin. The discovery of bubble inclusions in the Tertiary indicates that pulse-migration of hydrocarbons under faulting is an important mode of reservoiring in Qaidam basin.

Key words: Qaidam basin, Meso Cenozoic, basin evolution, hydrocarbon accumulation