Abstract: By systematic analysis of Decan-1 Well is systematically analyzed integrated with information from the field outcrop reviews and the seismic prospecting, the hydrocarbon and accumulation of Delingha fault depression in Qaidam basin is studied. It is proved that the oil and gas in Decan-1 Well was originated from the underlying Middle-Lower Jurassic or Carboniferous, and the N₁ to the upper E₃ are the regional cap formation in depth of 3 000~3 860 m, but it is hard to form oil-gas pools in overlying strata due to lack of effective caprocks. Hence, the petroleum exploration targets should be in the underlying Middle-Lower E₃ and Jurassic beds. The core analysis from depth of 4 000 m indicates that the sandstone reservoir is of better quality with porosity-developed sandstone, good storage capability and some asphaltic seepage, showing that petroleum migration had ever happened here. The existence of multi-fractural zones in 3 082~3 487 m suggests that the potential reservoir spaces could be shaped in them. The strata of 4 172~4 380 m is a combination of reservoircap formation of Upper Jurassic, within which natural gas could be found in its sandstone.

Key words: Qaidam basin, Decan-1 Well, caprock, reservoir rock, petrophysical parameter, hydrocarbon migration, hydrocarbon accumulation