Oil and gas reservoirs in western Qaidam basin are often associated with faulted structures. In the southern part of western Qaidam basin

several hydrocarbon accumulation zones are distributed along the faulted zones

such as Shaxi-Gas-Youshashan

Yuejin No. 2-Yuedong and Wunan-Lucaotan hydrocarbon accumulation zones. Structural-stratigraphic-lithologic composite oil and gas reservoirs controlled by faulted nose-like structures are distributed along Chaixi and other faults. in the foothill belt of the Altun Mountain in the west. Structural-fractured reservoirs

including Youquanzi

Kaitemilite

Nanyishan and Jiandingshan

are distributed along Yingbei

Nanyishan and Jiandingshan faults in the north. The formation of faults in western Qaidam basin has been related to the Meso-Cenozoic intense compressional and strike slip movements in Altun and Kunlun mountains. The faults are mainly of reverse and strike slip faults

with a few synsedimentary normal

decolle-ment and reversed faults. The fault trends include mainly NE

NW and nearly N-S. Horizontally

the faults appear as parallel

en echelon

oblique-crossing

orthogonal

reverse"S"

lenticular and divergent fault complexes. Vertically

they are combined in the form of imbricated

thrusted and flower-like fault complexes. The structural reservoirs formed by the thrust type and orthogonal and oblique-crossing fault complexes are best developed. Faults have not only controlled the distribution of hydrocarbon-generating sags and the formation of structural traps

but have also controlled

to a certain extent

the distribution of favorable reservoir facies belts

such as river delta and fan delta facies. Large amount of fractures formed by faulting improve the poroperm characteristics of reservoirs. Laterally connected oil pools

in which hydrocarbons were generated in the source rocks above and migrated through faults and accumulated in the reservoirs below

are common in the southern part of western Oaidam basin.