In Dawanqi oil/gas pool in Kuqa depression

Tarim basin

the enrichment of

38

Ar was related to the migration of anoxic fluids and volatile constituents along large faults.Tuzimazha fault is the major pathway

through which

38

Ar generated from fluid activities would have migrated to the oil and gas reservoirs.The low concentration of

38

Ar in Dabei reservoir reveals that gas would have been reservoired near the source rocks.Dawanqi oil/gas field is not an oil/gas pool as a result of later gas invasion

but is a primary oil/gas pool.The light components of gas partially dispersed along the fault due to the poor sealing ability of the trap at later reservoiring stage

leading to the formation of the current condensate gas reservoir with relatively low saturation.Hydrocarbons were generated from the Triassic and Jurassic major source rocks below

and were accumulated in the reservoir rocks above

i.e.

hydrocarbons have been generated from the organic matters in the Mesozoic fresh lake facies sediments during mature to high-mature evolutional phases.During the reseroviring process of Dawanqi oil/gas pool

hydrocarbons first migrated upward along Tuzimazha fault

and then entered Dawanqi structure from north to south.Dawanqi oil/gas pool has experienced early and late charging processes.The high-mature to over-mature natural gas charged in later stage would have mainly accumulated in the upper part

due to their relatively low density;while the relatively high density natural gas generated in early stage would have accumulated in the lower part.