Abstract:

Narengele drainage system,originated from Kunlun mountains in eastern Qaidam basin,has formed Na-Tuo groundwater circulation system in Pliocene and Pleistocene periods in Wutumeiren,east to Tainan,Sebei and Tuofengshan areas;and on its both sides,Dabuxun Lake subsag and Yiliping subsag are catchment basins characterized by stagnant hydrogeology.The formation water within the control area of Na-Tuo grounderwater circulation system to the south of Tainan structure,was distinctly salinized in the later period of late Pleistocene (about 30ka).The formation water was basically saturated with dissolved gas at that time.The reservoiring mechanism of biogenic includes two models:(1)during the distinct salinization of formation water,dissolved gas was released from the water,and then migrated, accumulated and finally became gas reservoirs;(2)the Na-Tuo groundwater circulation system,carrying the biogenic gas dissolved in the formation water with relatively low salinity in the south,migrated northward to the saline water area where the gas was then released,accumulated and became gas reservoirs.According to the characteristics of hydrogeology and petroleum system, the most favorable area for the enrichment of the Quaternary biogenic gas has been determined to be in eastern Chuanxingqiu structure-Yanan-Tainan-Sebei area,the relatively favorable area occur on both sides,north and south of the above-mentioned area and Tuofeng mountains-Yanhu and on the slope of Biele lake;the favorable belt for the enrichment of the Tertiary biogenic gas would occur in Chuanxingqiu-Yanan-Nanlingqiu-Yanhu structural belt.

Key words: Qaidam basin, eastern part, formation water, hydrogeology, biogenic gas, dissolved gas, reservoiring