P8-MO IDENTIFICATION OF POTENTIAL SOURCE ROCKS OF BIOGENIC GAS BY BIOMARKERS OF BACTERIA ACTIVITY IN THE QUATERNARY OF THE

Quaternary gas resource of the Qaidam Basin is enriched in the central and eastern part of the basin in the three lakes area. The proved and controlled Quaternary biogenic gas reserves of the basin have reached 290 billion cubic meters (BCM) (Dang et al, 2004). Up to now, the identification of the biogenic gas source beds in the Qaidam Basin is still a matter needing to be settled. Of the 44 core rock samples of Quaternary in the depth of 540m to 1536m from the Sebei No.1 gas field of the Qaidam Basin, the contents of TOC range from 0.10 % to 19.88%, with the majority of them range from 0.20 % to 0.30%; the contents of chloroform asphalt “A” range from 0.0017 % to 0.2294%, mostly lower than 0.01%, and the contents of total hydrocarbons range from 0.0003 % to 0.1218%, mostly lower than 0.005%. The abundance of the acyclic isoprenoid alkanes, especially pristane and phytane are high in the 17 analyzed samples, and the Pr/Ph ratios range from 0.10 to 0.68, with very high predominance of phytane; the nC21-/nC22+ ratios are lower than 1 for most of the samples, indicating that the depositional environment of the Quaternary in the Sebei No.1 gas field tend to be brackish to saline water environment, and the input of organic materials from higher plants are larger tha