Discovery of Carboniferous Oil Seepage in Qaidam Basin and Its Geological Significance

摘要

In this work, the oil seepage was found in calcite veins in Keluke formation of upper Carboniferous reservoirs. Based on the analysis of geochemical characteristics, the isomerization parameter of C-29 sterane 20S/(20S + 20R) was obtained as 0.39 and Ts/Tm value as 1.12, indicating that the oil seepage was mature. The Pr/Ph value was 0.64 and the tricyclic terpane was characterized by high abundance of gamacerane, C-27 > C-29 sterane, and a normal distribution with C-23 as the dominant peak. Moreover, the oil/oil and oil/source rock correlation of oil seepage and carboniferous source rock underground and surface indicated that the oil seepage was similar to crude in Mabei-2 well (1463m) and Sin-3 well (1076m) but was different from the other crude in north Qaidam basin. It is inferred that the oil seepage was authigenic crude in Carboniferous, and Carboniferous source rocks have contributed to the oils in Mabei-2 well (1463m) and Sin-3 well (1076m). This study offers new scientific evidence for the exploring of carboniferous in Qiandam basin.