Geochemistry of hydrocarbon source rocks in the Liupanshan basin at the northeastern margin of the Qinghai-Tibet Plateau

The authors have evaluated and analyzed hydrocarbon source rocks in the Liupanshan basin on the basis of previous knowledge and recent exploration results and found that among the three sequences of relatively unequivocal major hydrocarbon source rocks the source rocks of the Lower Cretaceous Naijiahe, Madongshan and Liwaxia formations are relatively widely distributed in the basin. Most of them have tended to be mature except in areas in the northern part where the source rocks are shallow-buried. The Carboniferous hydrocarbon source rocks are also important. Because they are deep-buried and have been subjected to significant late-stage modification, they should serve as the target for gas exploration. Triassic hydrocarbon source rocks have a high degree of maturity but are of limited distribution; so their potential of exploration is affected. Many oil-gas shows and features of surface response to oil-gas anomalies in the basin fully demonstrate that there was a process of hydrocarbon generation, migration and accumulation in the basin. The response features of petroleum geochemical anomalies in the whole basin are conspicuous and oil-gas seepages are abundant and widespread. Geochemical exploration has reveals three nearly E-W-trending petroleum geochemical anomaly areas (zones) in the basin. On the basis of the 3D fluorescence spectra, discrimination of the attributes of oil and gas had been made. All of them have the geochemical properties of light oil.