UPPER TRIASSIC POTENTIAL SOURCE ROCKS IN THE QIANGTANG
Y. H. Zeng1,2, X. G. Fu1,2*, S. Q. Zeng1 and G. Du1,2
2 Key Laboratory for Sedimentary Basin and Oil and Gas Resources,
Ministry of Land and Resources,
* Corresponding author, email: email@example.com
Upper Triassic coal-bearing strata in the
At Quemo Co in the NE of the basin, calcareous shale samples from the Tumengela Formation have total organic carbon (TOC) contents of up to 1.66 wt.%, chloroform bitumen A contents of up to 734 ppm, and a hydrocarbon generation capacity (Rock-Eval S1 + S2) of up to1.94 mg/g. The shales have moderate to good source rock potential. Vitrinite reflectance (Rr) values of 1.30% to 1.46%, and Rock-Eval Tmax values of 464 to 475 oC indicate that the organic matter is at a highly mature stage corresponding to condensate / wet gas generation. The shales contain Type II kerogen, and have low carbon number molecular compositions with relatively high C21-/C21+ (2.15–2.93), Pr/Ph ratios of 1.40-1.72, high S/C ratios (>0.04) in some samples, abundant gammacerane (GI of 0.50-2.04) and a predominance of C27 steranes, indicating shallow-marine sub-anoxic and hypersaline depositional conditions with some input of terrestrial organic matter.
Tumengela and Zangxiahe Formation mudstone samples from Xiaochaka in the southern Qiangtang depression, and from Woruo Mountain and Zangxiahe in the northern depression, have low contents of marine organic matter (Type II kerogen), indicating relatively poor hydrocarbon generation potential. Rr values and Tmax data indicate that the organic matter is overmature corresponding to dry gas generation.
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