Study on the comprehensive geochemical cross section of Mesozoic marine source rocks and prediction of favorable hydrocarbon generation area in Qiangtan basin, Tibeta

The comprehensive geochemical cross section in the main structures of the Qiangtang basin was established to evaluate the source rock and predict the favorable hydrocarbon generation areas, based on the data of organic abundance, type and maturity from a large number of outcrop samples in the Mesozoic marine mudstone and carbonate source. The results show that relation between TOC and hydrocarbon potential (S1+S2), chloroform bitumen A and total hydrocarbon content (HC) has good correlation, generally in positive liner, of which in carbonate and oil shale is higher than that in the mudstone and coal, dependent on their lithology to some extent. Subaerial weathering has small impact on organic abundance, but has significant impact on hydrocarbon potential, chloroform bitumen A and total hydrocarbon content (HC). The Mesozoic marine source rocks development varies in different structural unit, for example, carbonate rocks in the Suowa Formation and Delta mudstone in the Xiaochaka Formation of Dirangbicuo-Tumen sag are of good quality source rock. Oil shale and shale in the Xiaochaka Formation of Paducuo-Najiangcuo sag are of extreme good quality source rock, deep water shelf and platform carbonate rock are middle class source rocks. And platform carbonate rock in the Buqu Formation and Suowa Formation buried deep in the Dongcuo-Huluhu and platform carbonate in the Buqu Formation and upper carbonate in Xiaochaka Formation buried deep in the Tupocuo-Baitanhu are middle class quality source rock. Organic matter,is mainly Ⅱ type, with maturity various in different areas, ranging from mature to over-mature, most mature-high mature and increasing from top to bottom in a single cross section. Sedimentary environment is the main controlling factor of source rocks quality. Middle deep marine black shale or mudstone in Upper Triassic Xiaochaka, with wide hydrocarbon generation area, are the most important source rocks. While the still water mud-carbonate rocks in water closed carbonate plateform in the Jurassic Buqu Formation (J2b) and Suowa Formation (J3s) are important source rocks, with wide carbonate hydrocarbon-generation. Further study on the source rock characteristics and major source rock has significance for future oil and gas exploration.