| The Qiangtang Basin, located in the eastern part of the Tethys domain, is the only large-scale superimposed basin
in China where no industrial oil or gas fields have been discovered. Based on the new round of comprehensive research on oil
and gas geology in recent years, a set of widely distributed black mudstone with large thickness (600-800 m) of Bagong
Formation is found being developed in the front delta-shallow water shelf during the foreland basin stage of Late Triassic
in Qiangtang Basin, which is of great significance for oil and gas exploration. In order to study the organic geochemical
characteristics of the black mudstone of Bagong Formation in the eastern margin of the North Qiangtang Depression, 61
core samples from shallow well and 64 hand-drilled plunger samples are collected to carry out geochemical and
mineralogical analysis, and the source rock potential and sedimentary environment are evaluated. The results show that:
(1) The black mudstone of the Bagong Formation, with TOC of 0.06%-5.81%, is poor-medium source rock on the whole,
and some reach the standard of high-quality. Formed in weak oxidation-weak reduction environment, the organic matter
type is II2―III, mainly belonging mixed organic matter. It is in the late mature to high mature stage with Ro of 0.95%-
1.90%. (2) The Bagong source rock has great hydrocarbon generation potential, due to high organic matter abundance,
good organic matter type, and moderate maturity. (3) There developed a source-reservoir assemblage of “lower generation
and upper reservoir” between the Bagong source rock and the glutenite reservoir at the bottom of the Quemocuo
Formation, which lays a foundation for the formation of large and medium-size oil and gas fields. Besides, the Bagong
mudstone is a favorable layer for shale oil exploration. In general, the Bagong source rock is of great significance for
conventional and unconventional oil and gas exploration in the eastern margin of the North Qiangtang Depression. |
