Abstract:

Exploration practices and researches show that hydrocarbon in the source rocks of the Lucaogou Formation of the Permian, Malang sag was shale oil and also a typical low-mature oil with both sterane isomerization parameters (20S/(20S+20R) and ββ/(αα+ββ)) between 0.2 and 0.4. Through comprehensive study of geochemical and organic petrology characteristics in the hydrocarbon source rock of Lucaogou Formation, we find that the parent material of this low-mature shale oil was hydrogen-rich amorphous solid and experienced the bacteria transformation in the early sedimentary stage, which resulted in the formation of the particular hydrocarbon-generating evolution model. Namely, during the low-mature and early mature stage with R_o values 0.55%-0.75%, there is an oil generation peak whose burial depth ranges from 1 800 to 2 900 m, and the hydrocarbon-generating potential of source rock drops sharply beyond the main hydrocarbon-generating zone. The results of hydrocarbon-generating simulation experiments, rock pyrolysis analysis and organic extraction of mudstone prove that the low-mature shale oil in Lucaogou Formation was generated by the hydrocarbon source rocks within the range of main hydrocarbon-generating zone, where was the beneficial places of shale oil accumulation.

Key words: low-mature oil, shale oil, main hydrocarbon-generating zone, hydrogen-rich amorphous solid, geochemistry