Hydrocarbon accumulation mechanism near top overpressured surface in central Junggar Basin

Key words:  hydrocarbon accumulation mechanism  top overpressured surface  strong overpressured sedimentary clastic basin  Junggar Basin

Abstract:

Geochemistry, reservoir, drilling and geophysical features were investigated in the limited zones near the top overpressured surface in central Junggar basin, and the accumulation mechanism were analyzed. The results show that source rocks are in the overpressured compartment, thus the top overpressured surface is both tight lithostatic and unpermeable seal surface and balance surface of hydrocarbon migration near the top overpressured surface in central Junggar Basin, probably a hydrocarbon originated and post diagenesis stage overpressured basin. The thermal evolution of source rocks, the spatial composition of the transportation pathways, the evolution of the overpressure, the characteristics of the top overpressured seal, and the types and distributions of the advantageous traps and reservoirs, are all the controlling factors of the hydrocarbon accumulation processes and the hydrocarbon accumulation areas distribution near the top overpressured surface in central Junggar Basin. Closely related with the overpressure evolution, the Jurassic traps near the top overpressured surface in central Junggar Basin underwent two stages of hydrocarbon accumulation, and the late stage accumulation includes two main charging. As a result, the traps near the overpressured fluid focus releasing areas, and the advantageous traps in the overpressured compartment, are the advantageous exploration targets near the top overoressured surface in central Junggar Basin.