Fluid charging characteristics and hydrocarbon accumulation process in the Sinian Dengying Formation in Micangshan area
Associated with the new discovery of marine oil and gas in deep and ultra-deep formations,close attention has widely been attached on the high-quality source rock conditions of marine carbonate rocks in Micangshan area in the northern margin of Sichuan Basin.However,there is a lack of clear understanding on the complex hydrocarbon accumulation,transformation and adjustment processes.The scanning electron microscopy,fluid inclusions,U-Pb geochronology and other means are used to study fluid activity and bitumen characteristics in the Sinian Dengying Formation in Micangshan area,so as to identify multi-stage hydrocarbon accumulation,transformation and adjustment processes.Five stages of fluid activities generally occurred in Dengying Formation reservoir in Micangshan area,i.e.,fibrous-fine crystalline dolomite(486 Ma±5 Ma)→ medium-coarse crystalline dolomite(413 Ma±5 Ma)→ saddle dolomite(268 Ma±8 Ma)→ quartz/fluorite/lead-zinc ore(205 Ma±10 Ma)→ bitumen(123 Ma±4 Ma).The lumpy,rim-shaped autochthonous bitumen and brecciated,broken allochthonous bitumen were commonly developed in dissolution pores.The spatial comparison shows that from Micangshan paleo uplift,piedmont zone,to the foreland basin,the bitumen abundance decreases as a whole,the autochthonous bitumen relatively increases and the allochthonous bitumen relatively decreases.The further mineral filling sequence study shows that the low-maturity organic hydrocarbon inclusions were mainly developed in fine and medium-coarse crystalline dolomite in the Late Cambrian-Silurian,while the mineral-captured inclusions such as saddle dolomite in the Middle-Late Permian and quartz in the Late Triassic had a relatively high maturity.In summary,the bitumen and inclusion characteristics show that Micangshan paleo uplift and piedmont zone were the paleo oil and gas accumulation center(gas generation and storage center)in the Permian-Jurassic.The primary oil reservoirs were damaged by late tectonic deformation,and the hydrocarbon migration and accumulation center moved to the foreland basin.
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维普
