鄂尔多斯西南缘下古生界烃源岩生烃潜力评价

鄂尔多斯盆地西南缘早古生代陆缘沉积环境形成了碳酸盐岩和碎屑岩2种岩性的烃源岩。虽然有机质丰度较低,但勘探成果表明下古生界烃源岩曾经有过较高的生烃过程。较好的烃源岩一般发育在弱还原—还原、盐度较大的半深水环境中,多为Ⅰ、Ⅱ型。寒武系烃源岩主要生烃阶段在三叠纪,对现今的资源贡献有限,奥陶系马家沟组、平凉组烃源岩主要生烃阶段有侏罗纪、白垩纪2期。现今奥陶系烃源岩达到了高演化阶段,以马家沟组碳酸盐岩、平凉组暗色泥岩、碳酸盐岩3套烃源岩为主,但存在一定差异。模拟结果表明,下古生界累计生烃量为172.87×1012m3;北段生烃强度最大超过了40×108m3/km2,南缘地区最大为30×108m3/km2左右。 

Hydrocarbon generation potential of lower Paleozoic source rocks in southwestern margin of Ordos Basin

Carbonate and clastic source rocks generated in continental margin environment at the southwestern margin of the Ordos Basin during the early Paleozoic.Explorations proved that the lower Paleozoic source rocks experienced higher hydrocarbon generation even though their organic matter abundance was low.Good source rocks(usually type Ⅰ and Ⅱ) were found in weak-reducing and reducing bathyal environment with high salinity content.Cambrian source rocks generated hydrocarbon during Triassic and had limited contribution to the present reservoirs.The source rocks in Majiagou and Pingliang Formations of Ordovician generated hydrocarbon during Jurassic and Cretaceous.Ordovician source rocks are in high evolution stage,represented by the carbonate rocks in Majiagou Formation as well as the dark mudstones and carbonate rocks in Pingliang Formation.The hydrocarbon generation quantity of the lower Paleozoic is 172.87×1012 m3,while in the north it exceeds 40×108 m3/km2,and in the south it amounts to 30×108 m3/km2.