四川盆地震旦系-下古生界烃源岩热演化模式及主控因素

Thermal evolution patterns of the Sinian-Lower Paleozoic source rocks in the Sichuan basin,southwest China

烃源岩热演化是含油气盆地烃源岩评价的基本内容之一,也是油气动态成藏研究的基础.通过系统分析地层沉积样式,结合盆地热史恢复结果,应用Easy%Ro化学动力学模型,模拟了四川盆地86口代表性钻井和200余口人工井点震旦系—下古生界烃源岩热演化史.结果表明,在盆地不同构造单元,下寒武统和下志留统烃源岩热演化特征存在明显差异,并据此建立了四种热演化模式:①加里东期成熟,早晚二叠世期间快速演化定型,以川南地区下寒武统烃源岩为代表;②加里东期未熟,早晚二叠世期间一次快速演化定型,以川西南下寒武统和川南下志留统烃源岩为代表;③加里东期成熟,晚海西—燕山期再次增熟,以川东、川北地区下寒武统烃源岩为代表;④加里东期未熟,晚海西—燕山期持续增熟,以川中地区下寒武统和川东、川北下志留统烃源岩为代表.通过对比研究沉积速率、热流和增温速率之间的耦合关系,剖析了四川盆地震旦系—下古生界烃源岩热演化的控制因素,即川西南和川南局部地区主要受控于早晚二叠世期间峨眉山地幔柱和玄武岩的异常热效应,而盆地其它地区则受沉积地层埋深增热和盆地热流演化的共同作用,其中沉积地层埋深增热对烃源岩增温效应更加显著.

The thermal evolution is one of the most important parameters for source rock evaluation and hydrocarbon dynamic accumulation research in oil-gas-bearing basins.Using the Easy%Ro chemical kinetic model,we simulated the maturity evolution history of the Sinian-Lower Paleozoic source rocks in 86 representative boreholes and more than 200 pseudo-wells located in different tectonic units based on the sedimentation process and thermal history reconstruction of Sichuan Basin.The results showed that the maturity evolution characteristics of the Lower Cambrian and Lower Silurian source rocks were different from each other in various tectonic locations.Then,four thermal evolution patterns were established.(1) The Lower Cambrian source rocks in Southern Sichuan Basin entered the oil-window and began primary hydrocarbon generation during Caledonian period,then stopped after rapid secondary maturity evolution during the end of Early Permian-the beginning of Late Permian.(2) The Lower Cambrian source rocks in Southwestern Sichuan Basin and the Lower Silurian source rocks in Southern Sichuan Basin were representative of one rapid evolution stage during the end of Early Permian-the beginning of Late Permian.(3) The Lower Cambrian source rocks in Eastern and Northern Sichuan Basin were characterized by typical two-stage evolution.(4) Continuous evolution lasted after Late Permian to Yanshanian in the Lower Cambrian source rocks in Central Sichuan Basin and the Lower Silurian source rocks in Eastern and Northern Sichuan Basin.The main maturity evolution controlling factors of the Sinian-Lower Paleozoic source rocks in Sichuan Basin were studied on the basis of coupling relationship among sedimentation rate,heat flow and temperature rate.Generally speaking,it was controlled mainly by abnormal thermal effects of the Emeishan mantle plume and basalts in Southwestern and Southern(local area) Sichuan Basin.Whereas it was influenced by both deep burial and heat flow evolution in other areas of the basin,and the former dominated in temperature increase.