准中4区块侏罗系成藏动力子系统划分及勘探意义

Division of dynamic subsystem for hydrocarbon migration and accumulation in Jurassic middle 4 Block of Jungar Basin and its exploration significance

准噶尔盆地中部4区块侏罗系是一个下生上储并被区域性封隔层复杂化的成藏动力系统。通过层序地层学研究,结合异常流体压力分析,将侏罗系成藏动力系统进一步划分为3个子系统:顶部头屯河组常压-超压他源开放成藏动力子系统(Ⅰ);中部三工河组超压他源半封闭成藏动力子系统(Ⅱ);底部八道湾组高超压自源封闭成藏动力子系统(Ⅲ)。地化分析表明:油气从八道湾组烃源岩中生成之后,在三工河组砂体进行了广泛的侧向运移,并在适当位置聚集成藏;在喜山期,断裂带间歇性开启,油气可突破成藏动力子系统Ⅱ,沿断层运移至成藏动力子系统Ⅲ中进行聚集。这说明头屯河组油气主要来源于经过三工河组长距离侧向运移聚集的古油藏,并非来自深层油源断裂的直接输导。

Jurassic middle 4 Block is a"lower-generation and upper-reservoir"type dynamic system of hydrocarbon migration and accumulation,and it was complicated by regionality cap rock.Based on the research of sequence stratigraphy and abnormal fluid pressure,this dynamic system can be divided to three subsystems:the top subsystem is Toutunhe Formation which is normal pressure-overpressure and other-sourced opening dynamic subsystem(systemⅠ);the middle subsystem is Sangonghe Formation which is overpressure and other-sourced semi-closed dynamic subsystem(systemⅡ);the bottom subsystem is overpressure and self-sourced closed dynamic subsystem(systemⅢ).Geochemical analysis demonstrates that extensive parallel migration happened in Sangonghe Formation;the oil and gas accumulated in applicable place to form petroleum pool after these hydrocarbon was generated from oil source rock in Badaowan Formation.During the Himalayan orogenic movement,faults unsealed intermittently,hydrocarbon could break through dynamic subsystemⅡ,and migrated into dynamic subsystemⅢfollowing faults.In other words,the oil and gas in Toutunhe Formation which originated from paleo-petroleum pool in Sangonghe Formation experienced long distance parallel migration,rather than direct inputting from deep oil sources faults.