油气运移中断层精细刻画的优选方法——以南海北部珠江口盆地惠西南地区为例

OPTIMIZATION OF THE METHOD FOR DETAILED FAULT DESCRIPTION IN HYDROCARBON MIGRATION:TAKING SOUTHWEST HUIZHOU OF ZHUJIANGKOU BASIN,NORTH CHINA SOUTH SEA AS AN EXAMPLE

油气运移是油气成藏的关键要素之一,依据油气运移方式及动力和空间位置等可分为初次运移和二次运移2个阶段,其中,二次运移决定了油气主要运移方向以及源—汇—聚成藏的空间位置。二次运移包括:油气通过储集层及不同类型载体的运移;已形成油气聚集或油气藏在圈闭条件变化尤其是断层活动引起的再次运移。毋庸置疑,断层作为油气运聚的主要载体其在油气运移和聚集中起到了非常重要的作用。然而前人对断层在油气运移输导作用的研究多集中在运聚机理的定性描述上,对油气二次运移中断层运聚输导作用分析尚缺少宏观、立体及实际的手段。鉴此,在南海北部珠江口盆地惠西南转换带油气运移及断层对油气的封堵输导机制的研究中,尝试在应用地球物理方法获取的高质量断层剖面分析基础上,精细刻画断层走向以及微裂隙的分布特征,深入剖析断层对油气封堵与输导作用的差异,进而为油气运移路径分析等提供技术支持。采取的具体技术方法是:首先,对地震数据体做方差体属性分析,并提取时间切片进而确定断层空间展布特征;其次,在方差属性体基础上实施蚂蚁体追踪技术,进一步刻画断层微裂隙概貌,深入分析不同断层及其不同部位对油气封堵与输导差异;再次,利用成像精度较高的三维可视化技术进一步分析断层空间上对油气封堵与输导的作用,为剖析油气运移路径及方向提供新的思路与方法。总之,这种地震与地质相结合的研究思路及方法,大大提高了油气二次运移方向判识的精度及可靠性,故对油气勘探目标的评价优选具有参考借鉴意义。

Migration is one of the key elements to hydrocarbon accumulation. It includes two stages： primary and secondary migrations. The secondary migration is the process which determines the main migration directions of oil and gas, the spatial assemblage of source-reservoir-accumulation and the hydrocarbon migration through reservoir and other types of passages. Secondary migration is caused by the change of conditions prevailed in oil and gas accumulation, including the migration to a new reservoir along the pathways of faults and unconformities. Doubtlessly, faults play a very important role in hydrocarbon migration and accumulation. However, previous researches about faults and their effects on hydrocarbon migration and transportation are mainly qualitative which are too far from e- nough. Macroscopic, three dimensional and practical studies are obviously lacking. Therefore, in this paper, geophysical approaches are adopted firstly to obtain high quality fault profiles to describe in de- tail the faults strikes and microfraetures distribution patterns, then to analyze the difference between hydrocarbon sealing and transportation caused by faults, and finally to provide necessary support for the analysis of oil and gas migration pathways. The adopted methods includes the followings： at first, conduct variance cube attribute analysis for seismic data and extract time slices to acquire the spatial distribution of faults; then, based on the variance attributes, using ant-tracking technique to charac- terize the microfracture overview, and analyze the difference between hydrocarbon sealing and trans- portation for different faults and/or the different parts of a fault; then use 3D visualization with high imaging precision to further analyze the effect of faults on hydrocarbon sealing and transportation spa- tially to supply new ideas and methods for the in-depth study of hydrocarbon migration pathways. Such a research idea and method brings seismic and geology closely, and can much enhance the preci- sion and reliability of direction identification of hydrocarbon secondary migration. It has proved effi- cient to trap evaluation and optimization in hydrocarbon exploration.