断陷盆地中含油气系统的特征

我国东部断陷盆地含油气系统具有与盆地结构及勘探程度相对应的多层次性,其基本单元是以单一生烃凹陷(洼陷)为中心的子系统。复式含油气系统的基础是在盆地中存在不同地质时期的活跃烃源岩,它是强烈的多期块断运动和高地热场的产物。断层的活动强度及活动时间和期次控制了盆地中油气系统的分布及特征。用生物标志物进行油源对比可以划分系统并确定其分布范围,从而进一步研究成藏规律。以济阳坳陷中的沾化凹陷为例说明复式含油气系统的形成及特征。盆地中三套主要的生油层系分别是始新统的沙河街组第三段、第四段及渐新统的沙河街组第一段。这几套生油岩形成于不同的沉积环境,经历了不同的成熟演化阶段并形成了各自的原油。三类原油的特征明显地反映在其中生物标志物的组成上。以这三套生油层系为核心,三个成藏期为标志,形成了复式含油气系统。这些系统有着各自的生储盖组合,运移通道及分布范围,它们在空间中叠置或交叉,在时间上呈现阶段性。

THE CHARACTERISTICS OF PETROLEUM SYSTEM IN FAULTED BASIN

The petroleum system of the faulted basins in the eastern China has the characteristics of multi-levels, in accordance with the basin structure and exploration degree.The basic unit of system is proposed to have single center of oil generating depression (or sag). The basis of multiple petroleum system is the existence of active source rocks of different geological ages in the basin.It′s the result of activities of faulted-blocks with mullet-phase high geothermal field in the faulted basin. The occurrence and the distribution of petroleum systems in the basin are controlled by intensity and time of faulting activity.The petroleum systems can be defined by the oil-source correlation with the biomarkers.Taken the Zhanhua sag in the Jiyang depression as an example, the formation and characteristics of the multiple petroleum system are expounded. Three series of source rocks in the basin are the third member and fourth member of Shahejie formation of Eocene and the first member of Shahejie formation of Oligocene.Each of source rocks was deposited in the specific environment and experienced different evolutional stages, finally three kinds of crudeoil are generated. Attribute and maturity of crude oil are clearly displayed in their biomarker composition. There are three kinds of source rocks and three periods of pool formation in the multiple petroleum system of Eocene and Oligocene in the Jiyang Basin. These systems have own combination of the source-reservoir-caprock, migration path and distribution. They are superposed or intercalated in the geological space and have multi-phase in the geological ages.