断陷盆地浅部非生烃层系油气富集与断裂关系研究

Reservoirs in shallow non-hydrocarbon generation series of faulted basins are characterized by "lower generation-upper accumulation" and "allochthonous hydrocarbon accumulation", petroleum in the series is migrated from lower source rocks by the faults connecting with them which act as the vertical migration pathways for hydrocarbon. As the junction of source rocks and reservoirs,faults therefore play a significant role in controlling the formation and distribution of the allochthonous reservoirs in shallow series.The Neogene of Bohai Bay Basin is shallow non-hydrocarbon generation series which develop numerous faults and are rich in oil and gas, the hydrocarbon mainly originates from the lower Paleogene source rocks, therefore studying the genetic relationship between faults and the Neogene reservoirs is of great theoretical and practical importance. This project is designed to take the hydrocarbon-enriched Zhanhua and Nanpu Depression as example, based on the optimizing of faults which are influencial on the accumulation of hydrocarbon in shallow series by researching the relationship between the static feature of faults and the distribution of Neogene hydrocarbon,we mainly study the influence of fault activity and fault sealing ability on hydrocarbon migration and accumulation and links between faults activity ,the patterns of the movement of active faults and the Neogene hydrocarbon enrichment ,and finally fault sealing conditions are clarified and the links between faults' sealing ability and hydrocarbon accumulation are analyzed.Based on the research of the hydrocarbon migration and accumulation mechanics of typical area enriched in hydrocarbon, the hydrocarbon transportating and charging patterns along faults are summed up,and finally the forming model of reservoirs in shallow non-hydrocarbon generation series is established.

断陷盆地浅部非生烃层系油气藏具有"下生上储"、"它源成藏"的特点，油气来自下部生烃层系，油源断裂为其垂向运移通道。因此，断裂作为沟通"源-储"的重要桥梁，对浅部层系它源油气藏的形成及分布具有重要的控制作用。渤海湾盆地新近系为浅部非生烃层系，断裂发育且油气资源丰富，油气主要来自下部古近系烃源岩，因此研究断裂与新近系油气藏的成因联系，具有重要的理论和实用价值。本项目拟以该盆地新近系油气十分富集的沾化、南堡凹陷为例，从断裂的静态特征与新近系油气分布关系入手，优选与浅部层系油气聚集紧密相关的断裂，重点研究断裂的活动性、封闭性对油气运聚的影响，评价断层活动强度及方式与新近系油气富集的关系，明确断层封闭条件并分析断层封闭性与油气成藏的关系；解剖典型富集区油气运移聚集机制，总结油气沿断裂的输导及充注方式，建立浅部非生烃层系油气藏形成模式

断裂是断陷盆地流体垂向输导的重要通道，对油气的大规模纵向运移、聚集及分布起着重要的作用。本项目以渤海湾盆地盆地新近系油气十分富集的沾化、南堡、渤中等凹陷为研究对象，从断裂的静态特征与新近系油气分布关系入手，研究了断裂差异活动对油气运聚的影响，明确了断层封闭条件并分析断层封闭性与油气成藏的关系；结合典型富集区油气运移聚集机制解剖，建立了断裂与浅层油气运聚模式。研究表明，由于断裂带结构裂缝差异发育，断块间油气更趋向沿断裂上盘诱导裂缝带向上运移并向上倾砂体分流，在断层反向遮挡圈闭中聚集成藏。断层活动与凹陷类型密切相关，晚期型凹陷断层更加发育，浅层富集程度更高。断层活动性与烃源岩生烃史的匹配关系控制其输导油气的能力，二者匹配性变好，浅层油气更加富集。新生代断层晚期活动影响各成油组合油气宏观分布，控制新近系油气富集类型及富集区带。断层差异活动对油气富集的影响可用差异系数(FDC)表征，断层在主生排烃早中期活动较强、晚期活动较弱对油气聚集最为有利。浅部层系油源断层输导能力受断层静态特征、烃源岩排烃强度、主成藏期断层活动性等因素控制；油源断层输导能力越大，新近系油气富集程度越高。岩性对置关系、泥岩涂抹程度等是浅部层系断层能否侧向遮挡油气的关键因素，断层不同部位、不同深度的侧向封闭性具有差异，影响油气纵向富集层系。成藏时期断层垂向启闭性可利用断面垂直方向上所受的压应力与抗压应力的比值进行评价，基于此建立断层启闭系数（S）实现了断层垂向启闭性的定量表征。据此，建立了断陷盆地流体沿断裂带的输导模式：“原生供烃－通源断裂输导－构造控圈”披覆带聚集模式、“次生供烃－浅部断裂输导－断层控圈”浅凹带聚集模式及“混合供烃－复式输导－不整合控圈”斜坡带聚集模式3类，该模式对断裂发育区的油气勘探具有一定的理论指导作用。