环渤中缓坡带盖层逐级破裂与油气阶梯跃升式运移

Progressive rupture of cap rocks and step-wise hydrocarbon migration in gentle slope zone around Bozhong area

随着渤海凸起区勘探程度的提高,缓坡带成为重要的勘探接替区,但缓坡带勘探成功率较低,油气运移模式及运移路径精准预测是制约勘探成败的关键因素。以环渤中地区为重点,分析了断陷盆地缓坡带多层输导体系条件下盖层破裂与油气运移的关系,总结了相应的油气运移模式,并基于运移模式开展油气三维运移模拟,实现了缓坡带油气运移路径的精细预测。研究表明:①渤中凹陷周缘缓坡带普遍具有“盖-断双控阶梯式”油气成藏模式,主要包括古近系近源和新近系源外2类油气藏。近源成藏的油气直接来自于烃源岩,在东营组区域盖层控制下沿古近系第一输导层顺层运移;源外成藏的油气来自于二次调整运移的充注点,油气顺断层突破东营组盖层后,沿新近系多层楼式输导层呈阶梯式充注运移。②累计盖层断接厚度小于450m是下伏盖层破裂及浅层输导层充注发生的触发条件。③受盖层减薄和断裂活动的耦合控制,缓坡带不同构造部位油气运聚的阶梯环带不同,可以通过“盖-断耦合”分析来预测油气的空间分布,基于这一思路创新开展阶梯跃升式油气立体运移模拟,在蓬莱19-3缓坡带综合预测成功率达88%。④由于坡折断带坡坪转换的正断层的密集发育,加上盖层厚度及其断接厚度的剧烈变化,坡折带之下的斜坡外带通常为近源成藏,油气勘探应该以中深层为主;坡折带之上的斜坡内带,油气通常在源外成藏,油气勘探应该以浅层为主。该研究成果对于断陷盆地缓坡带油气勘探有利方向预测有着重要作用。

As exploration in the uplift area of the Bohai Bay Basin intensifies,the gentle slope zone has become an important subsequent exploration area.However,the exploration success rate in the gentle slope zone is relatively low,and accurate prediction of hydrocarbon migration patterns and pathways is a crucial factor that determines the success or failure of exploration.The Bozhong area was studied,and the relationship between cap rock rupture and hydrocarbon migration under the condition of multi-layer transport systems in the gentle slope zone of a faulted basin was analyzed.The corresponding hydrocarbon migration patterns were summarized,and three-dimensional hydrocarbon migration simulations were conducted based on the migration pattern,achieving precise prediction of hydrocarbon migration pathways in the gentle slope zone.The research findings are as follows:①The gentle slope zone around the Bozhong Sag generally exhibits a“cap rock-fault double-control stepwise”hydrocarbon accumulation pattern,which mainly includes two types of oil and gas reservoirs:Paleogene proximal and Neogene distal.Hydrocarbons in proximal reservoirs are directly sourced from source rocks and migrate along the first transport layer of the Paleogene system under the control of the regional cap rock in the Dongying Formation.Hydrocarbons in distal reservoirs originate from injection points undergoing secondary adjustment and migration.After breaking through the cap rock in the Dongying Formation along faults,hydrocarbons migrate in a stepwise manner along the multi-layer transport system of the Neogene system.②The cumulative cap rock juxtaposition thickness of less than 450 m is the triggering condition for the rupture of underlying cap rocks and the injection into shallow transport layers.③Controlled by the coupling of cap rock thinning and fault activities,different structural parts of the gentle slope zone exhibit different stepwise zones of hydrocarbon migration and accumulation.The spatial distribution of hydrocarbons can be predicted through“cap rock-fault coupling”analysis.Based on this idea,innovative three-dimensional stepwise hydrocarbon migration simulations were conducted,achieving a comprehensive prediction success rate of 88%in the PL19-3 gentle slope zone.@Due to the dense development of normal faults at the slope break zone where the slope platform transitions,coupled with significant variations in cap rock thickness and juxtaposition thickness,the outer slope zone below the slope break zone typically favors proximal hydrocarbon accumulation,and hydrocarbon exploration should focus on the middle-deep layers.In the inner slope zone above the slope break zone,hydrocarbons usually accumulate in distal reservoirs,and hydrocarbon exploration should prioritize shallow layers.This research plays a significant role in predicting favorable directions for hydrocarbon exploration in the gentle slope zones of faulted basins.