渤海湾盆地束鹿凹陷“牙刷状”油藏成藏特征与模式

Characteristics and reservoiring patterns of“teeth-brush-shaped”oil pools in the Shulu Sag,Bohai Bay Basin

冀中坳陷束鹿凹陷具有良好的油气成藏条件,然而实际勘探中许多直井无法获得工业产能。以束鹿凹陷车城油田沙河街组“牙刷状”油藏为研究对象,从储层特征、隔夹层特征、盖层特征、油气来源及运移路径,综合分析了“牙刷状”油藏成藏条件及成藏过程,并总结了其成藏模式。研究表明:“牙刷状”油藏富集于优势砂地比储层中,油藏间被盖层分隔成不同的压力系统,油藏内被相对致密的砂岩隔夹层分隔成一系列压力系统相同的储集单元;断层是“牙刷状”油藏成藏的平面运移及垂向运移主要通道。该地区存在两期油气充注,第一期原油充注是“牙刷状”油藏的主要油气来源,且该期充注的油气沿同期发育的断层运移至地表浅层并散失,使得油气层厚度随深度变浅逐渐减小;油气运移方向与优质储层展布方向大致垂直,导致油藏集中发育在油气运移方向上的断层圈闭中,形成了一系列“牙刷状”油藏。文章系统论述了“牙刷状”油藏的成因机制,为研究区后续勘探开发工作提供可靠的理论基础。

The Shulu Sag in Jizhong Depression possesses all the necessary factors for hydrocarbon to accumulate.However,many vertical wells drilled there failed to yield any industrial oil/gas flow.This paper takes the“teeth-brush-shaped”reservoirs in the Shahejie Formation,Checheng oilfield,Shulu Sag as study subject to crack the enigma.The characteristics,barrier bed features,cap rock features,oil and gas sources and migration paths for the reservoirs are investigated to analyze the conditions and process of hydrocarbon accumulation and summarize reservoiring patterns.The results shows that the“teeth-brush-shaped”oil pools occur with a high net-to-gross ratio,and adjacent oil pools are segmented into different pressure systems by cap rocks,while single oil pool is compartmentalized into a series of reservoir units of the same pressure system by relatively tight sandstone barriers.Faults were the major vertical and lateral migration pathways for hydrocarbon.Two stages of hydrocarbon charging occurred in the area with the first stage being the main contributor of hydrocarbons to the reservoirs.However,some of the hydrocarbons were dissipated while moving upward to the shallower layers along faults,resulting in a gradually thinning reservoirs with decreasing depth.With the migration direction roughly perpendicular to the distribution direction of reservoirs with dominant net-to-gross ratio,hydrocarbons tend to accumulate in fault traps along migration pathways,forming a series of“teeth-brush-shaped”oil pools.The genetic mechanism of the oil pools revealed by the study can be used as a reliable theoretical basis for subsequent exploration and development in the study area.