Structure Model of Weathered Crust on the Top of PreTertiary and Its Influence on Petroleum Migration and Accumulation in East Part of Yihezhuang Uplift
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摘要: 基于地质综合研究，系统分析了济阳坳陷义和庄凸起东部地区前第三系顶部风化壳结构特征，深入剖析了其形成主控因素，建立了该区风化壳结构发育模式，并探讨了风化壳结构对油气运聚的影响。研究认为，义和庄凸起东区前第三系顶部风化壳中，风化粘土层厚度薄，分布地区局限，物性差；半风化岩石全区发育，岩石类型多样，除部分半风化碳酸盐岩顶部存在一层致密“硬壳”外，物性多得到明显改善。风化壳结构形成受控于岩相、气候、时间、古地形、构造、后期保存程度等6大因素；多种因素相互耦合，决定了风化壳结构的空间发育；风化粘土层、半风化岩石顶部“硬壳”对油气起遮挡、封盖作用，顶部无“硬壳”的半风化岩石则可大大提高前第三系岩层的储集性能和不同层系之间的横向连通性。Abstract: Based on integrated study, the paper analyzed characteristics of the structure of weathered crust on the top of PreTertiary in the east part of Yihezhuang uplift of Jiyang depression. Key factors controlling its formation were anatomized, structure model of weathered crust was established, and its influence on petroleum migration and accumulation was discussed. Results show that weathered clay layer in the studied weathered crust is thin with limited distribution, and reservoir property is poor; while semiweathered rock of various lithologies extensively developed in the whole area, except for the tight “hard crust” on the top of semiweathered carbonate stone, reservoir property was improved obviously. Structure of weathered crust was controlled by lithofacies, paleoclimate, weathering time, paleotopography, tectonic structure, and later stage preservation. Reciprocal coupling of these factors determines spatial distribution of the structure of weathered crust. The weathered clay layer and “hard crust” on the top of semiweathered rock serves as caprock for petroleum reservoir, while semiweathered rock without “hard crust” can improve reservoir property of Tertiary system and serve as lateral migration path between different strata.
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