北部湾盆地乌石凹陷断坳转换期不整合结构特征及其成藏作用  

Characteristics of Unconformity Structure and its Implication for Petroleum Accumulation During Fault-depression Transition Period in the Wushi Sag,Beibuwan Basin

作　　者：吴孔友[1] 李彦颖 范彩伟 董方 洪梅[1] WU Kongyou;LI Yanying;FAN Caiwei;DONG Fang;HONG Mei(School of Geosciences,China University of Petroleum,Qingdao 266580,Shandong,China;Zhanjiang Branch,CNOOC China Limited,Zhanjiang 524057,Guangdong,China)

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266580 [2]中海石油(中国)有限公司湛江分公司,广东湛江524057

出　　处：《大地构造与成矿学》2022年第2期272-281,共10页Geotectonica et Metallogenia

基　　金：国家科技重大专项“地层圈闭描述及有效性分析技术研究”(2017ZX05001003004)资助。

摘　　要：北部湾盆地T60不整合是古近系与新近系的分界,且形成于盆地由断陷进入坳陷的转换阶段。本文通过地震资料精细解析,揭示位于盆地中部的乌石凹陷在该时期(T60)不整合发育明显,且剖面类型多样。依据不整合上、下地震反射特征,可划分为平行‒削截不整合、超覆‒削截不整合、平行‒褶皱不整合等8种不整合类型,且在平面上削截类不整合的分布范围最广。研究表明不整合类型的平面分布规律受控于构造部位及变形强度。不整合在纵向上发育三层结构,并依据测井曲线响应特征建立了纵向结构的识别方法。利用该识别方法,乌石凹陷新近系下洋组底部(T60)不整合纵向结构发育,多条曲线在不整合结构上、下层与中层之间出现台阶式突变,且中层是多条变化幅度差曲线的低值区。同时,对不整合结构中层风化黏土层重点分析,揭示其平面发育规律主要受控于不整合剖面类型及剥蚀厚度这两大要素。依据乌石凹陷东区不整合成藏条件及成藏模式,叠合不整合剖面类型、风化黏土层厚度、烃源岩厚度等因素,针对乌石凹陷东区,优选出2个地层圈闭有利勘探区带,为下一步勘探部署提供了方向。As the Paleogene-Neogene boundary,the T60 unconformity in the Beibuwan Basin recorded the transition of the faulted basin into the depression basin.Eight types of unconformities are identified to occur during the deposition of the T60 unconformity in the Wushi Sag,which is located in the central part of the basin,based on changes of seismic reflection characteristics of the unconformity.The unconformity types include parallel-truncation unconformities,overlap-truncation unconformities,and parallel-folding unconformities,among which truncation unconformities have the widest distribution range in the plan view.The plane distribution of each type of unconformity is controlled by structural location and deformation strength.Given the three layered structures of these unconformities,this study develops an efficient method to recognize the vertical structures of the unconformities on the logging curves.Vertical unconformity structures are found to be developed at the bottom of the Neogene Xiayang Formation in the Wushi Sag based on the comprehensive interpretation of the logging curves.Step-like changes occur in several logging curves at the contact surfaces between the middle weathered clay layer and the upper and lower layers of the unconformity structure.Moreover,the weathered clay layer corresponds to the low-value intervals in multiple changing amplitude difference curves,and its planar distribution is found to be mainly controlled by the unconformity types and denudation thicknesses.Eventually,two favorable exploration areas of stratigraphic traps in the eastern Wushi Sag are selected for further exploration and deployment,based on comprehensive analyses of the unconformity-related accumulation conditions and modes,unconformity types,weathered clay layer thickness,and source rock thickness.

关 键 词：乌石凹陷 断坳转换期 不整合类型 不整合结构 地层圈闭 

分 类 号：P548[天文地球—构造地质学] TE122[天文地球—地质学]