东部新生代盆地始新世末改造与原始面貌恢复——以歧口凹陷为例

Cenozoic rift basins in Eastern China and offshore are rich in oil and gas, previous studies show that rift basins experienced a multi-phase structure reformation in Cenozoic, the late Eocene reformation is the strongest among them, which lead to great changes in the appearance of original sedimentary basin. However, it is still lack of knowledge and research on the reformation in the past. The Eocene is the main formation period of source rocks in each basin. So the research on characteristics of late Eocene reformation and its original appearance restoration of basin are particularly important for both basin scientific theoretical research and petroleum exploration. The project selects Qikou sag in Bohai Bay Basin as a anatomic case, residual strata of sha-3 member in Eocene as the research emphasis, based on the structure quantitative research on seismic data and analysis on the late reformation form, intensity and spatial change, combining the analysis and verification on sedimentary, deposition environment and rock mineral space-time evolvement, constraining the exact age by the results of low-temperature and using a variety of methods of paleo tectonic restoration, removes the influence of late reformation and restores the Sha-3 period original structure-sedimentary appearance of Qikou sag. According to the research, the project can study the evolution-reformation process of Qikou sag and its impact on hydrocarbon accumulation, furthermore discuss regional dynamic environment of late Eocene tectonic event. The research of this project will also provide example and scientific evidence for late Eocene tectonic event in Eastern China, enrich the theory and research method of late reformation analysis and original appearance restoration in basin.

中国东部和近海新生代断陷盆地油气丰富。已有研究表明这些断陷盆地在新生代经历了多期构造改造，其中始新世末的改造最为强烈，使始新世的原始沉积面貌大为改观。然以往对其认识和研究不足。始新统是诸盆地的主力烃源岩。故研究始新世末改造特征并恢复其原始面貌，对盆地科学理论研究和油气勘探尤为重要。本项目选取渤海湾盆地歧口凹陷为解剖对象，以始新世沙三段现存地层为研究重点，在地震资料构造定量解析和后期改造形式、强度及其时空变化分析的基础上，结合沉积学、沉积环境及其岩矿时空演变的分析和验证，以低温年代学结果为约束，剔去后期改造的影响，运用多种古地质构造恢复方法，恢复沙三期原始沉积构造面貌，在此基础上研究该凹陷的演化-改造过程和对油气成藏的影响，进而探讨始新世末构造事件的区域动力学环境。本项目的研究将会为东部断陷盆地始新世末构造事件提供剖析实例和科学证据，丰富盆地后期改造分析和原始面貌恢复的理论和技术方法。

东部断陷盆地在新生代经历了多期构造改造，始新世末的改造尤为重要。本项目选取渤海湾盆地歧口凹陷为解剖对象，通过统计学、沉积学、构造学等方面的研究，得到以下认识：.①根据连片处理的三维地震资料及钻井、测井等资料，运用量化统计的方法对新生代各个层段的断裂体系进行统计分析，认为歧口地区古近纪断裂活动的强度由早到晚表现出由南向北、自西往东的迁移特征；断裂的主要走向为北东向和近东西向，且断裂的优势走向由沙三期的北东向到沙一期转变为近东西向。.②通过运用平衡剖面方法和古构造恢复技术，重演了区内各大主要凸起构造带的构造演化过程，如北大港凸起构造带、塘沽新港凸起构造带、埕北滑脱构造、滨海1号构造等。.③通过沙三段边缘相追索及边界断裂演化分析，恢复了沙三期的原始沉积-构造面貌，认为歧口地区在沙三期主体为一个范围相对广阔的湖盆，其沉积边界远远超出了现今残留地层范围，其沉积边界远远超出了现今残留地层范围，且区内各大凸起尚未成形，各凹陷与歧口深凹之间彼此连通，随后始新世末及其后的构造运动对其改造明显，现今区内古近系的构造格局是到馆陶期沉积前才逐步显现。.④综合笔者和前人丰富的研究资料，认为始新世末期的构造事件不只发生在歧口地区，在整个中国东部及近海都不同程度地受到这次构造事件的影响，总结了这次构造事件在中国盆地中诸方面的表现特征并探讨了其可能发生原因。.本项目的研究成果可为东部断陷盆地始新世末构造事件提供剖析实例和科学证据，有助于丰富研究区资料并加深对歧口凹陷及渤海湾盆地的认识。