歧口、南堡富油凹陷东营组堆积期构造活动的“双强效应”、驱动机制及油气意义研究

Taking Qikou and Nanpu sags as the research target, firstly, the features of intense tectonic activity in Dongying formation period within the two sags have been studied, especially the intense activity of EW striking faults, which was totally different from other fault rifted basins (most of them were undergoing fading tectonics in the late Paleogene period; the activity of major faults were weak) during the same time in eastern China. Then, the dynamic mechanism of simultaneously enhancement of both tectonic activities of the boundary faults and the depression effect in the two sags has been discussed. Under the joint effect of the above "double intense effects", the subsidence centers and depocenters both migrated away from the boundary faults and developed in the center in those two sags, which resulted in the accumulation of thick deep lacustrine mudstone and the development of fan deltas along faulted steep zone. The extra-thick Neogene strata caused source rocks reaching the threshold of hydrocarbon generation and hydrocarbon expulsion; later, the Neotectonic movements caused the activation of many synsedimentary faults, which effectively connected the Dongying reservoir bodies with the "hydrocarbon kitchen" of Shahejie formation, and transported the oil and gas to reservoir bodies in Dongying formation strata or even shallower strata. All of these lead to the great potential of hydrocarbon exploration in Dongying formation.

以歧口和南堡凹陷为对象，以古近纪东营组堆积期为研究时段，针对研究区异常强烈的构造活动性出发，尤其是东西向大断裂的强烈活动而有别于我国东部同时期发育的其它断陷盆地（多数该类盆地在古近纪晚期已进入构造活动的衰弱期，主干断裂的活动性均很弱）的特征。探讨歧口、南堡凹陷边缘断裂的强烈活动性和凹陷整体的坳陷作用同时进一步增强的驱动机制；在断裂活动强烈、基底坳陷作用强烈的 "双强效应"联合作用下，歧口和南堡凹陷的沉降中心、沉积中心均远离边界断层而发育于凹陷中心，导致深湖相泥岩沉积的发育；在凹陷的断控陡坡部位发育了扇三角洲体系。新近系巨大的地层厚度导致了东营组的烃源岩进入生烃门限而生烃，其后的新构造运动又导致了大量的同沉积断层的活动，并东营组储集体与下伏沙河街组的"烃源灶"沟通，并将下部油气垂向运移至东营组乃至更浅层位的储集体内聚集成藏，从而造就了东营组巨大的油气勘探潜力。

本研究以歧口、南堡富油凹陷为对象，以古近系晚期的东营组堆积期为研究时段，针对凹陷内具有强烈的构造活动性，尤其是东西向大断裂的强烈活动而有别于我国东部同时期发育的其它断陷盆地（多数该类盆地在古近系晚期已进入构造活动的衰弱期，主干断裂的活动性均很弱）的特征。探讨东营期“双强要素”联合作用的驱动机制及其重要的油气地质意义。.该研究取得的重要成果和认识如下：.1、构造－地层分析方面：一方面边界断裂活动强烈，尤其以近EW向延伸的西南庄断裂中段和高柳断裂的强烈活动为特征。另一方面沉降中心并不沿边界断裂展布，而是位于凹陷中部的林雀次凹和曹妃甸次凹处，表明拗陷作用也强烈。.2、沉积体系研究方面：东营组沉积期，渤海湾盆地普遍进入断拗转换期。①半深湖-深湖沉积环境广泛发育，凹陷处于欠补偿-补偿状态；②强烈的基底沉降为碎屑物堆积提供了充足的可容纳空间，加之物源碎屑供给充足，较短的时间内堆积了巨厚的东营组地层；③扇三角洲沉积体系、近岸水下扇沉积体系和滑塌重力流沉积体系有合适的坡降条件和可容纳空间。.3、构造活动的“双强效应”对沉积和储层的控制作用方面：构造活动的“双强效应”控制下，优质烃源岩、类型丰富的优质储层以及区域盖层的发育，使得南堡凹陷东营组具有极大的勘探潜力。.4、构造活动“双强效应”的油气意义：南堡凹陷在东营组发育期发育一套大面积的深湖相厚层烃源岩。近年来在南堡凹陷的油气勘探突破的实践成果业已证明了东营期近东西向边界断层的强烈活动与基底沉降强烈增速的“双强要素”的联合控制作用的油气意义重大。 .5、构造活动的“双强效应”成因机制的探讨：东营组沉积期，渤海湾盆地普遍进入断拗转换期，由热沉降引起的拗陷作用以渤中坳陷为中心向周围大致呈递减的趋势，紧邻渤中坳陷的南堡凹陷拗陷作用强烈。因此，构造活动的“双强效应”是深部动力过程与浅部构造应力场综合作用的产物。