苏北盆地高邮凹陷基底先存断裂成因及其对新生断裂的控制

真武断裂和吴堡断裂是苏北盆地高邮凹陷的2条重要基底先存断裂,形成于印支期下扬子板块与华北板块的俯冲碰撞,西部走向北东东、东部走向北北东。根据区域应力场、三维地震等资料,将这2条基底断裂对南部断阶带形成和演化的控制作用分为4个阶段:(1)构造挤压期,由于下扬子区北部与华北板块东南部的碰撞,形成了一系列的冲断构造、逆冲推覆及褶皱变形;(2)构造反转期,真武断裂由逆断层反转为正断层;(3)正向裂陷期,真1断层、吴1断层继承了真武断裂分段性特点,真武断阶带、吴堡断阶带分别受真1断层、吴1断层控制强烈;(4)斜向裂陷期,真武断阶带、吴堡断阶带受基底断裂控制作用逐渐减弱,南北向张应力起主导作用。真武断阶带和吴堡断阶带存在着构造差异变形,根据基底先存断裂对新生断裂的活动方式可分为4种类型,由强至弱依次分为继承型、派生型、调节型、诱导型。研究表明,基底先存断裂是高邮凹陷南部断阶带形成演化的基础,并强烈影响着新生断裂的发育。

Origin, Flow of Formation Water and Hydrocarbon Accumulation in the Zhenwu Area of the North Jiangsu Basin, China

In order to understand the origin and flow of formation water and to evaluate the hydrocarbon accumulation and preservation conditions, the properties of formation water chemistry and dynamics of the Zhenwu area in the southern Gaoyou Sag, North Jiangsu Basin, China, have been investigated. The results show that Xuzhuang oilfield is infiltrated discontinuously by meteoric water under gravity, which consequently leads to the desalination of formation water. Formation water in the Zhenwu and Caozhuang oilfields is less influenced by meteoric water infiltration, and the origin is interpreted to be connate water. Hydrocarbon migration, accumulation and preservation are closely related to the hydrodynamic field of formation water. Formation water concentrates gradually during the process of centrifugal flow released by mudstone compaction and the centripetal flow of meteoric water infiltration, leading to the high salinity of the central part. The geological conditions of the southern fault-terrace belt are poor for hydrocarbon accumulation and preservation as meteoric water infiltration, leaching and oxidation, while the central part, i.e., northern Zhenwu and Caozhuang oilfields is beneficial for an abundance of hydrocarbon accumulation. Most of the large scale oil-~as fields locate herein.

高邮凹陷南部断阶带构造沉降史与构造演化特征

通过去压实校正、剥蚀量恢复和去负荷校正等,计算了高邮凹陷南部断阶带构造不同时期的沉降量与沉降速率,并与深凹带进行对比,系统分析了沉降特征。结果表明,研究区构造沉降史总体上可划分为晚白垩世—古新世快速均匀沉降、始新世快速差异沉降和新近纪—第四纪缓慢沉降3个阶段。不同区段不同时期的沉降特征不尽相同,吴堡事件之前沉降量相近,始新世以来差异沉降特征明显,沉降中心由西往东逐渐迁移,反映了构造活动的阶段性和差异性。结合平衡剖面的分析,认为该区的构造演化可相应划分为3个阶段:晚白垩世—古新世断拗期、始新世断陷期和新近纪—第四纪拗陷期。

应用落差分析研究高邮凹陷南断阶主控断层

强烈的构造运动使高邮凹陷南部断阶带主控断层上升盘遭受剥蚀而缺失大套地层,难以用常规方法对其进行研究,而断层落差分析法恰恰能弥补这一不足,从而可以明确断层形成时期及发育历史.对真①、真②’、真②等断层的落差分析表明,真①断层形成于泰州期,阜宁期活动最为强烈;真②’断层形成于戴南初期,并在三垛期强烈活动;真②断层在许庄地区形成于三垛早期,三垛末期强烈活动,而在竹墩地区则形成于戴南末期,三垛期活动强烈.随着三垛运动的结束,南断阶构造活动趋于平静,各主控断层在盐城期相继停止活动.

高邮凹陷南部断阶带构造演化特征

根据构造演化剖面的分析结果,确定了高邮凹陷南部断阶带。随着三垛运动的结束,南断阶构造活动趋于平静,各断层在盐城期相继停止活动,形成了现今的构造格局。断裂的活动时期与油气运移时期良好匹配,断层成为油气垂向运移的主要通道,并在平面上相互切割形成有利的油气圈闭。