渤海海域及邻区拉分构造与油气勘探领域

渤海海域及其邻区经历过断陷、断坳和坳陷三个演化阶段。断陷期基本结构单元是半地堑和半地垒,区域上分三个区,西南区是走向北北东的黄弊断陷带,断陷西断东超;中南区断陷走向呈近东西向、北东向和北西向,断陷都是北断南超的半地堑;东北区断陷带走向北北东,断陷结构东断西超。断坳期和坳陷期,凸起与凹陷统一沉降,接受盆地以外的造山带剥蚀产物。盆地演化过程中,沉降一沉积中心逐渐由边缘分别向渤中和歧口凹陷迁移。构造格局与迁移呈现出典型的地慢卷人型拉分盆地特征。渤海海域在演化过程中曾发生多期反转,以第四纪期间规模最大,形成众多成带分布圈闭。渤海海域的油气勘探领域包括凸起区、断阶带和凹中隆等背景下圈闭。

PULL-APART TECTONIC AND HYDROCARBON PROSPECTING IN BOHAI BAY AND ITS NEARBY AREA

Bohai area is in the east part of Bohai Bay Basin,and experienced rifting,transfer and post-rifing phases in Tertiary. Half graben and half horsts are the basic units during rifting phase. According to the oritntation and dip of boundary faults between half graben and half horst,there were three groups of half graben in Bohai and nearby area, the first occurred in its south-western part (Huanghua Depression), most of half graben's boundary faults dipped eastwards;the second happened in its middle and south area (Chengning up-lift and Jiyang Depression and south part in Bohai area),most of graben boundary faults dip southward;the third in its northeastern area (Liaohe Depression,and northeast Bohai),most of half graben boundary faults dip westwards. In the transfer phase between rifting and post-rifting, thick strata of Dongying Formation formed in Bozhong and Qikou Sags (overstacked on Bozhong half graben and Qikou half graben),and horsts begun subsided during this phase. Post-rifting mainly occurred in Miocene and Pliocene and Quaternary,and formed Guantao, Minghuazhan and Pingyuan Formations. During the whole evolution, subsidence and sedimentary center migrated from southwest to Qikou Sag for south-west belt and from Damingtun Sag in northeast and Changwei Sag in southeast to Bozhong Sag respectively. All these phenomena show Bohai area is a pull-apart basin involved mantle activity in Tertiary. Many rich source-rock half grabens formed during pull-apart rifting,and lower part Dongying formed in transfer phase is potential. In Quaternary Bohai area was inverted by Tanlou movement,and formed a lot of traps in Bozhong area,particully along east part of Bozhong Depression. We here named the movement as "Bohai Movement". Controlled by tectonic history, there are three kinds of local background for trap development,those over horsts,along horsts and in sag.