渤海海域中生代火山岩喷发旋回划分及与油气的关系

摘要

渤海海域中生代火山岩分布广泛,但其空间叠置关系复杂,制约了火山岩油气藏勘探.基于大量钻井取心、壁心、薄片、测井、锆石U-Pb测年以及地震资料,综合运用地质分析、地球物理分析以及岩石年代学分析等方法对研究区火山岩喷发旋回进行了划分,建立了渤海海域中生代火山岩喷发旋回序列.渤海海域中生代火山岩可以划分为3个喷发旋回,分别为侏罗纪(旋回工)、早白垩世早中期(旋回Ⅱ)、早白垩世晚期至中生代末(旋回Ⅲ).旋回Ⅱ又可细分为3个亚旋回Ⅱ1、Ⅱ2、Ⅱ3,喷发时间分别为128～122、122～118、117.8～114.4Ma,岩性由基性向酸性演变,其中Ⅱ1亚旋回以溢流相中基性火山岩为主,沿深大断裂呈裂隙式喷发,分布广泛;Ⅱ3亚旋回酸性火山岩沿郯庐走滑断层成“串珠状”零星分布,多为中心式喷发;Ⅱ2亚旋回介于两者之间.在此基础上,研究了火山岩喷发旋回与油气的关系,认为沿郯庐断裂带分布的Ⅱ2和Ⅱ3亚旋回中酸性火山岩优质储层发育,靠近生烃凹陷,具有良好的油气输导和聚集条件,是渤海海域火山岩油气藏勘探的有利目标.本文研究对类似地区中生代火山岩喷发旋回划分具有一定的借鉴意义.%The Mesozoic volcanic rocks in the Bohai sea distribute widely with complex spatial superimposition,which restricts the petroleum exploration in volcanic reservoirs.Based on extensive drilling cores,sidewall coring,thin section,logging,zircon U-Pb dating data and seismic data,the eruption cycles of Mesozoic volcanic rocks in the study area are established with integrated study of geological analysis,geophysical analysis and rock chronology analysis,and the Mesozoic volcanic eruption cycle sequence is set up in the Bohai sea.The Mesozoic volcanic eruption in the Bohai sea can be divided into such three cycles as the Jurassic (cycle Ⅰ),early and middle of the Early Cretaceous (cycles Ⅱ),late of the Early Cretaceous to the end of the Mesozoic (cycle Ⅲ).Cycle Ⅱ can be subdivided into three sub-cycles Ⅱ1,Ⅱ2 and Ⅲ3,and the eruption time is 128～122,122～118 and 117.8～114.4 Ma,respectively,with a lithology from the basic to acidic evolution.Ⅱ1 sub-cycle widely distributes and mainly consists of intermediate-basic volcanic rocks of a flowing facies along the deep fauⅡ3 sub-cycle shows a "string beads" distribution along Tan-Lu strike-slip fault with central eruption;Ⅱ2 sub-cycle is intermediate.On this basis,the relationship between volcanic eruption cycle and oil and gas is studied,it shows that Ⅱ2 and Ⅱ3 sub-cycles along Tan-Lu strike-slip fault developing middle-acid volcanic rock high quality reservoir close to hydrocarbon generating depression,it has good transportation and accumulation conditions,and are favorable targets for volcanic reservoir exploration in the Bohai sea.The study has a certain significance to divide the Mesozoic volcanic eruption cycle in the similar areas.