摘要
鄂尔多斯盆地奥陶系马家沟组四段具备良好的天然气勘探潜力,白云岩分布是马家沟组四段天然气富集的重要控制因素。盆地北部大牛地气田马家沟组四段薄层白云岩分布规律及成因机制尚不清楚,制约了储层的预测及天然气的勘探。为此,利用层序地层学理论,在准层序类型研究的基础上,建立大牛地气田马家沟组四段准层序地层格架,通过对不同类型白云岩同位素与微量元素对比分析,研究白云岩的成因及分布规律。研究结果表明:①马家沟组四段发育3种类型的准层序列,石灰岩—云质灰岩型、石灰岩—白云岩型和石灰岩—白云岩/膏岩互层型。②马家沟组四段白云岩为渗透回流成因,随着海平面的下降,古隆起周缘的蒸发作用增强,重卤水向下倾方向渗透发生渗透回流白云石化。③白云岩发育在准层序的顶部,单层厚度小但平面分布稳定,物性较好;纵向上随着海平面的下降,自下而上白云岩厚度和层数增加;横向上自西向东白云岩发生减薄甚至尖灭,古隆起附近多层白云岩叠合形成厚层白云岩。该研究成果为盆地东部马家沟组四段白云岩储层的预测提供了地质模型。
The fourth member of Ordovician Majiagou Formation(Ma 4 Member)in the Ordos Basin has a good potential of gas exploration,where the gas accumulation is mainly controlled by dolomite distribution.However,the unclear distribution and genetic mechanism of thin-bedded dolomites of Ma 4 Member in the Daniudi gas field of the northern Basin restrict the reservoir prediction and gas exploration.Based on sequence stratigraphy and the research of parasequence type,a parasequence stratigraphic framework of Ma 4 Member was established.Then,the genesis and distribution regularity were studied by analyzing isotopes and trace elements of different dolomites.The following results are obtained:(1)There develops three types of parasequence in the Ma 4 Member,which are limestone-dolomitic limestone,limestone-dolomite,and interbedded limestone-dolomite/gypsum.(2)The genesis of dolomites in Ma 4 Member is infiltration and reflux.The evaporation around the paleouplift was intensified with the fall of sea level,and the infiltration of heavy brine in downdip direction induced infiltration-reflux dolomitization.(3)At the top of the parasequence,there develops dolomites featured by thin but stably distributed single layer,and good physical properties.Vertically,with the fall of sea level,the thickness and layers of dolomites increase from bottom to top;horizontally,dolomites thin or even pinch out from west to east,and multiple layers of dolomites are superimposed forming thick dolomites near paleouplift.This study provides a geologic model for predicting dolomite reservoir of Ma 4 Member in the eastern Basin.
作者
李春堂
祁壮壮
丁晓琪
刘四洪
高景云
朱颖
LI Chuntang;QI Zhuangzhuang;DING Xiaoqi;LIU Sihong;GAO Jingyun;ZHU Ying(Sinopec North China Petroleum Bureau(Oil&Gas Company),Zhengzhou,Henan 450006,China;College of Energy,Chengdu University of Technology,Chengdu,Sichuan 610059,China)
出处
《天然气勘探与开发》
2023年第1期32-41,共10页
Natural Gas Exploration and Development
基金
国家油气重大专项“海相碳酸盐岩层系重点领域储层形成机理与发育模式”(编号:2017ZX05005-001-010),中石化科技攻关项目“鄂尔多斯盆地元古-下古生界成藏条件与目标评价”(P20043-2)资助。
