塔北、塔中地区寒武系—奥陶系白云岩多成因模式  

Geochemical Characteristics and Origins of the Cambrian-Ordovician Dolomites in Northern and Central Tarim Basin

作　　者：王丹 WANG Dan(CNOOC International Limited,Beijing 100010,China)

机构地区：[1]中国海洋石油国际有限公司,北京100010

出　　处：《沉积学报》2024年第3期857-876,共20页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(U1663209)。

摘　　要：【目的】塔里木盆地下古生界厚层白云岩具有良好的油气勘探前景,但目前其成因尚未达成统一的认识。通过对这些白云岩的成因研究,可为塔里木盆地下古生界厚层白云岩的油气勘探提供一定的理论支撑。【方法】基于国际学术界通用的白云石分类方案,对塔北、塔中地区寒武系—奥陶系白云岩开展了详细的岩相学和地球化学(微量—稀土元素、δ^(13)C和δ^(18)O及^(87)Sr/^(86)Sr比值)研究。【结果和结论】基质白云石可识别出6种类型:(1)泥粉晶白云石(Md1);(2)残余拟晶白云石(Md2);(3)粉—细晶、直面、自形—半自形、漂浮状白云石(Md3);(4)细晶、直面、自形—半自形白云石(Md4);(5)细—粗晶、他形、曲面白云石(Md5);(6)粗晶、曲面、鞍形白云石(Md6)。Md1和Md2的成岩流体为不同程度蒸发浓缩的同期海水,形成于相对局限沉积环境的同生—准同生白云石化作用;Md3和Md4的成岩流体为地层中残留的海源孔隙水,形成于浅—中埋藏白云石化作用;Md5的成岩流体为海源流体,形成于深埋藏白云石化作用或早期白云石的重结晶作用;Md6的形成流体为与宿主白云岩发生强烈水岩反应的深部热液,主要形成于深部热液及围岩之间相互调节、再平衡过程中的“热液调节白云石化作用”对宿主白云岩的改造作用。[Objective]The genesis of dolomites is still controversy,and dolomite reservoirs play an important role in carbonate oil and gas exploration,whose reservoir properties(porosity and permeability)are largely influenced by the genesis types and texture characteristics of dolomites.In recent years,many large oil and gas fields have also been found in domestic dolomite reservoirs,such as Tarim Basin,Sulige gas field in Ordos Basin,Puguang and Yuanba gas field in Sichuan Basin and Anyue large or super large gas field.Therefore,systematic researches on the texture types and genetic mechanisms of dolomites yield profound theoretical significance,and also will promote greater advance in carbonate oil and gas exploration in China.The Tarim Basin shares large volume of oil and gas reserves,the exploration target horizons within which has gradually shifted from medium shallow-to medium-buried layers to ultra-deep layers.Especially,industrial oil and gas flows were encountered in the deeply-buried dolomites of the Lower Paleozoic in the Tarim Basin,making the formation,evolution and reservoir characteristics of deep dolomite reservoirs in this basin become the focus of scholars'research.However,the formation mechanism of the Cambrian-Ordovician dolomites in the Tarim Basin has not yet reached a consensus due to deep burial depth,complex genesis and difficult exploration of these dolomites.This study increases the understanding of their origin and provides theoretical support for oil and gas exploration in the region.[Methods]Detailed petrographic and geochemical(trace-rare earth elements,stable carbon and oxygen isotopes and ^(87)Sr/^(86)Sr ratios)studies of these dolomites were conducted on the Cambrian-Ordovician dolomites of northern and central Tarim Basin based on the international classification scheme of dolomite.[Results and Conclusions]According to the occurrence of dolomites,the Cambrian-Ordovician dolomites were divided into matrix and cement dolomites.Based on grain sizes,contact relationship between crystal plane

关 键 词：岩相学 地球化学特征 白云石化作用 下古生界 塔里木盆地 

分 类 号：P534.4[天文地球—古生物学与地层学]