表生岩溶系统中浅埋藏构造-热液白云岩成因——以四川盆地中部中二叠统茅口组为例  

Origin of structurally controlled hydrothermal dolomite in epigenetic karst system during shallow burial: An example from Middle Permian Maokou Formation, central Sichuan Basin, SW China

作　　者：刘宏[1,2] 马腾[1] 谭秀成[1,2] 曾伟 胡广[1,2] 肖笛[1] 罗冰[3] 山述娇[3] 苏成鹏 

机构地区：[1]西南石油大学油气藏地质及开发工程国家重点实验室 [2]中国石油碳酸盐岩储层重点实验室沉积与成藏分室 [3]中国石油西南油气田公司勘探开发研究院

出　　处：《石油勘探与开发》2016年第6期916-927,共12页Petroleum Exploration and Development

基　　金：四川省省属高校科研创新团队建设计划

摘　　要：基于露头、岩心、薄片及地球化学分析,对四川盆地中部中二叠统茅口组白云岩成因进行了研究。茅口组白云岩按宏微观组构可分为镶嵌状细晶白云岩和半自形—自形的硅质细晶白云岩,其地球化学特征差异明显。成因分析发现,晚二叠世龙潭组沉积早期,基底断裂沟通不充足的幔源和海源流体进入岩溶系统,与封存的壳源流体不同程度混合;在疏松多孔洞的岩溶系统内,充填的碳酸盐砂云化形成半自形—自形白云石;不充足的幔源热液与先期岩溶系统中流体混合,主要叠合改造先期岩溶系统中形成的孔渗性能优良而热液量相对充足区域,可导致灰岩角砾和围岩白云石化,形成他形镶嵌状白云石;后期因龙潭组沉积增厚使岩溶系统封隔,深部不充足的幔源热液与先期岩溶系统中流体混合,主要叠合改造先期岩溶系统中形成的孔渗性能优良的白云岩,而对较致密的他形镶嵌状细晶白云岩影响较小,从而形成了两类岩石学和地球化学特征差异明显的白云岩。结果表明,白云岩优质储集层和储渗体的形成主要与大陆型早成岩期层控岩溶相关,因此针对中二叠统茅口组的勘探应转变为按岩溶型储集层勘探的思路。Based on the outcrops, drilling cores, thin sections observation and geochemical analysis, studies were done on the genesis of dolomite in the Middle Permian of central Sichuan Basin. Mosaic fine-crystalline dolomite and subhedral-enhedral siliceous fine-crystalline dolomite can be identified microscopically, which have different geochemical characteristics. Genetic analysis indicates insufficient mantle-derived fluids and marine-derived fluids entered karst system through basement faults, and then were mixed with previously-preserved crust-derived fluids in varied degrees during early Longtan period; in the relatively porous karst system, carbonate sands were dolomitized to subhedral-enhedral dolomites; insufficient mantle-derived hydrothermal fluids were mixed with previously-preserved crust-derived fluids, with coincidence reconstruction on the regions where there were preexisting karst systems but short of hydrothermal fluids, resulting in precursor limestone breccias and host rocks dolomitized to form anhedral mosaic dolomite; during late Longtan period, the overlying sediments sealed the epigenetic karst systems, and the insufficient deep mantle-derived fluids were mixed with previous fluids within the karst systems, with coincidence reconstruction on the relatively porous dolomites, while the tight anhedral mosaic fine-crystalline dolomites didn＇t change much, forming two types of dolomites with different petrological and geochemical characteristics. Thus, the formation of preferable dolomite reservoir is possibly related to inland facies-controlled epigenetic karst, and therefore the exploration of Maokou Formation in Middle Permian should pay more attention to the karst-related reservoirs.

关 键 词：热液白云岩 白云岩储集层 表生岩溶 二叠系茅口组 四川盆地 

分 类 号：TE122.2[石油与天然气工程—油气勘探]