摘要：

铝土岩系天然气勘探开发存在巨大潜力,在沉积发育地质过程研究基础上对储集层特征进行分析是探寻有利区块的必要环节。以鄂尔多斯盆地东缘临兴地区铝土岩系为研究对象,利用矿物学、岩石地球化学及物性测试手段,分析了铝土岩系矿物组成、元素组成、碎屑锆石年龄分布及储集层孔渗特征,探究了铝土岩系的物源及沉积过程,揭示了铝土岩系沉积发育及储集层形成过程。研究表明,临兴地区铝土岩系主要发育铁质铝土矿/铝土质铁矿、铝土矿和黏土岩,主要由硬水铝石、赤铁矿、绿泥石、软水铝石、高岭石组成; 主要氧化物组分为SiO₂、Al₂O₃和Fe₂O₃,微量元素垂向呈现3组变化特征; 碎屑锆石主要峰值年龄为329.0 Ma和445.2 Ma,Zr/Nb值与下伏马家沟组石灰岩和北秦岭造山带岩浆岩处于2条风化线上,铝土岩系物源来自于北缘内蒙古古隆起和白乃庙岛弧中的长英质岩浆岩; 孔隙分布均以介孔为主,介孔孔体积占比56.53%~89.75%,且铝土矿吸附孔和渗流孔均有分布,孔隙度介于1.09%~21.37%之间,渗透率介于(0.002~10.883)×10^-3 μm²之间,孔隙度和渗透率整体上呈现正相关关系,表现出良好的储集潜力; 铝土岩系沉积发育可划分为岩溶风化阶段、物源输送阶段和成矿作用阶段,整体上发育于有障壁的潮坪潟湖体系,表生淋滤作用促进易溶组分流失形成溶蚀孔隙,形成铝土岩系储集层。

关键词: 铝土岩系, 物源, 沉积环境, 储集层特征, 临兴地区, 鄂尔多斯盆地

Abstract:

The aluminous-bearing strata hold significant potential for natural gas exploration and development. Analyzing reservoir characteristics based on the geological processes of sedimentary development is essential for identifying favorable blocks. This study focuses on the aluminous-bearing strata in the Linxing area,located on the eastern margin of the Ordos Basin. Through mineralogical,petrographic,geochemical analyses,and physical property testing,we examined the mineral composition,elemental composition,age distribution of detrital zircon,and pore-permeability characteristics of the reservoir. The research investigates the source and depositional processes of the aluminous-bearing strata,revealing the evolution of the bauxite system and the formation of the reservoir. Findings indicate that the aluminous-bearing strata in the Linxing area primarily consist of ferruginous bauxite/bauxite,bauxite and clay rock,composed mainly of diaspore,hematite,chlorite,boehmite,and kaolinite. The predominant oxides are SiO₂,Al₂O₃,and Fe₂O₃,with microelements exhibiting three distinct vertical variations. The main peak ages of detrital zircon are 329.0 Ma and 445.2 Ma. The ratio of Zr/Nb element content is located on two different weathering lines compared to the Lower Majiagou Limestone and the plutonic rocks of the North Qinling orogenic belt. The bauxite series source comes from the feldspathic magmatic rocks in the Xingmeng orogenic belt and Bainaimiao island arc in the north margin. Pore size distribution is predominantly mesoporous,with mesoporous pore volume accounting for 56.53%~89.75%. Both adsorption and seepage pores are present in the bauxite,with porosity ranging from 1.09% to 21.37% and permeability from 0.002×10^-3 μm² to 10.883×10^-3 μm². A positive correlation between porosity and permeability suggests good reservoir potential. The sedimentation of the bauxite series can be divided into three stages: the karst weathering stage,the material transport stage,and the metallogenic stage. The bauxite series formed within the tidal flat lagoon system with barrier. Supergene leaching facilitated the removal of soluble components, leading to the formation of dissolution pores and ultimately contributing to the development of a bauxite reservoir.

Key words: aluminous-bearing strata, provenance, depositional environment, reservoir characteristics, Linxing area, Ordos Basin