鄂尔多斯盆地陇东地区太原组含铝岩系储层矿物学微观特征

Mineralogical microscopic characteristics of bauxite rock series of Taiyuan Formation in Longdong area,Ordos Basin

近年来,长庆油田在二叠系太原组含铝岩系天然气勘探中取得重大突破,改变了以往对含铝岩系不能形成有效储层的传统认识。由于该类储层矿物难以识别,亟需通过系统分析测试探究含铝岩系储层矿物学微观特征、类型及孔隙发育情况。主要应用扫描电子显微镜、X射线衍射能谱仪,结合岩石薄片鉴定、X射线衍射分析等手段,研究了鄂尔多斯盆地陇东地区太原组含铝岩系储层矿物类型及微观特征。结果表明,研究区含铝岩系储层的主要矿物成分为水铝石和黏土矿物,还有锐钛矿、黄铁矿、菱铁矿等。根据矿物类型、含量、产状等特征,可以将含铝岩系储层分为三段:上部为铝土质泥岩和炭质泥岩,中部为铝土岩,下部为铝土质泥岩。上部地层中的黏土矿物主要为高岭石,富Al、Si等元素;中部以水铝石为主,富Al元素,孔隙发育,自生矿物类型多、晶形好;下部黏土矿物类型以伊利石为主,富K元素。矿物成分及结晶程度差异显示了矿物演化过程中的化学作用对储层孔隙的发育起着重要作用。

Significant breakthroughs have been made in the exploration of natural gas in aluminum-bearing rock series of Permian Taiyuan Formation in Longdong area,Ordos Basin,which has changed the traditional understanding that aluminum-bearing rock series cannot form effective reservoirs.As the minerals are difficult to identify,systematic analysis is necessary to clarify the characteristics and types of micro reservoir minerals and pore development mechanisms.This paper mainly applies scanning electron microscopy X-ray energy spectrometer,combined with rock thin section identification,X-ray diffraction analysis etc.to determine the mineral types and microscopic characteristics of aluminum-bearing rock series reservoirs of Taiyuan Formation.It was shown that the main mineral components of aluminum-bearing rock reservoirs include boehmite,clay minerals,rutile,pyrite,siderite,etc.According to the characteristics of mineral type,content,and occurrence,the aluminum bearing rock reservoir can be divided into three sections,the upper part is composed of bauxite mudstone and carbonaceous mudstone,the middle part is composed of bauxite rock,and the lower part is composed of bauxite mudstone.The upper clay mineral type is mainly kaolinite,rich in elements such as Al and Si.The central part is mainly composed of boehmite,rich in Al,with well-developed pores,multiple types of authigenic minerals,and good crystal shape.The lower clay mineral type is mainly illite,rich in K.The results indicate that the differences in mineral composition and crystallinity indicate that chemical processes during mineral evolution play an important role in the development of reservoir pores.