自生黏土矿物对深水致密砂岩储层微观非均质性的影响——以鄂尔多斯盆地西南部合水地区长6油层组为例

Impact of authigenic clay minerals on micro-heterogeneity of deep water tight sandstone reservoirs:a case study of Triassic Chang 6 oil reservoir in Heshui area,southwestern Ordos Basin

鄂尔多斯盆地合水地区上三叠统延长组长6油层组重力流砂岩储层自生黏土矿物发育,导致其孔喉结构复杂、微观非均质性强、物性较差。基于以往的研究成果,利用铸体薄片、图像粒度、扫描电镜、矿物X射线衍射、高压压汞、物性、激光共聚焦等资料,研究了自生黏土矿物对长6储层微观非均质性的影响。结果表明:①自生黏土矿物作为该地区最主要的成岩产物,对长6储层微观非均质性有重要影响,是导致储层致密化的重要因素之一。②储层中自生黏土矿物主要为绿泥石、伊利石及高岭石。绿泥石和高岭石在砂质碎屑流与浊流储层中的含量相近,伊利石在浊流储层中含量较高。③伊利石是影响储层渗流能力和控制储层微观非均质性的主要黏土矿物,从距今102 Ma之后,储层开始受伊利石胶结作用影响,其微观非均质性整体变强。④根据伊利石含量及渗透率大小将研究区划分为3类地区。第1类为伊利石弱胶结区,微观非均质性弱,主要分布于研究区东北部,为"甜点区"首要勘探目标;第2类为伊利石中等胶结区,微观非均质性中等,主要位于研究区中部,为"甜点区"次要勘探目标;第3类为伊利石强胶结区,微观非均质性强,主要位于研究区西南部,为非"甜点区"。该研究结果可为鄂尔多斯盆地长6油层组微观非均质性研究提供借鉴。

The intense development of authigenic clay minerals of the gravity flow reservoir in Chang 6 oil reservoir in Heshui area resulted in its complex pore throat structure,strong micro-heterogeneity,thus relatively poor physical properties.Based on the previous research results,the influence of authigenic clay minerals on the microheterogeneity of Chang 6 reservoir was studied by means of casting thin section,image grain size,scanning electron microscope,mineral X-ray diffraction,high-pressure mercury injection,physical properties and laser scanning confocal microscope.The results show that:(1)As the main product of diagenesis,authigenic clay minerals have an important influence on the micro-heterogeneity of Chang 6 oil reservoir,which is one of the major factors caused reservoir densification.(2)The authigenic clay mineral in the reservoir are mainly chlorite,illite and kaolinite.Among them,the content of chlorite is basically as same as that of kaolinite in sandy clastic flow and turbidity flow reservoirs,while illite content is higher in the turbidity flow reservoir.(3)Illite is the most important authigenic clay mineral that controls the percolation ability of the reservoir,and has an important influence on the micro-heterogeneity of the reservoir.The reservoir began to be affected by illite cementation and its heterogeneity became intense as a whole after 102 Ma.(4)Three zones can be divided at the study area based on the illite content and permeability of the reservoir.The first zone is the illite weak cementation area where the reservoir is of weak micro-heterogeneity and is mainly located in the northeastern of the study area,which is the priority exploration target area of the"sweet spot".The second zone is the illite moderate cemented area,where the reservoir is of moderate micro-heterogeneity and is mainly located in the central part of the study area,which is the secondary"sweet spot"exploration target.The third one is the illite intensively cemented zone,where the reservoir is of strong micro-heterogeneity and is mainly located in the southwestern of the study area,which is a"nonsweet spot area".The research results can provide a reference for the integrated research on the micro-heterogeneity of Chang 6 oil reservoir in Ordos Basin.