超深层砂岩粘土矿物特征及其对储层物性的定量控制作用——以库车前陆冲断带白垩系巴什基奇克组为例

Clay mineral properties： A characteristics and case of Cretaceous quantitative effects on the reservoir Bashijiqike of Kuqa foreland thrust

库车前陆冲断带超深层储层是当前天然气勘探开发的重要领域， 具有特低孔、特低渗—低渗， 裂缝—孔隙型， 测试高产储集特征。 为揭示储层中粘土矿物的特征及其对储层演化、储层性质的控制作用， 本文以大量微观实验分析（X 衍射、扫描电镜、激光共聚焦扫描、 铸体薄片、高压压汞）为依据， 研究表明：主要的粘土矿物含量为 5%～12%， 矿物类型以伊利石、伊蒙混层为主， 其次为绿泥石， 成因以成岩早期沉积水体继承性沉淀及成岩中晚期长石质次生溶蚀产物为主；砂岩中早期沉积型粘土矿物主要富集于三角洲前缘水下河道砂体的侧缘、水道砂体的顶底面附近， 其形成粘土薄膜可有效抑制超深层储层早中成岩期硅质、长石质次生加大， 保存基质孔隙， 不同期粘土杂基也可提供大量矿物晶间微孔隙， 微孔隙度可达 1%～4%， 是天然气的主要储集空间之一；粘土矿物是降低储层渗透率的主控因素， 6%～ 9%的粘土矿物含量（尤其是伊利石及伊蒙混层）可降低超深层储层渗透率 10～100 倍， 使渗透率总体为 0.01×10^-3 μm^2 ～0.1×10^-3 μm^2 。 粘土矿物含量及赋存特征：早期长期（130～23 Ma）浅 埋（〈 3 000 m）期储集性能保存良好， 晚期（23 Ma 左右）深埋（〉 3 000 m）期基质渗透性急剧降低， 总体致密化（〈 0.1×10^-3 μm^2 ）， 这是研究区的关键因素。 粘土矿物的特征及其分布对评价砂岩储集性质， 预测超深层天然气有利储层的分布具有重要地质意义。

The ultra-deep reservoir in Kuqa foreland thrust belt with properties of ultra-low porosity, ultra？low-low permeability, fracture-pore spaces and high yield test is very important target for gas exploration and development at present. To elucidate the characteristics of clay minerals and its control functions on reservoir evolution and reservoir characteristics, this paper is based on lots of micro-experiment analysis（X-ray diffraction, scanning electron microscope, confocal laser scanning microscope, casting thin sections, high pressure Hg injection）. Results indicated that clay mineral content is 5% ～12% composed by illite and illite-montmorillonite mixed-layer mainly and chlorite secondly. The clay minerals are generated by succession sedimentary water precipitation in early stage of diagenesis and feldspathic dissolution in middle and late stage of diagenesis. The early sedimentary clay mineral in the sandstone are mainly enriched in the edge of the delt front or near the top and bottom of the water channel, and its membrane can effectively inhibit overgrowth of quartz and feldspathic in the ultra-deep reservoir in early and middle stage of diagenesis and preserve matrix pores. The clay matrix of different stage can provide mineral intercrystal micropores with porosity of 1% ～4% and the intercrystal micropore is one of the main gas reservoir spaces. Clay minerals are the main controlling factor for reducing reservoir permeability. The clay mineral content of 6% ～9% （especially illite and illite-montmorillonite mixed-layer ）can reduce the permeability of ultra- 2 deep reservoir by 10～100 times, and result the overall permeability is 0.01×10^-3 μm^2 ～0.1×10^-3 μm^2 . The content of clay mineral and its occurrence characteristics are the key factors for the well preservation of reservoir in the long time（130～23 Ma）shallow buried（〈 3 000 m） period, the dramatic decrease of matrix permeability in late（23 Ma～）deep buried（〉 3 000 m）period and reservoir overall densifying（〈 0.1×10^-3 μm^2 ）. The characteristics and distribution of clay minerals with great geological significance to evaluate the sandstone reservoir properties and to predict the distribution of favorable reservoirs for ultra-deep gas.