库车坳陷冲断构造带下侏罗统阿合组砂岩沉积-成岩结构与储层形成机制

The complexity and heterogeneity of diagenesis greatly increase, where terrestrial clastic reservoirs are located in the thrust belt and deeply buried. How to analyze the characteristics of diagenesis and spatial and temporal variation in this situation has become a key factor in predicting the distribution of high-quality reservoirs. In this research, the Lower Jurassic Ahe sandstone reservoirs in the thrust belt of Kuqa Depression is chosen as research object, the objective of this research is to (1) carefully analyze sequence stratigraphy, sedimentary facies, microfacies and internal depositional configurations of the Ahe Formation based on the detailed field outcrop profile and drilling core study, and build deposition frameworks of various scales; (2) reveal the relationship between sedimentation and spatial-temporal differentiation of diagenetic alterations under the control of the deposition framework; (3) predict reservoir distribution according to the relationship and formation mechanism between different types of sedimentary-diagenetic frameworks and reservoir quality. The research on cooperation between depositional and diagenetic research, is necessary supplementary to comprehend evolution of the Mesozoic-Cenozoic sandstone reservoirs, Kuqa Depression. And the conclusion will provide theory basis for deep evaluation and prediction of continental clastic reservoir hosted within the typical foreland thrust belt.

当陆相碎屑岩储层位于山前构造冲断带，且埋深较大时，成岩作用的复杂性及非均质性大大增加，如何解析该环境下成岩作用特征及时空分异规律，成为预测优质储层分布的关键因素。基于此，本项目拟以库车坳陷冲断构造带下侏罗统阿合组储层为研究对象，在精细的野外露头剖面及钻井岩芯研究基础上，首先对阿合组层序地层、沉积相和微相以及内部沉积构型进行精细刻画，并搭建多种尺度的沉积格架。之后在沉积格架的控制下，开展成岩作用分析，揭示沉积作用与成岩作用时空分异关系的规律，构建相应沉积-成岩结构模型。最后根据不同类型沉积-成岩结构与储层质量之间的关系及形成机制，预测储层分布。项目拟开展的沉积-成岩协作研究，是对库车坳陷中新生代碎屑岩储层形成演化规律认识的重要补充，也为典型前陆冲断构造带下陆相碎屑岩储层成岩作用研究及储层高精度评价和预测提供理论依据。

库车坳陷侏罗系阿合组是我国“西气东输”大气田群的重要储集层位，其中迪北地区天然气储量丰富，但其砂岩储层以非均质性强、埋藏深为特点，致使勘探开发风险大、成本高，因此认识该区阿合组储层分布规律具有重要意义。通过铸体薄片、扫描电镜（SEM）、压汞法、电子探针、阴极发光、流体包裹体测温及碳氧同位素测试等分析手段，探究库车坳陷东部下侏罗统阿合组砂岩的沉积环境及成岩非均质性对储层质量的影响。主要取得以下认识：（1）研究区阿合组砂岩主要为长石岩屑砂岩及岩屑砂岩，成分成熟度较低。大部分砂岩分选性较好，碎屑颗粒磨圆度以次棱角状及次圆状为主，颗粒之间接触关系以点、线接触为主，部分为凹凸接触。（2）根据阿合组砂岩成岩作用特征识别出4种成岩相及其相应的孔隙成因类型，成岩相A型砂岩以最强压实作用，较少胶结及溶蚀作用为特征；成岩相B型砂岩经历了较强的压实作用，中等程度的胶结及溶蚀作用；成岩相C型砂岩以含有最多的碳酸盐胶结物及中等溶蚀作用为特征；成岩相D型砂岩经受了最强的溶蚀作用，中等程度的胶结及压实作用。（3）通过阿合组砂岩沉积相与成岩相的耦合关系分析，构建了不同沉积微相下的沉积-成岩构型，如辫状河道、水下分流河道及河口坝等微相的沉积-成岩构型。（4）根据砂岩的孔吼结构特征可知，阿合组砂岩中主要存在3种类型的孔吼结构。Ⅰ砂岩通常含有大量的纳米级及亚微米级孔隙，孔隙连通性不好，这类砂岩通常对应A类砂岩，储层质量较差。Ⅱ砂岩以亚微米级孔隙为主，孔隙连通性中等，这类砂岩通常对应B、C类砂岩, 储层质量中等至较好。Ⅲ砂岩以微米级孔隙为主，孔隙连通性较好，这类砂岩通常对应D类砂岩，储层质量最好。（5）沉积环境通过控制沉积结构及碎屑组分影响砂岩储层的非均质性，通常辫状河道及水下分流河道的物性条件最好。后期成岩改造使原始沉积物的孔吼结构发生了较大的改变，加剧了储层的非均质性。