流体-岩石相互作用下白云岩结构与孔隙协同演化机制-以川东北飞仙关组为例

Dolostones have several different fabric types, and the pore types and porosity in these different fabric dolostones are also variable. The fabric is not only of great significance to the dolostone origin, but also controls the development of pores. Therefore, it is much better for comprehensive analyses of pore evolution with fabric to determine the process of the evolution of the fabrics and pores in order to further understand the origin of dolostone and the formation mechanism of pores. Taking the Feixianguan Formation in the northeastern Sichuan Basin as an example, based on the analyses of the evolution of dolostone fabric, as well as the nature and sources of other diagenetic fluids, this project focuses on the co-evolution of rock fabric and pore controlled by fluid-rock interaction, to reveal the key factors controlling the fabrics and pores in dolostones with different fabrics, and to determine the formation mechanism of high-quality reservoirs. Firstly, based on thin section, cathodoluminescence, scanning electron microscopy and fluorescence technologies, the present and original fabrics of dolostones are identified, and then the distribution of rock fabrics is analyzed by combining sequence and sedimentary. Secondly, the nature and sources of dolomitizing fluids, as well as other diagenetic fluids, are determined by using carbonate clumped isotopes, conventional isotope and element analyses. Based on the analysis of the co-evolution of fabric and pore in dolostones, the model will be established.

白云岩具有多种结构类型，不同结构白云岩的孔隙类型和物性存在差异。白云岩结构不仅对白云岩成因具有重要的指示意义，同时也控制着孔隙的发育。因此，将孔隙演化纳入到岩石结构演化中综合分析，确定白云岩结构与孔隙演化过程，可以更加深入的理解不同结构白云岩的成因与孔隙发育机理。本项目以川东北飞仙关组为例，以白云岩结构演化为主线，以成岩流体性质和演化为媒介，分析流体-岩石相互作用下岩石结构与孔隙的协同演化机制，揭示白云岩结构与孔隙差异性的主控因素，阐明优质储层的发育机理。首先，基于薄片、阴极发光、扫描电镜和荧光等技术，识别白云岩的现今结构和原始结构，结合层序和沉积旋回划分，分析岩石结构分布规律；其次，利用团簇同位素新技术、常规同位素和元素分析等，确定白云石化流体和其它成岩流体的性质和来源，分析水-岩相互作用下岩石结构和孔隙协同演化机制，建立白云岩结构和孔隙演化模式。

白云岩是深层-超深层最为重要的油气储层类型之一，成为油气勘探的重点，然而有关白云岩成因和孔隙形成机理的认识仍存在较大争议，受到地质学家的广泛关注。本项目以四川盆地飞仙关组白云岩为主要研究对象，通过岩石学、地球化学的精细研究，阐明白云岩化流体性质和来源，建立了白云岩化模式。白云岩结构类型的差异主要受原岩结构和白云岩形成之后的重结晶作用影响，建立了白云岩岩石结构与孔隙协同演化模式，阐明了白云岩孔隙形成与保存的机理。白云岩的孔隙受控于灰岩原岩、白云岩化过程和白云岩化之后的成岩改造等。灰岩原岩的孔隙主要发育于沉积旋回上部，主要由粒内溶孔和微孔隙组成，抗压实能力强，在埋藏环境下得到有效保存。白云岩化过程是溶解-运移-再沉淀的微过程，存在少量晶间孔的形成，但对有效孔隙的贡献有限。白云岩形成之后的重结晶显著改造了岩石结构和孔隙类型，使得早期以粒内孔隙为主的颗粒白云岩转变为晶间孔为主的中粗晶白云岩。在深层油气勘探中，本项目研究成果为寻找优质白云岩储层提供理论基础。