湖盆深水砂岩中碳酸盐胶结物成因及分布规律-以鄂尔多斯盆地延长组为例

Carbonate cement volume and distribution of lacustrine deep-water tight sandstone has become an important influence factor of hydrocarbon reservoir, thus affecting hydrocarbon distribution. Many previous studies have examined the origin of carbonate cement in fluvial, deltaic, and turbidities sandstones. Relatively few of these studies have sufficient data to determine origin and distribution of carbonate cement in lacustrine deep-water settings tight sandstone. This project takes Triassic YanChang Formation of Ordos Basin as a case, conjugating the characteristics of micro thin-section with core, and log response, combining the characteristics of thin-section of rock and mineral with geochemical analysis datum, integrating the characteristics of point micro-profiling with region distribution of carbonate cement zone, analysised the diagenesis characteristics, the diagenetic environment and interaction of fluid and rock of the diagenetic evolution process in lacustrine deep-water tight sandstone, to determine the origin of the carbonate cement; quantitative estimation the effect of carbonate cement on the quality of the reservoir in different diagenetic evolutionary stages, established the relationship between the carbonate content and porosity and The lower limit of carbonate cement on oil sand stone; and distribution of carbonate content on space-time integrated with deposit and diagenetic environment.

湖盆深水成因砂岩中碳酸盐胶结物含量、分布已成为影响致密油气储层的一个重要因素，进而影响着油气分布。目前研究主要集中在河流-三角洲成因砂体和深海浊积岩中碳酸盐成因机理探讨，较少对湖盆深水成因砂岩中碳酸盐胶结物的成因和分布规律研究。本项目拟选取鄂尔多斯盆地三叠系延长组湖盆深水致密砂岩为对象，将薄片观察与岩心描述、测井响应相结合，将薄片观察的岩石特征与地球化学分析化验相结合，点的微观剖析与区域碳酸盐胶结带的分布相结合，分析湖盆深水成因砂体中碳酸盐胶结物特征、成岩环境、成岩演化过程中流体与岩石的相互作用，揭示湖盆深水砂岩中碳酸盐胶结物成因机理；定量评估不同成岩演化阶段碳酸盐胶结物对储层质量的影响，建立碳酸盐含量与孔隙度之间的关系，确定含油砂体碳酸盐胶结物含量的下限；结合沉积环境、成岩环境及成岩演化分析确定碳酸盐胶结物时空分布规律。

湖盆深水成因砂岩中碳酸盐胶结物含量、分布已成为影响致密油气储层的一个重要因素，进而影响着油气分布。通过对鄂尔多斯盆地华庆地区白153井区和黄陵地区长6段深水砂岩中碳酸盐胶结物的对比性研究，（1）确定了深水砂岩碳酸盐胶结物的类型、赋存状态、发育期次、（2）探讨了碳酸盐胶结物形成的条件、成岩环境及其成因机制和（3）总结了碳酸盐胶结物分布规律，从而揭示了湖盆深水砂岩中碳酸盐胶结物成因机制、孔隙演化过程中碳酸盐胶结物对储层质量影响和确定湖盆深水砂岩碳酸盐胶结物时空分布规律。.研究表明鄂尔多斯盆地深水砂岩中碳酸盐胶结物主要组成方解石、白云石、铁方解石和铁白云石；划分为三期胶结，早期方解石和白云石，中期铁方解石和晚期铁白云石；早期主要是在浅埋藏阶段从碳酸盐过饱和孔隙水介质中沉淀出的产物；中晚期与有机酸脱羧酸作用产生CO2有关，钙离子来自长石溶蚀、黏土矿物的转化及（铝）硅酸盐矿物的水化作用。理论计算，碳酸盐胶结物的时间上主要为成岩早期碳酸盐胶结，使储层致密；碳酸盐胶结物导致储层孔隙度下降12.05%-18.07%。钙质砂岩平面上主要分布在砂体边界，空间上主要分布在砂体顶底和构型界面处。.项目的研究成果对具有相似地质背景的沉积盆地，对湖盆中致密砂岩储层中储层甜点的预测、储层评价提供一定理论依据，为致密油储层注水开发方案的制定和剩余油预测提供一定地质依据；而且为准连续型-连续型砂岩油气成藏过程提供一定补充，将对鄂尔多斯盆地致密油气勘探和开发提供重要理论和现实意义。