鄂尔多斯盆地西南部上古生界致密砂岩中碳酸盐胶结物特征及成因

在盆地内部钻井岩心与盆地西南缘野外露头观察基础上，综合运用薄片鉴定、扫描电镜、电子探针、微区碳氧同位素、流体包裹体均一温度与激光拉曼成分分析，开展了鄂尔多斯盆地西南部上古生界盒8段致密砂岩储层中碳酸盐胶结的成因机制研究。结果显示，盒8段致密砂岩储层中存在4期碳酸盐胶结：①同生成岩阶段碳酸盐胶结物形成于烃类充注之前，直接从碳酸盐过饱和的沉积水中析出；②早成岩阶段B期和中成岩阶段A期的碳酸盐胶结物与烃源岩中生烃、排烃提供的有机碳源有关；③盆地抬升阶段形成的碳酸盐胶结物受到大气降水等无机碳源的影响。盆地西南缘盒8段储层中的烃类充注始于烃源岩演化早期（80 ℃左右），在早成岩阶段B期就形成了规模较大的有机碳源成因的碳酸盐胶结物；盆地内部规模较大的烃类充注发生在烃源岩成熟之后（120 ℃左右），有机碳源成因的碳酸盐胶结物主要形成于中成岩阶段A期。

Characteristics and genetic mechanism of carbonate cements in Upper Paleozoic tight sandstones， southwestern Ordos Basin

This study performed the analysis of genetic mechanism of carbonate cements from the tight sandstone reservoir of He8 member of Upper Paleozoic in southwestern Ordos Basin， based on measurement of thin sections identification， scanning electron microscopy， electron microprobe， micro-area carbon and oxygen isotope， homogenization temperature and laser Raman composition analysis of fluid inclusions. In this study， a comparative analysis was made between the drilling core in the basin and the outcrop in the southwest margin of the basin. The results show that there are four stages of carbonate cementation. （1） During the syngenetic stage， carbonate cement precipitated directly from the carbonate supersaturated sedimentary water， which was formed before the hydrocarbon charge. （2） The formation of carbonate cements in period B of early diagenetic stage and period A of middle diagenetic stage was related to organic carbon sources provided by hydrocarbon generation and expulsion in source rock. （3） Carbonate cements formed in uplift stage of the basin during middle diagenetic stage was affected by inorganic carbon sources such as atmospheric precipitation. The hydrocarbon charge of the southwestern margin of the basin started at the early stage of source rock evolution（around 80 ℃）， a large-scale carbonate cement of organic carbon origin was formed in the period B of early diagenetic stage. The major hydrocarbon charge inside the basin began after the maturity of source rock （about 120 ℃）， and carbonate cement of organic carbon origin was mainly formed in the period A stage of middle diagenetic stage.