致密砂岩层内强钙质胶结物成因机制及其意义——以鄂尔多斯盆地三叠系延长组长7油层组为例

通过岩心和薄片观察，利用荧光显微镜、阴极发光显微镜、同位素质谱仪、冷热台等设备，对鄂尔多斯盆地长7油层组强钙质胶结砂岩及其附近含油砂岩开展研究。结果表明：钙质胶结是致密砂岩储层含油非均质性的主要因素，胶结期次主要为一期；簇同位素揭示该期钙质胶结物的形成温度为18~42℃，对应地质时代为中晚三叠世—中侏罗世，为早成岩期产物，推测与盆地早期小规模构造运动相关；相邻的含油砂岩中油气包裹体伴生的同期盐水包裹体的均一化温度为90~120℃，结合盆地模拟揭示油气主要为一期充注，充注期为100~130 Ma，处于早白垩世；长7油层组不含油致密砂岩内钙质胶结物形成时间早于含油砂岩内石油的充注时间。

Mechanism of Strong Calcium Cementation in Tight Sandstone and Its Significance:A Case Study on Triassic Chang 7 Oil Formation of Yanchang Formation in Ordos Basin

Based on core and thin section observation, fluorescence microscope, cathode luminescence microscope, isotope mass spectrometer, and heating/freezing stage, the strong calcareous cementation sandstone and its nearby oil-bearing sandstone of Chang 7 oil formation in Ordos basin were studied. Thin section observation indicates that calcite cementation is the main factor that causes oil-bearing heterogeneity in tight sandstone reservoir, and the majority of cementation occurs at the same period. The result of clumped isotope of the calcite shows that the formation temperature is from 18 to 42 ℃. The corresponding geological period is from the Middle and Late Triassic to Middle Jurassic, a product of early diagenesis related to the early small scale tectonic movement of the basin. The homogenization temperature of the saltwater inclusions associated with oil and gas inclusions is from 90 to 120 ℃, which means that the time of oil filling is Early Cretaceous. In Chang 7 oil Formation, the formation time of the calcareous cement in the non oil tight sandstone is earlier than the oil filling time in the oil-bearing sandstone.