酒西盆地砂岩储层碳酸盐胶结物分布及碳、氧稳定同位素富集特征

碳酸盐胶结物是酒西盆地石油沟油田古近系白杨河群间泉子组（N₁b₁）M油组砂岩储层中最重要的自生矿物，其含量及分布是储层定量评价的主要参数。通过矿物学、岩石学和地球化学测试分析认为，该区碳酸盐胶结物主要以方解石为主，少量白云石胶结物，胶结物分布范围为2.11%~56.39%，平均为12.93%。碳酸盐胶结物以基底式、孔隙式结构为主，部分斑点状、环边状。研究表明，不同微相砂体中碳酸盐胶结物相对含量明显不同，其中沙坝微相含量最高，平均为14.6%，河心滩微相含量最低，平均为8.09％，而滞留沉积微相含量居中，平均为7.73％。碳、氧稳定同位素分析表明，δ¹⁸O（PDB）值为-11.14‰~-3.25‰，δ¹³C（PDB）值为-7.32‰~-0.42‰，显示了该区碳酸盐胶结物来自淡水—微咸水环境，与溶解—沉积作用相关。δ¹³C、δ¹⁸O 值呈现由深部到浅部逐渐变小、变轻的趋势，说明由深到浅大气淡水影响逐渐增强，水体盐度减小，成岩温度逐渐增高。研究还发现，碳酸盐胶结物δ¹⁸O、δ¹³C值的分异与油气富集程度具较好的分区性，油浸—含油级砂岩碳酸盐胶结物富集δ¹³C，油斑—油迹级砂岩缺少δ¹⁸O同位素，荧光级砂岩胶结物同时缺少δ¹⁸O和δ¹³C同位素。

Distribution of carbonate cements and enrichment characteristics of carbon and oxygen stable isotopes in sandstone reservoirs in Jiuxi Basin

Carbonate cements are the most important authigenic minerals in sandstone reservoirs of Paleogene Baiyanghe Group Jianquanzi Formation（N₁b₁） M oil formation in Shiyougou oilfield， Jiuxi Basin. The content and distribution of carbonate cements are the main parameters of reservoir quantitative evaluation. According to the analysis of mineralogy， petrology and geochemistry， the carbonate cements in this area are mainly calcite and a small amount of dolomite cements. The distribution range of cements is 2.11%-56.39%， with an average of 12.93%. Carbonate cements mainly have base-like structures， some of which are speckled and ringed. The distribution and content of carbonate cements are controlled by sedimentary microfacies. The braided river bar has the highest carbonate content with an average of 14.6%， the riverbank microfacies sand body has an average of 8.09%， and the retained conglomerate carbonate cements at the bottom of the river channel have a medium content with an average of 7. 73%.The δ¹⁸O（PDB） and δ¹³C（PDB） values range from -11.14‰ to -3.25‰ and from -7.32‰ to -0.42‰， respectively， indicating that the carbonate cements in this area come from fresh-bracky-water environment and are related to dissolution-deposition. The δ¹³C and δ¹⁸O values gradually decrease and become lighter from deep to shallow， indicating that the influence of atmospheric fresh water gradually increases， water salinity decreases and diagenetic temperature increases gradually from deep to shallow. It is also found that the differentiation of δ¹⁸O and δ¹³C values of carbonate cements and the degree of hydrocarbon enrichment have a good zonation. The carbonate cements of oil-immersed to oil-bearing sandstones are enriched in δ¹³C， the oil-spot to oil-trace sandstones lack δ¹⁸O isotopes， and the fluorium-grade sandstones lack both δ¹⁸O and δ¹³C isotopes.