塔河油田中下奥陶统岩溶缝洞方解石碳、氧、锶同位素地球化学特征

为了探讨塔河油田中下奥陶统古岩溶产物的地球化学特征以及评价不同期次古岩溶作用的影响区域, 系统分析了中下奥陶统岩溶缝洞方解石的碳、氧、锶同位素.不同产状的方解石碳、氧同位素具有明显的大气水岩溶特征, 早期岩溶产物以富集13C和低87Sr/86Sr比值为特征, 而海西早期岩溶产物以δ13C分布较宽和高87Sr/86Sr比值为特征, 两者的δ18O值分布均较宽.桑塔木组覆盖区比北部地区富集13C, 来自围岩的13C比重加大, 另一个原因是早期岩溶产物的δ13C值较高; 桑塔木组覆盖区岩溶产物具有高87Sr/86Sr比值特征, 说明有壳源锶的注入, 主要是受海西早期岩溶作用的影响, 并且高87Sr/86Sr比值特征比北部地区低, 其原因是来源于围岩的重溶锶比重加大.δ13C和87Sr/86Sr在区域上的变化, 结合区域地质背景, 表明海西早期岩溶对北部地区和桑塔木组覆盖区均有重要的影响, 是塔河油田中下奥陶统碳酸盐岩的主岩溶期, 也是其储层的主要形成时期. 

Geochemistry Characteristics of Carbon,Oxygen and Strontium Isotopes of Calcites Filled in Karstic Fissure-Cave in Lower-Middle Ordovician of Tahe Oilfield,Tarim Basin

For discussing the geochemistry characteristics of paleokarstic products of Lower-Middle Ordovician in Tahe oilfield, and evaluating the areas influenced by different stages of paleokarst, the carbon, oxygen and strontium isotopes of karstic fissure-cave calcites have been systematically analyzed.The carbon and oxygen isotopes of different attitude calcites are characterized by meteoric water karst, and the early paleokarstic products are featured with enriched 13C and lower 87Sr/86Sr ratios.The wide ranges of δ13C and high 87Sr/86Sr ratios are the characteristics of early Herlynian paleokarst, and both have wide ranges of δ18O.The areas covered with O3s Formation are enriched with more 13C than those of north areas, indicating the increased proportion of 13C from the host rock.And another reason is the higher δ13C of early paleokastic products.Under the influence of the early Herlynian paleokarst, the strontium isotopes of different attitude calcites are heavier than the background values, indicating the join of the terrestrial strontium.The features of heavier strontium in north areas are lower than those of the areas covered with O₃s Formation, indicating the increased proportion of the dissolved strontium from the wall rock.According to the regional variations of carbon, strontium isotopes and geologic background, the early Herlynian paleokarst exerted important impact on the carbonate rocks of the Lower-Middle Ordovician in the north areas and the areas covered with O3s Formation, and it is the main karst episode of Tahe oilfield and also the main formation episode of reservoir.