Geochemical characteristics and origins of fracture- and vug-fillings of the Ordovician in Tahe oilfield, Tarim basin
Geochemical characteristics and origins of fracture- and vug-fillings of the Ordovician in Tahe oilfield, Tarim basin
复制标题
DOI：
--
复制
发表时间：
2009
影响因子：
1.8
通讯作者：
C. Cai;Kaikai Li;Bin Li;Liulu Cai;Lei Jiang
中科院分区：
文献类型：
--
作者：
C. Cai;Kaikai Li;Bin Li;Liulu Cai;Lei Jiang
塔河油田奥陶系碳酸盐岩储层中裂缝充填方解石和巨晶方解石的~（87）Sr/~（86）Sr值主要高于块状灰岩和同期海水，表明该地区富Sr流体的贡献较大。富锶流体可能来源于海西造山运动期间流经碎屑岩地层的古淡水或深部热液。低Sr含量及δD与δ 18 O的关系指示古淡水。古淡水的渗入使早期侵位的原油发生生物降解，生成有机酸和阴离子（OAA），并产生δ 34 S降至-25 ‰的黄铁矿。流体包裹体的均一温度（150~190℃）明显高于环境灰岩，表明放射成因Sr可能来源于前寒武纪碎屑岩地层。热液、盆地流体和可能的新鲜流体的混合导致方解石的溶解，从而改善了局部地区的孔隙度。
Fracture-filling calcite and huge crystalline calcite from Ordovician carbonate reservoirs of Tahe Oilfield were measured to have ~(87)Sr/~(86)Sr mainly higher than bulk limestone and contemporaneous seawater, indicative of a significant contribution from external Sr-rich fluid in this area. Sr-rich fluid may have derived from paleo-freshwater flowing through detrital strata during Hercynian Orogeny or from deep hydrothermal fluid. Paleo-freshwater is indicated by low Sr concentrations and the relationship between δD and δ~(18)O. Infiltration of paleo-freshwater resulted in biodegradation of early emplaced oil and generation of organic acids and anions (OAAs) and pyrite with δ~(34)S down to - 25‰. Hydrothermal fluid is indicated by relatively high Sr concentrations and significantly higher homogenization temperatures of fluid inclusions (up to 150～190℃) than what ambient limestone experienced, suggesting that radiogenic Sr may have derived from deeper pre-Cambrian detrital strata. Mixing of hydrothermal, basinal and likely fresh fluids led to dissolution of calcite, thus improvement of porosity in local areas.