塔河油田下古生界溶洞充填巨晶方解石流体来源分析

塔河油田溶洞巨晶方解石充填物的微量元素、碳、氧、锶同位素地球化学和流体包裹体的对比研究表明,不同井位巨晶方解石可能来源于不同的流体体系。T417井和S76井鹰山组、T904井一间房组及TS1井丘里塔格组溶洞巨晶方解石样品具有富U、高V/Cr特征,且均一温度主要分布于148.9～169.9℃,相对围岩所经历最高温度约20℃,反映为还原性的热液流体体系,该流体具有高~(87)Sr/~(86)Sr及低δ~(18)O的特征。T904井良里塔格组巨晶方解石具有贫U、低V/Cr及均一温度较低的特征(75～81℃),反映为富氧低温流体体系,结合样品的高~(87)Sr/~(86)Sr及低δ~(18)O特征,可以推测该低温流体可能为大气水来源。热液流体与大气淡水的运移受断层、裂缝和不整合面等因素控制,从而使得不同井位、层位的巨晶方解石沉淀时具有不同的流体成分与温度特征。

Fluid origin of cave-filling giant crystalline calcites in the Early Paleozoic in Tahe Oilfield, Tarim Basin and the model of the fluid action

Trace elements,δ~(13)C,δ~(18)O and ~(87)Sr/~(86)Sr of cave-filling giant crystalline calcites and fluid inclusion homogenization temperatures(HTs)were analyzed from each formation in the Eopalaeozoic carbonate reservoirs. Result shows that the giant crystalline calcite samples in different wells may have various fluid origins. The shared characters of giant crystalline calcites in well T417(Yingshan Formation),S76(Yingshan Formation),T904(Yijianfang Formation)and TS1(Qiulitage Formation)are:U-rich,high V/Cr ratios and at least 20 ℃ higher than the ambient rocks. It reflects that there is a hot fluid in these wells and these fluids show high ~(87)Sr/~(86)Sr ratios and low δ~(18)O values. The giant crystalline calcite samples in well T904(Lianglitage Formation)are charactized by U-deplete,low V/Cr ratios and temperature(75～81 ℃),which indicates a low temperature fluid. The characters of ~(87)Sr/~(86)Sr-rich and low δ~(18) O values suggest that this low temperature fluid should be derived from meteoric water. The migration of the hot fluid and meteoric water is likely controlled by various elements:faults,cracks,and unconformity,etc. So the giant crystalline calcites in different formations and wells may origin from various fluids.