Origin and evolution of oilfield brines from Tertiary strata in western Qaidam Basin:Constraints from ^(87)Sr/^(86)Sr,δD,δ^(18)O,δ^(34)S and water chemistry  

作　　者：FAN Qishun MA Haizhou LAI Zhongping TAN Hongbing LI Tingwei 

机构地区：[1]Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China [2]Graduate School of Chinese Academy of Sciences, Beijing 100049, China [3]State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China

出　　处：《Chinese Journal Of Geochemistry》2010年第4期446-454,共9页中国地球化学学报

基　　金：supported by CAS Major Basic Preliminary Program (2004CCA03500);the National Natural Science Foundation of China (No. 40603007)

摘　　要：Chemistry of major and minor elements,87Sr/86Sr,δD,δ18O and δ34S of brines were measured from Tertiary strata and Quaternary salt lakes in the western Qaidam Basin.The water chemistry data show that all oilfield brines are CaCl2 type.They were enriched in Ca2+,B3+,Li+,Sr2+,Br-,and were depleted in Mg2+,SO42-,which indicated that these brines had the characteristics of deeply circulated water.The relationship between δD and δ18O shows that all data of these brines decline towards the Global Meteoric Water Line(GWL) and Qaidam Meteoric Water Line(QWL),and that the intersection between oilfield brines and Meteoric Water Lines was close to the local spring and fresh water in the piedmont in the western Qaidam Basin.The results suggest that oilfield brines has initially originated from meteoric water,and then might be affected by water-rock metamorphose,because most oilfield brines distribute in the range of metamorphosing water.The 87Sr/86Sr values of most oilfield brines range from 0.71121 to 0.71194,and was less than that in salt lake water(>0.712),but close to that of halite in the study area.These imply that salt dissolution occurred in the process of migration.In addition,all oilfield brines have obviously much positive δ34S values(ranging from 26.46‰ to 54.57‰) than that of salt lake brines,which was caused by bacterial sulfate reduction resulting in positive shift of δ34S value and depleteed SO42-in oilfield brines.Combined with water chemical data and δD,δ18O,87Sr/86Sr,δ34S values,we concluded that oilfield brines mainly originate from the deeply circulated meteoric waters,and then are affected by salt dissolution,water-rock metamorphose,sulfate reduction and dolomitization during the process of migration.These processes alter the chemical compositions of oilfield brines and accumulate rich elements(such as B,Li,Sr,Br,K and so on) for sustainable utilization of salt lake resources in the Qaidam Basin.Chemistry of major and minor elements,87↑Sr/86↑Sr,δ↑D,δ18↑O and δ34↑S of brines were measured from Tertiary strata and Quaternary salt lakes in the western Qaidam Basin.The water chemistry data show that all oilfield brines are CaCl2 type.They were enriched in Ca^2＋,B^3＋,Li^＋,Sr^2＋,Br^-,and were depleted in Mg^2＋,SO4^2-,which indicated that these brines had the characteristics of deeply circulated water.The relationship between δD and δ18O shows that all data of these brines decline towards the Global Meteoric Water Line（GWL） and Qaidam Meteoric Water Line（QWL）,and that the intersection between oilfield brines and Meteoric Water Lines was close to the local spring and fresh water in the piedmont in the western Qaidam Basin.The results suggest that oilfield brines has initially originated from meteoric water,and then might be affected by water-rock metamorphose,because most oilfield brines distribute in the range of metamorphosing water.The 87↑Sr/86↑Sr values of most oilfield brines range from 0.71121 to 0.71194,and was less than that in salt lake water（〉0.712）,but close to that of halite in the study area.These imply that salt dissolution occurred in the process of migration.In addition,all oilfield brines have obviously much positive δ34↑S values（ranging from 26.46‰ to 54.57‰） than that of salt lake brines,which was caused by bacterial sulfate reduction resulting in positive shift of δ↑34S value and depleteed SO4^2-in oilfield brines.Combined with water chemical data and δ↑D,δ18↑O,87↑Sr/86↑Sr,δ34↑S values,we concluded that oilfield brines mainly originate from the deeply circulated meteoric waters,and then are affected by salt dissolution,water-rock metamorphose,sulfate reduction and dolomitization during the process of migration.These processes alter the chemical compositions of oilfield brines and accumulate rich elements（such as B,Li,Sr,Br,K and so on） for sustainable utilization of salt lake resources in the Qaidam Basin.

关 键 词：柴达木盆地西部 油田卤水 第三纪 水化学 地层 硫酸盐还原 锶 演化 

分 类 号：P618.130.2[天文地球—矿床学] P618.510.4[天文地球—地质学]