摘要:
综合运用岩石学、矿物学和地球化学等方法,对柴达木盆地北缘中段平台地区古近系下干柴沟组下段储集岩中碳酸盐胶结物的成岩温度、形成环境和物质来源等进行了系统研究。结果表明,平台地区储集砂岩中主要发育方解石和白云石两种碳酸盐胶结物。自生黏土矿物主要以伊利石、绿泥石和伊-蒙混层为主,测定其碳同位素(δ13C)值分布范围在-7.5‰~-1.4‰之间,平均为-4.0‰;氧同位素(δ18O)值分布范围在-14.4‰~-10.1‰之间,平均为-11.6‰,推算古盐度(Z)值分布范围为106.38~119.23,平均值为113.24。平台地区古近系下干柴沟组下段储集岩在成岩阶段早期有少量有机碳加入,成岩流体以淡水环境为主。碳酸盐胶结物的形成温度在71.49~101.01℃之间,平均值为81.32℃。根据成岩特征及形成温度,揭示平台地区古近系下干柴沟组下段储集岩主要处于早成岩阶段晚期。
Abstract:
In the light of petrological, mineralogical and geochemical data, the present paper deals, in detail, with diagenetic temperature, genetic environment and origin of the carbonate cements in the lower member of the Palaeogene Xiaganchaigou Formation in the Pingtai region, northern Qaidam Basin. The reservoir sandstones comprise the carbonate cements calcite and dolomite, and authigenic clay minerals illite, chlorite and illitemontmorillonite. The carbonate cements have low carbon isotope (δ13C) values ranging from -7.5‰ to -1.4‰ with an average of -4.0‰, oxygen isotope (δ18O) values from -14.4‰ to -10.1‰ with an average of -11.6‰, and palaeosalinity (Z) values from 106.38 wt% to 119.23 wt% with an average of 113.24 wt%. All these values indicate the involvement of minor amount of organic carbon during the early diagenetic stage of the reservoir sandstones from the lower member of the Palaeogene Xiaganchaigou Formation in the Pingtai region. The carbonate cements have the formation temperatures from 71.49℃ to 101.01℃, with an average of 81.32℃. The abovementioned results show that the diagenetic stage of the reservoir sandstones from the lower member of the Palaeogene Xiaganchaigou Formation in the Pingtai region belongs to the late stage of the early diagenesis.
下载:
