塔里木盆地古城地区下奥陶统碳酸盐岩碳氧同位素特征

CARBON AND OXYGEN STABLE ISOTOPE FEATURES OF THE LOWER ORDOVICIAN IN GUCHENG REGION OF TARIM BASIN

摘要: 下奥陶统碳酸盐岩储层是塔里木盆地古城地区的主要产气层。为了探讨研究区下奥陶统碳酸盐岩碳同位素变化的原因,对取自塔中地区古城7、古城8、古城9和古城12等4口井的51块碳酸盐岩样品进行了分析,结果显示,δ¹³C值为-2.26‰~1.55‰,δ¹⁸O值为-10.57‰~-4.69‰,Mn/Sr也小于2~3的范围。结果表明,研究区碳酸盐岩样品基本保持了碳氧同位素的原始组成。δ¹³C值与海平面变化存在正相关关系,证明研究区早奥陶世晚期存在一海退期。

Abstract: The Lower Ordovician carbonate reservoirs in the Gucheng region of the Tarim Basin are mainly gas plays. 51carbonate rock samples collected from the Well GC7, 8, 9 and 12 are analyzed for carbon and stable oxygen isotopes. The results demonstrate that the δ¹³C fluctuates from -2.26‰ to 1.55‰(PDB), and the δ¹⁸O from -10.57‰ to -4.69‰(PDB). The Mn/Sr is less than 2 or 3. It suggests that the original ratios of C and O isotopes are well preserved. As δ¹³C_PDB values have positive correlation with sea-levels, the results indicate a regression period in Early Ordovician.