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

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.