陆西地区火山岩中碳酸盐矿物氧碳稳定同位素特征

Characteristic of Carbonate Oxygen-Carbon Stable Isotopes in Volcanic Rocks in Luxi Area,Junggar Basin

准噶尔盆地陆西地区火山岩孔隙中充填的碳酸盐岩对储集层物性产生巨大影响,通过对碳酸盐充填物的氧碳稳定同位素分析表明,δ13C和δ18O值均较轻且Z值较低,反映其形成于淡水环境,碳酸盐结晶温度大致分3种情况:早成岩作用阶段早期占大多数,部分形成于表生风化淋滤阶段,个别形成于热液作用阶段。通过氧同位素与古地温间的关系,推测碳酸盐充填物的结晶时间大致为晚三叠世到早侏罗世。烃源岩低成熟至成熟早期,靠近生烃凹陷的低凸带上,受淡水淋滤作用,火山岩中仍然存在部分未被碳酸盐岩充填的气孔。烃源岩大量排烃期,靠近凹陷区受溶蚀作用较强,可能存在相对优质的火山岩储集层发育区。

The study of the volcanic rocks in Luxi area of Junggar basin indicates that the carbonate minerals placing in pores has great effect on the reservoir property. The oxygen-carbon stable isotopes in them are analyzed, showing that the values of δ^13C and δ^18O are lighter and Z value is low, which reflect they are formed in fresh water environment. Based on the carbonate crystallization temperature they occur in three settings： the most carbonate minerals are formed in the early stage of early diagenesis, some formed in the weathered and leaching stage, a few in the hydrothermal stage. Through the relationship between the oxygen isotope and the paleo-temperature, it is deduced that the crystallization time of spacing carbonate minerals could be from Late Triassic to Early Jurassic. The source rocks reach the stage of low maturity to early high maturity. They are distributed in low swell zone adjacent to the source sag and subjected to freshwater leaching process. In the volcanic rocks there still exists part of the pores not filled by the carbonate minerals. In period of major hydrocarbon expulsion from the source rocks, the nearer the source sag, the stronger the solution is, and there could be relatively premium volcanic reservoirs in this area.