塔东地区英东2井寒武系-奥陶系储层流体地球化学示踪

Geochemical tracing of the Cambrian-Ordovician reservoir fluid in Well Yingdong-2,eastern Tarim Basin

系统分析了英东2井中、上寒武统和中、下奥陶统围岩及裂缝中充填物的碳、氧、锶同位素、稀土元素及流体包裹体等地球化学特征。在此基础上,根据示踪流体的形成期次、来源,划分流体充注的时序关系,探讨流体对储层改造的影响,进而对油气动态保存条件进行探索性评价。流体地球化学研究表明,中、上寒武统和中、下奥陶统存在3期外来壳源富锶流体,其中第一期流体的87Sr/86Sr比值为0.710 8,第二期流体的87Sr/86Sr比值介于0.709 8～0.710 0,最晚一期为来自地壳深部的热液流体,其87Sr/86Sr比值为0.713 8。3期流体对储层的储集性能均起到了破坏性作用,但晚期热液流体在对储层改造的同时具有一定的建设性作用。最早一期流体充注时,中、上寒武统储层具有相对较好的油气保存条件;随后两期流体充注时,中、上寒武统储层不再具有保存油气的能力。流体地球化学示踪为动态了解英东构造带乃至整个塔东地区深部流体活动提供了一个新方法。

The isotopes of carbon,oxygen and strontium,REE,and the geochemical features of the fluid inclusions in the Middle-Upper Cambrian and Middle-Lower Ordovician side-beds and fracture fillings of the well Yingdong-2 were systematically analyzed.Based on the results,we traced phases and sources of the reservoir fluids,determined chronogenesis of fluid charging,explored the impact of the fluids upon reservoir modification and discussed the dynamic preserving conditions for oil and gas in such settings.The geochemical study of the fluids suggests that there are three charging phases of allogenic fluids with abundant Sr from the crust in the Middle-Upper Cambrian and Middle-Lower Ordovician.The fluids charged in the first phase have a 87Sr/86Sr ratio of 0.710 8,the fluids charged in the second phase have a 87Sr/86Sr ratio in the range of 0.709 8-0.710 0,and the fluids charged in the last phase are hydrothermal fluid from the deep crust and have a 87Sr/86Sr ratio of 0.713 8.The fluids charged in these three phases all played a destructive role in the forming of reservoirs,but the hydrothermal fluids charged in the last phase were constructive to the reservoir formation.The Middle-Upper Cambrian reservoirs had relatively better hydrocarbon preserving conditions during the first phase of fluid charging,but lost them when the second and the third phase occurred.Geochemical tracing of fluids provides a new method for dynamic evaluation of deep fluid activities in the Yingdong tectonic belt as well as the whole eastern Tarim Basin.