塔北于奇地区奥陶系碳酸盐岩成岩环境分析——来自于流体包裹体的证据

Diagenetic environments of Ordovician carbonate rocks in Yuqi area, northern Tarim Basin: Evidence from fluid inclusion analysis

运用流体包裹体技术,从岩相学特征、均一温度及盐度特征等方面探讨了塔北于奇地区奥陶系储层碳酸盐岩的成岩作用环境及期次。分析结果表明:孔洞充填方解石胶结物中检测到的流体演化趋势为ⅠC(低温-高盐度盐水包裹体)→ⅡA-B(中温-低、中盐度盐水包裹体)→ⅢA(高温-低盐度盐水包裹体);裂缝充填方解石胶结物中检测到2期流体,分别为中温-低、中盐度流体(ⅡA-B)和中温-中、高盐度流体(ⅡB-C),这2期流体的盐度随均一温度的升高而降低。结合研究区沉积埋藏史,推断盐水包裹体指示该区成岩环境演化趋势为海洋成岩环境向大陆成岩环境演变,在加里东—海西早期经历了表生大气水环境的改造,其后随中新生界的沉积再次埋藏,构成了中期开启型成岩演化系统。

The Ordovician carbonate rock is one of the principal producing formations in Yuqi area, northern Tarim Basin. Through the use of fluid inclusion technology, this paper discussed the diagenetic environment and stages of Ordovician carbonate reservoir from the aspects of petrography characteristics, homogenization temperature and salinity. The result shows that three groups of saline water inclusions were detected in pore filling calcite, and the fluid evolutionary trends is I c（low temperature and high salinity）---＋ H A-S （middle temperature and low to middle salinity）--Ⅲ A （high temperature and low salinity）; there are two episodes of fluid activities in fracture filling calcite： Ⅱ A- （middle temperature and low to middle salinity） and Ⅱ B-C （middle temperature and middle to high salinity）, and both of their salinity decrease with homogenization temperature increase. Combined with burial history and saline water inclusions research in Yuqiarea, the evolution of diagenetie environments was determined to trend from marine to continental diagenetic environment. During Caledonian-early Hercynian stage, Yuqi area experienced exposure palaeokarst, and subsequently buried with the Meso-Cenozoic deposition, which constitutes a diagenetic evolution of a mid open-type system.