塔里木盆地麦盖提斜坡奥陶系风化壳成藏条件

Reservoir-forming conditions of the Ordovician weathering crust in the Maigaiti slope, Tarim Basin, NW China

基于地震、钻井资料综合研究,分析塔里木盆地麦盖提斜坡及其周缘古隆起背景上奥陶系风化壳特征及其储集层发育主控因素,探讨该区油气分布规律与勘探方向。区域构造成图与构造解析表明,麦盖提斜坡及其周缘发育塔里木盆地最大规模的奥陶系碳酸盐岩风化壳,与上覆志留系/石炭系泥岩形成优质储盖组合。奥陶系碳酸盐岩历经多期大型岩溶作用,以受古岩溶地貌、构造作用与岩性控制的小型缝洞体储集层为主。已有钻探多位于北部岩溶缓坡—洼地,岩溶作用较弱、充填严重,据古地貌分析与储集层预测,南部岩溶斜坡区储集层应更发育。构造演化与生烃演化史综合分析表明,碳酸盐岩古隆起演化与变迁控制了油气的运聚与分布,具有晚海西期成油、喜马拉雅晚期调整与原油裂解气再成藏的两期充注史。古隆起东西两端的玛南、麦西斜坡区长期位于油气聚集与调整的有利部位,具备形成大面积碳酸盐岩缝洞型岩性油气藏的地质条件,是塔里木盆地碳酸盐岩油气勘探的有利接替领域。

Based on the seismic and drilling data,the characteristics and reservoir controlling factors,as well as oil and gas distribution law and exploration direction,are analyzed in the Ordovician weathered crust in the Maigaiti slope and its periphery with paleo-uplift background in the Tarim Basin.Structure mapping and analysis reveal that the largest carbonate weathered crust is developed around the Maigaiti slope which forms a favorable reservoir-seal assemblage with the overlying Silurian/Carboniferous mudstone.The Ordovician carbonates experienced multi-stages of karstification and are dominated by small-size fracture-vug reservoirs which are controlled by the karst palaeo-geomorphology,tectonism and lithology.Drilled wells are located mainly in the northern karst depression which has weak karstification and heavy filling.Palaeo-geomorphology reconstruction and seismic reservoir prediction suggest that reservoirs be well-developed in the southern karst slope.The comprehensive analysis of structure revolution and hydrocarbon generation history demonstrates that the hydrocarbon migration and accumulation is controlled by the evolution and migration of the palaeo-uplift.There are two charging stages： large scale oil accumulation in the late Hercynian period and adjustment and re-accumulation of oil cracked gas in the late Himalayan period.The Manan and Maixi slopes in the eastern and western sides of the palaeo-uplift are the favorable areas for hydrocarbon accumulation and adjustment over a long period of time,have the conditions of forming large-scale carbonate fracture-vug type pools,and are important strategic relay exploration areas in the Tarim Basin.