鄂尔多斯盆地西缘克里摩里组古喀斯特洞穴特征及发育控制因素

Characteristics and controlling factors of paleokarst caves in Kelimoli Formation,west Ordos Basin,China

鄂尔多斯盆地西缘下奥陶统克里摩里组发育的古喀斯特洞穴具有良好的勘探前景,但洞穴预测难度大,勘探风险高,需要准确认识古喀斯特洞穴基本特征与储层发育规律,降低勘探风险。通过岩心观察、薄片鉴定以及录井、测井、地震等手段分析表明,该套喀斯特洞穴主要发育在颗粒灰岩内,横、纵向分布稳定,依据岩石学、录测井及地震响应特征可分为垮塌半充填型和暗河充填型,后者进一步分成角砾充填和泥质充填2种类型。喀斯特洞穴具有加里东期大气淡水顺层溶蚀特征,其发育受到岩性、古地貌及古地质条件的共同控制,台缘礁滩微相颗粒灰岩是优先可溶性基岩,古喀斯特斜披提供了有利的水动力条件,加里东期同生微断裂提供了渗流通道,上奥陶统是否覆盖决定了洞穴类型及充填程度。

Paleokarst caves developed in Lower Ordovician Kelimoli Formation in west of Ordos Basin are proved as potential reservoir,but the caves are difficult to predict and the exploration of oil and gas is full of risk.Study of drilling core,thin section,logging and seismic data shows that the caves exist in grain limestone and distribute stably in vertical and horizontal directions.According to characteristics of petrology,logging and seismic data,the caves can be divided into two types,collapse filled and underground river filled caves,and the latter can be further divided into breccia filled and mud filled caves.These caves are dissolved by layer of atmosphere fresh water,and are controlled by lithology,paleogeomorphic and geological conditions.It shows that the grain limestone is the optimal rock,paleokarst slope provides favorable hydrodynamic condition,the fractures of Caledonian period offers seepage channel,and the coverage determines the cave type and cave filling degree.