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鄂尔多斯盆地奥陶系的古岩溶洞穴主要包括碳酸盐岩溶洞和盐类岩石溶洞两大类。由于沉积环境的差异,前者主要发育于盆地西部,颗粒灰岩、生物灰岩、藻灰岩及细晶白云岩是主要成洞基岩;后者主要发育于盆地东部,膏质云岩、盐岩是主要的成洞基岩。成洞有利条件除沉积间断、气候、岩性外,盆地西部还与断裂体系的发育紧密相关。古岩溶洞穴由于埋藏较深,对于其识别目前主要采用钻井和测井方法。洞穴充填物的类型为石英、方解石、白云石、高岭石及硬石膏,储集空间为晶间孔、晶间溶孔、角砾间孔、溶缝和溶洞,因受到洞壁的保护而免受正常压实,是重要的天然气储层。充填物中的白云石可以进一步划分为微咸水微晶白云石、淡水白云石及马鞍状白云石三种类型,方解石可以进一步划分为微咸水粉细晶方解石、淡水方解石及铁方解石三种类型。利用电子探针、同位素及包裹体测温分析,微咸水微晶白云石和微咸水粉细晶方解石主要形成于同生期层间岩溶发育期,淡水白云石及淡水方解石主要形成于裸露期风化壳岩溶发育期,马鞍状白云石及铁方解石主要形成于中深埋藏环境。
The Ordovician paleokarst caves in the Ordos Basin include two major types of carbonate caves and salt rock caves. Due to the difference in sedimentary environment, the former mainly develops in the western part of the basin. Particulate limestone, bio-limestone, algal limestone and fine-grained dolomite are the major pore-forming bedrock. The latter mainly develops in the eastern part of the basin, Rock is the main cave bedrock. In addition to favorable conditions for the deposition of sedimentary discontinuities, climate, lithology, the western basin is also closely related to the development of the fault system. Ancient karst cave burial deeper, for its current recognition of the main drilling and logging methods. The types of cave fillings are quartz, calcite, dolomite, kaolinite and anhydrite. The reservoir space is intercrystalline, intergranular, intergranular, dissolved and karst. Due to the protection of the cave wall From the normal compaction, is an important natural gas reservoir. The dolomite in the filling material can be further divided into three types: brackish water microcrystalline dolomite, freshwater dolomite and saddle-shaped dolomite. The calcite can be further divided into three types: brackish water fine calcite, fresh water calcite and iron calcite . Using electron probe, isotope and inclusion temperature measurement, brackish water microcrystalline dolomite and brackish water fine calcite mainly formed during the same period of intergranular karst development. Freshwater dolomite and freshwater calcite formed mainly in exposed period In the karst developmental period, saddle-like dolomite and iron calcite mainly formed in the medium-deep burial environment.