Types and models of supergene karst of Ordovician and reservoir characteristics in Ordos basin
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摘要: 鄂尔多斯盆地奥陶系表生期岩溶储层是盆地碳酸盐岩油气勘探的主力类型,近年来岩溶储层勘探取得一些新突破,难以用风化壳岩溶完美解释,表明存在不同的岩溶作用类型。在钻井岩心、薄片观察基础上,结合古地形、古地貌及岩溶特征分析认为:鄂尔多斯盆地奥陶系表生期存在风化壳岩溶和顺层岩溶两种不同类型的岩溶作用,根据围岩性质细分为白云岩型、灰岩型风化壳岩溶和白云岩型、灰岩型顺层岩溶4个亚类;风化壳岩溶具有非组构选择性,岩溶特征因岩石组构差异而不同,顺层岩溶是组构选择性溶蚀,岩溶作用沿较陡地形顺层选择性溶蚀易溶组分形成孔-洞系统;风化壳岩溶储层受岩溶地貌、岩溶旋回和沉积相带共同控制,顺层岩溶储层预测则需综合考虑古地形、岩溶古地貌、沉积相及古沟槽、古裂隙等要素。Abstract: Supergene karst reservoirs of Ordovician in Ordos is the most important type of carbonate reser-voirs,while some breakthrough cannot be explained perfectly,indicating existence of different types of karst.Based on the analysis of paleotopography and cores and slices,this study suggests that the supergene karst of Ordovician can be divided into weathering crust karst and bedding karst,which include 4 subclasses in accordance with surrounding rocks.The characters of the weathering crust karst are different because of different rock fabric,while the easily dissolved component of rocks is dissolved preferentially when the bed-ding karst occurs.The weathering crust karst reservoirs are controlled by paleotopography and karst cycles as well as sedimentary facies,while paleotopography and sedimentary facies as well as grooves and fractures need to be considered when bedding karst reservoirs are forecasted.
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Key words:
- weathering crust karst /
- bedding karst /
- karst model /
- dissolution mechanism /
- karst reservoir
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