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鄂尔多斯盆地北部东段塔巴庙地区奥陶系风化壳岩溶作用过甚，破坏了地层的连续性及储集性能，是导致该区风化壳气藏勘探效果不佳的主要原因之一，根据岩心及电测资料，可从风化壳中鉴别出6种岩溶相：壳面堆积相，洞顶相，洞底相，隔层相，坍塌相和洞穴充填相；其中洞顶相砾岩，云岩和隔层相云岩为优良的储层或气层，洞底相灰岩和坍塌相云岩是潜在的储层或气层，该区奥陶系风化壳的地震波反射速度反映了风化壳的岩溶化程度，即岩溶化程愈高，泥质含量愈大，反射速度就愈低，反之亦然，根据G－LOG图上风化壳内高速带，中速带，低速带及上覆石炭系超低速带的发育程度和配置关系，可划分为9种岩溶地震相，其中II，III，IV型岩溶地震相，岩溶强度相对较弱，分布面积较广，是风化壳气藏的主力勘探目标，岩溶地震相经实践检验，对钻前的油气地质情况有较好的预见性，因而对研究区奥陶系风化壳天然气勘探具有一定的指导意义。

CHARCTERISTICS OFKARST-SEISMIC FACIES OF ORDOVICIAN WEATHERED CRUST AND NATURAL GAS EXPLORATION AT TABAMIAOREGION IN E'ERDUOSI BASIN

It is one of the major factors limiting the achievements of gas exploration in Ordovician weathered crust at Tabamiao region in the east of North E′erduosi Basin that the karstification at the region was so strong that the continuity formation and the reservoir characteristics were disrupted. In accordance with the data on cores and electric logging,six karst facies may be found in the weathered crust,i.e.surface accumulation facies,cave roof facies,cave floor facies,cave-barrier facies,collapse facies and cave-filling facies.The dolomites of the cave roof and cave-barrier facies are the good reservoirs or gas-bearing beds and the limestones of cave floor facies and the dolomites of collapse facies are the potential reservoirs or gas-bearing beds.Through research,it is indicated that at this region the seismic velocity of the Ordovician weathered crust is closely related to the degree of karstification,i.e.the higher the degree of karstification and the greater the shale content,the lower the seismic velocity;it's the same the other way round.According to the level of development and the interrelation of the high-velocity,middle-velocity and low-velocity layers within the weathered crust and the ultra low-velocity layers in the overlying Carboniferous on the G-LOG seismic cross-section,nine types of karst-seismic facies may be divided,in which the karst-seismic facies of Types Ⅱ,Ⅲ and Ⅳ are the major targets of exploration for gas reserviors in the weathered crust because of their relatively weak karstification intensity and extensive distribution.Through examining in practice,it is shown that the oil and gas geological circumstances may be predicted before drilling by use of the karst-seismic facies theory,thus providing a guide for gas exploration in the Ordovician weathered crust at the region.