鄂尔多斯盆地南部加里东期岩溶古地貌与天然气成藏条件分析

认识鄂尔多斯盆地南部地区岩溶古地貌和成藏条件是加快该地区勘探步伐面临的重要问题。鄂尔多斯盆地南部加里东期风化壳储集层的分布主要受岩溶古地貌、风化壳层位及沉积相控制。马五段为云坪相带，溶蚀孔洞较为发育；平凉组为深水斜坡相带，多形成断裂、裂缝及洞穴储集空间。中央古隆起西侧古地貌为岩溶斜坡，地表岩溶作用较弱，但断裂发育，洞穴系统较发育；中央古隆起南侧古地貌为岩溶台地，断裂、洞穴系统和风化裂隙相对较为发育；中央古隆起区古地貌为岩溶台地，地层较老，岩性致密，风化壳顶部垂直裂隙带发育，岩溶孔洞不发育；中央古隆起东侧古地貌多属于岩溶阶地或鞍地，风化壳多位于云坪及含膏云坪相带，溶蚀孔洞较为发育。岩溶古地貌天然气成藏主控因素主要为生烃中心、岩溶古地貌、风化壳的层位和沉积相带，有利区带主要在耀县、旬邑、淳化平凉组生烃中心和中央古隆起东侧马五段有利沉积相带。图9表1参13

Caledonian karst palaeogeomorphology and the forming condition of gas pool, southern Ordos Basin

The distribution of Caledonian residuum reservoirs in the south of Ordos Basin is mainly controlled by karst palaeogeomorphology,strata of residuum and sedimentary facies.The facies of the O1m5 residuum is dolomitic tidal flats,with well-developed dissolved pores;while that of O2p is deep water slopes,with abundant faults,fractures and caves.On the central palaeohigh,palaeogeomorphology is platforms composed of old strata and compacted rock,with vertical fractured zones at the residuum's top;on the west side,it is slopes with well-developed fractures and caverns;on the south side,it is platforms with well-developed faults,caverns,and weathering fractures;on the east side,it is mostly terraces or saddle-shaped terrain,with abundant dissolved pores in the residuum which locates on dolomitic or anhydrite-bearing dolomitic tidal flats.The main controlling factors of the forming of gas pool are hydrocarbon generating center,palaeogeomorphology,strata of residuum and sedimentary facies.Favorable zones are the O2p hydrocarbon generating center in Yaoxian,Xunyi and Chunhua and the O1m5 in eastern central palaeohigh.