基于古地理格局研究新进展,综合野外露头、钻井岩心、微观薄片和物性数据等资料,对鄂尔多斯盆地中东部奥陶系盐下沉积特征及有利储集相带展布规律进行研究.结果表明:①奥陶系盐下主要发育局限台地和蒸发台地2类沉积相,局限台地发育云坪、丘滩、云质潟湖和灰质潟湖等4类微相,蒸发台地发育泥云坪、含膏云坪、膏云坪和膏盐潟湖等4类微相,②受古气候、海平面升降变化和"三隆三坳"古地理格局控制,奥陶系盐下岩相古地理总体呈现出"隆控丘滩-坪、坳控潟湖"的平面展布特征,③台内丘滩储集性能好,是奥陶系盐下白云岩储层发育的有利储集相带.指出苏里格—城川、乌审旗—志丹和神木—米脂地区是奥陶系盐下有利储层发育区,是天然气勘探的重要方向.

Ordovician pre-salt dolomite is an important natural gas producing layer in Ordos Basin, which has great exploration potential. However, the distribution law of favorable facies of dolomite reservoir is not clear, which restricts the next exploration process. Therefore, based on the new progress of paleogeographic pattern research, combined with data of field outcrop, drilling core, rock slice and physical property, the sedimentary characteristics and the distribution law of favorable facies of Ordovician pre-salt strata in the cetral-eastern Ordos Basin are studied. The results show that: (1) There are mainly two types of sedimentary facies (eight types of sedimentary microfacies) in Ordovician pre-salt layer, which are restricted platform (dolomite flat, intra platform mound-shoal complexes, dolomitic lagoon and calcareous lagoon) and evaporation platform (mud-dolomite flat, gypsiferous dolomite flat, gypsum-dolomite flat and gypsum-salt lagoon). (2) Under the control of paleoclimate, sea level fluctuation and paleogeographic pattern of "three uplifts and three depressions", the Ordovician pre-salt paleogeography presents the plane distribution characteristics of "uplift controlled intra platform mound-shoal-flat and depression controlled lagoon". In periods of the 10th submember of Member-5 of the Lower Ordovician Majiagou Formation(O1m510) and O1m58, Mizhi depression and Taolimiao depression are gypsum-salt lagoon and calcareous lagoon respectively, Hengshan uplift and residual areas of central paleo uplift are gypsum-dolomite flat and mud-dolomite flat respectively. In periods of O1m59 and O1m57, Mizhi depression and Taolimiao depression are mainly calcareous lagoon and dolomite lagoon, Hengshan uplift and residual areas of central paleo uplift are mainly intra platform mound-shoal complexes and dolomitic flat. In periods of O1m56, Mizhi depression is gypsumsalt lagoon, Hengshan uplift is gypsum-dolomite flat, and the residual area of central ancient uplift is mud-dolomite flat. (3) The lithology of intra platform mound-shoal complexes is consisted of arenaceous dolomite, oolitic dolomite and agglomerate dolomite, with dissolution holes, intergranular dissolution holes, intergranular pores and intragranular pores developed, which has good relatively reservoir performance. It is a favorable facies belt for the development of Ordovician pre-salt high-quality dolomite reservoirs. It is concluded that Sulige-Chengchuan, Wushenqi-Zhidan and Shenmu-Mizhi areas are favorable reservoir development areas and an important direction of natural gas exploration.