鄂尔多斯盆地中部气田奥陶系马五1层的古岩溶作用与天然气富集

鄂尔多斯盆地中部气田的储层为奥陶系马家沟组白云岩风化壳，马五１层为其主力气层，该层可分为四个小层，沉积相为分布稳定的蒸发潮坪环境，经历了表生期和浅、深埋藏期岩溶作用，天然气主要聚集在岩溶孔洞缝中。

Paleokarstification and Natural Gas Enrichment in Horizen 51 of Majiagou Formation of Ordovician in Central Gas Field of Ordos Basin

The reservoir in central gas field of Ordos Basin is a dolomite weathering crust of Majiagou Fm.,Ordovician.Ma5_1 having undergone epidiagenetic,shallow and deep burial stage karsti- fication is a major gas horizon which may be devided into 4 in- tervals.The sedimentary facies was a stable evaporitic tidal flat environment.The gas is mainly accumulated in pore,cave and fracture spaces of the karst.For karst development,it is more developed in supratidal and intertidal deposit than in downtidal,and in paleogeomorphic upper part and slope than in lowland.Statistics in 68 gas wells in the region suggest that the dominant commercial gas wells are produced in the inter- vals of supratidal and intertidal zones.High productivity are got in these intervals,especially in Ma5_1~2 and Ma5_1~3.The gas wells penetrating the above two intervals in the supratidal and intertidal zones account for over 95% of total.It is obvious that the well production in paleogeomorphic upper part is high- er than in lower one.