鄂尔多斯盆地南部奥陶系天然气成藏条件分析

Analysis on accumulation condition of natural gas in southern Ordos Basin in Ordovician

对鄂南奥陶系风化壳天然气成藏的烃源条件、储集层形成机理和圈闭特征的研究认为,早奥陶世,黄陵古隆起分割秦岭坳拉槽与华北海,并在古隆起北侧形成蒸发台地斜坡云坪相膏云岩沉积。加里东运动期,黄陵古隆起随同鄂尔多斯盆地整体抬升,其北坡不同层位膏云岩、含膏白云岩差异溶蚀形成各类孔隙型储集层,并以探井钻遇的蜂窝状膏溶细晶白云岩、针孔状膏溶白云岩和膏溶角砾白云岩为代表广泛分布。海西—印支期,黄陵古隆起处于有利于接受秦岭坳拉槽运移流体的部位,目前已在其南北两翼发现较多的含沥青古油藏显示。古油藏中的石油在晚侏罗—早白垩世高古地温热演化阶段转化成天然气,可为富县斜坡提供充足的天然气源。米脂坳陷致密岩性带为风化壳天然气聚集提供了区域圈闭条件,从而使富县—甘泉地区成为天然气勘探的有利场所。

The study of hydrocarbon source condition,formation mechanism of reservoirs and trap characteristics of the Ordovician weathering crust gas accumulation in southern Ordos Basin showed that the Huangling paleouplift separated the Qinling aulacogen and Huabei sea during Early Ordovician,and formed evaporate platform slope gypsum dolomite sediments in northern paleuplift.The gypsum dolomites and gypsum-bearing dolomites formed various porous reservoirs by differences dissolution in the period of Caledonian orogeny in northern Huangling paleouplift,which uplifted accompanying with the Ordos Basin.The widespread dolomites were characterized by fine-grained dolomite honeycomb-like,dolomite pinhole-like and dolomite breccia shown in drilling.During the Hercynian-Indosinian,the paleouplift at the superior site by accepting the migration fluid came from Qinling aulacogen,and more old reservoirs have been found on the north and south wings of the Huangling paleouplift.The oil that stored in old reservoirs was transformed into gas by high palaeotemperature during the Late Jurassic-Early Cretaceous,which provided adequate gas source to Fuxian slope.Fuxian-Ganquan area became favorable for gas exploration as the dense rock band in Mizhi depression which provided regional trap condition for weathering crust natural gas gathering.