鄂尔多斯盆地志丹-甘泉地区奥陶系风化壳古地貌恢复

Palaeogeomorphology Recover of Ordovician weathering crust in Zhidan&Ganquan area,Ordos Basin

受加里东运动影响,鄂尔多斯盆地奥陶系马家沟组发育大规模风化壳岩溶作用,形成了以靖边气田为代表的大型古地貌气藏。古岩溶对储层的形成、演化和分布具有重要意义,其发育受多种因素影响,其中古地貌形态是控制古岩溶发育程度的关键。为了寻找有利勘探开发目标,必须进行古地貌恢复。在区域构造背景和地层展布的基础上,通过对马家沟组钻井小层的精细划分与对比及地震剖面的精细解释,综合利用古地质图法、残余厚度法和印模法并结合铝土岩厚度分布及古沟槽识别结果,恢复出研究区奥陶系风化壳古地貌分布格局。结果表明,研究区西北部表现为古岩溶高地,中部大部分地区表现为古岩溶斜坡,东部主要古岩溶洼地;近北东东向展布的古沟槽影响储层的形成、发育和天然气的富集。岩溶斜坡中残丘地带及古沟槽两侧是天然气富集有利区,工业气流井多分布于此;岩溶洼地、古沟槽地带由于缺少优质储层不利于天然气聚集,这些区域大多数钻井试气无产能或产气量极低。

Wide scale weathering crust karstification was developing of Majiagou Formation,Ordovician system in Ordos Basin,where large gas fields related to palaeogeomorphogy example because the Caledonian Movement.Jingbian Gas Field were finded,.Palaeokarst growth has an important effect on both formation,evolution and distribution of the Ordovician reservoir.Moreover,it is affected by a lot factors with palaeogeomorgraphy as the soul.So,it’s necessary to carry on a palaeomorphologic restoring so as to find out good exploration and development targets.On the basis of regional tectonic setting and formation distribution,utilizing comprehensively“methods of paleo-geology maps”,"methods of residual thickness"and"methods of moulage",combining with thickness distribution of bauxite and identifing results of ancient erosion grooves,the spatial pattern of palaeogeomorphic features from Ordovician weathering crust in study area is restored by fine subdivision and correlation of the Majiagou Formation and 2-D seismic explanation.It is showed from the results that it displays for karst highland in northwest,mostly of karst slope in middle parts,and mainly karst depression in east of study area.The formation and development of reservoir rocks and accumulation of gas are influenced by the spatial pattern of palaeogeomorphic features and distribution of ancient erosion grooves,which extend in NEE direction on a plane.The monadnock within karst slope,and both sides of groove are the favorable zones to accumulate gas,which has gain quantitative industry gas flow wells;both karst depression and palaeogroove which has no deliverability or very little daily production for most gas wells,.are unfavorable to accumulate gas because of reservoir.