陕甘宁盆地中部东西向构造带的确定及其聚气意义

CONFIRMATION OF EAST WEST STRUCTURAL BELTIN SHAAN GAN NING BASIN AND ITS GAS ACCUMULATING SIGNIFICANCE

陕甘宁盆地中部发育一个东西向构造带，其分布范围北至鄂托克旗，南达定边 靖边一线。该构造带最早在中元古代的长城纪即有表现，为地台内低幅度裂陷。早古生代早中期为东西向的浅台坳。奥陶系顶部风化壳形成阶段，古地貌表现为东西向的岩溶低地。晚古生代中晚期为陆、海（ 湖） 的过渡带。中生代为北陆南湖的过渡带。第四纪为控制地貌南北分异的分界线。该带显著特点是幅度低，它控制下的岩相类型和厚度，特别是厚度与相邻的南北地区差异较小，往往在数百米以内。低幅度是使得该构造带不易被识别和确定的重要原因之一。该带具有重要的天然气地质意义，它在古生代表现出的低凹地带，使得这里沉积较厚，形成了上、下古生界两大烃源中心；上古生界发育多期三角洲沉积体系，砂体重叠连片发育，形成有利的天然气储层发育带。目前沿该带已发现有长庆、吴堡、镇川堡、横山堡。

An east weststructuralbelt which extendsfrom Ertuok Bannerin the northto Dinbian Jingbian in the southdeveloped in middle Shaan Gan Ning Basin .It was a shallow platform depressionin early middle stage of Early Paleo zoic,a karst depression during the formation stage of Ordovician top weathered crust,a sea land transitional zone in mid late stage ofLate Paleozoic,alakelandtransitionalzoneinthe Mesozoic,andthe boundaryline between north and south Shaan Gan Ninginthe Cenozoic .Thetypicalcharacteristics ofthe beltisloweramplitude ,thatis,thelithofacies and stratathickness ofthe beltare similarto the adjoining area,the difference ofstratathickness is only several hun dred merters.This property made it difficultto find the belt.Along this belt,two centers of source rocks and multi deltaic sedimentary systems of Upper and Lower Paleozoic widely developed and connectedthere .The sand bodiesthat stacked are good reservoir rocks.Five gas fields (gas accumulation zone) ,i.e.,Hengshanpu,Changqing,Tianchi, Zhenchuanpu have been discoveried .