大牛地气田上古生界沉积相与天然气富集规律的再认识

New understandings of the Upper Paleozoic sedimentary facies and gas accumulation patterns in Daniudi gas field

通过构造沉积演化与宏观地质认识和微观地质证据相统一的沉积相分析方法,针对鄂尔多斯盆地大牛地气田近400余口完钻井进行了录井、测井资料分析、解释、对比研究及岩心的观察、描述。研究认为,大牛地气田上古生界太原组沉积相为在区域陆表海背景下形成的陆表海碎屑滨岸-碳酸盐台地和三角洲沉积,主要发育了三角洲分流河道和潮汐沙滩砂体;下石盒子组盒一段是在地形高差显著的古构造-沉积背景下形成的湖泊-辫状河三角洲沉积体系,主要发育分流河道和分流间湾微相。上述两个沉积时期的沉积相及砂体展布特点决定了太原组二段砂体物性及产能具有由北东向南西变差的特点,高产区带主要集中在研究区北北东向砂体的中北部;盒一段研究区发育高产富集区带的可能性较小,中产区带主要分布在研究区中北部。

By using sedimentary facies analysis method that unifies macroscopic geologic knowledge and microco-pic geologic evidences,we conduct the analysis,interpretation and correlation of logging data and observation of cores more than 400 wells.It is thought that the sedimentary facies of the Paleozoic Taiyuan Formation in the Da-niudi gas field is debris coastal-carbonate platform and delta in a regional epicontinental sea setting where delta distributary channel and tidal sand bar are deposited.The sedimentary facies of the 1st member of the Lower Shihezi Formation is lake-braided river delta in a paleostructure-sedimentary background with high relief where distributary channel and interchannel microfacies are developed.These sedimentary facies and sand distribution features determine the worsening of reservoir quality and productivity of sandbodies in the 2nd member of the Taiyuan Formation from northeast to southwest.The plays with high production potential mainly occur in the north-central part of NNE-trending sandbody in the study area.The chance is bad for them to occur in the 1st member of the Shihezi Formation in the study area.Plays with moderate production potential distribute in the north-central part of the study area.