靖边气田中区盒_8段储层沉积微相特征及其演化

Characteristics and evolution on sedimentary microfacies of Shihezi 8 Member, central Jinbian Gasfield

鄂尔多斯盆地靖边气田中区盒_8段气藏为典型的致密砂岩气藏,气层厚度薄、储层纵横向变化快,对砂体分布规律的认识尚待深入。故开展沉积微相研究工作,以地层精细划分和物源分析为基础,通过岩心相标志和测井相分析,划分盒_8段单井沉积微相发育特征,分析垂向及平面上的沉积微相组合关系,总结其变化规律,确定不同时期沉积微相平面展布特征,为砂体展布预测提供依据。结果表明:(1)靖边气田中部盒_8段沉积物源都来自北部阴山古陆中段变质岩系;(2)沉积相属于辫状河三角洲平原沉积,可识别出分流河道、心滩、废弃河道、河道间、沼泽5种沉积微相,其有利的沉积微相为心滩和分流河道;(3)具有盒_(8下)~2—盒_(8上)~2期"宽广式大面积连片分布分流河道与心滩砂体发育"与盒_(8上)~2期"局限式网状狭窄河道砂体发育"2种储集砂体的时空展布规律。

Shihezi 8 Member,central Jinbian gasfield,Ordos Basin,is typical tight sandstone gas reservoirs,which are characterized by thin gas layer,and fast vertical and lateral change.However,their sandbody distribution has not been made clear yet.So,based on fine stratigraphic division and provenance analysis,combined with core facies marker and electrofacies analysis,we classified the development characteristics of sedimentary microfacies for Shihezi 8 Member,analyzed the vertical and plane combination relationships of microfacies,and summed up their change laws to further determine the plane distribution of microfacies in different stages and provide the basis for the prediction of sandbody distribution.Results show that,(1)in Shihezi 8 Member,the sediments originated from metamorphic rocks in the middle Yinshan ancient land in the north;(2)for this member,its sedimentary facies are typical of braided delta plain facies,which can be subdivide into 5 microfacies,including distributary channel,point bar,abandoned channel,interchannel,and marsh,among which distributary channel and point bar are favorable ones;and(3)two time-space distribution laws are confirmed for reservoir sandbody,i.e.,distributary channel and point bar extensively and continuously distributed in one period of Shihezi 8 Lower 2 to Shihezi 8 Upper 2 and restricted narrow channel net in another period of Shihezi 8 Upper 2.