大牛地气田DK13井区山2段主力小层优选

Optimally selecting principal layers in Shanxi 2 Member,DK13 well area,Daniudi gasfield

大牛地气田位于鄂尔多斯盆地东北部,上古生界断裂基本不发育,DK13井区位于大牛地气田西南部,占地面积约为1/6气田,下二叠统山西组2段(以下简称山2段)为其主力开发层系之一,辫状河三角洲平原沉积特征明显。为了厘清DK13井区山2段沉积特征,优选主力小层,以山2段储层沉积微相为研究对象,分析了岩心、测井资料,指出了该储层主要发育心滩、分流河道、天然堤、废弃河道、分流间湾共5种微相。研究结果表明:①山2段分为山2-1、山2-2两个亚段,并可细分为山2-1-1、山2-1-2、山2-2-1、山2-2-2四个小层,地层垂向上共发育7期河道;②北东方向水体能量充足,心滩密集发育,纵轴长度介于2.5~4.0km,横轴长度介于1.5~2.0km,厚度介于10~14m,南西方向心滩零星分布,规模较小,泥质含量逐渐增多;③山2-1-1、山2-2-1气层厚度普遍超过4m,自然伽马值介于60~75API,泥质含量低于13%,试气效果较好,稳定日产气量在0.9×104m3以上。结论认为:①山2段不同期次砂体厚度差别明显,横向迁移频繁,多被厚层泥质沉积分隔;②自北东至南西,水体能量逐渐减弱,开始水退,河道横向范围逐渐缩小;③山2-1-1、山2-2-1气层发育,试气产量高,可以作为后期措施选井选层的主力小层。

In Daniudi gasfield,northeastern Ordos Basin,the Upper Paleozoic faults are almost underdeveloped.In DK13 well area just at the southwest of this field and accounting to one-sixth of Daniudi field,Shanxi 2 Member is one of the major payzones and has obvious features with the deposition of braided-river delta plain.In order to figure out its sedimen⁃tary characteristics in this well area for optimally selecting principal layers,sedimentary microfacies in Shanxi 2 reservoirs were identified by using core and well-logging data.There are five types of microfacies,including mid-channel bar,distrib⁃utary channel,natural levee,abandoned channel,and interdistributary bay.Results show that(i)Shanxi 2 Member can be divided into Shanxi 2-1 and Shanxi 2-2 submembers,which are subdivided into four layers from Shanxi 2-1-1 to Shanxi 2-2-2,and vertically developed with 7-epsode channels;(ii)in N-E direction,there exist sufficient water energy and dense mid-channel bar with long longitudinal and horizontal axes around 2.5–4.0 km and 1.5–2.0 km as well as the thickness of 10–14 m,respectively.While in S-W direction,concentric shoal represents a few scattered extension with a small scale and an increasing shale content;and(iii)with often more than 4 m in thickness,both Shanxi 2-1-1 and Shanxi 2-2-1 layers are characterized by GR value ranging from 60 API to 75 API,shale content less than 13%,good re⁃sults in gas testing,and a stable yield more than 0.9×104 m3/d.It is concluded that various stages of sandbodies in Shan-2 Member exhibit great differences in their thickness,migrate frequently in horizontal direction,and are mostly separated by thick muddy deposits.Moreover,from the northeast to the southwest,the water energy weakens gradually,regression occurs initially,and channel scope reduces gradually in the horizontal.On top of that,both Shanxi 2-1-1 and Shanxi 2-2-1 lay⁃ers are developed and reveal a higher production in gas testing,so they can be selected as the principal layers for subse⁃quent exploitation.