鄂尔多斯盆地北缘下石盒子组盒1段心滩砂体定量刻画

Quantitative characterization of channel bar sandbody in the Lower Shihezi 1 Member,northern margin of Ordos Basin

为了解决辫状河心滩规模难以刻画的问题,以鄂尔多斯盆地北缘二叠系下石盒子组盒1段辫状河砂体为研究对象,结合现今河流沉积特征,分析了冲积扇、冲积平原不同沉积相带中辫状河砂体的发育特征;利用地质统计学方法,针对不同沉积相带的辫状河心滩规模参数进行相关性分析,建立了地貌坡度与心滩长宽比等的定量关系;对目标区直井、水平井实钻心滩参数进行统计,经过压实校正,对定量关系进行验证及修正,实现了不同厚度、不同古地貌坡度下心滩的定量计算与描述。研究结果表明:①盒1段北部以冲积扇为主,南部发育冲积平原辫状河,中间过渡带则兼具有南北部的综合特征;②不同的古地貌坡度在心滩的碎屑物粒度、沉积构造、砾石结构、砂地比、单期旋回厚度等方面存在着显著的差异;③古地貌控制了心滩的形态,物源控制了心滩规模,并且古地貌坡度与心滩规模呈正相关关系。结论认为,通过公式法定量计算心滩长度、宽度、厚度与长宽比,精细刻画了心滩展布形态、提高了储层钻遇率、实现了气藏的高效开发。

So far,to characterize the scale of braided-river channel bar is a challenge.So,the braided-river sandbody in the first member of Lower Shihezi Formation(Shihezi 1 Member)along northern margin of Ordos Basin was taken as an objective to analyze the development characteristics of braided-river sandbody in two sedimentary-facies belts of both alluvi-al fan and alluvial plain based on depositional feature of modern rivers.Then,correlation was analyzed on the scale parameters of braided-river channel bar in different sedimentary-facies belts by means of geostatistics,and a quantitative relationship between topographic slope and morphological parameters of channel bar(e.g.aspect ratio)was established.Finally,these parameters of channel bar actually drilled by vertical and horizontal wells in the target area were summarized,and after compaction correction,this relationship was verified and corrected.And thus,the quantitative calculation and characterization on channel bar at different thickness and slope was realized.Results show that(1)the north of Shihezi 1 Member is mainly developed by alluvial fan,the south by alluvial-plain braided river,and the transition belt by both natures in the north and south,respectively;(2)channel bar at different paleogeomorphological slope is obviously distinct in clastic grain size,sedimentary structure,gravel texture,net/gross ratio,and single-phase cycle thickness;and(3)the paleogeomorphology may control morphological pattern and the provenance may affect channel-bar scale,and the paleogeomorphological slope presents a positive correlation with the scale.In conclusion,the length,width,thickness,and aspect ratio of channel bar may be quantitatively calculated by means of a formula method,so as to precisely characterize the distribution form of channel bar,improve the drilling rate,and realize the efficient development of gas reservoirs.