鄂尔多斯盆地苏5区块盒8段砂体结构与展布特征

研究鄂尔多斯盆地苏里格地区苏5区块下二叠统盒8段砂体特征,确定有利的勘探目标层位.通过岩芯观察,结合测井解释成果,对盒8段沉积相进行研究,确定盒8段下部主要发育缓坡型辫状河沉积,盒8段上部则主要为多河道低弯度曲流河沉积.根据测井曲线形态对盒8段小层砂体进行对比和追踪,确定盒8段砂体在研究区中部主要呈近南－北向展布,在研究区西部主要沿北西－南东向展布,而在研究区东部则呈北东－南西向展布的特征.综合砂岩累计厚度对砂体平面展布及演化特征进行研究,认为物源区构造活动的减缓和河流作用的减弱导致砂体规模逐渐变小.根据砂、泥岩厚度及其组合方式的不同,将盒8段砂体划分为4种结构类型:连续叠置型、间隔叠置型、互层型和透镜型.砂体结构与储集物性存在密切联系,连续叠置型砂体孔隙度和渗透性最高,而透镜型砂体物性最差,盒8段下部砂体结构及储集性能明显优于盒8段上部,为最有利的勘探目标层位.

Structural and distributional characteristics of sand bodies in the Member 8 of Xiashihezi Formation from the Su-5 Block,Ordos Basin,China

Based on the observation of drilling cores and the results of logging interpretation,the sedimentary facies of the Member 8 of Lower Permian Xiashihezi Formation (He-8) in the Block Su-5 of Sulige Gas Field,Ordos Basin are studied.It reveals that the lower part of He-8 Member consists of mainly gentle slope type braided river sediments,and the upper part is mainly composed of multichannel low-curvature meandering river deposit.Small sand bodies of the He-8 Member are compared and tracked according to the shape of the logging curve,and it is suggested that the sand bodies are mainly south-north trending in the middle of the study area,NW-SE trending in the western area,and NE-SW trending in the eastern area.The cumulative thickness of sandstone is used to study the plane distribution and evolution characteristics of sand bodies.It shows that the slow down of tectonic activity and fluviation in the provenance region leads to the decrease of sand body size in Su-5 Block.The He-8 Member sand bodies are divided into four types (continuous superposition type,interval superposition type,interbedded type and lens type) with different thickness and combination of sand and mudstone.The porosity and permeability of continuous superposition type sand body is the best,while the lens type was the worst.It indicates that the sand body structure is closely related with reservoir physical property,and the sand body structure and reservoir physical property of the lower part of the He-8 Member is obviously better than that of the upper part.Therefore,the lower part of the He-8 Member is the most favorable exploration target horizon.