鄂尔多斯盆地中东部山2段储层精细评价

鄂尔多斯盆地中东部山西组可划分为3个沉积层序,其中SQ8(山2段)可划分为低位、湖侵及高位体系域,主要砂体发育于低位体系域。SQ8—LST可细分为3个进积型准层序组,其砂体呈进积式向湖盆推进,自下而上分为L1,L2和L3准层序组,砂体厚度由薄变厚,分布面积由小变大。L1准层序组仅在研究区西北部发育一支近南北向展布的主砂带,砂岩厚2～10m,砂带宽10～15km,延伸约100km;L2,L3准层序组的砂体分布格局相似,砂岩厚度为4～20m,发育5～6支近南北向、北东向展布的砂带,砂带宽10～25km,延伸200～230km。L1准层序组为大规模海退之后的初始充填沉积,其砂岩成分复杂、分选差,储层物性相对较差,而向上至L2,L3准层序组,储层物性明显变好。有利的储集砂体为发育于低位体系域中上部准层序组的三角洲平原分流河道、前缘水下分流河道及河口坝砂体。三角洲前缘砂体物性略优于三角洲平原砂体,边滩砂体物性较差。

Refined reservoir evaluation of the second member of Shanxi Formation in mid-eastern Ordos Basin

Shanxi Formation in mid-eastern Ordos Basin can be divided into three sedimentary sequences.SQ8（the second member of Shanxi Formation）can be divided into lowstand system tract,transgression system tract and highstand system tract,with the main sand body developed in lowstand system tract.SQ8-LST can be subdivided into three progradational parasequence sets,which prograded into the lake.They are L1,L2 and L3 from below to top with the thickness varying from thin to thick and the distribution area from small to large.In L1 parasequence set,only one main sandstone belt deposited in the study area,which extends nearly north-southward with the length of 100 km,10~15 km in wide,and with the sandstone thickness of 2~10 m.In L2 and L3 parasequence sets,the sandstone distribution are very similar,developed 5~6 north-southward and north-eastward sandstone belts,which are 10~25 kmin wide,200~230 kmin length,with the sandstone thickness of 4~20 m.L1 parasequence set is initial filling deposition after large scale marine regression.Its sandstone composition is complicated with poor sorting and the reservoir property is relatively poor.But up to the parasequence sets of L2 and L3,the reservoir properties become better obviously.Favorable reservoir sandstones developed in sedimentary facies of distributary channel in delta plain,subaqueous distributary channel and mouth bar in delta front,which mainly distributed in middle-upper part of the lowstand system tract.The reservoir property of delta front sand body is better than that of delta plain sand body,while point barsand body is poorerin reservoir property.