Typical bituminous sandstone developed in the upper part of Silurian Kepingtage Formation at Sishichang section in western Tarim Basin, which are located in the middle-lower part of several normal graded sedimentary cycles.Based on the field outcrop section realism, identification under microscope, grain size analysis and X-ray diffraction analysis, detailed study was done on the bituminous sandstone of this section.It was found that bituminous sandstone developed in sand flat and mixed flat, which were in the lower part of intertidal zone in tidal flat depositional system.In bituminous sandstone, fine sandstone and siltstone were most, with typical bidirectional cross bedding and shallow biogenic trace developed.The sediment was transported as saltation form and reformed by tidal action greatly.Most mineral composition was quartz and bioclast, with little clay mineral and feldspar.On this basis, reservoir quality of bituminous sandstone was analysed combined with physical property measurement.It was showed that the quality of feldspar-quartz sandstone with medium compositional maturity was the best, of which the feldspar content was 5％ to 10％ and the quartz content was 75％ to 83％.The quality of quartz sandstone with higher compositional maturity was the next, of which the feldspar content was about 2％ and the quartz content was more than 90％.The quality of sandstone containing lots bioclast was the worst, of which the bioclast content was about 60％ and the quartz content was about 35％.This study has some reference meaning to the reservoir evaluation of Silurian bituminous sandstone.%塔里木盆地西部四十厂剖面志留系柯坪塔格组上部发育典型的沥青砂岩,分别位于若干个正韵律沉积旋回的中下部.通过典型露头剖面写实、沉积物粒度分析、矿物镜下鉴定、铸体薄片鉴定和X衍射等手段,对该剖面沥青砂岩进行了精细研究,发现沥青砂岩形成于潮坪沉积体系中潮间带下部的砂坪或混合坪内,岩性以细砂岩和粉砂岩为主,发育典型的双向交错层理和浅水动物遗迹等;其沉积物以跳跃搬运为主,受潮汐改造作用明显;碎屑矿物以石英或生物碎屑为主,含少量长石和粘土矿物.结合储层物性测试对沥青砂岩储集性进行了分析,结果表明,优质沥青砂岩储层往往是中等成分成熟度的长石石英砂岩,其内部长石含量在5%～10%之间,石英含量在75%～83%之间,其次是较高成分成熟度的石英砂岩,其内部长石含量一般在2%左右,石英含量在90%以上,较差的是含大量生物碎屑的砂岩,其内部生屑含量在60%左右,石英含量在35%左右.这对该区志留系沥青砂岩储层评价具有一定的借鉴意义.
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