Abstract:

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 ana-lysis 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 typi cal 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.

Key words: Tarim Basin, Silurian, Kepingtage Formation, bituminous sandstone