Abstract: The Lower Member sandstones in Devonian Donghetang Formation at Qun 6 well are made up of micro fine and fine lithoclastic quartz sandstones. It is a suit of high maturity, low porosity and low permeability reservoirs. The reservoirs have huge thickness and significant heterogeneity. According to the statistics of cores and thin-sections under microscope, the density of dense and semi-dense laminae in the sandstones sometimes attain one hundred or more per meter. The influential factors of heterogeneity in the reservoirs include syndepositional structures, dolomite cementation, filled with heavy bitumen except compaction and dissolution. These factors lead to low permeability and low oil-fluidity in the sandstones. The contents of bitumen and heterogeneity increase obviously from top to bottom the sandstones in Lower Member of Donghetang Formation. The more uniform block sandtones at lower and middle parts are favorable reservoirs

Key words: Tarim Basin, Qun 6 well, Donghetang Formation, reservoir characteristics, heterogeneity