Sedimentary environment evolution and shale gas geological features of dark mudstone from Nanmingshui Fm of Fuyun Basin,Xinjiang

To understand the sedimentary environment evolution,shale gas prospect and their relationship of Nanming- shui Fm dark mudstone from Shaerbulake Region,Fuyun Basin,the analysis on inorganic,organic geochemistry and mineralogy were performed. It shows that,influenced by large rivers import,water desalination occurred during the sed- imentation. Water openness decreased later,and the salinity re-increased gradually. It was warm and moist generally, then became warmer and drier in middle-late stage during Nanmingshui Fm sedimentation. There was a deep-shallow- deep change in water depth upward Nnmingshui Fm. Reducing condition occurred during dark mudstone sedimentation,but it weakened upward Nanmingshui Fm. The organic matter is dominated by type Ⅲ with a few type II2,and its evolution is in a high-over maturation. The second member of Nanmingshui Fm bears highest biological production and total organic matter (TOC:0. 42% -1. 11% ). Mineral composition is dominated by clay and quartz,especially in the dark mudstone from the second member ( clay:32% - 49% ;quartz:33% - 41% ;illite in clay:61% - 77% ),which have good factors for shale gas development. The study shows that brackish water with salinity lean to salt water,lack of large river import,stable sedimentary environment etc. are more beneficial to the development of gas-producing shale.