Abstract:

The factors controlling the low radioactivity of oil shales in the 7th Section of Dameigou Formation of Jurassic in Northern Qaidam Basin were primarily discussed.Taking oil shales and dark shales in typical wells in Yuqia area as the research objects,the constituent, watermedium condition, radioactivitysource supply and their relation with radioactivity were analyzed in detail combined with logging data, oilyield test and the analysis of organic geochemistry, Xray diffraction and element geochemistry.The results show that, compared with dark shales, oil shales are generally characterized by the following attributes, lower GR, higher oil yield and organic matter content,stronger reducingsedimentary water, lower claymineral content and weaker source weathering.Therefore, it can be inferred that the enrichment of organic matters and the condition of anoxic water medium hardly influence the radioactivity of oil shales, however, the limited input of terrestrial clay minerals and radioactive substances, caused by the semiarid climate, may dominate the low radioactivity of oil shales in the study area.

Key words: the 7th section of Dameigou Formation, oil shale, low radioactivity, organic matter content, paleoclimate, northern Qaidam Basin