Abstract:

Palaeo productivity values of the 1^st member of Shahejie Formation encountered in hundreds of wells in Dongying sag have been calculated with the formula of lake's productivity based on organic carbon method. The conture map shows the distribution of paleo productivity of the lake during the deposition of the 1^st member of Shahejie Formation. These values are then compared with those of the 3^rd member of Shahejie Formation, as well as with those of modern lakes having different nutrition types. The study indicates that Dongying sag was a super eutrophic lake during the deposition of the middle and low intervals of the third member and the first member of Shahejie Formation, which would be the most favorable for oil generation. The sag was a eutrophic lake during the deposition of the upper interval of the third member of Shahejie Formation, which also had certain capacity of oil generation. The quality of source rocks degrades in a sequence from the low interval of the 3rd member to the 1st member, the middle interval and the upper interval of the 3rd member of Shahejie Formation.

Key words: palaeo productivity, lake, Dongying sag, 1^st member of Shahejie Formation