Abstract
The successful development of shale gas and oil in North America has created considerable interest in shale. The analysis of genetic types, the sedimentary environment, and the mudstone development mechanism within sequences is critical for evaluating shale gas and oil exploration prospects, exploration favorable zones, and resource potential. This study focused on the shale of Shahejie Formation in Dongying Depression of Bohai Bay Basin. Shale lithofacies division, geochemical analysis, and well-log analysis were performed for a sedimentary environment and its related elemental response characteristics’ identification. Based on the results, we concluded that the sedimentary environment of the lake basin evolved from the saltwater lake to the ambiguous lake and then the open lake to the delta. In response, we observed gradually decreasing Sr/Ba and Ca/Mg ratios and increasing Rb/Ca and Fe/Mn ratios during the whole process during the reduction of the salinity and the decrease in PH value and sediments’ transport distance. The relationship between ratio elements and high-frequency sequences was initially established within the shale strata. Our results show that ratios of Sr/Ba and Ca/Mg ratios near the sequence boundary are relatively low, and ratios of Fe/Mn and Rb/Ca are relatively high, while ratios of Sr/Ba and Ca/Mg near the flooding surface are relatively high, and ratios of Fe/Mn and Rb/Ca are relatively low. Those features can be used as a marker for high-frequency sequence division of shale strata. Our results provided a new theoretical basis and technical method for shale gas and oil exploration and development.
Highlights
The analysis of genetic types, the sedimentary environment, and the mudstone development mechanism within sequences is critical for evaluating shale gas and oil exploration prospects, exploration favorable zones, and resource potential
Their study specified the significance of using geochemical elements in high-frequency shale sequence stratigraphy division study and has great significance for shale gas and oil exploration and development
Our study focused on sequence stratigraphy of shale in the third member of Shahejie
Summary
The analysis of genetic types, the sedimentary environment, and the mudstone development mechanism within sequences is critical for evaluating shale gas and oil exploration prospects, exploration favorable zones, and resource potential. Shale has been analyzed in various countries Those studies concluded that even in an environment favorable to organic matter accumulation, the properties and distribution of source rocks underwent systemic changes both vertically and laterally. Han, Wang, Guo, and Gao (2008) [25] found good correlations between the vertical change of geochemical elements and para-sequence cycle changes in lake-facies shales, and the cyclic change of the geochemical element can be used for the classification of high-frequency sequences’ stratigraphy division in shales. Their study specified the significance of using geochemical elements in high-frequency shale sequence stratigraphy division study and has great significance for shale gas and oil exploration and development. Our study provided a good example and basis for the high-frequency sequence division in shale and could be a guidance for the exploration and development of shale gas and oil
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