Discussion on "sandwich"structures and preservation conditions of shale gas in the South Yellow Sea Basin

In order to make a breakthrough in Mesozoic-Paleozoic shale gas exploration in the South Yellow Sea Basin,a comparison of the preservation conditions was made within the Barnett shale gas reservoirs in the Fortworth Basin,the Jiaoshiba shale gas reservoirs in Sichuan Basin and potential shale gas reservoirs in Guizhou Province.The results show that the "Sandwich"structure is of great importance for shale gas accumulation.Therein to,the "Sandwich"structure is a kind of special reservoir-cap rock assemblage which consist of limestone or dolomite on the top,mudstone or shale layer in the middle and limestone or dolomite at the bottom.In consideration of the Mesozoic-Paleozoie in the Lower Yangtze,and Laoshan Uplift with weak Paleozoic deformation and thrust fault sealing On both flanks of the Laoshan Uplift,a conclusion can be drawn that the preservation conditions of shale gas probably developed "Sandwich" structures in the Lower Cambrian and Permian,which are key layers for the breakthrough of shale gas in the South Yellow Sea.Moreover,the preferred targets for shale gas drilling probably locate at both flanks of the Laoshan Uplift.