Research Progresses on Muddy Gravity Flow Deposits and Their Significances on Shale Oil and Gas: A case study from the 3^rd oil-member of the Paleogene Shahejie Formation in the Dongying Sag

Key words: 
• gravity flow-generated fine-grained deposits /
• muddy debrites /
• muddy turbidites /
• muddy hyperpycnites /
• unconventional oil and gas /
• Dongying Sag /
• Paleogene

Abstract: With promotion of shale oil and gas development on intensive studies on depositional mechanisms of mudstone and shales, transportation and deposition of fine-grained sediment have currently become hot topics in both sedimentoligical studies and petroleum industries. However, muddy gravity flow deposits in the Cenozoic lacustrine environment have not yet arisen attentions of geologists, although literatures of gravity flow-generated muddy deposits in marine environments extensively existed. Based on extensive literature researches, detailed core examinations and thin section observations, this paper analyzes characteristics of gravity flow-generated fine-grained deposits in the 3^rd oil-member of the Paleogene Shahejie Formation (E₂s₃), Dongying Sag, Bohai Bay Basin. Discussions on their forming mechanisms have theoretical significances on lacustrine sedimentary environment study and have practical meanings on developments of shale oil and gas. Results: 1) there are various gravity flow deposits, including muddy mass flows, muddy debris flows, muddy turbidity currents and muddy hyperpycnal flows exist in E₂s₃ in the Dongying Sag; 2) muddy slumps, muddy debrites, muddy turbidites and muddy hyperpycnites co-generate and co-exist in spatio-temporal extents. Conclusions: 1) muddy sediments can deposit in turbulent waterbody and high hydrodynamic conditions; 2) muddy gravity flow deposits play an important role in deep water sedimentary regions; 3) muddy gravity flows are of great importance to transportation and deposition of coarse grains and organic matters, and so to preservation of organic matters; 4) muddy gravity flow deposits have important geological significances on unconventional oil and gas.