| 鄂西宜昌地区晚奥陶世—早志留世页岩气藏的主控地质因素与富集模式 |
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| 关键词:shale gas geological conditions enrichment pattern Huangling uplift Wufeng Formation Longmaxi Formation Ordovician Silurian Yichang |
| 基金项目:中国地质调查局项目(编号: DD20179615);国家重大科技专项(编号: 2016ZX05034-001-2) |
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| Main Geological Controlling Factors and Enrichment Pattern of Shale Gas Reservoirs in the Late Ordovician–Early Silurian Strata of Yichang, Western Hubei Province |
| The chronostratigraphic and lithostratigraphic framework of Ordovician Wufeng Formation–Silurian Longmaxi Formation in Yichang of Hubei Province indicates that there exists a conformable Ordovician–Silurian boundary in Yichang area. However, from south to north, varying degrees of missing deposits in the graptolite zone and thickness reduction of organic-rich shales were found from the uppermost Rhuddanian Stage to the lower part of Aeronian Stage. V/Cr, Ni/Co, V/(V+Ni) and chemical index of alteration (CIA) show an anoxic-suboxic marine environment and a cold and dry climate from the late Ordovician Kaitian Stage to the early Aeronian Stage of the Silurian period in the Yichang area. Thus, the variation in thickness of the organic-rich shales was affected by both sea-level falling caused by climate cooling and Yichang elevation, and the total organic carbon (TOC) in the shales was controlled by both redox environment and organic carbon flux (Mo-xs). According to the different correlations between TOC and biogenic Ni (Ni-xs) at different paleogeographic locations, the higher correlation between TOC and Mo-xs compared with TOC and Ni-xs along the sections close to the uplift and the carbon isotopic negative shift in the carbonates that is inconsistent with global trend, the authors infer that there should exist methane release from dissolution of gas hydrate due to sea-level falling or Yichang elevation, which led to increasing of organic carbon flux and further promotion of the reservation of organic matters. There are distinct positive correlations between TOC with gas-bearing property and porosity. However, the porosity should be mainly controlled by permeability and lithology and had an ambiguous relationship with gas-bearing property. This could be an evidence proving that the porosity was not the most important factor controlling the shale gas reservoir. Because the gas-bearing property was mainly controlled by TOC, thickness and pressure coefficient of the shale gas reservoir, the sedimentary facies and preservation condition constituted the key to the Silurian shale gas reservoirs. As for the preservation and enrichment of the Silurian shale gas reservoirs in Yichang area, the development of depression basin during the late Late Ordovician–early Early Silurian period and its rapid filling after the Silurian mid Llandovery Stage seem to have been the basic factors, and the development of the old basement and its slow uplift since the late Triassic may be the key. |
| CHEN Xiao-hong,ZHANG Bao-min,CHEN Lin,ZHANG Guo-tao,LI Pei-jun,ZHANG Miao.2018.Main Geological Controlling Factors and Enrichment Pattern of Shale Gas Reservoirs in the Late Ordovician–Early Silurian Strata of Yichang, Western Hubei Province[J].Acta Geoscientica Sinica,39(3):257-268. |
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