Sedimentary Characteristics and Paleoenvironment of Shale in the Wufeng-Longmaxi Formation, North Guizhou Province, and Its Shale Gas Potential  

作　　者：Chao Liang Zaixing Jiang Yingchang Cao Jinchuan Zhang Ling Guo 

机构地区：[1]School of Geosciences, China University of Petroleum, Qingdao 266000, China [2]Shandong Province Key Laboratory of Depositional Mineralization & Sedimentary Mineral, [3]Shandong University of Science and Technology,Qingdao 266590,China [3]Laboratory for Marine Mineral Resource, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China [4]State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing100083, China [5]School of Energy Resource, China University of Geosciences, Beijing 100083, China [6]Department of Geology, Northwest University, Xi'an 710069, China

出　　处：《Journal of Earth Science》2017年第6期1020-1031,共12页地球科学学刊（英文版）

基　　金：supported by the Certificate of China Postdoctoral Science Foundation (Nos. 2017T100523, 2015M582165);the National Science and Technology Special Fund (Nos. 2016ZX05006-007, 2016ZX05006-003);the National Natural Science Foundation of China (Nos. 41602142, 41372107);the Natural Foundation of Shandong Pronvince (No. ZR2016DB16);the Opening Fund of Shandong Province Key Laboratory of Depositional Mineralization & Sedimentary Mineral (No. DMSM2017064);the Fundamental Research Funds for the Central Universities (No. 15CX08001A)

摘　　要：The Paleozoic Wufeng-Longmaxi shale is one of the main horizons for shale gas exploration in Sichuan Basin. Outcrop, core and thin section observations, X-ray diffraction analysis, trace element geochemistry and other methods have been used to understand the sedimentary characteristics and identify hydrocarbon source rocks in suitable sedimentary paleoenvironments in the Wufeng-Longmaxi shale in northern Guizhou Province. The thickness of the Wufeng-Longmaxi Formation ranges from 20 to 200 m and it was mainly deposited on a deep-water shelf. The TOC content is high, up to 5.75%. The main non-organic minerals are detrital quartz and clay minerals, with a little plagioclase feldspar, potassium feldspar, calcite, dolomite and pyrite. There is also biogenic microcrystalline quartz. Six lithofacies have been identified： siliceous shale, clay shale, calcareous shale, silty shale, carbonaceous shale, and muddy siltstone. Using biological Ba, V/（V＋Ni）, TOC, V/Cr, B, Sr/Ba and other indicators, we estimate primary productivity, redox conditions and paleosalinity and show that the early stage of Wufeng-Longmaxi deposition occurred under strong anoxic conditions, high paleosalinity and yielded a high TOC content and an excellent potential shale gas source. The anoxic environment was destroyed at the late stages of Wufeng-Longmaxi deposition, the TOC content decreased, so that it is likely to be a high quality source rock. Organic pores acted as the key reservoir space in the shales, and the pores are mainly mesopose, with most pore diameters less than 20 nm. The siliceous shale has high TOC content and brittle mineral（quartz） content making it an important exploration target for shale oil and gas exploration.The Paleozoic Wufeng-Longmaxi shale is one of the main horizons for shale gas exploration in Sichuan Basin. Outcrop, core and thin section observations, X-ray diffraction analysis, trace element geochemistry and other methods have been used to understand the sedimentary characteristics and identify hydrocarbon source rocks in suitable sedimentary paleoenvironments in the Wufeng-Longmaxi shale in northern Guizhou Province. The thickness of the Wufeng-Longmaxi Formation ranges from 20 to 200 m and it was mainly deposited on a deep-water shelf. The TOC content is high, up to 5.75%. The main non-organic minerals are detrital quartz and clay minerals, with a little plagioclase feldspar, potassium feldspar, calcite, dolomite and pyrite. There is also biogenic microcrystalline quartz. Six lithofacies have been identified： siliceous shale, clay shale, calcareous shale, silty shale, carbonaceous shale, and muddy siltstone. Using biological Ba, V/（V＋Ni）, TOC, V/Cr, B, Sr/Ba and other indicators, we estimate primary productivity, redox conditions and paleosalinity and show that the early stage of Wufeng-Longmaxi deposition occurred under strong anoxic conditions, high paleosalinity and yielded a high TOC content and an excellent potential shale gas source. The anoxic environment was destroyed at the late stages of Wufeng-Longmaxi deposition, the TOC content decreased, so that it is likely to be a high quality source rock. Organic pores acted as the key reservoir space in the shales, and the pores are mainly mesopose, with most pore diameters less than 20 nm. The siliceous shale has high TOC content and brittle mineral（quartz） content making it an important exploration target for shale oil and gas exploration.

关 键 词：Wufeng-Longmaxi shale sedimentary characteristics geochemistry paleo-environment restoration shale gas 

分 类 号：P618.13[天文地球—矿床学]