Favorable lithofacies types and genesis of marine-continental transitional black shale: A case study of Permian Shanxi Formation in the eastern margin of Ordos Basin, NW China

WU Jin,WANG Hongyan,SHI Zhensheng,WANG Qi,ZHAO Qun,DONG Dazhong,LI Shuxin,LIU Dexun,SUN Shasha,QIU Zhen

Table 1 Shale lithofacies types and characteristics of the Permian Shanxi Formation in the eastern margin of the Ordos Basin.

Facies Geochemical characteristics Rock mineral composition Pore characteristics TOC/% Organic matter Type Siliceous mineral/% Clay min- eral/% Carbonate mineral/% Main type Total pore volume/ (cm3•g-1) Total specific surface area/ (m2•g-1) Poro- sity/% Low-TOC clay shale 1.0-2.0 Ⅲ 12-50 44-82 0-4 Clay mineral interlayer pore 0.011-0.022 5.54-11.59 0.6-1.9 Low-TOC siliceous shale 1.0-1.5 Ⅲ 40-58 30-53 2-9 Mineral interparticle pore 0.015-0.016 3.89-5.86 1.1-2.0 Medium-TOC siliceous shale 6.0-9.0 Ⅱ2 63-73 20-29 2-4 Organic matter pore- fracture, mineral interparticle pore 0.018-0.020 23.60-23.76 5.0-5.2 Medium-TOC mixed shale 6.0-8.0 Ⅱ2 20-30 30-40 30-45 Organic matter pore- fracture, mineral inter- particle pore, mineral dissolution pore 0.015-0.017 21.30 5.0-5.5 High TOC siliceous shale 10.0-12.0 Ⅱ2 47-52 30-33 10-20 Organic matter pore- fracture, mineral interparticle pore 0.02-0.023 43.63 5.0-5.5 High TOC clay shale 15.0-25.0 Ⅲ 15-35 65-85 0 Organic matter micro- pore, clay mineral interlayer pore 0.036 100.77 4.5-5.5