With the comprehensive application of the photography of full thin section

the optical microscope observation of small thin sections

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test

whole rocks X-ray composition test

physical property analysis and the observation of field emission scanning electron microscope

Ordovician Wufeng Formation amd Silurian Longmaxi Formation in Shuanghe Outcrop in Changning area are analyzed systematically. The results show that the black shale of Wufeng-Longmaxi Formation in Shuanghe Outcrop of Ch

angning area in southern Sichuan Basin is mainly siliceous shale

calcareous shale and mixed shale

and the average values of quartz

calcium carbonate and clay minerals are 42.5 %

37.4 % and 14.9 %

respectively

containing a small amount of plagioclase （average 2.5 %）

pyrite （average 2.7 %） and organic matter （average 5.6 %）. The black shale develops mud laminae and silty laminae

and these two types of laminae are composed of five bedding types: graded horizontal bedding

homogeneous bedding

banded silty sand horizontal bedding

sand mud graded horizontal bedding and sand mud thin interbedded horizontal bedding. Progressive horizontal bedding and homogeneity bedding are developed in Wufeng Formation

while strip silty sand horizontal bedding

sand-mud progressive horizontal bedding and sand-mud thin interbedded horizontal bedding are developed in Longmaxi Formation. On the basis of mineral composition and bedding types

eleven types of lithofacies are divided. LM1 member

which is the “sweet spot” interval in Shuanghe Outcrop in Changning area

is characterized by high

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content

high siliceous content

high porosity

high permeability

high horizontal/vertical permeability ratio and high organic pore content. The strip silty sand horizontal bedding develops here.