Based on geological

logging and experimental analysis data

normal-pressure shale gas reservoir of Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Member in Pengshui area has been researched by the established quantitative characterization method

and it is found that the reserving space of high-quality shale in ①—⑤ layers is mainly composed of organic pores and bedding joints. The arithmetic average aperture measured by FIB nanotechnology with higher resolution ranges is from 20 to 50 nm

being mainly mesopores. However

the volume weighted average aperture is 100 nm

being macropore. In terms of the measured pore

volume

macropore is the main contributor to total volume and porosity. Core-scale fractures lead to the abrupt decrease or increase of gas logging and the migration of shale gas at layer-level. The new method

Maps

show that the bedding joints in layer① of well-Longye-1 are open and continuous with an opening width of 4.69 μm

and the opening width of bedding shear joint is 1.1~2.67 μm. The sum of plane porosity for bedding and bedding shear joints is 1.39 %

which accounts for about 1/3 of the total porosity of the sample. It confirms the important contribution of bedding fracture and natural tectonic fracture for shale gas reservoir spaces. Comparing with the overpressure shale gas reservoirs

the porosity of shale reservoir in normal-pressure area is slightly low

and the high-angle seam and bedding joints are more developed. A new parameters and criteria method for evaluating normal-pressure shale gas reservoirs has been established. By this method

favorable reservoir area of type I reservoir is of 620.22 km

2

in layer ① to ⑤ of Wulong syncline.