The study analyzed the core samples from the Longmaxi Formation to investigate the types of fractures and their effects on reservoir properties by means of argon ion polishing-field emission scanning electron microscopy observation

experimental measurement of the porosity and permeability with overburden pressure

CT scanning and reconstruction

image mosaic

image grayscale recognition and threshold binarization

with a view to clarify the influence of microfractures on the physical properties of subsurface shale reservoir in Fuling shale gas field

Sichuan Basin.The results show that the microfractures for the shale samples can be divided into 6 types

including bedding fracture

particle edge fracture

dissolution fracture

diageneticcontraction fracture

abnormal pressure fracture and structural fracture.Microfractures can function to improve reservoir porosity and play an important role in increasing conductivity in shale reservoirs.Microfractures may form a net of fractures

connecting the various pores throughout the shale reservoir.Among them

particle edge fracturesare the main channels for vertical connection

while bedding fractures are mainly for lateral connection

both of which can be combined to form the best fracture network channels for shale reservoir.Effective fracture network can be composed by particle edge fractures in themselves

dissolution fractures can form fracture network in local area

improving the shale reservoir connectivity.The microfractures will exert a great influence on the permeability of shale reservoirs:the average permeability of microfracture samples is 62.9 times the mean permeability of microfracture-free shale samples.Under normal formation conditions

the microfractures in the shale reservoir should be open when they are shallow at a depth of 3

500 meters.Given the abnormal high pressure

sedimentation

tectonism and other rock mineral characteristics of shale reservoir fluid

the depth of the shale microfracture opening can be increased appropriately.