Shale samples were taken from the Wufeng-Longmaxi Formations in Jiaoshiba Block of Fuling shale gas field to study the key controlling factors of shale fractures and their influences upon gas production capacity through analysis methods including core observation

FMI logging interpretation

Ar-ion Milling SEM images and etc.The results show two main types of fractures:micro-fractures (cleavage fractures

intergranular fractures and grain-around fractures) and macro-fractures (high angle fractures-oblique fractures and vertical fractures

horizontal fractures-foliation fractures

interlayer slipping fractures).Their growth is clearly under the joint control of mechanical properties

abnormal high pressure

distance from the main decollement surface

and bentonite and tectonism.The micro-fractures and horizontal fractures are best developed at the bottom of both Formations

while high angle fractures are mainly developed in the Wufeng Formation in structurally stable regions far from fault belts and occur in all the shale gas formations in areas near the fault belts.The differential development of natural fractures in horizontal and vertical directions is found to control the productivity of single shale gas wells through the following ways.First

it controlled shale gas enrichment as the micro-fractures and horizontal fractures far from faults around Jiaoshiba Tectonic contributed greatly to the accumulation of shale gas in the stable structural zones.In contrast

the open fractures with high angles possibly acted as channels for shale gas to escape

thus leading to a low gas abundance and a low formation pressure.Secondly

it may lower the effectiveness of volume fracturing as the high-angle open fractures not only can cause severe drilling mud leakage

but also deter the formation of fracture networks through fracturing.