Review to shale gas formation damage for 30 years

The current researches on shale gas formation damage derive from the conventional theory of sandstone reservoir andcarbonate rock reservoir.To review the researches of shale gas formation damage,factors affecting penetration ability were focused on.It was thought that the internal factors have mainly been recognized as listed below: the low-permeability leads to water block;the highcontent of clay tends to swell and block channels;shale surface capillary force increases resistance to gas flow;the conditions of hightemperature and high pressure do harm to the performance of working fluids and easy to increase the reservoir fluids residual;the CO2flow contaminates the working fluids and increases the residual.While the external factors of formation damage include the followingitems: the swell of clays caused by the insufficient inhibition ability of working fluids;the invasion and residual of working fluids as wellas the additives;the biofilms generated by working fluids obstruct gas flow in reservoir;and the liquid volatilization speed around theborehole is too low to prevent water blocking and causes channel blocking,which results from low production pressure.The mechanismsof the formation damage during desorption and diffusion process in shale gas has not been systematically researched as well as the effectsof different processes such as drilling and completing,reservoir stimulation and drainage on desorption and diffusion capacity.The basictheory on the formation damage of the shale gas has not been established.Moreover,there is no agreed evaluation criterion on shale gasformation damage indoor and in the field on shale gas.