Volume fracturing is a necessary technical means to realize commercial development of shale gas

but the effectiveness of its stimulation mechanism and various auxiliary production-enhancing measures still needs further exploration.The effects of carbonate content

acid type and concentration and proppant on the permeability of acid-etching shear fractures in shale reservoir were investigated through experiments testing the permeability of acid-etching fractures

and the changes of the microscopic pore throat structures before and after acid etching were studied by CT scanning.The results show that when the carbonate content of shale is about 2%

the best acid etching effect can be obtained by using the mud acid formula of about 11.25% HCl+6.75% HF

while for the shale with a carbonate content of 15%

the acid concentration should be about 7.5% HCl for the best acid-etching effect

and for the shale with a carbonate content of 25%

the acid concentration should be about 2.5% HCl.If natural fractures filled with calcium cements are well developed in shale reservoir

optimal acid concentration should be raised appropriately.Nevertheless

if open natural fractures or fractures filled with calcium cements are not well developed in the shale reservoir

even acid with high concentration cannot drive through the cores due to the extremely low matrix permeability in shale.The experimental results provide more valuable information for the design of effective hydraulic fracturing in shale reservoirs.