The sustainable annular pressure (SCP) caused by sealing failure of cement sheath and the casing deformation during hydraulic fracturing

are the major well problems integrity encountered in shale gas development.Based on the existing research results

we focus on summarizing and analyzing the progresses in research of factors contributing to failure of shale gas well integrity.With the progress in researches about casing deformation during hydraulic fracturing in shale gas wells worldwide

we know that the major influential factors include temperature

stress

asymmetric fracturing in the reservoir

poor cementing and the slip of faults or natural fractures.Among them

the shear deformation mechanism of the casing in shale gas well caused by the slip of faults or natural fractures during fracturing has attracted more and more attention among the researchers.It is proposed that the casing deformation can be effectively reduced by increasing the casing strength and the cementing performance

or avoiding the areas with fault or natural fracture slips.Besides

the sealing failure of cement sheath in shale gas wells is mainly caused by yield failure of cement sheath out of pressure variation within the casing or eccentricity of casing and channeling through interface cracks.The sealing failure of cement sheath can be effectively reduced by applying expansive cement

flexible cement or annular pre-stressing techniques

while the optimization of special cement slurry system in shale gas wells is particularly important for improving the sealing integrity of cement sheath.Given the limitation of the cement sheath sealing ability

additional mechanical sealing methods can also be used to meet the requirements of sealing integrity for certain well annulus areas.The research results about the shale gas well integrity are also of referential value to the design and control of other unconventional oil & gas wells to be completed through volume-fracturing.