Research Progress on Shale Oil and Gas Well Integrity Technology
The general situation of wellbore integrity failure during the whole life cycle of shale oil and gas development at home and abroad is reviewed.The failure forms are classified into two categories:one is structural integrity failure,that is,casing deformation.The second is the failure of seal integrity,that is,the phenomenon of annular pressure.On the whole,the problem of shale gas wellbore integrity failure in China is obviously more serious than that in foreign countries,especially the casing deformation has been restricted the efficient develop-ment of shale gas in China.The failure mechanism of shale gas wellbore integrity is analyzed,including in phases of casing,cementing,ce-ment waiting and stage fracturing.The results show that complex ground stress conditions,formation anisotropy,long horizontal anisotropy,lithologic interface,fault and fracture development,poor quality of borehole track and difficulty in casing running have obvious effects on the original casing stress before fracturing.In the fracturing process,the casing is subjected to tension and compression alternating loads,the near-wellbore stress field and the dynamic change of formation properties,the fracture non-uniform expansion,micro-fault slip,the sharp change of casing temperature,and the micro-annulus or micro-crack in the cement sheath are the causes of wellbore integrity failure.For shale gas casing deformation in China,formation slip is the most significant influence factor.Finally,the wellbore integrity control methods are proposed,including well track optimization and trajectory control,casing steel grade and wall thickness optimization,cementing optimi-zation,cement slurry system optimization,segmentation clustering and fracturing parameter optimization,etc.,which can provide reference for the treatment of shale gas wellbore integrity failure in China.
shale oil and gaswell integritycasing runningcementingmultistage fracturing
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