Improving cementing quality by increasing pressure differential between the internal and external casing

How to improve the cementing quality is an issue the drilling engineers are always facing.This paper analyzed the relationship between the stress and strain on the casing during cementing operation based on the theory of medium-thick wall pipe mechanics,and then suggested increasing the pressure differential inside and outside the casing to improve the cementing quality.Once the external compression is exerted on the casing,there will produce inside the casing a kind of elastic energy,which will be released when the cement stone shrinks during the WOC to make up the micro annulus produced by cement shrinkage to avoid gas channeling.The cementing quality is thus improved.The applications in over 10 wells have proved that this method could effectively eliminate or reduce the micro annulus created by the casing stress change and casing strain change during the later stage of the cementing job,thus to improve the cementing quality.So it is recommended that the pressure differential between the casing and the annulus be increased to improve the cementing quality if the downhole conditions permit.