Stuck pipes have three different origins : hole geometry (excessive dog legs in highly deviated wells), pack off (wellbore instability or bad hole cleaning leading to a plugging of the annulus) and differential sticking (drill string embedded into the mud cake due to an excessive difference between mud weight and reservoir pressure). This paper presents three different examples of stuck pipes directly related to rock mechanics problems.
The first one results from a typical pack off in a highly unstable under compacted shale formation drilled in under balanced conditions.
The second stuck pipe is quite untypical since it occurred while drilling a 9 5/8 cemented shoe track. Finally, the third one occurred while drilling the reservoir section of a highly deviated well (720 inclination) and during a directional survey. The analysis of the surface data clearly showed that differential sticking was the cause of the stuck pipe.
In the three cases, the well had to be side tracked where each time the cost was in the range of 1M.