Abstract

Insufficient hole cleaning is one of the major challenges in drilling, particularly in extended-reach drilling (ERD). This paper presents a case study of a stuck pipe incident caused by cuttings pack off during drilling an extended-reach well. A generalized, transient, solid-transport model that can handle different flow patterns is used to replay the hole-cleaning process. Results show that, although cuttings beds in the deviated part of the wellbore are not significant while drilling ahead, cuttings can still cause problems during tripping. This study reinforces the facts that hole cleaning in wells with long deviated sections is complicated and a transient approach is required to fully understand the hole-cleaning condition. Effective hole cleaning does not only mean that the cuttings concentration is low or the cuttings transport ratio is high. In addition, the absence of additional cuttings being produced from the shale shaker during circulation does not necessarily indicate that the hole is clean. The cuttings accumulated behind the BHA can lead to tight spots and over-pull incidents during tripping. By conducting drill string reciprocations without circulation, the tight spots can be “worked through” but packed cuttings cannot be removed from the wellbore. This paper presents lessons learned from this incident, as well as recommendations for future operations.

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