Shale barrier verification: Rebound effects may affect the conclusions

ABSTRACT: Creeping shale formations can provide efficient barriers around deep wells. Such shale barriers are highly valuable both economically and functionally, however their presence and quality need to be verified by well tests. For the validity of a shale barrier verification test, it is not only important how the procedure is performed, but also when it is performed. Theoretical analyses and laboratory tests show that the sealing efficiency of a barrier can vary significantly with time, specifically in situations where formation of the barrier was initiated or accelerated by a dedicated well operation. A part of the sealing efficiency obtained during the well operation may potentially be lost during a following rebound process of comparable length as the well operation. Knowledge of the rebound effects provides necessary information on when verification tests may give results that are not representative for the long-term quality of the barrier. Hence such knowledge provides guidance for when verification tests should be performed.