Salt creep is the time-dependent deformation or flow of halite (or rock salt) under stress, causing the salt to gradually move into or close an underground opening, such as a cavern, tunnel or wellbore. Alongside its extremely low permeability, this natural sealing tendency makes halite well suited as a barrier to fluid movement in a range of subsurface projects, including those involving Carbon Capture and Storage (CCS), Deep Geological Disposal of Radioactive Waste, Gas Storage and Geothermal Energy.

A key challenge affecting many CCS projects is that legacy abandoned wells could compromise the integrity of a store if they have not been decommissioned to modern standards. In the long term, if a well passes through halite formations, the halite might contribute additional sealing as engineered well barriers (typically cement) degrade, making salt creep an important factor when assessing the risk of leakage through such wells. However, salt creep does not always result in rapid sealing. Trapped fluid may hold halite sections of plugged wells open, extending sealing timescales considerably. Josh’s master’s research modelled this process in QPAC, and the work was also presented at EAGE GET 2025 in Rotterdam, the Netherlands.

In general, salt creep is also strongly influenced by natural heterogeneities in grain size, water content and mineral impurities, meaning creep rates can vary considerably between different halite formations and even within the same formation. In addition, wells commonly pass through multiple geological formations, and there is considerable potential for creep in shales or other clay-rich rocks to contribute to long-term annular sealing around wells. Quintessa’s ongoing research is developing models to improve understanding of how natural creep processes could contribute to long-term well integrity and sealing in subsurface projects for application to a range of rock types, such as shale.

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