ABSTRACT
During the operation of salt caverns, the creep behaviour of rock salt leads to a subsurface volume loss (convergence), which is transmitted to the surface and results in a subsidence bowl. The abandonment scenario of a cavern is of high importance for the long-term development of convergence and surface deformations, since the respective abandonment scenario could lead to either very low or moderate deviatoric stresses around the cavern. Subsidence modelling has been carried out for the cavern field in Heiligerlee (eleven brine-production caverns, one gas cavern) using the DEEP.KBB subsidence model, which is based on the established approach by Sroka & Schober (1982) and extended by Buzogany (2019) by differentiating the transmission of cavern convergence inside the salt dome and in the surrounding non-salt rock mass.
For the abandonment phase, three different scenarios were investigated:
Hard shut-in (plugged cavern)
Soft shut-in (pressure control at maximum pressure)
No shut-in (open flow)
To assess if a stable situation is reached within 100 years after the end of the cavern operations, the subsidence and subsidence rates were calculated for up to 200 years after the end of operations. From the operator’s prospect, the investigation provided valuable information on the total subsidence as well as the subsidence rates per scenario.
