Long term stability evaluation of an old underground gas storage cavern using unique numerical methods

A novel approach for the analysis of the long term stability of an underground propane gas storage cavern in sedimentary rock formations is discussed in this paper. The cavern is located in Midwestern United States and is currently used to store propane at pressures of 130 pounds per square inch gauge (psig) or 0.9 MPa. It has been in service for more than three decades. An evaluation was performed of its long term potential for continued storage of liquefied petroleum gas. Numerical models with weakened peripheral elements to account for the possible deterioration of cavern pillars were developed using a boundary element code (LaModel) in order to simulate the current cavern conditions. Additional analyses were performed to study the effects of the de-pressurization, re-pressurization and pressure-testing procedures typically required to as part of the storage cavern re-commissioning process. The floor stability of the cavern, which has a layer of moisture-sensitive claystone, was also assessed. The analysis results indicated that the cavern was likely to remain competent for 30 more years of service life.

► A three-decade old underground propane gas storage cavern evaluated for long term stability.
► Boundary element tools used for cavern stability analysis.
► Empirical approach utilized for weak floor heave potential assessment.
► Analysis results indicated cavern to be likely competent for 30 more years of service life.