Minimum operating pressure for a gas storage salt cavern under an emergency: a case study of Jintan, China

Abstract

Decreasing the gas pressure is one of the most effective methods to increase the working gas capacity of salt cavern Underground Gas Storages (UGS). In this paper, KING-1 and -2 caverns of Jintan salt cavern UGS, Jiangsu province, China, are studied as an example to investigate their responses under extremely low gas pressure. A 3D geomechanical model of the two caverns is built based on the geological features and rock properties of the host rock salt formation. Different operating conditions are simulated. Safety evaluation criteria for completion casing and caverns are proposed. Thresholds of the indicators consisting of the criteria are given to find the potential minimum gas pressure and the safe working duration of the two caverns. Calculation results indicate that axial strain (along the vertical direction) can perfectly reflect the effects of low gas pressure on the safety of completion casing. The indicators calculated based on the stresses have advantages compared to those based on deformation in assessing the safety of the salt cavern under such low gas pressure and short operating time conditions. The minimum gas pressure gradient of KING-1 and -2 caverns at the casing shoe can decrease from about 7 kPa/m to 5 kPa/m, viz., the minimum gas pressure can decrease from 7 MPa to 5 MPa. The maximum duration for 5 MPa is no more than 118 days. Taking KING-1 cavern as an example, the working gas volume can increase about 17.3%. Research results can provide references for Jintan salt cavern UGS coping with gas shortages.