Time-dependent subsidence prediction model and influence factor analysis for underground gas storages in bedded salt formations

Taking into account the impurity and creep of rock salt, a newmodel is proposed to predict the time-dependent subsidence of the surface above underground gas storage caverns in bedded salt formations. In this model, the shape of the storage cavern is assumed to be a sphere. Formulae are developed for the volumeand volume reduction of the cavern over time during both the construction and the operating periods. A probability integralmethod is adopted to determine the shape of the subsidence regions, and corresponding formulae are derived for the time-dependent surface subsidence, radial tilt and radial curvature. FLAC3Dwas used to verify the proposed prediction model. Using the proposed model, parametric analyses are carried out to study the influences of draw angle, volume adjusting coefficient, brine withdrawal rate, internal pressure, cavern depth, material properties of the rock salt, cavern diameter, and operating time on the surface subsidence. The results show that: the subsidence increaseswith an increase of the drawangle, volume adjusting coefficient, brinewithdrawal rate, cavern diameter, material properties of the rock salt, and time, but decreaseswith an increase of internal pressure. Subsidence increases first and then decreases with increasing cavern depth. Draw angle, volume adjusting coefficient cavern depth, cavern diameter, material properties of the rock salt, time and internal pressure have a, large influence on the subsidence, but there is little influence from the brine withdrawal rate and salt impurity