Study On Mechanism And Numerical Simulation Of Surface Subsidence Caused By Salt Rock Gas Storage

Underground energy storage is the preferred storage type due to the characteristics of economy and safety, and salt rock is best medium because of its good creep property, low permeability, damage self-healing and abundant reserves. At present, the energy safety situation of China is becoming more serious, however the energy strategic reserve of China is limited and the construction of underground storage is just started which has a promising prospect. Many problems about the theoretical research and practical application of salt rock gas storage still remain unsolved, and subsidence is the main influence factor of the stability of gas storage.In view of the special geological characteristics such as interlayers and thin salt layers, firstly, the subsidence theory was analyzed based on the achievements from home and abroad, and came up with a new calculation model of surface subsidence based on Schnute growth curve, then the parameters of this model were determined by measured data, the laws of subsidence development with time was analyzed as well. Samples of salt rock, layered salt rock and mudstone were collected, then creep test and conventional mechanics test were conducted to determined the creep property and mechanical parameters, meanwhile the creep model was established by the series connection of Kelvin element and ideal viscoplastic element. The creep test results show that the creep includes initial creep and steady creep both under uniaxial and triaxial condition, and the steady creep rate of salt rock is bigger than mudstone, therefore the deformation of layered salt rock is mainly composed of salt rock creep. The creep test curve agrees with the creep model curve which proves the correctness of the model.In addition, the distribution and geometrical shape of salt cavity were determined by earth electric field lithology(CYT) detection technique, then the cavity was simplified to build numerical simulation model. The creep model was programmed by Fortran language and import into finite element software to calculated the influence scope of creep, the influence radius of subsidence and the reasonable cavity space under condition of different pressure, volume, depth and time. Then the applicability of the theoretical calculation model was verified by comparison of numerical results and theory results. Finally some suggestions about subsidence control were put forward according to the research results and provide some guidance for the construction of salt rock gas storage.