| Rock salt is a worldwide-recognized ideal medium for storing oil and natural gas. Rock salt underground gas storage has been studied for several years in our country. Discarded salt cavities in Jintan have been used to store natural gas for the first time in the world in 2007, and the feasibility of rock salt storage in Yunying has been demonstrated in 2009. From 1000 to 1500 meters, it is the most economical formation for rock salt underground gas storage. But there are some principles for selecting the suitable formation, so the selected formation may be not the most economical one. For the formation of over 1800m, which is called ultra-deep formation, its temperature and pressure are much higher than the common formation. According to the feather of the ultra-deep formation, systematic mechanical tests in high temperature and high pressure have been conducted for Qianjiang rock salt underground gas storage, which is in formation of 1990m to 2080m. Based on the fracture feather, strength theory of rock salt has been built. The stability of ultra-deep salt rock underground gas storage has been researched by numerical simulation method. The main contents and conclusions are as follows:1. Based on the temperature and pressure in 2000-meter formation, compression tests in different temperatures and pressures were conducted. The mechanical properties in high temperature and pressure were studied, and mechanical parameters were obtained. The differences of mechanical properties under high and normal temperatures and pressures were compared. The effects of confining pressure and temperature on rock salt mechanical property were researched.2. According to the characteristics of cyclic gas injection and production, uniaxial and axial cyclic loading and unloading test were conducted. The deformation properties of loading and unloading under yield surface were studied, and the constitutive relationship between loading and unloading was given.3. Creep tests in high pressure were conducted, and the feather of long-time creep curve was researched. Based on the test result, the steady-state creep rates were obtained. The primary creep constitutive relationship, which considering the effect of deviatoric stress, was built. Then global creep constitutive equation was given. The accelerated creep boundary line was presented to determine creep failure.4. Strength theory which is considering the effect of high temperature and pressure was built. Based on the tests, shear failure criterion, tension failure criterion and the stability criterion over critical confining press were built. The dilation criterion which represents permeability properties was built based on compress tests. The surrounding rock mass of rock salt dissolved cavity can be divided into elasticity zone, plasticity zone, dilation zone and failure zone; based on the zones, stability criterion was built.5. Based on the theory model built previous, self-defined constitutive was compiled to the interface of FLAC3D by VC++6.0, and validity of self-defined constitutive was verified by using a tunnel model. Based on the self-defined constitutive and parameters obtained by tests, numerical simulation analysis was conducted for the rock salt underground gas storage in ultra-deep formation. Considering results of stability and creep analysis, 17MPa was advised to be the long-term minimum pressure. When gas supply is emergency, the pressure can be dropped to 10MPa, and the storage capacity between 10MPa to 17MPa can be used as short-term emergency gas supply. The minimum distance between casing shoe and cavity roof is 8 meters, and two times of cavity diameter is feasible for the pillar width.
|
PDF Full Text Request