Dynamic prediction model for surface settlement of horizontal salt rock energy storage

Large-scale CO2 disposal/storage in bedded rock salt caverns of China: An evaluation of safety and suitability

For the sake of safety and stability, a salt roof with certain thickness is usually designed above the cavity. While some rock salt often contains multi-interlayers above the cavity roof in China, which brings new challenges to designing salt roof thickness and evaluating cavity stability. On this basis, the factors affecting the stability of cavity with multiple interlayers above cavity roof is investigated. Combining single factor sensitivity analysis and analytic hierarchy process, the influence of each factor on cavity stability and roof deformation is quantitatively analyzed. Numerical simulation results show that when there are multiple interlayers above cavity roof, the stress and deformation of the cavity are increased compared with general conditions. The rock salt roof thickness has little effect on the stability of the cavity, but the cavity tightness is at risk when it is small. When the operating pressure is setting reasonably, the rock salt roof thickness should be greater than 11 m at around 1000 m deep and 17 m at about 2000 m deep. When the depth of the cavity is less than 1700 m and greater than 2000 m, the minimum operating pressure should be 0.3 and 0.4 times of the gravity stress at the depth of cavity roof. The change of the interlayers stiffness has a little impact on the stability of the cavity. The quantitative analysis indicates that the minimum operating pressure and buried depth are two critical factors that need special attention to ensure the stable operation of the salt cavity gas storage.

Quantitative investigation on the stability of salt cavity gas storage with multiple interlayers above the cavity roof

The depth of the underground salt cavern for the storage of hydrocarbons mainly ranges from 500 to 1500 m. The target formation of the Ningjin salt district, Hebei province, China, for constructing a salt cavern gas storage is more than 2700 m in depth, which will be the deepest salt cavern worldwide. This study comprehensively analyzed the feasibility of storing natural gas in an extremely deep salt cavern. Hydraulic fracturing tests and the anelastic strain recovery (ASR) method were performed to measure the in-situ stress. Laboratory tests including uniaxial and triaxial compression, Brazil disk splitting, triaxial creep and permeability were conducted on cores to obtain their mechanical parameters. The target salt layer for constructing the salt cavern gas storage was determined. The cavern shape, dimension and operating gas pressure of the potential salt cavern were designed accordingly. A 3D geomechanical model was established to investigate the long-term stability of the salt cavern based on the geologic structure. An integrated index system was used to assess the cavern stability over the long term quantitatively. Simulation results show that the internal gas pressure is the critical parameter affecting the cavern stability, and 28 MPa is the lowest internal gas pressure to satisfy the stability requirement. Comprehensive analysis indicates that storing natural gas in an extremely deep salt cavern is feasible. The shrinkage in the open hole section should be accounted for, and no cushion gas technology is suggested to improve the economic benefits.

Feasibility analysis of salt cavern gas storage in extremely deep formation: A case study in China

The depth of the underground salt cavern for the storage of hydrocarbons mainly ranges from 500 to 1500 m. The target formation of the Ningjin salt district, Hebei province, China, for constructing a salt cavern gas storage is more than 2700 m in depth, which will be the deepest salt cavern worldwide. This study comprehensively analyzed the feasibility of storing natural gas in an extremely deep salt cavern. Hydraulic fracturing tests and the anelastic strain recovery (ASR) method were performed to measure the in-situ stress. Laboratory tests including uniaxial and triaxial compression, Brazil disk splitting, triaxial creep and permeability were conducted on cores to obtain their mechanical parameters. The target salt layer for constructing the salt cavern gas storage was determined. The cavern shape, dimension and operating gas pressure of the potential salt cavern were designed accordingly. A 3D geomechanical model was established to investigate the long-term stability of the salt cavern based on the geologic structure. An integrated index system was used to assess the cavern stability over the long term quantitatively. Simulation results show that the internal gas pressure is the critical parameter affecting the cavern stability, and 28 MPa is the lowest internal gas pressure to satisfy the stability requirement. Comprehensive analysis indicates that storing natural gas in an extremely deep salt cavern is feasible. The shrinkage in the open hole section should be accounted for, and no cushion gas technology is suggested to improve the economic benefits. 

Nan Zhang

Papers

Investigation on the influences of interlayer contents on stability and usability of energy storage caverns in bedded rock salt