Using salt caverns for an underground strategic petroleum reserve (SPR) is considered as an ideal approach due to the excellent characteristics of low porosity, low permeability, self-healing of damage, and strong plastic deformation ability of rock salt. Salt deposits in China are mostly layered rock salt structures, with the characteristics of many interlayers, bringing great challenges for the construction of SPR facilities. Studying the microscopic pore characteristics of the rock surrounding SPR salt caverns in different environments (with brine and crude oil erosion) is necessary because the essence of mechanical and permeability characteristics is the macroscopic embodiment of the microscopic pore structure. In this paper, XRD tests and SEM tests are carried out to determine the physical properties of storage media and surrounding rock. Gas adsorption tests and mercury intrusion tests are carried out to analyze the microscopic pore structure, specific surface area variation and total aperture distribution characteristics of SPR salt cavern host rock. Results show that: (1) Large numbers of cores in interlayer and caprock may provide favorable channels for the leakage of high-pressure crude oil and brine. (2) The blockage of pores by macromolecular organic matter (colloid and asphaltene) in crude oil will not significantly change the structural characteristics of the rock skeleton, which is beneficial to the long-term operation of the SPR salt cavern. (3) The water–rock interaction will bring obvious changes in the micro-pore structure of rock and increase the leakage risk of the storage medium. The results can provide theoretical bases and methods for the tightness analysis of China’s first underground SPR salt cavern.
The design of dam bodies for underground reservoirs must account for how water affects shear failure and the evolution of fractures in coal pillars. In this work, we detect acoustic emissions in raw coal samples with different water content (0%, 5.35%, 17.88%, and 20.40%) and under uniaxial compression shear and use computed tomography to analyze the failed samples. The results show that the shear strength, shear displacement, cohesion, and internal friction angle all decrease with increasing water content, which is described by the revised Mohr‐Coulomb model for the case of water intrusion. The acoustic emission counts correlate strongly with the change in stress, and the cumulative acoustic emission counts are combined with shear stiffness to separate the fracture evolution process into five stages: crack closure, elastic deformation, stable crack propagation, unstable crack propagation, and failure. The ratios of the crack closure, initiation, and damage stress to the corresponding peak shear stress are essentially unaffected by the water content. Most cracks are tensile cracks, and an increase in the water content promotes the development of parallel fractures. These results are helpful for determining the size of coal pillars in underground reservoirs and for solving other underground engineering problems, such as support for water‐rich coal roadways.
To fully utilize the abandoned salt cavern resources and to increase the total amount of the fossil energy reserve of China, reconstructing some of these salt caverns for underground gas storage (UGS) or strategic petroleum reserve (SPR) would be an effective method. The salt resources in China mainly are bedded salt, which brings great challenges for the cavern construction and safety evaluation. In this paper, the investigations are presented to evaluate the tightness of the UGS and SPR salt cavern facilities, located in the bedded rock of Jintan, China. Microcosmic analysis, and permeability and porosity tests of the surrounding rock are carried out to determine their properties, which provide the basic data for the tightness assessment. A 3-D numerical model is developed based on the test results and the geological features of the target formation. The numerical simulation results show that the seepage velocity, seepage range and loss rate of leakage of the SPR salt caverns are much smaller than those of UGS salt caverns. The cavern's pillar width with a pillar to diameter ratio (P/D) of 1.5 can satisfy the tightness requirement of SPR salt caverns, but it cannot meet the requirement of UGS caverns. This indicates that some existing abandoned salt caverns in Jintan which are unsuitable for UGS due to their small pillar width have the potential to be rebuilt for SPR. This would help to increase the storage capacity of crude oil in China. The results can also provide a reference for the implementation of similar projects in other bedded salt districts. INDEX TERMS Bedded rock salt, underground gas storage, strategic petroleum reserve, tightness, seepage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.