Analysis of the behavior of large underground oil storage caverns in salt rock

Abstract

The storage of petroleum products above ground surface has many constraints and limitations. A viable alternative is to excavate large underground spaces in rock to provide a safer way for oil storage. Soft rock formations such as salt domes provide suitable conditions from environmental and operational aspects. The potential for high volume storage and low permeability are among advantages of oil storage in caverns excavated in salt rocks. The complicated shape of oil storage caverns, complex behavior of salt rock, and boundary conditions associated with large underground openings are major challenges in the design of salt caverns excavated for oil storage purposes. In this study, the deformation mechanism and stability of salt caverns were investigated. A comprehensive 3D numerical study was carried out to investigate the effects of cavern size and depth, salt rock deformation modulus, and ground in-situ stress regime on the behavior of large salt caverns. The stress field and deformation mechanisms were studied numerically aiming at shedding lights into the design aspects of salt caverns for oil storage. The analysis results show that the cavern safety factor is reduced as a function of cavern depth and storage volume. Also, with decrease in k (ratio of horizontal to vertical in-situ stress), the stability of salt caverns will increase; however, with increase in salt rock young modulus, the sensitivity of cavern stability to k ratio is reduced. The Pwipp constitutive model was used in the numerical analysis. This model gives a good description of salt rock creep behavior under varying stress levels. This model also is calibrated based on laboratory and field testing [25]. A set of parameters given for the Pwipp model by [11] was used in the presented study (see Table I). Figure 16. Run no.16 stability analysis results (volume 1, E = 18 GPa, k = 0.75): a) Cavern wall displacement history, b) contours of minimum principal stress distribution, c) safety factor along measuring lines, d) contours of wall safety factor, e) SFR change along measuring lines, f) contours of SFR change. [Colour figurecan be viewed at wileyonlinelibrary.com]

Creep Properties and Constitutive Model of Salt Rock

“…erefore, the salt rock stratum is internationally considered as an ideal medium for underground storage of energy resources and disposal of radioactive waste. According to statistics, western developed countries, such as United States, France, and Germany, have built a large number of salt rock underground storages as national strategic energy reservoirs [8][9][10].…”

Stability Analysis on the Long-Term Operation of the Horizontal Salt Rock Underground Storage

“…Wang et al [23] selected factors such as deformation, plastic zone development, effective strain, safety coefficient, and volumetric shrinkage as indicators to evaluate the influence of the spacing between new and old caverns on the stability of salt rock underground storage. Mortazavi and Nasab [24] studied the influence of cavern size, buried depth, salt rock deformation modulus, and in situ stress state on the stability of large salt rock underground storage. Khaledi et al [25] studied the change rules of volume convergence, damage expansion, and permeability of salt rock underground storage during the construction and operation period using the elastic-viscoplastic creep model.…”