خزش

Compressed air storage is one of the methods of energy storage. One of the most important parts of a compressed air storage system is the storage cavern. In this study, the behaviour and the long-term stability of the salt cavern as a storage site for compressed air were investigated. Due to the construction and operation of the salt cavern, the in-situ stress conditions around the cavern will change. The difference between induce stress and pressure of compressed air will cause the cavern to converge and damage around it. In this study, the salt rocks from one of the regions of Iran were used to test creep. To investigate the creep behavior of salt rock, creep test was performed in three stress levels in a stepwise manner. Lubby2 model parameters were calculated. Then, using LOCAS finite element software, the compressed air storage cavern was simulated and its behavior and stability were investigated. The results of these experiments and modelling have shown that with increasing stress in each stage, the slope of the secondary part of the creep increases. Therefore, it can be concluded that with increasing stress, the Maxwell viscosity coefficient decreases. In addition, the amount of movement in the lower half of the cavern was more than the upper half of it. Value of the cavern safety factor according to the Devries dilation criterion also decreased with increasing depth and the probability of dilation in the cavern wall increased.

Rock Salt belongs to the group of inorganic chemical sedimentary rocks, which is mainly composed of halite. Salt domes are considered as one of the most important oil traps. Drilling in the salt regions is associated with many problems. Challenging problems in drilling include trapping of the drill pipe string and reducing diameter of the wellbore. Convergence of wellbore’s wall in rock salts is mainly attributable to creep phenomenon. Creep is a time dependent phenomenon that occurs under constant stress. In this research, the effect of confining pressure, deviator stress, and strain rate on creep behavior of rock salt was studied. Furthermore, a mathematical equation was developed to estimate the strain rate in various stress fields. The results revealed that strain rate increases by increasing the deviatoric stress and confining pressure.

Long-term rock deformation is one of the critical problems in rock engineering design. This study presents results of some laboratory creep tests for assessment of time-dependent behavior of two rocks with different brittleness: Sandstone as a semi-brittle and Marble as a brittle rock. Brazilian disk specimens are used to plan some indirect tension creep loading tests. Also, Single Edge Crack Brazilian Disk (SECBD) is employed to evaluate the effect of pre-crack on the creep behavior of rocks. Totally, 12 creep loading tests are performed on the two rock types with three loading severity. Result of experimental tests indicates that failure time reduction percent due to existence of pre-crack in Marble specimen is more than Sandstone. In other words, the effect of pre-crack on the reduction of failure time and strain is more noticeable in more brittle rock.

Salt domes are one of the most important oil traps. More over salt minerals can be present in other oil traps. Drilling in salt formations can result in many problems such as stuck pipe of drilling strings and casings، closure of borehole’s wall and therefore bad cementing and casing failure. These problems occur as the result of creep phenomenon which is the time dependent deformation of salt under constant stress. The aim of this paper is to study the mechanical behavior of salt rock. Based on obtained results، appropriate drilling fluids، the time for running the casing in the borehole، and the collapse pressure on the casing can be determined. The effect of drilling fluid’s weight on reducing the rate of borehole’s wall closure is evaluated by FLAC codes. Considering that drilling of oil and gas wells is an expensive operation، optimization of the drilling fluid''s weight can ensure oil well integrity. Heavier drilling fluids can reduce the rate of borehole’s wall closure and therefore the running of casing can be postponed.