Study on well bore damage by temperature cbange of underground natural-gas storage caverns

The injection-production well of an underground natural-gas storage cavern is the only hole connecting cavern and surface facilities, and the mechanical integrity of well bore is crucial to seal gas safely. There are many problems which are peculiar to salt cavern wells, such as long period of cavern construction by leaching. Problems in different working stages are discussed and the position where production casing shoe located is regarded as a dangerous point. Cement sheath below casing shoe can be washed out during subsequent operations and so casing shoe may move downwards freely when temperature rises. Temperature stresses are calculated and it is found that, near casing shoe, shearing stress in the casing-cement sheath interface in axial direction is high enough to surpass cement bonding strength. By comparing with experimental bonding strength from others, it is found that cement will break locally when temperature rises only about 20 degrees C. Precautions to avoid the failure, such as cementing method and casing sand adhesion technique, are discussed.