Please let me know the nuance and teach me which is correct.

"Enclosed" is preferable.

"Encased" would suggest a container or box.

— The gift was encased in clear plastic.
— On the shore of the frozen lake he discovered a fish encased in ice.

"Encircled" refers to the perimeter but not the structure.

— The arena was encircled by many flags.
— A pack of wolves encircled their prey.

"Enveloped" would be better applied to something atmospheric or ephemeral.

— The crowd was enveloped in smoke from the fireworks.
— A sense of relief enveloped the audience.