When I open a new box of tea bags, especially one that was sealed before I opened, I enjoy smelling the strong smell of the tea and/or various herbs that are in there.
Does this require a birkas hareiach (blessing for smell)? If so, which?
Yes, if one smells a herbal tea with the intention of enjoying its scent, one should recite a berachah. If one takes the tea to drink it, and only smells the scent by the way, one would not make a blessing. Note that the scent of ordinary teas is not strong enough to warrant a blessing upon “enjoying the scent,” and only if the tea is truly fragrant would one recite a blessing.
The blessing that one makes would be the appropriate blessing for the herb, and hence would usually be borei isbei besamim.
Additionally, the sefer Re'ach HaSadeh (p.142) quotes Rav Chaim Pinchas Scheinberg saying:
Common tea requires no blessing. However, some herbal teas are quite fragrant, and the tea bag requires a blessing, according to its source.