How to reduce this archive detection function and make it supports wildcards
Your regex can be shortened using {x}, which repeat a pattern x times. So your third regex would become:

exp = new Regex(string.Concat(Path.GetFileNameWithoutExtension(originalFile),
                              "_[0-9]{8}_[0-9]{3}",
                              Path.GetExtension(".log")));


As far as wildcards, if you use * it will be entered into the regex. It looks from MSDN that it won't be removed from the file name when you call GetFileNameWithoutExtension(). However, I was unable to test this as I don't have Visual Studio on my computer. It worked as a wildcard on my regex tests.