You want to find word_1, followed by anything, any number of times, followed by word_2. That should be
word_1.*word_2
You seem to be using * as it is often used in command line searches, but in regexes is it a quantifier for the preceding character, meaning match it at least 0 times. For example, the regex a* would match 0 or more as, whereas the regex a+ would match at least one a.
The regex metacharacter meaning “match anything” is ., so .* means “match anything, any number of times. See perlrequick for a brief introduction on the topic.