You could reasonably hope to get an annulment
1. If there was physical force exerted (a "shotgun marriage")
2. Deception as to the *identity* of the spouse (you thought you were marrying Alice, but her sister Betty pretended to be Alice and so you accidentally married Betty)
3. Insanity or lack of the use of reason at the time of the wedding (high or drunk while you made your vows)
4. No intention of getting married (i.e., an exclusive union until death, openness to children)
NOTE that priests will not let you get married unless you have a certain "preparation" which closes many doors (above). You HAVE to admit (even put in writing, in some cases) that marriage is for life, you are open to children, plan to raise them Catholic, etc.
So the "reasons" for annulment do NOT include youthful immaturity, various character flaws, or the classic "I had no idea who he was!" No, the spouse has to be actually committing FRAUD, as in forging docuмents and identity theft, for his "deception" to invalidate the marriage.
Having faults, sins (especially those which you chose to blindly overlook!) do NOT invalidate a marriage.
Also, once a (single) child is born from the marriage, a certain group= of "doors close" as it were.
There is a reason why annulments were so rare before Vatican II.
Annulments are not routine "Catholic divorce".
They literally mean A MARRIAGE NEVER TOOK PLACE, i.e., you were shacking up the whole time.
So many Catholics embrace this, and don't shed a single bead of sweat that they were "shacking up" for years -- because now they can get remarried and stop being lonely. When they get that annulment, it's 100% relief and celebration, with hope for the future as they move on with their life -- just like a secular divorce. It's sad.