How do I find out if I own/inherited mineral rights or property?

My boyfriend received a call many years back after his aunt passed away by a seismograph company requesting permission to survey his property. He assured my boyfriend that it was all legit and even went as far as sending him photos of the maps as well as documents stating the property was in his full name and left by his aunt who’s recently past at that time. He and his son drove down to Texas to the Liberty County Courthouse as the man had told him to do and after getting their found out the courthouse was closed. After getting back to Oklahoma he checked with an attorney in a nearby town who said that it was real and that if he had $3000 to pay up front he’d handle the case. Well he didn’t have that kind of money and got aggravated and tossed everything thinking there was nothing more that could be done. Well I’m trying to help him be get to the bottom of things but I’m not sure where to start. I’ve accessed liberty county court records, what I can find online, and I’m not finding his name. I’m wondering if it could be mineral rights rather than property. If it’s property he’s worried he’s lost it bc of back taxes but from what I can gather his Aunt was a very wise woman and very business minded. She had stocks, bonds, property all over, gas and drilling rigs on some, I just don’t see her setting this up without making certain somehow it would benefit him. Where would we need to begin? Im thinking the liberty county courthouse but what exactly do i ask them to search under? Any help is appreciated, thanks in advance!