If they have been sold then there will be a seperate deed recorded.
If they have been leased by one of the energy companies then there will be an agreement "lease option" recorded.
If they are being produced (well drilled and fracked) then TAD will show a separate mineral account for each well that you own a fractional percentage of. It will list the producer and Well and API number on that tax document. You can use those numbers and go to the Texas Rail Road Commission's web site and look up production statistics on the well.
www.rrc.state.tx.us