airports and mineral rights

Rented a tractor for the week to clear some area to train and fly from.  Not a lot to clear but what is there is very prickly and very bad for a paraglider wing.  Smoothing out about an acre on my property and 3 acres across the road from me.  I contacted the land owner about buying their 5 acre tract.  The family bought the land in 1979 and the last time they came out here was 1985.  They said they don't plan on ever doing anything with the property but they don't want to sell it because of the mineral rights.  I suggested to them that perhaps if there were any minerals worth extracting that someone would probably have found them in the last 30 years.  No deal on a sale yet but they gave me written permission to clear the few pesky mesquite on the property.

When I first moved out here I was told that all the land owners out here had 50% of their mineral rights.  I asked someone who knows how to get to the bottom of these kinds of matters and this is what she found.  http://www.recenter.tamu.edu/pdf/2026.pdf
"An April 2013 article on mineral rights west of the pecos.  It appears that based on case law, rather than on statutes and chain of title, the state of Texas owns 100% of the mineral rights under interpretations of "The Relinquishment Act".  However, the state seems to assign "executive rights" to the owner of the surface estate to be able to enter leases and for leases entered after Sept 1, 1987 the surface owner has a right to 20% of all bonuses, rents and royalties from a mineral lease on the property which they execute and must register with the state's General Land Office.  Based on this article, it appears that the chain of title and deeds that attempt to transfer mineral rights have no effect.  The article says that "Executive Rights" are not separable from the surface estate."   Bottom line:  20% of nothing doesn't add up to much.  44,62,46,0,C