EOG has massive experience in many basins in the USA - and has an excellent geological and engineering team that can evaluate key subsurface information to determine what has the most potential.
This area is not their first rodeo.
EOG has had a TON of experience in the Texas trend chasing not only the Eagle Ford but also the Austin Chalk. There is heterogeneity in both trends, but the Austin Chalk has more extremes as to reservoir quality.
Some areas in the AC just will NOT work with respect to drilling horizontals and frac’ing them to get production. EOG has cracked the code (as have others) as to what to look for in the AC to determine if the reservoir is such to make it viable for this approach.
They will have used all subsurface well control in the trend area to determine if the reservoir has the “right stuff”. Plus, have tied this log control to rock work (cores, cuttings) plus then acquired seismic (probably 3d) to ID subsurface risk areas (e.g. faults) plus map the structure which will be followed during Hz drilling efforts.
I have done this same type of trend analysis in my past companies.
So, to answer your question, EOG had defined an area of interest based on all the above work. Then put together a lease position based on this work - all with a high degree of confidence that this new trend should be economics.
Drilling, frac’ing and producing then “proves the point” and areas of further refined based on actual well results.
If some areas don’t meet the muster as to prospectivity, EOG will either flip the acreage to another operator or just let it expire. Acreage is the least expensive aspect of any play like this.
Hope this explanation helps - a bit difficult to try to explain on this in a discussion site without maps and other tools.