There is a long history of oil and gas production in that part of the county. There are many prospective geologic formations so I wouldnt get too concerned about being in the "dry gas" part of the Eagle Ford lots of production from the wilcox and shallower sands including one called the "Oakville formation" Does your family still have any surface land in the area ? One can always ask neighbors what they know about the local geologic conditions, often they are quite informed. A great place for you to start researching is to look up the wells you have and the ones on adjacent properties at the texas railroad commission website. it is map based so you can zoom in to the area around your tract and go from there
If you can give me a general idea of your location, as in miles and direction from the nearest town, or survey and abstract # I can look up some wells and logs specific to the area the next time I am in San Antonio
Here is a long explanation of how to look up well data at the Texas Railroad commission website that I posted a while back on the Goliad county group page. this is a place to start and it can help you get background so that you can better understand you potentials. It might seems complicated at first but once you get enough pieces the picture starts to come together. If you find some wells pay attention to what the name of the field is. often you can do a search for that oil field and you can find articles about the history of the field. geologic studies that reference it or even something from a company that is presently operating some wells there or is drilling new ones
If you want to know what you might have under some land in Goliad county a good place to look is the railroad commission website. look and see what wells nearby were drilled to and what they produced over time. To do that go to the TxRRC website and find the page that leads to "online research queries" go to the Public GIS viewer for oil & gas ect and launch the app. this will open a page with a map of Texas showing the commission districts ect. pick the "identify wells" from the map tools and scroll down counties to goliad , which happens to be # 175 the map will zoom to your county and you can zoom to where ever you wish to look up some wells. There are various things like the names of the quad maps, county lines ect. when you zoom in enough the wells will have their api identifier # visible and the original survey tracts will also be visible. the wells have different colors and symbols depending on whether they are oil wells gas wells, plugged, ect. find the wells near your land, be on the lookout for wells that are in a line, they are following a trend. that might tell you more than wells to the east or west or your tract. Now pick a well and click on it. a window that says GIS wellbore attributes pops up and there is a link to records for permits ect. click on the link operator/well bore/pdq that will take you to another window that says operator well bore and has the api # of the well you are looking up there is various information about the well and operator ect here but go to the links at the bottom, here you can look up production records, or go to imaged records for the lease. go to the lease records. this takes you to a window at "neubus" and there will be links that say "potential" or "oversized" potentials will list all of the api#s for all of the wells on the lease and are grouped by years. the oversized are big scans of either lease plat location maps, or well logs ( these are very rarely found here) when you hit the link for a potential record you will get a pdf downloaded. when you open this you will find a treasure trove of good information, buried in a giant mass of permit documents and correspondence from years ago.
now that you are looking at a pdf of drilling and completion records, among other things find the completion report. besides telling you the operator, lease name and well # there will be a report of initial production. it will list the depth to pay , which is going to be different from the total depth. the initial producing rate of how many barrels of oil, mcf of gas and bbls of water will be listed. pay close attention to the perforated intervals listed right below, these are the oil producing zones that were hit in this particular well. if you are lucky below that the depth to various geologic formations encountered drilling the well will be listed. if you root around for awhile you can get a good idea what sort of potential you might have on you tract. good luck with it.