I checked on TexasFile, and the document cited in the property description you supplied is available for purchase online. If you haven’t used TexasFile before, you have to prepay, but copies are $1 per page plus sales tax. The document on Vol. 115, p. 504 is four pages long; not sure what Texas sales tax is (I live in another state), but $5 should cover it. Once you sign up, click on Search County Records, select Fayette County in Texas, look for the line that starts with Book, and type in the volume and page number in the appropriate boxes (don’t worry about the book box - there’s only one record in their database with that volume and page number), then click the Search button to the right of that line. With any luck, this document will tell you exactly how many acres are in the tract.
By the way, once you download the document, make sure it’s the correct one. I’ve had problems in the past with TF where the date and volume, page and instrument numbers they cited did not correspond with the correct document. With any luck, though, you’ll get the right one. I’m assuming you have a copy of the deed whereby your father acquired his interest. If not, that should be available on TF as well; just do a search using the Grantor/Grantee box. Don’t worry about selecting one or the other; it’s always possible your dad owned interests in more than one tract, and if he was the grantor of an oil and gas lease (technically, he would then be a lessor, but TF doesn’t make that distinction), that would indicate that he owned an interest in the property being leased. It’s also a good idea to use wildcards if there’s any chance his name might be listed more than one way. For instance, if his first name was Joe, use Jo* so it will pick up both Joe and Joseph.
As far as establishing your ownership goes, first, was his will probated in Fayette County? If not, and you haven’t already done so, you should file a certified copy of his will and probate order with the Fayette County Clerk. From what I’ve been advised by an O&G attorney, this is better than an affidavit of heirship. Next, if you have the deed that establishes your dad’s ownership and can find the exact location of the tract, you can check on the Texas Railroad Commission’s GIS map to see if there are any wells on or near that tract. I just checked, and there are a good number of active horizontal wells in the Anna Powell League. If there is a well that touches on your tract in any way, either by the location of the wellhead or its terminus, or by the shaft crossing your tract, then it’s possible to find out on the map who the current well operator is. You can then contact the operator and ask if sending them the necessary documents is sufficient to establish your ownership. Usually, this would be the deeds showing the exact description and your dad’s ownership, plus a copy of his will and probate order. If there is an active well close to your tract, it’s usually possible to access that well’s drilling application; it should include plat map where you can see if your tract is included in that well’s perimeter. If it is, then follow the same procedure for contacting the operator. The RRC’s map can be found at Public GIS Viewer (Map). If you haven’t used this tool before, be sure to read the user guide first. The viewer is a wonderful resource through which you can find out a huge amount of detail about individual wells, but there is a learning curve involved to get the most out of it.
Again, assuming you’re eligible to receive royalties from one or more wells, if the operators aren’t willing to accept your documentation, I’d say the next step would be to hire a landman to research and fully document your ownership and contact the operators. If they still won’t budge, then it may be time to bring in an O&G attorney. Finally, have you searched the Texas Unclaimed Property website’s records? It’s possible that royalties were being held in suspense in your dad’s name, then turned over to the state. This isn’t likely given that your dad’s passing was only last year, but it never hurts to look.
Sorry for the long post. It assumes that you haven’t dealt much with mineral ownership, so I’ve gone into a lot of detail. If this isn’t the case, then my apologies. This is also not legal advice, and I’m not an attorney. Rather, I’m in a similar situation to yours, in my case having inherited a sizeable number of interests in multiple Texas counties, mostly from my granddad. I’ve been going through this same process both to discover any tracts he owned that I didn’t already known about and to establish my ownership of them. I’ve already been working with an attorney to help me through the process, but I’ve been doing most of the legwork myself.
Good luck. Even if your tract does turn out to be only 5.44 acres, there are enough producing wells in the Anna Powell League for there to be a good chance that at least one of them includes your tract in its pay zone. And even if that’s not the case, it’s worth it to establish ownership in case an outfit wants to lease your tract in the future.