Tom,
Back in 1996-1998 Sonat Exploration (Tyler, Texas) and Chesapeake drilled several gas wells in this area into the Austin Chalk formation. Most of these wells are still producing small amounts of gas even after producing for 20 years. In A-39 Sonat drilled gas well 30604 (W1 Search Results) and had an approved permit for well 30611 but never drilled it. Sonat Exploration has now changed their name to Tanos Exploration by turning the name around backwards. They are now drilling some fantastic gas wells in Smith, Cherokee, Rusk, Gregg, and Panola Counties.
In 2008 Southern Bay Operating drilled numerous gas wells to the South and Southeast of A-39. There are some decent gas wells in this area. Acaval Land Company I am not familiar with. Since there is production in the area you might try for a little more bonus money. The 20% and 3 year lease sound OK. One of the main items in your lease must be definitely no deductions for processing, gathering, treating, compressing, dehydrating, transporting, and marketing or otherwise making such gas or other substance ready for sale.
GIS Map of Grimes County A-39: