If you have to have something official, you’ll need a petroleum engineer that does appraisals/valuations. That can cost real money. Several hundred and up.
Otherwise, visit the Oklahoma Corporation Commission site and find production statistics for wells in your area. Focus on wells producing from the same formation. FYI - The OCC website is not the most user friendly site you’ll ever use. Join yours as well as adjacent County Mineral Groups to get help from locals.