So my FIL has a few wells in Tarrant County. They've been active for about 10 years, and each year he has paid taxes on the income from those wells.

He received a bill this year for the value of the wells for the first time out of the blue and isn't sure where to start on fighting the appraisal/valuation.

Anyone know someone who works in the space or can offer guidance? He's contact the folks that typically fight residential property valuations...

My family has worked with Michael Gulig out of Waco.

No doubt he's been paying ad valorem taxes on the wells since they've existed. If he has doubts about the appraised values being too high, suggest he communicate with the operator (oil company) who is also paying that same tax, although likely 75% more.

Most counties tax on value but show the production for further information.

Pritchett & Abbott do valuations for most counties. They inflate quite a bit, just like your home value with central appraiser. They never account for decline curve until you challenge it. Some counties cook the books by hand picking a high month for price of oil and gas.

DMS and Co. out of Abilene and KE Andrews out of Dallas specialize in this. There are others, but those are 2 that I'm familiar with.