Fair offer for portion of oil well partnership?

I need help evaluating an offer for a small portion of an oil well partnership that my mother purchased in 1972.

It is a 0.3105% working interest in Section 22, Block K covering 644.9 gross acres in Reagan County, Texas. This equates to 2.20024 net mineral acres (NMA) in the leasehold. The buyer is offering $10,000 total which equates to approximately $5,000 per NMA.

The well owner has also offered to let us participate in 3 new wells they will be starting but we are not interested in making the $45k investment.

Their offer of $10,000 to buy our interest expires in 3 days on 7/26/19.

How can I determine if this is a fair offer?

Thanks in advance for your help!