Kristi, I'm a CPA and I just dealt with the passing away of my mom who owned mineral rights in the Bakken. Whether or not you have an appraisal prepared will depend on if you have or might have an estate tax issue. There could be three estate taxes. The federal estate tax which starts at over $5M currently, the estate in the state where the deceased lived when they passed, and the estate tax in the state where the property is located.
My mom lived in Washington State when she passed. Washington has an estate tax that starts at $2M. Although North Dakota does have an estate tax statute, but for some reason no tax payment is required. My mom's total estate was well under the $2M. Because we were sure that there would be no estate tax, we did not have the rights appraised. I did do a little reading and assigned a value to the rights for purposes of the Washington State Probate.
However, here is something to think about. When an assets is sold, you pay tax on the difference between what you sold it for and its basis. Most of the time the basis is what you paid for the property. Federal tax code allows an up-step in basis to fair market value for appreciated property received from a decedent. If my mom had sold her mineral right for $10K and acre the day before she died, she would have paid tax on $10K because the basis in the rights was probable just about -0_. The tax would have been $1,500. If I sold the rights after receiving them from here estate for $10K, I would have paid no tax.
The issue here is being able to support a value for the up-step in the event that a beneficiary decided to sell the property at a later date. It could be years later. If there is significant value in mineral rights and there is a chance that the rights might be sold at a later date, it might be a very good idea to pay for an appraisal at date of death to reduce tax in a future sale.
Tax code is complex and can bite you if you are not careful. If you think you might have an estate tax problem, go see an "Estate" Attorney. It will be money well spent.
Greg