Greenlight Capital model DCF until year 2120?

"Walker Texas Banker" Jury is still out on how long horizontal wells will last but its a common assumption in the industry that they can produce for 50 years + with more aggressive long term projections going out past 100 years. What drives this is the use of Arps decline formulas with the key input in this case being the terminal decline, what occurs post-hyperbolic and exponential. Depending on who you're asking and where the wells are drilled, terminals can be anywhere from 5%-15%? I leave a question mark there because certain wells will produce steady and then just fall off the face of the earth when bottom hole pressure declines to a certain point.

Also after glancing at the appendices those look like NAV models which generally speaking assume all proved reserves are developed over time and a company with substantial reserves will need decades to develop their inventory completely.

That's all well and good, but given both the declining production profile of a well and the time value of money (especially at a 10% discount rate), is there really any point to projecting out for the entire life of a well?

Any business can exist for 30-100 years but there's a reason people don't do 30-100 year DCFs on Apple or Microsoft. It's not because the projections are inaccurate; it's because they're ultimately pointless. Your year 89 projections will account for a ridiculously small percentage of the total PV.