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That’s interesting. Whoever owns the lease on the current strata probably also got the lease for the deeper strata. As an attorney, I should have considered that angle. So when the top strata plays out, the drilling companies can just go deeper without having to haggle over the rights.

Question: could they use the current well shafts and just drill them deeper, or would they have to drill an entirely new shaft?

Whoever owns the lease on the current strata probably also got the lease for the deeper strata.

On an older lease almost certainly. Newer leases are more likely to be depth or even field limited. We have done that ourselves.

Question: could they use the current well shafts and just drill them deeper, or would they have to drill an entirely new shaft?

While it is technically feasible to put multi-laterals with perforations at different fields at different levels, it introduces complications not likely worth the savings in trying to produce oil from separate fields in the same well bore.

More likely would be a separate well that allows measurement and the like from each individual field, but put in the same area to share surface equipment and lower maintenance costs.

We do that on the Alaskan North Slope. Add a well 25~40 feet away with separate valving and ability to measure individually the production flow from each field. Then manifold the output together for separation, treatment and shipping of the oil.

Reservoir management can be an art-form to do it very well. Taking the chance of stranding oil or not maximizing production rates can be far more costly than the price of drilling a second well.

So when the top strata plays out, the drilling companies can just go deeper without having to haggle over the rights.

In the absence of a vertical severance provision in the original lease, yes. However, if the lease did contain a vertical severance, where the lease expires as to all rights lying 100' below the base of the deepest producing formation at the end of the primary term, then those deep rights would be open and available for lease.

Question: could they use the current well shafts and just drill them deeper, or would they have to drill an entirely new shaft?

If the original wellbore is no longer producing, they can re-enter it and deepen the well to exploit deeper objectives. Assuming, of course, that somebody hasn't dropped some junk in the hole that makes that effort problematic. If that has happened, they could enter the old wellbore at the surface and sidetrack the well above the junk to reach the objective, or they could just drill a new well.