Reply #44: That likely is the minimum pressure.

[Statistical]

You also have the pressure of natural gas inside the well. The organic material decayed into methane gas (expanding) that gas expansion adds even more reservoirs pressure.

Actually pressure will depending on a number of factors including geography, and geographical history (over time the pocket could have been compressed, or reduced due to geological activity).

Pressure could be 20,000 to 100,000 psi.