Re: Water Gradient 0.42 psi/ft
Yes, TVD errors can affect pressure measurements, as the pressures are referenced to TVDSS depths. This is especially true for deviated wells, where TVD depths are computed using survey data.
However, I have seen gradients of 0.42 psi/ft in vertical exploration wells.
Of course, there is also the possibility of uncertainty in the depth measurement, even for vertical wells.
To make things more complicated, if pressures are taken using LWD (Logging While Drilling) tools, the uncertainty on depth measurement is even higher because of using Driller's Depths.
The uncertainty in TVDSS has an impact on the determination of field-wide fluid contacts or Free Water Level.