As you know pore pressure prediction is performed in shale since one cannot measure pressure in shale. In pore pressure prediction, we develop compaction trend line for shale then predict pore pressure. What happens if there is no shale in the drilled field and measured pore pressure? How can we obtain pore pressure profile? Any suggestions or techniques?
One useful rule-of-thumb is to plot the mud weight, i.e. the standard gravity of the mud used to drill the well, versus depth. Alternatively, and more interestingly, you can plot the pressure that the mud column has at the bit at each depth point of the well (which is a function of the mud weight).
This kind of plot will show a straight line if all the formations of the well have the normal hydrostatic pressure (a very boring well, unlikely to have a gas or oil column).
If some formations are overpressured (or underpressured) and other formations are normally (hydrostatically) pressured, the plot will show departures from a pure theoretical hydrostatic trend.
You can enrich the plot with the indication of tight or permeable units, gas shows, lost circulation, and all the fenomena that directly or indirectly provide indications of the relative pressure between the borehole (where the mud weight is always known) and the formation being drilled.
If you have seismic velocities it can be converted into pore pressure in absence of lithology also. the d-exponent curves generated will give us an idea about hydrostatic pressure and deviation from hydro static regime.
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