In order to translate pressure from downhole gauge to the Datum one needs to:

1

Estimate gauge readings at formation top using the wellbore fluid density gradient

p_{\rm top}(t) = p_{\rm gauge}(t) + g \cdot \int_{z_{\rm gauge}}^{z_{\rm top}} \rho_f(z) dz

2

Recalculate the pressure at formation top to the Datum using regional hydrostatic pressure gradient

p_{\rm dat}(t) = p_{\rm top}(t) + GP \cdot (z_{\rm dat} - z _{\rm top})

where

	TVDss of downhoile gauge
	TVDss of formation top
	gauge pressure readings
	estimated wellbore pressure at formation top
	estimated Datum Pressure
	regional hydrostatic pressure gradient
	wellbore fluid density as function of TVDSS
	Standard gravity constant

When wellbore fluid density is fairly constant between the gauge location and formation top then one can simplify the Datum Pressure calculation to:

p_{\rm dat}(t) = p_{\rm gauge}(t) + g \cdot \rho_f \cdot (z_{\rm top} - z_{\rm gauge}) + GP \cdot (z_{\rm dat} - z _{\rm top})

In flowing conditions the equations and are both inaccurate as they do not account for pressure losses due to friction.

The equation should be replaced with a proper solver for wellbore pressure profile.

See Also