In offshore operations, the depth of the sea (length of the water column) determines how
much the overburden gradient is reduced. The reduction in overburden gradient is due to
water being less dense than rock and for a given height; the hydrostatic head caused by water
is less than that caused by any rock. The resultant effect is that as the water depth increases,
the numerical value of the overburden gradient and in turn the fracture gradient reduce.
Hence, offshore wells will have lower overburden gradient near the surface due to the
influence of seawater and air gap and the uncompacted sediments. In onshore wells, the near
surface overburden gradient is influenced mainly by the uncompacted surface sediments.
