A new downhole annular pressure-while-drilling (PWD) tool has been app
lied recently to assist in drilling the reservoir section on the Statf
jord field, offshore Norway. For drilling success in these high-angle
wells it is critical to maintain the mud weight and equivalent circula
ting density (ECD) within safe operating limits defined by the formati
on fluid, collapse, and fracture pressures. Operating outside these li
mits historically has led to expensive lost circulation, differential
sticking, and packoff incidents. Monitoring the actual downhole pressu
re in real time with a PWD tool, rather than relying on inferred press
ures from predictive models, has allowed the operator to stay within a
nd to better define these operating limits. The operator used this imp
roved hydraulics information to avoid pressure-related hole problems,
to optimize drilling practices, to test hydraulics models, and to obta
in a greater understanding of the formation pressure limits.