Rank wildcat wells in Ultra Deep-water present some of the greatest challenges to operators today. Decision making during drilling is challenging because of a lack of offset well data. 3D seismic data has significant uncertainty from the translation of two-way time to horizon depths which further induces risk into the pre-drill pore pressure model.

This page looks in detail at how the utilization of a high-tech logging while drilling suite in the execution of a rank wildcat well enabled key drilling decisions to be made, reducing risk and time vs. depth plan.

Seismic-While-Drilling technology guided drilling in each section from spudding to total depth by allowing up to 600 m look ahead. Together with real-time checkshot information, this reduced target depth uncertainties from +/-100 meters to less than +/-5 meters. Furthermore it permitted this complex S-shaped well trajectory to avoid accidental penetrations into the first target and a potential well control situation, placing the 13 3/8” casing shoe safely just above the first target, which was 80m shallower than planned. This ensured an increased mud weight window for the 12.25” section.

In the 12.25” section Formation Pressure While Drilling Technology (FPWD) was added to the Seismic and Sonic technologies to calibrate the pre drill pore pressure model. This was critical due to a challenging mud weight window. The acquired formation pressures coupled with the while drilling petrophysical data allowed for the pore pressure to velocity transform and normal compaction trend lines to be calibrated reducing the uncertainty in the pore pressure model ahead of the bit. Uncertainty in depth of targets and modeled pressure ramps ahead of the bit were further reduced with the Seismic data.

The combined approach permitted the operator to confidently make decisions and continue drilling in a single section to intercept key targets, eliminating a further casing string, with the assurance that the kick tolerance and safe overbalance were maintained at an optimal level to reduce the risk of mud losses.