This paper describes a comprehensive geomechanical assessment of the P2-NE Field in the North Sea. The objective was to review the available core, log, and drilling data to characterize the geomechanical performance of the P2- NE Field in order to explain observed behaviour, and extrapolate this to future drilling, particularly for Well P2-NE- 2 Horizontal. This study focussed on the inclined Well P2- NE-2 Pilot, which was drilled specifically to obtain reservoir data for the subsequent horizontal well. The geomechanical analysis is based upon the general geological setting, deductions made from field data, and geomechanical core tests. Wellbore stability analyses were conducted, using the mechanical properties and regional stresses as input.
Geomechanical tests and petrophysical logs were used to obtain realistic profiles of mechanical properties. Anomalously, the reservoir mudstones were of considerable strength, exceeding the strengths of the sandstones. Weak zones were found in the sandstone that would be stable while drilling if an adequate mud weight were used. These zones would likely be sand producers during production. This is because the rock stresses would continue to increase, due to the continued pressure decline during depletion.
To obtain stress data, a minifrac test from an adjacent field was analyzed. This provided the breakdown pressure, fracture propagation pressure, the ISIP, and most importantly the fracture closure pressure. The principal horizontal stress orientations were determined from borehole breakout analyses, and compared to residual strain relaxation tests on core. Other observed borehole elongations included wellbore washouts and keyseating. Finally, a stability analysis was conducted for the horizontal well, in order to assess the effect of increasing the mud weight.