Vigdis Field in the northern part of the North Sea produces oil from sandstone reservoirs in several deposits. In a well with a coarsening upward sequence of offshore shales and lower shoreface sediments, Equinor wanted to land as early as possible to ensure maximum net sand once inside the reservoir. Another objective was to stay high on the structure, maintaining between 3-m and 7-m TVD from the top. Because of a wedge geometry and predicted volume from seismic data, the ability to map the structural variations of the reservoir laterally and vertically would be a significant advantage. Equinor also wanted to optimize high-angle well placement for total hydrocarbon recovery and deployed geosteering support for both the landing and reservoir section.
A conventional reservoir mapping-while-drilling service provided 1D formation resistivity mapping while drilling, but real-time interpretation was limited by this type of inversion. More advanced 2D azimuthal inversions provide new information highlighting 3D structural complexity and fluid movements locally in the near-wellbore region.
While drilling, GeoSphere 360 service provides a better understanding of the 3D geological environment and fluid distribution with a deep depth of investigation, as well as the required information to make support for reservoir steering decisions for optimal well positioning.
The application of GeoSphere 360 service enabled steering away from the planned trajectory toward the sweet spot, which was located sideways from the planned trajectory. This was made possible by the real-time processing of the GeoSphere 360 2D transverse resistivity inversions while drilling from the heel up to the total depth of the 8.5-in horizontal section. GeoSphere360 service 2D advanced transverse inversions were incorporated into the current geosteering workflow to provide a complete 3D structural understanding from the landing zone when approaching the reservoir top all the way to steering inside the main section in the horizontal interval. This integrated approach was used for 3D reservoir mapping while drilling and provided relevant real-time information to steer laterally to keep the borehole within the optimal reservoir exposure.
Near the toe of the well, the quality in terms of net pay degraded along the planned trajectory. However, the GeoSphere360 2D transverse inversions while drilling mapped a higher resistive geobody located sideways from the wellbore path. From the inversion results, it was also possible to identify a lateral dip where inclination and direction correlated with the structural true dips derived from the borehole LWD density images. This novel real-time information supported a strategic change in the trajectory to turn fully westward, respecting the dogleg severity limit for running a production liner to target and intercept the sweet spot. This azimuthal 3D reservoir steering decision delivered nearly 100-m MD of extra net pay interval by extending the well inside this reservoir section.
