A well was drilled to target turbiditic channel sands of the Schiehallion field. The horizontal well was drilled from east to west to link multiple channel elements within the seismically mapped reservoir envelope. There were several challenges associated with the well, including uncertain sand distribution and geometry within the reservoir package and the risks of a potentially swept reservoir. To reduce the uncertainties, mitigate the risks and map the position and extent of the reservoir sands, a RMWD (Reservoir Mapping-While-Drilling) tool was selected to be used.
Well data from the Schiehallion field indicated the potential for significant anisotropy within the channel sands. To better handle the complications introduced by anisotropic sands, an innovative, deterministic parametric high-definition inversion (DPI-HD) for the RMWD tool was used. This new approach was selected following an evaluation of the pre-drill study, which showed that the DPI-HD processing could provide resolution of multiple thin layers within the sands, while also mapping the overall extent of the channel package.
In real-time, the DPI-HD processing indicated that the maximum vertical extent of the channel complexes encountered while drilling the reservoir section was circa 40m. This knowledge, paired with the information about channel geometry and internal architecture, enabled the planning and execution of the most informed adjustments to the trajectory to optimize the well's position within the sands. Additionally, while drilling between sand bodies, the RMWD tool confirmed that there were no significant sands packages around the wellbore that had been missed, providing the confidence that the trajectory was drilled at the optimal TVD position. This negated the need to adjust the trajectory to look for the sands, meaning a simple and smooth trajectory could be drilled and unnecessary borehole tortuosity avoided. Meanwhile, the mapping of the internal channel elements within the sand bodies allowed for an increased understanding of the nature and geometries of the sands.
The success of this well has shown the benefits of utilizing a new deterministic parametric deep resistivity inversion. The information about the channel sands’ extent and geometry as well as the identification of their internal architecture has reduced uncertainties and increased reservoir understanding.