The GeoSphere reservoir mapping-while-drilling service enables operators to precisely land wells by detecting the reservoir top and subsurface layers tens of feet before intersecting the reservoir without the use of a pilot hole. This maximizes reservoir exposure by preventing reservoir lateral loss and early water breakthrough. A North Sea operator drilled an appraisal well using the GeoSphere service to simultaneously map the upper and lower boundaries of a 100-ft reservoir in real time. Data transmitted to the surface confirmed the seismic interpretation over the length of the horizontal well, which enabled the operator to move forward with an early field development plan. The GeoSphere service revealed subsurface details at the reservoir scale to help refine geological and structural models and optimize production.