Chemosteering log and real-time decision facilitated by the use of elemental geochemical analysis. Planned trajectory versus realised trajectory, all depths are in meters. (a and c) Planned trajectory and realised trajectory over the tops from prognosis coloured according to the corresponding zone ((a) coloured as per prognosed tops; (c) coloured as per tops during drilling); (b) geochemical log and the realised well trajectory, with the decision points marked along the wellbore.