Carefully positioned horizontal wells are helping to maximise recoverable reserves from both new and mature North Sea producing fields. In many cases, the economic performance of these wells is very sensitive to position within the reservoir. For example, displacing the horizontal section in some reservoirs by five or ten feet TVD is sufficient to significantly change the asset value of the well.

To achieve ideal drainhole positioning, the surrounding formation must be sensed while drilling, and the hole trajectory modified accordingly. This geological steering, or geosteering, becomes particularly important when targets are small and the exact geometrical position of the target cannot be accurately determined from surface seismic or offset well data.

Drilling horizontal wells to almost pinpoint accuracy relative to surrounding geology has tremendous potential to unlock otherwise uneconomic reserves of oil and gas. The steering techniques reviewed in this paper are central to this process, and represent a new and challenging role for multi.disciplined field development teams in the coming years.

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