Blenheim Field: the appraisal of a small oil field with a horizontal well

Blenheim is a small Palaeocene oil field (c. 53 x 10(6) BBL oil in-place), in which significant seismic uncertainty complicated a development decision . Initial appraisal plans required a conventional deviated well sited to mi nimize the uncertainty, gather further reservoir and fluid data, and, if su ccessful, provide a production well. Later studies indicated improved economics if horizontal wells were success ful. Several well designs, with and without pilot holes, were analysed to d iscover the optimum balance of data gathering, risk reduction and developme nt cost reduction. The optimum well required accurate well steering in an a rea of seismic uncertainty. A high-resolution biostratigraphic study was ma de and provided detailed correlation of intra-reservoir mudstones, enabling wellsite analysis to aid steering decisions. The pilot hole proved the most likely; seismic interpretation to be correct and permitted the horizontal well to be drilled as planned. Wellsite biost ratigraphic analysis and real-time MWD aided steering decisions and contrib uted to a successful horizontal well being drilled. The well flowed in exce ss of the minimum economic rates required and allowed the field to be succe ssfully developed.