Blenheim is a small Palaeocene oil field (c. 53 × 106 BBL oil in-place), in which significant seismic uncertainty complicated a development decision. Initial appraisal plans required a conventional deviated well sited to minimize the uncertainty, gather further reservoir and fluid data, and, if successful, provide a production well.

Later studies indicated improved economics if horizontal wells were successful. Several well designs, with and without pilot holes, were analysed to discover the optimum balance of data gathering, risk reduction and development cost reduction. The optimum well required accurate well steering in an area of seismic uncertainty. A high-resolution biostratigraphic study was made 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 biostratigraphic analysis and real-time MWD aided steering decisions and contributed to a successful horizontal well being drilled. The well flowed in excess of the minimum economic rates required and allowed the field to be successfully developed.

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