--> Well Control Issues In A Mature Basin: A Case Study Of The Mckee-13 Blowout, Taranaki Basin, New Zealand

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

Datapages, Inc.Print this page

Well Control Issues In A Mature Basin: A Case Study Of The Mckee-13 Blowout, Taranaki Basin, New Zealand

Abstract

The McKee Field is situated in the Tarata Thrust Zone on the eastern boundary of the Taranaki Basin, New Zealand, and consists of a series of en echelon thrust faults and associated anticlines, of which the McKee structure is one. The McKee Field is comprised of a number of adjoining fault blocks that produces oil, gas and condensate from a steep south-easterly dipping (up to 60°) sandstone reservoir sequence truncated against a deep thrust. McKee-13 was spudded in January 1995, 11 years after production started, as the c.35th well to be drilled on the McKee Structure with the aim of improving drainage between two current producers. The well experienced a pressure kick on entering the Eocene Mangahewa Formation culminating in an underground blow out, which resulted in hydrocarbons breaching the surface and eventually a total loss of the well. The overpressure in the Mangahewa Formation was not predicted, so a light drilling mud of 9.8 ppg was used and a 1679m section was left uncased, resulting in a narrow drilling window and low kick tolerance. An offset well along the structure, Toe Toe-2, experienced a pressure kick in the Mangahewa Formation at the same depth as McKee-13. The calculated formation pressure from this kick is anomalously high for the depth, requiring a mechanism to transfer this pressure into the shallower stratigraphy. A recent well drilled in 2010, Beluga-1, down dip of the McKee field encountered overpressures of 1500psi in the Mangahewa Formation. If we assume that the Mangahewa Formation is confined and in lateral continuity, then that pressure is transferring up dip via the process of lateral transfer.

A mudweight of 12.3 ppg would be required to contain the pressure, which would easily breach the fracture pressure below the 9 5/8” casing set at 595 mTVDgl when transferred up-dip and into the borehole. This study highlights the need to ignore preconceptions, properly appraise all offset well data, and integrate regional geology into well planning.