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Application of Decision Tree to Determine Failure Modes for Dry Segments in the Deepwater Taranaki Basin, Offshore New Zealand


The petroleum exploration industry relies on various subsurface data and interpretations to minimize risks and uncertainties and maximize gains from wells. Dry holes provide a wealth of useful subsurface information. However, companies drilling dry holes often either do not conduct a post-drill analysis (post mortem) or incorrectly determine the well failure mode. We have developed and tested a post-drill methodology (decision tree) that helps identify the specific main failure mode for dry segments in conventional wells. Use of the decision tree allows the interpreter to evaluate and identify specific failure modes such as reservoir presence, reservoir deliverability, structure, seal, source maturity, and migration. We tested the decision tree on the Romney-1 well drilled in the Deepwater Taranaki Basin offshore New Zealand in 2013. The exploration well targeted two Late Cretaceous segments (North Cape and Rakopi), both of which were found to be dry. The failure modes were identified based the comprehensive multi-disciplinary integrated evaluation of both pre- and post-drill reports, 3D seismic, well logs, geochemical gas and source rock data, as well as other materials freely accessible through the New Zealand government. The North Cape segment failed due to lack of petroleum migration, and the Rakopi segment failed due to lack of lateral seal. We hope that the developed decision tree, or its customized versions, will become the best practice in post-drill analysis across the exploration industry.