Project Overview

New Zealand has over 960 onshore petroleum wells drilled across a 150-year history. The National Government Regulator (National Government Regulator) identified 104 wells without active permit holders that had outstanding plugging and abandonment (P&A) commitments. These orphaned wells represented an unknown risk to public health, safety and the environment — if hydrocarbons were able to migrate to shallow water aquifers or surface, the consequences could include pollution, fire and explosion risk.

SPD conducted a comprehensive desktop technical risk assessment of all 104 wells — providing integrity evaluations, a risk-ranked priority list, and Level 1 cost estimates for abandonment operations.

Key Challenges

• 104 wells had no active permit holder — no operator to engage, no ongoing monitoring and no obligation to fund abandonment
• Wells spanned over 150 years of drilling — early wells abandoned with wood plugs, scrap iron and sand, many with no completion reports or unknown depths
• New Zealand had no explicit P&A standard — review benchmarked against WorkSafe NZ, OGUK and NORSOK simultaneously
• 39 wells could not be physically located even using magnetometers and GPS coordinates

SPD’s Approach

Each of the 104 wells was individually reviewed by professional Drilling Engineers. The methodology proceeded in three structured phases: Data & Examination (standardised well schematics and gap analysis with worst-case assumptions where no data existed), Remedial Action & Cost Estimation (four principal methods: drilling rig, bull-heading cement, coil tubing, or skinny pipe), and Risk Ranking using a 26-attribute scoring model incorporating well age, data quality, location sensitivity, wellbore energy, hydrocarbon content, barrier integrity and crossflow potential.

Results & Value Delivered

• 6 Priority Action wells identified as capable of flowing hydrocarbons to surface
• 8 Priority Action (missing data) wells requiring immediate field data acquisition
• 22 wells scheduled for action; 48 placed on watching brief; 18 assessed as minimum risk
• NZD 3.54 million estimated to abandon the 6 Priority Action wells
• NZD 14.3 million total estimated abandonment cost across all assessable wells
• Bespoke 26-attribute risk ranking tool delivered to National Government Regulator for ongoing well management
• Batch abandonment strategy recommended to reduce per-well cost through mobilisation efficiencies