Australia offshore well inventory characterisation and decommissioning cost saving opportunities through cap rock restoration and rigless/riserless techniques

Abstract

This research utilises the Geoscience Australia and NOPIMS public database to characterise the national inventory of active offshore oil and gas (O&G) wells and, through representative examples of dry and wet completions, establish the current well decommissioning cost opportunities associated with using riserless and rigless techniques to restore cap rock. These techniques have been successfully applied in the Gulf of Mexico (GoM) and this study explores the potential savings and barriers to adoption in the Australian offshore operating and regulatory context. Third party studies (Bills 2018; Wood Mackenzie 2020) have reported Australian O&G decommissioning cost estimates in the range of USD 33–49 billion over the next 30–40 years. The well decommissioning contribution to the total project cost has been estimated at 49% (OGUK 2020). This cost is materially significant to the economic life of the asset, the operator’s financial liability and a significant cost burden to the Federal Government through Petroleum Resource Rent Tax (PRRT) offsets. In this context there is a paucity of detail and transparency for well decommissioning cost estimates, to establish whether there are cost saving opportunities whilst still maintaining an acceptable level of risk both during plug and abandonment (P&A) operations and in the longer term when relinquished back to the Federal Government. This study illustrates how and to what extent the Australian offshore Federal well inventory could be decommissioned using cap rock restoration and rigless/riserless techniques and proposes a staged strategy to realise a progressive cost reduction of 21–41% over the base estimate of circa USD 4.08 billion benchmarked with OGUK (2019). This significant cost reduction aligns with the OGTC (2019) technology roadmap target of 35% supported in part by the pursuit of a rigless and riserless well decommissioning philosophy.