Australia has been drilling offshore wells since the 1960s. Most of this is concentrated to the north-west shelf of Western Australia (Carnarvon Basin) and the Bass Strait (Gippsland Basin) with recent production coming from the area between Darwin and East Timor (the Bonaparte Basin around the Ashmore and Cartier Islands). Here’s what the drilling of wells looks like over time (note that this includes all wells – such as the exploration ones and the oil and gas producing ones, data taken from the NOPIMS database):     At the end of their productive life, wells and other infrastructure need to be decommissioned. For wells, this means plugging them to make them safe to abandon. For other infrastructure, this means cleaning and removing them from the ocean. The ‘base case’ decommissioning is to remove all infrastructure from the marine environment; however, there is a growing push to leave some infrastructure in situ. Benefits include the establishment of artificial reefs, cost savings, and potentially improved safety outcomes for workers. Questions remain about the ecological risk of this infrastructure, though. Contaminants including mercury and naturally occurring radioactive materials may be present in infrastructure such as pipelines. To make decisions about leaving infrastructure in the marine environment or not, we need to understand the impacts of these contaminants.   A recent report by the consultancy firm Advisian on behalf of National Energy Resources Australia (NERA) highlights that the cost of offshore oil and gas decommissioning in Australia may be ~$52 billion dollars (AUD). Of this, an expected $26 billion is needed in the next 10 years. The current inventory to be decommissioned includes:  

• 1008 wells
• 57 fixed facilities
• ~8000 km of pipelines

  The image below shows where the producing wells and pipelines are in Australia. There are many opportunities to reduce costs and improve safety in decommissioning this infrastructure. However, it needs to be balanced with a better understanding of the long-term risks. This will give all stakeholders more confidence in whatever decisions are made – by both oil and gas operators, and state and federal regulators.