The Cooper/Eromanga Basin is in central Australia and has been the focal point for oil and gas exploration and development in South Australia since the first commercial hydrocarbon discovery in 1963. In the years and decades following, thousands of subsequent wells have been drilled. The CE Basin spans across four states and territories covering an area ~35,000km2. The concentration of South Australian wells is situated in the Northeast of the state and sparsely concentrated in a 300km × 500km area (Figure 1) with the wells in this area being the focus of this research study.
Well decommissioning commonly referred to as Plug and Abandonment (P&A) aims to restore the natural integrity of geological formations that existed prior to drilling. It is a mandatory requirement for all wells and must account for the effects of any foreseeable chemical and geological processes from an eternal standpoint. The minimum requirement for abandonment of the South Australian wells is governed by Objective 6 Cooper Basin State Environmental Objectives (SEO): Drilling, Completions and Well Operations, November 2015 guidelines, which provides the compliance criteria for appropriate barrier installation and verification.
Well complexity is determined by the difficulty in achieving this minimum compliance requirement based on available data of well conditions, simplified in the form of a risk code.