Arquivos

Oil is the most important commodity in Brazil’s energy matrix (Ferreira et al., 2020a). Most of the country’s oil reserves are in offshore fields off the coast of the south-eastern states of Espírito Santo, Rio de Janeiro, and São Paulo (Zabanbark & Lobkovsky, 2020). Oil production across the Brazilian coast is diverse regarding the time since the fields were discovered, the beginning and timespan of operation, and the fields’ geographical location (Nogueira et al., 2017). Offshore oil and gas fields have a finite production lifespan of 20 to 30 years (Fam et al., 2018, Ferreira et al., 2020a). The end of activities can be due to technical factors, low resource levels, or economic unviability for exploitation (Ahiaga-dagbui et al., 2014).

Once an installation has ceased to produce and is abandoned, it must be decommissioned; that is, actions must be taken to avoid deleterious outcomes both to the environment and to the society (Tan et al., 2021). Decommissioning is an integral phase of the oil and gas production chain, an activity that uses large, often complex equipment, particularly in offshore operations (Techera & Chandler, 2015). The decommissioning phase encompasses deactivating the facilities and plugging the wells, retrieving the subsea pipelines and equipment, or leaving them in situ. In contrast to topsides (platforms, floating production storage and offloading units, and other floating structures), subsea equipment poses many more challenges and introduces much more complexity to decommissioning.

The offshore oil and gas operations in the Gulf of Mexico started in 1947, so the industry had to decommission these installations first (Bull and Love, 2019). Furthermore, the systems to be decommissioned may vary considerably regarding the types of equipment, the biological and oceanographic characteristics of the sites, and the specific national regulations (Techera & Chandler, 2015). In Brazil, the various stakeholders involved in the process – the industry, the regulatory agencies, and the environmental authorities – have just started dealing with this end-life phase of the oil and gas fields, some operating since the end of the 1960s. Several fields from that age, mostly in the Sergipe state, Potiguar, and Campos basins (Fig. 1), have reached maturity and ageing of the production installations, calling for an urgent discussion on decommissioning plans, strategies, and legal frameworks (Ferreira et al., 2020b).

According to the Brazilian agency for oil and gas, ANP (Agência Nacional de Petróleo), 2,800 fixed platforms and 160 floating platforms are planned to be deactivated by 2030. Most of them are in the Campos basin, followed by the Ceará, Sergipe-Alagoas, and Potiguar basins (Fig. 1). ANP’s decommissioning panel is handling more than one hundred projects for decommissioning offshore facilities (Delgado and Michalowski, 2021, Souza et al., 2021).

The complexity of the decommissioning activities of subsea installations depends on the type of structures (equipment and flexible and rigid pipelines), water depth, and the characteristics of the surrounding marine ecosystem. In Brazil, the offshore installations are rather complex, with several of them located in deep (300 to 1500 m) or ultra-deep waters (>1500 m) (Godoi & dos Santos Matai, 2021).

Estimating the cost of decommissioning a particular installation is difficult because of the uncertainties associated with the process. Costs are variable and may amount to hundreds of millions of dollars (Tan et al., 2021). Such complexity and costs mean that the decommissioning of subsea oil and gas structures requires a multidisciplinary approach that considers human health and safety, as well as technical, legal, economic, and environmental factors (Fowler et al., 2004; Martins et al., 2020).

The environmental dimension, which is our focus here, is one of the most important factors in the decision-making process concerning the decommissioning options of subsea oil and gas installations, such as leaving structures in situ with or without additional actions (e.g., burial of pipelines) or removing them using various techniques (Rouse et al., 2018, Rouse et al., 2018). These choices will determine the type, intensity, and duration of the impacts on the marine ecosystem. The Brazilian case offers new challenges as many installations are close to or in highly biodiverse, sensitive ecosystems, such as coral reefs and rhodolith beds (Snodgrass et al., 2020, Almada and Bernardino, 2017, Nilssen et al., 2015, Moura et al., 2016, Santos et al., 2016, Amado-Filho et al., 2012, Sumida et al., 2004).

In this study, we present the framework of a method for assessing the environmental impacts caused by the decommissioning activities of oil and gas structures that parallels previous approaches (see Burdon et al., 2018), but focusing on the characteristics of the Brazilian oil and gas installations and their marine ecosystems.