Environmental considerations around in-situ decommissioning of oil and gas pipeline infrastructure in marine environments

Abstract

The base case for decommissioning of oil and gas infrastructure under Australian laws and regulations is the full removal. However, alternative options may be considered, provided equal or better environmental, safety and well-integrity outcomes compared to complete removal can be demonstrated. In order to evaluate in-situ retention options, the composition of materials, including any contaminants, must be fully understood, along with degradation timeframes and exposure pathways to the marine environment. In this paper, we articulate measurable parameters for the evaluation of pipeline materials including their composition chemistry, material degradation products and their properties, environmental toxicity, and potential interaction of infrastructure components with seawater and ecological receptors. In the absence of measured data from the degradation of pipeline materials over time, theoretical modelling is an essential tool to evaluate the transportation, distribution, and fate of materials such as plastic particles from pipeline coatings. Most of the components present in oil and gas pipelines, when degraded, are either soluble in water or if insoluble, accumulate locally in the sediment. However, the accumulated components will be rapidly dissipated by the wave currents around the pipeline and physical movements within the sediments, which will prevent the chemicals from accumulating to concentrations that could cause toxicity.

Plasticiser Leaching from Polyvinyl Chloride Microplastics and the Implications for Environmental Risk Assessment

“…Exposure to agitated and heated seawater prompted a significant release of both DEHP and BPA plasticisers from PVC, confirming PVC microplastic contamination in aquatic ecosystems contributes to aqueous plasticiser pollution. These findings are in line with previous work (Henkel et al, 2022;Yan et al, 2021;Gulizia et al, 2023;Sun et al, 2019), and suggests accelerated leaching of plasticisers with rising water temperatures (i.e., global warming), in ecosystems with strong water currents (i.e., coastal environments) and during fragmentation of plastics (i.e., decommissioning of offshore/subsea infrastructure (Saeed et al, 2023;Koppel et al, 2023)). These kinetic behaviours impact the rate and concentration of leached plasticiser and suggest that the impacts of PVC leaching are expected to be highly localised, with immediate impacts to water quality before the materials settle on the seabed.…”

“…PVC microplastics are discharged into aquatic environments worldwide from various point sources, including from ineffective waste disposal, municipal wastewater, industrial (e.g., construction and decommissioning of subsea infrastructure (Saeed et al, 2023;Koppel et al, 2023)) and fishery activities (Geyer et al, 2017). Thus an understanding of their leachable properties in different aqueous matrices and under different environmental conditions is important to ensure an all-encompassing risk assessment of microplastics in the enivronment (Henkel et al, 2022).…”

“…However, in the context of leaching, the continual fragmentation and size reduction of microplastics into smaller particles (i.e., nanoplastics (Gigault et al, 2018)) is of the greatest ecological concern, and has the potential to significantly impact water quality at the source point. This highlights the critical need to manage plasticised plastics before they enter aquatic ecosystems, as well as to consider the implications of decommissioning plastic infrastructure already in the environment (i.e., offshore and subsea pipelines (Saeed et al, 2023;Koppel et al, 2023)).…”

“…Owing to their excessive annual production and high additive composition (10-70 % by weight (wt%) (Yan et al, 2021;Hahladakis et al, 2018)), PVC leaching is a significant pathway for additives into aquatic environments (Yan et al, 2021). While the unique carbon-chlorine backbone gives virgin PVC high tensile strength and rigidity suitable for application in building and construction sectors (Czogała et al, 2021), including subsea infrastructure (Davis et al, 2007;Wang et al, 2017;Saeed et al, 2023), most PVC products require flexibility and malleability that can only be achieved through the incorporation of plasticisers (Lithner et al, 2009;Sampson and De Korte, 2011). Common phthalate acid ester (PAE) and diphenol plasticisers such as diethylhexyl phthalate (DEHP) and bisphenol A (BPA), respectively, are produced annually in high concentrations (>10 million tonnes) mainly for the manufacturing of flexible PVC products (80-95 %) (Walters et al, 2020;Marturano et al, 2019).…”

“…These data and model outputs will allow for the prediction of aqueous plasticiser concentration in waters contaminated with PVC microplastics and provide novel insights into the behaviours of non-buoyant and plasticised-polymers in unique compartments of the aquatic environment (e.g.,benthic ecosystems (Cheang et al, 2018)), as well as during laboratory exposure studies (Bagel et al, 2011). Ultimately, this will contribute to the generation of a more comprehensive and accurate environmental risk assessment of plasticised microplastics from various point sources (Teuten et al, 2009;Saeed et al, 2023;Francis, 2015).…”