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.