A Comparative Emissions Assessment - Drill Cuttings Treatment Alternatives

Abstract

Abstract The offshore industry has for many years been cognisant of its impact on the marine environment. Since 1991, strict regulations relating to oil-based drill cuttings discharge have been in force in the signature countries to the OSPAR (Oslo/Paris) Convention. As the impact of greenhouse gas (GHG) emissions on climate change has become better understood, global carbon dioxide (CO2) emission reduction targets and how to meet them have risen up operators’ agendas. Offshore operations, which involve marine logistics, are also subject to limits on nitrogen dioxide (NOx) emissions, an indirect GHG that's toxic to humans and contributes to soil and water acidification. The choices that operators make today in how they operate, including the disposal of drill cuttings, must therefore address an increasing number of environmental and climate targets, in addition to health, safety and cost. This paper will outline the results of a comparative study between the offshore processing of drill cuttings and relevant conventional alternatives, including skip and ship, bulk transfer and cuttings reinjection (CRI). It is the first paper to show a direct emissions comparison between offshore processing and all other alternative methods for drill cuttings processing. The study assessed the carbon footprint and NOx emissions for each of the different alternatives for the treatment of drill cuttings. The values were then used to create an interactive emissions calculator that can be easily applied to specific projects to clarify the actual potential for emissions reduction within the drilling waste management process. A number of case studies were then run, comparing the different alternatives. For the examples run, the comparative assessment showed that wellsite thermal processing technology was the favourable alternative in terms of emissions, with an emission reduction in the order of 14 - 48%, compared with the onshore alternatives. Emissions of the alternatives, skip and ship and bulk transfer, were highly dependent on sailing and road transport distances, as well as power source for the onshore treatment facility. The assessment showed that CRI has the highest emissions of CO2 per tonne of cuttings. Alternatives involving onshore treatment had the highest NOx emissions when sailing distance was high, however this was highly dependent on the machinery and fuel source of the transport vessel - and for the offshore alternatives, the on-site energy production solution.