A life cycle assessment of drilling waste management: a case study of oil and gas condensate field in the north of western Siberia, Russia

Abstract

Oil production is currently impossible without drilling wells, so millions of tons of drilling waste contaminated with oil, chlorides, and heavy metals are generated every year in Russia alone. This article presents the results of a comparative life cycle assessment of water-based drill cuttings management technologies applied in Russia, including disposal, solidification, and reinjection. Life cycle assessment of the drilling waste management was performed using OpenLCA software, Ecoinvent 3.8 database and ReCiPe Midpoint (H) impact assessment method. Fossil depletion, climate change and human toxicity were chosen as impact categories. Data from oil producing companies on the composition of drilling waste and information from drilling waste treatment companies on the technologies and reagents used were also applied. To compare alternative technologies the following scenarios were compared: Scenario 0 «Landspraying», scenario 1 «Disposal», scenario 2 «Solidification» (scenario 2a – in a waste pit, scenario 2b – without a waste pit), and scenario 3 «Reinjection». Sensitivity analysis was performed to test for variations in results for oilfields located in different regions and for differences in mass of reagents used. The environmental impact of scenario 0 (landspraying) depends mostly on drilling waste composition, which is largely determined by human toxicity that can differ from 17 up to 2642 kg 1,4-DCB-eq per 1 t of drill cuttings, when for other scenarios it is from 24 up to 73 kg 1,4-DCB-eq per 1 t of drill cuttings. It means, that drilling waste landspraying is the best option only if the level of pollutants in the waste is very low. Among the other scenarios of drill cuttings management aimed at isolating pollutants from the environment, solidification technologies have the greatest environmental impact, primarily due to their use of binders. Among all scenarios, 2a and 2b have the biggest environmental effect in most impact categories. The production of cement and lime for drilling waste solidification was the main contributor to fossil depletion (64% of the total amount for scenario 2a and 54% for scenario 2b), and greenhouse gas emissions (49% of the total amount for scenario 2a and 70% for scenario 2b). However, the application of soil-like material (solidified drill cuttings) as an inert ground in swampy areas can make migration of heavy metals possible. Scenario 3 (reinjection) is associated with the least impact on the environment and the main contributor is electricity production (75% of greenhouse gas emissions). Sensitivity analysis shows that oilfield location does not affect the data for reinjection, but the impact assessment changes up to 60% for drill cutting disposal due to different waste pit design depending on permafrost and groundwater levels. Differences in the mass of used cement and lime change results for solidification scenarios considerably (up to 80%).