Extensive oil, ethane and propane discharge at the mega seepage system of Lusi, Indonesia

Natural hydrocarbon seepages constitute a substantial influx of oil and gas into hydrosphere and atmosphere, impacting the environment and greenhouse gas budgets. The Lusi seepage system (Indonesia) is one of the Earth’s largest surface hydrocarbon manifestations, and is intrinsically associated with the interaction of organic-rich sedimentary rocks and recent magmatism. Previous ground-based and satellite measurements revealed that Lusi is a mega emitter of thermogenic methane, releasing ~0.1 Mt methane per year. Here, linking the quantification of mud flow rates with oil concentration data, we estimate that Lusi released ~0.22-0.28 Mt of oil over 13 years of continuous fluid discharge. This emission is of the same order of magnitude as the Deepwater Horizon spill. The oil discharge into the Porong River and Madura Strait poses an environmental threat to aquatic ecosystems of north-east Java. Combining flux and concentration data, we have also estimated a release into the atmosphere of ~8-10 kt of ethane and ~6-8 kt of propane per year. Over 18 years, Lusi has already injected into the atmosphere more than 20 times the amount of ethane released by the 2015 Aliso Canyon gas storage accident (California), considered as one of the largest gas leaks in U.S. history. The Lusi mega seepage system in Indonesia released around 0.3 Mt of oil over 13 years of continuous fluid discharge, emitting 10 Kt of ethane and 8 Kt of propane annually, according to geochemical analysis of mud and gas samples collected at the site since 2006.