Modeling the Dispersion of Dissolved Natural Gas Condensates From the Sanchi Incident

Abstract

AbstractAn Iranian tanker with 136,000 tons of natural gas condensates collided with a freighter in the East China Sea in January 2018 and, after drifting ablaze for 8 days and over 200 km, capsized on the edge of the shelf near the Kuroshio Current. Different from the crude oil, the condensates consist of hydrocarbons that have relatively high solubility in seawater. We postulate that the leakage from the remaining condensate cargo at 110 m depth may result in a bottom layer of condensate‐enriched water in the vicinity of the resting tanker. A model is constructed in this study to simulate the dispersion of contaminated water through the processes of oceanic advection, diffusion, biodegradation, and volatilization. It is found that the scope and magnitude of the dispersion are most sensitive to the biodegradation. Even though the biodegradation time scale depends on several factors that are not well quantified in this region, using any value within the estimated range from a previous study results in significant contamination in the broad area. The dispersion is particularly effective in this incident because the tanker capsized near the Kuroshio Current—a fast‐moving western boundary current. The Kuroshio acts as a fast conduit to spread the contaminant to the east coast of Japan and the interior Pacific Ocean. In addition, we identify that the Tsushima Warm Current, a perennial flow into the Japan Sea, is the second major conduit for spreading the polluted water. This study indicates that dissolved hydrocarbons are the main environmental risk for maritime spills of natural gas condensates.