Transport of dissolved gas and its ecological impact after a gas release from deepwater

•Dissolved methane transport due to gas releases under water is modeled.•Dissolved oxygen depletion in water after a methane release is modeled.•Comparisons between model simulations and experimental data show good agreement.•Scenario simulations are provided to demonstrate the impact from methane releases.•The chance of water reaching hypoxic level is very low unless the methane release is extremely large.

Previous models on simulating gas releases in deepwater were not focused on the dissolved component and its impact on water quality. This paper presents a new model developed for simulating the transport/spread of dissolved methane from an underwater release and its impact on dissolved oxygen in ambient water. Methane dissolves into ambient water from gas phase, direct from hydrate phase, and from dissociating hydrates formed earlier. Dissolved methane affects the dissolved oxygen levels in ambient water due to microbial interaction and possible direct absorption of oxygen into methane bubbles. We use new model simulations of Deepspill field experiments to compare with instantaneous profiles which were unpublished until now. The comparisons are very good with a short time lag, but are within the acceptable discrepancy for models for emergency response and contingency planning. Scenario simulations show the effect on dissolved oxygen due to different methane release situations.