QICS Paper: Passive acoustic quantification of gas fluxes during controlled gas release experiments

The detection and quantification of an underwater gas release are becoming increasingly important for oceanographic and industrial applications. Whilst the detection of each individual bubble injection events, with commensurate sizing from the natural frequency of the acoustic emission, has been common for decades in laboratory applications, it is impractical to do this when hundreds of bubbles are released simultaneously, as can occur with large methane seeps, or leaks from gas pipelines or undersea facilities for carbon capture and storage. This paper draws on data from two experimental studies and demonstrates the usefulness of passive acoustics to monitor gas leaks of this level. It firstly shows experimental validation tests of a recent model aimed at inverting the acoustic emissions of gas releases in a water tank. Different gas flow rates for two different nozzle types are estimated using this acoustic inversion and compared to measurements from a mass flow meter. The estimates are found to predict accurately volumes of released gas. Secondly, this paper demonstrates the use of this method at sea in the framework of the QICS project (controlled release of CO2 gas). The results in the form of gas flow rate estimates from bubbles are presented. These track, with good agreement, the injected gas and correlate within an order of magnitude with diver measurements. Data also suggest correlation with tidal effects with a decrease of 15.1 kg d-1 gas flow for every 1 m increase in tidal height (equivalent to 5.9 L/min when converted to standard ambient temperature [25 °C] and absolute pressure [100 kPa] conditions, SATP). This is a publication in QICS Special Issue - International Journal of Greenhouse Gas Control, Peter Taylor et. al. Doi:10.1016/j.ijggc.2015.02.008.

水下气体释放的检测与量化在海洋学及工业应用中日益重要。尽管在实验室应用中，基于声发射的自然频率对单个气泡注入事件进行检测及其相应的尺寸测量已为数十年的常规做法，但在同时释放数百个气泡的情况下，如大型甲烷渗漏、天然气管道泄漏或海底碳捕获与存储设施泄漏，这种做法并不实用。本文借鉴了两次实验研究的数据，展示了被动声学在监测此类级别气体泄漏中的有效性。首先，本文展示了针对水槽中气体释放声发射反演的最近模型实验验证测试。利用该声学反演技术，对两种不同喷嘴类型的气体流量进行估算，并将其与质量流量计的测量结果进行比较。估算结果准确预测了释放气体的体积。其次，本文在QICS项目（二氧化碳气体控制释放）的框架下，展示了该方法在海洋中的应用。以气泡形式呈现的气体流量估算结果揭示了与注入气体的良好一致性，并与其量级相关，与潜水员测量结果的相关性在量级上相符。数据还表明，与潮汐效应的相关性，潮汐高度每增加1米，气体流量减少15.1千克/天（转换为标准大气压和绝对压力[25°C，100 kPa]条件下的5.9升/分钟）。这是QICS特别问题——《国际温室气体控制杂志》，由Peter Taylor等人发表的出版物。DOI：10.1016/j.ijggc.2015.02.008。