Geophysical quantification of seafloor greenhouse gas: the effect of gas bubble and hydrate morphology on sediment geophysical properties.

全球气候预测模型需要关于作为游离气体和气体水合物存在于海底沉积物中的温室气体（甲烷CH4和二氧化碳CO2）数量的准确信息。通过对世界各地大陆边的地球物理调查，已发现海底甲烷气和甲烷气水合物分布广泛，而随着未来全面的碳捕获和储存设施投入使用，监测海底以下二氧化碳储层的二氧化碳渗漏将变得越来越重要。然而，使用地球物理遥感方法量化原地天然气的数量仍然是一个挑战。在这项技术主导的提案中，我们打算提供所需的知识变化，使我们能够将海底地球物理测量与天然气含量联系起来，从而为海洋界提供必要的调查专门知识。大小和形状）对测量的地球物理沉积物特性的影响。已知沉积物中的气泡显示出受沉积物类型强烈影响的复杂形状和尺寸分布。泥质沉积物显示裂隙状气泡，而桑迪沉积物显示球状气泡。如果这些沉积物发生在大陆坡足够深的水中，那么甲烷气体水合物可能会形成，产生类似于裂隙状或浸染状的水合物形态。只有专门的、控制良好的实验室实验才有希望解开天然气和水合物形态、沉积物类型和观测到的地球物理性质之间复杂的相互作用。遗憾的是，目前还没有这样的实验能力，因此我们必须开发我们自己的实验室测量系统。我们的解决方案是建造世界上第一个用于含气体和气体水合物沉积物研究的声学脉冲管。它将能够在模拟的海底压力和温度下测量含有天然甲烷（或二氧化碳）气泡或水合物的长达1米的大型沉积物芯样的整体声学和电学特性。在已知甲烷和水合物含量的合成泥浆上进行的实验也将有助于我们理解这些物理性质之间的相互关系。我们还将研究相关的理论模型，这些模型将根据实验室实验结果进行测试。这些经过验证的模型是我们解释海底地球物理测量原位天然气和水合物含量所需要的。我们将与其他科学家进行互动，以量化与北极和海底二氧化碳储存地点的甲烷水合物相关的海底温室气体，并与海底地球物理技术的潜在行业和政府终端用户进行互动。

Global climate prediction models need accurate information on the amount of greenhouse gases (methane CH4 and carbon dioxide CO2) hosted by seafloor sediments as free gas and gas hydrates. Extensive distributions of seafloor methane gas and methane gas hydrate have been detected by geophysical surveys on continental margins around the world, while monitoring of carbon dioxide seepage from sub-seafloor CO2 reservoirs will become increasingly important as full scale carbon capture and storage facilities come online in future. However, quantification of the amount of in situ gas using geophysical remote sensing methods remains a challenge. In this technology-led proposal, we intend to provide the required step change in knowledge that will allow us to relate seafloor geophysical measurements to gas content and thus provide the marine community with the necessary survey know-how.The main barrier to progress is our poor state of knowledge of the effect of gas and gas hydrate morphology (i.e., size and shape) on the measured geophysical sediment properties acoustic velocity and attenuation, and electrical resistivity. Gas bubbles in sediments are known to show complex shapes and size distributions that are strongly influenced by sediment type. Muddy sediments show crack-like gas bubbles while sandy sediments show spheroidal gas bubbles. If these sediments occur in deep enough water on the continental slope, then methane gas hydrate may form producing equivalent crack-like or disseminated hydrate morphologies. Only dedicated, well controlled laboratory experiments can hope to unravel the complex interaction between gas and hydrate morphology, sediment type and the observed geophysical properties. Unfortunately, no such experimental capability exists at present, so we will have to develop our own laboratory measurement system.Our solution is to build the world's first acoustic pulse tube for gas- and gas hydrate-bearing sediment studies. It will enable the bulk acoustic and electrical properties of large sediment core samples, up to 1 m long, containing natural methane (or carbon dioxide) gas bubbles or hydrate, to be measured under simulated seafloor pressures and temperatures. Experiments on synthetic muds with known amounts of methane and hydrate will also assist our understanding of these physical property inter-relationships. We will also study relevant theoretical models that will be tested against the laboratory experimental results. These validated models are what we need to interpret seafloor geophysical measurements in terms of in situ gas and hydrate content. We will interact with other scientists seeking to quantify seafloor greenhouse gas associated with methane hydrates in the Arctic and sub-seafloor carbon dioxide storage sites, and with potential industry and government end-users of seafloor geophysical technologies.