中国近海浅层气调查研究进展

Advancements in the study of shallow gas in the coastal waters of China

随着海洋开发利用不断深入和全球气候变化持续加剧,近海沉积物中的浅层气(主要成分是甲烷)导致的灾害问题和可能产生的气候影响受到了进一步的关注,但目前为止对浅层气仍然缺乏系统的认识。在此对浅层气相关的主要认识进行了全面梳理,包括形成机理、存在形式、调查技术方法、分布特征、控制因素、主要危害等,以期为后续相关调查、理论研究和减灾防灾技术研发提供支撑。沿海三角洲平原第四纪下切河谷中充填的砂体和近海全新世细颗粒沉积物中普遍存在浅层气,以气包、分散气泡或溶解气的形式存在,近海大部分地区的浅层气主要来源于生物成因。含气沉积物的声学特性(声速、声衰减等)、孔隙水化学组成(如SO_(4)^(2-)、溶解气含量)会发生明显改变,这是支撑地球物理和地球化学探测技术应用的理论基础。浅层气的存在会改变土体力学特性,对工程建设造成较大危害;同时沉积物中的甲烷也会逸出到大气中,加剧全球变暖。基于对现有成果的总结,建议进一步加强海底浅层气形成机理、运移特性及其与气候变化的互馈机制方面的理论研究。

With the continuous deepening of ocean development and utilization and the ongoing exacerbation of global climate change,the disaster issues caused by shallow gas(mainly methane)in nearshore sediments and the potential climate impacts have received additional attention.However,systematic understanding of shallow gas remains lacking.A comprehensive review of the main knowledge related to shallow gas is conducted,including formation mechanisms,occurrence forms,investigation techniques,distribution characteristics,controlling factors,major hazards,etc.,to provide a support for subsequent related investigations,theoretical studies,and development in the technology disaster reduction and prevention.Shallow gas is commonly found in the sand bodies filled in the Quaternary incised valleys of coastal delta plains and in the fine-grained sediments of the nearshore Holocene,in the form of gas pockets,dispersed gas bubbles,or dissolved gas.In most nearshore areas,shallow gas is mainly of biogenic origin.The acoustic properties of gas-bearing sediments(such as sound velocity,sound attenuation,etc.)and the chemical composition of pore water(e.g.,SO_(4)^(2−),dissolved gas content)undergo significant changes,providing a theoretical basis for the application of geophysical and geochemical exploration technologies.The presence of shallow gas can alter the mechanical properties of sediments,causing significant hazards to engineering construction;meanwhile,methane in sediments can also escape into the atmosphere,exacerbating global warming.Based on the summary of existing achievements,it is recommended to further strengthen the theoretical research on the formation mechanisms,migration characteristics,and feedback mechanisms with climate change of submarine shallow gas.