海底流体逃逸活动的地球物理响应特征

Geophysical characteristics of seabed fluid escape

海底流体逃逸活动对海洋油气勘探、天然气水合物勘查和试采、海底固体矿产勘探与全球气候变化研究等方面具有重要意义.理解海底流体逃逸活动规律,研究流体逃逸活动演化过程,并建立综合探测体系显得尤为重要.本文系统梳理了海底流体逃逸活动在海底可视技术、综合声学水体成像技术、"磁亮点"技术以及卫星遥感技术等相关探测方法下的不同地球物理响应.分析认为,海底流体逃逸活动容易改变海底地层的物理性质和形态,在地震剖面和声学图像上表现为独特的流体异常反射特征和声学响应;烃渗漏形成烃蚀变带,在航磁图像上表现为弱磁异常;渗漏油膜在SAR卫星图像上表现为黑色斑块;天然地震控制下的断裂带流体逃逸活动在临震时震中附近在热红外图像上表现为亮温异常.结合不同探测方法的探测效率和优势特征,提出了利用卫星遥感和"磁亮点"等方法进行平面约束预测,用剖面或立体声学水体成像数据进行海底流体活动确认,再通过海底可视数据进行精细探测的综合地球物理探测方法,为深入研究海底流体活动系统理论提供参考,同时指出流体逃逸活动研究的相关方向.

Seabed fluid escape process is of great significance for the research on marine oil and gas exploration, gas hydrate exploration and production, submarine mineral exploration and global climate change. It is particularly of great importance to figure out the mechanism of seabed fluid escape, reveal the evolution process of seabed fluid escape activities and establish the comprehensive detection indicators. This paper systematically sorts out the different geophysical characteristics of seabed fluid escape activities under seafloor visualization technique, comprehensive acoustic water column imaging technologies, "Magnetic Bright Spot" technique and satellite remote sensing technique, which show that:(1) The fluids seeping from the sediments to seawater not only change the physical property of the submarine sedimentary strata but also change the topography and geomorphology of the seafloor, showing unique fluid-related abnormal reflection characteristics and acoustic responses in seismic profiles and acoustic images.(2) Hydrocarbon seepage alters shallow rock strata, inducing the formation of authigenic magnetic minerals, which create detectable small changes in the magnetic field that can be measured by high-sensitivity airborne magnetometers.(3) Oil and gas seepages form oil slicks in the ocean surface, dampening capillary and short gravity waves. Oil slicks significantly reduce the amount of energy backscattered to the satellite compared to the surrounding seawater. Sea surface covered by oil seepage appears as black streaks on SAR images.(4) Fluid escape associated with fault systems is constrained by seismic activity, showing brightness temperature anomalies on the satellite-based thermal infrared images near the epicenter, before the earthquake. Considering the detection efficiency and advantage of different methods, a comprehensive geophysical method is proposed. Satellite remote sensing and "Magnetic bright spot" method can be used to constrain and predict the distribution area, acoustic imaging profiles or stereoscopic acoustic water imaging data can be applied to confirm seabed fluid escape activities and seafloor visualization technique can be used for precise detection and exploration. It provides a reference for the in-depth study of the seabed fluid flow. Besides, the relevant geophysical research directions for seabed fluid escape are discussed here.