海洋沉积物中的天然气水合物与海底滑坡

天然气水合物是一种由天然气和水形成的类似冰状的固体物质 ,主要存在于在低温高压背景下的海底沉积物和陆地永久冻土地带中。赋存于海底沉积物中的天然气水合物虽然本身能作为准稳定的胶结物对海底有建造作用 ,但由于其稳定性对特定温度和压力的严格依赖 ,海平面的下降、海底的连续沉积、地震等自然因素以及海洋钻探等人为因素造成的海底温压条件的改变会引起其分解 ,从而使海底沉积物失稳甚至导致海底滑坡。本文详细介绍了海底天然气水合物分解导致滑坡的机制、实例以及该种海底滑坡体的特征 ,并对以后的研究进行了展望

Submarine Landslide Related to Natural Gas Hydrate within Benthal Deposit

Natural gas hydrate is a kind of ice-like solid material composed of gas and water, mainly consisted in sea floor and permafrost with low temperature and high pressure. The gas can either be microbially produced or catagenic gas from deeper sediments. Although gas hydrate within benthal deposit has the ability to construct seafloor by cement sediments, it has the potential to store enormous volumes of gas and water and then release the gas and water when the hydrate's equilibrium conditions are brocken, which can cause sediment transport leading to submarine landslide. Equilibrium conditions can be brocken by sea level lowing, continuing sedimentation, earthquake and ocean drilling. In either case, some of the solid gas-water matrix decompose. Released gas and water volume exceed the volume occupied by the hydrate, so the internal pressure rises dramatically if large volumes of hydrate are decomposed. Part of the rigid sediment is converted to a gas and water rich, relatively low density mud. When the internal pressure, due to the presence of the compressed gas or buoyancy, is sufficient high, the overlying sediment may be lifted and slide on a plane producing landslide. The less dense gas-cut mud can also ejected violently in some places.There are more than twenty submarine landslides found relevant to gas hydrate decompose, they distributed in almost all the continental edges. Sea floor geological survey and analysis indicate that this special landslide has three features commonly: occurred on the slope grade less than or equal to 5°; depth of the landslides' top close to the bottom of hydrate stability zone; no hydrate in the sediments below landslides.Submarine landslide related to gas hydrate decompose is a new direction for geo-hazard researchers; the research in our country is nearly blank. Following is the hot research aspects: quantifying mechanical features of sediments containing gas hydrate, sediments' dynamic response to the changes of physical and chemical conditions caused by gas hydrate forming and decompose, triggering mechanism research and simulation.