Hydrate Hazards

Abstract

The presence of clathrates (gas hydrates) is well established observationally in the offshore region of the South Caspian Basin, as well as in many other regions of the world. Hydrates of given composition can exist under particular pressure-temperature conditions. However, under the impact of neotectonic processes, those conditions can change. In that case part, or all, of the mass of hydrates can be dissociated and released. The dissociation can take place gradually, or explosively, depending on how fast the pressure drops or temperature increases. Five major variations of hydrate evolution are considered to illustrate possible patterns of behavior caused by variation of geological conditions:

• 1. Variations in hydrate existence conditions due to sediment and mud redeposition. Due to earthquakes, volcanic eruptions or other processes, part of the sediments can be released from a sloping sea bottom and transported and redeposited in other places, thereby changing pressure conditions at the top of a hydrate layer.

• 2. Variations in hydrate existence conditions due to glacial-interglacial conditions. Removal of ice cover not only decreases overlying pressure, but also allows water temperatures overlying the sediments to increase.

• 3. Variations in hydrates due to sea-level rise and fall.

• 4. Enrichment of ethane in hydrates as a consequence of varying neotectonic conditions.