The Caspian Sea - The Hydrate Resources.
When they were first discovered in the laboratory almost two centuries ago, gas hydrates in the world were taken as a curiosity of purely scientific interest. More recently, however, they were established as a huge potential wealth which might not be of use as a clean source of energy - an alternative to hydrocarbons - in the near future. But now, the hydrates are listed among the most important resources awaiting further technological development so they are exploitable at great commercial profit.
The technological element is key to developing the hydrates, particularly in dealing with the related hazards and huge environmental risks. Most challenging are the stability conditions for hydrate formation and retention, together with their physical properties. Of great interest, these two sets of properties decide whether gas hydrates exist, where they could exist, and the consequent ability to use them in some way or another.
The basic physical properties of gas hydrates range from density, speed of wave propagation, stability with respect to pressure and temperature, through to the effects of their composition. The influence of these properties on detecting hydrates and on their long-term stability has been the subject of extensive studies since the turn of the 20th century. There has since been particular emphasis on this resource's climate and sea level changes with time.
Prominent regional and world geologists have been studying the offshore gas hydrates in the Southern Caspian Basin, including their potential for explosive hazards and their ability to release huge amounts of methane into the atmosphere with time.
The gas hydrates of offshore Azerbaijan were the subject of a lengthy review paper written jointly by Ian Lerche of the Department of Geological Sciences at the University of South Carolina and Elchin Bagirov of Conoco. It was presented at a conference in Edinburgh in a session titled "The Role of Natural Gas Hydrates in the Evolution of Planetary Bodies and Life", and published in 2004 by the journal Energy Exploration & Production.
The gas hydrates of the Southern Caspian Basin show high ethane enrichment. But the three cores with such high ethane hydrates are from three very different parts of this basin, suggesting that a mechanism is called for which is more pre-disposed to being generic in character. One such possibility is to invoke the arrhythmic rise and fall of the sea level in the South Caspian Basin in association with the changes in phase stability conditions which a small addition of ethane makes to a hydrate.
Only those spatial regions of hydrate relatively enriched (compared to the average) in ethane will survive better than regions more nearly 100% methane hydrate. Thus fluctuations in time in both pressure and temperature will systematically remove pure methane hydrates in favour of hydrates which become progressively more enriched in ethane - the survival of the fittest scenario.
Thus the ethane enrichment observed in recovered cores containing hydrates in the Southern Caspian Basin may be an artefact of initial hydrate under changing pressure and temperature conditions after hydrate initiation - or both. In the Southern Caspian, massive sedimentation during the last five million years was a main reason for extremely high over-pressures, low temperature gradients and mud diapirs, the latter being bodies highly saturated in gas.
For example, mud volcanoes associated with the diapirs periodically erupt. Those eruptions sometimes lead to explosive dissociation, and the mud-flows drive some of the sediments down the slopes of the volcanoes. Those re-deposition conditions can be followed by changes of the current conditions of hydrates. Other regions have their own specific characteristics and should be studied individually.
Accordingly, perhaps this hazard is one which should be of serious concern to oil companies drilling in offshore regions in the Southern Caspian Basin.
Estimates of potentially recoverable reserves of ethane and methane in offshore Azeri hydrate formations for commercial use vary from 28 to 60 TCM. (Globally, the amounts of methane in gas hydrates are estimated to be around twice the size of carbon in all known fossil fuels on Earth).
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|Publication:||APS Review Downstream Trends|
|Date:||Jul 4, 2016|
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