Sediment-Hosted Gas Hydrates: New Insights on Natural and Synthetic Systems
There is much interest in gas hydrates in relation to their potential role as an important driver for climate change and as a major new energy source; however, many questions remain, not least the size of the global hydrate budget. Much of the current uncertainty centres on how hydrates are physically stored in sediments at a range of scales. This volume details advances in our understanding of sediment-hosted hydrates, and contains papers covering a range of studies of real and artificial sediments containing both methane hydrates and CO2 hydrates. The papers include an examination of the techniques used to locate, sample and characterize hydrates from natural, methane-rich systems, so as to understand them better. Other contributions consider the nature and stability of synthetic hydrates formed in the laboratory, which in turn improve our ability to make accurate predictive models.
Exploration strategy for economically significant accumulations of marine gas hydrate
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Published:January 01, 2009
Abstract
There are at present no validated methods for reliably finding economically significant accumulations of natural gas hydrate in marine environments. The seismic bottom simulating reflector (BSR) has been regarded as a primary indicator of hydrate presence in marine environments, but the presence of a BSR conveys no information about the abundance of hydrate in the sediments above it. Seafloor features such as gas seeps, pockmarks or hydrate outcrops may be qualitative markers of deeper hydrate presence, but cannot be interpreted quantitatively. Another approach to exploration geophysics is required to find exploitable gas hydrate reservoirs with high reliability. It is known that in many cases gas is supplied to the gas hydrate stability zone primarily through faults or fractures. In a certain range of gas flux, these fissures should become mineralized with gas hydrate and form vertical or subvertical dykes. The dip and strike of these dykes are controlled by the principal stress directions, which can be predetermined. Thus multiple hydrate dykes are expected to be parallel. Even if the greatest volume of gas hydrate is to be found in sub-horizontal permeable beds, the steeply dipping mineralized conduits that fed gas to them may be the most reliable marker of substantial subsurface hydrate presence. Geological and geophysical survey methods sensitive to parallel arrays of vertical and subvertical hydrate dykes are presented.