题目：Oceanic Gas Hydrate Activities and Research Review
报告人：Zijian Zhang (Fugro GeoConsulting, Senior Geophysicist)
Gas hydrates are ice-like crystalline structures of water that form “cages” that trap gas molecules. Gas hydrates have recently attracted international attention from government and scientific communities, especially after China successfully produced gas from gas hydrates in the South China Sea for 60 days. This presentation outlines the basic physical properties of gas hydrates, the major issues surrounding gas hydrates, and the potential roles that university may play in future activities.
The physical properties of hydrate-bearing sediment have been measured in several different regions and laboratories, therefore allow the opportunity to assess their relation to hydrates. Coarser-grained reservoirs (e.g., North Slope of Alaska; Mackenzie Delta, Gulf of Mexico) can contain high-saturation gas hydrates, while finer-grained reservoirs (e.g., South China Sea) tend to have more complex gas-hydrates, including nodules, layers, and high angle planar and rotational veins, than are present in coarse-grained counterparts. The presence of gas hydrates in sediments dramatically alters some of the normal physical properties of the sediment. An understanding of the physical properties is necessary for interpretation of geophysical data, and slope stability analyses, reservoir simulation, and production models. The understanding strongly depends on the measurement of physical properties of oceanic gas hydrates in variable gas hydrate morphologies.
The major issues related to gas hydrate include safety hazards, environmental, and energy Resource. Hydrates occur naturally as surficial outcrops and as a cementing agent in sediments. They are metastable and can easily dissociate, resulting in slumping or slides. Some researchers hypothesize that with slight changes in sea level and seawater temperature gas hydrates dissociate and re-form in such a way that they could release and/or sequester large volumes of methane gas, one of several greenhouse gases involved in global warming. Other researchers believe that gas hydrates have been located in vast quantities around the world in continental slope deposits and permafrost. If the hydrates can be economically recovered, they represent an enormous potential energy resource. However, even after more research, key challenges in the three aspects are likely to remain in locating gas hydrates and assessing the size of the gas hydrate reservoirs. As a potential energy, it is also vital to develop viable and safe production strategies and understand the economics of eventual gas production from gas hydrates. Drilling and reservoir simulation in aid of laboratory measurements would play important roles in modelling the production of oceanic gas hydrates.
Zijian Zhang is a senior geophysicist and professional geologist in Texas. He earned his M.S. in Geoscience from the University of Texas at Dallas and Ph.D. in Geophysics from the University of Houston. He has been conducting his research to investigate the formation, distribution, and accumulation of deepwater gas hydrate in many places, including the North and south slopes of the South China Sea. Recently, he focused on understanding the soil properties of gas hydrate reservoirs in the South China Sea. He has published twenty refereed conference and journal papers, and applied two U.S. patents. He served as a key person in China’s second, third and fourth gas hydrate expeditions in Dongsha, Shenhu, and Xisha areas.