Gas Hydrate Stability Zone in Offshore Southern Taiwan
Gas Hydrate Stability Zone in Offshore Southern Taiwan
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DOI：
10.3319/tao.2006.17.4.829(gh
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发表时间：
2006-12
影响因子：
0.8
通讯作者：
W. Chi;D. Reed;C. Tsai
中科院分区：
文献类型：
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作者：
W. Chi;D. Reed;C. Tsai
甲烷水合物被认为是碳氢化合物能源的主要潜在来源，在满足未来天然气需求方面可能很重要。为了研究从台湾南部近海地区回收甲烷的可行性及其对许多地质作用的影响，有必要知道该地区水合物的总量，这一点仍然不清楚。在这里，我们采取的第一步，使用一个模拟海底反射（BSR），以估计总体积的稳定场，可以容纳水合物在台湾南部近海的沉积物。我们用一个6道和120道反射剖面的密集网格来研究一个BSR的反射和浅海底深度。海底反射层的特征是极性相反的反射层，随着水深的增加，海底深度增加，这表明海底反射层标志着甲烷水合物稳定区的基础。台湾近海的BSR位于台湾造山带和中国大陆边缘的碎屑沉积物中。这些沉积物可能含有大量的有机碳，从而为甲烷提供了来源。我们记录了覆盖45000 km^2宽区域的海底反射带的分布范围和浅海底深度。根据与水合物相关的BSR地震特征的拟合程度，将BSR分为三类。Q1 BSR与在水合物边界底部发现的所有预期地震属性相符，而Q2和Q3 BSR是可能的，并且可能是由这样的边界产生的反射体。然后，我们估计的水合物稳定区之间的海底和映射的海底反射区在近海区域的体积。至少有1023 km^3的水合物稳定性区域位于最高质量的海底地震带之下，而多达11522 km^3的区域位于所有绘制的海底地震带之下。然后，我们推测水合物的总量存储在该地区使用已公布的区域孔隙度-深度关系，并假设在孔隙空间中的水合物的饱和度值的范围。一旦获得额外的孔隙度和饱和度信息，就可以更好地估计超孔隙度储存。
Methane hydrates are considered a major potential source of hydrocarbon energy and could be important in meeting natural gas demand in the future. To study the feasibility of recovering methane from the offshore southern Taiwan region and its impact on many geological processes, it is necessary to know the total amount of hydrate in the region; something that is still unclear. Here we take the first step using a bottom-simulating reflector (BSR) to estimate the total volume of the stability field that can hold hydrates in the sediments offshore of southern Taiwan. We used a dense grid of 6-channel and 120-channel reflection profiles to study the istribution and sub-bottom depth of a BSR. BSRs are marked by a reversed polarity reflector that increases in sub-bottom depth with increasing water depth, suggesting that BSRs mark the base of methane hydrate stability zones. For offshore Taiwan a BSR is located in offscraped sediments derived from the Taiwan orogen and the Chinese continental margin. These sediments may have high amounts of organic carbon, thereby providing a source for the methane. We document the areal extent and subbottom depth of BSRs covering a 45000 km^2-wide region. The BSRs were classified into three categories based on how well they fit the seismic characteristics of the BSR associated with hydrates. Q1 BSR fits with all the expected seismic attributes to be found at the base of a hydrate boundary, while Q2 and Q3 BSRs are possible and probable reflectors resulting from such a boundary. We then estimate the volume of the hydrate stability zone bounded between the seafloor and the mapped BSRs in the offshore region. At least 1023 km^3 of the hydrate stability field is underlain by the highest quality BSRs while as much as 11522 km^3 is underlain by all mapped BSRs. We then speculated on the total amount of hydrate stored in the region using published regional porosity-depth relations and assuming a range of saturation values of hydrates in the pore spaces. Hydrate storage can be better estimated once additional porosity and saturation information becomes available.