IN SITU MEASUREMENTS OF P-WAVE ATTENUATION IN THE METHANE HYDRATE – AND GAS-BEARING SEDIMENTS OF THE BLAKE RIDGE
IN SITU MEASUREMENTS OF P-WAVE ATTENUATION IN THE METHANE HYDRATE – AND GAS-BEARING SEDIMENTS OF THE BLAKE RIDGE
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甲烷水合物和布莱克海岭含气沉积物中 P 波衰减的现场测量
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
H. Hoskins
中科院分区：
文献类型：
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作者：
W. Wood;W. Holbrook;H. Hoskins
最近在海洋钻探计划第 164 段期间在布莱克海岭顶部进行的钻探提供了一个机会，将地震数据的衰减估计值与该地区的水合物和天然气的直接样本进行比较，目的是利用衰减来远程量化水合物和天然气。在沉积物颗粒接触处而不是在孔隙空间中形成水合物可能会显着降低地震衰减。由于衰减可以根据单通道数据进行估计，因此它在水合物检测中比速度更有用，而速度需要更昂贵的多通道数据。在此分析中，使用频谱建模技术对单道地震数据和垂直地震剖面（VSP）数据进行反演。对于单通道数据，这是使用模拟退火算法执行的，对于 VSP 数据，模型更新是手动实现的。两个独立数据集的结果在每个水合物和气体稳定区中都是一致的。含水合物沉积物的质量因子 Q 值落在非水合物细粒海洋沉积物的预期范围内，范围为 ~90 至 600，表明少量水合物不会显着影响 Q。所有小于 ~90 的 Q 值都与气态沉积物有关；有些低至 Q = 6。水稳定场内的 Q 发生系统变化，在山脊顶部正下方达到最小值。正如预期的那样，含气沉积物中的 Q 值似乎与反射强度成反比。
Recent drilling on the crest of the Blake Ridge during Ocean Drilling Program Leg 164 has provided an opportunity to compare estimates of attenuation from seismic data with direct samples of hydrate and gas in this region with the objective of using attenuation to remotely quantify hydrate and gas. Hydrate formation at the sediment grain contacts rather than in the pore spaces may significantly decrease the seismic attenuation. Because attenuation may be estimated from single-channel data, it would be more useful in hydrate detection than velocity, which requires more expensive multichannel data. In this analysis both single-channel seismic data and vertical seismic profile (VSP) data were inverted using a spectral modeling technique. For the single-channel data, this was performed using a simulated annealing algorithm, and for VSP data, the model updates were implemented manually. The results from both independent data sets are consistent with each other in each of the hydrateand gas-stability zones. Values of the quality factor Q for hydrate-bearing sediments fall within the range expected of nonhydratebearing, fine-grained marine sediments, ranging from ~90 to 600, suggesting that small amounts of hydrate do not significantly affect Q. All values of Q less than ~90 were associated with gassy sediments; some were as low as Q = 6. Q within the hydratestability field changes systematically, reaching a minimum directly below the ridge crest. As expected, Q in the gassy sediments appears to correlate inversely with reflection strength.