Seismic Imaging of High Impedance Mineral and Gas Hydrate Deposits

高阻抗矿物和天然气水合物矿床的地震成像

• 批准号: 249857-2012
• 负责人: Milkereit, Bernd
• 金额: $ 3.35万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=570745
• 关键词: Seismic; Imaging; Impedance; Mineral; Gas

Applying conventional seismic exploration techniques to image gas hydrate accumulations of deep mineral deposits poses a problem: seismic wave scattering caused by strong local contracts in physical rock properties. Massive sulfide exhibit variable compressional and shear wave velocities but density contrasts often exceed 50%. Gas Hydrate accumulations are characterized by high compressional and shear wave contrasts (up to 100%, highly variable attenuation (Q-factor) and no significant density contrasts. Modeling studies of such local high impedance (velocity-density product) contrasts require accurate 3D geological /petrophysical models consistent with all available borehole geophysical, geological and structural data. when strong local contracts in physical rock properties are present, seismic waves are scattered by the inhomogeneities. Two effects can be observed: the attenuation of the transmitted (direct) wave, the excitation of seismic coda (due to P-S wave conversion). Robust modeling capabilities of strong seismic impedance contrasts are important for a better understanding of wave propagation effects in small scale structures. 3D elastic/visco-elastic modeling of high impedance exploration targets (massive sulfide and gas hydrates) revealed that a local high impedance contrasts lead to strong and complex scattering responses, often dominated by converted shear waves. In addition, amplitude focusing caused by the shape of the deposit (scale factors) will lead to pronounced amplitude versus offset/azimuth trends. Thus seismic data acquisition geometries and source frequencies must be carefully selected in order to observe characteristic amplitude and phase variations. If observed, the scattering response may serve as a diagnostic tool to classify the composition of the seismic exploration target.The 3D earth/exploration models will be based on full waveform sonic and density logs, VSP, 2D/3D seismic data and extensive drill hole data from some of the largest massive sulfide and gas hydrate deposits on earth (The Red Dog Zn-Pb deposit in Alaska, Ni-Cu deposits at Thompson and Sudbury, gas hydrate accumulations in the Mackenzie Delta (NWT)).

应用传统的地震勘探技术对深层矿藏的天然气水合物聚集进行成像会带来一个问题：物理岩石特性的强烈局部收缩导致地震波散射。块状硫化物表现出可变的压缩波和剪切波速度，但密度对比通常超过 50%。天然气水合物聚集的特点是高压缩波和横波反差（高达 100%、高度可变的衰减（Q 因子）且没有显着的密度反差）。 这种局部高阻抗（速度密度乘积）对比的建模研究需要与所有可用的钻孔地球物理、地质和结构数据一致的精确 3D 地质/岩石物理模型。当物理岩石特性存在强烈的局部收缩时，地震波会因不均匀性而散射。可以观察到两种效应：传输（直达）波的衰减、地震尾波的激励（由于 P-S 波转换）。强地震阻抗对比的强大建模能力对于更好地理解小规模结构中的波传播效应非常重要。高阻抗勘探目标（块状硫化物和天然气水合物）的 3D 弹性/粘弹性建模表明，局部高阻抗对比度会导致强烈且复杂的散射响应，通常以转换的剪切波为主。此外，沉积物形状（比例因子）引起的振幅聚焦将导致明显的振幅与偏移/方位角趋势。因此，必须仔细选择地震数据采集几何形状和源频率，以便观察特征幅度和相位变化。如果观察到，散射响应可以作为对地震勘探目标的成分进行分类的诊断工具。3D 地球/勘探模型将基于全波形声波和密度测井、VSP、2D/3D 地震数据以及来自地球上一些最大的块状硫化物和天然气水合物矿床（阿拉斯加的 Red Dog Zn-Pb 矿床、Thompson 的 Ni-Cu 矿床和 萨德伯里，麦肯齐三角洲（NWT）的天然气水合物堆积。