Making seismic frequency measurements in the laboratory: construction of a system for measurement of the dynamic bulk modulus of rock at seismic frequencies

在实验室进行地震频率测量：构建地震频率下岩石动态体积模量测量系统

• 批准号: 358929-2008
• 负责人: Schmitt, Douglas
• 金额: $ 6.17万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Research Tools and Instruments - Category 1 (<$150,000)
• 财政年份: 2007
• 资助国家: 加拿大
• 起止时间: 2007-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=364204
• 关键词: Making; seismic; frequency; measurements; laboratory

Seismic waves travel in the earth with periods from many seconds for teleseisms to milliseconds in  logging,  typical seismic exploration occurs over a narrow range of frequencies from about 5 Hz to 250 Hz. These 'low' frequencies contrast with the 'high' frequencies, typically of about 1 MHz (10^6 Hz), employed in almost all laboratory measurements of P and S wave velocities and attenuation.  This is a serious problem as the observed seismic velocities and attenuations of such rocks, and particularly those rocks hosting pore fluids, can depend strongly on frequency. This frequency dependence is known as velocity dispersion, and the dispersion limits our abilities to properly interpret seismic (5 Hz to 250 Hz) and well logging  (20 kHz) observations when we use a physical property framework developed primarily using ultrasonic (MHz) frequencies.  We propose to overcome this limitation by developing a new system to allow us to make make measurements in the laboratory of the seismic properties (specifically the dynamic compressibility) at truly seismic frequencies.  The method will employ a 'forced oscillation' technique to measure the changes in the volume of the rock samples while they are subject to small oscillating pressure variations. By analysis of the resulting pressures within the cell, one is able to determine not only parameters that directly relate to the seismic velocity at a given frequency but also the corresponding seismic attenuation.  This method has long been used by polymer scientists to study the detailed characteristics of plastics. Although the problems with comparing conventional ultrasonic laboratory measurements to seismic observations is well known, there are only a small number of groups worldwide carrying out these tests and all of these groups are measuring complementary shear properties.  This proposed system will be the only one within the geoscience and porous media research communities capable of directly obtaining the dynamic compressibiltiy (or bulk modulus) at such frequencies under realistic conditions of stress and pore pressure. This information will allow us to  both carry out new fundamental tests of existing theories of wave propagation and to learn more about the anelastic properties of real rocks at seismic frequencies.

地震波在地球中传播的周期从地震的几秒到测井的几毫秒，典型的地震勘探发生在从大约5Hz到250Hz的窄频率范围内。这些“低”频率与“高”频率形成对比，“高”频率通常约为1 MHz（10^6 Hz），用于几乎所有P波和S波速度和衰减的实验室测量。这是一个严重的问题，因为观察到的此类岩石的地震速度和衰减，特别是那些含有孔隙流体的岩石，可能强烈依赖于频率。这种频率依赖性被称为速度色散，分散性限制了我们正确解释地震的能力（5 Hz至250 Hz）和测井（20 kHz）观察，当我们使用主要使用超声波（MHz）开发的物理属性框架时，我们建议通过开发一种新的系统来克服这种限制，使我们能够在地震实验室中进行测量。该方法将采用一种“强迫振荡”技术来测量岩石样品在受到小的振荡压力变化时的体积变化。通过分析单元内产生的压力，不仅可以确定与给定频率下的地震速度直接相关的参数，还可以确定相应的地震衰减。这种方法长期以来一直被聚合物科学家用来研究塑料的详细特性。尽管将常规超声波实验室测量与地震观测进行比较的问题是众所周知的，全世界只有少数几个小组进行这些试验，所有这些小组都在测量互补的剪切特性。这个拟议的系统将是地球科学和多孔介质研究界中唯一一个能够直接获得动态压缩性的系统。在应力和孔隙压力的实际条件下，在这样的频率下的体积模量（或体积模量）。这些信息将使我们能够对现有的波传播理论进行新的基本测试，并更多地了解地震频率下真实的岩石的滞弹性特性。