Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: new insights and implications for wave propagation mechanisms
Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: new insights and implications for wave propagation mechanisms
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DOI：
10.1016/j.ijggc.2017.02.009
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发表时间：
2017-04
影响因子：
3.9
通讯作者：
Kelvin Amalokwu;G. Papageorgiou;M. Chapman;A. Best
中科院分区：
文献类型：
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作者：
Kelvin Amalokwu;G. Papageorgiou;M. Chapman;A. Best
地震时移技术是一种有价值的工具，用于估计枯竭储层中储存的二氧化碳的动员和分布。这些技术的成功取决于准确地了解部分饱和岩石的地震特性。使用受控实验室规模的实验来确定流体含量如何影响其性质是司空见惯的。在这项工作中，我们测量了一组孔隙度约为30%的合成砂岩的超声波P波和s波速度。用一种精确的方法，我们跨越了空气-水系统的整个饱和范围。我们表明，岩石的弹性行为与斑块饱和和喷射流动模型是一致的，但在90%的气体饱和度下观察到不连续性，这可以用两种截然不同的方式来解释。在一种解释中，负责机制是发生在优先饱和的狭窄孔隙中的频率依赖的喷射流。一种同样合理的机制是，一旦孔隙被润湿，孔隙中的流动流体就会发生变化。根据地震频率推断，我们的研究结果表明，岩石的地震性质可能会受到润湿效应的影响，从而影响现场数据的解释，但可能不会受到喷射流效应的影响。这为在较低频率下进行部分饱和样品的实验室规模实验提供了强大的动力，或者理想情况下，在地震-声学范围内的频率范围内。
Seismic time-lapse techniques are a valuable tool used to estimate the mobilization and distribution of stored CO2in depleted reservoirs. The success of these techniques depends on knowing the seismic properties of partially saturated rocks with accuracy. It is commonplace to use controlled laboratory-scale experiments to determine how the fluid content impacts on their properties. In this work, we measure the ultrasonic P- and S-wave velocities of a set of synthetic sandstones of about 30% porosity. Using an accurate method, we span the entire saturation range of an air-water system. We show that the rocks’ elastic behaviour is consistent with patchy saturation and squirt flow models but observe a discontinuity at around 90% gas saturation which can be interpreted in two very different ways. In one interpretation, the responsible mechanism is frequency-dependent squirt-flow that occurs in narrow pores that are preferentially saturated. An equally plausible mechanism is the change of the mobile fluid in the pores once they are wetted. Extrapolated to seismic frequencies, our results imply that the seismic properties of rocks may be affected by the wetting effect with an impact on the interpretation of field data but would potentially be unaffected by the squirt flow effect. This provides strong motivation to conduct laboratory-scale experiments with partially saturated samples at lower frequency or, ideally, a range of frequencies in the seismo-acoustic range.