Assessing the Effect of Velocity Model Accuracy on Microseismic Interpretation at the In Salah Carbon Capture and Storage Site
Assessing the Effect of Velocity Model Accuracy on Microseismic Interpretation at the In Salah Carbon Capture and Storage Site
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DOI：
10.1016/j.egypro.2014.11.473
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
A. Stork;J. Verdon;J. Kendall
中科院分区：
文献类型：
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作者：
A. Stork;J. Verdon;J. Kendall
2004年开始注入二氧化碳（CO2），储存在In Salah碳捕获和储存场址的深处，随后于2009年安装了一口试验性微震监测井。该项目是仅有的两个工业规模的存储项目之一，已监测微震活动。这些项目对于证明CCS技术的有效性和微震监测的作用至关重要，微震监测是一种可用于实时调节场地对CO2注入的地质力学响应的技术。位于InSalah注入威尔斯井正上方80米深的单个三分量地震检波器记录了大量微震活动（超过9000次事件）。这些事件发生在两个主要的集群中，其中一个集群中记录良好的事件的估计位置在距离地震检波器1 km的水平距离内，深度在2.1 km和2.7 km之间，至少在注入深度和CO2储存间隔以下200 m。事件位置的深度范围内的错误进行了调查，使用修改后的速度模型，揭示了10%的速度慢创建的不确定性高达450米的深度。或者，在浅地下或各向异性模型中减慢20%的速度具有类似的效果。与绝对深度无关，事件位置不随时间向较浅深度迁移。剪切波分裂延迟时间分析的证据表明，在2009年至2011年期间，CO2注入正在打开预先存在的裂缝，然后随着压力降低而关闭，而不是创建新的裂缝。估计的主要裂缝方向约为NW-SE，与从测井数据推断的裂缝方向一致，观察到的最大矩震级MW= 1.7，也与注入深度处估计的预先存在的裂缝尺寸一致。这项工作证明了CCS项目的微震监测的价值，即使是有限的阵列，但是精确的速度模型对于可靠地解释数据是至关重要的。我们建议在未来的CCS站点注入CO2之前进行微震监测，以进行基线和比较研究。实时微震监测将有助于为注水决策提供信息，并有助于项目的安全运行。
Injection of carbon dioxide (CO2) to be stored at depth at the In Salah Carbon Capture and Storage (CCS) site began in 2004 with the subsequent installation of a pilot microseismic monitoring well in 2009. The project is one of only two industrial-scale storage projects to have been monitored for microseismicity. Such projects are vital to demonstrate the validity of CCS technology and the role of microseismic monitoring, a technology that could be used in real-time to regulate the geomechanical response of a site to CO2injection.Substantial microseismicity (over 9000 events) was recorded by a single three-component geophone situated at 80m deep almost directly above one of the In Salah injection wells. The events occur in two main clusters with estimated locations of well- recorded events within one of these clusters to be within 1 km horizontal distance from the geophone and between 2.1 km and 2.7 km deep, at least 200m below the injection depth and CO2storage interval. Errors in the depth range of event locations are investigated using modified velocity models, revealing that 10% slower velocities create uncertainties up to 450m in depth. Alternatively, 20% slower velocities in the shallow sub-surface or an anisotropic model have a similar effect. Independent of the absolute depth, there is no migration of event locations to shallower depths with time. Evidence from the analysis of shear-wave splitting delay times implies that, between 2009 and 2011, CO2injection is opening pre-existing fractures that then close as pressure decreases, rather that creating new fractures. The estimated dominant fracture orientation is approximately NW-SE, in agreement with fracture orientations inferred from logging data, and the observed maximum moment magnitude,MW= 1.7, is also consistent with estimated pre-existing fracture dimensions at the injection depth.This work demonstrates the value of microseismic monitoring of CCS projects, even with a limited array, but an accurate velocity model is critical to allow reliable interpretation of the data. We recommend that microseismic monitoring is conducted prior to CO2injection at future CCS sites to enable baseline and comparative studies. Real-time microseismic monitoring would help inform injection decision and contribute to the safe operation of a project.