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Multiple-order moments of the transient electromagnetic response of a one-dimensional earth with finite conductance – the Gaussian variation applied to a field example
Exploration Geophysics ( IF 0.6 ) Pub Date : 2021-05-10 , DOI: 10.1080/08123985.2021.1925105
Richard S. Smith 1 , Terry J. Lee 2
Affiliation  

Formulae for the moments of the magnetic field response can be derived for simple models which have conductivities that vary suddenly as a function of depth (thin and thick sheets) or not at all (half space). In a companion paper we have derived expressions for the moments of a conductivity-depth profile that varies smoothly, taking the form of a Gaussian function. In this paper we apply the Gaussian model to data from Russell South, an area in the Athabasca Basin of Canada. The low signal-to-noise ratio in this area means that estimating the overburden thickness is a challenging problem, so this dataset is a good candidate for demonstrating the applicability of our approach. The estimated thicknesses can be compared with drill information, also somewhat problematic as a reliable source of information. If we constrain the Gaussian model to be similar to a thin sheet or a thick sheet at surface, we get estimates of the overburden thickness which are much greater than what is inferred from drill information. However, if the overburden is allowed to vary gradually and the depth and value of the maximum conductivity can vary, then we find that the depth of the most conductive part of the overburden is realistic as it is generally above the base of overburden as determined from drilling. Features of geological interest that are not apparent on the original data can be identified on the derived images.



中文翻译:

具有有限电导的一维地球瞬态电磁响应的多阶矩——应用于场示例的高斯变化

对于简单模型,可以推导出磁场响应矩的公式,这些模型的电导率会随着深度(薄板和厚板)或根本不随深度(半空间)而突然变化。在一篇配套论文中,我们导出了平滑变化的电导率-深度剖面矩的表达式,采用高斯函数的形式。在本文中,我们将高斯模型应用于加拿大阿萨巴斯卡盆地的 Russell South 地区的数据。该区域的低信噪比意味着估计覆盖层厚度是一个具有挑战性的问题,因此该数据集是证明我们方法适用性的良好候选者。估计的厚度可以与钻探信息进行比较,作为可靠的信息来源也有些问题。如果我们将高斯模型限制为类似于地表的薄板或厚板,我们得到的上覆层厚度估计值远大于从钻探信息中推断的值。然而,如果允许覆盖层逐渐变化并且最大电导率的深度和值可以变化,那么我们发现覆盖层中导电性最强的部分的深度是现实的,因为它通常高于覆盖层底部,由下式确定钻孔。在原始数据上不明显的地质特征可以在衍生图像上识别出来。如果允许覆盖层逐渐变化并且最大电导率的深度和值可以变化,那么我们发现覆盖层中导电性最强的部分的深度是现实的,因为它通常在钻孔确定的覆盖层底部之上。在原始数据上不明显的地质特征可以在衍生图像上识别出来。如果允许覆盖层逐渐变化并且最大电导率的深度和值可以变化,那么我们发现覆盖层中导电性最强的部分的深度是现实的,因为它通常在钻孔确定的覆盖层底部之上。在原始数据上不明显的地质特征可以在衍生图像上识别出来。

更新日期:2021-05-10
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