Abstract

The Newark basin is one of the largest Mesozoic rift basins in Eastern North America, which preserves tectonic and climatic archives and has been considered for geologic CO₂ storage. This paper describes geomechanical properties of the Newark basin formation, focusing primarily on mudstone intervals. Compressive strength, elastic moduli and acoustic velocities were evaluated with a series of triaxial tests at confining pressures ranging from 0 to 41 MPa. The predominantly lacustrine mudstones are characterized by XRD clay content from 30 to 70%, and a large range of compressive strength, from 50 to 300 MPa, in excess of most published values for clay-rich rocks. The strength does not exhibit a strong relationship to clay content and can vary significantly for similar lithotypes. Important factors affecting rock strength in these rift basin formations are: (a) albitization by sodium metasomatism, which increases strength; and, (b) thin bedding, which introduces significant strength anisotropy, most pronounced in the Lockatong mudstones. Unlike rock composition, the elastic moduli correlate well with compressive strength. Overall, our results indicate high spatial heterogeneity of mechanical properties in these rift basin formations and a lack of characteristic strength ranges for common lithotypes in the Newark Supergroup and/or specific formations in the Newark basin. However, a strong correlation of acoustic velocity and elastic moduli with compressive strength would allow using those parameters to estimate strength when direct measurements are not available.

Article highlights

• Compressive strength of the Newark basin mudstones exhibits poor correlation to clay content

• The mudstone strength is greater than most published values for similar lithologies

• The mudstone strength is affected by albitization due to sodium metasomatism

中文翻译：

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中生代裂谷盆地地层力学特性

摘要

纽瓦克盆地是北美东部最大的中生代裂谷盆地之一，保留了构造和气候档案，并已被考虑为地质 CO ₂贮存。本文描述了纽瓦克盆地地层的地质力学特性，主要关注泥岩层段。压缩强度、弹性模量和声速通过一系列三轴试验在 0 到 41 MPa 的围压范围内进行评估。以湖相为主的泥岩的特征是 XRD 粘土含量为 30% 至 70%，抗压强度范围大，为 50 至 300 MPa，超过了大多数已发表的富含粘土岩石的值。强度与粘土含量没有很强的关系，对于相似的岩型，强度可能会有很大差异。在这些裂谷盆地地层中影响岩石强度的重要因素是： (a) 钠交代作用引起的白化作用，这增加了强度；(b) 薄层理，引入了显着的强度各向异性，在 Lockatong 泥岩中最为明显。与岩石成分不同，弹性模量与抗压强度密切相关。总体而言，我们的结果表明，这些裂谷盆地地层的力学性质具有高度的空间异质性，并且缺乏纽瓦克超群和/或纽瓦克盆地特定地层中常见岩型的特征强度范围。然而，当无法直接测量时，声速和弹性模量与抗压强度的强相关性将允许使用这些参数来估计强度。我们的结果表明，在这些裂谷盆地地层中，机械性质的空间异质性很高，并且缺乏纽瓦克超群和/或纽瓦克盆地特定地层中常见岩型的特征强度范围。然而，当无法直接测量时，声速和弹性模量与抗压强度的强相关性将允许使用这些参数来估计强度。我们的结果表明，在这些裂谷盆地地层中，机械性质的空间异质性很高，并且缺乏纽瓦克超群和/或纽瓦克盆地特定地层中常见岩型的特征强度范围。然而，当无法直接测量时，声速和弹性模量与抗压强度的强相关性将允许使用这些参数来估计强度。

文章亮点

• 纽瓦克盆地泥岩的抗压强度与粘土含量的相关性较差

• 泥岩强度大于大多数类似岩性的公布值

• 泥岩强度受钠交代白化作用的影响