This paper presents a case study of the geotechnical characterization for subsidence analyses of an Italian clastic rock gas reservoir at about 1200–1400 m sub sea level. A coherent and exhaustive dataset including lab data and well log measurements allowed to address the main aspects of the rock material characterization. The a priori qualitative inspection of the cores showed significant variability in the quality of rock material, typical feature of soft rocks. However, data from lab triaxial compressive tests showed good quality rock material characterized by high Young’s modulus values primarily affected by lithological differences between reservoir and non-reservoir facies in general and, for sandstone reservoir facies in particular, by cementation and grain sides. In relation to scale effects, the discrepancy between stiffness specimens and stiffness rock mass can be mainly ascribed to formation heterogeneities in terms of lithologies organized in thin layers with centimeter thickness below the resolution of the conventional logs. Finally, the decay of specimen stiffness in relation to induced strain was also inferred: the effects of induced strain from very small to small strain, which represents the range of strain amplitude induced by gas production in a clastic formation, is almost negligible, thus the adoption of constant formation stiffness values during reservoir production life is a realistic assumption for subsidence predictive analyses.

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含气碎屑岩变形行为的实验表征：软岩石还是硬岩石？案例研究

本文介绍了一个岩土工程特征的案例研究，用于意大利海平面约1200-1400 m的碎屑岩气藏的沉降分析。一个连贯而详尽的数据集，包括实验室数据和测井记录，可以解决岩石材料表征的主要方面。岩心的先验定性检查显示，岩石材料的质量存在明显的差异，这是软岩石的典型特征。但是，实验室三轴压缩试验的数据表明，高质量的岩石材料具有较高的杨氏模量，主要受储层和非储层相之间的岩性差异影响，特别是对于砂岩储层，尤其是胶结作用和粒面作用。关于比例效应，刚度样本与刚度岩体之间的差异主要归因于地层非均质性，这些岩性是组​​织成薄层的，其厚度小于常规测井仪的厘米数。最后，还可以推断出试样刚度相对于诱发应变的衰减：诱发应变从很小的应变到很小的应变的影响几乎可以忽略不计，该应变代表了碎屑岩中产气引起的应变幅度范围。在储层生产期间采用恒定的地层刚度值是沉降预测分析的现实假设。