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<p>This study examines the geological and geomechanical properties of marly limestones from the Vale das Fontes Formation. It is a key source rock and a potential unconventional reservoir in the Lower Jurassic Lusitanian Basin, Portugal. The study aims to establish reliable relationships between uniaxial compressive strength, Young’s modulus, and Poisson’s ratio with mineralogical composition and porosity. The results indicate that samples are mainly characterised by calcite (ranging from 59.2% to 96.9%), followed by quartz (2.0% to 14.7%) and phyllosilicates (ranging from 0.0% to 22.0%). Porosity ranges from 0.4% in sample 6 to 15.1% in sample 7. The results of uniaxial compressive strength, Young’s modulus, and Poisson’s ratio demonstrate the influence of mineralogy and porosity. Compressive strength values (21.40&#xa0;MPa, sample 7–155.98&#xa0;MPa, sample 1) increase as the combined calcite and quartz content increases (73.8%, sample 8–99.5%, sample 6) and as the porosity decreases (15.1%, sample 7–0.4%, sample 6). Samples characterised by high calcite and quartz contents (99.2%, sample 1, and 99.5%, sample 6) reflect high values of Young’s modulus (30.27 GPa, sample 1, and 39.47 GPa, sample 6) and Poisson’s ratio (0.26, sample 1, and 0.20, sample 6). On the other hand, samples with high porosity values (15.1%, sample 7, and 11.7%, sample 8) exhibit low values of Young’s modulus (1.93 GPa, sample 7, and 5.12 GPa, sample 8) and Poisson’s ratio (0.14, sample 7, and 0.06, sample 8). This study highlights how variations in geomechanical properties significantly influence stability, which is a crucial parameter in modelling and mitigating risks in unconventional reservoirs.</p>

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Geological and geomechanical properties of soft rocks from the Lower Jurassic Vale Das Fontes Formation (Lusitanian Basin, Portugal): an exploratory study

  • 期刊论文

  • 发表日期：

    2025年11月18日

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  • P. F. Moreira,
  • C. F. Rodrigues,
  • L. V. Duarte,
  • J. P. Temporão de Sousa,
  • A. Vega y de La Fuente,
  • A. Maldonado-Zamora,
  • M. J. Lemos de Sousa,
  • H. I. Chaminé

摘要

This study examines the geological and geomechanical properties of marly limestones from the Vale das Fontes Formation. It is a key source rock and a potential unconventional reservoir in the Lower Jurassic Lusitanian Basin, Portugal. The study aims to establish reliable relationships between uniaxial compressive strength, Young’s modulus, and Poisson’s ratio with mineralogical composition and porosity. The results indicate that samples are mainly characterised by calcite (ranging from 59.2% to 96.9%), followed by quartz (2.0% to 14.7%) and phyllosilicates (ranging from 0.0% to 22.0%). Porosity ranges from 0.4% in sample 6 to 15.1% in sample 7. The results of uniaxial compressive strength, Young’s modulus, and Poisson’s ratio demonstrate the influence of mineralogy and porosity. Compressive strength values (21.40 MPa, sample 7–155.98 MPa, sample 1) increase as the combined calcite and quartz content increases (73.8%, sample 8–99.5%, sample 6) and as the porosity decreases (15.1%, sample 7–0.4%, sample 6). Samples characterised by high calcite and quartz contents (99.2%, sample 1, and 99.5%, sample 6) reflect high values of Young’s modulus (30.27 GPa, sample 1, and 39.47 GPa, sample 6) and Poisson’s ratio (0.26, sample 1, and 0.20, sample 6). On the other hand, samples with high porosity values (15.1%, sample 7, and 11.7%, sample 8) exhibit low values of Young’s modulus (1.93 GPa, sample 7, and 5.12 GPa, sample 8) and Poisson’s ratio (0.14, sample 7, and 0.06, sample 8). This study highlights how variations in geomechanical properties significantly influence stability, which is a crucial parameter in modelling and mitigating risks in unconventional reservoirs.