How does cement influence the mechanical properties of sands and sandstones?

Student thesis: Doctoral Thesis

Abstract

Deformation bands can act as barriers and baffles in sandstone reservoirs. An increasing number of deformation bands have been studied in poorly cemented sandstones, yet there are questions about how grains can break (rather than slide past one another) in such loose sediments/rocks. The strength and distribution of cement may provide an answer. Detailed 3D observations are required to understand the cement and porosity variability that may control the formation of deformation bands.Integrating x-ray microtomography (X-CT) with microscopic observations, the first part of this thesis analyses cement and porosity distribution across deformation band samples from Utah, Hungary and Arran by comparing 2D slice to 3D sub-volume analysis methods.Characterisation of cement in outcrops of sand(stone)s is complex due to variable mineralogy and multiple periods of cementation. The second half of this thesis strips back the compositional complexities of sand(stone)s to recreate poorly cemented synthetic sandstones in the laboratory. Here gypsum and calcite were used as cementing phases with percentage of cement in the synthetic samples ranging from 3.5 – 26.7%. X-CT analysis shows that gypsum cement forms a network of needles encasing the sand grains meanwhile the calcite (formed by microbially induced calcite precipitation) forms at point contacts between the sand grains.In order to quantify the strength of each of the synthetic sandstones a series of shear box, uniaxial compression testing (UCS) and triaxial experiments were carried out. The results from these experiments show that as the percentage of cement increased the shear and compressive strengths of these samples also increased. The maximum shear strengths of the synthetic samples produced ranged from 103 to 458 kPa.Meanwhile, maximum UCS results ranged from 139 to 2408 kPa. In addition, the mineralogy of these poorly cemented synthetic sandstones was shown to impact the mechanics and hydraulics of the synthetic sandstones.
Date of Award28 Aug 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorAndrea Hamilton (Supervisor) & Zoe Shipton (Supervisor)

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