An Experimental and Numerical Study on Complex Behaviour of Cement Paste under SAGD Operating Conditions

• Author / Creator

  Hamza, Ehab AM

• During the exploration stage for oil sands mining or in situ thermal projects, many wells are drilled to recover core for resource assessment: these wells are referred to as stratigraphic wells. These stratigraphic wells are subsequently plugged with either thermal or non-thermal quality cement and permanently abandoned. The integrity of these cement plugs is a key factor for ensuring the long-term performance of these abandoned stratigraphic wells. While generally not an issue for mining projects since abandoned stratigraphic wells are simply mined as part of operations, the presence of abandoned stratigraphic wells within or adjacent to thermal in situ recovery projects poses potential integrity risks due to an increase in fluid pressure and temperature. These variations in both pressure and temperature may compromise the integrity of cement, especially in the case of non-thermal cement, and potentially result in leakage pathways into the shallow subsurface.
  To attain and ensure a better understanding of well cement characterization for wellbore integrity, the performance of both thermal and non-thermal cements under SAGD operation conditions were studied and compared in terms of mechanical, thermal and shrinkage behavior.
  The initial phase of this research encompassed examining the early-age shrinkage behavior of cement paste. To take into account the effect of curing conditions, a new approach was developed to enable us to measure the shrinkage of hardening samples at pressure and temperature encountered in the field. In the second phase, the alterations that may occur for the mechanical properties of cement paste due to high temperature were investigated by studying the impact of elevated temperature on the compressive strength, tensile strength, and Young’s modulus of cement. The behavior of cement paste under triaxial compression test conditions at several confining pressures was explored as well.
  A critical stage of any modeling work is the selection of the simulation parameters. The accuracy of simulation results is mainly dependent on this choice. One of the most crucial properties, needed in simulation, is shear strength parameters of cement-shale interface because the interface between cement and formation is one of the potential leakage paths. Accordingly, both cement-shale interfacial shear behavior and the shear strength parameters of cement itself were investigated in detail through direct shear test. Cohesion and friction angle of cement were determined for different cement mixes with various water-to-cement ratio (w/c).
  The knowledge of the behavior of cement slurry is essential to specify the appropriate mix design. The latter has to be determined to allow the cement paste to gain a certain level of early-age strength, which is required to achieve hydraulic isolation of the borehole. Accordingly, the variations in the development of early-age mechanical properties of cement, due to changing of curing conditions, were evaluated acoustically. Elastic moduli and compressive strength of cement were monitored continuously and investigated as a function of pressure and temperature. Correlations between curing conditions and the mechanical properties of cement paste were developed. These correlations will increase our ability to predict the performance of cement under different curing conditions.
  Since both mechanical and transport properties of cement are highly affected by the cement matrix, a better understanding of the microstructure evolution of cementitious material during hydration would enable us to not only understand the reaction kinetics of this process, but also to obtain a complete and accurate prediction of the performance of cement paste. Consequently, one part of this thesis was focused on examining the solidification process of cementitious material with an emphasis on the influence of curing conditions on this process. The importance of exploring cement microstructure evolution during solidification process was evident. It was observed that there is a direct link between mechanical properties development and the hydration process.
  In the last part of this research, the behavior of stratigraphic wells, abandoned with non-thermal cement and exposed to SAGD operation conditions, was further investigated numerically. To increase the efficiency and decrease the computational time, a shared boundary modeling approach was utilized. The dependence of stratigraphic well performance on its relative position to the steam chamber was also explored by inspecting several stratigraphic wells at different locations. Simulation results indicated that the performance of stratigraphic wells was very sensitive to the proximity of the steam chamber.

• Subjects / Keywords

  • Mechanical properties
  • Cement
  • Chemical shrinkage
  • SAGD

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-h31r-tv40

• License

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