Effect of temperature on nano- and microscale creep properties of organic-rich shales
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2018 Elsevier B.V. Understanding the creep properties of gas shales at elevated temperatures is critical for accurately predicting reservoir performance and assessing the effect of viscous behavior on closure rate, production rate, and conductivity loss. In order to better understand creep properties at in-situ conditions, a quantitative relationship between temperature, mechanical properties, and complex chemo-physical mechanisms that cause thermal alteration needs to be obtained. In this study, the elastic, strength, and creep properties of organic-rich shales are investigated by a combination of nanoindentation, energy dispersive x-ray spectroscopy, and micromechanical modeling over a range of temperatures (23350 C). Within the allotted temperature range, the elastic and strength properties of the porous clay/kerogen phase remain unchanged. A similar behavior is noticed in the creep modulus from temperatures 23200 C where it remains relatively unchanged and shows an isotropic characteristic. However, the creep modulus of the clay phase increases at 300 C in both parallel and perpendicular directions to the bedding plane. While the analysis of creep data at lower temperatures shed light on the dictating role of organic matter and porosity on creep properties of organic-rich shales (Slim et al., 2018), at high temperature (above 200 C) creep properties are affected by removal of clay-bound water. The results show that this small water content assists in mechanical compaction and grain sliding responsible for time-dependent deformation. We argue that the removal of clay-bound water at temperatures above 200 C increases the frictional coefficient between clay particles and between clay particles and organic matter.
