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45700-AC2
Constitutive Surfaces for the Macroscopic Behavior of Expansive Clay Minerals in the Crystalline Swelling Regime

William J. Likos, University of Missouri (Columbia)

Introduction: Interactions between clay minerals and water play a critical role in numerous geologic, engineering, industrial, and commercial processes and phenomena. Clay-water interactions are a vital component of the entire petroleum system, from deposition of source rock, to generation, to migration, to exploration, to trap. Our current understanding of how these interactions govern and influence macroscopic (bulk) clay behavior, however, remains largely uncertain, most notably for expansive clay minerals within the crystalline interlayer swelling regime.

Objective: The objective of this research is to obtain experimental evidence for the swelling pressure and volume change behavior of expansive clay minerals in the crystalline swelling regime. Constitutive surfaces defining relationships among bulk volume change, swelling pressure, and interlayer water potential during mineral hydration and dehydration will be obtained.

Progress Report: An experimental system has been designed and assembled to allow computer automated control of stress, strain, and relative humidity for highly consolidated clay specimens in the crystalline swelling regime. A graduate research assistant (GRA) has been hired to carry out detailed experimental tasks. Results have been obtained for specimens of Na+-smectite consolidated to relatively loose and relatively dense particle fabrics, respectively. Relationships have been obtained for Na+-smectite specimens undergoing interlayer hydration (increasing relative humidity) under constant volume conditions. Differences observed in the response are interpreted as indicative of differences in the particle micrsostructure; relatively loose particle packing corresponds to inefficient upscaling of interlayer volume change to bulk swelling pressure, while relatively dense particle packing corresponds to efficient upscaling of interlayer volume change. A microstructural model accounting for these fabric effects has been proposed and presented (Wayllace and Likos, 2007). Additional experiments are being conducted to examine partially confined conditions and variables associated with mineral and pore fluid composition and to develop 3D constitutive surfaces.

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