Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C–150°C, effective stresses of 20–47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO 3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 μ m. The aim was to determine if creep occurs by intergranular pressure solution (IPS) under these conditions and to identify the rate‐controlling process. The wet samples showed significant creep, while dry and oil‐flooded samples did not. Wet samples were also characterized by microstructures such as sutured grain contacts, grain indentations, and overgrowths, suggesting the operation of IPS. The behavior of the wet samples at low strains (<4–5%) agreed well with the predictions of standard models for diffusion‐controlled pressure solution. However, at higher strains (5–10%), creep slowed down compared with the model predictions. Transient flow‐through tests performed in this regime led to an acceleration of creep, consistent with models for precipitation‐controlled IPS, and demonstrated an increase in the impurity content of the pore fluid toward higher strains. Since some of these impurities (notably Mg 2+ ) retard precipitation in calcite, we suggest that creep occurred by diffusion‐controlled IPS at low strain, giving way to precipitation control at larger strains as impurities accumulated. Fitting of the diffusion‐controlled IPS model to the low strain data yielded values of the grain boundary diffusion product DS in calcite of ∼10 −19 m 3 s −1 at 150°C.