Using geochemistry to constrain reaction rates during compaction creep experiments in granular calcite

The compaction and diagenesis of calcite-bearing sediments control the porosity, permeability and strength of these sedimentary rocks. Understanding the mechanisms of diagenesis is the key to producing reliable predictive models of the properties and behavior of carbonate hydrocarbon reservoirs, aquifers, caprocks for geological storage and fault damage zones. Although significant progress has been made in understanding the mechanisms of compaction creep, separating the contributions of pressure solution and subcritical cracking remains a persistent challenge. We present the results of a series of flow-through calcite compaction experiments designed to make use of geochemical measurements to directly calculate in-situ reaction rates. Stress, strain, permeability, temperature and fluid chemistry are monitored throughout two experiments. Analysis of the effluent chemistry, including trace element and Sr-isotope ratios, is used to link the observed compaction to calcite reaction rates and a constitutive model is used to evaluate the contribution of pressure solution relative to other compaction mechanisms. Our results indicate that while pressure solution dominates early compaction, pressure solution and subcritical cracking contribute equally to deformation on longer timescales. These results provide a proof of concept that our geochemical analysis is a powerful tool for monitoring chemo-mechanical deformation which could provide insight into other difficult to measure coupled processes.