The Dynamic Stability of Chalks During Flooding of Non-equilibrium Brines and CO2

We have shown how the dynamic evolution of the creep curve depends upon pore fluid composition and CO2 content. The presented experiment were performed on Kansas outcrop chalk which serves as model to understand chemical and physical procesess in chalk reservoirs. The test was performed at in-situ stress, pressure and temperature conditions. The stresses imposed to the chalk was in the plastic regime such that the plug deformed under pore collapse. The creep curve, i.e. deformation at constant stresses, is recognized by a monotonous increasing function with varying rate, dependent upon pore fluid composition. A statistical model is fitted to the different creep periods. Special emphasis is made on how the changes from the inert NaCl-brine to sea water brine (SSW) after 46 days; and from SSW to SSW+CO2 at 116 days and 130 days altere the creep curve dynamics. Injection of SSW induces a period of accelerating creep whilst the addition of CO2 seems to reduce the observed creep rate. More data is required to support these observations.