Assessing the impact of the interaction supercritical CO2/interstitial fluid on the nanostructure of caprocks by using adsorption techniques. Application to the safety assessment of CO2 geological storage

CO2 storage is envisioned as a technique which reduces large quantities of CO2 rejected in the atmosphere because of many human activities. The effectiveness of this technique is mainly related to the storage capacity as well as its safety. The safety of this operation is primarily based on the conservation of petro-physical properties of the caprock, which prevents the transport of CO2 through it. However when CO2 reaches the reservoir/caprock interface due to buoyancy effects, the interaction between interstitial fluid and injected fluid creates a series of dissolution/precipitation reactions affecting the properties of containment of the caprock, which is generally characterized by low transport properties. This study aims to assess the impact caused by CO2/interstitial fluid interaction on the nanostructure of the caprock under geological storage conditions. In order to do this, degradation experiments at high pressure of CO2 (83 bar) and isothermal (55°C) conditions have been conducted using batch reactors. The sample used for these experiments is shale from the formation Tournemire (Aveyron-France). Volumetric Techniques of adsorption at low pressure have been used in order to quantify the changes on the sample nanostructure. The variations on the microporosity, mesoporosity and intrinsic permeability were determined by using the methods of Dubinin-Astakov, BJH (Barret-Joney-Hallenda) and Carman-Kozney respectively. At short time (58 days) the results show an increasing in the density of pores in a range less than 10nm, which represents an overall increase on the petrophysical properties, suggesting that integrity of the caprock is affected by dissolution/ precipitation reactions