CO2 flow baseline : key factors of the geochemical monitoring program of future CO2 storage at Claye-Souilly (Paris basin)

Two main deep saline aquifers have been identified in the Paris basin for possible CO2 injection: carbonate reservoirs from the Dogger and Triassic sandstones. These two targeted reservoirs are located at convenient depths for supercritical CO2 storage between 1500 and 2500 m in the center of the Paris basin and show good sealing properties on the upper cap rock. To control long term storage efficiency of CCS projects it is essential to design and implement an appropriate monitoring program that proves that CO2 can be stored safely for a long time. A future monitoring program will be focused on three main axes: a geophysical, geochemical and biological. This paper presents the global monitoring methodology developed to address geochemical aspects of future CO2 storage sites. Three major compartments must be monitored for a well representative CO2 flow baseline: the geosphere, biosphere and atmosphere compartments of the specific site. Viability of any CCS project is strongly dependent on the of our capacity to well establish a realistic quantitative baseline system integrating natural and anthropogenic contributions in each compartment. For these reasons, our technical strategy must a combination of in situ and continuous monitoring systems. On the basis of previous and present day research programs conducted on natural CO2 storage sites, an in-situ monitoring combined methodology matrix adapted to CO2 storage at Claye-Souilly site in Paris basin deep saline aquifer is argued. The presentation will also integrate the proposal of new development in optical sensors (Infrared, Raman and Laser) for gas quantification and traceability including the isotopic aspects. Geosphere monitoring strategy must be mainly conducted through an original multi packers system allowing simultaneously reservoir, rock formations and strategic aquifers observations. In the reservoir, continuous acquisition of geochemical and hydrodynamic parameters is of first importance for adjusting and limiting the divergence criteria of the models and to adapt the injection procedure. In upper rock formations, establishment and modeling of gas transfer curves, will constitute a sensitive and powerful in-situ leakage detector tool. Biosphere survey strategy can be based on conventional accumulation chambers and dynamic flow chambers systems. The surface sampling network must be adapted on the basis of geological and structural characteristics of overburden rock as revealed by previous geophysical investigations. A remote infrared scanning sensing system combined with a laser remote system must support the atmosphere compartment survey strategy. The use of such combined remote system yields a spatial and temporal imaging of the CO2 and its dynamics in air. Sensitivity of leakage detection will depend on the chosen sensing system and the amount of CO2 injected. While variability of CO2 flux and concentration vary with time and with geographic location, they will both depend on the investigated compartment, the natural carbon cycle and the anthropogenic events. Both, sensitivity and variability should be considered in order to establish the alert levels. Given the complexity of data, the time needed to quantify sensitivity and, variability aspects and to establish a base line system, must be longer than one year (one seasonal cycle). This aspect is of first importance to define and provide the remediation operations that must be applied in the case of CO2 leakage on the basis of combined deep, surface and sub-surface measured gas data. Compilation of previous experiments strongly argued that our capacity to quantify variability of CO2 flux/concentration baseline must be one major key factor in the choice of a future monitoring program for CO2 storage site.