On Baseline Determination and Gas Saturation Derivation from Downhole Electrical Monitoring of Shallow Biogenic Gas Production

Adequate hydrogeophysical monitoring of CO2 geological storage remains a challenge as different parameters might be modified during storage. That implies to compare real-time measurements to an adequate baseline. At the Maguelone shallow experimental site a representative baseline for electrical resistivity was built from a large number of downhole geophysical measurements. At this coastal site this issue is particularly important due to the production of biogenic gas from the subsurface sediments. For this, a modified petrophysical model based on the Waxman-Smits model is proposed to estimate gas saturation found to vary from 2 to 7% within shallow sand layers.