An Innovative Solution For Groundwater Characterization And Monitoring Below Oil And Gas Sites: From The Lab To The Industrial Demonstration Scale
Authors: Credoz Anthony 
Published: November 2020

Abstract
In the TOTAL R&D HSE and CCUS Programs, ‘Soil and Groundwater’ is one of the primary environmental compartments of interest for better characterization, monitoring and reduction of environmental impacts for long-term and sustainable exploration, production, refining, manufacturing, services operations and CO2 geological storage. Over the last few years, studies have been dedicated to better understand the dynamics of groundwater flow and the transport of dissolved hydrocarbons below our industrial sites. At PERL, the TOTAL Research Center of Lacq in the southwest of France, meter-scale laboratory sandbox experiments were designed to develop innovative probes and prototype sensors for groundwater velocity and in-situ contaminant concentration measurements. At the industrial pilot-scale, ADYCHATS (Aquifer DYnamic CHAracterization Tools System), a research and development platform, was launched to address the challenges of shallow and deep, dynamic, groundwater characterization and monitoring. The alluvial geology of the shallow unconfined aquifer can include preferential pathways comprising high-permeability deposits. Multi-level point velocity probes (PVPs) were installed to measure the groundwater velocity in two distinct hydrostratigraphic facies. The results revealed structural heterogeneities at or below the meter scale that must be considered to identify and characterize the preferential pathways that may dominate solute transport in groundwater. Finally, a demonstrator was implemented at the industrial scale to validate the prior lab and pilot scale tests along a 100-m transect. This third scale of testing illustrated the utility of the approach for a real-world case of contaminant plume monitoring. It consisted of a transect of 10 boreholes instrumented with two depth-specific PVP probes, each equipped with micro-sampling ports, in an unconsolidated shallow aquifer. This transect of probes was oriented perpendicular to the local groundwater flow direction and hydrocarbon plume to validate the innovative mass flux assessment system. This demonstration is one of the first to show a high-resolution assessment of contaminant mass flux of hydrocarbon species through a heterogeneous shallow aquifer, based on detailed point measurements of both velocity and concentration data. At each of the three test scales, numerical modeling was performed and calibrated with COMSOL Multiphysics or FEFLOW softwares to better design the experiments and validate the results. Geophysics provided previous data for the identification of potential preferential flow channels at the pilot and industrial scales through 3 main techniques performed. The final aim of the studies will be to provide to operators and managers of industrial sites an in-situ, real-time, continuous and cost-effective solution using in-situ probes piloted by an intelligent user's interface with optimized data management to monitor and preserve groundwater resources, alert specialists, and minimize impacts.