Gas Monitoring in Wells in CCS Context: Application of a Mobile Cabin for Detecting Low Content of Gas Dissolved in Water

Abstract

One major concern of CO2 geological storage is monitoring the injected CO2 to define its fate into the reservoir of injection (aquifer or depleted field) and to detect eventual CO2 leakage in the adjacent aquifers. This requires regular monitoring of geological formations by analysing the in-situ fluids sampled in observation wells. One known inconvenience of the conventional industrial sampling equipment is the degassing of the sample during the transfer and analysis from geological formation. IFP Energies nouvelles (IFPEN) and Semm Logging (industrial partner) have collaborated to propose an innovative mobile cabin. This collaboration was partly associated to the GECOSAMPA project funded by the ADEME national funding agency and the SECURe project funded by the European Commission through the H2020 programme. This cabin contains a sampling tool, a transfer unit to extract the gas phase, a micro gas chromatograph to analyse the gas composition and a thermodynamic model (pc installed package) to predict the dissolved gas composition at different conditions. It is capable to combine the following steps directly on the studied site: (1) fluid samplings in well at reservoir conditions i.e. pressure up to 350 bar and temperature up to 125°C, (2) gas/dissolved gas extraction and measurement of its composition (He, Ar, H2, hydrocarbons, H2S, N2, O2, CO2) and 3) thermodynamic prediction of the dissolved gas composition in the aqueous phase at different conditions of pressure and temperature. One of the major advantages of the presented measuring tool in comparison to the existing industrial tools is the capability of keeping, transferring and analysing the sample while minimizing leaks and air contamination. The other main advantage is to deliver fluid composition analysis in a reduced time (0.5 sample per day) and to be able to optimize in-situ the experimental design of the fluid samplings according to the fluid analysis results. This cabin can be easily displaced by a truck on a site at different locations. For GHGT-16, we propose to present the different devices of this mobile cabin, their conception, their operating conditions and their installation in the cabin. Then, some laboratory validation tests of the sampler and the fluid transfer unit are presented. A first sealing test was realized by injecting water in the sampler chamber with a piston-pump to increase the pressure up to 350 bar at ambient temperature. The second sealing test was performed to verify the sampler’s compatibility to conditions close to operational temperature and pressure using an autoclave. The tested temperature and pressure conditions were 95°C and 250 bar. These two tests demonstrated the conformity of the sampler to the set-point temperature and pressure since no leakage was observed during these operations. Regarding the cell transfer validation, a comparison test between the simulated and analysed gas composition was performed using an initial solution containing dissolved gas in water at 120 bar and 20°C. After the degassing phase at the saturation pressure of the solution, the composition gas was analysed and compared to the results of a flash compositional software. Finally, two on-site missions have been carried out in Switzerland on two different wells of SIG (Geothermal stakeholder in Switzerland): GEO-1 and GEO-2. The first mission on GEO-1 has allowed to highlight an important air contamination (>90%) and the requirement to modify the cell transfer to analyse fluids with low gas water ratio (GWR). Based on these observations, three main improvements have been made: a glass burette was designed to be adapted to low GWR, the dead volume was reduced and a work on the tightness of the entire system was done. The results of the second mission show that our process has been improved between the two on-site field tests and became robust. The atmospheric contamination was reduced from more than 90% to 3.5% and an excellent repeatability of the gas composition measurements was reached (< 5%). The results have shown an increase in the quality of GWR measurements and specifically for low GWR (value < 0.02).

Keywords: CO2 storage, fluid sampling, gas composition analysis, monitoring