Environmental monitoring around the In Salah Gas Field

We have been measuring quantities of surface CO2 gas and characterising vegetation and microbiology at the In Salah Gas project in Krechba, Algeria, as a means to assess the environmental impact of underground CO2 storage at the site. The measurements provide baseline environmental data against which any future changes in atmospheric and biological conditions at the site can be gauged.

Gas Storage Project

The In Salah Gas Project is a joint venture between Sonatrach, BP and Statoil. In an operation that began in 2004, CO2 is being stripped from the natural gas produced at the site and reinjected within a 20 m thick sandstone reservoir at around 1800 m depth. To date, some 3 Mt of CO2 has been injected. The risk of leakage of CO2 from the geological formation is very small but monitoring is required to detect any environmental changes and provide confidence in the long-term security of the storage facility.

BGS has been collaborating with BRGM and Sapienza University of Rome in a project to investigate evidence for CO2 leakage at the site. A range of monitoring approaches has been adopted.

Environmental measurements

Figure 1. Near-surface atmospheric CO2 measurements (ppm) around a now-abandoned well. Concentrations from laser-probe measurements are near background except where impacted by vehicle exhaust fumes.

Our field investigations, carried out in 2009–2010, consisted of:

  • near-ground atmospheric CO2 measurements with a mobile open-path laser system;
  • soil gas pressure and flux measurements;
  • botanical and microbiological surveys;
  • initiation of longer-term subsurface monitoring of radon and other gases.

Laser measurements of atmospheric CO2 did not reveal evidence of leakage but did suffer initial problems from interference from vehicle exhausts, windblown dust and rain (Figure 1). The findings also highlighted the uncertainties and needs for better constraints on natural atmospheric CO2 variation, against which the monitoring results can be assessed.

Soil gas CO2 pressures and fluxes were also low but indicated possible low-level leakage from one of the wells. This could have been associated with a previous breakthrough at the well. The well has since been sealed and abandoned.

Local vegetation consisted of typical desert flora (Spermatophytes). This was sparse in all areas except the dry wadi channels. Soil microbial counts were also usually low (typically around 10,000 per gram at depths up to 50 cm). No evidence for CO2 leakage was detected in the surveys.

Radon probe measurements at the site showed an average value of 1.45 kBq/m3 and also showed no evidence for subsurface leakage.

Further monitoring is required to assess the longer-term environmental impacts of underground CO2 storage but initial investigations show promising results and outline the baseline surface conditions present at the In Salah site.

Funding

The investigation has been funded under the EC FP6 programme as part of the CO2ReMoVe project.

Further information

Jones, D. G., Lister, T. R., Smith, D. J., West, J. M., Coombs, P., Gadalia, A., Brach, M., Annunziatellis, A. and Lombardi, S. 2011. In Salah gas CO2 storage JIP: surface gas and biological monitoring. Energy Procedia, 4, 3566-3573.

Contact

Contact Dr David Jones for further information