Monitoring gas from space
Space satellites used to gather military intelligence on the ground are proving successful at monitoring carbon dioxide (CO2) stored deep underground
A BP study has found that satellite images are capable of picking up minute surface movements, which when taken over time have been shown to reflect shifts in the CO2 buried below as part of carbon capture storage (CCS) projects.
Satellite image of the earth's surface
The finding comes from a six-year study, involving BP and world-leading technology development organisations, to find a cost-effective way to show that CO2 can be safely stored and monitored at industrial scale.
The study was centred at the In Salah Gas project at Krechba, in the Algerian Sahara Desert – one of four full-scale CO2 capture projects in operation in the world today – operated jointly by BP, Statoil and Sonatrach. The In Salah natural gas field produces high levels of carbon dioxide along with the desired methane, and it is this CO2 which is captured and stored deep underground nearby.
The technology of CCS projects like the one at In Salah could contribute about 20% of carbon dioxide emissions reductions (according to the International Energy Agency), by capturing the CO2 produced by the use of fossil fuels at large, fixed sources, such as power plants and refineries.
Instead of venting the unwanted CO2 into the atmosphere and contributing to climate change, it can be compressed, dehydrated, and re-injected back into deep geological formations.
The satellite or Permanent Scatterer Interferometry synthetic aperture radar (PSInSAR) technique is a remote-sensing system capable of measuring small displacements of the earth’s surface. It has been used to monitor the movements of ancient buildings in Rome and the impact of flooding on the city of New Orleans.
As the satellite passes over the point on the earth’s surface, onboard instruments emit electromagnetic and then record the strength and time delay of the returning signal to produce images of the ground. Repeated passes of the satellite over the same location enable images to be combined to give ‘interferograms’, which can identify any changes in surface deformation to within fractions of millimetres.
The satellite imagery is so sophisticated that it can rule out the natural daily ‘tidal’ movements of the earth’s surface caused by the gravitational pull of the moon, the sun and planets.
The findings from the satellite data gathered from In Salah has been confirmed with findings from a 2009 seismic imaging survey, which up until now, was considered the best way to monitor the movement of CO2 in the deep sub-surface.
However, the terrain and geology of the Sahara makes satellite monitoring ideal. In comparison, seismic imaging is more costly and difficult – several million dollars for one specific set of data, as opposed to around $100,000 per year for satellite imaging. Satellite data is non-invasive and can be updated every couple of weeks when the satellite flies by, allowing for a continuous picture of the movement of the CO2 in the deep subsurface.
Satellite data and a range of other monitoring technologies and their results are under ongoing review by the In Salah project partners and an advisory group of independent academics from a range of institutions around the world, including Cambridge, Princeton and Stanford. This data indicates that the CO2 is behaving within expected parameters, and remains securely stored within the geological storage complex. The findings have been made available for technical review over the past years and can be viewed via the link below.