It should be possible to use negative-relief trapping configurations for CO2 sequestration
When CO2 is dissolved in water or brine, the resulting solution is denser than the original CO2-free fluid. Given the negative buoyancy of CO2-rich brines, it should be possible to use negative-relief trapping configurations for CO2 sequestration – the opposite of what is typically considered a conventional structural trap for hydrocarbon accumulations or indeed positively buoyant, pure CO2. Negative relief structures, synforms for example, can be identified using existing hydrocarbon subsurface data sets. By analysing such data from basins globally, Simon Stewart at Saudi Aramco, Saudi Arabia, has highlighted the opportunity of considering systematic differences between typical hydrocarbon traps and geological storage options for CO2-rich brines
Stewart’s analysis highlights that a trap’s spatial scale is an important consideration
Stewart’s analysis highlights that a trap’s spatial scale is an important consideration. In flexural sedimentary basins, synformal traps can be very large, with some reaching sizes approaching the basin scale. In this case, the traps will form the upper end of a multiscale geometry that may include a population of smaller structures. For conventional oil-and-gas exploration targets, the entire basin is rarely mapped in sufficient detail, or with the required data quality, to fully evaluate the population of negative-relief traps. Therefore, the use of existing hydrocarbon exploration data to quantify the storage potential of a basin in negative-relief traps comes with great uncertainty, which must be factored into risk analyses of volumetric assessments.
Despite this uncertainty, the work highlights the potential to store large volumes of CO2 in the subsurface via an additional mechanism (that is, in addition to the more conventional positive-buoyancy traps for immiscible pure CO2), supporting the CO2-sequestration aspect of the energy transition. Stewart’s approach exemplifies the innovation required to meet the challenge of net-zero efforts and may prompt review of data acquired through decades of hydrocarbon exploration and production activities, and repurposing of the data to open alternative means of CO2 sequestration.
Petroleum Geoscience 28 (2022); doi.org/10.1144/petgeo2021-074