Carbon Management: Offshore Geologic Focus
Services
- Site overview for selection of deep sediment CO2 injection via seismic, geochemical, heatflow data integration
- Complete monitoring of injected CO2 transport, trapping and biotic and abiotic cycling
- Accurate evaluation of sequestered CO2 residence time
- Preliminary site environmental health evaluation
- Long term monitoring ecosystem health monitoring, geochemical focus on the entire ecosystem
If geologic CO2 storage is one of the principal opportunities to mitigate and reduce global atmospheric carbon emissions, the geologic carbon storage sites will require confirmation of long-term trapping. Through our long term and extensive coastal focuses we apply a combination of seismic data, heatflow profiles and shallow sediment porewater geochemistry to evaluate deep sediment gas hydrate loading to evaluate the residence time of offshore, deep sediment stored carbon. Geologic carbon sequestration current includes focus on injection of supercritical CO2 into reservoirs, often in a depleted hydrocarbon field. Seal integrity above these reservoirs is therefore critical for safe long-term storage of CO2. It is generally assumed that if a reservoir was able to contain hydrocarbon for millions of years, it should be suitable for CO2 storage. However, many hydrocarbon reservoirs leak horizontally and vertically, probably best documented by the ubiquitous natural gas and oil seeps observed from the sediment, through the water column and to the water column – atmosphere interface e.g., in the Gulf of Mexico. With integration of seismic and geochemical data and fate-transport modeling there is capability to select efficient storage locations in the deep coastal sediment and provide accurate assessment of CO2 residence time
With a focus on CO2 residence time, we know if reservoirs leak CO2, abiotic and biogeochemical reactions from the injection point up to the ocean floor surface provide diverse traps that result in efficient sediment CO2 sequestration. First, during the migration concentration in porewater becoming super saturated can result in carbonate formation. This carbonate formation may cause a trap and with subsequent CO2 build up there can be pressurization that results in horizontal migration to a new vertical path or pressurizations that result in horizontal migration to a new vertical path or pressurization that creates fractures of carbonate or clay layers. This transport can occur and multiple intervals during migration to the surface sediment and this step-by-step trapping slows down and potential terminates long-term vertical migration.
Upon final transport to the shallow sediment there is a complex series of biogeochemical cycles, controlled by the presence of electron acceptors, that will sequester deep sediment sourced CO2 (see figure).
Moving down the biogeochemical eH gradient to the absence of sulfate, CO2 is a near final electron acceptor and can be cycled by bacteria into methane or organic material. This potential effectiveness of the seafloor to act as a buffer depends on localized flux rates of CO2 and organic carbon loading that controls microbial metabolism rates. Highly concentrated CO2 flux, at or approach advection, will overwhelm the biogeochemical systems and result in a direct flow of CO2 to the overlying water column, In contract, lower vertical migration rates due to trapping and low permeability through clay seals would slow down any biogeochemical reactions as well as move these reaction fronts deeper in the seafloor. With understanding the key carbon pools, we can monitor the fate of CO2 carbon in abiotic and biotic cycles between these pools. For accurate assessment of CO2 residence time and fate it is important to include assessment of all carbon pools in related abiotic and biotic carbon cycling; sediment organic carbo (SOC), porewater dissolved organic carbon (DOC) and calcium carbonate (CaCO3) and carbon source is determined to calculate the deep sediment CO2 carbon transport and cycling. These data are integrated through the sediment to determine the stored CO2 residence time.
For complete monitoring of CO2 storage geochemical data integrated with geophysical data to provide a thorough overview of vertical CO2 migration. With high resolution seismic data, locations for gas trapping, carbonate precipitation and active migration can be reviewed to provide regions to survey for CO2 escape from the injection point. Assessment of these layers through the vertical migration provides an assessment of the total fate of injected CO2 (see figure). This edited seismic profile provides an example of geochemical interpretation of potential vertical gas migration and levels at which CO2 could be trapped, biotically and abiotically cycled. Subsequent pressurization could result in further vertical migration and the final trapping would occur in the shallow sediment where higher organic carbon loading would result in reduction of the CO2. Further evaluation of the carbon fate is confirmed with our predictive mathematical modelling of geochemical predictions with specific site geochemical data.
Contact us for information of the geochemical data collection, seismic data acquisition and interpretation and mathematical modelling and data interpretation for prediction of the CO2 transport and residence time.
