Injection and injection-relevant processes in geological storage reservoirs

As an example: CO2 pipes to injection wells in In-Salah, Algeria Source: BGR

In this work package, the following aspects were investigated:

• fluid/transport properties of the CO₂ stream in the injection well when injecting CO₂ as a high-density fluid;
• fluid dynamics in storage reservoir (in particular spreading of CO₂ plume and potential back diffusion of formation water) with special emphasis on impacts of variable injection volumes/rates on the reservoir pressure near the injection well and the resulting geomechanical strain of the reservoir rocks;
• equilibrium concentration and reaction rates of systems (i.e. fluid, formation water, minerals/rocks, pressure, and temperature) selected according to the base scenario;
• impacts of varying CO₂ stream composition on water-rock interactions in the vicinity of the injection well and their implications for injection-relevant rock properties (in particular porosity, permeability, pore space structure/geometry, geomechanical rock properties).

Based on the results of this work package, recommendations were set up for tolerable pressure fluctuations and variations of CO₂ stream composition during injection and geological storage.

Comparison of grain structure of a reddish (top) and a greyish (bottom) Wesersandstein variety Source: MLU

Like during CO₂ transportation, phase transitions or significant changes in fluid density must also be avoided in the injection well during injection operation. Thus, a simulation tool was developed, tested and validated that allows for exact calculations of fluid state, fluid properties and flow behavior in the injection well.

In addition, potential impacts of variable injection rates on the reservoir pressure and resulting implications for geomechanical properties of reservoir and barrier rocks were assessed using thermal-hydraulic-mechanical simulations.

Potential reactions of reservoir rocks with CO₂ as well as with different impurities and varying concentrations thereof were investigated by laboratory experiments (batch and flow-through experiments) and by geochemical simulations. Both laboratory experiments and numerical simulations focussed on investigating potential changes in porosity, permeability, pore space structure/geometry and impacts on geomechanical rock properties induced by variations of CO₂ stream composition with time.

Simulated spatial distribution pattern of ankerite dissolution due to injection of a CO2-SO2-mixture (99:1 mol%:mol%) into a saline aquifer; point of injection at R = 0 m (Wolf et al., 2016).