Andreas Eckert

Factors affecting CO 2 storage capacity and efficiency with water withdrawal in shallow saline aquifers

Carbon sequestration in shallow aquifers can be facilitated by water withdrawal. The factors that optimize the injection/withdrawal balance to minimize potential environmental impacts have been studied, including reservoir size, well pattern, injection rate, reservoir heterogeneity, anisotropy ratio, and permeability sequence. The effects of these factors on CO2 storage capacity and efficiency were studied using a compositional simulator Computer Modeling Group-General Equation of State Model, which modeled features including residual gas trapping, CO2 solubility, and mineralization reactions. Two terms, storage efficiency and CO2 relative breakthrough time, were introduced to better describe the problem. The simulation results show that simultaneous water withdrawal during CO2 injection greatly improves CO2 storage capacity and efficiency. A certain degree of heterogeneity or anisotropy benefits CO2 storage. A high injection rate favors storage capacity, but reduces the storage efficiency and CO2 breakthrough time, which in turn limits the total amount of CO2 injected.

Geomechanical Simulation of CO2 Leakage and Cap Rock Remediation

CO{sub 2} sequestration into porous and permeable brine filled aquifers is seen as one of the most likely near-term solutions for reducing greenhouse gases. Safely storing injected CO{sub 2}, which is less dense than water, requires trapping the CO{sub 2} under an impermeable rock which would act as a seal. One of the concerns with CO{sub 2} sequestration is the generation of new fractures or reactivation of existing fractures and faults caused by CO{sub 2} injection into the sealing formation. Mitigation strategies must be developed to remediate potentially leaking faults or fractures. This project evaluated potential storage scenarios in the state of Missouri and developed coupled reservoir and geomechanic simulations to identify storage potential and leakage risks. Further, several injectable materials used to seal discontinuities were evaluated under subsurface conditions. The four sealant materials investigated were paraffin wax, silica based gel, polymer based gel, and micro-cement, which all significantly reduced the fracture permeability. However, the micro-cement was the most effective sealing agent and the only sealant able to withstand the large differential pressure caused by CO{sub 2} or brine injection and create a strong seal to prevent further fracturing.