Geomechanical stability analysis for carbon dioxide sequestration in carbonate formation.

摘要

Geomechanical analysis is one of the fundamental pillars to build up the confidence of geological sequestration of CO2. Large scale CO2 sequestration in deep carbonate formation is a complicated geological process, which will non-reversibly transform the presumed equivalent and stable status of a sedimentary basin that formed over millions of years: chemically, hydraulically, geothermally, and geomechanically. In this dissertation, thermoporoelasticity guides the theoretical establishment of a conservative baseline for the geomechanical stability analysis of CO 2 sequestration.;Extensive laboratory tests, including CO2 flooding tests, permeability tests, uniaxial and triaxial tests, Brazilian tensile strength tests, poroelasticity tests, point load tests, and fracture toughness tests, etc., were conducted on Indiana limestone and Pierre shale to investigate the effects of CO2 sequestration on storage rock and caprock. Numerical simulations using finite difference method of FLAC3D were also conducted to understand the mechanism of strain localization due to pore pressure fluctuation.;Based on these laboratory and numerical tests, it is concluded that two mechanisms are competing for rock failures in deep carbonate formations during CO2 sequestration. One is the faulting induced by pore-pressure buildup, and another is the compaction failure because of rock quality deterioration due to exposure to CO2 enriched solution.;Fracture toughness measurements on limestone and shale suggest that the fracture toughness of target formation may not be necessarily lower than that of cap rock formation; then the fractures developed in target formation may be easily extended to the cap rock formation, ruining the sealing mechanism. As such, preventing extensive fracturing, and monitoring the seismicity in target formation are essential.;Finally, the potential problems of CO2 sequestration in the Williston Basin were investigated. The in-situ stress regime of the Williston Basin was estimated as a mixture of normal and strike-slip faulting regimes, in favor of a vertical or sub-vertical fracture development pattern, which is negative to the CO2 sequestration. However, as the basin is not very close to an incipient failure, compaction failures are expected to be more pronounced, and naturally occurred geological phenomena, stylolites, will help to understand the CO2 sequestration in deep carbonate formation in the long run.