Date of Award

2015

Document Type

Open Access Dissertation

Department

Earth and Ocean Sciences

Sub-Department

Geological Sciences

First Advisor

Camelia Knapp

Abstract

This study numerically simulated the injection of supercritical phase CO2 into the South Georgia Rift (SGR) basin to evaluate the feasibility and efficacy of long term geologic storage. The injection simulation modeling was divided into two phases. During phase one of the modeling, very little geologic and reservoir dynamics data was known about the SGR basin. Due to lack of basin data, an equilibrium model was used to estimate the initial hydrostatic pressure, temperature and salinity gradients that represent our study area. For the equilibrium model, the USGS SEAWAT program was used and for the CO2 injection simulation, TOUGH2-ECO2N was used. A stochastic approach was used to populate the permeability in the injection horizon within the model domain. The statistical method to address permeability uncertainty and heterogeneity was Sequential Gaussian Simulation. The target injection depths are well below the 1 km depth required to maintain CO2 as a supercritical fluid. This study simulated 30 million tons of CO2 injected at a rate of 1 million tons per year for 30 years. This is USDOE’s stated minimum capacity requirement for a viable CO2 storage reservoir. In addition to this requirement, a 970 year shut-in time (no injection) was also simulated to better determine the long term fate and migration of the injected CO2 and to ensure that the SGR basin could effectively contain 30 million tonnes of CO2. The preliminary modeling of CO2 injection indicated that the SGR basin is suitable for geologic storage of this DOE stated minimum capacity. During phase two, newly acquired seismic and well data were used to build a 3-D geologic model that included structure for the injection simulation model. Phase two of the injection simulation modeling looks at the effects of faulting on the numerical simulation of CO2 injection into the South Georgia Rift basin. For this study, two software packages were employed to build the injection simulation model. Petrel™ was used to construct geo-cellular grid based on the 3-D geologic model. CO2 injection simulation was achieved using the compositional reservoir simulator CMG-GEM. The total simulation time was 100 years during which a total of 30 million tonnes of CO2 was injected at a rate of 1 million tonnes per year for 30 years followed by a 70 year shut-in period. Multiple experiments were run to find the effects of fault permeability on the resultant fate of the injected CO2. Fault permeabilities were: 0 mD representing a sealing fault, 1 mD representing a low permeability fault, and 100 mD representing a conduit fault. The results from this research illustrate that with a permeability of 1 mD, significant leakage of CO2 occurs up the faults. This is evidence that fault analysis is a critical factor in injection simulation modeling and ultimately in determining the efficacy of long term geologic storage of CO2 and that even low permeability faults make the geology potentially unsuitable. Conclusion of this research are: 1) the SGR basin is composed of numerous sub-basins, 2) this study only looked at portions of one sub-basin, 3) in SC, 30 million tonnes of CO2 can be injected into the diabase units if the fracture network is continuous through the units, 4) due to the severity of the faulting there is no way of assuring the injected CO2 will not migrate upward into the overlying Coastal Plain aquifers, and 5) the SGR basin covers area in three states and this project only studied two small areas so there is enormous potential for CO2 sequestration in other portions the basin and further research needs to be done to find these areas.

Rights

© 2015, Daniel Eric Taylor Brantley

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