THE EFFECTS OF CO2 FLOW WITHIN PROPOSED SEQUESTRATION LITHOLOGIES

The purpose of this research project is to determine mineralogical and physical changes occurring within rock samples from various proposed CO2 sequestration sites. We examined sandstone samples from Svalbard, Norway, and shale and sandstone samples from the San Rafael Swell, Utah. The San Rafael samples include the Navajo Sandstone, Entrada Sandstone, Nugget Sandstone, and Mancose Shale. We also examined a fossiliferous Indiana Limestone to observe the reaction within carbonates. Samples were submerged in distilled water and injected with a stream of room-temperature gas-phase CO2 to replicate shallow subsurface ground water conditions. The samples were tested for pH changes in the water, CO2 gas flow rates through samples, and visual and microscopic analysis. Initial results indicate dissolution of carbonates within the limestone samples, and precipitation of minerals in the Navajo and Svalbard samples. No visual changes have yet been noted in the Entrada, Mancose, and Nugget samples. The Svalbard core was started at 30 PSI pressure with a flow of 8mL/min and pH of 6.83, this sample ended with a non-measurable flow below 1mL/min and a pH of 5.45. Microscopic analysis of the Svalbard sample showed recrystallization within the matrix. The limestone sample was started with a flow of 10mL/min and pH of 6.83, and ended with a flow of 6mL/min and a pH of 5.88. Visual and microscopic analysis of this sample indicates strong dissolution and possible development of fractures or aligned dissolution seams. The Navajo sample was started with flow of 6mL/min and pH of 6.83, and ended with a flow of 2mL/min and pH of 5.04. Marked reductions or increases in gas flow can be observed visually in samples within one to two days. A second suite of experiments is ongoing and examines duplicate samples to verify the initial results. The Mancose Shale and Entrada Sandstone are being tested for the first time in this suite. These initial results show that flow of concentrated CO2 in rocks at low temperature and pressure may significantly alter water chemistry, rock fabric, and produce neomineralization that may hinder flow in some lithologies.