Self-sealing mafic sills for carbon and hydrogen storage

Abstract

Tabular igneous intrusions (sills) are common features in sedimentary basins and have the potential to be useful seals for fluids (e.g. CO2 or H2) in geological storage scenarios, and may be important as the need for geological carbon sequestration and alternative fuel storage increases. This is advantageous in regions without ready access to large-volume reservoirs in depleted hydrocarbon plays and saline aquifers, such as the north-eastern USA. Moreover, geological H2 storage requires more demanding conditions than those typically associated with oil and gas. An enhanced seal will have the properties of a traditional seal – competent, low permeability and laterally extensive – with the addition of being able to self-seal pre-existing and induced frac-tures. Self-sealing will occur along fluid pathways like fractures where CO2, water and minerals like plagioclase, olivine and pyroxene react together. Dolerite sills from the Gettysburg Basin, Pennsylvania, have remarkably low permeability and homogeneous compositions that include minerals that will readily react with CO2 dis-solved in water. Here, we characterize the physical properties and chemical gradients within several mafic sills cored in five boreholes. In addition, preliminary CO2-reaction experiments on dolerite samples demon-strated rapid carbonate mineralization.