Enigmatic occurrences of liquid oil in diabase intrusions and vesicular basalt

The presence of liquid petroleum trapped within low-permeability vesicular basalt or mafic intrusions is more than a scientific curiosity, as it also challenges the conventional fluid migration and storage models in porous media. Its presence is significant because it may suggest complex primary magmatic porosity development, low temperature alteration and resulting fluid pathways, nano-scale deformation, or other processes leading to secondary porosity development. Thus the cases offer insights into processes controlling hydrocarbon and fluid flow systems in volcanic areas. In this contribution, we present the study of a Permian dolerite dyke at Tvedestrand in Norway and a vesicular basalt sample from West Greenland, both of which contain liquid oil. The Tvedestrand dyke is emplaced in Precambrian gneiss that was previously overlain by Cambrian black shales. The Greenland basalt is part of the North East Atlantic igneous province, underlain by petroleum-bearing sedimentary strata. Organic geochemistry indicates both oils to be immature, hence suggesting migration through these rocks after emplacement and cooling. We also show ultrahigh-resolution photographs in natural and ultraviolet light to show the distribution of petroleum compounds and image the microstructures controlling fluid migration. The parameters controlling fluid migration in tight crystalline rocks are important to constrain, as these are directly relevant to hydrocarbon exploration in unconventional settings and for hydrogen or carbon storage. We discuss the most likely mechanisms enabling fluid migration in these systems and their broader implications.