Hydrocarbon-bearing volcanic lava deltas as potential reservoirs: A case study from the North Atlantic Igneous Province, Faroe-Shetland Basin

More than 150 volcanic-related hydrocarbon reservoirs have been
discovered around the world. In 2010, three gas intervals (lower,
middle, and upper, with a total thickness of 350 m [1150 ft])
were found in the offshore Anne-Marie exploration well in a
present-day deep-water volcanic setting in the Faroese sector in
the Faroe-Shetland Basin, northeast Atlantic Ocean. Seeps, shows,
and traces of hydrocarbons in the area indicate that an active
petroleum system is in place. The geology is characterized by submarine
and subaerial basaltic volcanism such as hyaloclastites, volcaniclastics,
lava flows, and intrusions. A core from the middle gas
interval comprises vesicular palagonite lavas, vesicular glassy lavas,
and vesicular subaqueous lavas. Measurements from this core
reveal median porosity of 33.1%, 15%, and 3.9%, and a median
permeability of 0.35, 0.22, and <0.05 md, respectively. The porosity
is comparable to producing onshore volcanic fields elsewhere.
Our study suggests that the gas is likely trapped in leaching or dissolution
in both pore spaces and fractures. Based on our interpretation
of wire-line logs and three-dimensional seismic data, the
well drilled a paleocoastal setting and the upper gas interval is
found within subaerial lavas, whereas the middle and lower gas
intervals are found within a marine volcanic setting, such as pillow
lavas and hyaloclastites associated with lava deltas. Because hyaloclastites
are rather common on the Faroe continental shelf and
along volcanic paleocoastal lines, this suggests a possibility for similar
hydrocarbon-bearing volcanic units in the Faroe region and
elsewhere with a similar setting.