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.