Qiliang Sun, Christopher Aiden-Lee Jackson , Craig Magee , Xinong Xie

Buried volcanoes are increasingly identified in the sedimentary basins both on lands and continental margins. However, their roles on the post-eruption fluid flows are still poorly understood, which greatly influence the estimate of seal integrity and increase the hydrocarbon exploration/production risks. Here we use high-resolution 3D seismic reflection and borehole data from the northern South China Sea to show that ancient (Miocene) volcanoes, buried several kilometers below the seabed and fed by magma exploiting underlying, rift-related faults, controlled the bulk permeability of hydrocarbon seal rocks. Differential compaction and doming of strata above these large (up to 10 km diameter by 590 m tall), igneous rock-cored volcanoes promoted the formation of post-eruption extensional faults. Seismic reflection and borehole data suggest hydrocarbons produced by more deeply buried source rocks were either trapped within the volcanoes and/or in porous strata overlying them, with the supra-volcano faults acting as long-lived hydrocarbon migration pathways. Considering that volcanism and related deformation are both common on many magma-rich passive margins, the interplay between the magmatic products and hydrocarbon migration documented here may be more common than currently thought. More specifically, volcanoes may locally degrade seal quality and facilitate cross-stratal migration of hydrocarbons from source to reservoir.