3D Seismics and Isotopic Analysis Provides Constraints on the Origin of Methane in the Earths Deep Subsurface.

Understanding and quantifying the sources of methane (CH4) in sedimentary environments is critical for studies of climate change, biogeochemical cycling, energy exploration, and for the mitigation of risks posed by methane explosions in deep mining environments. It was first suggested that the gases in deep gold mines of the Witwatersrand Basin (South Africa) were biogenic, that is, they originated from shallow coal deposits in the basin and were transported as dissolved phases in groundwater into the underlying strata via cross-cutting faults and igneous dykes. However, the integration of 3D seismic data with underground mapping data, gas compositions, hydrogen and carbon isotope signatures provide the new evidence for the abiogenic origin of the methane gas. This holistic approach has further demonstrated that the faults, dykes and fracture systems, as well as compositional variation, hydrogen and carbon isotopic analysis play an important role in unravelling the origin of methane gas in Earth’s deep subsurface, as well as in understanding the methane-water-transportation mechanism.