Analysis of legacy geophysical data to delineate geologic hydrogen occurrences in the Midcontinent Rift System, Iowa, USA

Geologic hydrogen is among contemporary global interests to minimize carbon dioxide emissions. It is mainly produced by serpentinization of olivine within mafic rocks, which comprise the Midcontinent Rift System (MRS) of the midwestern United States. Exploration is active along the MRS in Iowa, where in 1969, a 96.3% hydrogen gas measurement was reported from a natural gas storage field near Vincent. Data useful to geologic hydrogen exploration in Iowa are limited to legacy petrophysical logs and seismic lines from early fossil energy exploration. Legacy data from the Vincent area were evaluated for evidence of subsurface hydrogen and system components. Hydrogen shows are indicated in multiple wells within the upper Eau Claire carbonate. Faults that would serve as migration pathways are evident in the MRS basalts and overlying sedimentary strata. The response of petrophysical logs in interpreted zones of hydrogen accumulation suggest the obsolete neutron-gamma logging tool is sensitive to the presence of geologic hydrogen, but ancillary resistivity, acoustic, and density logs are necessary for further interpretation. Pilot study natural gas injections may have displaced accumulated hydrogen to wells at the structure’s flanks, and some samples were likely from intervals outside the accumulation, which could be tested by reservoir modeling studies.