Subsurface Characterization of the Pennsylvanian Clare Basin, Western Ireland, by Means of Joint Interpretation of Electromagnetic Geophysical Data and Well‐Log Data

Abstract

AbstractThe integration of passive electromagnetic geophysical data and well‐log data for basin characterization and interpretation has been investigated in the Clare Basin, western Ireland. The Clare Basin is overmature and has a clear contrast in electrical resistivity between the Clare Shale Formation, a widespread organic rich shale unit, and the surrounding stratigraphy. The electrical resistivity distribution beneath the Clare Basin was determined by means of three‐dimensional (3‐D) joint inversion of three distinct and differently sensitive electromagnetic parameters: (1) the MT impedance tensor (Z), (2) the geomagnetic transfer function (T), and (3) the interstation horizontal magnetic transfer function (H). Well‐log data from a local exploration well, Doonbeg‐1, were analyzed by means of multivariate statistical methods identifying three groups with distinct resistivity values. The groups were propagated along the basin using the 3‐D electrical resistivity model, showing those regions in the basin with significant organic content at high maturity stage. The lack of continuity of these regions supports the hypothesis of advective fluid heating as the cause of the high maturity levels. The results also help to define the geometry of the basin at depth and have identified an area within the basin, near the Loop Head, where organic‐rich clay/shale is either poorly developed, and/or the organic matter is less mature and less conductive. Finally, the potential of the basin for both CO2 storage and geothermal energy was considered, supporting the use of the Clare Basin as a potential site for geothermal energy but not for the storage of CO2.