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Calibrating Apparent Resistivity Traces, Lines, and Volumes Derived From Lightning Strike Data in South Texas


Lightning data has been demonstrated to be a useful geophysical tool for petroleum and mineral resource exploration. (Haggar, K. S., L. R. Denham, and H. R. Nelson, Jr., 2014, Aquifers, Faults, Subsidence, and Lightning Databases, GCAGS v. 64, p. 161-177; and Haggar, K. S., L. R. Denham, and L. J. Berent, 2015, Analysis of the Goose Point area near Lacombe, Louisiana, Validates New Geophysical Data Type - Natural Sourced Electromagnetism (NSEM) - for Detection of Lineaments Associated with Faults and Sedimentary Features. GCAGS, v. 65, p. 139-153.) Each of these papers won the GCAGS Grover E. Murray – Best Published Paper Award (in 2014 and again for 2015). Lightning-derived resistivity and attribute maps, traces, lines, and volumes can be used to build a structural framework for an exploration play, to fill gaps between control data, to highlight exploration sweetspots, and to predict anisotropy. In addition, recent studies indicate potential application to geothermal exploration as well as to the geotechnical and environmental industries. However, this technology is so new, additional calibration against known geological and geophysical data is still required to better understand the full scope of this technology's resolution and application. This paper presents theoretical and empirical work to calibrate lightning derived apparent resistivity traces, lines, and volumes against well logs, seismic traces, 2-D seismic lines, geologic cross-sections, seismic volumes, and other geological and geophysical data. There are two calibration foci: (1) depth of calculated apparent resistivity anomalies against well log, geologic cross-section resistivity anomalies, and 3-D seismic horizon and fault interpretations; and (2) calculated apparent resistivity in ohm-meters against well log measurements in ohm-meters. Since lightning-sourced electromagnetic data is spatially scalable from regional to play fairway to prospect-sized project areas, this new geophysical data type can be used to both extrapolate beyond existing traditional data sets, such as well control, geologic cross-sections, and 3-D seismic as well as to fill data gaps and identify geologic trends in areas with less complete coverage. Furthermore, an integrated seismic, subsurface, and electrical rock property data set not only provides new views of subsurface geology, but also an opportunity to see previously invisible anomalies in order to obtain more meaningful geologic insights and interpretations.