Joint Interpretation of Electric and Elastic Measurements in Frontier Exploration

In frontier exploration, explorationists often struggle with lack of information, particularly due to lack of well data. Exploration thus relies primarily on elastic (e.g., 2D/3D seismic) and electric (e.g., 3D controlled-source electromagnetic surveys) data sets between the few (if any) wildcat boreholes. Traditional exploration involving rock physics relies almost exclusively on elastic parameters derived from seismic inversion, in itself a challenging task without adequate well control. Inversion of CSEM data, on the other hand, is much more robust in the absence of well control and provides a geologically meaningful representation of sub-surface resistivity. Having two geophysical data sets sensitive to the same subsurface, but relying on different physics, reduces uncertainty in frontier exploration if these are integrated at the interpretation stage. Furthermore, universal rock physical relationships linking elastic and electric properties to various geological parameters (e.g., Hashin-Shtrikman bounds, Archie’s Law) can be used to relate the two measurement types to geological drivers, such as porosity and fluid trends. Here we present a simple workflow incorporating both elastic and electric data sets in frontier exploration, combining them using cross-plotting. We illustrate how the workflow can be used on a regional-scale case study where resistivity and velocity maps can be used together to provide a qualitative background porosity map.