Petrophysics from the air to improve understanding of rock properties in the UK

Electromagnetic geophysical applications exploit a petrophysical relationship governing the electrical
properties of rocks. Given the extensive nature of many airborne electromagnetic surveys it seems
natural to classify, and hence simplify, the spatially aggregated conductivity information on the basis
of rock lithology. This provides an important link between lithological rock parameters and the
petrophysical parameters controlling bulk conductivity. This classification procedure has been
applied to over 8 M conductivity estimates obtained from airborne surveys conducted in the UK over
a period of 10 years. The analysis has provided new information on the conductivity characteristics
of many UK geological formations and allowed a new UK national map of bedrock conductivity to be
developed. Here we highlight the complex conductivity variations observed in mudstone and shale
rocks across a Carboniferous basin. The potential interplay of increasing conductivity due to clay
content and decreasing conductivity due to the presence of pore‐scale hydrocarbons is noted. The
geological‐geophysical analysis described is a new procedure that provides a framework for further
detailed petrophysical understanding of rock properties at depths accessible to EM techniques.