Introduction to Controlled-Source Electromagnetic Methods: Detecting Subsurface Fluids

Controlled-source electromagnetic (CSEM) methods are used to determine the electrical conductivity and fluid content of the upper few kilometres of the Earth. Reservoirs containing hydrocarbons are more resistive, while those containing saline water are more conductive. CSEM can help assess the hydrocarbon or geothermal potential prior to invasive drilling. This introduction presents the theory and practical application of CSEM methods on land and at sea.
Electromagnetic wave propagation in conducting materials is a diffusion process that limits the highest detectable frequency from the target. The authors show how the signal-to-noise ratio of the measured data may be maximised via a suitable choice of acquisition and processing parameters and selection of subsequent data analysis procedures (depending on the source time function). Proceeding from Maxwell’s equations, the theory of electromagnetic propagation in anisotropic layered media is presented using straightforward notation for components of the electromagnetic fields and analysis that involves only Fourier and Laplace transforms. Complete impulse responses for every electric and magnetic source and receiver configuration are derived, providing a guide to the expected response for real data. 1-D, 2-D and 3-D modelling and inversion procedures for recovery of Earth conductivity from the data are presented, emphasising the importance of updating of model parameters using complementary geophysical data and rock physics relations.
Requiring no specialist prior knowledge of electromagnetic theory, and providing a step-by-step guide through the necessary mathematics, this book provides an accessible introduction for advanced students, researchers and industry practitioners in exploration geoscience and petroleum engineering.