Delineation of Onshore Hydrocarbon Reservoirs Using the Multi-Transient Electromagnetic Method (MTEM)

Bruce A. Hobbs, Anton M. Ziolkowski, and David A. Wright
MTEM Ltd, Edinburgh, United Kingdom

We describe the Multi-Transient Electro-Magnetic (MTEM) method to delineate on-shore hydrocarbon reservoirs. In most cases the MTEM method augments seismic information by determining the resistivity of a potential reservoir – a resistive reservoir indicates hydrocarbons, a conductive one implies water. Seismic data and other information aid interpretation, but the technique can also be applied to virgin areas.

To determine resistivity structure, current is injected into the ground through two grounded electrodes (the source) and the resulting voltage is measured between two further electrodes (the receiver). Acquisition geometry is similar to that of 2-D seismic reflection surveying, with many source and receiver positions. We currently operate a 40-channel receiver system and inject current in the form of a pseudo-random binary sequence; we extract the impulse response of the earth from the recorded response at the receiver. Real-time appraisal of these impulse response data in the time domain indicates the depth and lateral extent of subsurface resistors. Further analyses involve modelling and inversion of the full transient waveform and of its late time DC value.

Case studies presented include a ‘blind' trial demonstration over a gas storage reservoir in France, where both the depth and lateral extent of the reservoir were delineated.