Geological Pitfalls in CSEM-Driven Hydrocarbon Exploration

Rotevatn, Atle ¹; Davies, Roy C.²
(1)Centre for Integrated Petroleum Research, University of Bergen, Bergen, Norway. (2) E.ON Ruhrgas Norge AS, Stavanger, Norway.

The basic principle of Controlled Source ElectroMagnetic (CSEM) surveying is the remote detection of the electrical (resistive/conductive) properties of rocks and fluids in the subsurface. The emergence of CSEM as an offshore hydrocarbon exploration tool over the past decade has initially been met with significant scepticism from parts of the E&P industry. This is probably a result of a mismatch between expectations and results, caused by a combination of aggressive marketing of CSEM as a Direct Hydrocarbon Indicator (DHI) by data vendors and other strong proponents of the technology, and a lack of understanding of the limitations of the technology within many E&P companies. In reality, CSEM is an excellent tool for subsurface resistivity detection, but as a hydrocarbon exploration tool it is associated with a range of potential geological pitfalls that must be understood and addressed in order to avoid false-positive interpretations and the drilling of dry exploration wells, or false-negatives whereby potential discoveries are missed.

This study presents an overview of typical resistivity distribution and variation in sedimentary basins. Particular emphasis is placed on highly resistive rocks and other factors that are likely to cause false-positive interpretations in CSEM-driven hydrocarbon exploration, and the most common causes of false-negative interpretations whereby known hydrocarbon accumulations have been ‘missed’ by CSEM surveys. We present results from synthetic forward modelling studies in addition to examples from real datasets.

Through this contribution we seek to present a balanced view of the strengths and weaknesses of CSEM technology and to highlight the potential pitfalls associated with CSEM-lead exploration. We also aim to demonstrate the importance of properly analysing the causes of supposed ‘failures’ when assessing the value of CSEM, or any other new hydrocarbon exploration tool. In most cases this requires proper integration of the CSEM data with all the other available subsurface data, which in turn illustrates the need for E&P companies to develop internal competence in using new and emerging technologies as opposed to relying on interpretation provided by acquisition and processing companies.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.