During the past several years, we have seen an increasing focus on the use of CSEM technology for hydrocarbon exploration in marine environments and, recently, a number of success stories have been published. The technology has been demonstrated to aid both detection and delineation of hydrocarbon-filled reservoirs.

When acquiring EM data, there is always a risk that the EM results are not fully in accordance with the results of a subsequently drilled well. These cases are commonly denoted as 'false negatives', a discovery which is not detected by EM, and 'false positives', a dry well drilled at the location of an EM anomaly. In the statistical database comprising 87 wells where EM data is available, 11 wells fall into each of these categories. It is quite natural that such cases cause skepticism in the industry, especially in the part where knowledge and skills in the use of EM data is low. However, when looking into the facts behind these cases, it can be shown that there is no evidence that significant discoveries can be left behind after use of EM data. Regarding the false positive examples, it is evident that the risk of drilling a dry well is still present, even when there is a significant EM anomaly. In conclusion, the full value of EM, as with any other geophysical method, can only be obtained by an improved understanding of the nature of the measurements, through thorough geological work and integration with other geophysical information and through understanding of the uncertainties which allows the method being part of the decision process.

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