ALBERT

Description: Electromagnetic (EM) method, especially Controlled Source Electromagnetic (CSEM) are a unique way of observing fluid movement at depth from the surface. The depth range of interest for hydrocarbon and geothermal applications is from about 500m to 5-7 km. For hydrocarbon reservoirs monitoring we focus to improve the recovery factors and understand fluid movement resulting in lower carbon footprint per produced barrel of oil. For geothermal applications, we can observe magma movements as aid for volcano eruption prediction or monitor producing geothermal field to improve production efficiency and to observe (in correlation with microseismic) reservoir damage and potential induced seismicity. To see percentage level variations, more detailed attention is required at all data handling stages. During acquisition, more effort is required to obtain long term stable transmitter and receiver sites including not only daily monitoring of contact resistance but also controlling them during the acquisition process to better than 1% variations. Because of the large dynamic range of the signal, a highly accurate reference level with active adjustment before the transmitted signal is necessary. While processing the data, a feedback loop between filter selection and noise suppression in the reservoir signal band allows you to optimize the filter and to reduce their effect on the anomaly itself. For a sedimentary environment, anisotropy is the biggest cause for error and misinterpretation. It is derived before the survey from existing logs using end members derived from the resistivity log based on the interaction of the layers on reservoir scale. Another serious issue is the image focus. In principle, we assume the information comes from underneath the receiver but for different measurements it comes from various volume between transmitter and receiver. As with focusing of laterologs, we use a focusing method either by differential measurements or additional borehole receivers. We are using real field measurements as example for potential misinterpretation to illustrate the severance of these issues.