Detection and Delineation of hydrocarbon reservoirs using Controlled Source EM Imaging

The adoption of 3D seismic at the end of the last century dramatically improved drilling success. The annual spend by the hydrocarbon industry on seismic acquisition now exceeds $5 billion, and the resulting data are an integral part of risk management and drilling strategies. However, despite this the majority of exploration wells drilled globally are commercially unsuccessful. To make a significant improvement in exploration performance more prospects must be tested to avoid relinquishing productive acreage, including those prospects considered high risk (for example stratigraphic plays, which often have little or no seismic expression). There is therefore a pressing need for a non-invasive technology able to minimise the risk of drilling unsuccessful exploration wells by confirming (or otherwise) the presence of hydrocarbons prior to drilling. Controlled source electromagnetic imaging (CSEMI) does just that, by bridging the gap between traditional seismic exploration methods and drilling. Whilst seismic data identify the geological structures that may contain hydrocarbons, under many circumstances they do not reveal the presence of hydrocarbons themselves. The presence of hydrocarbons in a reservoir typically increases its electrical resistivity compared to the surrounding water saturated sediments by an order of magnitude or more. This property of hydrocarbon saturated reservoirs is commonly exploited well logging applications. However these methods require a borehole to be drilled. CSEMI provides a method of determining the resistivity within an identified prospect before drilling. CSEMI detects and delineates resistive sub-seafloor layers, which can be associated with hydrocarbons, and gives an indication of their spatial extent. If correctly applied, this means that the possibility of drilling dry exploration wells is significantly reduced, as is the need for extensive appraisal drilling.