Borehole methods for controlled source electromagnetic exploration

The Controlled Source ElectroMagnetic (CSEM) method has been developed over the past two decades, to provide information on oceanic crustal structure. The stark contrast between the low resistivity of rock structure saturated with salt water, compared to the high resistivity of oil, has meant that the method is increasingly being adopted by the hydrocarbon industry at the exploration stage. During initial assessment, and subsequent development of oil and gas fields, wells are routinely drilled for a variety of purposes. The boreholes provide a possible means of placing either EMsources or receivers within or beneath the target reservoir. This in turn presents the opportunity of applying CSEM methods, using a combination of seafloor and borehole sources and receivers to improve the characterisation and monitoring of the reservoir. In this thesis, forward modelling is used to test out the various survey configurations, in terms of the improvement Borehole CSEM (BCSEM) affords the appraisal and monitoring of hydrocarbon reserves. The results from 1D modelling have shown that the use of downhole instruments (either source or receivers) increased the amplitude anomalies associated with target layers when compared to conventional CSEM. The edge detection capabilities of BCSEM were tested and it was found that a single downhole receiver and a towed seafloor source produced a significant change in the amplitude of the electric field as the source moved over the edge of the modelled reservoir. The method also returned promising results for 3D bodies, showing sensitivity to small structures that are below the detection threshold for conventional CSEM. There is evidence to support that BCSEM could prove to be a useful 4D tool in monitoring reservoir changes during production. The modelling of a depleting anticline reservoir showed that the anomalies associated with the depletion are at potentially detectable levels.EThOS - Electronic Theses Online ServiceGBUnited Kingdo