Constrained 1-D inversion of MCSEM data on resistive oil reservoir

Recently a new and very important geophysical method for detection of oil-filled layers in deep-water areas has been introduced to the petroleum industry. The method, called Marine Controlled Source Electromagnetic (MCSEM) maps the contrast of electrical resistivity between the reservoir and the host sedimentary layers. Usually the resistivity of the former is greater than that of the latter. The method is based on the diffusion of electromagnetic energy at low frequency generated by a mobile horizontal electrical dipole and detected by an array of receivers distributed on seafloor. In this paper an efficient algorithm is proposed for inversion of 1-D MCSEM in-line electrical field data. The bathymetry and the seawater resistivity, usually knowing a priori, are used as constrains for regularization of the algorithm. The efficiency of the algorithm was tested with three models with good results. The resolution of the inversion scheme improves greatly if one uses normalized data. The information of the background resistivity distribution for the normalization process can be obtained via well logging or through MMT surveys.