PetroMarker (Norway)

Electromagnetic (EM) methods are an accepted tool to reduce offshore hydrocarbon exploration risk. One of the companies offering such a service is the Norwegian geophysical company PetroMarker, which acquires offshore time domain CSEM data with a vertical stationary transmitter and vertical E-field sensors placed on the sea bed. In many cases a 1D inversion approach will give a good enough understanding of such data. Still, to fully exploit the information inherent in the data set and enhance the resolution of subsurface features it is necessary to account for geometrical effects such as bathymetry and the lateral extension of the resistive features through 2D or 3D inversion. Recently a new 2D time domain inversion code for CSEM data with induced polarization (IP) capability was developed based on the well-established frequency domain MARE2DEM finite element code. Accounting for induced polarization allows for a wider range of transmitter receiver offsets in a single 2D inversion run. In this paper we show some first examples of this code on synthetic and field data. It is found that a resistivity structure can fast and reliably be recovered, also in the presence of induced polarization.

The EM code of Newman and Commer can be used for inversion of the time domain vertical dipole data of Petromarker. A depth gradient weight function has been calibrated to obtain the original target depth in the inversion. The main goal of the 3D inversion development is to combine all the measurements in an offshore survey so the data fit a resistivity model. A synthetic data example is presented where the inversion use forward modelled data from a reservoir case. The inversion recovers the depth and horizontal size of the reservoir. The inversion code has the potential to improve subsurface imaging by geometrical averaging over all transmitter/receiver combination in a survey, and to include seabed topography and known stratigraphic horizons.