CSEM — Block Q, Offshore Equatorial Guinea
Nawahl Razak and George Smith
Geological Sciences, University of Cape Town, Cape Town, South Africa
CSEM has in recent times become a valuable, non invasive means of acquiring complementary resistivity information on the subsurface for the purpose of identifying hydrocarbon accumulations. CSEM may enable one to distinguish between gas accumulations that are economically viable and those that are not. This method has also been valuable in identifying additional targets which were not evident on seismic data.
Block Q lies offshore Equatorial Guinea and forms part of the West African Aptian salt basin, where several petroleum discoveries have already been made, and it is likely that an abundance of undiscovered accumulations still lie hidden in the subsurface. Block Q lies in relatively deep waters and is unstructured compared to the shelf region. The 3D seismic survey carried out here reveals primarily near-horizontal subsurface layers. If hydrocarbons are present in the subsurface, these would reside in stratigraphic traps. Because of the lack of borehole data, the region presents a high risk for drilling. In order to reduce the drilling risk, a CSEM survey has been carried out in order to determine resistivities of the subsurface, to investigate suspected hydrocarbon targets. CSEM lines were recorded over targets which appear most promising in the 3D seismic data.
In this work, I present an analysis and discussion of the CSEM results. Analysis is carried out using inverse modelling. The analysis is carried out using finite element modelling to reconstruct the observed CSEM resistivity responses measured at the seafloor.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery