Estimating Horizontal Resistivity Trends in Sedimentary Rocks: A Case Example from the Northern North Sea

Abstract

Understanding the major controlling factors on the horizontal resistivity-depth trends of sedimentary rocks in any given basin around the world are interesting from both scientific and commercial perspectives. Hence, we propose a workflow that combines a widely accepted rock physics model with petrophysical analysis and in-situ subsurface conditions such as temperature, salinity and pore pressure. By utilizing log data from wells within a given basin area, the workflow exploits the lithological variation present within major stratigraphic group units of a sedimentary column and applies it in a forward modeling process to predict 1-D horizontal resistivity depth profile. Until now, we have applied our workflow and compared the predicted resistivity-depth profiles against log resistivity responses acquired in wellbores across the Norwegian Continental Shelf (NCS). Our predictions capture the overall resistivity trends successfully in all selected wells within each individual basin across the shelf. The predicted 1-D resistivity profiles can be used, among others things, as a priori models in controlled source electromagnetic (CSEM) data inversion schemes, or to provide ‘‘what if’’ scenarios as part of the CSEM data analysis and risk assessment in the exploration phase.