Resolution and Precision of Resistivity Models from inversion of Towed Streamer EM data

Abstract

Summary Towed Streamer EM acquisition facilitates dense spatial sampling of Controlled Source Electromagnetic (CSEM) data. The spatial sampling density, i.e. the separation between each spatial measurement point along a survey line has a fundamental effect on the ability to recover a cross section of vertical and horizontal resistivity from 2.5D inversion. It is shown with a real data case from the North Sea that a 1000 m separation between the data points results in a poorly resolved overburden where the estimated resistivity structure is clearly not geologically consistent. This also affects the deeper structure where the resolution of the image of the reservoir is degraded. The inversion performance in terms of resolution and covariance is improved significantly when using all data in the Towed Streamer EM data set. A decrease of the spatial data point separation to 250 m makes the resulting overburden resistivity consistent and geologically sound when comparing with available geological information in the area of the survey. As a result, the resolution of the resistivity cross sections improve by a factor of 5 to 10. The covariance is on the other hand slightly increased by a factor of 2.