Interpreting CSEM data in complex resistivity regime

Abstract

CSEM has been applied as a risk mitigation tool in the Krishna-Godavari Basin, East Coast India. A workflow for application of CSEM in a portfolio ranking process is described, ranging from feasibility assessment to interpretation and post-drilling analysis. Data interpretation was based on relative response analysis, unconstrained inversion and 3D modelling. A major challenge, encountered in the data interpretation was the lack of suitable calibration areas for the interpretation model. Nevertheless, several robust resistivity anomalies were identified, which were then prioritised for drilling. The drilling of a CSEM positive prospect yielded commercial hydrocarbons. This additional calibration information, obtained from the well, was then fed back into the integration work-flow and robustness analysis for the previously lower-ranked resistors. Even using this more complex model, the presence of the resistors was confirmed. This motivated Reliance to review the seismic to upgrade the CSEM leads to prospects.