CSEM & MMT Base Basalt Imaging

Seismic imaging for hydrocarbon beneath basalt is often challenging due to the high velocity and extreme heterogeneity of basalt flows. When assessing the prospectivity beneath basalt, a critical factor is the presence of sediments within a depth range that will accommodate hydrocarbons. If sediments are present, the depth extent and structure of the overlying basalt is critical to constructing accurate velocity models for migration of seismic data and to develop drilling plans. Recent drilling results based on interpretation of the basalt thickness from seismic data on the Norwegian North Atlantic Margin (NAM) have shown miss-interpretation of the basalt thickness in excess of 1 km in some cases. Exploration wells in the NAM cost in the range of hundreds of millions of US dollars so there is a significant motivation for using new technology to improve base basalt location. In this paper we demonstrate that a combination of controlled source electromagnetic (CSEM) and marine magnetotelluric (MMT) data can provide inverse images of the basalt section along with underlying sediment and structures that can be used to discriminate between differing seismic interpretations and hence reduce the risk for drilling predictions and improve migration velocity models.