Uncertainty Analysis of Velocity to Resistivity Transforms for Near Field Exploration

Joint analysis of seismic and electromagnetic data is difficult because the data sets lack a common physical parameter, and rock physics is usually applied to link the two methods via porosity. However, rock physics parameters are not well known in near field exploration, and estimates are likely to have large errors associated with them. In this work, we use the Gassmann equation to link velocity to porosity, and the self-similar model to link porosity to resistivity. We calculate a simple depth-trend from the data, and estimate the uncertainty of our model. We apply our methodology to well logs from the North Sea. We show that the background resistivities of a field can be modelled by (1) calibrating the rock physics model on a well log from an adjacent field (including a depth-trend), and (2) calculating the corresponding uncertainty. This method is a useful tool for joint analysis of seismic and electromagnetic data.