Presented at the Lawrence Berkeley National Lab Geophysics Seminar.
Economic and social motivations to understand the impact of activities such as hydraulic fracturing and carbon capture and storage continue to increase. Electromagnetic (EM) imaging techniques have the potential to be a valuable method for monitoring these activities. One particular challenge is the presence of steel-cased wells. Steel has both a high electrical conductivity (~106 S/m) and a significant magnetic permeability (~100𝜇0), thus, it can considerably (and non-intuitively) impact the behaviour of the currents, fields, and fluxes in an EM survey. Several authors have demonstrated that the presence of the casing can be beneficial because the casing acts as an “extended electrode” and can channel current to depth. However, there are still many open questions, particularly with respect to the role of magnetic permeability, about the finer details of the EM responses. To make progress on these questions we need to be able to simulate the responses from realistic wells. The geometry of steel-cased wells is a complicating factor as the wells are often a centimeter thick and may extend for several kilometers. We have developed software for simulating Maxwell’s equations using a 3D cylindrical discretization. The software is included within the open-source SimPEG ecosystem, which supports forward simulations and inversions across a range of geophysical methods including magnetics, gravity, direct current resistivity, induced polarization, electromagnetics and fluid flow. In this presentation, we will explore aspects of the physical responses in a time-domain EM experiment with a steel-cased well and I will provide context for how these developments fit into the wider open-source ecosystem of tools for geophysics.