ABSTRACT

Wellbore integrity is of paramount importance to subsurface resource extraction, energy storage, and hazardous waste disposal. We have developed a simple noninvasive technology for casing integrity screening, based on the continuity of electrical current flow. Applying low-frequency current to a wellhead, with a distant return electrode, produces a casing current dependent on the background formation and the properties and depth extent of the well casing. These currents in turn generate surface electrical fields that can be captured in a radial profile and can be used to analyze properties of the well casing. Numerical modeling results reveal a strong relation of the electric field to the casing properties and depth extent of the well. A small breakage in the casing produces a profile coincident to a cased well with a completion depth above the break. A corroded patch, in which the casing conductivity is reduced, also alters the field profiles, and its depth may be estimated by comparing to the profile expected from the well completion diagrams. The electric field profiles are also strongly dependent on background resistivity distributions and on whether the well was drilled using water- or oil-based drilling fluids. We validate the proof of concept in a field experiment, in which we apply currents at the wellheads of two adjacent wells with different casing lengths in an area of known background resistivity. The two profiles are similar in appearance but are offset in amplitude by more than a factor of five, consistent with the theoretical analysis and the 3D modeling results. These results demonstrate that our approach has promise for mapping the general casing condition without well intervention. This approach can be a practical and effective tool for rapidly screening several wells before expensive logging-based technologies are used for casing inspection in detail.

You do not currently have access to this article.