Study of Casing Shielding Effect for Rotating Magnet Ranging in Non-Conventional Decommissioning Applications with Partial Access to a Target Well

Abstract

Abstract Regardless of their complexity, all wells must be properly plugged and abandoned at the end of their lifecycle to ensure a permanent seal between hydrocarbon-bearing layers, fresh-water zones, and the surface. In most cases, such a seal can be established via conventional well intervention where complete access to the target well is available. Complex plug and abandonment techniques using access-independent magnetic ranging methods for subsurface well intervention are available for scenarios without access to the target well. In some cases, the access to a target well may be available from the surface but restricted deeper down the well due to completion specifics, multi-wellbore structure, or well damage. In these cases, access-dependent magnetic ranging, such as the rotating magnet method, can be used to locate and follow the target well until the access restriction before employing access-independent techniques. This approach may significantly reduce the time and capital spending required for well abandonment. This paper discusses the rotating magnet ranging method in application to the abandonment of wells with partial access. In these scenarios, magnetic ranging sensors are deployed in one or more concentric casing strings that cause a magnetic shielding effect and must be accounted for. The nature of this effect, its interference with the ranging measurements and correction techniques will be described. A series of surface tests have been performed with the ranging sensor assembly placed within one, two, and three concentric casing strings to study the casing shielding effect on magnetic ranging measurements. The measurements were collected at different relative orientations and distances between the sensors and the signal source, simulating various downhole scenarios. The results show that triple concentric casing reduces the cross-axis signal 30-fold, double casing – 8.5-fold, and single casing – 4-fold. However, even in the worst-case scenario, the signal stays strong enough to still be able to detect the source more than 20m away. Access-dependent magnetic ranging methods can be employed in subsurface intervention decommissioning scenarios with partial access to the target well. The challenges associated with running magnetic sensors in a casing can be addressed allowing to minimize time and capital expenditures in non-conventional plug and abandonment.