The Sound of Silence: Innovative Approach to Confirm Barriers using Spectral Noise Logging

Abstract

This paper details the deployment of Spectral Noise logging confirming barriers in a complex abandonment of an onshore field in the Netherlands to fulfil regulatory requirements and to support sustainable abandonment. After initial plug and abandonment (P&A) activities on the main reservoirs, measurements showed pressure build up inside annuli. Spectral noise, high precision temperature and production logging were performed to determine the cause of sustained annulus pressure (SAP) and the location of leaks. The data acquisition was performed both under shut-in and pressure bleed-off conditions and both log responses were compared to identify changes in noise patterns. The noise from specific events such as channelling or reservoir activity was detected, so the abandonment program could remediate these issues successfully. Application of spectral noise logging in this field yielded evidence that this technology can identify annulus flow for very minor build-up rates (0.1 bar/day). This paper further demonstrates the ability to allocate the SAP source behind multiple barriers and to validate plug integrity. It was observed that noise responses have a good correlation with ultrasonic cement evaluation logs aiding better understanding of the gas migration mechanism and change in noise patterns. The temperature logging in most of the wells did not indicate any difference between shut-in and bleed-off regimes due to the very low leak rates. However, it did demonstrate the absence of any major cross-flow between formations. Insights in behind-casing flow geometry along the borehole helped to work out a remedial strategy to proceed with a sustainable abandonment of the logged wells. For specific and complex cases, where conventional pressure monitoring and pressure test techniques cannot provide conclusive results, the spectral noise logging technology becomes a useful differentiator in selecting between possible scenarios during execution, The technology therefore brings significant value by reducing project cost without compromising the quality of the abandonment.