Identifying the Source of Very Low Sustained Casing Pressure Using DAS Acoustic and Strain Data

Summary An Australian coal seam gas well with the reservoir section abandonment completed had a low level (up to 20 psi) of Sustained Casing Pressure (SCP). A dynamic un-spooling fibre system was deployed and a Distributed Acoustic Sensing (DAS) survey conducted to pinpoint the leak source. With bare fibre optic in the well the sustained casing pressure was vented and production casing pressure tested during DAS acquisition. The data analysis workflow included a screening exercise using Frequency Band Energy plots to identify acoustic anomalies, followed by further analysis of raw strain data at the times and depths of FBE anomalies. Intermittent chevron type strain leak signatures were identified at 210m and 352m which enabled targeted remediation efforts, specifically casing slotting and micro-fine cement squeeze, to effectively seal the well. The case study illustrates the DAS workflow and highlights the advantages of bare fibre optic systems for detecting small, intermittent leaks behind casing. The simplicity of dynamic unspooling fibre deployment enhances the value of DAS surveys for well decommissioning diagnostics. Ultimately, the approach improves high-sensitivity leak detection and contributes to safer well abandonment practices. The document acknowledges AGL Energy for sharing well survey data.