Ultrasonic cement evaluation tools have traditionally been used for cement bond evaluation and pipe condition assessment. However, in plug and abandonment (P&A) operations, there is a growing need to assess annular contents and characterize fluids behind casing to ensure safe circulation before casing recovery. This need is particularly critical in offshore wells with integrity challenges, where unintentional hydrocarbon circulation can pose safety risks, cause operational delays, and lead to potential platform shutdowns. This study presents an advanced ultrasonic fluid characterization workflow that integrates pulse-echo and pitch-catch techniques, applied in a North Sea P&A case where fluid identification in the B annulus (13-3/8 in × 10-3/4 in) was essential. The well had been shut in due to integrity issues—specifically, tubing-to-A annulus and potential A-to-B annulus communication—further increasing the risk of hydrocarbon accumulation in the B annulus. Additionally, since the well was being used as a donor for a new infill sidetrack, the main bore required P&A. Determining the B annulus content before circulation was critical. If hydrocarbons were present, recovery operations would become more complex, requiring the mobilization and installation of a bleedoff package. The platform lacked the infrastructure to safely route annular fluids to processing facilities, and the rig’s well control equipment was not designed to separate crude oil from returning annulus fluid returns. As a result, any crude oil in the returns would flow directly into the mud pits, creating a substantial safety hazard. To mitigate this risk, a bleedoff package would need to be mobilized for safe containment if hydrocarbons were detected. Annular fluid characterization data were acquired during the same descent as the cement evaluation logging, which was performed to confirm reservoir isolation in the deeper section of the well and assist in cut-and-pull depth selection. This advanced ultrasonic fluid characterization workflow enabled the operator to proactively plan and mobilize the bleedoff package if crude oil was detected in the annulus. Conversely, if no crude oil was found, the B annulus fluid could be circulated without the need for mobilization and rig-up of the bleedoff package. This proactive approach enabled hydrocarbon detection in B annulus before casing cutting, reducing unnecessary mobilization. By accurately characterizing annular fluids, the workflow minimized safety risks, optimized logistics, and prevented costly possible platform shutdowns. The successful application of this advanced ultrasonic fluid characterization workflow improved operational efficiency by avoiding premature mobilization and rig- up of the bleedoff package on a limited-space deck platform, while enhancing the safety of the P&A operation and ensuring minimal disruptions to production.
Zahmuwl et al. (Sat,) studied this question.