Dual Annuli Closed System Perforate, Wash and Cement

Abstract

The Perforate, Wash and Cement technique has been widely implemented in the remediation of annular cement in recent years, with the application gaining increasing confidence within the Well Integrity, Plugging and Abandonment sectors. With the increase in confidence in the technique to successfully remediate annulus cement comes the evolution of the process; pushing of limitations to meet new and previously challenging plugging and abandonment projects with confidence. The first attempted and successful ‘Closed System’ type Perforate, Wash and Cement of Dual Annuli is discussed and evaluated in this paper as an effective mean for environmental plugging and abandonment. For the dual annuli application to be successful, the perforation of 10-3/4" and 13-3/8" casings must be effective without damaging the 18-5/8" casing to ensure efficient hydraulic communication that allows for washing out of annular debris and placement of cement across both annuli and this was verified by a full system test of the charge. Utilizing a ‘closed system’ (cup tool) perforate, wash and cement method enables constant communication between the isolated swab cups and the annulus behind the perforated casing during the process of washing. As a result of this specific methodology, the amount of annular obstruction is visibly confirmed from surface using standpipe pressure variations long before any debris is seen at surface. The reduction in standpipe pressure over subsequent washing pass is evidence that annular debris has been removed and this is visually confirmed by debris at surface. Dual annuli washing introduces additional uncertainty regarding effectiveness of washing within the second annulus and the effectiveness of this has been verified by both Computational fluid dynamics analyses (CFD), and full scaled yard test. Large volumes of debris consisting of approximately 30% formation cuttings / metal and 70% cement were observed at surface throughout the washing sequence. Cement was efficiently placed using the ‘Pump and Pull’ method. Utilizing the ‘closed system’ benefit of the cup tool, fresh cement was placed across the entire perforated interval ensuring the highest chance of a successful cement bond. Post-execution verification was performed on the cement plug and validation of successful placement of the plug was confirmed. Volumetric analysis verified the effective placement of cement into the 10-3/4", 13-3/8" and 18-5/8" annuli.