08098 Downhole CRA Materials Performance - Failure Analysis of a Sub Surface Safety Valve

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Product Number: 51300-08098-SG

ISBN: 08098 2008 CP

Author: Jonathan Marsh

Publication Date: 2008

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This publication discusses the failure of a sub surface safety valve (SSSV) from a sour service gas well in the Mobile Bay area of Alabama, after four years in service. The well in question was prone to sulphide scale formation from metal sulphides in the formation water. The history of the SSSV began as a work over of an existing well, where installation occurred. Also installed simultaneously with the SSSV and the tubing string were two chemical injection points (lower and upper) for scale inhibitor injection. The lower injection point failed immediately, leading to the use of frequent acidizing treatments (acid jobs) to provide flow assurance in the well tubing. The upper injection point failed after 2 years in service. This lead to some malfunctioning of the SSSV due to scaling, and an increased frequency of acidizing to ensure SSSV functionality. However, after a further year of operation the SSSV stuck in the open position and could no longer be freed by acidizing alone. Mechanical manipulation via slick line and an exercise tool restored functionality to the SSSV, which could then be operated by control line pressure. After this point functionality of the SSSV could only be maintained by mechanical manipulation in addition to acidizing.