Packer repair utilizing CT is an important non-rig remediation in the greater Prudhoe Bay Area, Alaska where rig workover costs are significant. To date, approximately 22 CT packer repairs have been performed with a 100% success rate. This high success rate has resulted in investigating possible improvements in efficiency. These are primarily associated with reducing cement and plug milling operations.
This paper presents the history of packer leak detection and repair at Prudhoe Bay. Diagnostics are detailed, including conventional logging methods with temperature, spinner, and waterflow logs. Additionally, the newly developed ultrasonic leak detection log is described. This tool has the ability to detect ultra small leaks and has led to an increase in number of candidates.
Cement packer repair design is discussed, as well as detailed CT operation guidelines. Recent improvements and optimizations to techniques are presented along with areas for future investigations.
Prudhoe Bay, Alaska, is a mature EOR/waterflood oil field. Mechanical problems with the original completions have traditionally been repaired with a rig workover (RWO). With conventional RWO's costing an average of $1.2 million to replace tubing, significant cost savings can result by deploying alternative remediation.
Packer remediation is designed to replace a failed production packer with a cement packer to isolate the perforation interval from the "A" annulus (Figure 1).
Figure 1: Diagram of typical packer leak and subsequent CT cement repair.
Many changes have been made to initial procedures to improve diagnostics and minimize mechanical risk. CT cement packer diagnostics, remediation, and field operations are discussed below.
History of packer leaks at Prudhoe Bay, Alaska. Production in the Prudhoe Bay unit began in mid 1970's. The first packer failure was in 1978. To date 32 production packers have confirmed failures (Figure 2). Of these completions, three were injectors and the remaining were producers. Thirteen of these packers were one particular vendor's run between 1988 and 1992. This packer had metallurgical problems which led to premature failure and reduced pressure ratings.