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Abstract
An outer casing leak can be a significant well integrity issue, primarily due to the inability to easily access the leak site for intervention. Recent outer casing failures caused by external corrosion on some wells in the Kuparuk Field of Alaska prompted research for a non-invasive repair method to delay or negate the need for a rig workover. Limited options for downhole access on outer concentric casing strings have an impact on the ability to define the leak in terms of location, size and shape, and consequently the ability to effect a seal of the casing.

The Platelet® technology discussed in this paper is an innovative means of sealing leaks which involves the remote injection of discrete particles into a well which are then carried to the leak site in the fluid flow. When the platelets reach the vicinity of the leak, fluid forces entrain them into the leak and hold them against the casing wall thus facilitating a seal allowing the well to be returned to service.

Previously proven for applications in subsea pipelines, platelet technology over the last 12 months has successfully been developed for downhole use. In January 2009, specifically engineered platelets were deployed into well annuli for the first time.

Two case studies will be presented where the technology has been used in the Kuparuk field in Alaska. In the first instance a ¼” corrosion induced hole in the surface casing at a depth of 126 ft was sealed with a single platelet by a deployment from surface into the outer annulus. The well was initially leaking at a rate of 0.5 bpm and subsequently passed an 1800 psi mechanical integrity test. The second study will review a seal of a 0.26 bpm leak at 30 ft depth which eventually gave out.

The paper will review the front end engineering development, the well site deployment, and lessons learned. The paper concludes by demonstrating the successful use of the platelet technology for sealing annulus leaks and how the technology has successfully postponed or negated the need for a rig workover to repair a surface casing leak. The results from this study have provided valuable insight into the behavior of the platelets in the fluid flow before entrainment and the behavior in the leak after entrainment.

Introduction
The Kuparuk field is located on the North Slope of Alaska, approximately 30 miles west of Prudhoe Bay (Figure 1). The Greater Kuparuk Area (GKA) includes the Kuparuk reservoir as well as several other smaller oil pools in the operating unit. The majority of GKA wells are completed with a conductor casing (CC), a surface casing (SC), a production casing (PC) and tubing.

Historical records, field investigation and lab results from a previous study (SPE Paper 100432) indicate the near surface casing corrosion is a result of cyclic or consistent ingress of oxygenated water into the annulus between the CC and SC. Elevated well operating temperatures in conjunction with an extremely corrosive environment caused by the soluble salts that leach from the cement create a very aggressive corrosion environment1. Over the last few years, the aggressive corrosive environment has become increasingly evident as 53 GKA wells have been discovered with SC corrosion failures at shallow depths typically less than 30 ft, but also as deep as 150 ft. Limited options for accessing and repairing leaks sites in SC prompted the interest in pursuing the new technology.