RIASSUNTO
Abstract
In Prudhoe Bay, Alaska, non-rig tubing repairs have become a viable alternative to rig workovers (RWO's) to provide an economic remediation for wells with production tubing by ""A?? annulus communication. Electricline (EL)-set patches can eliminate tubing communication at a significant cost savings and are particularly attractive in areas where RWO cost is significant, such as offshore, remote, or arctic locations. The advantage of tubing patch repair over a conventional RWO is that there is no need to pull tubing, resulting in the well being returned to service faster. Typical patch deployment costs are less than 5% of the costs for tubing replacement with a RWO. To date, 263 permanent and retrievable tubing patches have been set in 181 wells at Prudhoe Bay.
This paper discussesthe history of conventional tubing patches at Prudhoe Bay, recommended pre-patch diagnostics, and the use of 3-D advanced caliper viewing software. The paper also provides a systematic approach for the design and deployment of conventional tubing patches.
Introduction
Prudhoe Bay, Alaska, is a mature EOR/waterflood oil field. When mechanical problems with the original completions arise, they have traditionally been repaired with a rig workover (RWO). The majority of these wells were completed with 4-1/2?? and 5-1/2?? L-80 carbon-steel production tubing. With conventional RWO's costing an average of $1.2 million to replace tubing, significant cost savings can result by deploying alternative remediation. These cost savings dramatically improve economics and may result in additional reserves recovered.
Tubing patches are designed to straddle and eliminate production tubing by ""A?? annulus communication (Figure 1). Patches can be successfully installed in producers or injectors to isolate leaks in damaged gaslift mandrels (GLM's), jewelry, tubing collars, and eroded or corroded tubulars. For the purpose of this paper, only conventional patches will be considered. Additional patch types include gaslift straddles and perforation straddles and have been deployed at Prudhoe Bay, but are not discussed in this paper.
Many changes have been made to initial procedures to improve diagnostics and minimize mechanical risk. Patch operation principles, history, annular communication mechanism, diagnostics, candidate selection, patch design, deployment, and retrieval are discussed below.
Patch Operation Principles
Tubing patches consist of two sealing elements connected by a pipe spacer to straddle and isolate the source of tubing by ""A?? annulus communication (Figure 2). Typically, patches are modular, and can be adapted to special applications such as CT hang offs or extended-length patches (Reference 1). Once set, the patch results in a restriction in the tubing, however, most EL, slickline (SL), coiled tubing (CT), and pumping operations can still be carried out through the tubing patch. Even hydraulic fracturing and CT cement squeeze operations can be performed successfully through patches, although these operations may make patch retrievability challenging, if not impossible.
Patches are available for most API tubing sizes, and are available in permanent and retrievable models.
Permanent Patches. Permanent patches are classified by seal type and can have 1.) metal-to-metal primary seals with elastomer secondary seals, or 2.) elements that are made of soft metal, either low carbon steel or 300 series stainless steel, with molded rubber on the outside. These are called ""soft-set?? and provide more effective sealing in corroded tubulars because the seals can conform to tubing irregularities. ""Soft-set?? patches are run on a pressure-operated setting tool that exerts a pushing force on the top tapered swage and a pulling force on the bottom tapered swage. Both swages are simultaneously driven into the soft metal elements, which expand and seal against the tubing walls. The sealing elements form a metal-to-metal seal, backing up the molded rubber seal.