Rigless Tubing Repair Using Permanent and Retrievable Straddles on the North Slope, Alaska

Abstract

At Prudhoe Bay, Alaska, nonrig tubing repairs have become a viable alternative to rig workovers (RWOs). They provide economic remediation for wells with production tubing by "A" annulus communication. Electricline (EL)-set straddles can eliminate tubing communication at a significant cost savings. They are particularly attractive in areas in which RWO cost is significant, such as offshore, remote, or Arctic locations. The advantage of tubingstraddle repair over a conventional RWO is that there is no need to pull tubing, resulting in the well being returned to service faster. Typical straddle deployment costs are less than 5% of the costs for tubing replacement with an RWO. To date, 263 permanent and retrievable tubing straddles have been set in 181 wells at Prudhoe Bay.This paper discusses the history of conventional tubing straddles at Prudhoe Bay and the recommended prestraddle diagnostics. The paper also provides a systematic approach for their design and deployment.Tubing/"A"-Annulus Communication Mechanism. The primary cause of tubing/"A"-annulus communication at Prudhoe Bay is related to gas lifting operations. Sixty percent of the straddled wells have had communication problems because of damaged GLMs, broken or stuck gas lift valves (GLVs), and tubing-punch isolation. As the field matured, failure increasingly became caused by corrosion, and 28% of the straddles were set to isolate tubing holes. Fig. 3 describes the most common causes of communication repaired with tubing straddles.GLMs. The most common source of annular communication is caused by damaged sidepocket GLMs, resulting in 80 wells requiring straddle repair. The majority of these failures were at the lowermost GLM. Premature damage to the GLM can occur when (1) the liquid in the "A" annulus is unloaded too quickly when the well is placed on production, (2) a GLV is not fully seated in the GLM pocket, or (3) a GLV is flow cut while pumping down the "A" annulus.