Effect of Well Variables on the Performance of Chemical, Jet, and RCT Tubing Cutters

Abstract

Summary An analysis of 72 workover tubing cuts made were completed to determine the effect of well variables on the cutting performance of chemical, jet, and radial cutting torch (RCT) tubing cutters. Performance data indicated that cutting success was only 65, 50, and 77% for the chemical, jet, and RCT cutters, respectively. While it was found that some cutting failures could be attributed to specific causes, such as heavy paraffin in the well, improper detonation, low-pressure tool leaks, exceeding tool pressure limits, and improper tool gas ventilation, other failures did not have any apparent cause. Therefore, the data was analyzed against specific well variables to look for trends to determine other possible failure causes. The most significant results indicated that chemical cutter success in CaBr2 completions fluids was significantly reduced. For comparison, cuts in bromide fluids accounted for 71% of the total number of failed cuts but only comprised 32% of the total attempted cuts. Based on this data, along with examining the chemical reaction between the acid in the chemical cutter, bromine trifluoride, and the other completion fluids, it is believed that the chemical cutter acid reacts more efficiently with bromide completion fluids, therefore, limiting the amount of acid available to sever the pipe. Additionally, it was concluded that placing the pipe in tension significantly increased cutting performance. No other significant correlations were found to other well variables. Introduction Choosing the best cutter for any particular drilling or workover cutting job is not always trivial. Success rates over 72 tubing cut attempts during offshore workovers were only 65, 50, and 77% for the chemical, jet, and RCT cutters, respectively (Fig. 1). Several potential causes likely contributed to this larger than expected number of failures. First, the many logistical and operational issues that must be considered, such as transportation safety, temperature limitations, cut flaring, and wellbore restrictions, often predetermines which cutter must be run, even though it may not be the most efficient choice. Additionally, service companies generally rate tools only based on pipe size, pressure, temperature, and the maximum and minimum standoff between the tool and the pipe wall, even though other well variables are likely important. This is supported by the lower than expected success rates. As well, access to specific cutter performance data is proprietary or limited, and for this reason, it is often necessary to rely on the service company's experience to choose the most effective tool for conditions. This choice is complicated by the fact that service companies tend to specialize on one type of cutter, potentially limiting the possibility that the most efficient cutter for well conditions is selected for the job. This paper has two primary goals:to identify other variables that may be important to cutter performance, andto provide a resource of data that may be useful for tool selection.

Drillpipe Cutting at Ultrahigh Pressure Proven for Remediating Deepwater Stuck-Pipe Hazards

“…The molten plasma performing the cutting operation flows at approximately 6,000°F, eliminating the resistance of high-stainless-alloy tubulars experienced in the oxidation process of chemical cutters. These cutters have a proven market base and accepted success rate (Cole 1999;Zeringue 2005;Jurgens 2009;Portman et al 2006), but are currently limited to pressures up to 15,000 psi. These cutters also provide a flare-free cut (Fig.…”