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: (1) to identify other variables that may
be important to cutter performance, and (2) to provide a resource of data that
may be useful for tool selection.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
13 August 2007
- Meeting paper published:
11 November 2007
- Manuscript approved:
23 April 2008
- Published online:
9 July 2009
- Version of record:
28 September 2009
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