Summary
A detonated shaped charge fired from a perforating string or perforating gun
will not only perforate its targets, but also possibly cause excessive damage
or swell to its carrier. Comprehensive understanding of the post-perforating
conditions of the perforator or perforator system is required if such damage
and potential retrievability risks are to be avoided. In practice, the
perforating design engineers do not have a well-established analytical tool to
help them understand post-perforating behavior of perforators. They have to
rely on their own experiences and previous perforating histories to roughly
estimate the swell or damage conditions of similar perforators.
In this paper the failure modes of continuously phased perforators for both
gas well and oilwell applications are analyzed. Important factors
concerning carrier serviceability are discussed. A method based on energy
conservation is used to establish a swell model to predict the post-detonation
conditions of the perforator. The model takes the total expendable energy from
the explosives into account, relates it to the energy consumed by the
functional and nonfunctional processes, and describes the relationship of
energy distribution among them. A criterion is proposed to establish the
serviceability of the perforators.
Analytical results from the model are compared with the data collected from
surface tests. The results indicate that the model can reasonably predict the
perforator swell and damage after detonation, and as such will be a useful tool
that shortens the required time to develop future perforators.
Introduction
A perforating project manager has to carefully plan a perforating job for
both maximized system performance and minimized risk associated with incidents
such as perforating gun carriers stuck downhole. Maximized performance usually
requires use of more powerful shaped charges or higher shot density of shaped
charges, which consequently inflicts more damage to the perforator carrier or
gun. Examples of serious damages are over swollen or split guns. It is true
that all guns will swell after shaped charges are detonated. However, an
over-swollen gun refers to the swell of the gun that exceeds the specified
diametric tolerances and thus cannot be retrieved from the well without costly
intervention operations. A split gun is one that is fractured, with a crack
extending from one shot exit hole to adjacent shot exit holes, which is also
unacceptable. The risk associated with either an over-swollen or split gun is
extremely high and should be avoided during perforating job planning and system
development. A validated analytical model for predicting perforating gun swell
can certainly enhance the effectiveness of both job risk management and system
development.
An analytical model of perforating gun swell can help risk management in at
least two respects. First, analytical tools such as swell modeling can serve as
a supplemental measure to further verify whether existing guns are adequately
qualified within their respective ratings, and therefore, will be useful to
both perforating job planners and perforating system developers.
A second application is to special perforating jobs that may require some
alterations to an existing perforating system in order to meet a specific
technical requirement. If the job is imminent with little time for engineers to
run another round of full qualification tests, the engineers or project
managers can decide whether the gun will survive (be retrievable) by using the
modeling tool, instead of merely relying on their experiences to make the tough
decision.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
8 November 2007
- Meeting paper published:
13 February 2008
- Revised manuscript received:
6 November 2008
- Manuscript approved:
25 November 2008
- Published online:
23 July 2009
- Version of record:
28 September 2009
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