Perforating Multiple Strings of Pipe

• Multiple string perforating is possible under the right conditions.

• Use Largest gun possible with deep penetrating charges.

• Expect hole size loss and reduced penetration in outer strings.

• Small charges may not work well.

• When in doubt – test the gun and target.

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The distance

between the casing

strings influence

both hole size and

penetration. Grade

and thickness of the

pipe is a small to

moderate influence.

Density of the fill

(cement, mud, or

gas) has only a small

influence.

Simple Tests

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Notice the area reduction in the perforated hole from the inner

string to the outer string.

Three String Target – but misleading?

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Note the reduction of hole area from inner to outer

string.

This target was a test – but not an accurate reflection of what strings may

be placed in a well. These sizes could not be run through each other.

Hole size and shape does vary beyond the first string – very difficult to accurately predict.

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Perforating

through three

strings of pipe:

5-1/2 free

hanging in 9-

5/8 (cemented

in ) 13-3/8”.

Perforated

with a 3-3/8”

gun with DP

charges.

This was the

“perforation”

on the

maximum

standoff side

of the pipe.

The position of the gun (standoff and clearance makes a difference)

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The “perforation” produced in this case is too

small to be an effective flow path. It probably

would scale up quickly.

The near side perf – too small to be of value?

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Modeling the Penetration

A model prediction of a

multiple string target – this

type of completion is often

more problematic than

shown in models.

Perforator and multiple

string target testing is

suggested for unusual

applications or small guns.

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Conclusions • Perforating multiple strings of pipe has the best opportunity for success when

the following rules are followed.

• Use the largest diameter gun that can be run to the target. If more than 1.5” of clearance (between gun and casing wall) is possible, consideration should be given to decentralizing the gun.

• Use deep penetrating, powdered metal liner charges. Big hole charges will not adequately penetrate outer casing strings. The slug produced by wrapped metal liners (open apex liners) can be trapped between the target layers and plug flow paths.

• Double the number of perforations usually made when two or more strings are penetrated.

• Perforation of three strings of pipe in field conditions is very difficult.

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