Perforation Collapse: Failure of Perforated Friable Sandstones
Authors: Antheunis D. , Vriezen P.B. , Schipper B.A. , van der Vlis A.C. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
To simulate perforation collapse, a number of thick-walled cylinders of rock material have been loaded to failure. To cover a wide range of possible loading situations, a series of possible loading situations, a series of experiments has been performed with various ratios of axial and radial loads. In addition the influence of perforation diameter on failure has been investigated. The experiments were carried out with two types of friable sandstone, selected on the basis of Brinell hardness.
The thick-walled cylinder experiments were numerically analysed with the aid of elastic-plastic theory. For this purpose the stress-strain behaviour of the formation material was determined by performing numerous triaxial experiments on massive core samples. From the calculated stress and strain distributions at the experimentally observed failure load an instability criterion could be derived in terms of limiting value of shear strain.

Introduction
In our investigations on sand influx in producing wells we studied the stability of producing wells we studied the stability of perforation tunnels. A description of perforation perforation tunnels. A description of perforation stability is of practical significance, because it is indispensable in deciding whether a given well will remain sand-free during its productive life. In cases where perforation failure is foreseen, predictions cover the following practical aspects: predictions cover the following practical aspects:*prediction of the moment of failure allowing a timely decision on a sand exclusion technique to be applied, in order to avoid costly remedial treatment*indication of the zone(s) prone to perforation failure, which will Provide guidance in matters of completion policy, particularly when this knowledge is available before a particular well is perforated.
Instabilities are attributed to erosion of grains and/or chips from the perforation wall on the one hand and to failure of the surrounding rock on the other. In a separate paper the effect of erosion due to gas flow on the stability of perforation tunnels has been reported. In the perforation tunnels has been reported. In the present contribution a laboratory investigation present contribution a laboratory investigation on the mechanical failure of perforated formation material, i.e. friable sandstone from the Rotliegendes formation of the Groningen gas field, is described.