Shaped charge perforating subjects the formation to shock-loading and large impact stresses, causing damage to the rock surrounding the perforation tunnel. This damage can lead to reduced productivity and to an enhanced risk of sand production, both of which are undesirable. The impact stresses fracture sand grains in the vicinity of the perforation tunnel, resulting in a zone of reduced permeability called the crushed zone. Additionally, the impact stresses plus the outward traveling shock wave severely weaken the rock matrix by de-bonding the cohesive inter-granular cementation, leading to the creation of a zone of reduced strength called the damage zone. As a result, the damage zone extends to a greater depth than the crushed zone. This weakened damage zone is an important factor in crushed zone removal and in the onset of sand production.

An essential first step in modeling perforation clean-up is to characterize the extent and magnitude of both the permeability and strength impairment. An indirect measure of the amount of permeability impairment created by the perforating process is obtained from perforation flow experiments, where the post-shot production flow is compared to an idealized flow measurement in the virgin rock. Direct measurement of the extent of the crushed and damaged zones, and the degree to which strength and permeability damage occurred has received very little attention. In this paper new methods are described to directly determine the extent of the strength and permeability damage caused by shaped-charge penetration. The crushed zone permeability impairment is characterized using thin section analysis and the strength damaged zone is characterized using a Scratch-Tester. These methods allow the quantitative assessment of both damage zones,. The implications of the results for productivity impairment and sand production will be discussed.

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