ABSTRACT:
Shaped charge penetrators are used in the petroleum industry to perforate cased and cemented wellbores to gain access to the reservoir formation. One of the main factors influencing the performance of cased and perforated completions is the penetration depth of the perforations. Traditionally the penetration depth of shaped charges is tested on cement targets under ambient conditions. In this paper we describe the results of an exhaustive experimental program to evaluate shaped charge penetration in rock under downhole conditions. It was found that penetration depth decreases with increasing rock strength, which confirms results from previously published studies. Some of the examined rocks also show a pronounced dependency of penetration depth on effective stress, although for some rocks this effect appears to be less pronounced than for others. An effective stress law, linking the penetration depth to effective confining stress was developed, which also fits better historical penetration data.
1 INTRODUCTION
Shaped charge penetration is one of the factors determining the productivity of perforated wellbore completions. Other perforating factors include shot density, phasing, and the cleanliness of the perforation tunnel. Additionally, productivity is heavily influenced by the severity of drilling induced damage. One of the main ways that penetration depth can improve the productivity of a perforated completion is by shooting past the drilling induced damage. Thus, it has been an ongoing effort in the petroleum industry to optimize shaped charges for maximum penetration. Historically, penetration depth has been determined using concrete targets shot under ambient conditions, which can largely overpredict downhole performance. This paper focuses on the determination of the target properties that influence the performance of a shaped charge under downhole conditions. These properties can be summarized by using the term “target strength,” which is a combination of the rock strength and the in situ stresses.
