Maximum Well Productivity in Damaged Formations Requires Deep, Clean Perforations
Authors: Klotz J.A. , Krueger R.F. , Pye D.S. 
Published: December 2007

This paper was prepared for the Society of Petroleum Engineers of AIME Symposium on Formation Damage Control, to be held in New Orleans, La., Feb. 7–8, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
A computer model was used to study the effects on well productivity of formation damage resulting from perforating and drilling or workover operations. The effects of perforation depth and shot density were compare perforation depth and shot density were compare for damaged and undamaged perforations. The results show that:To maximize well productivity perforations must penetrate productivity perforations must penetrate substantially beyond the zone of drilling damage,In a well with drilling damage, a few deep perforations are more effective than many perforations are more effective than many shallow ones, andPerforation quality is more important than either shot density or penetration.
The effect of severe damage in penetration. The effect of severe damage in the perforations cannot be entirely overcome by increasing either shot density or depth of penetration, within the limits of present day penetration, within the limits of present day technology and economics.

Introduction
Gun perforation has been used for over 40 years for generating a flow channel between oil and gas reservoirs and the wellbore of injection or production wells. The first well reported to be gun perforated was a Union Oil Company of California well in the Montebello field, Los Angeles County, California in 1932. Since that time many types of special bullets and jets have been introduced to improve the perforating process, and we include both devices perforating process, and we include both devices in the term "gun perforating".
Although gun perforating became widely accepted as a practical completion method, engineers long suspected that well productivities should be better than observed. productivities should be better than observed. Experimental and field studies, ranging over more than a 20-year period, exposed deficiencies in perforator design and perforating procedures perforator design and perforating procedures that accounted for the reduced productivities or injectivities and lead to improved field results. Laboratory observations on linear, perforated cores demonstrated that crushing and perforated cores demonstrated that crushing and compaction of rock during perforating resulted in substantial impairment of the flow capacity of the hole.
Although this experimental work provided a better understanding of the physical effects of perforating into rock, our ability to estimate how much oil, gas or water should flow into a wellbore through perforations formed under downhole conditions has been limited by the simplifying assumptions required to handle this problem. We have been able to eliminate most of the simplifying assumptions used in the previous studies through use of a computerized finite element method that is described in a previous publications.