Experience with Perforating Efficiency in Underbalanced Completions of Geopressured Reservoirs
Authors: Salz Larry B. 
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
Underbalanced perforating has been proposed as a method of improving perforating proposed as a method of improving perforating efficiency in gas wells. However, it has not proven to be an effective means of establishing unimpaired communication with geopressured Vicksburg gas reservoirs in South Texas. Lack of effective jet perforating guns in the small diameter sizes is the probable cause. Average skin factors and AP probable cause. Average skin factors and AP skins of 8.09 and 3352 psi respectively were determined on ten wells after perforating with an underbalance of 4700 psi. The results in South Texas emphasize the need for improved through-tubing perforating guns.

Introduction
Underbalanced perforating is the routine completion practice in geopressured gas reservoirs in South Texas. Within the last two years, ten wells have been drilled and completed in the Vicksburg formation at depths ranging from 11,200' to 12,700'. Reservoir pressures encountered in these completions varied from 9,570 psi to 11,390 psi with formation temperatures near 300 psi with formation temperatures near 300 degrees F. Bottom-hole pressure data and log analysis indicated very low permeability and porosity reservoirs. Permeability varied from porosity reservoirs. Permeability varied from 0.11 to 0.81 millidarcies with an average porosity of 16.1%. These wells were all porosity of 16.1%. These wells were all perforated in an underbalanced condition perforated in an underbalanced condition with the tree installed to reduce the potential hazardous conditions existing when potential hazardous conditions existing when perforating high-pressured gas wells with a perforating high-pressured gas wells with a large casing gun and no tubing in the well. During perforating an average underbalance of 4700 psi was obtained.

Completion Technique
Procedures and production equipment used in completing these geopressured wells were developed to aid in optimizing limited entry or modified limited entry stimulation treatments. Table 1 presents physical characteristics of the wells prior to perforating. It is noted that both oil base perforating. It is noted that both oil base and water base drilling muds were used in the drilling of these wells. Prior to perforating, either fresh water or calcium chloride water was circulated to the completion interval to provide a hydrostatic underbalance for perforating. Figure 1 presents a typical perforating. Figure 1 presents a typical log section and completion detail.
Perforating was conducted with a selective fire, 1-9/16" carrier shaped charge perforating gun equipped with premium charges.