Analysis and Evaluation of Perforating and Perforation Cleanup Methods

Abstract

Analysis and Evaluation of Perforating and Perforation Perforating and Perforation Cleanup Methods Summary Fifty-two completions made in the Gulf of Mexico between June 1978 and May 1982 have been analyzed to evaluate three commonly used techniques for perforating and cleaning up perforations before gravel packing. Since detailed flowing bottomhole pressure (BHP) information was not available in all cases, a method was developed to evaluate the completion efficiencies by using an inhouse computer program. This program models well performance by simultaneously solving the equations performance by simultaneously solving the equations governing fluid flow in the reservoir, the near-wellbore region, the gravel-packed perforation tunnels. and up the production tubing. The results showed that perforating production tubing. The results showed that perforating underbalanced with a tubing-conveyed casing gun yielded more efficient completions than the other two techniques. Introduction With the advent of different perforating and perforation cleanup techniques and procedures, more options are available to the production engineer when designing gravel-packed completions. The three most common techniques currently used arewith a casing gun on electric line and surging the perforations,with a casing gun on electric line and washing the perforations, andunderbalanced with a tubing-conveyed casing gun. The first two techniques require perforating with the pressure differential into the formation, whereas the last technique allows the pressure differential to be into the wellbore. Recent work by Bell indicates that reverse pressure (underbalanced) perforating yields more productive perforations than do positive pressure (overbalanced) perforations than do positive pressure (overbalanced) techniques. To evaluate the three techniques, gravel-packed wells completed with each of these methods during 1978–82 were considered. All the wells in the data base were completed following like procedural operations with the exception of the perforating and perforation cleanup technique. Therefore, it was possible to relate any differences in completion efficiencies to the technique used. Perforating and Perforation Cleanup Techniques Perforating and Perforation Cleanup Techniques A brief outline is presented of the operations that were involved in each of the three basic techniques to perforate and clean up perforations before gravel packing. These procedural operations have remained consistent over the procedural operations have remained consistent over the time frame of this study. Therefore, the perforating and surging technique described would have been conducted in essentially the same manner in 1982 as it would have been in 1978. Of the zones considered in this study, 20 (38.5 %) were completed with the perforating followed by surging technique ("perf-surge"). These zones were completed primarily during 1978 and 1979. All 20 zones were primarily during 1978 and 1979. All 20 zones were completed in a 500-psi [3447-kPa] overbalanced clear brine system with solids filtered to less than 0.2%. The basic procedure for the operation was as follows. procedure for the operation was as follows.Casing was perforated with an electric line casing gun at 4 to 12 shots/ft [13.12 to 39,37 shots/m] with a 500-psi [3447-kPa] overbalance.Surging assembly was run in the hole (Fig. la). The surge chamber was sized using a 0.5-gal [1.89 X 10 M] per perforation criterion. per perforation criterion.Bottom disk was sheared and 1 hour was allowed for the chamber to fill and debris to settle.The upper disk was sheared, an internal bypass was opened on the packer, and formation fluid was reversed out with two tubing volumes.The packer was released and the well washed out as deep as necessary. The surge tool was pulled out of the hole.The well was gravel packed. Washing the perforations following perforating with an electric line casing gun ("perf-wash") was performed 20 (38.5%) times. The majority of these zones were completed in 1980. As with the perf-surge technique, these zones were completed in a 500-psi [3447-kPa] over-balanced clear brine system filtered to 0.2% solids. The following procedure was used to carry out the perf-wash technique.Casing was perforated with an electric line casing gun at 4 to 12 shots/ft [13.12 to 39.37 shots/m] with a 500-psi [3447-kpa] overbalance.A wash tool assembly was run in the hole, (Fig. 1b),The cups were tested to 1,000 psi [6895 kPa] and the perforations were washed from top to bottom by reverse-circulating a clean nondamaging fluid pumped at a rate of 1 to 2 bbl/min [0.159 to 0.318 m /min].The circulating valve was opened and the well washed as deep as necessary. The wash tool was pulled out of the hole.The well was gravel packed. The remaining 12 zones (23 %) were perforated under-balanced with a tubing-conveyed casing gun (surge-pert). This method was used first in mid-1980, with the majority of the work being done in 1981–82. JPT p. 505