Paper: Calibrated Impression Packers define Perforation Size, Shape and Connection To Permeability In Situ

Inflatable impression packers are not new; they have been around for a number of years.1"2"3 However, their use has been very limited, probably due to one or more of the following limitations: 1. High differential pressure was required to squeeze impressionable material into cracks or perforations, which necessitated an inflatable packer which was expensive to manufacture and difficult to make longer than about 10 feet. 2. The inflation pressure often had to be held for up to 10 hours in order to be able to retain an impression. 3. The inflatable packer had to be returned to its manufacturing plant to be repaired or redressed. A new field-redressable, 30-ft long, low differential pressure inflatable impression packer system has been developed. Also, new impression materials which are oil resistant and which can make and retain in situ impressions in 10 minutes or less have been developed.4 During the development and field testing of this inflatable impression packer system, the minute detail and consistency of the impression retrieved on the new impression material suggested that, with careful calibration, accurate correlations could be made between impression size and actual in situ hole size. Further investigation indicates that the amount of impression material extruded into a perforation. This paper originally appeared as SPE 5707 and is reprinted here through the courtesy of the Society of Petroleum Engineers. under a head of noncompressible fluid is proportional to the formation permeability connected to the perforation. This paper describes the eight critical parameters which must be known and/ or controlled to calibrate impression size to actual size and extrusion height to effective connection to formation permeability in situ.