Interference Testing for Reservoir Definition The State of the Art
Authors: Swift S.C. , Brown L.P. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. 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 request 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
Extensive interference tests were conducted on Cities Service's El Dorado Micellar-Polymer demonstration project in Butler County, Kansas. The intent of these tests was simply to define directional flow tendencies of the reservoir and to design the project so as to minimize the detrimental effects of any such trends which were detected.
Interference data was collected on 64 well pairs located on approximately 50 acres. The pairs located on approximately 50 acres. The interpretation of this detailed data was extremely enlightening from both the theoretical and practical points of view.
It was discovered that the value of permeability calculated by all conventional permeability calculated by all conventional pressure transient techniques (Horner method, pressure transient techniques (Horner method, pulse testing, interference testing, etc.) has pulse testing, interference testing, etc.) has a meaning quite different than commonly believed. This value is a geometric mean permeability which yields little or no useful data on the directional properties of a reservoir. In fact, in at least some cases, it is inversely related to channeling tendencies, and thus, very misleading if not properly interpreted.
From an understanding of flow in a nonhomogeneous reservoir, a new parameter, the directional permeability, is defined. This parameter, while strictly correct only for parameter, while strictly correct only for ideally anisotropic reservoirs, can be used to better predict channeling tendencies in a generally heterogeneous reservoir. By calculating the directional permeabilities for the well pairs tested in the El Dorado project, a sound pairs tested in the El Dorado project, a sound basis for selecting between various pattern options was obtained. Thus it was ultimately possible to attain the desired objective—to possible to attain the desired objective—to select a pattern which minimizes the detrimental effects of permeability variations.

Introduction
From a pressure transient point of view, the 51.2 acres in the pilot area of the El Dorado Micellar-Polymer project have probably been observed more carefully than any other piece of reservoir rock in the world. Analysis piece of reservoir rock in the world. Analysis of these observations has required a major modification of the basic techniques heretofore used in pressure transient analysis.
The first interference data from the area involved the test wells and were analyzed using conventional techniques. Permeability variations were observed to be acceptably small. Somewhat larger variations were noted in the storage (phich) terms. This surprising situation was initially explained by natural variations in porosity, compressibility and thickness.